Layered sources in non-orthogonal amplify-forward relay networks

In this paper, we consider broadcasting layered source codes over a single-relay network using a half duplex non-orthogonal amplify-forward (HD-NAF) relaying protocol. Distortion exponent (i.e., the SNR exponent of the average distortion) is taken to evaluate the system performance in the high SNR regime. We prove that the HD-NAF relay network with two-layered codes corresponds to a successive refinable diversity multiplexing tradeoff (DMT) curve.With the identified property, a closed-form expression for an achievable upper bound of the system distortion exponent is derived, which can be achieved via properly allocated power and rate of each layer. Numerical evaluation is conducted to show performance advantages of the considered two-layered HD-NAF protocol against its counterparts.

I. Introduction

Layered code was first deployed under a fading channel in [1], aiming to adapt the transmission to the fluctuating channel condition without having channel knowledge at the transmitter side. Launching layered codes in relay networks has been considered in several papers [2]–[5]. [2] established the diversity multiplexing tradeoff (DMT) curve as a powerful tool to characterize expected distortion (ED) over different channels when channel SNR is sufficiently high. [3] further showed that channels with one degree of freedom can demonstrate successive refinable DMT curves, implying that each layer can simultaneously achieve the diversity gain on the DMT curve that characterizes the underlying network.