Predicting Wireless Channels for Ultra-Reliable Low-Latency Communications

Ultra-reliable, low-latency wireless communication is essential to enable critical and interactive applications. The cooperative communication schemes for such ultra-reliable communication must harvest multi-user diversity to achieve their specifications. The underlying low-latency space-time codes for a large number of users (> 10) place burdens on practical implementations due to the large number of simultaneous relays they must use. To address this, we propose an adaptive relay selection technique that selects a small set of good relays, instead of using every available radio to relay. Using our simple relay-selection schemes, we can support a network with 30 nodes requiring system failure probability under 10(-9) and 2 ms latency with only 3 simultaneously active relays per message. In contrast, in the absence of adaptive relay selection, we must rely on 13 relays to achieve the same reliability. To arrive at such relay selection schemes, we revisit the fading dynamics of wireless channels in the context of ultra-high reliability. Contrary to what has been claimed in the literature, we find that standard Rayleigh fading processes are not bandlimited. However, these fading processes are fairly predictable on the short time scales of the regime of interest.