inter-carrier interference cancellation in ofdm systems by: dharamveer meena vinodkumar pralia
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Inter-carrier interference cancellation in OFDM systems
By: Dharamveer
Meena Vinodkumar Pralia
Basic OFDM system Multi-carrier modulation Multiple frequency channels are
orthogonal to each other.
OFDM modulated signal N symbols mapped
to bins of IFFT. IFFT bins correspond
to the orthogonal sub-carriers.
11 2
0
1( )
N j nmN
mm
x n X eN
Baseband OFDM transceiver system
Drawbacks Frequency offset
Local oscillator frequencies Doppler shift
Result: Loss in Orthogonality Inter-carrier interference
Frequency offset model y(n) : received
sequence normalized
frequency offset N:number of sub
carriers w(n) : complex
AWGN
( 2 / )( ) ( ) ( )j n N
S
y n x n e w n
fNT
Standard OFDM systems Received signal:
ICI coeffiecient:
Carrier to interference ratio:
Solutions to combat ICI
Self-cancellation scheme Maximum likelihood estimation Extended Kalman Filter
Extended Kalman Filtering A linear approximation of a non linear
system Linear : Nonlinear :
( ) ( ( )) ( )y n f n w n ( ) ( ) ( ) ( )y n a n d n v n
( 2 / )( ( )) ( ) j n Nf n x n e
Offset estimation scheme
State-Space Model:
Recursive steps:
Offset correction scheme
ˆ(2 ) /ˆ ( ) { ( )
j n Nx n FFT y n e
ˆ ( )x n
: symbol data QAM - M Restored
: received data symbol distorted by frequency offset
: estimated normalized frequency offset
: number of subcarrier
( )y n
N
References P. H. Moose, “A Technique for Orthogonal Frequency Division
Multiplexing Frequency Offset Correction,” IEEE Transactions on Communications, vol. 42, no. 10, October 1994.
J.Armstrong, “Analysis of new and existing methods of reducing intercarrier interference due to carrier frequency offset in OFDM,” IEEE Transactions on Communications, vol.
47, no. 3, pp. 365 – 369, March 1999. C. Muschallik, “Improving an OFDM reception using an
adaptive Nyquist windowing,” IEEE Transactions on Consumer Electronics, vol. 42, no. 3, pp. 259 – 269, August 1996.
Thank You
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