01 FO_BT1101_C01_1 LTE FDD Principles and Key Technologies.pptx

LTE Principles and Key
Technologies

Objectives
 To fully understand the LTE network architecture.
 To fully understand the functions and interfaces of NEs in the LTE
wireless network.
 To learn about the protocols and features of the LTE wireless
network.
 To fully understand the frame structure and resource block division in
the LTE physical layer.
 To fully understand the key LTE technologies and the benefits they
bring.
 To learn about the differences and similarities between two LTE
systems and their respective features.
2

Contents
 LTE Overview
 A Brief Introduction to LTE
 LTE-Related Organizations
 LTE Network Architecture
 LTE Protocols
 Key LTE Technologies
 LTE FDD vs. TD-LTE
3

© ZTE Corporation. All rights reserved
LTE Background
 3GPP: 3rd Generation Partnership Project
 LTE: Long Term Evolution, a UMTS long-term evolution standard
series developed by the 3GPP.
4

Why LTE?
 Why we need LTE?
 The CDMA-based 3G standard, after being enhanced by the HSDPA and Enhanced
Uplink technologies, can guarantee the competitiveness in the next few years. However,
how can it ensure its competitiveness in a longer period of time to
 Respond to the marketing pressure from the WiMAX technology
 Get prepared for the 4G standards of the ITU
5

Why LTE – LTE Brings More Mobile Services
6
Mobile Broadband Brings
Changes in Future Life
 Mobile Email
 Netmeeting
 HD video
conference
 Video on demand
 Online gaming
 HD video streams
 Mobile shopping
 Mobile banking
 Mobile securities
 Video sharing
 Video blog
 Video chat
 Information service
LTE improves user experience with large capacity, fast
response, high rate and better QoS

Evolution Path of the Mobile Communications
Technology
7
 Multiple standards, convergence
 Multiple frequency bands
 Broadband and IP trend of the mobile network
2G 2.5G 2.75G 3G 3.5G 3.75G 3.9G
GPRS EDGE
HSDPA
R5
HSUPA
R6
MBMS 4G
MBMS
CDMA 2000
1X EV-DO
802.16 e 802.16 m
HSDPA
HSPA+
R7
FDD/
TDD
4G
GSM
TD-
SCDMA
WCDMA
R99
802.16 d
CDMA
IS95
CDMA
2000 1x
LTE
EV-DO
Rev. A
EV-DO
Rev. B
HSUPA
HSPA+
R7

Better
coverage
Peak rate
DL: 150 Mbps
UL:75 Mbps
Low latency
CP: 100 ms
UP: 5 ms
Lower
CAPEX &
OPEX
Spectrum
flexibility
Higher
spectrum
efficiency
LTE
Objectives of LTE
8

Peak Data Rate
9
1
Significant peak
rate increase.
The peak rate is
proportional to
the system
bandwidth.
2
Downlink peak
rate of 150
Mbit/s
(spectrum
efficiency of 7.5
bit/s/Hz) within
the 20 MHz
bandwidth.
3
Uplink peak rate
of 75 Mbit/s
(spectrum
efficiency of 3.75
bit/s/Hz) within
the 20 MHz
bandwidth.
Objectives

LTE Frequency Division (R8)
10

Contents
 LTE Overview
 A Brief Introduction to LTE
 LTE-Related Organizations
 LTE Protocols
11

LTE Standard Organizations
12
Function
requirement
Standard
formulation
Technical
verification
TSG RAN
TSG SA
TSG CT
PCG
TSG GERAN

3GPP Architecture
13
Project Co-ordination Group (PCG)
TSG GERAN
GSM EDGE
Radio Access Network
GERAN WG1
Radio Aspects
GERAN WG2
Protocol Aspects
GERAN WG3
Terminal Testing
TSG RAN
Radio Access Network
RAN WG1
Radio Layer 1 spec
RAN WG2
Radio Layer 2 spec
Radio Layer 3 RR spec
RAN WG3
lub spec, lur spec, lu spec
UTRAN O&M requirements
RAN WG4
Radio Performance
Protocol aspects
RAN WG5
Mobile Terminal
Conformance Testing
TSG SA
Service & Systems Aspects
SA WG1
Services
SA WG2
Architecture
SA WG3
Security
SA WG4
Codec
SA WG5
Telecom Management
TSG CT
Core Network & Terminals
CT WG1
MM/CC/SM (lu)
CT WG3
Interworking with external
networks
CT WG4
MAP/GTP/BCH/SS
CT WG6 Smart Card
Application Aspects

2005 2006 2007 2008 2009
LTE Standardization Progress
14
LTE
start
Work Item
Start
Study Item
Stage 1 Finish
Work Item
Stage 3 Finish
Work Item
Stage 2 Finish
First Market
Application
 3GPP R8 defines the basic functions of LTE. This version was frozen in March
2009.
 3GPP R9 works on improved performance of the LTE home ENodeB,
management and security, and the LTE picocells and self-organizing
management functions. This version was frozen in December 2009.
 3GPP R10 defines the key LTE-A technologies including relay, carrier
aggregation, and 8x8 MIMO. This version was frozen in March 2011.
2010 2011
LTE-A
start

Evolution of Key LTE Technologies
15

Contents
 LTE Overview
 LTE Protocols
16

LTE Network Architecture
17
MME / S-GW MME / S-GW
X2
S1
 Mobility management entity
 Serving gateway
 Interface between
MME/SGW and eNB
EPC
E-
UTRAN
 Interface among eNBs
Node B
RNC
+ =
eNB
EPS
eNB
X2
X2
eNB
eNB
Uu
 eNode B (eNB): The only NE in E-UTRAN
 EPC: Evolved Packet Core
 EPS: Evolved Packet System

LTE Network Architecture
18
SGi
S4
S3
S1-MME
PCRF
Gx
S6a
HSS
S10
UE
GERAN
UTRAN
SGSN
LTE-Uu
E-UTRAN
MME
S11
S5
Serving
Gateway
PDN
Gateway
S1-U
Operator's IP Services
(e.g. IMS, PSS etc.)
Rx+
 Flat network structure
 E-UTRAN has only one type of NE: eNB
 All-IP
 Separation between media plane and
control plane
 Interoperability with traditional networks
S8

Functions of E-UTRAN and EPC
19
3GPP TS 36.300

Contents
 LTE Overview
 LTE Protocols
20

LTE/SAE Protocol Structure
21
Signaling stream
eNB
PHY
UE
PHY
MAC
RLC
MAC
MME
RLC
NAS
NAS
RRC RRC
PDCP PDCP
APP
UDP
GTPU
IP
S1AP
SCTP
SGW
IP
UDP
GTPU
IP
SCTP
S1AP
X2AP
Data stream

Same as the PS domain of UMTS
eNB
PHY
UE
PHY
MAC
RLC
MAC
S-GW
PDCP
PDCP
RLC
LTE Radio Interface – User Plane
22

LTE Radio Interface – Control Plane
23
eNB
MAC
UE
MAC
RLC
PDCP
RLC
MME
PDCP
NAS NAS
RRC RRC
PHY
PHY

Radio Frame Structure – Type 1
 Every 10 ms radio frame is divided into ten subframes
 Every subframe has two TSs, each of which is 0.5 ms
 Ts=1/(15000*2048), the basic time unit
 All subframes can work as either uplink or downlink
24
#0
1 radio frame Tf = 307200 TS = 10 ms
1 Tslot = 15360×TS = 0.5ms
#1
1 subframe
…… ……
#2 #17 #18 #19

1 subframe
Subframe #5
DwPTS
GP
UpPTS
… Subframe #9
1 half frame 153600 TS = 5 ms
1 subframe
Subframe #0
DwPTS
GP
UpPTS
30720TS
… Subframe #4
1 Tslot=15360TS
1 radio frame Tf = 307200 Ts = 10 ms
Radio Frame Structure – Type 2
 Each 10-ms radio frame consists of two half-frames at a length of 5 ms, each consisting of 4 data subframes
and 1 special subframe.
 A special subframe includes 3 special time slots: DwPTS, GP and UpPTS. The total length being 1 ms.
 5-ms switch-point periodicity and 10-ms switch-point periodicity are supported.
 Subframes 0, 5 and DwPTS are always used for downlink transmission.
25

Uplink-Downlink Configuration Mode
 "D" means that this
subframe is for downlink
transmission. "U" means
that this subframe is for
uplink transmission. "S"
means a special
subframe, which is made
up of one DwPTS, GP,
and UpPTS.
 The length of DwPTS and
UpPTS in the special
subframe is configurable,
on condition that the
total length of DwPTS,
GP and UpPTS is 1 ms.
Configuration
Normal cyclic prefix Extended cyclic prefix
DwPTS GP UpPTS DwPTS GP UpPTS
0 3 10
1 OFDM
symbols
3 8
1 OFDM
symbols
1 9 4 8 3
2 10 3 9 2
3 11 2 10 1
4 12 1 3 7
2 OFDM
symbols
5 3 9
2 OFDM
symbols
8 2
6 9 3 9 1
7 10 2 - - -
8 11 1 - - -
26
Uplink-
downlink
configuration
Downlink-to-
Uplink
Switch-point
periodicity
Subframe number
0 1 2 3 4 5 6 7 8 9
0 5 ms D S U U U D S U U U
1 5 ms D S U U D D S U U D
2 5 ms D S U D D D S U D D
3 10 ms D S U U U D D D D D
4 10 ms D S U U D D D D D D
5 10 ms D S U D D D D D D D
6 5 ms D S U U U D S U U D

Analysis of System Bandwidth Occupied
 Occupied bandwidth = Subcarrier width x number of subcarriers per RB
x RB number
 Subcarrier width = 15 KHz
 Number of subcarriers per RB = 12
27
Theoretical
bandwidth
(MHz)
1.4 3 5 10 15 20
Number of
RBs
6 15 25 50 75 100
Actual
bandwidth
(MHz)
1.08 2.7 4.5 9 13.5 18

LTE Physical Resource Allocation – Concept of Antenna Port
 Antenna port (R8)
 LTE uses antenna ports to differentiate resources in space. The antenna port is
defined from the perspective of the receiver. That is, if the receiver needs to
distinguish the difference of resources in space, it is necessary to define multiple
antenna ports. There is no one-to-one correspondence between the antenna port
and the actual physical antenna port.
 As LTE uplink supports transmission of only a single RF link, resources do not
need to be distinguished in space, so the concept of antenna ports is not
applicable to the uplink.
 Currently, three types of antenna ports are defined for the LTE downlink,
corresponding to the antenna port numbers 0 to 5 respectively.
 Cell-specific reference signal transmission antenna ports: antenna ports 0 ~ 3
 MBSFN reference signal transmission antenna port: antenna port 4
 Terminal-specific reference signal transmission antenna port: antenna port 5.
28

LTE Physical Resource Allocation – RE/RB
29
Time/OFDM symbol (serial
number l)
Frequency/subcarrier
(serial
number
k)
l = 0
k = 0
1 subframe = 1 ms = 14 OFDM
symbols (regular CP)
1 TS = 0.5 ms = 7 OFDM symbols
(regular CP)
RE (Resource Element)
The minimum resource unit. 1
symbol in the time domain
and 1 subcarrier in the
frequency domain
Marked with (k, l)
RB (Resource Block)
The resource unit of the traffic
channel. 1 time slot in the time
domain and 12 subcarriers in the
frequency domain.

REG
RBG
LTE Physical Resource Allocation –
REG/CCE/RBG
30
RS
RS
RS
RS
REG n+1
REG n
1st
OFDM symbol
REG n+2
REG n
RS
RS
RS
RS
REG n+1
REG n
2nd
OFDM symbol
(4 common antenna ports)
3rd
OFDM symbol
2nd
OFDM symbol
(½ common antenna port)
REG n+1
REG n+2
REG n
REG n+1
The REG (Resource Element Group) is a set of REs in
the control area for mapping the downlink control
channel. Each REG contains four consecutive data
REs.
RBG (Resource Block Group) is a resource unit
used for allocation of traffic channel resource. It is
composed of a set of RBs. The group size is
related to the system bandwidth.
CCE (Channel Control Element) is a PDCCH resource
unit used for allocation of the PDCCH source. It is
composed of 9 REGs.
System Bandwidth
(RB)
RBG Size
(P)
≤10 1
11 – 26 2
27 – 63 3
64 – 110 4
CCE

Overview of LTE Physical Channel
31
Radio Resource Control (RRC)
Medium Access Control
(MAC)
Transport channels
Physical layer
Control
/
Measurements
Layer 3
Logical channels
Layer 2
Layer 1
Wireless Interface Protocol Structure Around The Physical Layer

LTE Uplink/Downlink Channels
32
BCCH PCCH CCCH DCCH DTCH MCCH MTCH
PCH DL-SCH MCH
BCH
PBCH PDSCH PMCH
Logic
channel
Transmission
channel
Physical
channel
CCCH DCCH DTCH
UL-SCH
PRACH PUSCH
RACH
PUCCH
Downlink Channel
Uplink Channel
Logic
channel
Transmission
channel
Physical
channel
PDCCH

Logic Channels
 The MAC provides services to the RLC in the form of logical channels. The logical
channel is defined by the type of information it carries, and is classified into CCH
and TCH. CCH is used for the transmission of control and configuration
information needed by the LTE system. TCH is used for the transmission of user
data.
33

Transmission Channel
 As the physical layer is concerned, the MAC uses the services
provided by the physical layer in the form of transport channels.
34

Physical Channel and Signal
 Uplink physical channel
 PUSCH
 PUCCH
 PRACH
 Uplink physical signal
 Reference Signal: RS
35
 Downlink physical channel
 PDSCH:
 PBCH
 PMCH
 PCFICH
 PDCCH
 PHICH
 Downlink physical signal
 Synchronization Signal
 Reference Signal
 Physical channel
 A collection of REs that carry information originating from higher layers.
 Physical signal
 A collection of REs that does not carry any information originating from
higher layers.

Downlink RS
36

TD-LTE Channel Map
37
2端口
子帧0 子帧1 子帧2 子帧5
时隙0 时隙1 时隙2 时隙3 时隙4 时隙5 时隙10 时隙11
RB
53~99
RB52
RB51
RB48
RB47
RB
0~46

FDD-LTE Channel Map (Downlink)
38

FDD-LTE Channel Map (Uplink)
39

 Search the PSCH, determine 5 ms timing, and
obtain the cell ID
 Demodulate the SSCH, obtains 10 ms timing, and
obtains the cell ID group
 Detect the downlink reference signal, and obtains
the antenna configuration of the BCH
 The UE can read the MIB system messages
(including system bandwidth, system frame number
SFN, and PHICH configuration information) of the
PBCH
 The SIB information is typically in the downlink
shared channel, and ultimately carried in the PDSCH
channel without a separate channel.
5 ms timing, obtain
(2)
ID
N
10 ms timing, obtain
(1)
ID
N
Obtain
(2)
ID
(1)
ID
cell
ID 3 N
N
N 

Read MIB
Read SIB
Physical Layer Process – Cell Search
40
DL
subframe #0
GP
SSS PSS
UL
subframe #2
UpPTS
RS/Control
DwPTS
Data
Cell search is the basis for the UE to access the network to provide users with services.

Physical Layer Process – Random Access
 The UE sends RACH preamble
through the PRACH
 The UE monitors the PDCCH to
obtain the corresponding uplink
and downlink resource
configuration, and obtains the
random access response from the
corresponding PDSCH, including an
uplink grant, a timing message and
an identifier assigned to the UE
 The UE sends a connection request
from the PUSCH
 The eNB sends a collision detection
from the PDSCH
41
2
UE eNB
Msg1: preamble
on PRACH
Msg2: RA response on
PDCCH and PDSCH
min delay
2ms
1
Msg3: connection
requirement, ect
3
Delay about
5ms
Msg4: contention
resolution 4
Delay
Based on eNB

Cell reselection
Cell update
LTE intra-system mobility
Intra-frequency handover
Inter-frequency handover (same
band)
Inter-frequency handover (diff band)
LTE <-> UTRAN inter-working
Reselection LTE<-> UTRAN
PS handover LTE->UTRAN
PS handover UTRAN -> LTE
LTE <-> GERAN inter-working
Reselection LTE<-> GERAN
eNACC LTE ->GERAN
PS handover GERAN -> LTE
LTE
GERAN
LTE－>GERAN
GERAN－>LTE
LTE UTRAN
LTE－>UTRAN
UTRAN－>LTE
eNB
LTE Intra-system HO
eNB
LTE Mobility Management
42

LTE Mobility Management
43
Handover
CELL_PCH
URA_PCH
CELL_DCH
UTRA_Idle
E-UTRA
RRC_CONNECTED
E-UTRA
RRC_IDLE
GSM_Idle/GPRS
Packet_Idle
GPRS Packet
transfer mode
GSM_Connected
Handover
Reselection Reselection
Reselection
Connection
establishment/release
Connection
Connection
CCO,
Reselection
CCO with
optional
NACC
CELL_FACH
CCO, Reselection

Contents
 LTE Overview
 LTE Protocols
 Frequency Domain Multiple Access Technology – OFDM/SC-FDMA
 MIMO Technology
 High-Order Modulation Technology
 HARQ Technology
 Link Adaptation Technology – AMC
 Quick MAC Scheduling Technology
 Cell Interference Elimination
44

Requirements of the LTE Multi-Access
Technology
 Larger bandwidth and greater bandwidth flexibility
 As the bandwidth increases, the OFDMA signal will remain orthogonal and the
CDMA performance will be affected by multipath.
 In the same system, the OFDMA can be used to flexibly handle multiple system
bandwidths.
 Flat architecture
 When the function of packet scheduling is located at the eNB, the capacity of the
cell can be improved by fast scheduling, including frequency domain scheduling.
Frequency domain scheduling can be achieved by OFDMA, which is impossible for
the CDMA system.
 Facilitates the realization of the uplink amplifier
 Compared to OFDMA, SC-FDMA can achieve a lower peak-to-average ratio, which
is conducive for the terminal to use more efficient power amplifier.
 Simplifies multi-antenna operation
 Compared to CDMA, OFDMA can achieve MIMO more easily.
45

Overview of Multiple Access Mode
 LTE uses the OFDMA as the downlink multiple access mode.
 LTE uses the DFT-S-OFDM (OFDM: Discrete Fourier Transform Spread OFDM), or
referred to as SC-FDMA (Single Carrier FDMA) as the uplink multiple access mode.
46
IFFT
QAM
(QPSK/16QAM/64QAM)
Serial-
>parallel ..
.
Add CP
OFDM
Subcarrie
r
mapping
..
.
..
.
Channel coding/
interleaving/scra
mbling
Frequency-domain
Time-
domain
IFFT
Channel coding/
interleaving/scra
mbling
DFT
DFT-SOFDM
Add CP
..
. Subcarrier
mapping
..
.
..
.
Time-domain
Time-
domain
Frequency-
domain
QAM
(QPSK/16QAM/64QAM)

Principle of OFDM
 OFDM, Orthogonal Frequency Division Multiplexing, the subcarriers modulated
by which can overlap each other and can stay orthogonal to each other, as
compared to the conventional Multi-Carrier Modulation (MCM).
 The basic principle of OFDM is to decompose the high-speed data streams into N
parallel low-speed data streams and transmit them on N subcarriers at the same
time. These data symbols transmitted simultaneously on N subcarriers constitute
an OFDM symbol.
47
Frequency
Frequency
Save bandwidth resource
Traditional FDM multi-carrier modulation technology
OFDM multi-carrier modulation technology
Figure Comparison of Bandwidth Utilization Between FDM and OFDM

OFDM Orthogonality – Time-Domain
Description
48

OFDM Orthogonality – Frequency-Domain
Description
49
Time domain
Frequency domain
Rectangular
function
4 subcarriers
4 subcarriers in the
OFDM symbol period
0
1
1
exp exp -
0
T
n m
m n
j t j t dt
m n
T
 


  


 （）（）

In the case of multiple paths, the interference caused by idle guard
interval among subcarriers
OFDM – Cyclic Prefix
50
 All subcarriers are required to be completely orthogonal,
and each subcarrier is completely synchronized in
transmission and reception.
 Transmitter and receiver are to be precisely at the same
frequency and in synchronization.
 The multipath effect can cause intersymbol interference and
intercarrier interference - the signal within the integration
interval does not have an integer number of cycles.
 Guard Interval and cyclic prefix
OFDM symbol with a cyclic prefix

Channel bandwidth
(MHz)
1.4 3 5 10 15 20
Number of
subcarriers
72 180 300 600 900 1200
In an LTE system, the sampling period of NFFT=2048 is used to define the basic time
unit: Ts = 1/Fs = 1/(15000x2048) seconds.
OFDM – Main OFDMA Parameters
 Subcarrier spacing
 15 kHz, for unicast and multicast (MBSFN)
transmission
 7.5kHz, can only be applied to the MBSFN
transmission of independent carrier
 Number of subcarriers
 Length of cyclic prefix
 The lengths of the cyclic prefixes for
different OFDM symbols are different in one
slot.
51

Centralized and distributed frequency-division
multiple access based on DFTS-OFDM
OFDM – Uplink SC-FDMA Mode
 The features of DFTS-OFDM can be used to achieve SC-FDMA in a convenient way.
 By changing the correspondence between the outputs of the DFTs of the different users to the IDFT input
terminals, the spectrum of the input data symbols can be moved to different positions, thereby realizing
multi-user multiple access.
52

Channel bandwidth
(MHz)
1.4 3 5 10 15 20
Number of subcarriers 72 180 300 600 900 1200
OFDM – Key DFTS-OFDM Parameters
 Subcarrier spacing
 15kHz
 Number of subcarriers
 Length of cyclic prefix
 The lengths of the cyclic
prefixes for different DFTS-
OFDM symbols are different
in one slot.
53
53

OFDMA vs. SC-FDMA
54

Contents
 LTE Overview
 LTE Protocols
 MIMO Technology
 HARQ Technology
55

The basic configuration for LTE R8 is DL 2*2 and UL 1*2, supporting up to 4*4.
Multi-Antenna Technology
 Uplink multi-antenna technology
 Uplink transmit antenna selection (Time
Switched Transmit Diversity, TSTD)
 MU-MIMO
 Downlink multi-antenna technology
 Transmit diversity: SFBC, SFBC+FSTD, closed
loop Rank1 pre-coding
 Spatial multiplexing: open-loop spatial
multiplexing, closed-loop spatial multiplexing,
and MU-MIMO
 Beamforming
 Classification of multi-antenna technologies
 MIMO
 SISO
 SIMO
 MISO
56

Multi-Antenna Technology
57
eNode B
UE
 SU-MIMO: Spatial Division Multiplexing
 Two data streams are transmitted to the UE in
one TTI.
eNode B
UE
 SU-MIMO: Transmit diversity
 Transmit only one data
stream to the UE
 MU-MIMO in combination with SDM.
 Transmit two data streams to each UE.
 MU-MIMO combined with transmit diversity
 Transmit only one data stream to each UE
UE
eNode B
UE
UE
eNode B
UE
 Uplink supports MU-MIMO
 Currently supported configuration is: 1x2
or 1x4
 To support 2x2 or 4x4 in the future

LTE Downlink MIMO Mode (R9)
58
There are currently eight LTE downlink MIMO transmission modes
(notifying the UE from high level through transmission mode)
Improve user’s peak rate
Improve cell throughput
Improve cell coverage
Compatible with single transmit
antenna
1 Single antenna port, Port 0
2 Transmit diversity
3
Open-loop space division
multiplexing
4
5
7
Closed-loop space division
multiplexing
Multi-user MIMO
Beamforming, port 5
6 Closed-loop Rank =1 Precoding
8
Twin-flow beamforming, ports 7
and 8
Improve downlink signal SNR

Contents
 LTE Overview
 LTE Protocols
 MIMO Technology
 HARQ Technology
59

High-Order Modulation
60
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0
1
LTE BPSK Constellation Map
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
00
01
10
11
LTE QPSK Constellation Map
-1.5 -1 -0.5 0 0.5 1 1.5
-1.5
-1
-0.5
0
0.5
1
1.5
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
LTE 16QAM Constellation Map
-1.5 -1 -0.5 0 0.5 1 1.5
-1.5
-1
-0.5
0
0.5
1
1.5
000000
000001
000010
000011
000100
000101
000110
000111
001000
001001
001010
001011
001100
001101
001110
001111
010000
010001
010010
010011
010100
010101
010110
010111
011000
011001
011010
011011
011100
011101
011110
011111
100000
100001
100010
100011
100100
100101
100110
100111
101000
101001
101010
101011
101100
101101
101110
101111
110000
110001
110010
110011
110100
110101
110110
110111
111000
111001
111010
111011
111100
111101
111110
111111
LTE 64QAM Constellation Map
 High-order
modulation can
help improve
peak rate.
 LTE supports
BPSK, QPSK,
16QAM, and
64QAM.

Contents
 LTE Overview
 LTE Protocols
 MIMO Technology
 HARQ Technology
61

Hybrid Automatic Repeat reQuest (HARQ)
 FEC: Forward Error Correction
 ARQ: Automatic Repeat reQuest
 HARQ = FEC + ARQ
62

FEC Communications System
63
Data
Sending
FEC
Coding
Channel
FEC
Decoding
Data
Receiving
Disadvantages:
• Reliability is low;
• The adaptive ability of the channel is
lower;
• A longer code is required to ensure
higher reliability, resulting in lower
coding efficiency, higher complexity
and higher cost.
Advantages:
• Higher system transmission
efficiency;
• Automatic error correction, no
feedback and retransmission;
• Low latency.

ARQ Communications System
64
Data
Sending
Channel
Data
Receiving
ACK/NA
CK
Disadvantages:
 Low continuity and real-time
performance
 Low transmission efficiency
Advantages:
 Low complexity
 High reliability
 High adaptability

HARQ Mechanism
65
HARQ has actually integrated the high reliability of ARQ and high efficiency
of FEC
FEC Coding
If receive ACK, then send the
next code group;
If receive NACK,
so re-send the original code
group.
FEC Error Correction &
Detection
Receive code group without
error, and feedback ACK,
otherwise feedback NACK.
Forward
Channel
Feedback
Channel

TDD UL/DL
Configurati
on
DL subframe index n
0 1 2 3 4 5 6 7 8 9
0 4 6 - - - 4 6 - - -
1 7 6 - - 4 7 6 - - 4
2 7 6 - 4 8 7 6 - 4 8
3 4 11 - - - 7 6 6 5 5
4 12 11 - - 8 7 7 6 5 4
5 12 11 - 9 8 7 6 5 4 13
6 7 7 - - - 7 7 - - 5
TDD UL/DL
Configuration
UL subframe index n
0 1 2 3 4 5 6 7 8 9
0 4 7 6 4 7 6
1 4 6 4 6
2 6 6
3 6 6 6
4 6 6
5 6
6 4 6 6 4 7
ACK/NACK  PDSCH
ACK/NACK  PUSCH
HARQ – Timing Relationship
 ACK/NACK timing: For data transmission inside Subframe n, the ACK/NACK
messages are transmitted in the n+k subframes (k=4 for FDD, k>3 for TDD).
66

Configuration DL/UL allocation Process number
(UL)
Process number
(DL)
0 1DL+DwPTS : 3UL 7 4
6 3DL+2DwPT : 5UL 6 6
HARQ – RTT and Number of Processes
 For TDD, its RTT (Round Trip Time) size is not only related to transmission delay,
reception time and processing time, but also with the TDD system’s slot
proportion, and which subframe the transmission is located.
 Number of TDD system processes:
67

HARQ – Timing Relationship
 The timing relationship between retransmission and initial transmission: synchronous HARQ protocol;
asynchronous HARQ protocol.
 Synchronous HARQ Protocol for LTE uplink: If the retransmission is performed at a predefined time, the
receiver does not need to display the process number, which is called the synchronous HARQ protocol.
 The transmission subframe position of the PUSCH is determined according to the subframe position of the PHICH
transmission.
 The timing relationship is the same as PDCCH → PUSCH.
 Asynchronous HARQ Protocol for LTE downlink: If the retransmission is made at any available time after the
previous transmission, the receiver needs to display a specific process number. This is called the
asynchronous HARQ protocol.
68

HARQ – Adaptive/Non-adaptive HARQ
 Adaptive HARQ means that the retransmission can change part or all the
attributes of the initial transmission, including modulation mode and resource
allocation. Change of these attributes need additional signaling notification.
 Non-adaptive HARQ means that the attributes that change at retransmission are
negotiated beforehand by the transmitter and the receiver, and do not require
additional signaling announcements.
 The LTE downlink uses adaptive HARQ.
 The LTE uplink supports both adaptive HARQ and non-adaptive HARQ.
 The non-adaptive HARQ is only triggered by the NACK response information carried in
the PHICH channel.
 The adaptive HARQ is realized by PDCCH scheduling, that is, after the eNB discovers that
the output error is received, the NACK is not fed back, but the parameters used by the
scheduler are scheduled by the scheduler.
69

HARQ – HARQ and Chase Combine (CC)
 In pure HARQ mechanism, the received error packets are directly discarded.
 HARQ combined with CC: The error packet received are saved in the memory and
combined with the retransmitted data packets for decoding, to improve
transmission efficiency.
 The HARQ technology has two implementation approaches: 1. The retransmitted
data is the same as that initially transmitted. This approach is called CC. 2. The
retransmitted data is the same as that initially transmitted. This approach is called
Incremental Redundancy (IR). IR is further divided into Partial Incremental
Redundancy (PIR) and Full Incremental Redundancy (FIR). PIR means that during
the retransmission, the parity bit is different from that in the initial transmission,
the system bits are the same, and the retransmitted data is capable of self-
decoding. FIR means that the parity bit is transmitted with priority, the system
bits are not complete, and therefore data is not capable of self-decoding.
70

IR combining
LTE supports the HARQ
that uses IR combining,
where CC combining can
be deemed as an
exception of IR
combining.
HARQ – HARQ and CC
CC Combining
71

Contents
 LTE Overview
 LTE Protocols
 MIMO Technology
 HARQ Technology
72

Link Adaptation Technology
 Link adaptation can be achieved in two ways: power control and
rate control.
 Generally link adaptation is achieved through rate control, which,
in LTE, is namely the Adaptive Modulation and Coding
technology. The use of AMC technology can make the eNB
promptly adjust the modulation mode (QPSK, 16QAM, or 64QAM)
and coding rate according to the channel status fed back by the
UE. In this way, data transmission can keep up with the changing
situation of the channel in time. This is a good link adaptation
technology.
 For long-delay packet data, AMC can increase the system
capacity without increasing the interference of adjacent cells.
73

AMC Principles for Link Adaptation
74
 QPSK, 16QAM and 64QAM.
 “Continuous” coding rate (0.07-0.93).
eNode B
UE
1. CQI, PMI, Rank
6. Data
2. To check buffer.
3. To schedule a UE
4. To issue a HARQ Process
UE
5. To set modulation, RBs, RV, etc.

CQI index modulation coding rate x 1024 efficiency
0 out of range
1 QPSK 78 0.1523
2 QPSK 120 0.2344
3 QPSK 193 0.3770
4 QPSK 308 0.6016
5 QPSK 449 0.8770
6 QPSK 602 1.1758
7 16QAM 378 1.4766
8 16QAM 490 1.9141
9 16QAM 616 2.4063
10 64QAM 466 2.7305
11 64QAM 567 3.3223
12 64QAM 666 3.9023
13 64QAM 772 4.5234
14 64QAM 873 5.1152
15 64QAM 948 5.5547
Link Adaptation Technology – Link Adapatation of LTE
Uplink/Downlink
 The LTE uplink
adaptation is to
directly determine
specific modulation
and coding modes
based on the uplink
channel quality
measurement of eNB.
 The LTE downlink link
adaptation is to
choose the specific
modulation and
coding modes from
the CQI table (shown
in the right) based on
the CQI fed back by
the UE.
75
75

Power control can effectively help inter-user interference in a cell.
Link Adaptation Technology – Power Control
 By dynamically adjusting the transmit power to maintain a certain signal-to-noise ratio at the
receiver, the transmission quality of the link is guaranteed.
 When the channel conditions are poor, the transmission power needs to be increased. When
the channel conditions are good, the transmission power needs to be reduced, thus ensuring
a constant transmission rate.
76

 Time domain AMC
 Frequency domain AMC
 Spatial domain AMC
SINR
Frequency
UE 1
UE 2
UE 3
SubBand 1 SubBand 2 SubBand 3 SubBand k SubBand m
Modulation mode
adaptation
Coding efficiency
adaptation
User data is effectively transmitted by
making full use of the channel conditions
Good channel conditions: high-rate transmission
of user data
Channel condition is bad: low-rate transmission
of user data.
Combination of the modulation modes and coding modes makes efficient and flexible
AMC technology.
SINR
Time
UE 1
UE 2
UE 3
TTI 1 TTI 2 TTI 3 TTI k TTI m
Link Adaptation Technology – Rate Control (That
Is, AMC)
77

Rate control can make full use of all
powers.
Link Adaptation Technology – Rate Control (That
Is, AMC)
78

Contents
 LTE Overview
 LTE Protocols
 MIMO Technology
 HARQ Technology
79

Downlink: based on common
reference signal
Uplink: based on sounding
reference signal
Channel Scheduling
 The LTE system supports channel scheduling based on frequency
domain
 A typical characteristic of LTE systems over single-carrier CDMA systems is that channel
scheduling and rate control can be performed in the frequency domain.
80

MAC Scheduling Algorithm
 Common packet scheduling algorithm
 Maximum C/I algorithm
 Round Robin: RR
 Proportional fair (PF) algorithm
 Other scheduling algorithm
 Persistent scheduling: PS
 Semi-persistent scheduling: SPS
 Dynamical scheduling: DS
81
illustration of UL
scheduling

Multi-user diversity
Maximum C/I Algorithm
82

Fast Scheduling
83
Time-based RR
Traffic-based RR
Maximum C/I
PF
RR

Contents
 LTE Overview
 LTE Protocols
 MIMO Technology
 HARQ Technology
84

Inter-Cell Interference Elimination
 The technologies for inter-cell interference elimination are:
 Scrambling
 Frequency hopping transmission
 Transmitter-side beamforming and IRC
 Inter-cell interference coordination
 Power control
85

Inter-Cell Interference Elimination – Scrambling
 The LTE system fully utilizes the randomization of sequences to avoid inter-cell
interference.
 Under normal circumstances, the scrambling after channel coding and before
data modulation is the bit-level scrambling
 PDSCH, PUCCH format 2/2a/2b, PUSCH: The scrambling sequence is related to UE ID, cell ID, and start
position of time slot.
 PMCH: The scrambling sequence is related to the MBSFN ID and start position of time slot.
 PBCH, PCFICH, PDCCH: The scrambling sequence is related to the cell ID, and start position of time slot.
 The scrambling of the PHICH physical channel is performed after the modulation
and when the sequence spreading is performed.
 The scrambling sequence is related to the cell ID and start position of time slot.
86

Inter-Cell Interference Elimination – Frequency
hopping transmission
 Both LTE uplink and downlink support the current frequency
hopping transmission, which can randomize the inter-cell
interference
 In addition to the PBCH, the resource mapping of the other downlink physical
control channels is related to the cell ID
 PDSCH, PUSCH, and PUCCH use intra-subframe intra-frequency hopping
transmission
 The PUSCH may use frequency hopping transmission between subframes.
87

Intended
user
Intended user
interferenced
Inter-Cell Interference Elimination – Transmitter-
Side Beamforming
 Increases the signal strength of the intended user
 Reduce the signal interference to other users
 In particular, if the azimuth of the user being disturbed is already known at the
time of beamforming, it is possible to actively reduce the radiant energy.
88

Downlink
Uplink
Inter-Cell Interference Elimination – IRC
 When the receiving end has multiple antennas, the receiver can also use multiple antennas to
reduce inter-user interference. The main principle is to suppress the strong interference by
weighting the received signal. This is called Interference Rejection Combining (IRC).
89

An Example of Frequency Resource
Coordination
Inter-Cell Interference Elimination – Inter-cell
interference coordination
 The basic idea is to limit the use of resources in an inter-cell coordination manner,
including limiting which time-frequency resources are available, or limiting their
transmit power over a certain time-frequency resource.
 Static inter-cell interference coordination
 No standard support is required.
 Frequency resource coordination/power resource coordination.
90

Inter-Cell Interference Elimination – Inter-cell
interference coordination
 Semi-static inter-cell interference
coordination:
 Inter-cell exchange of information, such as
resource usage information, is required.
 At present, LTE has determined that inter-
cell interference coordination (uplink) of
frequency resources can be performed by
exchanging information of PRB use (that is,
which PRBs are allocated to users at the cell
edge, and which PRBs are sensitive to inter-
cell interference) at the X2 interface.
 At the same time, the cells can exchange
Overload Indicator (OI) information at the
X2 interface to perform uplink power
control between cells.
91

UE
Serving cell
Non- serving cell
Interference to non -serving cell
Overload indicator
Inter - cell TPC
TPC command
Desired signal
Intra - cell TPC
Inter-Cell Interference Elimination – Power
Control
 Inter-Cell Power Control
 A method of controlling own cell IoT by informing other cells of the cell IoT information.
 Intra-Cell Power Control
 Compensation to path loss and shadow fading, to save the terminal's transmit power
and minimize interference to other cells, thus making IoT lower than a certain level.
92

Contents
 LTE Overview
 LTE Protocols
93

TD-LTE vs. LTE FDD
94
Technology System TD-LTE LTE FDD
Same key technologies used
Flexible configuration of channel
bandwidth
1.4M, 3M, 5M, 10M, 15M, 20M 1.4M, 3M, 5M, 10M, 15M, 20M
Frame length
10ms (semi-frame 5 ms,
subframe 1 ms)
10ms (subframe 1 ms)
Channel coding Convolutional code, Turbo code Convolutional code, Turbo code
Modulation mode QPSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM
Power control Open-loop with closed-loop Open-loop with closed-loop
MIMO multi-antenna technology Supported Supported
Technological differences
Multiplex mode TDD FDD
Subframe uplink/downlink
configuration
Multiple radio subframe
uplink/downlink
configuration modes
Either uplink or downlink
configuration for all radio
frames
HARQ
Quantity and delay vary with the
uplink/downlink
configuration mode
Fixed quantity and delay
Scheduling period
Vary with the uplink/downlink
configuration modes, at
least 1 ms
1 ms

Comparison of Duplex Modes
95
UL/DL Frequency
UL/DL Time
Guard interval
DL UL DL Time
Frequency
DL
UL
Duplex filter
Guard band
 Time is used to separate the receiving and
transmitting channels. The time resources
are allocated in both directions. The eNB and
the mobile station must cooperate in order
to operate smoothly.
 When symmetric services are supported, it
can take full advantage of the uplink and
downlink spectrums. But when asymmetric
services are supported, spectrum utilization
is greatly reduced.
TDD FDD

Design Difference Between TDD and FDD Sync
Signals
 The LTE sync signal has a period of 5 ms. The sync signal can be either Primary
Synchronization Signal (PSS) or Secondary Synchronization Signal (SSS).
 In TD-LTE and LTE FDD frame structures, the position/relative position of the sync signal is
different.
 Using the difference in the relative position of the PSS and SSS, the terminal may identify at
the initial stage of the cell search whether the system is TDD or FDD.
96

Comparison Between TDD and FDD Networks
97
 The link-level key technologies used in FDD and TDD networks are basically the same, so are the their demodulation performances.
 Flexible application of the multi-antenna technology in the TDD system can help resist interference well and improve performance and
coverage.
Coverage
Co-Frequency Networking Capability
Specific Mechanism
Interference Source Inside System
Frequency Planning and TS Planning
 Both support co-frequency networking with the service channel working on the basis of ICIC.
 Their signaling channels and control channels have roughly the same link gain. Both support co-frequency networking, theoretically.
 Both have the same handover and power control mechanisms. Their synchronization, reselection, and coding and decoding
capabilities of the physical layer channel are basically the same.
 The TDD system is a time-division system. There may be interference between its uplink and downlink time slots that need time slot
planning for coordination.
 FDD has only frequency planning, which is done with the ICIC considered.
 A TDD system has both frequency planning and time slot planning. The frequency planning is done with the ICIC considered, while the time
slot planning is made with also the traffic distribution and interference isolation considered in the networking.

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