Joint EM Channel and Covariance Estimation with Sufficient-Statistic Chip Combining for a SIMO MC-CDMA Antijam System

Joint iterative channel and covariance estimation with sufficient-statistics (SS)-based chip combining is studied for a multicarrier code division multiple access (MC-CDMA) system operating under partial-band noise jamming (PBNJ). The expectation maximization (EM) algorithm, which exploits the log- likelihood ratio (LLR) from the decoder, is employed to estimate the channel impulse response and interference-plus-noise covariance matrix. The proposed chip combiner guarantees no loss of information in the soft output generated by the demapper. In our approach, the channel estimator or the chip combiner needs only the AWGN-plus-PBNJ power of each subcarrier to suppress jamming. Therefore, significant complexity reduction is achieved because the receiver does not need to estimate the jammer state information (JSI) and individual variances of AWGN and PBNJ on each subcarrier for chip combining. Simulation results demonstrate that the sufficient-statistic chip combiner (SSCC) always provides a smaller bit error rate (BER) than the minimum mean square error (MMSE) chip combiner.