Broadcast underlay cognitive radio with dirty paper coding over fading channels

In this paper, the bit error rate (BER) performance analysis of an underlay cognitive radio (CR) network, which is considered as a broadcast scheme, over fading channels, is investigated. Particularly, the underlay CR network is studied as a closed loop multiple antenna system, presented with dirty paper coding (DPC) approach with the aim of allowing the secondary user (SU) transmission to utilize the spectrum resources efficiently and avoiding harmful interference to the primary user (PU) receiver. The proposed approach is capable of achieving the same performance as that of the zero-forcing (ZF) algorithm over Rayleigh fading channels at the SU receiver. We further show that the BER performance of the PU under Rician fading channel is significantly improved for the proposed study. Finally, numerical and simulation results are provided to demonstrate the performance and corroborate the theoretical analysis.

1. Introduction

The limited available frequency bandwidth and the inefficient usage for the radio spectrum necessitate a new communication policy to exploit the unused spectrum holes opportunistically for the existing wireless spectrum resources. Cognitive radio (CR) systems have been proposed as a new approach for wireless communication systems to utilize the existing spectrum resources much more efficiently [1]–[3]. Spectrum utilization can be increased by allowing the unlicensed secondary users (SUs) to utilize the licensed band in the absence of the primary user (PU). In CR terminology, the PU is defined as the user who has legacy rights and higher priority to use the licensed spectrum. On the other hand, an unlicensed SU has lower priority and is allowed to utilize the idle spectrum holes opportunistically without causing harmful interference to the PU [4]–[7].