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HUAWEI TECHNOLOGIES CO., LTD.
LTE Basic Principle
Author/ Email:
Version:01(20130820)
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Charter 1 LTE Background IntroductionCharter 2 LTE Network Architecture and
Protocol Introduction
Charter 3 LTE Physical Layer Structure
Introduction
Charter 4 LTE Layer 2 Structure Introduction
Charter 5 LTE Air Interface Key Technology
Introduction
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Page 3HUAWEI TECHNOLOGIES CO., LTD.
LTE Background Introduction
What is LTE
LTE (Long Term Evolution)is known as the evolution of radio
access technology conducted by 3GPP. The radio access network will evolve toE-UTRAN (Evolved UMTS
Terrestrial Radio Access Network), and the correlated core
network will evolved to SAE(System Architecture Evolution).
LTE Design Target
Flexible bandwidth configuration: supporting 1.4MHz, 3MHz, 5MHz,
10Mhz, 15Mhz and 20MHz
Peak date rate (within 20MHz bandwidth): 100Mbps for downlink and
50Mbps for uplink
Time delay:
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Specification in 3GPP
R99 R4* R5 R6 R7 R8 (LTE/SAE) R9R
L
3GPP
1999 20102008 2009
05Q1, LTE project (Rel.
8) start
09Q1, LTE specification (Rel.
8) frozen
10Q1, Rel. 9
specification frozen
11Q1, Rel. 10 specification
( LTE-A) frozen
Oct. 2010, LTE-A accepted as 4G
(IMT-Advanced) technology by
ITU-R
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SAE Brief Introduction
SAE (System Architecture Evolution) considers evolution for the whole system architecture, i
Flat Functionality: Take out the RNC entity and part of the functions are moved to e-NodeBthe latency and enhance the schedule ability, such as interference coordination, internal load
Part of the RNC functions are moved to core network;
To enhance the mobility management, all IP technology is applied, user-plane and control-p
The compatibility of other RAT is considered.
SGi
S4
S3S1-MME
PCRFS7
S6a
HSS
Operators IP S(e.g. IMS, PSS
Rx+S10
UE
GERAN
UTRAN SGSN
LTE-UuEUTRAN
MME
S11
S5ServingSAE
Gateway
PDNSAE
GatewayS1-U
LTE Background Introduction
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Charter 1 LTE Background Introduction
Charter 2 LTE Network Architecture and
Protocol Introduction
Charter 3 LTE Physical Layer Structure
Introduction
Charter 4 LTE Layer 2 Structure Introduction
Charter 5 LTE Air Interface Key Technology
Introduction
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Charter 2 LTE Network Architecture and ProtocolIntroduction
2.1 LTE Network Architecture
2.2 LTE Network Element Function
2.3 LTE Protocol Stack Introduction
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LTE Network Architecture
Main Network Element of LTE
E-UTRAN: e-NodeBs, providing the user plane and control
plane.
EPC: MME, S-GWand P-GW.
eNB
MME / S-GW MME / S-GW
eNB
eNB
S1
S1
S1
S1
X2
X2
X2
Compare with traditional 3G network
becomes much more simple and flat,
to lower networking cost, higher netw
and shorter time delay of user data a
signaling.
Network Interface of LTE
The e-NodeBs are interconnected with each other by means of
the X2 interface, which enabling direct transmission of data
and signaling.
S1is the interface between e-NodeBs and the EPC, more
specifically to the MME via the S1-MME and to the S-GW via
the S1-U.
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eNB
RB Control
Connection Mobility Cont.
eNB Measurement
Configuration & Provision
Dynamic ResourceAllocation (Scheduler)
PDCP
PHY
MME
S-GW
S1
MAC
Inter Cell RRM
Radio Admission Control
RLC
E-UTRAN
RRC
MobilityAnchoring
EPS Bearer Co
Idle State Mob
Handling
NAS Securi
e-Node Functions:
Radio Resource Management: Radio Bearer Control, Radio
Admission Control, Connection Mobility Control, Dynamic
allocation of resources to UEs in both uplink and downlink ;
IP header compression and encryption of user data stream;
Routing of User Plane data towards Serving Gateway;
Paging and broadcast messages;
Measurement and measurement reporting configuration for
mobility and scheduling.
MME (Mobility Management Entity) Functions:
NAS signaling and security;
AS Security control; Idle state mobility handling;
EPS (Evolved Packet System) bearer control;
Support paging, handover, roaming and authentication. S-GW (Serving Gateway) hosts the
Packet routing and forwarding; Local m
handover; Lawful interception; UL and
and QCI; Accounting on user and QCI
charging.
P-GW (PDN Gateway) Functions:
Per-user based packet filtering; UE IP address allocation; UL and
DL service level charging, gating and rate enforcement;
LTE Network Element FunctionRRC: Radio Res
PDCP: Packet Da
RLC: Radio Lin
MAC: Medium A
PHY: Physical
EPC: Evolved P
MME: Mobility M
S-GW: Serving G
P-GW: PDN Gat
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Introduction of LTE Radio Protocol Stack
Two Planes in LTE Radio Protocol:
User-plane: For user data transfer
Control-plane: For system signaling transfer
Main Functions of User-plane:
Header Compression
Ciphering
Scheduling
ARQ/HARQ
eNB
PHY
UE
PHY
MAC
RLC
MAC
PDCPPDCP
RLC
eNB
PHY
UE
PHY
MAC
RLC
MAC
RLC
NAS
RRC RRC
PDCP PDCP
Main Functions of Control-plane:
RLC and MAC layers perform the same
plane
PDCP layer performs ciphering and inte
RRC layer performs broadcast, paging
RB control, mobility functions, UE mea
control
NAS layer performs EPS bearer manag
security control
User-plane protocol stack
Control-plane protocol stack
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Charter 1 LTE Background Introduction
Charter 2 LTE Network Architecture and
Protocol Introduction
Charter 3 LTE Physical Layer Structure
Introduction
Charter 4 LTE Layer 2 Structure Introduction
Charter 5 LTE Air Interface Key Technology
Introduction
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Charter 3 LTE Physical Layer Structure Introduction
3.1 LTE Supports Frequency Bands
3.2 Radio Frame Structure
3.3 Physical Channels
3.4 Physical Signals
3.5 Physical Layer Procedures
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Frequency Band of LTE
E-UTRABand
Uplink (UL) D
FUL_low
FUL_high FD
1 1920 MHz 1980 MHz 2110 MH
2 1850 MHz 1910 MHz 1930 MH
3 1710 MHz 1785 MHz 1805 MH
4 1710 MHz 1755 MHz 2110 MH
5 824 MHz 849 MHz 869 MHz
6 830 MHz 840 MHz 875 MHz
7 2500 MHz 2570 MHz 2620 MH
8 880 MHz 915 MHz 925 MHz
9 1749.9 MHz
1784.9 MHz 1844.9 MH
10 1710 MHz 1770 MHz 2110 MH
111427.9 MHz 1452.9 MHz 1475.9 MH
12 698 MHz 716 MHz 728 MHz
13 777 MHz 787 MHz 746 MHz
14 788 MHz 798 MHz 758 MHz
17 704 MHz 716 MHz 734 MHz
...
E-UTRA
Band
Uplink (UL) Downlink (DL) Duplex
ModeFUL_low
FUL_high FDL_low
FDL_high
33 1900 MHz 1920 MHz 1900 MHz 1920 MHz TDD
34 2010 MHz 2025 MHz 2010 MHz 2025 MHz TDD
35 1850 MHz 1910 MHz 1850 MHz 1910 MHz TDD
36 1930 MHz 1990 MHz 1930 MHz 1990 MHz TDD
37 1910 MHz 1930 MHz 1910 MHz 1930 MHz TDD
38 2570 MHz 2620 MHz 2570 MHz 2620 MHz TDD
39 1880 MHz 1920 MHz 1880 MHz 1920 MHz TDD
40 2300 MHz 2400 MHz 2300 MHz 2400 MHz TDD
TDD Frequency Band
FDD Frequency Ban From LTE Protocol:
Duplex mode: FDD and TDD
Support frequency band form 700MHz to 2.6GHz
Support various bandwidth: 1.4MHz, 3MHz, 5MHz, 10MHz,
15MHz, 20MHz
Protocol is being updated, frequency information could be
changed.
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Radio Frame Structures Supported by LTE:
Type 1, applicable to FDD
Type 2, applicable to TDD
FDD Radio Frame Structure: LTE applies OFDM technology, with subcarrier spacing f=15kHz and 2048-order
IFFT. The time unit in frame structure is Ts=1/(2048* 15000) second;
FDD radio frame is 10ms shown as below, divided into 20 slots which are 0.5ms. One
slot consists of 7 consecutive OFDM Symbols under Normal CP configuration.
#0 #1 #2 #3 #19#18
One radio frame, Tf = 307200Ts = 10 ms
One slot, Tslot = 15360Ts = 0.5 ms
One subframe FDD Radio Frame Structure
Concept of Resource Block:
LTE consists of time domain and frequency domain resources. The minimum unit for schedule
is RB (Resource Block),which compose of RE (Resource Element);
RE has 2-dimension structure: symbol of time domain and subcarrier of frequency domain;
One RB consists of 1 slot and 12 consecutive subcarriers under Normal CP configuration.
Radio Frame Structure (1)
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TDD Radio Frame Structure:
Applies OFDM, same subcarriers spacing and time
unit with FDD;
Similar frame structure with FDD. radio frame is 10ms
shown as below, divided into 20 slots which are 0.5ms;
The uplink-downlink configuration of 10ms frame are
shown in the right table.
One slot,Tslot=15360Ts
GP UpPTSDwPTS
One radio frame, Tf= 307200Ts= 10 ms
One half-frame, 153600Ts= 5 ms
30720Ts
One subframe,
30720Ts
GP UpPTSDwPTS
Subframe #2 Subframe #3 Subframe #4Subframe #0 Subframe #5 Subframe #7
Uplink-downlink Configuratio
Uplink-downlinkconfiguration
Downlink-to-UplinkSwitch-point
periodicity 0 1 2
0 5 ms D S U
1 5 ms D S U
2 5 ms D S U
3 10 ms D S U
4 10 ms D S U
5 10 ms D S U
6 5 ms D S U
DwPTS
GP: GuUpPTS
TDD Radio Frame Structure
Radio Frame Structure (2)
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Special Subframe Structure:
Special Subframe consists of DwPTS, GP and UpPTS .
9 types of Special subframeconfiguration;
Guard Period size determines the maximal cell radius. (100km);
DwPTS consists of at least 3 OFDM symbols, carrying RS,
control message and data;
UpPTS consists of at least 1 OFDM symbol, carrying sounding
RS or short RACH.
Configuration of specia
Special Subframe Structure
Special subframe
configuration
No
DwPTS
0 3
1 9
2 10
3 11
4 12
5 3
69
7 10
8 11
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Radio Frame Structure (3)
CP Length Configuration:
Cyclic Prefix is applied to eliminate ISI of OFDM;
CP length is related with coverage radius. Normal
CP can fulfill the requirement of common
scenarios;
Extended CP is for wide coverage scenario;
Longer CP, higher overhead.
Configuration DL OFDM CP LengthUL SC-FDMA C
Length
Normal CP f=15kHz160 for slot #0
144 for slot #1~#6
160 for slot #0
144 for slot #1~#
ExtendedCP
f=15kHz 512 for slot #0~#5 512 for slot #0~#
f=7.5kHz 1024 for slot #0~#2 NULL
CP Configuration
Slot structure under Normal CP
configuration
(
f=15kHz)
Slot structure under Extended CP
configuration
(
f=15kHz)
Slot structure under Extended CP
configuration
(
f=7.5kHz)
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Brief Introduction of Physical Channels
Downlink Channels
Physical Broadcast Channel (PBCH): Carries system information for cell
search, such as cell ID.
Physical Downlink Control Channel (PDCCH) : Carries the resource
allocation of PCH and DL-SCH, and Hybrid ARQ information.
Physical Downlink Shared Channel (PDSCH) : Carries the downlink user
data.
Physical Control Format Indicator Channel (PCFICH) : Carriers
information of the OFDM symbols number used for the PDCCH.
Physical Hybrid ARQ Indicator Channel (PHICH) : Carries Hybrid ARQ
ACK/NACK in response to uplink transmissions.
Physical Multicast Channel (PMCH) : Carries the multicast information. Uplink Channels
Physical Random Access Channel (PRACH) : Carries the random
access preamble.
Physical Uplink Shared Channel (PUSCH) : Carries the uplink user data.
Physical Uplink Control Channel (PUCCH) : Carries the HARQ
ACK/NACK, Scheduling Request (SR) and Channel Quality Indicator
(CQI), etc.
BCH PCH DL-SMCH
PBCH PDSCHPMCH
UL-SCH
PUSCH
RACH
PUCCHPRACH
Mapping between downlin
channels and downlink ph
Mapping between uplink
and downlink physical c
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Downlink Physical Channel
ScramblingModulation
mapper
Layermapper
Precoding
Resource elementmapper
OFDM genera
Resource elementmapper OFDM generaScrambling Modulationmapper
layerscode words
Downlink Physical Channel Processing
scrambling of coded bits in each of the code words to be transmitted on a physical channel
modulation of scrambled bits to generate complex-valued modulation symbols
mapping of the complex-valued modulation symbols onto one or several transmission layers
precoding of the complex-valued modulation symbols on each layer for transmission on the antenna ports
mapping of complex-valued modulation symbols for each antenna port to resource elements
generation of complex-valued time-domain OFDM signal for each antenna port
Modulation Scheme of Downlink Channel
Phy Ch Modulation Scheme Phy Ch Modulation Scheme
PBCH QPSK PCFICH QPSK
PDCCH QPSK PHICH BPSK
PDSCH QPSK, 16QAM, 64QAM PMCH QPSK, 16QAM, 64QAM
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Downlink Resource Structure
Downlink Resource Structure
Type I frame, single antenna, F = 15 kHz
Standard RB:
One of center 6 RBs:
Legend:Downlink Reference SignalsPBCH (Physical Broadcast Channel)
PSS (Primary Synchronisation Signal)
SSS (Secondary Synchronisation Signal)
PDCCH / PHICH / PCFICH (Physical - Downlink Control / HARQ Indicator / Control Format Indicator -
PDSCH (Physical Downlink Shared Data Channel)
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Downlink Resource Structure
OFDM
Symbol 0CP
OFDM
Symbol 1CP
OFDM
Symbol 3CP
OFDM
Symbol 4CP
OFDM
Symbol 5CP
OFDM
Symbol 2CP
Legend:
Downlink Reference s
PBCH
PSS
SSS
PDCCH / PHICH / PCF
PDSCH
1 subframe = 2 slot (1 ms)
1 fra
10 s
SF 0 SF 1 SF 2 SF 3 SF 4 SF 5 SF 6 SF 7 SF 8 SF 9
7 OFDM symbols at normal CP per slot (0.5 ms)
0 1 2 3 4 5 6 0 1 2 3 4 5 6
Centre6RBs
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Uplink RS (Reference Signal):
The uplink pilot signal, used for synchronization between E-
UTRAN and UE, as well as uplink channel estimation.
Two types of UL reference signals:
DM RS (Demodulation Reference Signal), associated with
PUSCH and PUCCH transmission;
SRS(Sounding Reference Signal), without associated
with PUSCH and PUCCH transmission.
Characteristics:
Each UE occupies parts of the system bandwidth since SC-
FDMA is applied in uplink. DM RS only transmits in the
bandwidth allocated to PUSCH and PUCCH.
The slot location of DM RS differs with associated PUSCH andPUCCH format.
Sounding RSs bandwidth is larger than that allocated to UE, in
order to provide the reference to e-NodeB for channel estimation
in the whole bandwidth.
Sounding RS is mapped to the last symbol of sub-frame. The
transmitted bandwidth and period can be configured. SRS
transmission scheduling of multi UE can achieve
time/frequency/code diversity.
DM Rto the
Time
Freq
Time
Freq
Time
Freq
DM R
UL AC3 sym
DM RS
CQI si
slot
PUCCH is mapped to up & down
ends of the system bandwidth,
hopping between two slots.
Alloc
Sys
Uplink Physical Signals
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Uplink esource Structure
OFDM
Symbol 0CP
OFDM
Symbol 1CP
OFDM
Symbol 3CP
OFDM
Symbol 4CP
OFDM
Symbol 5CP
OFDM
Symbol 2CP
Legend:
UL DMRS (Uplink Demodulation Refe
UL SRS (Uplink Sounding Reference
PUCCH (Physical Uplink Control Cha
(incl.HARQ feedback and CQI report
Demodulation Reference Signal for P
PUSCH (Physical Uplink Shared Data
SF 0 SF 1 SF 2 SF 3 SF 4 SF 5 SF 6 SF 7 SF 8 SF 9
7 OFDM symbols at normal CP per slot (0.5 ms)
0 1 2 3 4 5 6 0 1 2 3 4 5 6
1 subframe = 2 slot (1 ms)
1 fra
10 s
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0l
0R
0R
0R
0R
6l 0l
0R
0R
0R
0R
6l
Resource element (k,l)
Not used for transmission on this antenna port
Reference symbols on this antenna port
0l
0R
0R
0R
0R
6l 0l
0R
0R
0R
0R
6l 0l
1R
1R
1R
1R
6l 0l
1R
1R
1R
1R
6l
0l
0R
0R
0R
0R
6l 0l
0R
0R
0R
0R
6l 0l
1R
1R
1R
1R
6l 0l
1R
1R
1R
1R
6l
0l 6l 0l
2R
6l 0l 6l 0l 6l
2R
2R
2R
3R
3R
3R
3R
even-numbered slots odd-numbered slots
even-numbered slots odd-numbered slots
even-numbered slots odd-numbered slots
even-numbered slots odd-numbered slots
Downlink Physical Signals (1) Downlink RS (Reference Signal):
Similar with Pilot signalof CDMA. Used for downlink physical ch
channel quality measurement (CQI)
Three types of RS in protocol. Cell-Specific Reference Signal is
types RS (MBSFN Specific RS & UE-Specific RS) are optional.
Cell-Specific RS
Mapping in Time-
Frequency DomainOne
AntennaPort
TwoAntennaPorts
FourAntennaPorts
Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3
Characteristics:
Cell-Specific Reference Signals are generate
and frequency shift mapping. RS is the pseud
the time-frequency domain.
The frequency interval of RS is 6 subcarriers.
RS distributes discretely in the time-frequenc
situation which is the reference of DL demodu
Serried RS distribution leads to accurate chan
overhead that impacting the system capacity.
M
S
RE
Not used for RStransmission on thisantenna port
RS symbols on thisantenna port
R1: RS
R2: RS
R3: RS
R4: RS
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Synchronization Signal:
synchronization signals are used for time-frequency synchronization between UE and E-UTRAN during cell se
synchronization signal comprise two parts:
a. Primary Synchronization Signal, used for symbol timing, frequency synchronization and part of the ce
b. Secondary Synchronization Signal, used for detection of radio frame timing, CP length and cell group
Synchronization Signals Structur
Characteristics:
The bandwidth of the synchronization signal
is 62 subcarrier, locating in the central part of
system bandwidth, regardless of system
bandwidth size.
Synchronization signals are transmitted only
in the 1st and 11rd slots of every 10ms frame.
The primary synchronization signal is located
in the last symbol of the transmit slot. The
secondary synchronization signal is located in
the 2nd last symbol of the transmit slot.
Downlink Physical Signals (2)
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Basic Principle of Cell Search:
Cell search is the procedure of UE synchronizes with E-UTRAN in time-
freq domain, and acquires the serving cell ID;
Two steps in cell search:
Step 1: Symbol synchronization and acquirement of ID within
Cell Group by demodulating the Primary Synchronization Signal;
Step 2: Frame synchronization, acquirement of CP length and
Cell Group ID by demodulating the Secondary Synchronization
Signal.
About Cell ID
In LTE protocol, the physical layer Cell ID comprises two parts: Cell
Group ID and ID within Cell Group. The latest version defines that
there are 168 Cell Group IDs, 3 IDs within each group. So totally
168*3=504 Cell IDs exist.
represents Cell Group ID, value from 0 to 167;
represents ID within Cell Group, value from 0 to 2.
(2)ID
(1)ID
cellID 3 NNN
(1)IDN
(2)IDN
Initial Cell Search:
The initial cell search is carried on after the UE
know the network bandwidth and carrier freque
UE repeats the basic cell search, tries all the ca
to demodulate the synchronization signals. Thistime requirement are typically relatively relaxed
time, such as recording the former available ne
search target.
Once finish the cell search, which achieve sync
and acquirement of Cell ID, UE demodulates th
information, such as bandwidth and Tx antenna
After the procedure above, UE demodulates the
that allocated by system. UE wakes up from the
paging period, demodulates PDCCH for monito
PDSCH resources will be demodulated to recei
Physical Layer Procedure Cell Search
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Basic Principle of Random Access :
Random access is the procedure of uplink
synchronization between UE and E-UTRAN.
Prior to random access, physical layer shall receive the
following information from the higher layers:
Random access channel parameters: PRACH configuration,
frequency position and preamble format, etc.
Parameters for determining the preamble root sequences and
their cyclic shifts in the sequence set for the cell, in order to
demodulate the random access preamble.
Two steps in physical layer random access:
UE transmission of random access preamble
Random access response from E-UTRAN
Detail Procedure of Random Access:
Physical Layer procedure is triggered up
transmission by higher layers.
The higher layers request indicates a prepreamble received power, a correspondi
resource .
UE determines the preamble transmissio
received power + Path Loss. The transm
the maximum transmission power of UE.
path loss estimate calculated in the UE.
A preamble sequence is selected from th
using the preamble index.
A single preamble is transmitted using th
sequence with calculated transmission p
PRACH resource.
UE Detection of a PDCCH with the indica
during a window controlled by higher laye
corresponding PDSCH transport block is
The higher layers parse the transport blo
grant.
RA-RNTI: Random Access Radio Netwo
Physical Layer Procedure Random Access
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Basic Principle of Power Control:
Downlink power control determines the EPRE (Energy
per Resource Element);
Uplink power control determines the energy per DFT-
SOFDM (also called SC-FDMA) symbol.
Uplink Power Control:
Uplink power control consists of opened loop power and closed loop power
control.
A cell wide overload indicator (OI) is exchanged over X2 interface for
integrated inter-cell power control, possible to enhance the system
performance through power control.
PUSCH, PUCCH, PRACH and Sounding RS can be controlled respectively by
uplink power control. Take PUSCH power control for example:
PUSCH power control is the slow power control, to compensate the path loss
and shadow fading and control inter-cell interference. The control principle is
shown in above equation. The following factors impact PUSCH transmission
power PPUSCH: UE maximum transmission power PMAX, UE allocated resource
MPUSCH, initial transmission power PO_PUSCH, estimated path loss PL,
modulation coding factor TFand system adjustment factor f (not working
during opened loop PC)
UE report CQI
DL Tx Power
EPRE: Energy per Resource Eleme
DFT-SOFDM: Discrete Fourier Trans
f(i)}(i)PL(j)(j)P(i))(M,{P(i)P TFO_PUSCHPUSCHMAXPUSCH 10log10min
Downlink Power Control:
The transmission power of downlink R
The transmission power of PDSCH is
transmission power.
Downlink transmission power will be a
comparison of UE report CQI and targ
power control.
UL Tx Power
System ad
parameter
Physical Layer Procedure Power Control
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Charter 1 LTE Background Introduction
Charter 2 LTE Network Architecture and
Protocol Introduction
Charter 3 LTE Physical Layer Structure
Introduction
Charter 4 LTE Layer 2 Structure IntroductionCharter 5 LTE Air Interface Key Technology
Introduction
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Charter 4 LTE Layer 2 Structure Introduction4.1 LTE Layer 2 Brief Introduction
4.2 MAC Layer Introduction
4.3 RLC Layer Introduction
4.4 PDCP Layer Introduction
4.5 Summary of Layer 1 & 2 Data Flow
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Layer 2 is split into the following layers:
MAC (Medium Access Control) Layer
RLC (Radio Link Control ) Layer
PDCP (Packet Data Convergence Protocol ) Layer
Main Functions of Layer 2:
Header compression, Ciphering
Segmentation and concatenatio
Scheduling, priority handling, mu
demultiplexing, HARQ
Segm.
ARQ etc
Multiplexing UE1
Segm.
ARQ etc...
HARQ
Multiplexing UEn
HARQ
BCCH PCCH
Scheduling / Priority Handling
Logical Channels
Transport Channels
MAC
RLCSegm.
ARQ etc
Segm.
ARQ etc
PDCP
ROHC ROHC ROHC ROHC
Radio Bearers
Security Security Security Security
...
Multiplexing
...
HARQ
Scheduling / Priority H
MAC
RLC
PDCP
Segm.
ARQ etc
Se
ARQ
ROHC RO
Security Sec
Layer 2 Structure for DL Layer 2 Structur
Overview of LTE Layer 2
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Main functions of MAC Layer:
Mapping between logical channels and transport channels
Multiplexing/demultiplexing of RLC PDUs (Protocol Data Unit)
belonging to one or different radio bearers into/from TB (transport
blocks ) delivered to/from the physical layer on transport channels
Traffic volume measurement reporting
Error correction through HARQ
Priority handling between logical channels of one UE
Priority handling between UEs (dynamic scheduling)
Transport format selection
Padding
Logical Channels of MAC Lay
Control Channel: For the transf
information
Traffic Channel: for the transfer
Multiplexing
HARQ
Scheduling / Priority Handling
Transport Channels
MAC
Logical Channels
MAC Layer
Structure
BCCHPCCH CCCH DCCH DTCH MCCH M
BCHPCH DL-SCH
Control Channel
Traffic Channel
Introduction of MAC Layer
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Main functions of RLC Layer:
Transfer of upper layer PDUs supports AM, UM or TM data
transfer
Error Correction through ARQ (no need RLC CRC check,
CRC provided by the physical) Segmentation according to the size of the TB: only if an RLC
SDU does not fit entirely into the TB then the RLC SDU is
segmented into variable sized RLC PDUs, no need padding
Re-segmentation of PDUs that need to be retransmitted: if a
retransmitted PDU does not fit entirely into the new TB used
for retransmission then the RLC PDU is re-segmented
Concatenation of SDUs for the same radio bearer
In-sequence delivery of upper layer PDUs except at HO
Protocol error detection and recovery Duplicate Detection
SDU discard
Reset
RLC PDU Structure:
The PDU sequence number carried
independent of the SDU sequence n
The size of RLC PDU is variable acc
scheme. SDUs are segmented /concsize. The data of one PDU may sour
...
RLCSegm.
ARQ etc
Segm.
ARQ etc
Logical Channels
RLC Layer
Structure
RLC PDU Structure
RLC header
RLC PDU
...
n n+1 n+2RLC SDU
Segmentation Concatenation
Introduction of RLC Layer
f C
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Main functions of PDCP Layer:
Functions for User Plane:
Header compression and decompression: ROHC
Transfer of user data: PDCP receives PDCP SDU from theNAS and forwards it to the RLC layer and vice versa
In-sequence delivery of upper layer PDUs at handover for RLC
AM
Duplicate detection of lower layer SDUs at handover for RLC
AM
Retransmission of PDCP SDUs at handover for RLC AM
Ciphering
Timer-based SDU discard in uplink
Functions for Control Plane:
Ciphering and Integrity Protection
Transfer of control plane data: PDCP receives PDCP SDUs
from RRC and forwards it to the RLC layer and vice versa
PDCP PDU Structure:
PDCP PDU and PDCP header a
PDCP header can be either 1 or
PDCP
ROHC RO
Security Sec
ROHC: Robust Header Com
PDCP header
PDCP P
PDCP PDU S
Introduction of PDCP Layer
S f D t Fl i L 1 & 2
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Data Transfer in Layer 1 and Layer 2
Data from the upper layer are headed and packaged, sent to the lower layer, vice versa.
Scheduler effect in the RLC, MAC and Physical Layers. User data packages are multiplexed in the MAC Lay
CRC in Physical Layer.
Summary of Data Flow in Layer 1 & 2
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Charter 1 LTE Background Introduction
Charter 2 LTE Network Architecture and
Protocol Introduction
Charter 3 LTE Physical Layer Structure
Introduction
Charter 4 LTE Layer 2 Structure Introduction
Charter 5 LTE Air Interface Key Technology
Introduction
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Charter 5 LTE Air Interface Key Technology Introduction
5.1 OFDM & SC-FDMA
5.2 MIMO
5.3 Cell Interference Control
5.4 Schedule and Link Auto-Adaptation
5.5 E-MBMS
OFDMA & SC FDMA
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OFDM & OFDMA
OFDM(Orthogonal Frequency Division Multiplexing) is a
modulation multiplexing technology, divides the system bandwidth
into orthogonal subcarriers. CP is inserted between the OFDM
symbols to avoid the ISI.
OFDMAis the multi-access technology related with OFDM, is used
in the LTE downlink. OFDMA is the combination of TDMA and
FDMA essentially.
Advantage:High spectrum utilization efficiency due to orthogonal
subcarriers need no protect bandwidth. Support frequency link auto
adaptation and scheduling. Easy to combine with MIMO.
Disadvantage:Strict requirement of time-frequency domain
synchronization. High PAPR.
DFT-S-OFDM & SC-FDMA
DFT-S-OFDM (Discrete Fourie
OFDM) is the modulation multi
in the LTE uplink, which is simi
release the UE PA limitation ca
Each user is assigned part of th
SC-FDMASingle Carrier Fre
Accessingis the multi-access
DFT-S-OFDM.
Advantage:High spectrum uti
orthogonal user bandwidth nee
Low PAPR.
The subcarrier assignment sch
mode and Distributed mode.
OFDMA & SC-FDMA
TTI: 1ms
System Bandwidth
Sub-band12Sub-carriers
Time
TTI: 1ms
System Bandwidth
Sub-band12Sub-carriers
Time
Sub-carriers
TTI: 1ms
Frequency
Time
System Bandwidth
Sub-band12Sub-carriers
User 1
User 2
User 3
Sub-carriers
TTI: 1ms
Frequency
Time
System Bandwidth
Sub-band12Sub-carriers
User 1
User 2
User 3
User 1
User 2
User 3
MIMO
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Downlink MIMO
MIMO is supported in LTE downlink to achieve spatial
multiplexing, including single user mode SU-MIMO and
multi user mode MU-MIMO.
In order to improve MIMO performance, pre-coding is usedin both SU-MIMO and MU-MIMO to control/reduce the
interference among spatial multiplexing data flows.
The spatial multiplexing data flows are scheduled to one
single user In SU-MIMO, to enhance the transmission rate
and spectrum efficiency. In MU-MIMO, the data flows are
scheduled to multi users and the resources are shared
within users. Multi user gain can be achieved by user
scheduling in the spatial domain.
Uplink MIMO
Due to UE cost and power consump
implement the UL multi transmission
Virtual-MIMO, in which multi single a
associated to transmit in the MIMO munder study.
Scheduler assigns the same resourc
user transmits data by single antenn
data by the specific MIMO demodula
MIMO gain and power gain (higher T
freq resource) can be achieved by V
of the multi user data can be control
also bring multi user gain.
Pre-coding vectors
User k data
User 2 data
User 1 data
Channel Information
User1
User2
User k
Scheduler Pre-coder
S1
S2
Pre-coding vectors
User k data
User 2 data
User 1 data
Channel Information
User1
User2
User k
Scheduler Pre-coder
S1
S2
User 1 data
Channel
Scheduler
MIMO
DecoderUser k data
User 1 data
User 1 data
Channel
Scheduler
MIMO
DecoderUser k data
User 1 data
DL-MIMO Virtual-M
MIMO
DL MIMO
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DL MIMO
codeword
UE1
User1S
FB
C
Mod
SFBC (Transmit Diversity)
Same stream transmitted simultaneously in certain
form of MIMO coding at the same time-frequency
resource from both antenna ports (Rank = 1)
Depending on the environment & number of
antennas, SFBC can reduce fading margin by 2~8
dB, to extend coverage, and enhance system
capacity
Layer 1, CW1, AMC1
Layer 2, CW2, AMC2
MIMOencoder and
layer
mapping
MCW (Spatial Multiplexing)
Multiple data streams transmitte
frequency resource from differen
The terminal must have at least
spatial multiplexing (SM)
Cell Interference Control
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PowerPower
PowerPower
ICIC
Inter-Cell Interference Coordination
ICIC is one solution for the cell interference control, is essentially a schedule strategy. In LTE,
coordination schemes, like SFR (Soft Frequency Reuse) and FFR (Fractional Frequency Reus
the interference in cell edges to enhance the frequency reuse factor and performance in the ce
SFR Fundamentals
SFR is one effective solution of inter-cell interference control. The system bandwidth is separa
primary band and secondary band with different transmit power.
1
2
3
6
5
7
4
1
2
3
6
5
7
4
The primary band is assigned to the
users in cell edge. The eNB transmit
power of the primary band can be high.
SeconBand
Cell 2,4,6 Primary Band
Frequency
Cell 1Power
Frequency
Cell 1Power
Cell 1 Primary Band
Secondary Band
Cell 3,5,7P Prim
The secondary band is assigned to the usersin cell center. The eNB transmit power of thesecondary band should be reduced in orderto avoid the interference to the primary bandof neighbor cells.
SecondaryBand
SecondaryBand
Cell Interference Control
Huawei SFR 1 3 1 Frequency Planning
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ICIC is introduced into 131 planning to reduce inter cell interference. Higher cell
service throughputenhances users experience.
Huawei SFR 1
3
1 Frequency Planning
SFR 131 UL ICIC
Cells from different sites:frequency division, could be
adjusted periodically due to edge load
Cells in the same site:time division. Edge users are
scheduled in odd and even subframe
SFR 131 DL ICIC
Cell edge:frequency division,se
power
Cell central:all bandwidthare tra
coverage to reduce interference
High sector throughput and spectrum efficiency
Suitable for high capacity scenarios (dense urban & urban) Expansion solution for traditional 131
Adaptive Modulation and Coding
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Adaptive Modulation and Coding
The most appropriate modulation and coding scheme can be adaptively selected according to t
propagation conduction, then the maximum throughput can be obtained for different channel sit
Schedule and Link Auto-adaptation
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User Multiplexing and Scheduling
Large system bandwidth (10/15/20MHz) of LTE will facing the
problem of frequency selected fading. The fading
characteristic on subcarriers of one user can be regarded as
same, but different in further subcarriers.
Select better subcarriers for specific user according to the
fading characteristic. User diversity can be achieved to
increase spectrum efficiency.
The LTE schedule period is one or more TTI.
The channel propagation information is feed back to e-NodeB
through the uplink. Channel quality identity is the overhead of
system. The less, the better.
Schedule and Link Auto-adaptation
Link Auto-adaptation
LTE support link auto-adaptation i
frequency-domain. Modulation sch
on the channel quality in time/freq
In CDMA system, power control is
auto-adaptation technology, which
by far-near effect. In LTE system,
OFDM technology. Power control
uplink interference from adjacent c
path loss. It is one type of slow lin
scheme.
Channel Propagation FadingUser Multiplexing and Sch
Enhance MBMS
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HUAWEI TECHNOLOGIES CO., LTD.
E-MBMS
All e-NodeBs apply same frequency resource and send MBMS data simultaneously.
For UE, the signals from different e-NodeBs can be treat as component of multi paths. Not nec
signal from e-NodeBs, which can be soft combined by UE.
Enhance MBMS
E-MBMS Features SFN (Single Frequency Network) mode
MBMS is limited by the cell edge user performance. SFN enhance the performance in cell edg
MBMS effect.
Need downlink air-interface synchronization in SFN mode.
Time delay is much different for e-NodeBs, the signal combination will cause time delay increa
will be configured.
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