Low Complexity Delay-Constrained Beamforming for Multi-User MIMO Systems With Imperfect CSIT

Abstract

In this paper, we consider the delay-constrained beamforming control for\ndownlink multi-user MIMO (MU- MIMO) systems with imperfect channel state\ninformation at the transmitter (CSIT). The delay-constrained control problem is\nformulated as an infinite horizon average cost partially observed Markov\ndecision process. To deal with the curse of dimensionality, we introduce a\nvirtual continuous time system and derive a closed-form approximate value\nfunction using perturbation analysis w.r.t. the CSIT errors. To deal with the\nchallenge of the conditional packet error rate (PER), we build a tractable\nclosed- form approximation using a Bernstein-type inequality. Based on the\nclosed-form approximations of the relative value function and the conditional\nPER, we propose a conservative formulation of the original beamforming control\nproblem. The conservative problem is non-convex and we transform it into a\nconvex problem using the semidefinite relaxation (SDR) technique. We then\npropose an alternating iterative algorithm to solve the SDR problem. Finally,\nthe proposed scheme is compared with various baselines through simulations and\nit is shown that significant performance gain can be achieved.\n