Improved Success Probability Of Code-Expanded Single-Attempt Random Access By Massive Mimo

Code-expanded Random Access (CeRA) is a promising RA technique to enable massive access. Unfortunately, if the uplink resources are limited, the code ambiguity problem in CeRA will largely affect the success probability of single-shot attempt RA. In this paper, we propose a codeword detection method with the support of massive MIMO to address the code ambiguity problem in CeRA. The merit of the proposed codeword detection method is that the uplink resources could be effectively allocated to the actually transmitted codewords, thus resulting in significantly improved success probability. To this end, we first model the codeword signal of CeRA in massive MIMO system and then demonstrate that the proposed codeword detection method is able to detect the codewords without ambiguity by exploiting the quasi-orthogonality characteristic of massive MIMO. Simulation results verify the effectiveness of resource allocation in the CeRA with massive MIMO. Moreover, properties of the success probability of single-shot attempt RA with respect to system parameters are revealed. Compared to CeRA and LTE, it is shown that the CeRA with massive MIMO benefits from increasing of preamble space size and could provide a much higher success probability of single-shot attempt RA.