A cheap relaying protocol for orthogonal relay channels

The proposed relaying scheme, which is an optimized scalar quantize-and-forward (QF) protocol, has at least three attractive features: 1. it is simple; 2. it exploits the signal-to-noise ratios (SNR) of the source-relay and relay-destination channels; 3. it can be seen as a digital alternative of the conventional (analog) amplify-and-forward (AF) in a digital relay transceiver. The presented QF protocol is optimized in terms of end-to-end distortion, extending the idea of joint source-channel coding. Using this cooperation protocol over orthogonal relay channels, it is shown that the quantization noise introduced by the relay can significantly degrade the receiver performance if the latter uses a maximum ratio combiner (MRC) to combine the two signals from the source and relay. In order for the receiver to compensate for this effect, we propose a maximum likelihood detector (MLD), which is optimum for the QF protocol.