CHANNEL ESTIMATION FOR MIMO-OFDM COMMUNICATION SYSTEM

PRESENTER: OYERINDE, OLUTAYO OYEYEMI

SUPERVISOR: PROFESSOR S. H. MNENEY

AFFILIATION: SCHOOL OF ELECTRICAL, ELECTRONIC

AND COMPUTER ENGINEERING, UKZN

SOUTH AFRICA

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OUTLINE

• INTRODUCTION• MIMO SYSTEM• OFDM SYSTEM

• MIMO-OFDM SYSTEM• NEED FOR CHANNEL ESTIMATION FOR MIMO-OFDM SYSTEM• PROPOSED ITERATIVE CHANNEL ESTIMATION SCHEME FOR

MIMO-OFDM• VSSNLMS ALGORITHM• PERFORMANCE OF VSS-NLMS ALGORITHM• CONCLUSION

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INTRODUCTIONMIMO SYSTEM

• WHAT IS MIMO SYSTEM?

• WHY MIMO IN COMMUNICATION SYSTEM?

• CAPACITY OF MIMO SYSTEM

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INTRODUCTION OFDM SYSTEM

• ORIGIN OF OFDM • BASIC IDEA OF OFDM SYSTEM :

Fig.1: Comparison between (a) Conventional FDM and (b) OFDM• PRESENT STATUS:

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INTRODUCTION ADVANTAGES OF OFDM SYSTEM

The following are the advantages of OFDM systems: • High spectral efficiency• Simple implementation using FFT (fast Fourier transform)• Low receiver complexity, robust ability for high-data-rate

transmission over multipath fading channel• High flexibility in terms of link adaptation• Low complexity multiple access schemes such as orthogonal

frequency division multiple access.

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INTRODUCTION BASEBAND OFDM TRANSCEIVER

• A typical baseband OFDM transceiver is shown below

• Fig. 2: Typical baseband OFDM transceiver

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MIMO-OFDM SYSTEM• ORIGIN OF MIMO-OFDM• A broadband MIMO-OFDM system model is shown below

Fig. 3: A broadband MIMO-OFDM System

• The data stream b[n, k] is first encoded by a space-time or space-frequency encoder. Then, the coded data is divided into MT substreams with each substream forming an OFDM block transmitted through one transmit antenna.

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THE NEED FOR CHANNEL ESTIMATION FOR MIMO-OFDM SYSTEM

• MIMO-OFDM RECIEVER: At the receiver, the received signals at multiple receive

antennas are decoded using channel state information obtained through a training-based symbol (resulting in coherent detection of the transmitted symbol) .

• Therefore, channel state information in terms of channel impulse response (CIR) or channel frequency response (CFR) is critical to achieve the advantages (diversity gains and the expected increase in data rate) of a MIMO-OFDM system.

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PROPOSED ITERATIVE CHANNEL ESTIMATION SCHEME FOR MIMO-OFDM

• Fig. 4: Proposed Iterative channel estimation scheme

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PROPOSED ITERATIVE CHANNEL ESTIMATION SCHEME FOR MIMO-OFDM

• Temporal Channel Transfer Function Estimator• Based on VSSNLMS algorithm

• Channel Impulse Response Estimator• Based on Fast Data Projection Method for Stable Subspace

Tracking algorithm by (X. G. Doukopoulos and G. V. Moustakides 2005)

• Channel Impulse Response Predictor• Based on VSSNLMS algorithm

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VSSNLMS ALGORITHM

• VARIABLE STEP SIZE NLMS: The VSSNLMS algorithm is given by(1) and the step-size expression by (3) and (4):

• In (3), is a small positive constant that controls the adaptive behavior of the step-size sequence.

• ,where

1 2ˆ ˆ (1)n

n n n n

n

xh h

xe

_ˆ (2)T

nnn n xhe z 1 1

21

1

ˆ (3)T

n n n nn n

n

e e x x

x

max max

min min

ˆ

ˆ (4)

ˆn

if

if

otherwise

min max0 2

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PERFORMANCE OF VSS-NLMS ALGORITHM

• The VSS-NLMS algorithm has been used to simulate channel estimation for single input single output system shown below

•

• Fig. 5: The system model

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SIMULATION RESULTS

• RESULT IN FIG. 6: This is based on ensemble error variance for the channel estimation

• RESULT IN FIG. 7: This is obtained based on the following performance index - normalized means square error, given as:

2

2

ˆ(5)

nn n

nn

h h

h

ENMSE

E

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FIG 6: Simulated ensemble error variance for the channel estimation algorithms, at

each symbol interval n in a frame of training and data symbols. Simulation setup:

SNR = 10 dB;=0.02, L=sigma, fd /fs , and =lamda as shown above the plots.

Fig. 6

0 100 200 300 400 500 600 7000.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time index n

Ens

embl

e-er

ror

varia

nce(

n)

Channel estimation parameters:sigma =1, fd/fs =1/2400, lamda = 0.98

LMS

APRmodRLSRLS

VSSNLMS

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FIG. 7: Normalized MSE for the channel estimation algorithms, at each SNR in a frame

of training and data symbols. Simulation setup: =0.02, L=sigma, fd /fs , and =

lamda as shown above the plots

1 2 3 4 5 6 7 8 9 10

10-0.23

10-0.21

10-0.19

10-0.17

10-0.15

10-0.13

SNR[dB]

Nor

mal

ised

mea

n-sq

uare

d er

ror

Channel estimation parameters:sigma =1, fd/fs =1/2400, lamda = 0.98

LMS

APRmodRLSRLS

VSSNLMS

Fig 7

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CONCLUSION

• It is obvious from the above results that VSSNLMS which is less complex than RLS and exhibited close convergence rate to RLS for the channel estimation simulated for single input single output (SISO) communication system will be a good candidate for CTF estimator and CIR predictor for the proposed iterative channel estimator for MIMO-OFDM communication systems.

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THANK YOU