Approximate Message Passing-Based Detection for Asynchronous NOMA

A novel low-complexity multiuser detection scheme is proposed for the asynchronous non-orthogonal multiple access (NOMA). Directly applying the conventional symbol-synchronous detection techniques for the asynchronous NOMA would result in high complexity. For low-complexity, we divide one frame with a large number of symbols into several small blocks. Furthermore, for real-time and low-delay processing under the scenario with a large number of users, each block is independently processed in a parallel way by an approximate message passing-based algorithm. Furthermore, a jointly detection technique is proposed to address the large detection error in the boundary of the blocks, which is induced by the non-interaction between neighbor blocks. Simulation results demonstrate that the proposed detection scheme can achieve near optimal performance with a much lower complexity.