Receiver Designs for Low-Latency HF Communications

High frequency (HF) radio communications offer latency advantages over fiber-optics in certain long-distance communication applications. As a result, there is interest in using HF for high-frequency trading (HFT), to make trans-continental market decisions that leverage the lower latency path of HF channels. The HF skywave channel is a dynamic medium and is one of the most challenging communication channels. Latencies in existing HF modems from coding and interleaving over several packets are prohibitive for HFT, which motivates the development of receivers that provide good performance given a delay constraint. In this paper, we present receiver designs that can be employed for low-latency reliable communication. We introduce a multitrellis adaptive Viterbi algorithm (MAVA) for sparse and time-varying intersymbol interference (ISI) channels, where the conventional Viterbi algorithm would lead to a large trellis. While multitrellis receiver designs have previously been considered, MAVA also incorporates real-time channel tracking, which is necessary for a practical HF receiver. We combine the MAVA algorithm with maximum a posteriori (MAP) detection to obtain a hybrid receiver with high-fidelity, low-delay performance. Finally, we conduct an asymptotic efficiency analysis of the hybrid receiver to gain insight into how deferring decisions improves performance in the high signal-to-noise ratio (SNR) regime.