Achieving cooperative diversity with multiple frequency offset estimation

In cooperative communications, estimation and compensation of multiple carrier frequency offsets is an important implementation issue that needs to be addressed in practice. This paper proposes an efficient maximum likelihood estimator (MLE) using alternating projection technique, for the joint estimation of Rayleigh fading channels and multiple carrier frequency offsets (MCFO) in cooperative communication systems. Our proposed equalizer incorporates these channel and MCFO estimates and uses matrix inverse technique to decode the transmitted symbols. Unlike existing schemes for equalizer design, the proposed design does not assume any perfect MCFO and/or channel estimate knowledge at the receiver or code redundancy or delay diversity and works for the full range (±0.5 cycles/sec) of the normalized frequency offsets. We present simulation results to illustrate that the Mean Square Error (MSE) of MCFO achieves the Cramér Rao Bound (CRB) above 7 dB signal-to-noise ratio (SNR) while the MSE of channel estimation achieves the CRB for all SNR values. In addition, the Bit Error Rate (BER) performance shows that our proposed equalizer can achieve the full spatial diversity gain of space-time block codes.