On the Capacity of Decode-and-Forward Relaying over Rician Fading Channels

TL;DR

This paper derives the capacity of decode-and-forward relaying over Rician channels, showing that adaptive power and rate strategies outperform fixed power schemes, with channel inversion suffering capacity loss.

Contribution

It provides exact analytical expressions for the capacity of various adaptive protocols over Rician fading channels, a novel contribution in this context.

Findings

Optimal power and rate adaptation outperform fixed power schemes.

Channel inversion suffers significant capacity loss.

Derived exact capacity expressions for adaptive protocols.

Abstract

In this letter, we derive the probability density function (PDF) and cumulative distribution function (CDF) of the minimum of two non-central Chi-square random variables with two degrees of freedom in terms of power series. With the help of the derived PDF and CDF, we obtain the exact ergodic capacity of the following adaptive protocols in a decode-and-forward (DF) cooperative system over dissimilar Rician fading channels: (i) constant power with optimal rate adaptation; (ii) optimal simultaneous power and rate adaptation; (iii) channel inversion with fixed rate. By using the analytical expressions of the capacity, it is observed that the optimal power and rate adaptation provides better capacity than the optimal rate adaptation with constant power from low to moderate signal-to-noise ratio values over dissimilar Rician fading channels. Despite low complexity, the channel inversion based adaptive transmission is shown to suffer from significant loss in capacity as compared to the other adaptive transmission based techniques over DF Rician channels.