Leveraging massive MIMO spatial degrees of freedom to reduce random access delay

Random access is a crucial building block for nearly all wireless networks, and impacts both the overall spectral efficiency and latency in communication. In this paper, we analytically show that the spatial degrees of freedom, e.g. available in massive MIMO systems, can potentially be leveraged to reduce random access latency. Using one-ring propagation model, we evaluate how the random access collision probability depends on the aperture size of the array and the spread of user's signal Angle-of-Arrivals (AoAs) at the base-station, as a function of the user-density and the number of random access codes. Our numerical evaluation shows that for practically sized large arrays in outdoor environments, a significant reduction in collision probability is possible, which in turn can decrease the random access latency.