Unsourced Random Access Under Quasi-Static Fading Channel: A Less-Is-More Strategy

In this work, the unsourced random access problem over a quasi-static fading channel is discussed with a massive number of antennas at the receiver. A novel transmission protocol called the Less-Is-More (LIM) strategy is proposed. Only a small portion of the data needs to be encoded and transmitted into the channel, while the remaining data bits are embedded into the patterns of sparse frames and implicitly transmitted without requiring power assumptions. Specifically, LIM divides the entire blocklength into several chunks and split the transmission in each chunk into two phases: one for pilot signals and the other for sparsely scattered modulated constellation symbols. Each user selects a single chunk to send its frame into the channel, and the frame consists of multiple scattering patterns determined by a large portion of the message bits. Consequently, the proposed scheme can implement strong channel coding with a relatively long code length, sparse frames with tolerable multi-user interference, and a high level of constellation power. Furthermore, we analyze the performance of the proposed scheme using normal approximations and provide a detailed complexity analysis of the major decoder component. Numerical results indicate that the proposed scheme performs competitively compared to state-of-the-art methods, achieving near-theoretical bound performance.