Interference-Resilient Hybrid Multi-Antenna ARQ

Abstract

Hybrid automatic repeat request (HARQ) protocols use forward error correction and detection to trigger additional transmissions, until a packet is correctly decoded. Type-I HARQ (HARQ-I) uses packet retransmission and so-called chase combining of the received packets. HARQ protocols are widely used at the radio link / transport layer of wireless standards like 5G and WiFi to guarantee practically error-free end-to-end message delivery. Existing HARQ protocols are not designed to handle strong interference, which must be normally dealt with at the physical layer. On the other hand, recent work has shown that, with the right kind of multi-antenna signal processing at the receiver, based on canonical correlation analysis (CCA), retransmissions can be leveraged to eliminate interference. This creates an opportunity for synergistic cross-layer design, where a modified HARQ protocol will also excise interference. This paper proposes combining CCA-based interference excision and HARQ-I. The resulting protocol uses CCA in place of chase combining for interference immunity and better performance at low signal to noise ratios, while HARQ-I controls how many retransmissions are needed on the fly. The combination offers the best of both worlds and is backwards-compatible with the HARQ-I standard. Simulations for a 5G scenario with Rayleigh fading and one interferer that is 20 dB above the noise floor indicate impressive gains in terms of throughput and delay relative to standard HARQ-I with chase combining.