Channelization:Information flow between protocol layers is the channel.
Types of channels
Logical what to transfer
Transport how to transfer
Physical where to transfer
Logical channel:Logical channels define what type of information is transferred. These channels define the data-transfer
services offered by the MAC layer. Data and signalling messages are carried on logical channels between
the RLC and MAC layers.
Logical channels further can be divided into two categories as control channels and traffic channels.
control channels carry signalling messages in the control plane and they can be either common channel
or dedicated channel. A common channel means common to all users in a cell (Point to multipoint ) where
as Dedicated channels means channels can be used only by one user (Point to Point).
Traffic channels carry data in the user plane, while logical control channels carry signalling messages in the
control plane.
LTE have 7 logical channel in Downlink and 3 Logical channels in Uplink
Downlink Logical Channel :
Control channel: In Downlink there are 4 Control channel which carried Common channel information as
well as dedicated channel information
•Broadcast Control Channel (BCCH) – It Used for broadcasting MIBs/SIBs
•Paging Control Channel (PCCH) – It is used for paging the UE
•Common Control Channel (CCCH) -It is Common to multiple UE’s
•Dedicated Control Channel (DCCH) – It used to transmit dedicated control information for a particular UE
•Multicast Control Channel (MCCH) – It is used for transmit information for Multicast
Traffic Channel: In Downlink we have 2 Traffic channel
•Dedicated Traffic channel (DTCH): Dedicated Traffic for a particular UE
•Multicast Traffic Channel (MTCH): used to transmit Multicast data
Uplink Logical Channel : In Uplink we have 2 control channels and one traffic channel.
•Common Control Channel (CCCH) -It is Common to multiple UE’s
•Dedicated Control Channel (DCCH) – It used to transmit dedicated control information
for a particular UE
•Dedicated Traffic channel (DTCH): Dedicated Traffic for a particular UE
Transport Channels:
Transport channels define how and with what type of characteristics the data is
transferred to the physical layer. Data and signalling messages are carried on transport
channels between the MAC and the physical layer.
Downlink Transport Channels :LTE has 4 Downlink Logical Channels
•Broadcast Channel (BCH) : This LTE transport channel maps to Broadcast Control
Channel (BCCH) and carries information like used for MIB and send information to
Physical Broadcast channel (PBCH)
•Downlink Shared Channel (DL-SCH) This transport channel is the main channel for
downlink data transfer. It is used by many logical channels like BCCH, CCCH, DCCH
DTCH,MCCH,MTCH and send its information to Physical Downlink Shared Channel
(PDSCH). The information carried by this channel is SIB, Data transfer
•Paging Channel (PCH) : To convey the PCCH information and mapped to Physical
Downlink Shared Channel (PDSCH) and carries Paging Information
•Multicast Channel (MCH) :
This transport channel is used to transmit MCCH
information to set up multicast transmissions. This channel is mapped to Physical
Multicast Channel (PMCH) this is basically used for MBMS services.
Uplink Transport channel: LTE has two channels
•Uplink Shared Channel (UL-SCH) : This transport channel is the main channel for uplink
data transfer. It is used by many logical channels like CCCH, DCCH DTCH.
•Random Access Channel (RACH) : This is used for random access procedure.
Physical Channels
These channels are also in both direction downlink and uplink directions. So we can divide these into
Downlink Physical channels and uplink Physical Channels. Based on Data and signalling messages are
carried on physical channels in LTE ,we can further classified as
•Physical Data channels (DL, UL)
•Physical Control Channels (DL,UL)
Downlink Physical Channel:
•Downlink physical Data Channel (PBCH, PDSCH,PMCH)
•Downlink Physical Control Channel (PCFICH,PHICH,PDCCH)
1.Physical Broadcast Channel (PBCH) This physical channel carries system information for UEs requiring to
access the network. It only carries what is termed Master Information Block, MIB, messages
2.Physical Downlink Shared Channel (PDSCH): The PDSCH can carry DL-SCH or PCH. It carries SIB
information, Paging Information and user plan Data.
3.Physical Multicast Channel (PMCH) : This channel type is used to carry MCH and mainly used for MBMS
Services.
4.Physical Control Format Indicator Channel (PCFICH) : As the name indicates the PCFICH informs the UE
about the format of the signal being received. It indicates the number of OFDM symbols used for the
PDCCH channel, whether 1, 2, or 3. The information within the PCFICH is essential because the UE does
not have prior information about the size of the control region (PDCCH). A PCFICH is transmitted on the
first symbol of every sub-frame and carries a Control Format Indicator CFI.
5.Physical Downlink Control Channel (PDCCH) : The PDCCH carries information known as the Downlink
Control Information or DCI . It carries the control information for a particular UE or group of UEs. Basically
A DCI provides the following information. Downlink resource scheduling, Uplink power control
instructions. Uplink resource grantThe DCI format has several different types which are defined with
different sizes. The different format types include: type 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A etc
6.Physical Hybrid ARQ Indicator Channel (PHICH): This channel is used to report the Hybrid ARQ status. It
carries the HARQ ACK/NACK signal indicating whether a transport block has been correctly received.The
PHICH is transmitted within the control region of the subframe and is typically only transmitted within the
first symbol. If the RF conditions are poor, then the PHICH is extended to a number symbols for
robustness
Uplink Physical Channel:
•Uplink physical Data Channel ( PUSCH,PRACH)
•Uplink Physical Control Channel (PUCCH)
1.Physical Uplink Shared Channel (PUSCH) : This physical channel is used for Uplink data transmission by
the UE. They may also carries the uplink control information sometimes. This channel is the counterpart
of PDSCH channel in Uplink
2.Physical Random Access Channel (PRACH) :This Uplink physical channel is used for random access
procedure called RACH procedure. UE does RACH procedure to get the Uplink synchronization
3.Physical Uplink Control Channel (PUCCH) : The Physical Uplink Control Channel, PUCCH provides the
various control signalling. These signalling are known as Scheduling request, Downlink data ACK/NACK
and CQI information.
OFDMA & SCFDMA
Advantages of OFDM
•The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of
high frequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without complex equalization
filters.
•Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidlymodulated wideband signal.
•The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate inter symbol interference
(ISI).
•This mechanism also facilitates the design of single frequency networks (SFNs), where several adjacent transmitters send the same signal
simultaneously at the same frequency, as the signals from multiple distant transmitters may be combined constructively, rather than interfering
as would typically occur in a traditional single-carrier system.
Drawbacks of OFDM
•High peak-to-average ratio
•Sensitive to frequency offset, hence to Doppler-shift as well
SC-FDMA Technology
LTE uses a pre-coded version of OFDM called Single Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink. This is to compensate for
a drawback with normal OFDM, which has a very high Peak to Average Power Ratio (PAPR).
High PAPR requires expensive and inefficient power amplifiers with high requirements on linearity, which increases the cost of the terminal and
drains the battery faster.
SC-FDMA solves this problem by grouping together the resource blocks in such a way that reduces the need for linearity, and so power
consumption, in the power amplifier. A low PAPR also improves coverage and the cell-edge performance.
Parameters
Description
Frequency range
UMTS FDD bands and TDD bands defined in 36.101(v860) Table 5.5.1, given below
Duplexing
FDD, TDD, half-duplex FDD
Channel coding
Turbo code
Mobility
350 km/h
Channel Bandwidth (MHz)
•1.4, 3, 5, 10, 15, 20
Transmission Bandwidth Configuration NRB : •6 ,15,25,50,75,100
(1 resource block = 180kHz in 1ms TTI )
Modulation Schemes
UL: QPSK, 16QAM, 64QAM(optional)
DL: QPSK, 16QAM, 64QAM
Multiple Access Schemes
UL: SC-FDMA (Single Carrier Frequency Division Multiple Access) supports 50Mbps+
(20MHz spectrum)
DL: OFDM (Orthogonal Frequency Division Multiple Access) supports 100Mbps+
(20MHz spectrum)
Multi-Antenna Technology
UL: Multi-user collaborative MIMO
DL: TxAA, spatial multiplexing, CDD ,max 4x4 array
Peak data rate in LTE
UL: 75Mbps(20MHz bandwidth)
DL: 150Mbps(UE Category 4, 2x2 MIMO, 20MHz bandwidth)
DL: 300Mbps(UE category 5, 4x4 MIMO, 20MHz bandwidth)
MIMO
(Multiple Input Multiple Output)
UL: 1 x 2, 1 x 4
DL: 2 x 2, 4 x 2, 4 x 4
Coverage
5 - 100km with slight degradation after 30km
QoS
E2E QOS allowing prioritization of different class of service
Latency
End-user latency < 10mS
2G/3G
LTE
GERAN and UTRAN
E-UTRAN
SGSN/PDSN-FA
S-GW
GGSN/PDSN-HA
PDN-GW
HLR/AAA
HSS
VLR
MME
SS7-MAP/ANSI-41/RADIUS
Diameter
DiameterGTPc-v0 and v1
GTPc-v2
MIP
PMIP
Subcarrier
Bandwidt Resource s
Subcarrier
REs
h
Blocks
(downlink s (uplink)
)
1.4 MHz
3 MHz
5 MHz
10 MHz
15 MHz
20 MHz
6
15
25
50
75
100
73
181
301
601
901
1201
72
180
300
600
900
1200
Res(with
Cyclic
Prefix)
504
1260
2100
4200
6300
8400
432
1080
1800
3600
5400
7200
Operating band and function
Protocol stacks user & control plane
User Plan stacks
Packets received by a layer are called Service Data Unit (SDU) while the
packet output of a layer is referred to by Protocol Data Unit (PDU) and IP
packets at user plane flow from top to bottom layers.
Control Plan stacks
The control plane includes additionally the Radio Resource Control layer
(RRC) which is responsible for configuring the lower layers.
The Control Plane handles radio-specific functionality which depends on
the state of the user equipment which includes two states: idle or
connected.
Protocol stacks cont….
Physical Layer (Layer 1):- Responsible for Takes care of the link adaptation (AMC), power control, cell search (for
initial synchronization and handover purposes) and other measurements (inside the LTE system and between
systems) for the RRC layer.
Medium Access Layer (MAC)
MAC layer is responsible for Mapping between logical channels and transport channels, Multiplexing of MAC SDUs
from one or different logical channels onto transport blocks (TB) to be delivered to the physical layer on transport
channels, de multiplexing of MAC SDUs from one or different logical channels from transport blocks (TB) delivered
from the physical layer on transport channels, Scheduling information reporting, Error correction through HARQ,
Priority handling between UEs by means of dynamic scheduling, Priority handling between logical channels of one UE,
Logical Channel prioritization.
Radio Link Control (RLC)
RLC operates in 3 modes of operation: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged
Mode (AM).
RLC Layer is responsible for transfer of upper layer PDUs, error correction through ARQ (Only for AM data transfer),
Concatenation, segmentation and reassembly of RLC SDUs (Only for UM and AM data transfer).
RLC is also responsible for re-segmentation of RLC data PDUs (Only for AM data transfer), reordering of RLC data
PDUs (Only for UM and AM data transfer), duplicate detection (Only for UM and AM data transfer), RLC SDU discard
(Only for UM and AM data transfer), RLC re-establishment, and protocol error detection (Only for AM data transfer).
Radio Resource Control (RRC)
The main services and functions of the RRC sublayer include broadcast of System Information related to the nonaccess stratum (NAS), broadcast of System Information related to the access stratum (AS), Paging, establishment,
maintenance and release of an RRC connection between the UE and E-UTRAN, Security functions including key
management, establishment, configuration, maintenance and release of point to point Radio Bearers.
Packet Data Convergence Control (PDCP)
PDCP Layer is responsible for Header compression and decompression of IP data, Transfer of data (user plane or
control plane), Maintenance of PDCP Sequence Numbers (SNs), In-sequence delivery of upper layer PDUs at reestablishment of lower layers, Duplicate elimination of lower layer SDUs at re-establishment of lower layers for radio
bearers mapped on RLC AM, Ciphering and deciphering of user plane data and control plane data, Integrity
protection and integrity verification of control plane data, Timer based discard, duplicate discarding, PDCP is used for
SRBs and DRBs mapped on DCCH and DTCH type of logical channels.
Non Access Stratum (NAS) Protocols
The non-access stratum (NAS) protocols form the highest stratum of the control plane between the user equipment
(UE) and MME.
NAS protocols support the mobility of the UE and the session management procedures to establish and maintain IP
connectivity between the UE and a PDN GW.
Protocol stacks cont….
•IP Layer submits PDCP SDUs (IP Packets) to the PDCP layer. PDCP layer does
header compression and adds PDCP header to these PDCP SDUs. PDCP Layer
submits PDCP PDUs (RLC SDUs) to RLC layer.
PDCP Header Compression : PDCP removes IP header (Minimum 20 bytes)
from PDU, and adds Token of 1-4 bytes. Which provides a tremendous
savings in the amount of header that would otherwise have to go over the
air.
•RLC layer does segmentation of these SDUS to make the RLC PDUs. RLC
adds header based on RLC mode of operation. RLC submits these RLC PDUs
(MAC SDUs) to the MAC layer.
RLC Segmentation : If an RLC SDU is large, or the available radio data rate is
low (resulting in small transport blocks), the RLC SDU may be split among
several RLC PDUs. If the RLC SDU is small, or the available radio data rate is
high, several RLC SDUs may be packed into a single PDU.
•MAC layer adds header and does padding to fit this MAC SDU in TTI. MAC
layer submits MAC PDU to physical layer for transmitting it onto physical
channels.
•Physical channel transmits this data into slots of sub frame.
Channels
The information flows between the different protocols are known as channels and signals. LTE uses several different types of logical, transport and physical channel, which are
distinguished by the kind of information they carry and by the way in which the information is processed.
•Logical Channels : Define whattype of information is transmitted over the air, e.g. traffic channels, control channels, system broadcast, etc. Data and signalling messages are carried
on logical channels between the RLC and MAC protocols.
•Transport Channels : Define howis something transmitted over the air, e.g. what are encoding, interleaving options used to transmit data. Data and signalling messages are carried
on transport channels between the MAC and the physical layer.
•Physical Channels : Define whereis something transmitted over the air, e.g. first N symbols in the DL frame. Data and signalling messages are carried on physical channels between
the different levels of the physical layer.
Logical Channels
Logical channels define what type of data is transferred. These channels define the data-transfer services offered by the MAC layer. Data and signalling messages are carried on
logical channels between the RLC and MAC protocols.
Logical channels can be divided into control channels and traffic channels. Control Channel can be either common channel or dedicated channel. A common channel means
common to all users in a cell (Point to multipoint) while dedicated channels means channels can be used only by one user (Point to Point).
Logical channels are distinguished by the information they carry and can be classified in two ways. Firstly, logical traffic channels carry data in the user plane, while logical control
channels carry signalling messages in the control plane. Following table lists the logical channels that are used by LTE:
Channel Name
Acronym
Control
channel
Traffic
channel
Broadcast Control Channel
BCCH
X
Paging Control Channel
PCCH
X
Common Control Channel
CCCH
X
Dedicated Control Channel
DCCH
X
Multicast Control Channel
MCCH
X
Dedicated Traffic Channel
DTCH
X
Multicast Traffic Channel
MTCH
X
Transport Channels
Transport channels define how and with what type of characteristics the data is transferred by the physical layer. Data and
signalling messages are carried on transport channels between the MAC and the physical layer.
Transport Channels are distinguished by the ways in which the transport channel processor manipulates them. Following table
lists the transport channels that are used by LTE:
Channel Name
Acronym
Downlink
Uplink
Broadcast Channel
BCH
X
Downlink Shared Channel
DL-SCH
X
Paging Channel
PCH
X
Multicast Channel
MCH
X
Uplink Shared Channel
UL-SCH
X
Random Access Channel
RACH
X
Physical Channels
Data and signalling messages are carried on physical channels
between the different levels of the physical layer and accordingly they
are divided into two parts:
•Physical Data Channels
•Physical Control Channels
Physical data channels
Physical data channels are distinguished by the ways in which the
physical channel processor manipulates them, and by the ways in
which they are mapped onto the symbols and sub-carriers used by
Orthogonal frequency-division multiplexing (OFDMA). Following table
lists the physical data channels that are used by LTE:
•The transport channel processor composes several types of control
information, to support the low-level operation of the physical layer.
Physical Control Channels
The transport channel processor also creates control information that
supports the low-level operation of the physical layer and sends this
information to the physical channel processor in the form of physical
control channels.
The information travels as far as the transport channel processor in
the receiver, but is completely invisible to higher layers. Similarly, the
physical channel processor creates physical signals, which support the
lowest-level aspects of the system.
The base station also transmits two other physical signals, which help
the mobile acquire the base station after it first switches on. These are
known as the primary synchronization signal (PSS) and the secondary
synchronization signal (SSS).
Channel Name
Acronym
Downlink
Physical downlink shared channel
PDSCH
X
Physical broadcast channel
PBCH
X
Physical multicast channel
PMCH
X
Physical uplink shared channel
PUSCH
X
Physical random access channel
PRACH
X
Field Name
Acronym
Downlink
Downlink control information
DCI
X
Control format indicator
CFI
X
Hybrid ARQ indicator
HI
X
Uplink control information
UCI
Uplink
Uplink
X
Channel Name
Acronym
Downlink
Physical control format indicator channel
PCFICH
X
Physical hybrid ARQ indicator channel
PHICH
X
Physical downlink control channel
PDCCH
X
Relay physical downlink control channel
R-PDCCH
X
Physical uplink control channel
PUCCH
Uplink
X
Physical layer
FDD frame type 1
In FDD mode, uplink and downlink frames are both 10ms long and are separated either in frequency or in time.
For full-duplex FDD, uplink and downlink frames are separated by frequency and are transmitted continuously and synchronously.
For half-duplex FDD, the only difference is that a UE cannot receive while transmitting.
The base station can specify a time offset (in PDCCH) to be applied to the uplink frame relative to the downlink frame.
TDD frame type 2
In TDD mode, the uplink and downlink subframes are transmitted on the same frequency and are multiplexed in the time domain. The
locations of the uplink, downlink, and special subframes are determined by the uplink-downlink configuration. There are seven
possible configurations given in the standard. The following is an illustration of a TDD frame with uplink-downlink configuration set to
2 and special subframe configuration set to 6.
Time Unit
Value
Frame
10 ms
Half-frame
5 ms
Subframe
1 ms
Slot
0.5 ms
Symbol
(0.5 ms) / 7 for
normal CP
(0.5 ms) / 6 for
extended CP
Ts
1/(15000 * 2048)
sec » 32.6 ns
Special subframes
Special subframes are used for switching from downlink to uplink and contain three sections: DwPTS, GP, and UpPTS.
DwPTS is the Downlink Pilot Time Slot. DwPTS contains P-SS. PDSCH can also be transmitted during DwPTS when DwPTS is configured
to be longer than a slot.
UpPTS is the Uplink Pilot Time Slot. UpPTS can contain PRACH and SRS, but cannot contain or PUCCH or PUSCH.
GP is a guard period between DwPTS and UpPTS. PRACH format 4 begins in the guard period. Otherwise, nothing else is transmitted
during the guard period.
The lengths of these three sections are determined by the special subframe configuration index (specified by the Dw/Gp/Up
Len parameter). There are 9 possible configurations.
UL/DL configuration
The uplink-downlink configuration (specified by UL/DL Config) of a TDD frame determines the locations of uplink, downlink, and
special subframes. There are 7 possible uplink-downlink configurations.
Note:- Subframes 0 and 5 and DwPTS in TDD frames are always allocated to downlink transmissions.
UpPTS and the subframe after a special subframe are always allocated to uplink transmissions.
Subframe 1 is always configured to be a special subframe. Subframe 6 can also be configured to be a special subframe.
RLF Timers
E Timers Function at Start/Stop/Expiry
>>Starts at the RRC connection REQ transmit
T300
>>Stops at the Receipt of RRC connection setup or reject message OR at the cell reselection time OR upon abortion of connection establishment by Higher layers (L2/L3).
>>At the expiry performs the actions
>>Starts at the RRC Connection Re-establishment REQUEST
>>Stops at the Receipt of RRC Connection Re-establishment OR
T301
RRC Connection Re-Establishment REJECT message OR
When selected cell becomes unsuitable to continue further
>>At expiry, it Go to RRC_IDLE mode
>>Starts when access is barred while performing RRC CONNECTION ESTABLISHMENT for MO(Mobile Originating) calls
T303
>>Stops while entering RRC_CONNECTED and upon cell re-selection mode
>>At expiry, Informs higher layers about barring alleviation
T304
T305
T310
T311
T320
T321
>>Starts at the Receipt of RRC CONNECTION RECONFIGURATION message along with Mobility Control Info OR at the receipt of mobility from EUTRA command message including CELL CHANGE ORDER
>>Stops at the successful completion of HANDOVER to EUTRA or CELL CHANGE ORDER is met
>>At expiry, it performs action based on need.
1. In the case of CELL CHANGE ORDER from E-UTRA OR intra E-UTRA handover, initiate the RRC connection re-establishment procedure.
2. In case of HANDOVER to E-UTRA, perform the actions defined as per the specifications applicable for the source RAT.
>>starts when access is barred while performing RRC CONNECTION ESTABLISHMENT for MO signaling
>>Stops when entering RRC_CONNECTED and when UE does cell re-selection
>> At expiry, Informs higher layers about barring alleviation
>>Starts when UE detects PHY layer related problems (when it receives N310 consecutive out-of-sync INDs from lower layers)
>>Stops 1. When UE receives N311 consecutive in-sync INDs from lower layers/
2. Upon triggering the HANDOVER procedure
3. Upon initiating the CONNECTION RE-ESTABLISHMENT procedure
>> At expiry, if security is not activated it goes to RRC IDLE else it initiates the CONNECTION RE-ESTABLISHMENT Procedure
>>Starts while initiating RRC CONNECTION RE-ESTABLISHMENT procedure
>>stops upon selection of suitable E-UTRA cell OR a cell using another RAT
>>At expiry it enters RRC IDLE state
>> Starts upon receipt of t320 or upon cell re- selection to E-UTRA from another RAT with validity time configured for dedicated priorities (in which case the remaining validity time is applied).
>>Stops upon entering RRC_CONNECTED state, when PLMN selection is performed on request by NAS OR upon cell re-selection to another RAT
>> At expiry, it discards the cell re-selection priority info provided by dedicated signaling
>>starts upon receipt of measConfig including a reportConfig with the purpose set to reportCGI
>> Stops at either of following cases:
1. Upon acquiring the information needed to set all fields of globalCellId for the requested cell
2. upon receipt of measConfig that includes removal of the reportConfig with the purpose set to reportCGI
>> At expiry initiates the measurement reporting procedure, stop performing the related measurements and remove the corresponding measID