LTE – Long Term Evolution
Introduction
1
Outline
Evolution and Adoption
Features
Architecture
Radio Interface
Overview of Protocols and Channels
LTE-Advanced
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Evolution
EDGE
TDMA
GSM
GPRS
WCDMA
PDC
cdmaOne
HSPA
LTE
CDMA2000
1x
CDMA2000
1x EV/DO
2G
evolved 2G
3G
evolved 3G
9.6 - 14.4 kbps
64–144 kbps
384 kbps - 2 Mbps
384 kbps - 100 Mbps
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LTE-A
4G
>1 Gbps
LTE Adoption (as of May 2012)
Red – countries with LTE service
Dark Blue – planned or ongoing deployment
Light Blue – LTE system trials (pre-commitment)
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Features
All IP Network (VoIP for voice)
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Can also use other 3GPP technologies for voice
Spectrum Flexibility
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(1.25MHz – 20MHz)
TDD/FDD (full-duplex and half-duplex)
Multi-antenna transmissions (4 MIMO on downlink, 2
MIMO on uplink)
300 Mbps peak downlink in 20MHz x 4 MIMO x 64 QAM
75 Mbps peak uplink
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Features (cont)
100 km macro cells (5 km with optimal performance)
Up to 200 active users in a cell
OFDM downlink and Single Carrier FDMA (SC-FDMA)
uplink
HARQ (Hybrid ARQ)
Co-existence with existing technologies (calls can be
started in LTE and transferred to GSM/GPRS, WCDMA)
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Architecture
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UE – User Equipment
eNodeB – evolved NodeB (BS)
S-GW – Serving Gateway
P-GW – PDN Gateway
MME – Mobility Management Entity
HSS – Home Subscriber Server
PCRF – Policy Rules and Charging Control
Function
Elements
HSS – Home Subscriber Server – stores subscriber
information, roaming capabilities, QoS profiles, current
registration; may integrate AUC functionality
P-GW – PDN Gateway – allocates UE IP address, QoS
enforcement, filters downlink packets in different QoS bearers
S-GW – Serving Gateway local mobility anchor as UE switches
between eNodeBs, buffers downlink data until paging
completes, charging for visiting users
MME – Mobile Management Entity controls flow between UE
and CN (corresponding node) – handles idle mobility
PCRF – Policy Control and Charging Rules Function –
charging, policy control, QoS authorization
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Standardized QoS Class Identifiers (QCI)
GBR – Guaranteed Bit-Rate
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Radio Interface
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Multiple Access Scheme
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Downlink uses OFDMA
Uplink uses Single Carrier
FDMA (SC-FDMA)
BLER – Block Error Rate
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Adaptive Modulation and
Coding
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Downlink uses QPSK, 16QAM
and 64QAM
Uplink uses QPSK and 16QAM
Generic Frame Structure
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Allocation of physical resource blocks (PRBs) is handled
by a scheduling function at the 3GPP base station
(eNodeB)
Frame 0 and frame 5 (always downlink)
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Resource Blocks
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2D – Time x Frequency
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Common Physical RB (PRB) Formats
Channel
Bandwidth
(MHz)
NRBDL/NRBUL
Typical IDFT size
Number of Non-Zero
Sub-carriers (REs)
1.25
6
128
72
5
25
512
300
10
50
1024
600
15
75
1024 or 2048
900
20
100
2048
1200
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PRBs are mapped onto contiguous OFDMA/SC-FDMA symbols in the time-domain
(6 or 7)
Each PRB is chosen to be equivalent to 12 (15 kHz spacing) sub-carriers of an
OFDMA symbol in the frequency-domain
Because of a common PRB size over different channel bandwidths, the system
scales naturally over different bandwidths
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UEs determines cell bandwidth during initial acquisition and can be any of above
Example: 300 REs, 25 RBs (5 MHz channel)
PRB24
PRB23
PRB22
PRB21
PRB20
PRB19
PRB18
PRB17
PRB16
PRB15
PRB14
PRB13
PRB12
PRB11
PRB10
PRB9
PRB8
PRB7
PRB6
PRB5
PRB4
PRB3
PRB2
PRB1
PRB0
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PRB13
PRB12
NRBDL/NRBUL
NSCRB
PRB11
l=0
l=6
NULsymb /NULsymb
“Normal” Cyclic
Prefix Mode
(7 symbols)
“Extended” Cyclic
Prefix Mode
(6 symbols)
Sub-frame and Frame
One frame = 10ms
Tslot=500ms
0
1
2
3
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19
One subframe
71.3ms 71.9ms
Normal Prefix
4.69ms
Frequency
Domain
View
83ms
Extended Prefix
13.9ms
15
5.2ms
Time-domain
View
OFDM
LTE
uses OFDM for the downlink – that is, from the base station to the terminal. OFDM meets the LTE
requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high
peak rates. OFDM uses a large number of narrow sub-carriers for multi-carrier transmission.
The
basic LTE downlink physical resource can be seen as a time-frequency grid. In the frequency
domain, the spacing between the subcarriers, Δf, is 15kHz. In addition, the OFDM symbol duration time is
1/Δf + cyclic prefix. The cyclic prefix is used to maintain orthogonality between the sub-carriers even for
a time-dispersive radio channel.
One
resource element carries QPSK, 16QAM or 64QAM. With 64QAM, each resource element carries
six bits.
The
OFDM symbols are grouped into resource blocks. The resource blocks have a total size of 180kHz
in the frequency domain and 0.5ms in the time domain. Each 1ms Transmission Time Interval (TTI)
consists of two slots (Tslot).
In
E-UTRA, downlink modulation schemes QPSK, 16QAM, and 64QAM are available.
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SC-FDMA
The
LTE uplink transmission scheme for FDD and TDD mode is based on SC-FDMA (Single Carrier
Frequency Division Multiple Access).
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 also 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.
Still, SC-FDMA
signal processing has some similarities with OFDMA signal processing, so
parameterization of downlink and uplink can be harmonized.
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SC-FDMA
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Localized
Mapping and Distributed Mapping
User Plane Protocol Stack
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PDCP – Packet Data Convergence Protocol
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RLC – Radio Link Control
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GTP-U – GPRS Tunneling Protocol – User Plane
Control Plane Protocol Stack
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NAS – Non-Access Stratum
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RRC – Radio Resource Control
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PDCP – Packet Data Convergence Protocol
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RLC – Radio Link Control
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STCP – Stream Transport Control Protocol
Layer 2
The three sublayers are
Medium access Control(MAC)
Radio Link Control(RLC)
Packet Data Convergence Protocol(PDCP)
[Source: E-UTRAN Architecture(3GPP TR 25.012 ]
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Layer 2
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MAC (media access control) protocol
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handles uplink and downlink scheduling and HARQ signaling.
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Performs mapping between logical and transport channels.
RLC (radio link control) protocol
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focuses on lossless transmission of data.
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In-sequence delivery of data.
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Provides 3 different reliability modes for data transport. They are
 Acknowledged
Mode (AM)-appropriate for non-RT (NRT) services such as file downloads.
 Unacknowledged
Mode (UM)-suitable for transport of Real Time (RT) services because such
services are delay sensitive and cannot wait for retransmissions
 Transparent
Mode (TM)-used when the PDU sizes are known a priori such as for broadcasting
system information.
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Layer 2
PDCP
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(packet data convergence protocol)
handles the header compression and security functions of
the radio interface
RRC (radio resource control) protocol
handles radio bearer setup
 active mode mobility management
 Broadcasts of system information, while the NAS
protocols deal with idle mode mobility management and
service setup
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Three Types of Channels in LTE
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In GMS only logical and physical
In LTE:
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Logical Channels – what type of information is transported
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Transport Channels – how is the information transported
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Modulation, coding, antenna port
Physical Channels – where is the information transported
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Control x 5
Traffic x 2
What resource blocks are allocated
LTE Downlink Channels
Paging Control Channel
Paging Channel
Physical Downlink Shared Channel
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LTE Uplink Channels
Random Access Channel
CQI report
Physical Uplink Shared Channel
Physical Radio Access Channel
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LTE Downlink Logical Channels
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LTE Downlink Transport Channel
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LTE Downlink Transport Channel
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LTE Downlink Physical Channels
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LTE Downlink Physical Channels
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LTE Uplink Logical Channels
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LTE Uplink Transport Channel
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LTE Uplink Physical Channels
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LTE Advanced
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Features
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100MHz Bandwidth supported
1Gbps DL, 500 Mbps UL
Carrier Aggregation
Relays
Carrier Aggregation
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Carrier Aggregation
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Enhanced Techniques to Extend Coverage
Area and/or Data Rates
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LTE vs. LTE-Advanced
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