Performance analysis of diversity combining method for OFDM blind carrier synchronization

Orthogonal frequency division multiplexing (OFDM) communications transform frequency selective channels into multiple low rate subchannels robust against frequency selective fading. Carrier frequency offset (CFO) between transmitter and receiver local oscillators must be estimated and compensated at the receiver to maintain orthogonality of these subchannels. It's necessary to reduce the frequency offset to a small fraction of the sub-channel signaling rate for reliable communications. A diversity branch weighted nonlinear least squares (NLS) estimator was proposed by the authors for carrier offset estimation. Here, various diversity combining methods are studied; e.g. we prove estimator facilitates maximal ratio combining (MRC) by simply weighting each receive branch proportional to it's respective signal to noise ratio (SNR). Numerical and experimental results against Cramer-Rao bound (CRB) verifying these results are presented.