10 LTE Basic Knowledge

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LTE Basic Knowledge

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HUAWEI TECHNOLOGIES CO., LTD.

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Huawei Confidential

Agenda 1

LTE Network Architecture

2

LTE Protocol

3

LTE Key Technology

4

Compsirson b/w LTE and UMTS

HUAWEI TECHNOLOGIES CO., LTD. PDF created with pdfFactory Pro trial version www.pdffactory.com

Huawei Confidential

Page 2

Network Architecture of LTE

•

Compare with traditional 3G network, LTE architecture becomes much more simple and flat, which can lead to lower networking cost, higher networking flexibility and shorter time delay of user data and control signalling. HUAWEI TECHNOLOGIES CO., LTD.


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Page 3

Network Architecture of LTE

•

The E-UTRAN consists of e-NodeBs, The e-NodeBs are interconnected with each other by means of the X2 interface, which enabling direct transmission of data and signaling.

•

The EPC (Evolved Packet Core) consists of MME, S-GW, PGW,HSS,PCRF and son on.


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EPC Network Simplification

Page 4

Network Architecture of LTE Paging, handover, bearer control, idle state mobility handling

Routing, mobility, charge and account, PDN, and QCI

IP address allocation, gating and rate enforcement


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Function of LTE Network Element e-Node hosts the following functions: p

p p p p

p

Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling); IP header compression and encryption of user data stream; Selection of an MME at UE attachment; Routing of User Plane data towards Serving Gateway; Scheduling and transmission of paging and broadcast messages (originated from the MME); Measurement and measurement reporting configuration for mobility and scheduling;

MME (Mobility Management Entity) hosts the following functions:

p

NAS signaling and security; AS Security control; Idle state mobility handling; EPS (Evolved Packet System) bearer control;

p

Support paging, handover, roaming and authentication.

p p p

S-GW (Serving Gateway) hosts the following functions:

P-GW (PDN Gateway) hosts the following functions: p

p

Per-user based packet filtering; UE IP address allocation; UL and DL service level charging, gating and rate enforcement;


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Packet routing and forwarding; Local mobility anchor point for handover; Lawful interception; UL and DL charging per UE, PDN, and QCI; Accounting on user and QCI granularity for inter-operator charging.

Page 6

Comparison b/w UTRAN&E-UTRAN

S1

S1

S1

S1

X2

X2

UTRAN

The main difference between UMTS and LTE: the removing of RNC network element and the introduction of X2 interface, which make the network more simple and flat, leading lower networking cost, higher networking flexibility and low latency


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Agenda 1


2

LTE Protocol

3

LTE Key Technology

4



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Page 8

Radio Frame Structure •

•

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 2048order IFFT. The time unit in frame structure is Ts=1/(2048* ∆f) second

§

FDD radio frame is 10ms shown as below, divided into 20 slots which is 0.5ms. One slot consists of 7 consecutive OFDM Symbols under Normal CP configuration

FDDRadio Frame Structure

l

Concept of Resource Block： p

p p

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


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Time-Frequency Resource Unit DwPTS

TDD #1

System Bandwidth

GP

D

UpPTS

U

U

D

D

Sub-carrier

1 Sub-frame, TTI: 1ms 2 Slots

Frequency

User 1

FDD

User 2 User 3

Time

-

7 Symbols

1 Resource Block: 12 Sub-carriers 1 Sub-carrier = 15KHz 180KHz (Total 200KHz with Guard)

1 Sub-frame 2 Slots 2 RBs

1 Sub-frame = 2 Slots, 14 Resource Elements (RE)


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Page 10

U

U

D

Frame and Slot Structure (Normal CP)


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Resource Element Mapping (6 RBs, 2 Antenna)


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Introduction of LTE PHY- Physical Channels Downlink Channels： p

Physical Broadcast Channel (PBCH): Carries system information for cell search, such as cell ID.

p

Physical Downlink Control Channel (PDCCH) : Carries the MAC Layer

resource allocation of PCH and DL-SCH, and Hybrid ARQ

Physical Layer

information. p

Physical Downlink Shared Channel (PDSCH) : Carries the downlink user data.

p

Physical Control Format Indicator Channel (PCFICH) : Carriers information of the OFDM symbols number used for the PDCCH.

p

Mapping between downlink transport channels and downlink physical channels

Physical Hybrid ARQ Indicator Channel (PHICH) : Carries Hybrid ARQ ACK/NACK in response to uplink transmissions.

p

Physical Multicast Channel (PMCH) : Carries the multicast information.

Uplink Channels： p

Physical Random Access Channel (PRACH) : Carries the

MAC Layer

random access preamble. p

Physical Layer

Physical Uplink Shared Channel (PUSCH) : Carries the uplink user data.

p

Physical Uplink Control Channel (PUCCH) : Carries the HARQ ACK/NACK, Scheduling Request (SR) and Channel Quality

Mapping between uplink transport channels and downlink physical channels

Indicator (CQI), etc.


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PHY

PHY

MAC

MAC

Channel Mapping


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One Antenna Port

Introduction of LTE PHY- DL Physical Signals(1) RS (Reference Signal): p R0

R0

R0

R0

R0

Two Antenna Ports

p

Cell-Specific RS Mapping in TimeFrequency Domain

R0

R0

l=0

l=6 l=0

Similar with Pilot signal of CDMA. Used for downlink physical channel demodulation and channel quality measurement (CQI) Three types of RS in protocol. Cell-Specific Reference Signal is essential and the other two types RS (MBSFN Specific RS & UE-Specific RS) are optional.

Characteristics:

l=6

p

RE R0

R0

R0

R1

R0

R0

R0

R1

R0

R1

R0

l=0

Four Antenna Ports

R0

R0

R0

l=6

R0

l=0

p

l=6

R1

R1

p

R1

R1

R0

p

RS symbols on this antenna port

l =6 l=0

R1

R0

R0

R1

R1

l=6 l=0

Not used for RS transmission on this antenna port

R1

Cell-Specific Reference Signals are generated from cellspecific RS sequence and frequency shift mapping. RS is the pseudo-random sequence transmits in the time-frequency domain. The frequency interval of RS is 6 subcarriers. RS distributes discretely in the time-frequency domain, sampling the channel situation which is the reference of DL demodulation. Serried RS distribution leads to accurate channel estimation, also high overhead that impacting the system capacity.

R2

R1

R3

R1: RS transmitted in 1st ant port

R2

R1

R2: RS transmitted in 2nd ant port

R3

R2

R3: RS transmitted in 3rd ant port

R3

R4: RS transmitted in 4th ant port R0 l=0

R0 l=6 l=0

Antenna Port 0

R1 l=6

l=0

R1 l=6 l=0

R2 l=6

Antenna Port 1

l=0

R3 l=6 l=0

l=6

Antenna Port 2


l=0

l =6 l =0

l=6

MBSFN: Multicast/Broadcast over a Single Frequency Network

Antenna Port 3

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Page 15

Introduction of LTE PHY- DL Physical Signals(2) Synchronization Signal: p p

synchronization signals are used for time-frequency synchronization between UE and E-UTRAN during cell search. synchronization signal comprise two parts: n Primary Synchronization Signal, used for symbol timing, frequency synchronization and part of the cell ID detection. n Secondary Synchronization Signal, used for detection of radio frame timing, CP length and cell group ID.

Characteristics: p

p

p

The bandwidth of the synchronization signal is 72 subcarrier, locating in the central part of system bandwidth, regardless of system bandwidth size. Synchronization signals are transmitted only in the 1st and 11th 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.

Caution: Synchronization signals are sometimes named as Synchronization Channel (P-SCH & S-SCH) in some documents. The meaning should be the same, which represents the signals transmitted in the specified time-frequency locations. Please don’t be confused with Share Channel (SCH).


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Synchronization Signals Structure

Page 16

Introduction of LTE PHY- UL Physical Signals Reference Signal: p

p

Freq

The uplink pilot signal, used for synchronization between E-UTRAN and UE, as well as uplink channel estimation. Two types of UL reference signals: n DM RS (Demodulation Reference Signal), associated with PUSCH and PUCCH transmission. n SRS (Sounding Reference Signal), without associated with PUSCH and PUCCH transmission.

Allocated UL bandwidth of one UE

DM RS associated with PUSCH is mapped to the 4th symbol each slot Time Freq

Characteristics: p

p

p

p

Each UE occupies parts of the system bandwidth since SCFDMA 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 and PUCCH format. Sounding RS’s 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.

Caution：The SRS mapping will be difference in many documents, since the protocol are still under discussion when these document been compiled. The mapping shown in this slide is the result from the latest protocol version.


DM RS associated with PUCCH (transmits UL ACK signaling) is mapped to the central 3 symbols each slot Time Freq

DM RS associated with PUCCH (transmits UL ACK signaling) is mapped to the 2 symbols each slot Time

System bandwidth

PUCCH is mapped to up & down ends of the system bandwidth, hopping between two slots.

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Introduction of LTE PHY- Cell Search Initial Cell Search:

Basic Principle of Cell Search: p

p

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: n Step 1: Symbol synchronization and acquirement of ID within Cell Group by demodulating the Primary Synchronization Signal; n Step 2: Frame synchronization, acquirement of CP length and Cell Group ID by demodulating the Secondary Synchronization Signal.

p

p

About Cell ID： p

p

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.

p

cell (1) (2) N ID = 3N ID + N ID p

(1) N ID

represents Cell Group ID, value from 0 to 167;

(2) N ID

represents ID within Cell Group, value from 0 to 2.

The initial cell search is carried on after the UE power on. Usually, UE doesn’t know the network bandwidth and carrier frequency at the first time switch on. UE repeats the basic cell search, tries all the carrier frequency in the spectrum to demodulate the synchronization signals. This procedure takes time, but the time requirement are typically relatively relaxed. Some methods can reduce time, such as recording the former available network information as the prior search target. Once finish the cell search, which achieve synchronization of time-freq domain and acquirement of Cell ID, UE demodulates the PBCH and acquires for system information, such as bandwidth and Tx antenna number. After the procedure above, UE demodulates the PDCCH for its paging period that allocated by system. UE wakes up from the IDLE state in the specified paging period, demodulates PDCCH for monitoring paging. If paging is detected, PDSCH resources will be demodulated to receive paging message.

Caution: 170 Cell ID groups are defined in the earlier protocol version. So totally 170*3=510 Cell IDs exists, which is mentioned in some early-written documents. Please be noticed this differences.


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Introduction of LTE PHY- Random Access Detail Procedure of Random Access:

Basic Principle of Random Access : p

p

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: n

n

p

p

Random access channel parameters: PRACH configuration, frequency position and preamble format, etc.

p

p

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: n

UE transmission of random access preamble

n

Random access response from E-UTRAN

p

p

p

Physical Layer procedure is triggered upon request of a preamble transmission by higher layers. The higher layers request indicates a preamble index, a target preamble received power, a corresponding RA-RNTI and a PRACH resource . UE determines the preamble transmission power is preamble target received power + Path Loss. The transmission shall not higher than the maximum transmission power of UE. Path Loss is the downlink path loss estimate calculated in the UE. A preamble sequence is selected from the preamble sequence set using the preamble index. A single preamble is transmitted using the selected preamble sequence with calculated transmission power on the indicated PRACH resource. UE Detection of a PDCCH with the indicated RA-RNTI is attempted during a window controlled by higher layers. If detected, the corresponding PDSCH transport block is passed to higher layers. The higher layers parse the transport block and indicate the 20-bit grant. RA-RNTI: Random Access Radio Network Temporary Identifier


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Page 19

Introduction of LTE PHY- Power Control Basic Principle of Power Control: p

p

Downlink Power Control:

Downlink power control determines the EPRE (Energy per Resource Element); Uplink power control determines the energy per DFTSOFDM (also called SC-FDMA) symbol.

p

p

The transmission power of downlink RS is usually constant. The transmission power of PDSCH is proportional with RS transmission power. Downlink transmission power will be adjusted by the comparison of UE report CQI and target CQI during the power control.

Uplink Power Control: p

p

p

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.

UE report CQI DL Tx Power

PUSCH, PUCCH, PRACH and Sounding RS can be controlled respectively by uplink power control. Take PUSCH power control for example:

X2

PPUSCH (i) = min {PMAX ,10 log 10 (M PUSCH (i)) + PO_PUSCH (j) + α(j) ⋅ PL + ΔTF (i) + f(i)} p

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 △TF and system adjustment factor f (not working during opened loop PC)


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UL Tx Power System adjust parameters

EPRE: Energy per Resource Element DFT-SOFDM: Discrete Fourier Transform Spread OFDM

Page 20

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

Main Functions of Control-plane: p

p

p

p

RLC and MAC layers perform the same functions as for the user plane PDCP layer performs ciphering and integrity protection RRC layer performs broadcast, paging, connection management, RB control, mobility functions, UE measurement reporting and control NAS layer performs EPS bearer management, authentication, security control Control-plane protocol stack

User-plane protocol stack

Layer 2

Layer 1


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Page 21

Introduction of LTE Layer 2 - Overview Layer 2 is split into the following layers:

Main Functions of Layer 2:

p

MAC (Medium Access Control) Layer

p

Header compression, Ciphering

p

RLC (Radio Link Control ) Layer

p

Segmentation and concatenation, ARQ

p

PDCP (Packet Data Convergence Protocol ) Layer Layer 2 Structure for DL


p

Scheduling, priority handling, multiplexing and demultiplexing, HARQ Layer 2 Structure for UL

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Page 22

Introduction of LTE Layer 2 - MAC Layer Main functions of MAC Layer: p

p

Logical Channels 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

p

Traffic volume measurement reporting

p

Error correction through HARQ

p

Priority handling between logical channels of one UE

p

Priority handling between UEs (dynamic scheduling)

p

Transport format selection

p

Padding

p

p

Control Channel: For the transfer of control plane information Traffic Channel: for the transfer of user plane information

Control Channel

UL Channel Mapping of MAC Layer

Traffic Channel

DL Channel Mapping of MAC Layer

MAC Layer Structure


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Page 23

Introduction of LTE Layer 2 - RLC Layer RLC PDU Structure:

Main functions of RLC Layer: p

Transfer of upper layer PDUs supports AM or UM

p

TM data transfer

p

p

p

p p

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

The PDU sequence number carried by the RLC header is independent of the SDU sequence number The size of RLC PDU is variable according to the scheduling scheme. SDUs are segmented /concatenated based on PDU size. The data of one PDU may source from multi SDUs

p

p

Segmentation

Concatenation

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

p

Protocol error detection and recovery

p

Duplicate Detection

p

SDU discard

p

Reset


RLC PDU Structure AM: Acknowledge Mode UM: Un-acknowledge Mode TM: Transparent Mode TB: Transport Block SDU: Service Data Unit PDU: Protocol Data Unit

RLC Layer Structure

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Page 24

Introduction of LTE Layer 2 - PDCP Layer Main functions of PDCP Layer: p

p

PDCP PDU Structure:

Functions for User Plane: n Header compression and decompression: ROHC n Transfer of user data: PDCP receives PDCP SDU from the NAS and forwards it to the RLC layer and vice versa n In-sequence delivery of upper layer PDUs at handover for RLC AM n Duplicate detection of lower layer SDUs at handover for RLC AM n Retransmission of PDCP SDUs at handover for RLC AM n Ciphering n Timer-based SDU discard in uplink Functions for Control Plane: n Ciphering and Integrity Protection n Transfer of control plane data: PDCP receives PDCP SDUs from RRC and forwards it to the RLC layer and vice versa


p

p

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PDCP PDU and PDCP header are octetaligned PDCP header can be either 1 or 2 bytes long

PDCP PDU Structure

PDCP Layer Structure

ROHC: Robust Header Compression

Page 25

LTE 3GPP Specification Overview Physic Layer

TS 36.xxx for LTE Specification

Interfaces and Procedure

Layer 2 and Control Protocol 36.300 E-UTRAN Overall Description: Stage 2 36.302 E-UTRAN Services Provided by the Physical Layer 36.304 User Equipment (UE) Procedures in Idle Mode 36.306 User Equipment (UE) Radio Access Capabilities 36.321 Medium Access Control (MAC) Protocol Specification 36.322 Radio Link Control (RLC) Protocol Specification 36.323 Packet Data Convergence Protocol (PDCP) Specification 36.331 Radio Resource Control (RRC) Protocol Specification


36.201 LTE Physical Layer: General Description 36.211 Physical Channels and Modulation 36.212 Multiplexing and Channel Coding 36.213 Physical Layer Procedures 36.214 Physical Layer Measurements

36.401 E-UTRAN Architecture Description 36.410 S1 General Aspects and Principles 36.411 S1 Layer 1 36.412 S1 Signalling Transport 36.413 S1 Protocol Specification 36.414 S1 Data Transport 36.420 X2 General Aspects and Principles 36.421 X2 Layer 1 36.422 X2 Signalling Transport 36.423 X2 Protocol Specification 36.424 X2 Data Transport

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Agenda 1


2

LTE Protocol

3

LTE Key Technology

4



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Page 27

LTE Key Technology — OFDMA & SC-FDMA •

•

OFDM & OFDMA

§

DFT-S-OFDM (Discrete Fourier Transform Spread OFDM) is the modulation multiplexing technology used in the LTE uplink, which is similar with OFDM but can release the UE PA limitation caused by high PAPR. Each user is assigned part of the system bandwidth.

§

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.

SC-FDMA（Single Carrier Frequency Division Multiple Accessing）is the multi-access technology related with DFT-S-OFDM.

§

Disadvantage: Strict requirement of time-frequency domain synchronization. High PAPR.

Advantage: High spectrum utilization efficiency due to orthogonal user bandwidth need no protect bandwidth. Low PAPR.

§

The subcarrier assignment scheme includes Localized mode and Distributed mode.

§

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.

§

OFDMA is the multi-access technology related with OFDM, is used in the LTE downlink. OFDMA is the combination of TDMA and FDMA essentially.

§

§

DFT-S-OFDM & SC-FDMA

System Bandwidth Sub-carriers System Bandwidth

Sub-carriers

TTI: 1ms

TTI: 1ms Frequency

Frequency

User 1 User 2

User 1 User 2 Time

Sub-band： 12Sub-carriers

User 3

Time Sub-band：12Sub-carriers

User 3


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OFDMA Benefits

CP resist ISI caused by multipath effect

GSM FDM Spectrum

OFDM system spectrum

Spectrum Efficiency Improvement

Multi-element Transmitter

N

Multi-element Receiver

Frequency-selective scheduling & Adaptive modulation and coding

M

eNB

UE

Easy to co-work with MIMO


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Page 29

Uplink SC-FDMA for PAR resistance l

Compared with single carrier system, OFDM will cause high peak-to-average ratio (PAR), which will caused problem for the amplifier design and increase the UE implementation cost accordingly.

Ø

The main difference between OFDMA and SC-FDMA is that the latter performs DFT before performing IFFT for transmission, which can be taken as a time-domain precoding operation.


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Comparing OFDM and SC-FDMA(QPSK example, M=4 subcarriers) 1, 1

-1,-1

-1, 1

1, -1

1, 1

-1,-1

-1, 1

1, -1

V

V

CP

Frequency

fc

15 kHz

CP

fc

60 kHz

Frequency

OFDMA

SC-FDMA

Data symbols occupy 15 kHz for one OFDMA symbol period

Data symbols occupy M*15 kHz for


1/M SC-FDMA symbol periods

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LTE Key Technology — MIMO •

•

Downlink MIMO §

MIMO is supported in LTE downlink to achieve spatial multiplexing, including single user mode SUMIMO and multi user mode MU-MIMO.

§

In order to improve MIMO performance, pre-coding is used in 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 MUMIMO, 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 consumption, it is difficult to implement the UL multi transmission and relative power supply. Virtual-MIMO, in which multi single antenna UEs are associated to transmit in the MIMO mode. Virtual-MIMO is still under study.

§

Scheduler assigns the same resource to multi users. Each user transmits data by single antenna. System separates the data by the specific MIMO demodulation scheme.

§

MIMO gain and power gain (higher Tx power in the same time-freq resource) can be achieved by VirtualMIMO. Interference of the multi user data can be controlled by the scheduler, which also bring multi user gain. User1

Pre-coding vectors User1 User 1 data User 1 data

Scheduler User k data

User 1 data

S1

User 2 data

User k data

Pre-coder

MIMO Decoder

User2

User2

S2

User k Channel Information

Channel Information

MU-MIMO


User k

Scheduler Virtual-MIMO

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s0

s2

s1

s3

Lay 0

Lay 1

Precoding

s 0 s 1 s2 s3

Layer Mapping

Transmit Diversity

s0 s 1 s 2 s3 -s 1* s 0* -s 3* s 2*

Ant 0

Ant 1


Precoding

Layer Mapping

2 Antenna Transmit Diversity (SFBC)

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2 Antenna MIMO


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4 Antenna MIMO W0

W1

s0

s2

Lay 0

W2

∑

W3

s0 s1 s2 s3

y0

y1

Ant 0

y0 = w0·s0 + w4·s1 + w8·s0 + w12·s1 y1 = w0·s2 + w4·s3 + w8·s2 + w12·s3

W4

W5

s1

s3

Lay 1

W6

∑

y1

Ant 1


W7 Layer Mapping

y0

W8

W9

s0

s2

Lay 2

W10

∑

y1

Ant 2


W11

s0 s1 s2 s3

y0

W12

W13

s1

s3

Lay 3

W14

∑

W15

y0

y1

Ant 3


4 Antenna Spatial Multiplexing (Two Codewords, Without CDD) D-TxAA ( Double Transmit Antenna Array ) Scheme


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MIMO Operation in LTE Tx Diversity extends coverage

Spatial Multiplexing boosts capacity User1

User1 codeword

Mod

S F B C

User 1 data User 1 data User k data

MIMO Decoder

User2

User k

Scheduler Channel Information

UE1

Virtual-MIMO in UL Layer 1, CW1, AMC1 MIMO encoder and layer mapping

Beamforming extends coverage

UE2

Layer 2, CW2, AMC2 UE2 User1 codeword

Mod

Beamforming Precoding Processing

DL SU-MIMO Layer 1, CW1, AMC1 MIMO encoder and layer mapping

UE1

Layer 2, CW2, AMC2

DL MU-MIMO


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UE2

UE1

MIMO, the Key to Improve Cell Throughput -- System Gain: 2X2 MIMO over SIMO

1x2 SIMO UE 1

Macro LLL TTT EEE

Throughput (Mbps)

eNodeB

2x2 MIMO eNodeB

SIMO MIMO

xx.xx%: Gain

18.15% 16.4

28.34%

15.12%

12.09

14.23

13.88

9.42

12.36

ISD:500m ISD:500m ISD:1732m Speed:3km/h Speed:30km/h Speed:30km/h

UE 1

SIMO MIMO

xx.xx%: Gain

Micro In typical urban area:

Throughput (Mbps)

46.94%

46.40% 35.18

34.15

56.68% 26.87 23.24

24.03 17.15

15%~28% gain over SIMO @ Macro ~50% gain over SIMO @ Micro Outdoor-to-Indoor Outdoor-to-Outdoor Outdoor-to-Outdoor Speed: 3km/h Speed: 3km/h Speed: 30km/h


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Adaptive Modulation and Coding

2 bits per symbol in each carrier.




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Mobility Velocity (km/h)

Adaptive MIMO Increasing Cell Throughput Cell Center

Cell Edge

Open Loop

Adaptive MIMO Adjust MIMO mode according to channel quality and user’s velocity

DL:OL-SM UL:MU-MIMO

DL:SFBC UL:Rx Diversity

Benefits: Closed Loop

Different MIMO modes fit different scenarios

DL:CL-SM UL:MU-MIMO

DL:CL-Tx Diversity UL:Rx Diversity

SFBC and CL Tx Diversity (rank=1) increase link reliability and coverage OL SM and CL-SM (rank=2) increase throughput 10% gain in average cell throughput

Channel Quality (SINR)


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over non-adaptive MIMO.

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Cell Interference Control ICIC（Inter-Cell Interference Coordination） p

ICIC is one solution for the cell interference control, is essentially a schedule strategy. In LTE, some coordination schemes, like SFR (Soft Frequency Reuse) and FFR (Fractional Frequency Reuse) can control the interference in cell edges to enhance the frequency reuse factor and performance in the cell edges.

SFR Solution p

SFR is one effective solution of inter-cell interference control. The system bandwidth is separated into primary band and secondary band with different transmit power. The primary band is assigned to the users in cell edge. The eNB transmit power of the primary band can be high.

Secondary Band

Secondary Band

Secondary Band

Power Power

Cell 2,4,6

Cell 1

2 Cell 1 Primary Band

Frequency

7

Total System BW

The total system bandwidth can be assigned to the users in cell center. The eNB transmit power of the secondary band should be reduced in order to avoid the interference to the primary band of neighbor cells.


Cell 2,4,6 Primary Band

Frequency

3 Secondary Band

1 6

4

Power

Cell 3,5,7

5

Frequency Cell 3,5,7P Primary Band

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Agenda 1


2

LTE Protocol

3

LTE Key Technology

4



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Technology comparison for features UMTS (R99)

HSPA

HSPA+

LTE

Radio Access

W-CDMA

W-CDMA

W-CDMA

OFDMA DL SC-FDMA UL

Bandwidth

5 MHz

5 MHz

5MHz or 10MHz (DC)

Scalable from 1.4MHz to 20MHz

Modulation DL

QPSK

QPSK/16QAM

QPSK/16QAM/64QAM

QPSK/16QAM/ 64QAM

Modulation UL

BPSK

QPSK

QPSK/16QAM

QPSK/16QAM/ 64QAM

Antenna Systems

Rx Diversity

Rx Diversity

2x2 MIMO

2x2 - 4X4 MIMO

Network Structure

Node B + RNC

Node B + RNC

NodeB + RNC Or eHSPA NodeB

eNodeB to EPC

Services

Circuit & Packet Switched

Circuit & Packet Switched

PS but compatible to CS

PS Only

Transport

ATM/ Mixed ATM & IP

ATM/ Mixed ATM & IP

Option for All IP

All IP


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LTE vs. HSPA+ comparison summary (1/2) R8 HSPA(+) Time To Market Market / Operator adoption

Commercial deployment by 2009

Commercial deployment by 2010

66+ operators commited 54% Mobile BB users by 2015 (HSPA&HSPA+)

~59 operators commitments 20% Mobile BB users by 2015

Infrastructure commercial 2009 date 1st commercial terminal Evolution from Legacy

2009

2009

2010

Smooth evolution based on Huawei Uni-BTS and One Unified Core

Smooth evolution based on Huawei Uni-BTS and One Unified Core

Backwards compatibility Inherent & roaming with legacy Frequency band

Frequency bandwidth

LTE

LTE commercial terminal are multi-mode GSM/UMTS/LTE allowing inter-RAT HO

IMT2000 (Technology Neutral) Common trends for 850MHz, 900MHz, AWS, 2.1GHz

IMT2000 (Technology Neutral) Common trends for DD, 1800MHz, AWS, 2.1GHz, 2.6GHz

5MHz – 10MHz

1.4, 3, 5, 10, 15, 20MHz


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LTE vs. HSPA+ comparison summary (2/2) R8 HSPA(+) Peak rates Average throughput in a cell DL Throughput at cell edge with 800 m ISD multi cell – single user Latency Scalability

Fading

• 42 Mps DL/ 11 Mpbs UL in 5 MHz • 84Mbps DL / 22Mbps UL in 10 MHz

LTE • 43 Mps DL/ 28 Mpbs UL in 5 MHz • 86 Mbps DL / 57 Mbps UL in 10 MHz • 173 Mbps DL / 115 Mbps UL in 20 MHz

5.8 Mbps DL MIMO 2X2 16QAM (5MHz-ISD 500m)

7.8 Mbps DL MIMO 2X2 (5MHz-ISD 500m)

1 Mbps ( 2.1 GHz, 5 MHz, MIMO 2X2 16QAM)

5.8 Mbps ( 2.6 GHz, 20 MHz, MIMO 2X2 64QAM)

User plane: 40ms

User plane: 13-20ms

Multi-carrier (5MHz stepping), Single User MIMO up to 2x2

Single carrier, linear scaling in bandwidth from 1.4 to 20 MHz - Single user MIMO up to 4x4

Time dependent scheduling and frequency diversity gain vs less efficient spreading over carrier bandwidth (5MHz)

Frequency AND Time dependent scheduling mitigates fading impact Soft frequency re-use ICIC

Interference


(better OFDM orthogonality, less interference)

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Thank you www.huawei.com


10 LTE Basic Knowledge

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