WiMax Principle and Key Technology

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WiMAX Principle and Key Technology


Foreword

WiMAX （ Worldwide Interoperability for Microwave Access ）

WMAN (Wireless Metropolitan Access Network) technology Multiple Broadband Services


Contents

1. OFDM/OFDMA Principle

2. Key Technologies of WiMAX


Contents

1. OFDM/OFDMA Principle

1.1 OFDM Principle

1.2 OFDMA Principle


Evolution of FDMA SystemSingle Carrier

OFDM ：

Orthogonal Frequency Division Multiplexing

frequency

Multi-carrier

frequency

OFDM

frequency


Principle

Convert one high speed serial data into several low speed

parallel data

Generate several orthogonal sub-carriers

Modulate low speed parallel data onto different sub-carriers

Realization of OFDM

0,ns

1, Nns

NN

f0

fN-1

P/SIFFT

0,ns

1, Nns

N N


High spectral efficiency

Overcome frequency selective fading

Overcome the multi-path interference

Simple channel estimation

Easy to combine with other technologies

OFDM Characteristics

High requirements of time synchronization

High sensitivity to frequency delay

High PAPR (Peak to Average Power Ratio)


Overcome Frequency Selective Fading

Fading

Transmit Signal Received Signalff

P(f) P(f)

BroadbandSystem

BroadbandSystem

NarrowbandSystem

NarrowbandSystem

Fading

Transmit Signal Received Signalff

P(f) P(f)


Multi-path Environment

Received

signal

Transmitted

signal

time

time


Overcome the Multi-path Inference

In OFDM system, the multi-path interference can be reduced by adding CP


Importance of Time Synchronization


Importance of Frequency Synchronization


Contents

1. OFDM/OFDMA Basic Principle

1.1 OFDM Principle

1.2 OFDMA Principle


What’s OFDMA?(1) OFDMA: Orthogonal Frequency Division Multiple Access

All carriers are divided into several groups (sub-channels)

Coding, modulation and amplification are set separately for each

sub-channel based on channel conditions

Different sub-channels can be allocated to different users at the

same time

Frequency

Time

OFDM OFDMA

Ou

tput

Pow

er

Frequency

OFDM OFDMA


Frequency

Subcarrier-N

Subcarrier-1

Time Bandwidth

Subcarrier-2

Subcarrier-3

Subcarrier-4

Guard Time

OFDM Slot/FrameIFFT

IFFT

IFFT

S1 S2 S3 S4 S5 S6 S7SN

SN+1 SN+2 SN+3 SN+4

OFDM Symbol (FTT duration) S2N

OFDMA is the foundation of 4G!OFDMA is the foundation of 4G!

What’s OFDMA?(2)


Contents

1. OFDM/OFDMA Basic Principle

2. Key Technologies in WiMAX System


Contents

2. Key Technologies in WiMAX system

2.1 Communication Model 2.2 Channel Coding 2.3 AMC 2.4 HARQ 2.5 Multiple Antennas


Common Communication Model

Source decoding

Source

coding Interleaving

deinterleaving

Modulation

Demodulation

Transmitting

Receiving

Radio channel

Deinterleaving &channel deco

ding

Channel coding & interleaving


WiMAX Communication Model

FEC ModulationMapping

Randomization IFFTCyclicPrefixInterleave

DL PHY Process

UL PHY Process

RemoveCyclicPrefix

FFTFreq.

Domain Equalizer

De-MapSymbols

Decoder

De-Randomization

De- Interleave

Data toMAC layer

Data from MAC layer

RFTX

baseband

RF RX(Timing &FrequencyCorrection etc)

baseband


Contents




Definition :

A technique which combines of error detection, error correcting, rate

matching, interleaving and so on

Purpose:

Reduce the probability of error

Reduce the required signal-to-noise ratio

Coding Efficiency ： k/n

Coding Types in 802.16e:

CC (Convolutional Coding) ： 1/2 ， 2/3 ， 3/4 ， 5/6

CTC (Convolutional Turbo coding) ： 1/2 ， 2/3 ， 3/4 ， 5/6

Channel Coding


Questions

Does the coding mode with higher coding efficiency

must be better than a lower one?


Contents




AMC

Adaptive Modulation and Coding

Purpose:

To select the suitable modulation and coding modes

according to different channel qualities

AMC

16QAM QPSK64QAM


Modulation Modes in 802.16e Constellation of QPSK/16QAM/ 64QAM


Modulation and Coding Mode in WiMAX

Supported Modulations and Codings

Modulation TypesDL UL

QPSK 、 16QAM 、 64QAM

QPSK 、 16QAM 、64QAM

CC (Convolutional Code) 1/2, 2/3, 3/4, 5/6

1/2, 2/3, 3/4, 5/6

CTC (Convolutional Turbo Code) 1/2, 2/3, 3/4, 5/6

1/2, 2/3, 3/4, 5/6

Repetition x2, x4, x6 x2, x4, x6


Questions Please calculate the effective information bits per symbol

with different modulation and coding modes.

For example:

QPSK1/2, the effective information bits per symbol=2*1/2=1bit

How is about the 16QAM3/4 and 64QAM1/2?

If the AMC decision is wrong, what will happen?


Contents




HARQ (Hybrid Automatic Repeat reQuest)

A combination of ARQ and FEC

Types of ARQ:

SAW: Stop-and-wait

GBN: Go-Back-N

SR: Selective Repeat

Types of HARQ:

Type I

Type II(IR)

Type III

What is HARQ ？


Performance of HARQ


Improve the transmission reliability and system throughout

Reduce the average re-transmission and data transmission

delay

HARQ decreases the sensitivity of instantaneous channel

quality change

Combination with AMC, decreases the wrong decision

because of the feedback delay or the wrong feedback

decoding

Characteristics of HARQ


Contents




Contents2.5 Multiple Antennas

2.5.1 MIMO

2.5.2 AAS


MIMO ： Multiple input and multiple output

What is MIMO?


Diversity mode （ Matrix A ） Transmit the same data in different antennas Enhance the capacity indirectly The number of receiving antenna can be less than the number of tra

nsmitting antennas

Spatial Multiplexing mode (Matrix B) Transmit different data in different antennas Enhance the capacity directly The number of receiving antenna can not be less than the number o

f transmitting antennas

Working Mode of MIMO


MIMO in 802.16e


Contents

2.5 Multiple Antennas

2.5.1 MIMO

2.5.2 AAS


AAS: Adaptive/Advanced Antenna System

What is AAS?

Omni antenna Directional antenna AAS


Switched Beam Antennas

Cell is covered by some fixed beams

Types of AAS

Adaptive Antenna

Arrays

Beam can trace the

user’s position

automatically


Increase the SNR and the sensitivity of BS

Decrease the error bit of system

Decrease the system interference

Enhance the coverage

Improve the spectrum efficiency by adopting the SDMA technology

Improvement to performance

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WiMax Principle and Key Technology