Q. What is LTE Frame Structure?
(FDD)Frame Type 1
(TDD) Frame
Type 2
10 ms
10 ms
2 Subframes per Frame
10
10
3 Subframe Length (ms)
1
1
4 Slots per Subframe
2
2
5 Symbols/Slot, normal CP
7
7
6 Symbols/Slot, extended CP
6
6
Configuration
1 Frame Length
Q. What is Difference between MIB and SIB?
MIB and SIM are two types of System Information (SI) that is broadcasted in the serving are of
particular cell. SI is carried by the logical channel BCCH, which in turn is carried by either of the transport
channels BCH or DL-SCH.
Master information Block (MIB): is a static part of SI and contain information like number of antennas,
system bandwidth,PHICH configuration, transmitted power and scheduling information on how the SIBs
are scheduled together with other data on DL-SCH. MIB is transmitted on the BBCH–> PBCH with
periodicity of every 40 ms.
System Information Block (SIB): is a dynamic part of SI. It carries relevant information for the UE, which
helps UE to access a cell, perform cell re-selection, information related to INTRA-frequency, INTERfrequency and INTER-RAT cell selections. It is mapped on DL-SCH –>PDSCH with periodicity of every 80
ms, 160ms or 320ms for SIB1,SIB2 and SIB3 respectively.
Q. How many types of SIBs are available in LTE?
There are 13 types of SIBs for LTE.
Q. What does SIB1/SIB2/ … /SIB13 do?
Each SIB carry information related to specific tasks.
SIB-1
Carries Cell access related parameters like cell ID, MCC, MNC, TAC, scheduling of other SIBs
SIB-2
Carries Common and shared channel configuration, RACH related configuration are present;
RRC, uplink power control, preamble power ramping, uplink Cyclic Prefix Length, sub-frame
hopping, uplink EARFCN
SIB-3
Parameters required for intra-frequency, inter-frequency and I-RAT cell re-selections
SIB-4
Information regarding INTRA-frequency neighboring cells (E-UTRA) carries serving cell and
neighbor cell frequencies required for cell reselection as well handover
SIB-5
Information regarding INTER-frequency neighboring cells (E-UTRA); carries E-UTRA LTE
frequencies, other neighbor cell frequencies from other RATs.
SIB-6
Information for re-selection to INTER-RAT (UTRAN cells)
SIB-7
Information for re-selection to INTER-RAT (GERAN cells)
SIB-8
Information for re-selection to INTER-RAT (CDMA2000)
SIB-9
Information related to Home eNodeB (FEMTOCELL)
SIB-10
ETWS (Earthquake and Tsunami Warning System) information (Primary notification)
SIB-11
ETWS (Earthquake and Tsunami Warning System) information (Secondary notification)
SIB-12
Commercial Mobile Alert Service (CMAS) information.
SIB-13
Contains the information required to acquire the MBMS control information associated with
one or more MBSFN areas.
Q. On which channels SIBs are transmitted?
BCCH–> DL-SCH–> PDSCH.
Q. Which SIBs are essential?
In LTE, for a UE to access the eNB, at the most minimum 2 SIBs are required (SIB1 and
SIB2). Information regarding SIB2-SIB13 are carried in SI messages and are included in scheduling Info
List which is part of SIB1.
Q. Why we need SIB19?
SIB 19 is needed when UE is coming back from 3G to 4G. LTE priority should be set high in 3G. SIB19
carries the absolute priority of the serving UMTS cell, the absolute priorities of the LTE frequencies, and
the cell reselection thresholds.
Q. How can we calculate LTE DL/UL throughput?

Lets’ assume we have 20 MHz channel bandwidth.

we need to calculate the resource elements in a sub frame for this band i.e.
12subcarriers x 7 OFDMA symbols x 100 resource blocks x 2 slots= 16800 REs per subframe.

Assume we have 64 QAM modulation and no coding, one modulation symbol will carry 6 bits.
16800 modulation symbols x 6 bits / modulation symbol = 100800 bits.
So, the data rate is 100800 bits / 1 ms = 100.8 Mbps.

With 4×4 MIMO, the peak data rate goes up to 100.8 Mbps x 4 = 403 Mbps.

Estimate about 25% overhead e.g. PDCCH, reference signal, sync signals, PBCH, and some We get
403 Mbps x 0.75 = 302 Mbps.
Q. What is SON & how does it work in LTE?
Self-configuring, self-optimizing wireless networks is not a new concept but as the mobile
networks are evolving towards 4G LTE networks, introduction of self-configuring and self-optimizing
mechanisms is needed to minimize operational efforts. A self-optimizing function would increase
network performance and quality reacting to dynamic processes in the network. This would minimize
the life cycle cost of running a network by eliminating manual configuration of equipment at the time of
deployment, right through to dynamically optimizing radio network performance during operation.
Ultimately it will reduce the unit cost and retail price of wireless data services. See Self-configuring and
self-optimizing Networks in LTE for details.
Q. How does Timing Advance (TA) works in LTE?
In LTE, when UE wish to establish RRC connection with eNB, it transmits a Random Access
Preamble, eNB estimates the transmission timing of the terminal based on this. Now eNB transmits a
Random Access Response which consists of timing advance command, based on that UE adjusts the
terminal transmit timing. The timing advance is initiated from E-UTRAN with MAC message that implies
and adjustment of the timing advance. See Timing Advance (TA) in LTE for further details.
Q. How does LTE UE positioning works in E-UTRAN?
UE Positioning function is required to provide the mechanisms to support or assist the
calculation of the geographical position of a UE. UE position knowledge can be used, for example, in
support of Radio Resource Management functions, as well as location-based services for operators,
subscribers, and third-party service providers. See LTE UE positioning in E-UTRAN for more details.
Q. How does Location Service (LCS) work in LTE network?
In the LCS architecture, an Evolved SMLC is directly attached to the MME. The objectives of this
evolution is to support location of an IMS emergency call, avoid impacts to a location session due to
an inter-eNodeB handover, make use of an Evolved and support Mobile originated location request
(MO-LR) and mobile terminated location request MT-LR services. Release 9 LCS solution introduces new
interfaces in the EPC:
SLg between the GMLC and the MME
SLs between the E-SMLC and the MME
Diameter-based SLh between the HSS and the HGMLC
Q. How does Lawful Interception work in LTE Evolved Packet System?
3GPP Evolved Packet System (EPS) provides IP based services. Hence, EPS is responsible only for
IP layer interception of Content of Communication (CC) data. In addition to CC data, the Lawful
Interception (LI) solution for EPS offers generation of Intercept Related Information (IRI) records from
respective control plane (signaling) messages as well. See Lawful Interception Architecture for LTE
Evolved Packet System for more details.
Q. What is carrier aggregation in LTE-Advanced?
To meet LTE-Advanced requirements, support of wider transmission bandwidths is required
than the 20 MHz bandwidth specified in 3GPP Release 8/9. The preferred solution to this is carrier
aggregation. It is of the most distinct features of 4G LTE-Advanced. Carrier aggregation allows expansion
of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources
across multiple carriers. Multiple component carriers are aggregated to form a larger overall
transmission bandwidth.
Q. What is LTE Intra E-UTRAN Handover?
Intra E-UTRAN Handover is used to hand over a UE from a source eNodeB to a target eNode
Busing X2 when the MME is unchanged. In the scenario described here Serving GW is also unchanged.
The presence of IP connectivity between the Serving GW and the source eNodeB, as well as between the
Serving GW and the target eNodeB is assumed. The intra E-UTRAN HO in RRC_CONNECTED state is UE
assisted NW controlled HO, with HO preparation signaling in E-UTRAN. To prepare the HO, the source
eNB passes all necessary information to the target eNB (e.g. E-RAB attributes and RRC context) and UE
accesses the target cell via RACH following contention-free procedure using a dedicated RACH
preamble. The HO procedure is performed without EPC involvement, i.e. preparation messages are
directly exchanged between the eNBs.
Q. What RBS Hardware does Ericsson use for LTE Technology?
RBS 6000 series
Q. What is considered a good RSRP and RSRQ threshold, good for LTE radio conditions?
RSRP = >-95 dBm (Planning with -113 dBm)
RSRQ=<-7db span="">
Q. What latency (RTT) have you experienced while pinging with 32 bytes?
40-200ms
Q. What technology is used in the uplink and in the downlink?
Uplink: SCFDMA
Downlink: OFDMA
Q. How many Transmission modes we have? What are they? How they are configured in moshell?
Transmission mode:
1. Single Input Multiple Output (SIMO)
2. Transmit Diversity
3. Open Loop Spatial Multiplexing (OLSM)
Q. What other DT tool or any LTE tool have you ever used?
TEMS Discovery & Actix
Q. What are the Radio Frame Structures Supported by LTE?
LTE Radio Frame:

Air Interface For 3G LTE.

Manage the different types of information that needs to be carried between the eNodeB and
the User Equipment.

The frame structures for LTE differ between the Time Division Duplex, TDD and the Frequency
Division Duplex, FDD

Two adjacent slots constitute a sub-frame of length 1 ms

There are two types of LTE frame structure:
o
Type 1: used for the LTE FDD mode systems.
o
Type 2: used for the LTE TDD systems
Q. What is eNodeB Capacity?
eNodeB Capacity
Peak Bit Rate(Mbps)=bit per Hz x N subcarriers x N symbol per subframe in 1ms
Modulation
Bandwidth (MHz)
QPSK
16 QAM
64 QAM
1.4
2.016 Mbps
4.032 Mbps
6.048 Mbps
3
5.04 Mbps
10.08 Mbps
15.12 Mbps
5
8.4 Mbps
16.8 Mbps
25.2 Mbps
10
16.8 Mbps
33.6 Mbps
50.4 Mbps
15
25.2 Mbps
50.4 Mbps
75.6 Mbps
20
33.6 Mbps
67.2 Mbps
100.8 Mbps
Q. Whats difference b/w video download and video streaming?
Streaming is playing audio/video content in real time through the Internet. This does not eat up any
space on your computer’s hard drive.
A fast Internet connection is required to view the videos at its clearest because the video quality is
dependent on the speed of your connection. If you experience frequent pauses or buffering on your
viewing or if you’re not satisfied with the quality, consider downloading the clip (if possible).
Downloading is transferring data from a server into your own computer. You need to have sufficient
hard drive space to be able to save the content.
Although downloading may take some time, the advantages are that you can watch the content anytime
since it’s already saved in your computer and you don’t need to be connected to the Internet to watch
the video. The video will also be of higher quality with no interruptions upon playback
Question . What Is Lte?
LTE (Long Term Evolution) is initiated by 3GPPi to improve the mobile phone standard to cope with
future technology evolutions and needs.
Question . What Is Goal Of Lte?
Answer :
The goals for LTE include improving spectral efficiency, lowering costs, improving services, making use of
new spectrum and reformed spectrum opportunities, and better integration with other open standards.
Question . What Speed Lte Offers?
Answer :
LTE provides downlink peak rates of at least 100Mbit/s, 50 Mbit/s in the uplink and RAN (Radio Access
Network) round-trip times of less than 10 ms.
Question . What Is Lte Advanced?
Answer :
LTE standards are in matured state now with release 8 frozen. While LTE Advanced is still under works.
Often the LTE standard is seen as 4G standard which is not true. 3.9G is more acceptable for LTE. So why
it is not 4G? Answer is quite simple - LTE does not fulfill all requirements of ITU 4G definition.
Brief History of LTE Advanced: The ITU has introduced the term IMT Advanced to identify mobile
systems whose capabilities go beyond those of IMT 2000. The IMT Advanced systems shall provide bestin-class performance attributes such as peak and sustained data rates and corresponding spectral
efficiencies, capacity, latency, overall network complexity and quality-of-service management. The new
capabilities of these IMT-Advanced systems are envisaged to handle a wide range of supported data
rates with target peak data rates of up to approximately 100 Mbit/s for high mobility and up to
approximately 1 Gbit/s for low mobility.
Question 5. What Is Lte Architecture?
Answer :
The evolved architecture comprises E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved
Packet Core) on the core side
Question 6. What Is Eutran?
Answer :
The E-UTRAN (Evolved UTRAN) consists of eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY)
and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each
other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the
EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the
S1-MME and to the Serving Gateway (S-GW) by means of the S1-U.
Question . What Are Lte Interfaces?
Answer :
The following are LTE Interfaces : (Ref: TS 23.401 v 841)
o
S1-MME :- Reference point for the control plane protocol between E-UTRAN and MME.
o
S1-U:- Reference point between E-UTRAN and Serving GW for the per bearer user plane tunnelling and inter eNodeB
path switching during handover.
o
S3:- It enables user and bearer information exchange for inter 3GPP access network mobility in idle and/or active
state.
o
S4:- It provides related control and mobility support between GPRS Core and the 3GPP Anchor function of Serving
GW. In addition, if Direct Tunnel is not established, it provides the user plane tunnelling.
o
S5:- It provides user plane tunnelling and tunnel management between Serving GW and PDN GW. It is used for
Serving GW relocation due to UE mobility and if the Serving GW needs to connect to a non-collocated PDN GW for the
required PDN connectivity.
o
S6a:- It enables transfer of subscription and authentication data for authenticating/authorizing user access to the
evolved system (AAA interface) between MME and HSS.
o
Gx:- It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging Enforcement Function
(PCEF) in the PDN GW.
o
S8:- Inter-PLMN reference point providing user and control plane between the Serving GW in the VPLMN and the PDN
GW in the HPLMN. S8 is the inter PLMN variant of S5.
o
S9:- It provides transfer of (QoS) policy and charging control information between the Home PCRF and the Visited
PCRF in order to support local breakout function.
o
S10:- Reference point between MMEs for MME relocation and MME to MME information transfer.
o
S11:- Reference point between MME and Serving GW.
o
S12:- Reference point between UTRAN and Serving GW for user plane tunnelling when Direct Tunnel is established. It
is based on the Iu-u/Gn-u reference point using the GTP-U protocol as defined between SGSN and UTRAN or
respectively between SGSN and GGSN. Usage of S12 is an operator configuration option.
o
S13:- It enables UE identity check procedure between MME and EIR.
o
SGi:- It is the reference point between the PDN GW and the packet data network. Packet data network may be an
operator external public or private packet data network or an intra operator packet data network, e.g. for provision of
IMS services. This reference point corresponds to Gi for 3GPP accesses.
o
Rx:- The Rx reference point resides between the AF and the PCRF in the TS 23.203.
o
SBc:- Reference point between CBC and MME for warning message delivery and control functions.
Question 8. What Are Lte Network Elements?
Answer :
o
eNB : eNB interfaces with the UE and hosts the PHYsical (PHY), Medium Access Control (MAC),
Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers. It also hosts Radio
Resource Control (RRC) functionality corresponding to the control plane. It performs many
functions including radio resource management, admission control, scheduling, enforcement of
negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane
data, and compression/decompression of DL/UL user plane packet headers.
o
Mobility Management Entity : manages and stores UE context (for idle state: UE/user identities,
UE mobility state, user security parameters). It generates temporary identities and allocates
them to UEs. It checks the authorization whether the UE may camp on the TA or on the PLMN. It
also authenticates the user.
o
Serving Gateway : The SGW routes and forwards user data packets, while also acting as the
mobility anchor for the user plane during inter-eNB handovers and as the anchor for mobility
between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic
between 2G/3G systems and PDN GW).
o
Packet Data Network Gateway: The PDN GW provides connectivity to the UE to external packet
data networks by being the point of exit and entry of traffic for the UE. A UE may have
simultaneous connectivity with more than one PDN GW for accessing multiple PDNs. The PDN
GW performs policy enforcement, packet filtering for each user, charging support, lawful
Interception and packet screening.
Question 9. What Are Lte Protocols & Specifications?
Answer :
In LTE architecture, core network includes Mobility Management Entity (MME), Serving
Gateway (SGW), Packet Data Network Gateway (PDN GW) where as E-UTRAN has E-UTRAN NodeB
(eNB).
Protocol links are as below
o
Air Interface Physical Layer
o
GPRS Tunnelling Protocol User Plane (GTP-U)
o
GTP-U Transport
o
Medium Access Control (MAC)
o
Non-Access-Stratum (NAS) Protocol
o
Packet Data Convergence Protocol (PDCP)
o
Radio Link Control (RLC)
o
Radio Resource Control (RRC)
o
S1 Application Protocol (S1AP)
o
S1 layer 1
o
S1 Signalling Transport
o
X2 Application Protocol (X2AP)
o
X2 layer 1
o
X2 Signalling Transport
Question 10. What Is Volga?
Answer :
VoLGA stands for "Voice over LTE via Generic Access". The VoLGA service resembles the 3GPP Generic
Access Network (GAN). GAN provides a controller node - the GAN controller (GANC) - inserted between
the IP access network (i.e., the EPS) and the 3GPP core network.
The GAN provides an overlay access between the terminal and the CS core without requiring specific
enhancements or support in the network it traverses. This provides a terminal with a 'virtual' connection
to the core network already deployed by an operator. The terminal and network thus reuse most of the
existing mechanisms, deployment and operational aspects.
Question 11. What Is Cs Fallback in Lte?
LTE technology supports packet based services only, however 3GPP does specifies fallback for circuit
switched services as well. To achieve this LTE architecture and network nodes require additional
functionality, this blog is an attempt to provide overview for same.
In LTE architecture, the circuit switched (CS) fallback in EPS enables the provisioning of voice and
traditional CS-domain services (e.g. CS UDI video/ SMS/ LCS/ USSD). To provide these services LTE reuses
CS infrastructure when the UE is served by E UTRAN.
Question 12. How Does Lte Security Works?
The following are some of the principles of 3GPP E-UTRAN security based on 3GPP Release 8
specifications:
o
The keys used for NAS and AS protection shall be dependent on the algorithm with which they
are used.
o
The eNB keys are cryptographically separated from the EPC keys used for NAS protection
(making it impossible to use the eNB key to figure out an EPC key).
o
The AS (RRC and UP) and NAS keys are derived in the EPC/UE from key material that was
generated by a NAS (EPC/UE) level AKA procedure (KASME) and identified with a key identifier
(KSIASME).
o
The eNB key (KeNB) is sent from the EPC to the eNB when the UE is entering ECM-CONNECTED
state (i.e. during RRC connection or S1 context setup).
Question 13. What Is Ip Multimedia Subsystem (ims)?
Answer :
The 3GPP IP Multimedia Subsystem (IMS) technology provides an architectural framework for delivering
IP based multimedia services. IMS enables telecom service providers to offer a new generation of rich
multimedia services across both circuit switched and packet switched networks. IMS offers access to IP
based services independent of the access network e.g. wireless access (GPRS, 3GPP’s UMTS, LTE,
3GPP2’s CDMA2000) and fixed networks (TISPAN’s NGN)
IMS defines a architecture of logical elements using SIP for call signaling between network elements and
Provides a layered approach with defined service, control, and transport planes. Some of IMS high level
requirements are noted below:
The application plane provides an infrastructure for the provision and management of services,
subscriber configuration and identity management and defines standard interfaces to common
functionality.
The IMS control plane handles the call related signaling and controls transport plane. Major element of
control plane is the Call Session Control Function (CSCF) , which comprises Proxy-CSCF (PCSCF), Interrogating-CSCF (I-CSCF) and Serving-CSCF (S-CSCF). The CSCF (Call/Session Control Function)
is essentially a SIP server.
The IMS transport plane provides a core IP network with access from subscriber device over wireless or
wireline networks.
Question 14. How Does Measurements Work in Lte?
Answer :
In LTE E-UTRAN measurements to be performed by a UE for mobility are classified as below
o
Intra-frequency E-UTRAN measurements
o
Inter-frequency E-UTRAN measurements
o
Inter-RAT measurements for UTRAN and GERAN
o
Inter-RAT measurements of CDMA2000 HRPD or 1xRTT frequencies
Question 15. What Is Automatic Neighbor Relation?
Answer :
According to 3GPP specifications, the purpose of the Automatic Neighbour Relation (ANR) functionality
is to relieve the operator from the burden of manually managing Neighbor Relations (NRs). This feature
would operators effort to provision.
Network Administrator Interview Questions
Question 16. How Does Intra E-utran Handover Is Performed?
Answer :
Intra E-UTRAN Handover is used to hand over a UE from a source eNodeB to a target eNodeB using X2
when the MME is unchanged. In the scenario described here Serving GW is also unchanged. The
presence of IP connectivity between the Serving GW and the source eNodeB, as well as between the
Serving GW and the target eNodeB is assumed.
The intra E-UTRAN HO in RRC_CONNECTED state is UE assisted NW controlled HO, with HO preparation
signalling in E-UTRAN.
Question 17. How Does Policy Control And Charging Works In Lte?
Answer :
A important component in LTE network is the policy and charging control (PCC) function that brings
together and enhances capabilities from earlier 3GPP releases to deliver dynamic control of policy and
charging on a per subscriber and per IP flow basis.
LTE Evolved Packet Core (EPC) EPC includes a PCC architecture that provides support for fine-grained
QoS and enables application servers to dynamically control the QoS and charging requirements of the
services they deliver. It also provides improved support for roaming. Dynamic control over QoS and
charging will help operators monetize their LTE investment by providing customers with a variety of
QoS and charging options when choosing a service.
The LTE PCC functions include:
o
PCRF (policy and charging rules function) provides policy control and flow based
charging control decisions.
o
PCEF (policy and charging enforcement function) implemented in the serving gateway,
this enforces gating and QoS for individual IP flows on the behalf of
o
the PCRF. It also provides usage measurement to support charging
o
OCS (online charging system) provides credit management and grants credit to the PCEF
based on time, traffic volume or chargeable events.
o
OFCS (off-line charging system) receives events from the PCEF and generates charging
data records (CDRs) for the billing system.
4G Interview Questions
Question 18. What Is Son & How Does It Work In Lte?
Answer :
Self-configuring, self-optimizing wireless networks is not a new concept but as the mobile networks are
evolving towards 4G LTE networks, introduction of self configuring and self optimizing mechanisms is
needed to minimize operational efforts. A self optimizing function would increase network performance
and quality reacting to dynamic processes in the network.
This would minimize the life cycle cost of running a network by eliminating manual configuration of
equipment at the time of deployment, right through to dynamically optimizing radio network
performance during operation. Ultimately it will reduce the unit cost and retail price of wireless data
services.
Question 19. How Does Network Sharing Works In Lte?
Answer :
3GPP network sharing architecture allows different core network operators to connect to a shared radio
access network. The operators do not only share the radio network elements, but may also share the
radio resources themselves.
Question 20. How Does Timing Advance (ta) Works In Lte?
Answer :
In LTE, when UE wish to establish RRC connection with eNB, it transmits a Random Access Preamble,
eNB estimates the transmission timing of the terminal based on this. Now eNB transmits a Random
Access Response which consists of timing advance command, based on that UE adjusts the terminal
transmit timing.
The timing advance is initiated from E-UTRAN with MAC message that implies and adjustment of the
timing advance.
Question 21. How Does Lte Ue Positioning Works In E-utran?
Answer :
UE Positioning function is required to provide the mechanisms to support or assist the calculation of the
geographical position of a UE. UE position knowledge can be used, for example, in support of Radio
Resource Management functions, as well as location-based services for operators, subscribers, and
third-party service providers.
Question 22. How Many Operators Have Committed for Lte?
Answer :
List of operators committed for LTE has been compiled by 3GAmericas from Informa Telecoms & Media
and public announcements. It includes a variety of commitment levels including intentions to trial,
deploy, migrate, etc.
Question 23. What Is Single Radio Voice Call Continuity (srvcc)?
Answer :
Along with LTE introduction, 3GPP also standardized Single Radio Voice Call Continuity (SRVCC) in
Release 8 specifications to provide seamless continuity when an UE handovers from LTE coverage (EUTRAN) to UMTS/GSM coverage (UTRAN/GERAN). With SRVCC, calls are anchored in IMS network while
UE is capable of transmitting/receiving on only one of those access networks at a given time.
Question 24. How Does Location Service (lcs) Work In Lte Network?
Answer :
In the LCS architecture, an Evolved SMLC is directly attached to the MME. The objectives of
this evolution is to support location of an IMS emergency call, avoid impacts to a location session due
to an inter-eNodeB handover, make use of an Evolved and support Mobile originated location request
(MO-LR) and mobile terminated location request MT-LR services.
Release 9 LCS solution introduces new interfaces in the EPC:
o
SLg between the GMLC and the MME
o
SLs between the E-SMLC and the MME
o
Diameter-based SLh between the HSS and the HGMLC
Question 25. How Does Lawful Interception Works In Lte Evolved Packet System?
Answer :
3GPP Evolved Packet System (EPS) provides IP based services. Hence, EPS is responsible only for IP layer
interception of Content of Communication (CC) data. In addition to CC data, the Lawful Interception (LI)
solution for EPS offers generation of Intercept Related Information (IRI) records from respective control
plane (signalling) messages as well.
Question 26. What Is Carrier Aggregation In Lte-advanced?
Answer :
To meet LTE-Advanced requirements, support of wider transmission bandwidths is required than the 20
MHz bandwidth specified in 3GPP Release 8/9. The preferred solution to this is carrier aggregation.
It is of the most distinct features of 4G LTE-Advanced. Carrier aggregation allows expansion of effective
bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple
carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth.
Question 27. What Is Relay Node And How Does Relaying Works In Lte-advanced?
Answer :
For efficient heterogeneous network planning, 3GPP LTE-Advanced has introduced concept of Relay
Nodes (RNs). The Relay Nodes are low power eNodeBs that provide enhanced coverage and capacity at
cell edges. One of the main benefits of relaying is to provide extended LTE coverage in targeted areas at
low cost.
The Relay Node is connected to the Donor eNB (DeNB) via radio interface, Un, a modified version of EUTRAN air interface Uu. Donor eNB also srves its own UE as usual, in addition to sharing its radio
resources for Relay Nodes.
Question 28. What Are the Measurement Events in Lte?
Answer :
Intra/Inter Frequency Events:
o
Event A1 (Serving becomes better than threshold)
o
Event A2 (Serving becomes worse than threshold)
o
Event A3 (Neighbour becomes offset better than PCell)
o
Event A4 (Neighbour becomes better than threshold)
o
Event A5 (PCell becomes worse than threshold1 and neighbour becomes better than
threshold2)
o
Event A6 (Neighbour becomes offset better than SCell)
Inter RAT Events:
o
Event B1 (Inter RAT neighbour becomes better than threshold)
o
Event B2 (PCell becomes worse than threshold1 and inter RAT neighbour becomes
better than threshold2)
Question 29. When Radio Link Failure Is Detected?
Radio link failure to be detected:
o
upon T310 expiry
o
upon random access problem indication from MAC while neither T300, T301, T304 nor
T311 is running
o
upon indication from RLC that the maximum number of re-transmissions has been
reached
Question 30. What Is Srs Used For?
Answer :
UL reference signal used to measure the channel quality over a section of the bandwidth.
Node B use this information for frequency selective scheduling and link adaptation decisions.
Question 31. What Is Dmrs/drs?
Answer :
DMRS/DRS is uplink reference signal.
Used for :
o
Channel Estimation and synchronization in UL
o
EnodeB can use DMRS for calculating TA command for each UE.
Two Types: 1) PUSCH DMRS.
2) PUCCH DMRS.
PUSCH DMRS:
o
Included in every resource block allocated to UE for PUSCH transmission.
o
Distributed only in Frequency domain to preserve the PAPR characteristic of SC-FDMA.
o
12 Resource element per resource block allocated to PUSCH DMRS.
PUCCH DMRS:
o
Included in every resource block allocated to UE for PUCCH transmission(if
transmitted).PUCCH occupies 2 resource block per 1 ms subframe when transmitted.
o
No of REs used for PUCCH DMRS depends on
a) PUCCH format to be transmitted and whether
b) normal or extended cyclic prefix used.
o
PUCCH DRMS used more no of bits in case of format 1,1a,1b and less no of bits in caseof
format 2, 2a, 2b.
Question 32. What Is Timing Advance? What Happens If Timing Advance Timer Expires?
Answer :
The timing of UL radio frame is relative to DL radio frame. EnB provides timing advance command to
each UE such that all UL transmissions arrive at the eNodeB in synchronous manner.
If TA timer expires UE goes of reestablishment procedure or move to idle.
Question 33. What Is Backoff Indicator? What Is The Use Of Backoff Indicator?
Answer :
Backoff Indicator is a special MAC subheader that carries the parameter indicating the time delay
between a PRACH and the next PRACH.
if the Random Access Response contains a Backoff Indicator subheader:
set the backoff parameter value in the UE as indicated by the BI field of the Backoff Indicator subheader
else,
set the backoff parameter value in the UE to 0 ms.
Question 34. What Is Bsr?
Answer :
The Buffer Status reporting procedure is used to provide the serving eNB with information about the
amount of data available for transmission in the UL buffers of the UE.
Question 35. At What Scenario Ue Triggers Bsr?
Answer :
o
UL data, for a logical channel which belongs to a LCG, becomes available for
transmission in the RLC entity or in the PDCP entity and either the data belongs to a
logical channel with higher priority than the priorities of the logical channels which
belong to any LCG and for which data is already available for transmission, or there is no
data available for transmission for any of the logical channels which belong to a LCG, in
which case the BSR is referred below to as "Regular BSR";
o
UL resources are allocated and number of padding bits is equal to or larger than the size
of the Buffer Status Report MAC control element plus its subheader, in which case the
BSR is referred below to as "Padding BSR"
o
retxBSR-Timer expires and the UE has data available for transmission for any of the
logical channels which belong to a LCG, in which case the BSR is referred below to as
"Regular BSR"
o
periodicBSR-Timer expires, in which case the BSR is referred below to as "Periodic BSR".
Question 36. When Different Types Of Bsr Are Triggered?
Answer :
For Regular and Periodic BSR:
if more than one LCG has data available for transmission in the TTI where the BSR is transmitted
report Long BSR
else,
report Short BSR.
For Padding BSR: if the number of padding bits is equal to or larger than the size of the Short BSR plus its
sub header but smaller than the size of the Long BSR plus its sub header:
if more than one LCG has data available for transmission in the TTI where the BSR is transmitted: report
Truncated BSR of the LCG with the highest priority logical channel with data available for transmission;
else
report Short BSR.
else if the number of padding bits is equal to or larger than the size of the Long BSR plus its sub
header, report Long BSR.
Question 37. What Is the Content of Rare?
Answer :
A MAC RAR consists of the four fields
o
R
o
Timing Advance Command
o
UL Grant
o
Temporary C-RNTI
Question 38. In What Are the Scenario Ue Triggers Rrc Connection Reestablishment?
Answer :
UE Triggers RRC Connection Reestablishment procedure on following condition:
o
Upon detecting Radio Link Failure
o
Handover Failure
o
Mobility From E-UTRA Failure
o
Integrity Failure Indication Received From Lower Layers
o
RRC Connection Reconfiguration Failure
Question 39. When Ue Activates Integrity and Ciphering?
Answer :
o
The SECURITY MODE COMMAND message is used to command the UE for the activation
of AS security. E-UTRAN always initiates this procedure prior to the establishment of
Signalling Radio Bearer2 (SRB2) and Data Radio Bearers (DRBs).
o
AS security comprises of the integrity protection of RRC signalling (SRBs) as well as the
ciphering of RRC signalling (SRBs) and user plane data (DRBs). The integrity protection
algorithm is common for signalling radio bearers SRB1 and SRB2. The ciphering
algorithm is common for all radio bearers (i.e. SRB1, SRB2 andDRBs). Neither integrity
protection nor ciphering applies for SRB0.
o
The eNodeB sends integrity protected SECURITY MODE COMMAND message to the UE.
The UE shall derive KeNB and KRRCint which is associated with integrity protection
algorithm indicated in the SECURITY MODE COMMAND. Then, UE verifies the Integrity
of the received SECURITY MODE COMMAND by checking the Message Authentication
Code (MAC) in the SECURITY MODE COMMAND message. If the SECURITY MODE
COMMANDmessage fails the integrity protection check, then the UE sends SECURITY
MODE FAILURE to the eNodeB.
o
If the SECURITY MODE COMMAND passes the integrity protection check, then the UE
shall derive the encryption keys KRRCenc key and the KUPenc keys associated with the
ciphering algorithm indicated in theSECURITY MODE COMMAND.
o
The UE shall apply integrity protection using the indicated algorithm (EIA) and the
integrity key, KRRCintimmediately, i.e. integrity protection shall be applied to all
subsequent messages received and sent by the UE, including the SECURITY MODE
COMPLETE message.
o
The UE shall apply ciphering using the indicated algorithm (EEA), KRRCenc key and the
KUPenc key after completing the procedure, i.e. ciphering shall be applied to all
subsequent messages received and sent by the UE, except for the SECURITY MODE
COMPLETE message which is sent un-ciphered.
Question 40. What Is the Difference Between Lte FDD And Lte TDD?
Answer :
The difference lies in the LTE frame structure in both the FDD and TDD versions of the LTE. In FDD there
will be pair of frequencies assigned in the downlink and uplink directions and hence transmissions from
multiple subscribes can happen at the same time but on different frequencies as mentioned. In TDD,
one single frequency will be used at different time instants by multiple subscriber terminals (UEs). Both
frame versions of LTE will have 1 ms sub-frame duration and 0.5 ms slot duration.
Question 41. What Is Resource Block In Lte?
Answer :
LTE frame is divided based on time slots on time axis and frequency subcarrier on frequency axis.
Resource block is the smallest unit of resource allocation in LTE system. It is of about 0.5ms duration and
composed of 12 subcarriers in 1 OFDM symbol. One time slot is equal to 7 OFDM symbols in normal
cyclic prefix and 6 OFDM symbols in extended cyclic prefix. One full resource block is equal to 12
subcarriers by 7 symbols in normal CP. Hence it consists of total 84 time/frequency elements referred as
resource elements in LTE network.
Question 42. What Are The Lte Logical, Transport And Physical Channels?
Answer :
All these channels help LTE UE establish the connection with the eNodeB, maintain the connection and
terminate the same. Logical channels are characterized by the information that is transferred. Transport
channels are characterized by how the data are transferred over the radio interface. Physical channel
corresponds to a set of resource elements used by the physical layer. Channels are further divided into
control channel and traffic channel at logical channel stage.
Question 43. Explain The Difference Between Reference Signal (rs) And Synchronization Signal (ss) In
The Lte? Also Mention Types Of Rs And Ss?
Answer :
Reference signal (RS) is used as pilot subcarrier in LTE similar to other broadband wireless technologies
such as WLAN, WIMAX etc. Synchronization signal is used as preamble sequence in LTE for
synchronization purpose. RS is used for channel estimation and tracking. SS are of two types viz. P-SS
and S-SS. P-SS is used for initial synchronization. S-SS is used for frame boundary determination.
RS are of two types viz.
o
Demodulation RS (DRS)
o
Sounding RS (SRS).
DRS is used for sync and channel estimation purpose. SRS is used for channel quality estimation
purpose. DRS is used in both the uplink and downlink, while SRS is used only in the uplink.
Question 44. What Is The Function Of Lte Physical Broadcast Channel I.e. Pbch?
Answer :
After initial cell synchronization is completed, UE reads MIB (Master information block) on PBCH
(Physical channel). Broadcast channel is referred as BCH at transport level and BCCH at logical level. MIB
composed of downlink channel bandwidth in units of RBs, PHICH duration, PHICH resource and system
frame number.
Question 45. What Is The Advantage Of Using Sc-fdma In The Lte Uplink?
Answer :
The main advantage of SC-FDMA is low PAPR compare to OFDMA used in LTE downlink. This increases
the efficiency of power amplifier and hence increases the battery life.
Question 46. What Is Rssi?
Answer :
RSSI stands for Received Signal Strength Indication. It is used almost in all the RATs to identify power
received from the cell in idle as well as connected/dedicated modes. This helps UE always camped on to
the best cell all the time. In case of drop in power measured using RSSI, either UE or network initiates
the handover or cell re-selection is carried out.
Question 47. Explain Circuit Switch Fall Back I.e. Csfb With Respect To Lte And Gsm?
Answer :
Framework allowing the provisioning of voice services by reuse of legacy GSM served CS infrastructure
when the UE is served by E-UTRAN (LTE).To provide voice call support, Circuit Switch Fall Back is carried
out to GSM RAT from LTE RAT to facilitate the voice over LTE (VoLTE) feature.
Question 48. Explain Lte Network Architecture And Various Interfaces?
Answer :
There are various entities forming the LTE network architecture, the main interfaces are Uubetween UE
and eNB, X2 interface between eNBs and S1 interface between eNB and EPC(Evolved Packet Core).
Question 49. Is Lte A 4g Protocol?
Answer :
The networking industry recognizes LTE a 4G technology along with WiMax and HSPA+. None of these
qualified as 4G based on the original definition of the International Telecommunications Union (ITU)
standards group, but in December 2010 the ITU redefined 4G to include them.
While some marketing professionals and press have labeled LTE-Advanced as 5G, no widely-approved
definition of 5G exists to justify the claim.
Question 50. What Is The Difference Between Lte And Lte Advanced?
Answer :
LTE is specified in 3GPP release 8 and release 9. LTE advanced is specified in 3GPP release 10. The main
difference between them is carrier aggregation is introduced in LTE advanced. Number of antennas
supported by MIMO has been increased to 8 in LTE advanced.
Question 1. What Are The Bandwidths Used For Lte Deployment?
Answer :
This following Bandwidths being used for LTE,
1.4 MHz
3 MHz
5 MHz
10 MHz
15 MHz
20 MHz
Question 2. What Is Subcarrier Bandwidth In Lte?
Answer :
15 kHz
Networking Interview Questions
Question 3. What Maximum Lte Throughput Can Be Achieved In The Field?
Answer :
upto 70Mbps on TDD network with 20 MHz bandwidth channel.
Question 4. How Many States A Ue Can Have?
Answer :
There are 2 UE stats i.e. UE Idle and UE Connect.
UE can either be on Connected or on Idle state at a time.
Networking Tutorial
Question 5. What Is Difference Between Ho , Redirection, Cell Selection And Re-selection?
Answer :
Handover (HO): UE moves from one eNB to target eNB while keeping its connected state. LTE Services
will be uninterrupted.In handover procedure, target cell would be prepared and UE will latch on target
cell based on the configuration sent by source enodeb to UE.
Redirection: UE changes its state from connected to Idle mode during Redirection. LTE Service will be
interrupted. Meaning the Source ENB shall release the connection of the UE and will ask the UE to
redirect itself onto the target ENB by indicating the carrier frequency or the cell id in the RRC connection
release message. For example, During CS Fallback, the UE is redirected from LTE RRC_CONNECTED mode
to (2G/3G) idle mode).
Cell Selection: It allows a UE to search and camp on a suitable cell. Cell selection occurs during Initial cell
selection (when UE switches ON), Stored information cell selection (uses stored cell info to identify
appropriate cell), and Cell selection when leaving RRC connected mode (When UE move from RRC
CONNECTED to RRC IDLE mode)
Cell Reselection: Its Idle mode procedure and happens from idle mode to idle mode. Reselection can
occue on cell within same RAT (Intra-RAT) or different RAT(Inter-RAT).
Question 6. What Is Rrc Reconfiguration?
Answer :
RRC CONNECTION RECONFIGURATION message is the command to modify an RRC connection. Main
purposes of RRC Connection Reconfiguration are to,
o
Establish/modify/release Radio Bearers
o
Perform Handover
o
Setup/modify/release Measurements
o
Add/modify/release SCells
o
Dedicated NAS Information might also be transferred from eNodeB to UE
Question 7. What Are The Handover Types In Lte ?
Answer :
The Handover is the process of transferring an ongoing data session/Call from
one (source) cell connected to the core network to another (target) cell. Handovers are needed when UE
moved out of its serving cell’s coverage or for load balancing purposes.
In mobile communication, Handover can either be Network controlled (i.e. HO decision is with network)
or Mobile Evaluated (i.e. Mobile terminal makes HO decision and inform Network to arrange resources
on target cells)
LTE uses both the approaches in a way that, LTE capable UE sends measurement report to network and
based on this report; network directs UE to move to a target cell.
Handover Types in LTE:
Intra-LTE Handover: Source and target cells are part of the same LTE network.
Handover using X2 Interface
Handover using S1 Interface
Inter-LTE Handover: Handover happens towards other LTE nodes. (Inter-MME and Inter-SGW
Inter-MME Handover
Inter-MME/SGW Handover
Inter-RAT Handover: Handover between different radio technologies. For example handover from LTE
to WCDMA.
Question 8. Difference Between X2 And S1 Hand Over?
Answer :
X2 Hand Over:
HO occurs when source and target eNBs are served within the same MME pool. The procedures relies
on the presence of X2 interface between Source and Target eNB,
which is summarized as follows:
o
Source eNB makes HO decision and setup a direct tunnel i.e X2 transport bearer
between Source and target eNB.
o
Detach UE from Source eNB and Forward traffic from source eNB to Target.
o
Path switch procedure between Target eNB and MME
o
Releases S1 bearer of source eNB
o
Release X2 transport bearer for direct packet forwarding.
S1 Hand Over:
S1 handover is when If two eNodeBs are not connected with same MME or the X2 interfaces are not
defined between eNB or when X2 procedure fails(due to unreachability/Error response etc).
Summary of S1-HO is as follows:
o
Source eNB makes HO decision and setup a indirect tunnel i.e S1 bearer between Source
eNB and SGW, and target eNB and SGW.
o
S1 bearer for UL setup between target and source eNB
o
Detach UE from Source eNB and indirect packet forwarding
o
No need for the Path switch procedure between Target eNB and MME, as MME is aware
of HO
o
Releases S1 bearer of source eNB
o
Release S1 transport bearer for indirect packet forwarding.
o
If the two eNodeBs are connected with same MME, it is preferred to perform X2 based
handover but there is no restriction in using S1 based handover even in this case. If two
eNodeBs are not connected with same MME, you have to perform S1 based handover
even in this case.
Question 9. What Is The Difference Between Erlang And Gos?
Answer :
Both Erlang and GoS are used in telephone exchange for measurement of calls such as calls dropped,
calls passed etc.
Question 10. What Is Bit Error Rate And How It Is Calculated?
Answer :
Bit error rate (BER) is used to measure performance of the wireless or wired system in channel or
impairment environment. BER is the ratio of received erroneous bits to the total number of bits
transmitted.
Question 11. What Is The Difference Between Cas And Ccs?
Answer :
CAS stands for Channel Associated Signaling and CCS stands for Common Channel Signaling. Both are
associated with PCM used in telephony.
Question 12. Explain Multipath Fading.?
Answer :
The variation is received signal strength over time is referred as fading. When the signal traverse from
transmit end to receive end, it will have many reflections from buildings and walls till it reaches receive
end. This results into multipath fading.
Question 13. What Is Type Of Modulation Used In Gsm?
Answer :
GMSK stands for Gaussian Minimum Shift Keying.
Question 14. What Is the Difference Between Lte And Lte Advanced?
Answer :
o
LTE is specified in 3GPP release 8 and release 9.
o
LTE advanced is specified in 3GPP release 10.
o
The main difference between them is carrier aggregation is introduced in LTE advanced.
o
Number of antennas supported by MIMO has been increased to 8 in LTE advanced.
Q1. What is LTE?
Ans: LTEi (Long Term Evolution) is initiated by 3GPPi to improve the mobile phone standard to cope with
future technology evolutions and needs.
Q2. What speed LTE offers?
Ans: LTE provides downlink peak rates of at least 100Mbit/s, 50 Mbit/s in the uplink and RAN (Radio
Access Network) round-trip times of less than 10 ms.
Q3. What is goal of LTE?
Ans: The goals for LTE include improving spectral efficiency, lowering costs, improving services, making
use of new spectrum and reformed spectrum opportunities, and better integration with other open
standards.
Q4. What is LTE Advanced?
Ans: LTE standards are in matured state now with release 8 frozen. While LTE Advanced is still under
works. Often the LTE standard is seen as 4G standard which is not true. 3.9G is more acceptable for LTE.
So why it is not 4G? Answer is quite simple - LTE does not fulfill all requirements of ITU 4G definition.
Brief History of LTE Advanced: The ITU has introduced the term IMT Advanced to identify mobile
systems whose capabilities go beyond those of IMT 2000. The IMT Advanced systems shall provide bestin-class performance attributes such as peak and sustained data rates and corresponding spectral
efficiencies, capacity, latency, overall network complexity and quality-of-service management. The new
capabilities of these IMT-Advanced systems are envisaged to handle a wide range of supported data
rates with target peak data rates of up to approximately 100 Mbit/s for high mobility and up to
approximately 1 Gbit/s for low mobility.
Q5. What is EUTRAN?
Ans: The E-UTRAN (Evolved UTRAN) consists of eNBs, providing the E-UTRA user plane
(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are
interconnected with each other by means of the X2 interface. The eNBs are also connected by means of
the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management
Entity) by means of the S1-MME and to the Serving Gateway (S-GW) by means of the S1-U.
Q6. What are LTE protocols & specifications?
Ans:

Air Interface Physical Layer

GPRS Tunnelling Protocol User Plane (GTP-U)

GTP-U Transport

Medium Access Control (MAC)

Non-Access-Stratum (NAS) Protocol

Packet Data Convergence Protocol (PDCP)

Radio Link Control (RLC)

Radio Resource Control (RRC)

S1 Application Protocol (S1AP)

S1 layer 1

S1 Signalling Transport

X2 Application Protocol (X2AP)

X2 layer 1

X2 Signalling Transport
Q7. What are LTE Interfaces?
Ans: The following are LTE Interfaces : (Ref: TS 23.401 v 841)

S1-MME :- Reference point for the control plane protocol between E-UTRAN and MME.

S1-U:- Reference point between E-UTRAN and Serving GW for the per bearer user plane
tunnelling and inter eNodeB path switching during handover.

S3:- It enables user and bearer information exchange for inter 3GPP access network mobility in
idle and/or active state.

S4:- It provides related control and mobility support between GPRS Core and the 3GPP Anchor
function of Serving GW. In addition, if Direct Tunnel is not established, it provides the user plane
tunnelling.

S5:- It provides user plane tunnelling and tunnel management between Serving GW and PDN
GW. It is used for Serving GW relocation due to UE mobility and if the Serving GW needs to
connect to a non-collocated PDN GW for the required PDN connectivity.

S6a:- It enables transfer of subscription and authentication data for authenticating/authorizing
user access to the evolved system (AAA interface) between MME and HSS.

Gx:- It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging
Enforcement Function (PCEF) in the PDN GW.

S8:- Inter-PLMN reference point providing user and control plane between the Serving GW in
the VPLMN and the PDN GW in the HPLMN. S8 is the inter PLMN variant of S5.

S9:- It provides transfer of (QoS) policy and charging control information between the Home
PCRF and the Visited PCRF in order to support local breakout function.

S10:- Reference point between MMEs for MME relocation and MME to MME information
transfer.

S11:- Reference point between MME and Serving GW.

S12:- Reference point between UTRAN and Serving GW for user plane tunnelling when Direct
Tunnel is established. It is based on the Iu-u/Gn-u reference point using the GTP-U protocol as
defined between SGSN and UTRAN or respectively between SGSN and GGSN. Usage of S12 is an
operator configuration option.

S13:- It enables UE identity check procedure between MME and EIR.

SGi:- It is the reference point between the PDN GW and the packet data network. Packet data
network may be an operator external public or private packet data network or an intra operator
packet data network, e.g. for provision of IMS services. This reference point corresponds to Gi
for 3GPP accesses.

Rx:- The Rx reference point resides between the AF and the PCRF in the TS 23.203.

SBc:- Reference point between CBC and MME for warning message delivery and control
functions.
Q8. What is CS Fallback in LTE?
Ans: LTE technology supports packet based services only, however 3GPP does specifies fallback for
circuit switched services as well. To achieve this LTE architecture and network nodes require additional
functionality, this blog is an attempt to provide overview for same.
In LTE architecture, the circuit switched (CS) fallback in EPS enables the provisioning of voice and
traditional CS-domain services (e.g. CS UDI video/ SMS/ LCS/ USSD). To provide these services LTE reuses
CS infrastructure when the UE is served by E UTRAN.
Q9. Why sub carrier spacing is more for wifi than LTE
Ans: I think LTE support high mobility support compare to WiFi, which means LTE technology support
you service even when you are moving with very high speed of the order of around 300Km/h. as we
know as the high the mobility of channel less will be the coherence time ( high doppler shift), due to
which we have keep sub-carrier spacing small for LTE.
Q10. Difference between OFDM and OFDMA
Ans: Basically while asking this question they know that guy must be knowing OFDM but can he
differentiate OFDMA.
So without giving details of OFDM (go to my webpage for details) the OFDMA is multiple access
technique in which individual users are assigned subsets of available subcarriers within one OFDM
symbol and hence multiple users can access the link at the same time.
Q11. What are LTE Network elements?
Ans:
eNB
eNB interfaces with the UE and hosts the PHYsical (PHY), Medium Access
Control (MAC), Radio Link Control (RLC), and Packet Data Control
Protocol (PDCP) layers. It also hosts Radio Resource Control (RRC)
functionality corresponding to the control plane. It performs many
functions including radio resource management, admission control,
scheduling, enforcement of negotiated UL QoS, cell information
broadcast, ciphering/deciphering of user and control plane data, and
compression/decompression of DL/UL user plane packet headers.
Mobility Management Entity
manages and stores UE context (for idle state: UE/user identities, UE mobility state, user security
parameters). It generates temporary identities and allocates them to UEs. It checks the authorization
whether the UE may camp on the TA or on the PLMN. It also authenticates the user.
Serving Gateway
The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user
plane during inter-eNB handovers and as the anchor for mobility between LTE and other 3GPP
technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW).
Packet Data Network Gateway
The PDN GW provides connectivity to the UE to external packet data networks by being the point of exit
and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one PDN GW
for accessing multiple PDNs. The PDN GW performs policy enforcement, packet filtering for each user,
charging support, lawful Interception
and packet screening.
Q12. How does measurements work in LTE?
Ans: In LTE E-UTRAN measurements to be performed by a UE for mobility are classified as below

Intra-frequency E-UTRAN measurements

Inter-frequency E-UTRAN measurements

Inter-RAT measurements for UTRAN and GERAN

Inter-RAT measurements of CDMA2000 HRPD or 1xRTT frequencies
Q13. Advantage and Disadvantage of OFDMA over OFDM
Ans: ADVANTAGE:

Allow simultaneous low data rate for several carriers.

Bursty transmission is minimised

Contention based multiple access is simplified

Provide frequency diversity by spreading the carrier across complete available spectrum

Interference within cell can be minimised on an average by allocating carrier based on cyclic
permutation within band
DISADVANTAGE:

Frequency and phase error sensitivity

diversity gain is not achieved if only few carriers are allocated or same carrier allocated again.

Fast feedback based mechanism required which is more complex

Does not suit to asynch bursty data communication.
Q14. What is VoLGA?
Ans: VoLGA stands for "Voice over LTE via Generic Access". The VoLGA service resembles the 3GPP
Generic Access Network (GAN). GAN provides a controller node - the GAN controller (GANC) - inserted
between the IP access network (i.e., the EPS) and the 3GPP core network.
The GAN provides an overlay access between the terminal and the CS core without requiring specific
enhancements or support in the network it traverses. This provides a terminal with a 'virtual' connection
to the core network already deployed by an operator. The terminal and network thus reuse most of the
existing mechanisms, deployment and operational aspects.
Q15. How does Intra E-UTRAN Handover is performed?
Ans: Intra E-UTRAN Handover is used to hand over a UE from a source eNodeB to a target eNodeB using
X2 when the MME is unchanged. In the scenario described here Serving GW is also unchanged. The
presence of IP connectivity between the Serving GW and the source eNodeB, as well as between the
Serving GW and the target eNodeB is assumed.
The intra E-UTRAN HO in RRC_CONNECTED state is UE assisted NW controlled HO, with HO preparation
signalling in E-UTRAN.
Q16. Advantage and disadvantage of Cyclic Prefix
Ans:
ADVANTAGE:

It makes an OFDM signal insensitive to time dispersion as long as the span of the time dispersion
does not exceed the length of the cyclic prefix.

As a repetition of the end of the symbol, it allows the linear convolution of a frequency-selective
multipath channel to be modelled as circular convolution, which in turn may be transformed to
the frequency domain using a discrete Fourier transform. This approach allows for simple
frequency-domain processing, such as channel estimation and equalization.
DISADVANTAGE:

Only a fraction Tu /(Tu+TCP) of the received signal power is actually utilized by the OFDM
demodulator, implying a corresponding power loss in the demodulation.

CP insertion also implies a corresponding loss in terms of bandwidth as the OFDM symbol rate is
reduced without a corresponding reduction in the overall signal bandwidth.
Q17. What is CS Fallback in LTE?
Ans: LTE technology supports packet based services only, however 3GPP does specifies fallback for
circuit switched services as well. To achieve this LTE architecture and network nodes require additional
functionality, this blog is an attempt to provide overview for same.
In LTE architecture, the circuit switched (CS) fallback in EPS enables the provisioning of voice and
traditional CS-domain services (e.g. CS UDI video/ SMS/ LCS/ USSD). To provide these services LTE reuses
CS infrastructure when the UE is served by E UTRAN.
Q18. What is SON & how does it work in LTE?
Ans: Self-configuring, self-optimizing wireless networks is not a new concept but as the mobile networks
are evolving towards 4G LTE networks, introduction of self configuring and self optimizing mechanisms
is needed to minimize operational efforts. A self optimizing function would increase network
performance and quality reacting to dynamic processes in the network.
This would minimize the life cycle cost of running a network by eliminating manual configuration of
equipment at the time of deployment, right through to dynamically optimizing radio network
performance during operation. Ultimately it will reduce the unit cost and retail price of wireless data
services.
Q19. How does LTE Security works?
Ans: The following are some of the principles of 3GPP E-UTRAN security based on 3GPP Release 8
specifications:

The keys used for NAS and AS protection shall be dependent on the algorithm with which they
are used.

The eNB keys are cryptographically separated from the EPC keys used for NAS protection
(making it impossible to use the eNB key to figure out an EPC key).

The AS (RRC and UP) and NAS keys are derived in the EPC/UE from key material that was
generated by a NAS (EPC/UE) level AKA procedure (KASME) and identified with a key identifier
(KSIASME).

The eNB key (KeNB) is sent from the EPC to the eNB when the UE is entering ECM-CONNECTED
state (i.e. during RRC connection or S1 context setup).
Q20. How does Network Sharing works in LTE?
Ans: 3GPP network sharing architecture allows different core network operators to connect to a shared
radio access network. The operators do not only share the radio network elements, but may also share
the radio resources themselves.
Q21. What is LTE architecture?
Ans: The evolved architecture comprises E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved
Packet Core) on the core side.
LTE and LTE advanced technology is fast evolving in cellular arena and demand in the industries have
been increased for LTE skilled engineers. These top 12 LTE interview questions and answers help
engineers seeking LTE technology job to crack the interview with ease. One can refer page links
mentioned on left side panel to learn more about LTE. These questions are very useful as viva questions
also.
Question-1: What is the difference between LTE FDD and LTE TDD?
Answer-1:The difference lies in the LTE frame structure in both the FDD and TDD versions of the LTE. In
FDD there will be pair of frequencies assigned in the downlink and uplink directions and hence
transmissions from multiple subscribes can happen at the same time but on different frequencies as
mentioned. In TDD, one single frequency will be used at different time instants by multiple subscriber
terminals (UEs). Both frame versions of LTE will have 1 ms sub-frame duration and 0.5 ms slot duration.
Question-2: What is resource block in LTE?
Answer-2:LTE frame is divided based on time slots on time axis and frequency subcarrier on frequency
axis. Resource block is the smallest unit of resource allocation in LTE system. It is of about 0.5ms
duration and composed of 12 subcarriers in 1 OFDM symbol. One time slot is equal to 7 OFDM symbols
in normal cyclic prefix and 6 OFDM symbols in extended cyclic prefix. One full resource block is equal to
12 subcarriers by 7 symbols in normal CP. Hence it consists of total 84 time/frequency elements referred
as resource elements in LTE network. Refer
.
Question-3: What are the LTE logical, transport and physical channels? Answer-3:All these channels
help LTE UE establish the connection with the eNodeB, maintain the connection and terminate the
same. Logical channels are characterized by the information that is transferred. Transport channels are
characterized by how the data are transferred over the radio interface. Physical channel corresponds to
a set of resource elements used by the physical layer. Channels are further divided into control channel
and traffic channel at logical channel stage.
Question-4: Explain the difference between Reference signal (RS) and synchronization signal (SS) in
the LTE? Also mention types of RS and SS.
Answer-4:Reference signal (RS) is used as pilot subcarrier in LTE similar to other broadband wireless
technologies such as WLAN, WIMAX etc. Synchronization signal is used as preamble sequence in LTE for
synchronization purpose. RS is used for channel estimation and tracking. SS are of two types viz. P-SS
and S-SS. P-SS is used for initial synchronization. S-SS is used for frame boundary determination. RS are
of two types viz. Demodulation RS (DRS) and Sounding RS (SRS). DRS is used for sync and channel
estimation purpose. SRS is used for channel quality estimation purpose. DRS is used in both the uplink
and downlink, while SRS is used only in the uplink
Question-5: Explain LTE cell search procedure followed by UE.
Answer-5:LTE cell search procedure is used by UE to camp onto the LTE cell i.e. eNodeB. Refer LTE
UE cell search procedure and network entry procedure.
Question-6: What is the function of LTE physical broadcast channel i.e. PBCH?
Answer-6:After initial cell synchronization is completed, UE reads MIB (Master information block) on
PBCH (Physical channel). Broadcast channel is referred as BCH at transport level and BCCH at logical
level. MIB composed of downlink channel bandwidth in units of RBs, PHICH duration, PHICH resource
and system frame number.
Question-7: What is the advantage of using SC-FDMA in the LTE uplink?
Answer-7:The main advantage of SC-FDMA is low PAPR compare to OFDMA used in LTE downlink. This
increases the efficiency of power amplifier and hence increases the battery life.
Question-8: What is RSSI?
Answer-8:RSSI stands for Received Signal Strength Indication. It is used almost in all the RATs to identify
power received from the cell in idle as well as connected/dedicated modes. This helps UE always
camped on to the best cell all the time. In case of drop in power measured using RSSI, either UE or
network initiates the handover or cell re-selection is carried out.
Question-9: Explain Circuit Switch Fall Back i.e. CSFB with respect to LTE and GSM.
Answer-9:Framework allowing the provisioning of voice services by reuse of legacy GSM served CS
infrastructure when the UE is served by E-UTRAN (LTE).To provide voice call support, Circuit Switch Fall
Back is carried out to GSM RAT from LTE RAT to facilitate the voice over LTE (VoLTE) feature.
Question-10: Explain LTE network architecture and various interfaces.
Answer-10:There are various entities forming the LTE network architecture, the main interfaces are
Uu between UE and eNB, X2 interface between eNBs and S1 interface between eNB and EPC(Evolved
Packet Core).
Question-11: What is SRVCC?
Answer-11:SRVCC is the short form of Single-Radio Voice Call Continuity. SRVCC handover is supported
from E-UTRAN (i.e. LTE) to UTRAN/GERAN (WCDMA/GSM). SRVCC procedure is used for transferring an
on-going PS voice call (IMS) in LTE to a CS voice call via Handover from LTE to GERAN/UTRAN
Question-12:What is the difference between LTE and LTE Advanced?
Answer-12:LTE is specified in 3GPP release 8 and release 9. LTE advanced is specified in 3GPP release 10.
The main difference between them is carrier aggregation is introduced in LTE advanced. Number of
antennas supported by MIMO has been increased to 8 in LTE advanced,Read more.
ACCESSIBILITY

IDLE
Reference signal is used to measure quality

Cell Selection
QRxLevMin -128 to -110 to discourage camping QRxLevMinOffset 0 to 2 will discourage
camping,
Qqualmin -22 to 18 to discourage camping
Pcompensation max (PEMAX –PPowerClass, 0), pMaxServingCell, pMaxGeran

PMAX (max UE power)

Criteria for camping of Less power UEs is hard, pMaxServingCell 1000
Reselection


Start Reselection
o
SIntraSearch 29*2=-58dBm to 31 will encourage reselection
o
sNonIntraSearch 2 to 5 will discourage IRAT reselection, -114+5*2=-104dBm
o
TcrMaxConnMode (mobility calc) T_CRMAX_30S to T_CRMAX_60S will discourage
reselection but increase precision, celResTiF, sIntrasearch, sNonIntrsearch
o
High mobility scaling QHystSfHigh DB0_Q_HYST_SF_HIGH(0dB) to
DB_2_Q_HYST_SF_HIGH will discourage reselection, qRxlevminoffset 0 to 2
o
TreselectionRAT increase to decrease reselection, treSelection 7s
Reselection Decision
o
IdleQhyst1s (current cell) 4 to 2 will discourage sticking to current cell qHyst, qHyst 4
o
Cell offset qOffsetCellEUtran, qOffsetCell, qOffCell, interTResEut,
qRxLevMinInterF, offsetFreq 2 to 0
o
CellReselPriority 0 to 2 for high priority, cellReselectionPriority 5 to 3 èdiscourage
reselection, threshXHighHrpd, tReselectionEutra 2 to 4, tReselectionEutraSfHigh 3 to 2
o
NcellReselectionHigh 16 to 10 è UE enters high mobility state earlier
o
threshXHigh, threshXLow, tReselectionEutraSfHigh, threshServingLow 62,
sPrioritySearch1,
o
interFrqThrH, tResEutSF, eutResTiFHM, celResTiFHM, cellReSelPrio 3 to 0 will
discourage, mobStateParamNCelChgHgh, mobStateParamTEval, qRxLevMinOffset 0 to
2dB, q-RxLevMin, spStResPars, qHystSfHigh, tReselEutr, timeToTriggerSfMedium,
tResUtra, tResUtraSF, utrResTiFHM
o
Qrxlevmeas

Tevaluation 30 to 60s, tEvaluation 240

T320

o
ATTACH T3410 (UE), T3450 (eNodeB)
o
System Information Messages SIB1(Access/Message scheduling, reselection),SIB2(UE
timers, common/shared channel, UL RBs),SIB3(intra-freq reselect)
systemInformationBlock3,SIB4(Intra neigh),SIB5 (inter-freq neigh), SIB6(Reselect to
WCDMA),SIB-7(Reslect to GSM),SIB8(Reselect to CDMA)
Sib3Period RF16 to RF32 èless resources used but delay in access, maxCrSibDl,
si4Periodicity
o

RRC setup success rate (service)
o

CellRadius
pZeroNominalPucch -117
RB=SRB+DRB
o
SRB0 is for RRC messages transmitted over the Common Control Channel CCCH
o
SRB1 is transmitted over the Dedicated Control Channel DCCH. RRC connection
establishment is Signaling Radio Bearer-1. Theis is for NSN and RRC
o
SRB2: bearing NAS signaling and transmitted over the DCCH, This is for NAS and RRC
of high priority
o
DRB bears data maximum of eight DRBs per UE with eNodeB
o
T302 4 to 6 s, timer b/w retries for RRC connection establishment
o
tlnactivityTimer

Causes emergency high Priority Access Mobile terminating Mobile Originating Signaling
and mo-Data.

RRC failures RRC.ReEst.ReconfFail.Rej L.RRC.ReEst.HoFail.Rej, RA measurement(Random
Access failures), PDCP discards, s1RetryTimer 30 to 40,

T300-5, T301, 200 to 300 ms, N310, N311

T310 indicates physical failure 200 to 300

T311 10000 to 150000 ms, RRC reestablishment

T3446

T3460 supervises authentication request.NAS timer

T3470 sueprvises identity request. NAS timer

T3410 UE timer supervises attach request

T3417, T3421 or T3430 retransmission timers

T3421 UE timer supervises detach procedure

RRC Setup Success Rate (Signaling)

PRACH (SIB2)
o
o
o
prach- Configuration Index, Max Preambles, contention/non contention (specified
RACH), Power ramping step DB0 to DB2, Preamble initial received target power
DBM_104 to DBM_100, RA retries, PreambInitRcvTargetPwr DBM_120(-120dBm) to
DBM_92(-92dBm) è performace of cell at the cost of interference on others,
RachAlgoSwitch, maxCrRa4Dl, PRACH cyclic shift, prachFreqOff, prachPwrRamp,
preambTxMax, raContResoT, raMsgPoffGrB, raNondedPreamb, raPowRampSetup,
raRespWinSize, rootSeqIndex, ulpcIniPrePwr, ulpcRarespTpc, RACH density

Early contention resolution can improve the Access success rate

accessBarringTime s32 è T303

numberOfPRBsForDynamicallyScheduledPUSCHForRACHRegion,
maxHARQmsg3Tx, maxRACHTransmitPower,
pRACHPreambleDetectorThreshold, pRACHpowerSetting,
prachFrequencyOffset, preambleInitialReceivedTargetPower,
preambleTransMax, preambleTransmitPowerStepSize,
adaptiveMsg3PowerControlEnable, sctpAccessAssociationMaxRetrans,
sctpAccessEstablishmentMaxRetries
RA (Random Access) update for service request, location update, and paging. RACH is
provided to UE.

Contention (preamble collision) initial RRC connection establishment, RRC
connection reestablishment, uplink data arrival

Non Contention (preambles allocated) handover, downlink data arrival

BackOffSwitch adjust the back off time dynamically to relieve load on RACH

RACH process influences the call setup delay, handover delay, data resuming
delay, call setup success rate and handover success rate.

AcBarringFactorForCall P95(95%) to 80 will discourage access
ATTACH

Incorrect LAC at MSC, TAC at MME
o
T3412 TAC update
o
T3414 UE attach with NAS
o
S1_implicitDetachTimer
o
S1_MobileReachableTimer

SON

RACH load (call arrival rate, HO rate, tracking area update, traffic pattern)

Interference on PUSCH channel

Paramaters that can be controlled are PRACH configuration index, RACH
preamble split, RACH back off parameter value, PRACH transmission power
control parameters
o
FACH
o
PAGING
o
Discarded Paging Messages over the Uu Interface, pagingDiscardTimer 3 to 5s, T3413,
, DefaultPagingCycle or DRX cycle rf128 to fr64 è shorter paging cycle. AS (UE &
eNodeB) RRC service request, location update, and paging, maxCrPgDl, maxNumRrc,
pagingNb, raCrntiReuseT, modificationPeriodCoeff 2, rrcConnReestActive 0 to 1 è RRC
success, cellRange 15 to 10Km è success, coverageIndicator,
nrOfRrcConnectedReserved, dlGbrAdmThresh,
o
T=defaultpagingcycle 1T to 1/2T è less paging time, high paging traffic, fewer groups,
more UEs in a group,
o
nB T to 1/4Tè fewer and larger groups, less paging capacity
o
T=defaultpagingcycle 1T to 2T è more paging time, low paging traffic, more groups,
less UEs in a group,
o
Nb è ONET (1T) to TWOT(2T) more paging capacity
o
maxNoOfPagingRecords3 to 5 èmore UEs in a paging message
o
Single paging message can accommodate a maximum of 16 paging records. Small TA è
more LAC updates and chances of missing paging message increase
o
pagingForceMCSmin -1 to 2 èmin MCS scheme
o
NAS (UE & MME) procedure consists of attach, detach, tracking area (TA) update,
service request, and extended service request.
o
RRC connection reestablishment caused by handover failure, RRC reconfiguration
failure, or radio link failure downlink data arrival. uplink data arrival.
o
initial coding is set by parameter
o
CCCH

SRB-0

RRC(SRB-1) over DCCH Connection Request (Over CCCH from UE to eNodeB)
èUE context/SRB1 allocation è RRC Connection Setup (eNodeB to UE) è RRC
Connection Setup Complete (UE to eNodeB) è Initial UE Message (eNodeB to
MME) è Initial Context Setup message (MME to eNodeB) è Security Mode
command (eNodeB to UE)èRRC Connection Reconfiguration message(eNodeB
to UE)è RRC Connection Reconfiguration Complete message (UE to eNodeB)

RRC(SRB-2) for ERABover DCCH,
o
Signaling Link Release RRC Release UeInactiveTimer 1800 to 2000s, load rebalancing
o
ERAB Setup Success Rate (VoIP)
o
ERAB Setup Success Rate (All)

E-RAB establishment = Signaling Radio Bearer-2 (SRB2) establishment and
Data Radio Bearer (DRB) establishment. ERAB=RB(Um)-S1(S1)
o
Radio Network Unavailability Rate
o
9 Radio Bearers RadioBeare rs _QCI _ 1 (highest) to 9

RRC reconfiguration establishment, modification and Release of RBs

SRB2 Inititial Context Setup Request (MME to eNodeB) è RRC connection
reconfiguration (enodeB to UE)è RRC connection reconfiguration complete
(UE to eNodeB) èIntial context setup (eNodeB to MME) èERAB setup request
(MME to eNodeB) è RRC reconfiguration (enodeB to UE) è RRC
reconfiguration complete (UE to eNodeB) è ERAB setup response (eNodeB to
MME)

DRB ERAB modify request (MME to eNodeB) è RRC connection
Reconfiguration (eNodeB to UE) è RRC Reconfiguration complete(UE to
eNodeB) èERAB modify response(eNodeB to MME). 8 DRB max.
o
csFallbackPrio, s1RetryTimer, CS Fall-Back feature, Gold Service ArpThd 5 to 8 è
access, Qci1HoThd 90 to 95 è access, NewGoldServiceOffset 10 to 5 è access to gold at
the cost of silver/copper, a2TimeToTriggerRedirect, ocAcProbFac, acBarSig,
sigAcProbFac, addAUeRrHo, qRxLevMinUtra
o
RAC is based on No. of RRCs and active users, maxNumActDrb
o
RRM, Dynamic Resource Allocation = Scheduling, resources modified are PRBs, Power,
PDCCH/PUCCH Resources, TX rank, baseband power, UlBasebandCapacity
DlBasebandCapacity
o
isRrcReEstablishmentAllowed
o
o
Channels

Downlink Control Channels

PCFICH (no of symbols in PDCCH depending upon signaling), maxNrSymPdcch,

PDCCH (scheduling, Downlink control info-DCI, MIMO mode, precoding,
modulation, SIB, paging, broadcast, RACH response)

DCI-0 uplink scheduling, RB group assignment, UL grant

DCI-1 modulation, TPC, coding, RB assignment

Resource allocation type-0

Resource allocation type-1

Resource allocation type-2 Resource indication Value-RIV (like pointer)

DCI-2 downlink shared channel assignments in case of closed loop spatial Mux

DCI-2A downlink shared channel assignments in case of open loop spatial Mux

DCI-3 TPC

CQI request

cFI 1 to 2 è increase in no. of PDCCH symbols, dynamicCFIEnabled

initial coding is based on control data volume

PHICH ack/nack

PBCH MIB 40 ms, pBCHPowerOffset, initial coding is set by parameter

PSS & SSS symbol and frame timing as well as cell identities

RS reference signals for cell recognition, channel estimation, path loss
estimation, and handover measurement. srsBandwidth, srsHoppingBw,
srsPwrOffset, nbrSRSperTTI

PCI 504 = 168 (secondary x 3 (primary group)

PDSCH for downlink data, deliver RA-RNTI,TA, uplink grant, contention
response by eNB, Pb 0 to 3 & ReferenceSignalPwr 182 to 200 (20dBm) è high
coverage/capacity but interference on others, PDSCH power boosting, initial
coding is set by parameter

Paging initial coding is set by parameter

Uplink channels
PUCCH ack/nack, channel quality indication (CQI) reports, precoding matrix
information (PMI) and rank indication (RI) for MIMO, and scheduling requests (SR).
Control info is ent on this channel if PUSCH is not assigned to UE, pucchSize,
pZeroNominalPucch, noOfPucchSrUsers, dynamicPUCCHEnabled
o
PUSCH data, freq hopping can be used, Intra-frame or Inter frame hopping, type 1 or 2
hopping demodulation reference signal is used for channel estimation sounding
reference signal provides uplink channel quality CQI 16 values representing
modulation scheme and coding format, pZeroNominalPusch -103 (power),
HoppingMode HoppingOffset, cqiReportingModeAperiodic
o
PRACH Preambles, initial access, handover, UL sync and UL SCH resource requests.
initial coding is set by parameter, NCS(prachCs)
o
DRS Demodulation reference signals for channel estimation
o
Sounding reference signals (SRS) are used to control frequency-dependent scheduling
by the eNodeB and PSrsOffsetDeltaMcsDisable -30 to -15 increase power of SRS.
Estimate channel quality, transmitted where there is no user data
o
Measurement messages are sent
o
POWER CONTROL

FPC Fractional Power Control, applicable on Cell-specific reference signal,
PBCH. estimation, and handover measurement.

Commands are sent through DCI

Reference signal power -57, PCFICH power -3175, PBCH power -3174,
Synchronization signals power, -3173, DBCH power -3172, Paging power 3171, Rach respond power

-3170, Prs Power -3169

SINR target and CQI, Downlik ICIC, scheduling affect power control

ICIC SON can change parameters HII, OI and DL TX Power indicator. ICIC
changes scheduling strategies on serving and neighbor cells

CellDlpcPdschPa (enable PC or even power distribution)

partOfRadioPower 100, confOutputPower 20 to 40, confOutputPower,
maximumTransmissionPower, rlfailureT, noutsyncInd, MinpwrRL, MinpwrMa,
qRxLevMinInterF, dFpucchF1, dlPathlossChg, dlpcMimoComp, enablePcPdcch,
p0NomPucch, p0NomPusch, pMax, pMaxIntraF, pMaxOwnCell,
rxPowerScaling, tpcStepSize, ulpcAccuEnable, ulpcAlpha, ulpcEnable,
ulpcIniPrePwr, ulpcLowlevCch, ulpcPucchEn, ulpcReadPeriod, ulpcUplevCch,
ulpcUpqualCch, pMaxUtra, networkSignallingValue NS_01 (UE power
attenuation)

Power Control of Signals

ReferenceSignalPwr 182(18dBm), offset of Sync signal SchPwr 0, PbchPwr 600(-3dB), PcfichPwr -600(-3dB), They affect the coverage. The cell-specific
reference signal is used for cell recognition, channel estimation, path loss,
Scaling factor Pb 1 to 3 (01,2,3)è High Power of Reference signal but at the
cost of PDSCH, CellUlpcDedic, referenceSignalPower

PRACH PreambInitRcvTargetPwr DBM_104(-104dBm) to -102 ,
PwrRampingStep DB2 to DB4, retries, Increase in Power è more interference
but good accessibility, FilterRsrp

PDCCH Carrying RACH Response, Paging Messages, SIBs. RaRespPwr,
PagingPwr -3171, DbchPwr, They affect accessibility. Increase in Power è more
interference but good accessibility.

PDCCH (RRC or SD)PC is dynamic w.r.t SIR targets and Static based on
PdcchPwrDedi larger value è less drops but less UEs accommodated,
throughput and accessibility is affected, PdcchBndPcSw is the switch for
dynamic PC. maxNrSymPdcch,

PHICH carries HARQ and affects throughput. PC is dynamic w.r.t SIR targets
and Static based on PhichPcOff, PhichResource 1 to 2 è more control
resources. SINRRS(based on CQI) ≤SINRTarget then increased power

PDSCH Increase Pb and Pa to increase power of PDSCH. PaCenterUe PA_0,
PPDSCH_A, PO_PDSCH, pDCCHPowerOffsetSymbol1, paOffsetPdsch,
pDCCHPowerControlMaxPowerDecrease

In Dynamic scheduling: CQI, transmission block, GBR, AMBR are considered
to arrive at Pa value

In Semi-persistent scheduling: BLER target is considered

ICIC informs if user is at the centre or edge

PUSCH (UE) affects throughput ,PCMAX, Alpha (0.4 to 0.8) ègood for cell edge
users but not of system performance, P0NominalPUSCH -67 to -58 large
value è throughput of the cell increases but network
decreases, DeltaMcsEnabled 0 to 1 è MCS value affects power control and
throughput increases


Dynamic

SINR based

PH, RBs,

RBs and OI of neighbor
Semi persistent

BLER
o

PUCCH (UE) affects throughput. The PUCCH carries the ACK/NACK
information, CQIs, and schedule request (SR) information related to
downlink data. DeltaFPUCCHFormat1, PucchAlgoSwitch, P0NominalPUCCH 105 to -100 increases throughput but decreases network throughput

primarySyncSignalPowerOffset

SRS for uplink channel estimation and uplink timing, PSRS OFFSET, low
power è low performance

maximumTransmissionPower, confOutputPower, sectorPower, pMaxInterF,

RaRspPwr PchPwr DbchPwr SchPwr PbchPwr PcfichPwr PrsPwr

PaPcOff

Open loop PC is based on path loss, broadcasted/RRC parameters

Closed Loop PC is based on UL level and quality measurements,
CELL_PWR_RED
LOAD CONTROL

T320

RacAlgoSwitch enable admission and load control algo, MlbAlgoSwitch load
balancing algo

ulAccGbrAdmThresh

loadTargetForOCNS RB based

loadTargetForOCNSonPDCCH Power based

Load Monitoring


Resource Limitation Indications

Downlink power limitation indication

PUCCH resource limitation indication

Sounding resource limitation indication PUSCH

Transport resource limitation indication

Cell Congestion AqmAlgoSwitch (queueing at the cost of
integrity)
PRB usage, QoS satisfaction rate of GBR services, and resource
limitation, DlRbHighThd 95 to 90 to encourage load control


UlRbHighThd 95 to 90 è Load control
QOS Satisfaction Rate, based on QCI, admission based on QOS



Admission Control

Check UE capability

Resource prediction or QoS satisfaction rate of Admitted services or
check no. of PRBs

Resource: Allocation and Retention Priority (ARP), SRB for
location updates and detach, GoldUserArpThd 5 to 4 will
increase priority, MaxNonGbrBearerNum 3000 to 4000 will
enhance admission. By limiting the number of PRBs used by
GBR services, admission control increases the admission
success rate

QoS: admission threshold for new gold services is QcixHoThd
plus NewGoldUserOffset.

Service preemption and Redirection, PreemptionArpThd 5(ARP value)
to 3 to encourage preemption

MaxNonGBRBearerNum 3000 to 4000 è admission

GbrRbUseHighProportion, dlAccGbrAdmThresh
Load Balancing

Intra-Frequency CIO(for connected mode), Qoffset in idle mode,
Increase CIO and decrease Qoffset

IntraFreqMlbThd 60 to 50 for traffic shifting, LoadOffset 8 to
5,Neighbor with the lowest load is considered or in A category

Auto adjust CIO(for connected mode), Qoffset in idle mode

CIO decrease to discourage HO to neighbor

InterFreqMlbThd 60 to 55

InterRatMlbThd 75 to 70 unidirectional only, based on UE attributes,
service attributes, load factors, and system performance.

LoadExchangePrd 10s to 8 èload control, imLoadBalancingActive,
threshServingLowHystMin, threshXHighHystMin
Congestion Control

Preemption of GBR services with low energy efficiency rate (EER)


PreemptionArpThd 5 to 3 è congestion relief
GBR service rate downsizing

CopperGbrCongProportion 90% to reduction 80 reduction è
congestion relief

Qci1CongThd 65 + CongRelOffset 20 < Qci1HoThd 90 to 85 è
congestion relief? QcixHoThd is small èoverall QoS satisfaction rate of
the admitted services is low but the admission of incoming handovers
is easy and drop rate may increase.

Energy efficiency rate (EER) depend upon data amount, PRB used,
Downlink Power. More data with less power è efficiency

if ARP is >= LdcMeaArpThd 10 to 5 è EER is calculated

LdcMeaArpThd 10 to 13 è congestion relief but drops increase
RETAINBILITY-CDR
Call Drop Rate (VoIP)
Service Drop Rate (All)
Radio Network Unavailability Rate
pZeroNominalPusch
RAB Failures ERAB relase causes (normal,abnormal,HO, congestion, unavailability), ERAB
modification causes, CQI measurement, MAC traffic retransmissions, no of users/edge
users,PDCP discards/packet loss, UE context releases, Check RACH and power parameters
Raw counters, Traces, Layer3, DT, PM events for diagnosis,
CSFallBackBlindHoCfg
CQI 0 to 15, MCS 0 to 31, QC1 to QC9, RANK 1 to 4
T310 indicates physical failure 200 to 300
UeInactiveTimer 1800 to 2000s
T321
Interference
o
IRC works at physical layer è MIMO
o
ICIC works at MAC layer, adjust center CCU and edge CEU UE loading
o
dlInterferenceManagementActive switch, noOfRxAntennas, tHODataFwdReordering 50
to 100 ms
o
tInactivityTimer, a5B2MobilityTimer, s1RetryTimer, tHODataFwdReordering, cellRange 15
to 10Km è low drops, coverageIndicator, ulInterferenceManagementActive,
pMaxServingCell
MIMO
o
Fading=Variance in SINR, 6dB gain with 4 antennas, adjust antenna weights to either
minimize interference gain (MRC) – white Noise or maximize signal gain (IRC) – colored
interference, Closed loop for slow moving and open loop for fast moving
E-RAB Release Service, handover, actRedirect, taTimerMargin, addAUeRrHo, dlTargetBler,
p0NomPusch, riEnable, riPerOffset, taMaxOffset, taTimer, ulamcSwitchPer, qQualMinUtra,
qRxLevMinUtra
DeltaPreambleMsg3 4 to 6, DeltaFPUCCHFormat2a DELTAF2(2dB), P0NominalPUCCH
The definition of an abnormal release is that there shall be buffered data to be transmitted at the
time of release èrelease of the E-RAB had a negative impact on the end-user.
o
Voice release, normalized to releases
o
PS releases, normalized to session time

tlnactivityTimer

T301

tTimeAlignmentTimer (Timer for TA UL sync)

T3411 failure in NAS signaling

T3410 failure in NAS signaling

T3430 failure in NAS signaling

T3417 failure in NAS signaling

T3440
o
GroupHoppingEnabled, isRrcReEstablishmentAllowed, isS1EnhancementsAllowed,
isTrafficBasedContextReleaseAllowed, vswrUrgentThreshold 20 to 15 è early trigger of
alarm, minimumCQIForFSS, connTimer, hARQMaxTimer, initialMCSIndexForBearerSetup,
mIMOMode, sctpAccessPathMaxRetrans
o
Closed Loop PC is based on UL level and quality measurements, CELL_PWR_RED, upper
and lower thresholds
MOBILITY
General Causes
o
Path imbalance, connectors, hardware, antenna tilt, serving/neighbor config,
discontinuous coverage, parameter settings, interference, cell degraded, PCI
collisions,unavailabilities, check equipment health,
T304 supervises the Intra-LTE HO
Events
o
A1(stop Inter-freq/Inter-RAT meas due to good quality), A2(start Inter-fre/Inter-RAT
meas due to good quality) RRC Connection Release with Redirect, A3(start intra-freq HO
due to good neighbor) better cell HO, A4(start inter-freq HO due to good neighbor, B1
(start inter-RAT HO due to good neighbor), A5 coverage HO

o
a3offset (serving) 30 to 40 è discourage HO, timeToTriggerA3 40 to 64,
hysteresisA2Sec (neighbor) 10 to 20, hysteresisPm, reportAmountA2Prim 1 to 2
è discourage A2, reportAmountA3, reportIntervalA2Prim MS120 to MS240,
reportQuantityA2Prim, timeAndPhaseSynchCritical, x2BlackList,
x2retryTimerStart, reportIntervalPm MS_480 to MS_640, removeNcellTime 1 to
2 min, b1ThresholdEcNoUtra, hysteresisA3 3dB, timeToTriggerA3 320 ms,
filterCoefficientEUtraRsrp 4, tHODataFwdReordering 300 to 400 ms
UE Level Oscillating Handover Minimization feature
SON
o
AnrSwitch, MroSwitch, TpeSwitch
o
Power Control
o
Reference signal power -57, PCFICH power -3175, PBCH power -3174, Synchronization
signals power, -3173, DBCH power -3172, Paging power -3171, Rach respond power, 3170, Prs Power -3169
o
Neighbor-ANR

maxReportCellsPm, measurementPriority, cellAddRankLimitEutran,
isRemoveAllowed, cellAddRsrpOffsetEutran, cellAddRsrpThresholdEutran, remo
veNrelTime, ctrlMode, maxMeasInterFreqEUtra, filterCoefficientEUtraRsrq,
dlInterferenceManagementActive, anrUesThreshInterFMax,
minBestCellHoAttempts 1, x2BlackList, anrIntraFreqState, ANR add cell
threshold(%),Fast ANR PCI report amount, FastAnrRsrpThd, Fast ANR checking
period, covTriggerdBlindHoAllowed

ANR is suggested for early phases

anrEnable, isBlindPsHoToUtraFddAllowed

Event triggered, Detection of missing neighboring, PCI collisions and abnormal
neighboring cell coverage

NRTCellHOStatNum no of HOs with N and ANR DelCellThd 60 to 50% è
discourage deletion, HOSR with N, FastAnrRprtAmount,

Drawbacks, HO delayed, data delay
o

Periodic or Fast, detects only missing neighbor, FastAnrRprtInterval 2048 ms to
1024 ms will speed up the ANR èhigh speed, FastAnrIntraRatMeasUeNum 5 to 7
will improve HOSR. Periodic measurements èincrease power and decrease
throughput. FastAnrRsrpThd -102 to -90 è make ANR tough èURBAN

Manual configure black and white list, intrFrBCList, intraEnbPrio, statusRepReq,
A3 offsets, a3ReportInterval, a3TimeToTrigger, addAUeRrHo, addAUeTcHo,
cqiPerNp, dlsUsePartPrb, maxNumAUeHo, p0NomPusch, p0UePusch, pMax,
taMaxOffset, threshold1

CsfbHoUtranTimeToTrig,
HO Parameter-MRO minimizes HO failures, service drops, Early/Drag/Ping-pong by
adjusting CIO. Enable during initial phase, MRO (Mobility Robust Optimization) feature
optimizes the handover parameters automatically. Deals premature handover, delayed
handover, and ping-pong handover. It changes the CIO, NcellOptThd, PingpongTimeThd,
Ping-Pong RatioThd 10 to 5 % (to encourage MRO), MRO optimization period(min), Ncell
optimization threshold(%)

CIO, PingpongTimeThd 5 to 3, PingpongRatioThd 5 to 3 è SON or MRO

OptPeriod 1440 to 1300, OptParaThd 70 to 80% HOSRè SON

Ealry Hos>Delayed Hos è decrease CIO of neighbor
2. Detect early or late HO

IRAT HO a2ThresholdRsrpPrim, a2ThresholdRsrpSec, b2Threshold1Rsrp, Uemeasurements
active, triggerQuantityA2Sec, hysteresisA2Prim,
timeToTriggerA2Prim, isForcedDrxForCsFallbackAllowed no to yes, isX2LoadIndicationAllowed,
threshold2EutraRsrq 8 (-7,-6.5) to 9 (-10,-9.5) è discourage A5, tReselectionEUTRAN,
maxTimeAllowedForCsfbMobilityAttempt

a3offset 30 to 35 è discourage A3 or adding Intra freq neighbor, a1ThresholdRsrqPm

pMaxGer, qRxLevMinGer

KPIs handover success rate, call drop rate, and ping-pong handover rate are set per QCI.

RACH-PDCCH

CIO decrease to discourage HO to neighbor. Intra-Frequency CIO(for connected mode), Qoffset
in idle mode

LTE system uses hard handovers

RRC = connected mode, HO Types, Coverage, Load, service based,

Measurements gaps=compressed mode, frequency-specific offset 0 to 2 encourages HO

PBGT HO minBestCellHoAttempts, qOffsetFreq

Event-Triggered Periodical Reporting Hysteresis, time-to-trigger, filtering coefficient for
L3- EutranFilterCoeffRSRP FC0 to FC2 will delay HO, reporting configuration.

Intra-frequency Handover Out Success Rate
o
Cell group ID is critical
o
In load based, CIO is changed automatically
o
A3 Mn + Ofn + Ocn – Hys > Ms + Ofs + Ocs + Off (IntraFreqHoA3Offset)
o


MeaBandwidth MBW-50 MBW-60, QoffsetFreq, IntraFreqHoA3Offset 2 to 4 will
discourage HO, IntraFreqHoA3Hyst 2 to 4(2dB), IntraFreqHoA3TimeToTrig 40 to
60 ms, IntraFreqHoA3TrigQuan, IntraRATHoMaxRprtCell 4 to 6,
IntraFreqHoRprtInterval 240 to 480ms, EutranFilterCoeffRSRP FC6 to FC8,
IntraRATHoRprtAmount r2 to r4

High values for cells with large signal fading variance
CellIndividualOffset (Auto) dB-0 to dB-2 will encourage HO

Ocs less value will discourage HO

Ocn (connected mode) high will encourage HO
o
Retry and Penalty
o
Handover failure è cell selection procedure è RRC connection re-establishment
Measurement Gaps
o
GapPatternType

GAP measurement pattern1 Tperiod 40ms, TGAP 6ms

GAP measurement pattern2 Tperiod 80ms, TGAP 6ms
o
RRC connection re-establishment towards the selected cell only
o
Blind HO In the case of a load-based or service-based handover, the eNodeB may select
a target cell in the absence of the measurement information, in order to reduce the
delay
o
Inter-frequency Handover Out Success Rate

A2 Ms + Hys < Thresh


InterFreqHoA1A2Hyst 4 to 6(3dB), InterFreqHoA2ThdRSRQ -24(-12dB)
to -28(-14dB),
A4 Mn + Ofn (QoffsetFreq) + Ocn – Hys > Thresh

QoffsetFreq 0 to 3 , InterFreqHoA4Hyst 4 to 6


InterFreqHoA1ThdRSRQ -20 to -22, InterFreqLoadBasedHoA4ThdRSRP 103 to -105

Timer304 GEAN IRAT timer
Load Based

Based on frequency capability of UEs, ARPs, and resource usage

Handover In Success Rate

Inter-RAT Handover Out Success Rate (LTE to CDMA)

Inter-RAT Handover Out Success Rate (LTE to WCDMA)

InterRatHoA2ThdRSRQ -20 to -22, InterRatHoA1ThdRSRQ -20 to -18,
InterRATHoUtranB1ThdEcN0 -20 to -16, LdSvBasedHoGeranB1Thd -98
to -94, UtranFilterCoeffRSCP FC0 to FC2, InterRatHoRprtAmount,
InterRatHoGeranRprtInterval

T311 10000 to 150000 ms

Inter-RAT Handover Out Success Rate (LTE to GSM)

GeranFilterCoeff FC0 to FC2

T304 ms4000 to ms8000

redirectionInfoRefPrio1, OffsetFreq, ThreshXHigh, ThreshXLow,
PciConflictAlmSwitch

tMobilityFromEutraCCO
INTEGRITY

ulChBw, redBwMaxRbDl 10 to 15 PRBs Maximum number of PRBs assigned in downlink,
tPeriodicBsr 20 to 60s.

Throughput depends upon
o
Channel environment (e.g. stationary or mobile, speed) and fading conditions.
o
Reception conditions impaired by traffic load levels, and by interference between the
cells, in short by the user’s SINR.
o
Network layout, type of antenna.
o
Position of users in the cell (implies e.g. path loss and fading).
o
Restriction of user data rates (e.g. by terminal category)
o
Link sharing weights (Quality of Service (QoS) configuration)
o
Backhaul capacity
o
Troubleshoot Throughput

Check alarms

Check UE capability

Check AMBR of user service

Check parameters like
dlChannelBandwidth/ redBwMaxRbDl noOfUsedTxAntennas,
pZeroNominalPucch, noOfUsedTxAntennas

Check Licenses 64-QAM

Check Radio IE CQI, MCS, PRBs, Transmission mode,RI, HARQ, RLC
retransmisssions, CFI, buffer status, PHR, rxPowerReport, TTI scheduling, RLC
discards, tStatusProhibit

Check reports from L1 to MAC

Check UE variables, ARP,buffer status, PHR report of UE, interference,
pZeroNominalPusch of neighbours/serving, Max PRBs allowed

Check PDCCH, if CCE are occupied by donwlink grants than UL grants cannot be
scheduled

QoS profile QCI, priority bit, AMBR, ARP

Transport Network
1. GE link counters (packet delays, errors, re-trans),SCTP, synch, IpInterface
2. Use wireshark (throughput result and signalling analysis)

Service Downlink Average Throughput

Service Uplink Average Throughput

AQM (automated queue management)-discard large data volume, relieves queue congestion,
reduce transmission delay

ROHC (Robust Header Compression)

Traffic Volume, no of RBs, MCS coding, usage of PRB (Physical resource blocks), MAC
retransmission, no of users/edge users

CQI 0 to 15, MCS 0 to 31, QC1 (highest) to QC9, RANK 1 to 4, modulation scheme

RRM, Dynamic Resource Allocation = Scheduling, resources modified are PRBs, Power,
PDCCH/PUCCH Resources, TX rank, baseband power, UlBasebandCapacity DlBasebandCapacity

Common Low Data Rate Issues: TCP/UPD/IP Config, transport network, cable swaps,
pmIfInOctetsLink1Hi, CRC errors, RxPower at eNB, GINR on DL, TA, sync

isLargePdcpSduAllowed, maxNbOfCallCapacityLicensing, sRPeriodicity 10 to 5ms,
numberOfPRBsForDynamicallyScheduledPUSCHForCentralRegion 16 to 20,
srsBandwidthConfiguration, dlBasicSchedulingMode, dlResourceAllocationType,
dlSchedulerMode, expectedNumberOfUEPerTTIForDLRR, maxNumberOfRBsPerUE,
nbrUserThrFDS, maximumFSSUsers, operationalMode, pmcMaxResultStringBlockSize,
mIMOMode

Reducing Low CINR impact
o
Resource Block Group Assignments
o
Frequency Selective Scheduling
o
Inter-Cell Interference Coordination (ICIC)

KPITYPE (alarm)

Power is distributed along subcarriers, high bandwidth è less power è less coverage

NAS authentication, service request, connection setup

MimoAdaptiveParaCfg (Transmission mode fixed 3/adaptive), ECGI, PCI, scheduling recources,
LBBP (baseband resources), Qam64Enabled, RachAlgoSwitch, AqmAlgoSwitch (queueing at the
cost of integrity), BfAlgoSwitch beamforming algo, DlSchSwitch, DlschStrategy
(DLSCH_PRI_TYPE_RR(RR) to DLSCH_PRI_TYPE_MAX_CI(MAX C/I)), UlSchSwitch,
BtServiceWeight, PdcchSymNumSwitch, MaxReportCellNum, measBdw, dlTrmBw, ulTrmBw,
drbPrioDl, packLoss, resType, ulsBSD, ulsPrio, prio, resType, raLargeMcsUl, PucchRS,
dSrTransMax, deltaPreMsg3, deltaTfEnabled, dl64QamEnable, dlCellPwrRed, dlChBw,
dlMimoMode, dlRBM, harqMaxTrDl, hopBwPusch, hopModePusch, iniMcsDl, iniPrbsUl,
maxBitrateDl, maxNumAUeHo, maxNumUeDl, mbrSelector, mimoOlCqiThD, minBitrateDl, pMax,
redBwEnDl, redBwMaxRbDl, redBwRpaEnUl, riEnable, ulChBw, ulTargetBler, ulamcEdgFugEn,
ulamcSwitchPer, ulatbEnable, trafficType, rtoMax, qQualMinUtra, qRxLevMinUtra, proportional
fair scheduler, Preamble format affects UL throughput, Traffic Marking (transport), PRB, PDSCH
power boosting

More users èservice fair è bit rate,

Less users è resource fair

spatial multiplexing and transmit diversity

Adaptive Transmission bandwidth ulatbEventPer

preamble sequence subset è uplink resources

MIMO featureStateDualAntDlPerfPkg, noOfTxAntennas

The resources managed by the downlink scheduler are downlink Physical Resource Blocks,
downlink power, PDCCH capacity and base-band processing capability. The resources managed
by the uplink scheduler are block resources for PUSCH, PDCCH, PHICH and base-band processing
capacity.

100 simultaneous UEs, 8 DRBs max per User, licenseCapacityConnectedUsers,
licenseCapacityDlBbCapacity,, number of OFDM symbols for PDCCH

PUCCH Overdimensioning feature for Rural sites

DRX introduces extra delay to scheduling EnterDrxSwitch, DrxInactivityTimer, DrxReTxTimer,
ShortDrxCycle, FddEnterDrxThd, TrmSwitch, DiscardTimer, UeMaxRetxThreshold,
ENodeBMaxRetxThreshold, UlschPriorityFactor, DlMinGbr, PreAllocationWeight,
PrioritisedBitRate, LogicalChannelPriority, SriPeriod, UlschPriorityFactor, defPagCyc

noOfPucchSrUsers 50, nrOfSymbolsPdcch 1, allowedMeasBandwidth, channelBandwidth,
noOfPucchSrUsers, noOfRxAntennas, priority, pucchOverdimensioning 0, schedulingStrategy
(round robin to strict priority), ulChannelBandwidth, ulMinBitRate, pdb, dscp, dlMinBitRate,
resourceAllocationStrategy, dlChannelBandwidth, dlTransNwBandwidth,
dlFrequencyAllocationProportion, ulTransNwBandwidth, dlMaxRetxThreshold, mtu,
tPollRetransmitDl, rlcMode, dlPollPDU, tReorderingDl, ulMaxRetxThreshold, ulPollPDU,
dlMaxHARQTx, priority bit
o
Poor Uplink P0NominalPUSCH -67 to -58 uplink thorughput at the cost of network
performance
o
Increase PreambInitRcvTargetPwr, PwrRampingStep èimproved accessibility and
throughput
PLANNING

LINK BUDGET TX Diversity of MIMO, Adaptive array gain, occupied sub-carrier bandwidth, RX
diversity Gain, Maximal Ratio Combining (MRC Gain)-requires two antennas and software in UE,
HARQ Gains

Propagation Models Hata upto 1Ghz, Cost-Hata 2Ghz, Greenstien 2 Ghz, Ray Tracing (Dense
Urban). Propagation related parameters mean frequency dependent parameters, LTE is
interference limited, System gain, also known as the maximum allowable pathloss, use fixed
interference/load margin or Monte Carlo simulation

LTE network poses also similar effects such as network breathing due to UL interference and cell
range dependency upon user data rate. PRACH planning is done in LTE. COST model is used by
Nokia. Low Tx power for small bandwidth, high Tx power for large bandwidth.

Ray Trace model for URBAN with vectors provided

LTE network poses also similar effects such as network breathing due to UL interference and cell
range dependency upon user data rate

DL load as % of total capacity, UL load in terms of interference margin

MAPL è Signal Strength threshold of Coverage based planning

Best server areas should be contiguous and should not be fragmented.

F 5 to 20Mhz è RSRP reduce and RSRQ increases with RSSI being constant
SON

Self Healing, Optimization, configuration

Coverage and capacity optimization

MimoAdaptiveSwitch

DefDopplerLevel affects all KPIs

Energy Savings

Load generator ailgActive, dlPrbLoadLevel, trafficModelPrb

Interference Reduction, Interference Rejection Combining (IRC)

Beamforming

Automated Configuration of Physical Cell Identity

Mobility robustness optimisation

Mobility Load balancing optimisation

Random Access Channel Optimisation

Automatic Neighbour Relation Function

ROHC compression feature

CounterCheckTimer, CounterCheckTimer

Inter-cell Interference Coordination over X2 interface, ReportInterval, MaxReportCellNum,
ReportAmount, TriggerQuantity, Hysteresis, TimeToTrigger, A3Offset

neighbour cell list optimization

interference control

handover parameter optimization

Quality of Service related parameter optimization

load balancing

RACH load optimization

optimization of home base stations

Adaptive Transmission bandwidth

FTP and HTTP are sensitive to end-to-end delay

Access Stratum b/w UE and eNodeB via RRC

o
RRC idle
o
RRC connected
Non Access Stratum procedure consists of attach, detach, tracking area update, service request,
and extended service request.
o
EMM-DEREGISTERED:
o
EMM-REGISTERED: MME establishes and stores the UE context
o
ECM-IDLE:
o
ECM-CONNECTED: S1 connection is established,

3GPP causes ref 24.301

Random Access Radio Network Temporary Identifier (RA-RNTI)

Subscriber/Cell/Interface/Cell traffic/terminal/traces

ROHC (Robust header compression)

PORTS and TRACE rbsUeTraceEventStreamingPort streamPortPmUeTrace
streamStatusPmCellTrace streamStatusPmUeTrace
Internet Protocol

A class Subnet mask 255.0.0.0/8, less networks (inter) but more Host (intra)

B class Subnet mask 255.255.0.0/16

C class Subnet mask 255.255.255.0/24, 255=network address, 0=host address, more networks
(inter) but less Hosts (intra)

Default gateway (eNodeB IP address): 169.254.1.10

Ping command, tracert, sniffer capture, show route

SCTP is use for signaling e.g NBAP

X2 and S1 are using GPRS Tunneling Protocol for User data (GTP-U) to transfer the user plane
traffic.

ICMP reports erros of IP e.g ping, arp

The process of finding the new next hop after the network changes is called convergence

254.x.x IP addresses are self-assigned when your computer can’t get an address any other way.
It’s an almost sure sign of a problem

The Domain Name System (DNS) is used by RBSs to translate host names of other nodes (for
example RBSs, MMEs, synchronization servers) to IP addresses

Registered State
o

IDLE state
o

PDN,TAU update
No NAS signaling b/w UE and network
CONNECTED state:
o
RRC b/w UE and eNodeB
o
S1 b/w UE and MME
Ericsson tools
CCR, Nexplorer, Auto-integration, TRUC, LTE troubleshooting WIKI, Moshell/BB/RU
commands,

Moshell,
ITK,FlowFox,LTEDecoder,TeRouter/TeViewer,Multimon,uetrace,Japy,scheduling_parser,CDA
Web,Hammerhead Web,LTELogTool,TET.pl,decode,LTE Trace Tools, UE Trace Recording (UETR)

Cell Trace Recording (CTR), mtd-signal trace

COMMAND LINE MP, RU, Moshell, RRU, BB, AMOS, BCM

TRACES CPP, baseband LPP, MTD, RDR, RRT, RBS, UE, T&E, HiCap, UE, Cell, CEX, NSD

LTE torubleshooting wiki

DUMP configuration report, Dumpcap (network traffic)

SYSTEM CRASH DUMPS baseband core, Post Mortem.

LOGS alarm, availability, HW, audit, trace&error, autointegration, board error, event, system,
upgrade trace, security, exceptions, trace-error, dump network traffic

EVENTS RB&UE Trace, EHB, exceptions

Ericsson Network IQ Reports

COLI, NCLI,OSS-RC, MicroCPP, ANR, equinox

PM-initiated UE Measurements

Layer 3 and S1/X2 (Flowfox, LTEDecoder, scripts), LTELogtool

LLDM for data rate diagnosis

Cell Traces are streamed using TCP while UE Traces are streamed using UDP, Iperf, TCP
Optimizer, Filezilla (FTP), VLC (Streaming/media), Neoload (Web browsing), wireshark, Element
Manager, AMOS,Netpersec(realtime thorughput), Iperf(inject TCP/UDP packets)

Iperf generates TCP/UDP traffic

Netpersec monitor thorughput

MMR = Channel Feedback Report (CFR)

Nethawk, wireshark (open source), TCP dump, Agilent

Cell Trace files .ROP
o
te e all Ft_RRC_ASN
o
te e all Ft_S1AP_ASN
o
te e all Ft_X2AP_ASN
o
te e all Ft_LTE_EXCEPTION
o
te e all LTE_EXCEPTION
o
te e all CELL_CONFIG
o
te e all Ft_RRC_CONN_SETUP
o
te e all Ft_ANR_COMMON

ENIQ ericssons’ tool like Optima

Moshell commands
o
Teviewer to view trace commands
o
Te enable trace
o
Pset UETR trace
o
Diff for parameter audit of RNC.zip
o
Moshell rnc7
o
momd . power|pwr //list power control parameters
o
set primarycpichpower
o
pmr get specific KPI
o
pmom
o
lgx, lgo alarm
o
inv check licenses
o
KO UE capability
o
Te e get QCI, AMBR, ARP values
get counter

COLI commands are for trouble shooting

L12 features, RoHC, 4-way receive diversity, service based HO, System info-9 tunneling, preempt
low priority users, oscillating HO minimization
NSN tools

TTI Trace, Emil, LTE browser, BTS-Log, RF Unit console, Memory Dumper
KPIs

Delay

Delay Variation

Latency, throughput, packet drop, Packet Loss

Availability

Service Access time is a Latency KPI

Event A1: Serving becomes better than absolute threshold;

Event A2: Serving becomes worse than absolute threshold;

Event A3: Neighbor becomes amount of offset better than serving;

Event A4: Neighbor becomes better than absolute threshold; Inter-Freq

Event A5: Serving becomes worse than absolute threshold1 AND Neighbor becomes better than
another absolute threshold2.

Event B1 Inter-RAT neighbor becomes better than threshold

Event B2 Inter-RAT neighbor becomes better than threshold and serving becomes worse than
threshold

The RRCConnectionReconfiguration message is the command to modify an RRC connection. It
may convey information for measurement configuration, mobility control, radio resource
configuration (including RBs, MAC main configuration and physical channel configuration)
including any associated dedicated NAS information and security configuration.

PDCP: integrity protection and ciphering;

RLC: reliable and in-sequence transfer of information

RSSI = wideband power= noise + serving cell power + interference power

RSRP (dBm)= RSSI (dBm) -10*log (12*N), high BW è less RSRP


o
Value 00 (-140) to 97 (-44), step 1
o
Independent of load
RSRQ = N x RSRP / RSSI, high BW
o
Value 00 (-19.5) to Value 34 (-3), step .5
o
Dependent on load
RSRQ -3 to -19, RSRP -140 to -44
o
RSRQ=RSRP/(RSSI/N) = RSRP*N/(IN_n + ρ*12*N*Psc) and
o
SINR=S/(IN_m)

SNR -15 to 40

CINR=RSRQ

UE estimates SINR based on the Power Spectral Density of the downlink RS and PSD offset
between PDSCH and RS. The SINR is Channel Quality Indicator (CQI).

UE will report lower CQI values when using MIMO as opposed to SIMO in same RF
environment (SINR), UE will typically use lower Modulation/MCS

CQI 0 to 15, MCS 0 to 28

CINR -25 to 40dB

RSRP -150 to -30

RSSI -120 to 0

UE PRACH TX Power -10 to 23 dBm

RSRQ 0 to -40

BLER 0 to 100% tolerable till 10%

FER 0 to 100%

UE categories 1(low) to highest(5)

Transmission modes Mode 1 to 9 (highest), open/closed loop, antenna ports, MIMO (tm3) vs.
TxD (tm2) vs. SIMO (tm1)

GINR Gain to interference and Noise Ratio

A UE is said to be ‘in session’ if any data on a DRB (UL or DL) has been transferred during the
last 100 ms

PHR (power headroom report).

PSD è SINR èCQI Channel Feedback Report (CFR) ètransport format. RI i suded with MIMO

link quality (SINR, BLER, HARQ OPP)è MCS and coding rate èTBS
eNodeB Hardware

D2U V2 (1 uCCM + 3 eCEM)

TRDU (remote-radio-heads comprising of amplifiers and filters), 40W Tx power
DT Performance Metrics


Air Interface
o
UE Tx power
o
RSSI
o
SINR
o
BLER
o
Retransmission statistics (HARQ and RLC)
o
Transport Format
o
Number of resource blocks (DL/UL)
o
Channel rank statistics
o
MIMO mode (Tx diversity or Spatial Multiplexing)
o
Serving sector
o
Location (GPS)
o
UE Velocity
Throughput
o
Individual user throughput and aggregated sector throughput
o
UDP individual user throughput and aggregated sector throughput

o
TCP individual user throughput and aggregated sector throughput
o
User statistics (peak rates, average rates, standard deviations)
Latency
o
U-plane latency
o
Connection set up times
o
Handover interruption time within the same site and across different sites

Open loop PC is based on path loss, broadcasted/RRC parameters

Closed Loop PC is based on UL level and quality measurements

The power per subcarrier will be higher in smaller bandwidths è downlink coverage will be
higher for smaller bandwidths than for larger ones

Downlink AMC/fast AMC, SINRè CQI è modulation and coding scheme, per TTI, scheduling,
Uplink AMC/ slow AMC, SRS, BLER è modulation and coding scheme, scheduling, Emergency
Downgrade, Fast Upgrade’

Current BLER and Target BLERè CQI offset

PESQ 4 (best) to 1(worst)

SFN=system frame numer, 10ms, 0 to 1024

Sub-frame number, 1ms, 0 to 9

Paging Occasion = System and sub frame number

SFNmode 4 è 40 ms

THE UE reads P-SS and S-SS every 5ms to stay in synch. If UE successfully detected Cell ID/PCI, it
means UE successfully completed the time-sync.

Network not detected but signal bars are there èRACH error

There are 64 PRACH sequences. Same PRACH preamble from multiple UE reaches the NW at the
same time. This kind of PRACH collision is called “Contention”

Preamble format 0-4

Precoding matrix 0-3. Related to MIMO

PDCCH format 0-3

Failure to decode SIB2 by the UE, will affect PRACH process

PMI precoding matrix indication, (codebook index,no.of layers) Table 6.3.4.2.3-2, 36.211,
reported in case of TM=4

Transmission mode 1-7

PDCCH format 0(1)-3(8 CCEs)

T is the DRX cycle or defaultPagingCycle

QCI 1(Highest) to 9(Lowest)

RRC Connection Reconfiguration for measurement configuration, handover/mobility control,
radio resource configuration (RBs, MAC, physical channel), dedicated NAS information and
security configuration

RACH procedure initial access, handover, RRC recon estb, Sync loss in RRC connected mode

RBs/BW 25/5Mhz, 50/10, 75/15, 100/20

RRS Re-estb after UE tirggered RF failure, HO failure, RRC re-config failure

For RSRP: RSRP based threshold for event evaluation. The actual value is IE value – 140 dBm.

For RSRQ: RSRQ based threshold for event evaluation. The actual value is (IE value – 40)/2 dB.

RSRQ_00 = RSRQ < -19.5, RSRQ_34= -3 £ RSRQ 36.133

PH Power headroom , is defined as the difference between the nominal UE maximum transmit
power and the estimated power for PUSCH transmission PH_0= -23 £ PH < -22 & PH_62 = 39 £
PH < Low value index means UE has limited power. To transmit more PRBs, more power is
required

EMM = EPS mobility management, timers ref: 10.2, 24.301

ESM = EPS session management, bearer assignment, timers ref: 10.3, 24.301

TA 0,1(156m) ,………1282 (200km)

RRC function SIB, RRC, connection, handover, paging, security message, NAS messages,
selection/reselection

CFI no. of scheduling bits, (number of OFDM symbols for PDCCH) vs. MCS vs. % scheduling HARQ

TM Transmission mode 1-7, 7.2.3-0 36.213

CQI 0 to 15, MCS 0 to 31, QC1 to QC9, RANK 1 to 4
o
WCQI, wide-band CQI reported periodically
o
SCQI, sub-band CQI, reported aperiodically on request from enodeb, 1(worst) to 7(best)

RI Rank indicator, UE reports that info has been decoded from how many antennas, 2/4 layer
spatial multiplexing 7.2.3-1 36.213,

Assignable bits means the amount of data in the downlink buffer available for the scheduler to
schedule for this UE.

RLC DISCARDs will trigger TCP congestion control and lower throughput

BSR buffer status report 0(0KB) to 64 (15KB), power headroom report

Interference power > -104dBm

Link adaptation considers PHR, recived power of UE and UL interference power

QoS profile QCI, priority bit, AMBR, ARP

DSCP differentiated servise code point. QCI is mapped to DSCP

GTPU, GPRS tunneling protocol

DCI Downlink scheduling control indicator, channel coding formats, which resource block carries
your data, power control, transport format,HARQ, L1 signaling, DCI format 1, 1A, 1B, 1C, 1D, 2 or
2A

UCI Uplink scheduling control indicator, it contains, SR, Ack/Nack, CQI. Transmistted in PUSCH is
there is data and on PUCCH otherwise.

Resource Indication Value (RIV),that informs the device which RB to use and which start offset
to apply.

Hopping bits are
o
Type1 00,01,10, follows one pattern only
o
Type2 11 random based on subband, offset and mirror function. Unique to the cell

PDCCH format 0(low capacity) to 3(high signaling capacity)

DL Scheduling of RBs is determined TYPE & DCI format
o
TYPE 0 to 2
o
DCI format 0,1A,1B,1C,2,3,3A

RB assignment is carried in RIV (resource indication value)

RB= 1 slot x 12 carriers, resource block

RGB = 4 RBs or 48 carriers

If 20Mhz, 100 RBs and 25 RGBs

RGB subset 0,1,2,3

1 RE = 1 carrier x symbol

I REG=4 RE

g. 1CCE = 9 REGs or 36 REs, 72 bits if REG-8bits

1, 2, 4 or 8 CCE(s) (1 CCE = 9 REGs = 9*4 REs = 72 bits

Aggregation Level – a group of ‘L’ CCEs. (L can be 1,2,4,8)

In order to get the assigned RB resources (and the location) in PDSCH, DCI bits and format TYPE
has to be decoded

29 MSC schemes sector capacity is approximated by the harmonic mean of the MPR distribution

LTE smart antenna arrays focuses the beam towards the user

ARP allocation and retention priority. This determines if bearer can be dropped if congestions
occurs, or it cause other bearers to be dropped

C-RNTI, P-RNTI (Paging UE identifier), RA-RNTI(RACH), SI-RNTI(System information)

TPC 0(-6dB) to 7(8dB) è DCI format0/3

PUSCH channel TPC 0(-4dB) to 3(4dB) è DCI format0/3 + TPC-PUSCH-C-RNTI

PUCCH channel TPC 0(-1dB) to 3(3dB) è DCI format0/3 + TPC-PUSCH-C-RNTI

PDSCH Power is determined in the following manner
o
If RS is not present in the RB of PDSCH, offset from RS power is defined by Pa, which is UE
specific offset. Pa is signaled by higher layers and is changes every 1ms, values are -6 to 3
dB.
o
If RS is present then Pb and antennaPortsCount together will determine the offset. It is
cell specific and changes only when there is change in system message e.g if
antennaPortsCount=1 and Pb=2 then Offset = -2.218

Tranmist diversity same stream sent on diff antennas

Spatial diversity means diff stream on diff antennas

Cyclic Delay Diversity (CDD) Addition of antenna specific cyclic shifts

Fast Power control is per slot

Pcmax = min(p-Max,Pumax), Pcmax is max UE power
o
p-Max 23 dBm
o
PuMax

MPR (max power reduction) table 6.2.4-1 36.101

additionalSpectrumEmission =1 them MPR =0dB

RIV resource indication values indicates the starting position and number of RBs
assigned. It is given in DCI-0

Assigned PRBs in layer3

In order to save signaling bits on the downlink control channel (physical
downlink control channel, PDCCH), these two parameters are not
explicitly signaled. Instead, a resource indication value (RIV)is derived
which is signaled in the downlink control information on the PDCCH.

Alpha range 0,0.4,0.5,0.6,0.7,0.8,0.9,1.0. It is used as path loss compensation
factor as a trade-off between total uplink capacity and cell edge-data rate. Higher
value will be good for cell edge user but not for the overall capacity due to high
uplink power

Short and Long DRX cycles are configured to trade off battery saving and latency

PBR prioritized bit rate

timeAlignmentTimer

RBG a group of radio bearer with similar QoS requirements

SRS uplink scheduling, BSR, PHR. SRS is uplink counterpart of CQI report for
downlink scheduling

Cylic shifts and sub-carrier offsets and used to define transmission combs for UEs
or in other words schedule reference signals of UE, cell edge user cannot use

srs-BandwidthConfig range 0(high bw) to 7 (Low bw)

srs-Bandwidth range 0 (whole band) to 3 narrowest band

Scheduling techniques

In dynamic scheduling, the resources are distributed in 1 ms intervals.
Quick link adaptation

In persistent scheduling, longer transmission period is allocated for user
with the one grant. Poor link adaptation, fixed resources TB

RB Power is the power of 1 RB

TX Power is the power of all assigned RBs

TTI is subframe=1msec

A cyclic shift in the time domain (post IFFT in the OFDM modulation) is equivalent
to a phase rotation in the frequency domain (pre-IFFT in the OFDM modulation).

Common SRS is also called Cell Specific SRS and Dedicated SRS is also called UE
Specific SRS.

MAC CE, MAC control info

1 PDCCH = 8 DCIs

PDCCH

Carries common control info RACH response, Broadcast, SIB, paging, UL
TPC