Hybrid ARQ in Multicell MU-SIMO With Large-Scale Antenna Arrays

We consider hybrid automatic repeat and request (HARQ) schemes in the uplink of a multicell multiuser single-input multiple-output system with large-scale antenna arrays at the base station (BS) for improving the spectral efficiency while limiting the number of retransmissions. Assuming a zero-forcing receiver at each BS and that each BS knows only the channel gains of users in its own cell, we derive the expressions for the outage probability and long-term average transmission rate (LATR) of the Type-I HARQ, HARQ with chase-combining (HARQ-CC), and HARQ with incremental redundancy (HARQ-IR). We then formulate the optimal rate-selection problems for the three schemes and provide methods to find a solution. Since the optimal-rate selection methods for the HARQ-CC and HARQ-IR schemes are computationally intensive, we propose sub-optimal rate-selection methods, which yield a closer LATR performance to that of the optimal methods. For the Type-I HARQ and HARQ-IR, we also present a parameterization-based method showing the approximate relation between the expressions of the optimized-LATR, optimal rate, and number of antennas. Illustrative results show that the HARQ-IR has significant gain over HARQ-CC and Type-I HARQ in terms of LATR, while Type-I HARQ yields practically similar performance to HARQ-CC as the number of antennas at the BS increase.