jeeva review3

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OBJECTIVE

To model and simulate the Carrier Phase

Offset (CFO) with aid of ML sequence.

Simulation Tool : Matlab



WORK DONE SO FAR

Estimation of Timing Offset

Estimation of Carrier Frequency Offset

Work done nowo Estimation of Phase Offset



BLOCK DIAGRAM OF OFDM SYSTEM

Data BitsQPSK

MappingIFFT

Cyclic

Prefix

Rayleigh,

AWGN

Channel

Synchroni

zation

Removal OfCyclic

Prefix,training

Sequence

FFTEquailizatio

nSymbol

Detection

PN

sequence

Generator



FRAME STRUCTURE OF OFDM SYSTEM

Pilot

s(M

L

seq)

sym

1

sym

2

…… sym

100

Pilot

s(M

L

seq)

sym

1

sym

2

…… sym

99

Sym

100

For every 100 OFDM symbols , one block type pilotsare used.



PN SEQUENCE

It is a deterministically signal but looks like random

sequences.

Assume order = 9, the generator polynomial is

x^9+x^4+1.It is generated using linear feedback

shift register and exclusive OR gate as below

1 2 763 4 5 98



C ARRIER PHASE OFFSET

Frequency estimation alone could not complete the

carrier synchronization, additionally it requires

estimating and correcting the phase offset also.

The technique involves the received signal is

multiplied with conjugate of pilots, which is

represented as

y(k) = E[r(k) * (conj (pilots))]



MODELING OF SIGNAL

Delay

Frequency

and phase

offset

AWGN & Fading

channel noise

Signal from

transmitter

Signal to

Receiver



DESIGN SPECIFICATION

PARAMETERS VALUE

Nfft 512

N Used Carriers 496Number of lower

frequency guard

subcarriers

8

Number of upperfrequency guard

subcarriers

7

Cyclic Prefix 32



CONT…

PARAMETERS VALUE

Sampling frequency 1.6MHz

Sampling time (Ts ) 625ns(1/1.6MHz)

Number of frame 10OFDM symbol interval 174.08µs( 544 * Ts)

CP length 20µs ( 32*Ts )

Sub carrier spacing 6.25KHz(1.6MHz/256)

Number of Pilots 256

Modulation QPSK



FADING CHANNEL SPECIFICATION

Sampling Time in ns 0.1

Path delays in ns 0 781 156 2344

Path gains in dB 0 -3 -6 -9

Delay spread 2344ns

Doppler shift 0

Fading type Frequency selective & slow

fading



SIMULATION RESULT(MSE PLOT FOR PHASE

OFFSET = 0.5235 IN RADIANS)

In MSE plot, as SNR

varies the MSE value

reduces and move to

zero



Phase offset(in

radian)

Estimated

offset(AWGN

channel)

Estimated offset

(Rayleigh channel)

0.5236 0.5241 0.5396 0.6109

0.6107

0.6170

0.6989 0.6990 0.6953 0.7854 0.7850 0.7916 0.8727 0.8730 0.8854 0.9599 0.9596 0.9658 1.0472 1.0468 1.0340 1.1345 1.1348 1.1503 1.2217 1.2218 1.2973 1.3090 1.3090 1.4966

SIMULATION RESULT (AT SNR=5dB)



Publication



REFERENCE

Lee. J, Lou, H and Toumpakaris, D. (Oct.

2004)’Maximum likelihood estimation of time and

frequency offset for OFDM systems ’- Electronics

Letters. Volume 40, Issue 22, 28 Page(s):1428 – 1429

Van de Beek J J, Sandell M, Boriesson P (1997)’ MLestimation of time and frequency offset in OFDM

Systems’ - IEEE Transaction on Signal Processing,

volume 45 No.7 pp.1800 – 1805

Michele Morelli, Member IEEE, C.-C. Jay Kuo, Fellow

IEEE, and Man-On Pun, Member IEEE –

‘Synchronization Techniques for Orthogonal Frequency

Division Multiple Access (OFDMA) ‘: A Tutorial Review

jeeva review3

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