On Design and Analysis of Asynchronous Repetition Slotted ALOHA for Massive Access

This paper studies asynchronous repetition slotted ALOHA (a-RSA) for massive random access. Each user's packet is repeated and allocated to randomly selected slots. Then, the users transmit simultaneously and arrive at the base station (BS) receiver with different delays, i.e., without user-synchronization. The BS receiver carries out an over-sampling-based operation, yielding an over-sampled signal space. We develop an iterative soft cancellation detection and decoding that exploits the interference structure of the over-sampled signal for powerful multi-user decoding. Afterwards, packet cancellation for a-RSA is utilized to solve packet collision. To characterize the performance of a-RSA, we analyze the achievable channel parameter region (ACPR) and outage probability. Further, we present an asymptotic analysis of the throughput of a-RSA system. It is demonstrated that the normalized throughput of a-RSA exceeds that of traditional RSA by about 20% ~ 30%.