Cooperative relaying in cellular networks for improving receiver diversity and cell radius

Abstract

Wireless network sharing has been the principal idea in the recent developments of wireless communication systems not only for improvement in capacity, data rates and coverage area but when considering an emergency service model, establishing reliable communication is the foremost requirement. With the inception of cooperative relaying technology, a novel wireless relaying method of sharing the terminal node capabilities to forward the signal created a new paradigm to greatly improve the quality of the services and soon became the significant research area in 3G/4G cellular networks. The cooperative terminals (relays) exploit a larger form of space diversity to relay signals to destinations when placed in between source and destination to combat the effects of fading induced by multipath signal propagation. However, the position of the relay in between the source and destination plays a significant role in affecting the overall network performance. Our attempt in this thesis is to show how a cooperative relay can be used to provide improved coverage at the cell edge with certain reliability and also extend the cell radius by effectively positioning the relay. First, we investigate the famous 3-node relay assisted cellular system model and study the receiver diversity combining results by changing the relay positions with a relay forwarding the signal using the amplitude and forward protocol (AAF). The figure of merit of the considered 3-node system model is expressed in terms of Bit error rate (BER) and signal to noise ratio (SNR). The BER vs. SNR plots are computed for various linear receiver diversity combining techniques and are used to evaluate performance of the system. These results are also compared to the conventional cellular network performance with a single point-to-point link between source and destination. Second, we provide the problem formulation of the diversity results observed and solve to find the effective relay position with respect to the source and also compute the effective cell radius of the 3-node system model. To compute effective relay position, we use the Bernardin's coverage area probability relation with cell radius at the cell edge of the source where the relay is assumed to be placed with its probability of successfully forwarding the signal conditionally depending on its cell edge probability. We have obtained results of the two above problem formulations using MATLAB simulations. We have emulated the cooperative relaying technique in a cellular system to achieve 2nd order diversity when compared to the conventional cellular system. The BER vs. SNR plots for each of the combining techniques show the significant difference in the diversity results when the channel quality estimations are used compared to the other methods which don't. Signal to noise ratio combining (SNRC) and Estimated SNRC (ESNRC) perform 4≅5dB better than the other combining methods provided their SNR estimation is accurate. The highest diversity order (2nd) is achieved when the relay is placed close to the source and drops as the relay is moved towards the destination. Cell range extension results show that moving the relay to its optimal position between source and destination in a cell provides capabilities to extend the cell range to nearly 1.5 times the cell radius of the source and still performs within the acceptable coverage area probabilities.