Iterative EM Estimation Based LDPC CDMA Receiver

This paper proposes a scheme of iteratively obtaining an estimate of channel coefficient and noise power spectral density (PSD), initially with the aid of pilot symbols. The iterative receiver employs a low-density parity-check (LDPC) code and channel estimation based on expectation maximization. Pilot bits are distributed among subframes followed by spreading and binary phase-shift keying. At the receiver, an initial estimate of channel coefficient and noise PSD is obtained using pilot information. Subsequent values of channel coefficient and noise PSD are both iteratively updated by the soft feedback from the LDPC decoder. The updated channel coefficient and noise PSD are iteratively passed to the LDPC decoder, which results in an improved decoding accuracy, as shown.