Receiver algorithm for coded multiuser CPM systems

The performance of multiuser systems employing coded continuous- phase modulation (CPM) in frequency-division multiplexed (FDM) uplink satellite communications is investigated. The spectral efficiency is improved reducing the inter-carrier frequency spacing. Since severe inter-channel interference (ICI) occurs in such cases, a simple iterative ICI cancellation algorithm is applied in conjunction with a bank of single-user (SU) receivers to perform demodulation and decoding. When modulation and coding parameters are suitably chosen, such a receiver achieves a performance close to the non-interfering multiuser case. ICI causes further degradation since the SU receivers are not perfectly matched to the received signal model. Moreover, the SU receivers require a perfect knowledge of the channel state information (CSI) in order to perform optimal demodulation in additive white Gaussian noise. To reduce the degradation caused by ICI, a new heuristic method for estimating the optimal CSI values to provide to the SU receiver is proposed. The proposed method is based on an approximation of the CSI vector provided to each SU receiver. Such a method proves useful since it leads to significant performance improvements of the considered schemes and exhibits a negligible complexity.