A joint activity and data detection scheme for asynchronous grant-free rateless multiple access

This paper considers the frame-asynchronous grant-free rateless multiple access (FA-GF-RMA) scenario, where users can initiate access at any symbol time, using shared channel resources to transmit data to the base station. Rateless coding is introduced to enhance the reliability of the system. Previous literature has shown that FA-GF-RMA can achieve lower access delay than frame-synchronous grant-free rateless multiple access (FS-GF-RMA), with extreme reliability enabled by rateless coding. To support FA-GF-RMA in more practical scenarios, a joint activity and data detection (JADD) scheme is proposed. Exploiting the feature of sporadic traffic, approximate message passing (AMP) is exploited for transmission signal matrix estimation. Then, to determine the packet start points, a maximum posterior probability (MAP) estimation problem is solved based on the recovered transmitted signals, leveraging the intrinsic power pattern in the codeword. An iterative power-pattern-aided AMP algorithm is devised to enhance the estimation performance of AMP. Simulation results verify that the proposed solution achieves a delay performance that is comparable to the performance limit of FA-GF-RMA.