On Noncoherent Fading Relay Channels at High Signal-to-Noise Ratio

TL;DR

This paper investigates the capacity limits of noncoherent fading relay channels at high SNR, revealing conditions under which relays do or do not enhance communication rates based on fading predictability.

Contribution

It provides new insights into when relays improve capacity in noncoherent fading channels, depending on the predictability of fading coefficients from past observations.

Findings

Relay does not increase capacity if the transmitter-receiver channel is more predictable.

Achievable rates near the MISO channel capacity when the transmitter-relay channel is more predictable.

High SNR capacity characterization based on fading predictability assumptions.

Abstract

The capacity of noncoherent fading relay channels is studied where all terminals are aware of the fading statistics but not of their realizations. It is shown that if the fading coefficient of the channel between the transmitter and the receiver can be predicted more accurately from its infinite past than the fading coefficient of the channel between the relay and the receiver, then at high signal-to-noise ratio (SNR) the relay does not increase capacity. It is further shown that if the fading coefficient of the channel between the transmitter and the relay can be predicted more accurately from its infinite past than the fading coefficient of the channel between the relay and the receiver, then at high SNR one can achieve communication rates that are within one bit of the capacity of the multiple-input single-output fading channel that results when the transmitter and the relay can cooperate.