Cooperative spectrum sharing with two-way relaying

Abstract

Modern wireless communication seeks more capacity and higher data rates as the cellular technology evolves from one generation to next generation standards (for instance 3G to 4G, and from 4G to presumably 5G). As a consequence researchers and technologists are looking for solutions that can provide very high data rates and better coverage to the end user notwithstanding the problems of channel fading, interference and spectrum scarcity etc. To cater the above, many new paradigms like cooperative relaying, cognitive radio, adaptive techniques and two-way relaying has been proposed in literature from time to time. Cooperative communication can be realized as a relay network, in which the relay simply forwards the source information to the destination by a different path to provide spatial diversity thus improving the performance of a communication system. Along with this to have efficient spectrum utilization, cognitive radio has been proposed where different wireless systems operate on the same spectrum but with different priorities. The system with higher priority is termed as the primary system and the one with lower priority is termed as the secondary system. Cognitive radios work with a constraint that the secondary spectrum access should not adversely affect the performance of primary. Recently, in order to get the benefits of both cooperation and cognition, techniques such as cooperative spectrum sharing (CSS) have been considered by. In the CCS framework, the secondary system acts as a relay and helps the primary to have spatial diversity in exchange for OSA. In the proposed work, a Bit Error Rate based Selection Combining (BER-SC) protocol for adaptive cooperative cognitive radios (CCR) is proposed, where the secondary system utilizes adaptive mode of transmission (with M-QAM where M = 4, 16 or 64 depending on the received channel feedback) to help the primary system to achieve the desired quality of service (QoS) in exchange for opportunistic spectrum access (OSA). BER-SC is employed to retrieve the primary signal, and at SR interference cancellation is used to retrieve the secondary signal. Moreover, a two-way CSS protocol under Nakagami-m fading has been proposed to improve the spectrum efficiency. The primary system which has higher priority seeks the assistance of low priority secondary system to improve its QoS in-exchange for allowing the secondary system to access its spectrum. Apart from above, we have also proposed a novel approach to solve the problems of spectrum efficiency where we have used AF relaying secondary node for two-way communication between the primary transceivers. As the decoding at the secondary node is not taking place due to amplify and forward (AF) approach being used at the secondary transmitter (ST), reducing the complexity of the system.