Beamforming Optimization in MU-MISO URLLC Systems

This paper considers a downlink ultra reliable low latency communication (URLLC) system in which a BS equipped with multi antenna arrays simultaneously serves multi single antenna user equipments (UEs) by transmitting short packet. With the objective of maximizing achievable data rate (ADR) for all UEs, we consider the beamforming optimization design. In the short packet transmitting, the ADR is a complicated function of bandwidth, beamform vectors and decoding error probability, which makes the max-sum ADR optimization problems challenging to solve. This problem is firstly decoupled via Lagrange dual transform and the beamforming at BS is optimized based on fractional programming (FP) method. Then, alternative optimization (AO) algorithm is proposed to solve this problem. Performance of the proposed algorithm is analyzed through extensive simulations under various settings of transmission power budget, transmission time, total bandwidth and the number of antennas. The simulation results clearly demonstrate the merits of the proposed algorithm, and shown that the URLLC ADR obtained by proposed algorithm are quite close to Shannon ADR over a wide range of simulation parameters.