Low Complexity Activity Detection for Massive Access with Massive MIMO

We propose a low complexity activity detection scheme for massive access scenarios with massive multiple-input multiple-output (MIMO) communication systems. Numerous devices with sporadic access behavior characterize these scenarios; therefore, only a subset is active. Limited by massive potential devices in the network and coherence time, which contains L signal dimensions, it is infeasible to assign a unique orthogonal pilot to each device in advance. In this case, device detection is the first critical problem to be solved. A compressed sensing-based (CS) activity detection algorithm has an excellent performance in the case of sparse active devices. However, due to the massive number of potential devices and non-orthogonal pilots, the algorithm's complexity is very high, and the base station (BS) needs much cache to store the pilot codebook for all potential devices is unacceptable in this scenario. In order to solve this problem, this paper proposes a low complexity activity detection scheme. The scheme uses a linear combination of orthogonal pilots to construct non-orthogonal pilots, which does not need to store the pilot codebook at BS. Also, we propose a device by device activity detection algorithm for this scheme. When the number of potential devices is less than L ² -L, and the number of antennas goes to infinity, the error probability of the proposed algorithm approaches 0, and the complexity of the algorithm is 50-100 times lower than the compressed sensing-based algorithm.