Faster Activity and Data Detection in Massive Random Access: A Multiarmed Bandit Approach

This article investigates the grant-free random access mechanism for massive Internet of Things (IoT) devices. By embedding the data symbols in the signature sequences, joint device activity detection and data decoding can be achieved, which, however, significantly increases the computational complexity. Coordinate descent algorithms that enjoy a low per-iteration complexity have been employed to solve this detection problem, but previous works typically employ a random coordinate selection policy which leads to slow convergence. In this article, we develop multiarmed bandit (MAB) approaches for more efficient detection via coordinate descent, which achieves a delicate tradeoff between
exploration
and
exploitation
in coordinate selection. Specifically, we first propose a bandit-based strategy, i.e., Bernoulli sampling, to speed up the convergence rate of coordinate descent, by learning which coordinates will result in more aggressive descent of the
nonconvex objective function
. To further improve the convergence rate, an inner MAB problem is established to learn the exploration policy of Bernoulli sampling. Both convergence rate analysis and simulation results are provided to show that the proposed bandit-based algorithms enjoy faster convergence rates with a lower time complexity compared with the state-of-the-art algorithm. Furthermore, our proposed algorithms are generally applicable to different scenarios, e.g., massive random access with low-precision analog-to-digital converters (ADCs).