Multiuser MIMO Short-Packet Communications: Time-Sharing or Zero-Forcing Beamforming?

In this paper, we investigate a multiuser MIMO system consisting of one multiple-antenna access point (AP) and multiple single-antenna users under short-packet communication scenarios. Two fundamental schemes, i.e., time division multiple access (TDMA) and zero-forcing beamforming (ZFB), are considered for the users to receive individual information from the AP in the downlink. To analyze the performance of TDMA and ZFB in finite blocklength regime, we derive approximate closed-form expressions of the block error rate (BLER) for each user for both schemes. Simple asymptotic expressions at high signal-to- noise ratio (SNR) are also derived. Based on the derived expressions, we then formulate sum-BLER minimization problems in terms of blocklength allocation to each user in TDMA scheme and power allocation in ZFB scheme. We resolve the formulated problems by performing their convexity analysis. We finally validate our theoretical analysis and compare the performance of TDMA and ZFB schemes by simulation results, which show that TDMA and ZFB can outperform each other in different system setups.