Joint Scheduling and ARQ for MU-MIMO Downlink in the Presence of Inter-Cell Interference

TL;DR

This paper proposes a joint scheduling, MU-MIMO beamforming, and ARQ framework for MU-MIMO downlink systems to effectively manage inter-cell interference, introducing a novel HARQ scheme that approaches optimal throughput without prior interference knowledge.

Contribution

It introduces a game-theoretic stochastic optimization framework for joint scheduling and ARQ, and develops a new incremental redundancy HARQ scheme for interference management.

Findings

The proposed HARQ scheme achieves throughput close to genie-aided limits.

The joint framework effectively handles unknown inter-cell interference.

The new HARQ scheme outperforms conventional adaptive coding with ARQ.

Abstract

User scheduling and multiuser multi-antenna (MU-MIMO) transmission are at the core of high rate data-oriented downlink schemes of the next-generation of cellular systems (e.g., LTE-Advanced). Scheduling selects groups of users according to their channels vector directions and SINR levels. However, when scheduling is applied independently in each cell, the inter-cell interference (ICI) power at each user receiver is not known in advance since it changes at each new scheduling slot depending on the scheduling decisions of all interfering base stations. In order to cope with this uncertainty, we consider the joint operation of scheduling, MU-MIMO beamforming and Automatic Repeat reQuest (ARQ). We develop a game-theoretic framework for this problem and build on stochastic optimization techniques in order to find optimal scheduling and ARQ schemes. Particularizing our framework to the case of "outage service rates", we obtain a scheme based on adaptive variable-rate coding at the physical layer, combined with ARQ at the Logical Link Control (ARQ-LLC). Then, we present a novel scheme based on incremental redundancy Hybrid ARQ (HARQ) that is able to achieve a throughput performance arbitrarily close to the "genie-aided service rates", with no need for a genie that provides non-causally the ICI power levels. The novel HARQ scheme is both easier to implement and superior in performance with respect to the conventional combination of adaptive variable-rate coding and ARQ-LLC.