wimax principle and key technology
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WiMAX Principle and Key Technology
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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential
Foreword
WiMAX ( Worldwide Interoperability for Microwave Access )
WMAN (Wireless Metropolitan Access Network) technology Multiple Broadband Services
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Contents
1. OFDM/OFDMA Principle
2. Key Technologies of WiMAX
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Contents
1. OFDM/OFDMA Principle
1.1 OFDM Principle
1.2 OFDMA Principle
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Evolution of FDMA SystemSingle Carrier
OFDM :
Orthogonal Frequency Division Multiplexing
frequency
Multi-carrier
frequency
OFDM
frequency
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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
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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)
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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)
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Multi-path Environment
Received
signal
Transmitted
signal
time
time
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Overcome the Multi-path Inference
In OFDM system, the multi-path interference can be reduced by adding CP
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Importance of Time Synchronization
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Importance of Frequency Synchronization
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Contents
1. OFDM/OFDMA Basic Principle
1.1 OFDM Principle
1.2 OFDMA Principle
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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
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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)
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Contents
1. OFDM/OFDMA Basic Principle
2. Key Technologies in WiMAX System
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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
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Common Communication Model
Source decoding
Source
coding Interleaving
deinterleaving
Modulation
Demodulation
Transmitting
Receiving
Radio channel
Deinterleaving &channel deco
ding
Channel coding & interleaving
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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
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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
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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
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Questions
Does the coding mode with higher coding efficiency
must be better than a lower one?
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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
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AMC
Adaptive Modulation and Coding
Purpose:
To select the suitable modulation and coding modes
according to different channel qualities
AMC
16QAM QPSK64QAM
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Modulation Modes in 802.16e Constellation of QPSK/16QAM/ 64QAM
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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
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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?
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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
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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 ?
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Performance of HARQ
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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
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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
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Contents2.5 Multiple Antennas
2.5.1 MIMO
2.5.2 AAS
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MIMO : Multiple input and multiple output
What is MIMO?
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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
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MIMO in 802.16e
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Contents
2.5 Multiple Antennas
2.5.1 MIMO
2.5.2 AAS
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AAS: Adaptive/Advanced Antenna System
What is AAS?
Omni antenna Directional antenna AAS
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Switched Beam Antennas
Cell is covered by some fixed beams
Types of AAS
Adaptive Antenna
Arrays
Beam can trace the
user’s position
automatically
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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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