User detection and channel estimation for SCMA uplink system in dispersive channel

Sparse code multiple access (SCMA) is a new non-orthogonal multiple-access technique in future wireless networks. In SCMA uplink burst transmission, user detection and channel estimation require significant pilot overhead. Dispersive channels with relative small coherent frequency / time, as well as fading diversity techniques, both lead to a result that multiple fading blocks are taken during one transmission. In this paper, a new method of separating SCMA user detection and channel estimation among different fading blocks in dispersive channels is proposed to reduce pilot overhead. Further more, according to the sparsity of SCMA codebooks, a new mapping pattern from SCMA layers to physical resources is proposed to improve channel estimation performance with given pilots. The effectiveness of the proposal are described and analyzed, meanwhile the complexity is evaluated. Numerical simulations are performed to substantiate the performance of the proposed algorithm.