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Adaptive alpha-Expectation-Conditional-Maximization DS-CDMA Receivers under Frequency-Selective Fast Fading Circumstances

The expectation-maximization-based (EM-based) receiver provides a decent solution for conquering the delay problem of estimating the channel side information (CSI) via detecting data sequence iteratively at the expense of increasing the processing time. To accelerate the processing time, an α-expectation-conditional-maximization (ECM) design for direct-sequence (DS) code-division multiple access (CDMA) systems over frequency-selective fading channels is studied. Simulation results reveal that the adaptive α-ECM receiver can speed up the convergence speed of joint estimation and detection under severe Doppler shifts when the value of α is increasing. Furthermore, the BER performance of the adaptive α-ECM-based DS-CDMA receiver for joint channel estimation and symbol detection under single-user and multiuser systems is also scrutinized.