Channel capacity of adaptive transmission in fading environment with diversity combining techniques

Wireless communication services have been growing at a rapid pace in recent years. This remarkable growth is projected to increase during the next years, which will increase the demand for scarce radio spectrum. Thus, channel capacity is of fundamental importance in the design of wireless communication systems as it determines the maximum attainable throughput of the system. Since wireless systems are subject to fading, which is known to cause degradation in link performance, fading mitigation schemes are required. Diversity combining is known to be a powerful technique that can be used to combat fading in wireless systems resulting in improving link performance. Adaptive transmission is another effective scheme than can be used to overcome fading.; In this dissertation, we study the capacity of four different diversity combining systems over fading channels for two adaptive transmission schemes: optimal rate adaptation with constant power (ora), and channel inversion with fixed rate (cifr). We first study the capacity of independent Rician and Nakagami-q (Hoyt) fading channels with maximal ratio combining (MRC) diversity for the ora scheme. In particular, we derive closed-form expressions for the probability density function (PDF) of the received signal-to-noise ratio (SNR) at the output of an L-branch MRC combiner for the Rician and Hoyt fading environments. We then use the PDF expressions to derive closed-form expressions for the capacity of Rician and Hoyt fading channels with MRC diversity by using the ora scheme. Additionally, we propose bounds on the truncation error resulting from truncating the infinite series in the final capacity expressions.; Then, we study the capacity of independent and correlated Nakagami- m fading channels with different diversity combining techniques for both ora and cifr. Specifically, we derive closed-form expressions for the capacity of dual-branch MRC, equal gain combining (EGC), selection combining (SC), and switch and stay combining (SSC) diversity systems over independent and correlated Nakagami-m fading channels for the ora and cifr cases. We also derive expressions that can be used to numerically determine the optimum adaptive switching threshold for the case of SSC. Closed-form expressions for the optimum adaptive switching threshold are derived however for the cases of capacity of independent diversity branches. The capacities of L-branch SC and MRC systems over independent Nakagami-m fading channels for both ora and cifr are also considered. Since some of the final capacity expressions for Nakagami- m fading are in the form of an infinite series, bounds on the capacity and errors resulting from truncating the infinite series are proposed.