Integrated Sensing and Communications for Unsourced Random Access: A Two-Phase Approach With Slotted Transmission

In this work, we address the problem of concatenated code design for unsourced integrated sensing and communications (UNISAC). Specifically, UNISAC formulates the multiple access design in integrated sensing and communications (ISAC) as a theoretical coding problem, where echo signals for sensing and message information for communication are encoded and mapped onto a common codebook. The receiver then decouples the overlapped signals and decodes the sensing and communication information using this shared codebook. As system activity increases, conventional ISAC multiple access schemes such as TDMA, ALOHA, and TIN either fail to support the system or require intolerably high levels of energy consumption. While theoretical bounds have been established in UNISAC, practical solutions for access codes remain an open challenge. To provide insights into practical UNISAC code design, we introduce a two-phase concatenated code with slotted transmission. The proposed approach significantly outperforms conventional schemes under various parameter setups, generating 15 to 30 dB capacity gains. More importantly, the gap between the proposed scheme and the theoretical achievable bound is very small-less than 2.5 dB before 1000 active users.