Performance analysis of efficient receivers and modulation techniques for digital communication systems

The dissertation analyzes the performance of efficient receivers and modulation techniques for multiple and single user digital communications systems. It is partitioned into four main parts. In the first part, the average error performance of direct sequence code division multiple access (DS-CDMA) employing noncoherent orthogonal modulation in the presence of additive white Gaussian noise (AWGN) and partial-band interference (PBI) is analyzed over generalized fading channels. The noncoherent equal-gain combining (NC-EGC) (which is also known as the square-law combining) is used to achieve diversity gain. New generalized results for the system average error performance are derived for the cases of independent identically distributed (i.i.d), independent nonidentically distributed (i.n.d), and arbitrarily correlated diversity branches. The analysis considers four channel fading models; Rayleigh, Nakagami- m, Rician, and Nakagami-q distributions. These channel fading distributions are widely used to describe multipath small scale fading in real mobile and satellite radio links. The second part of the dissertation proposes designs for noncoherent and differentially-coherent diversity receivers to mitigate the disadvantages of the conventional square-law receiver over nonidentically distributed Nakagami-m, Rician, and Nakagami- q fading channels. It is shown that the proposed diversity receivers result in simple expressions for the average error performance, and achieve performance improvements over that of the conventional square-law receiver for both cases of independent and arbitrarily correlated diversity branches. The third part presents a new design for noncoherent modulation technique based on combining power-efficient noncoherent orthogonal multilevel frequency-modulated signals and bandwidth-efficient multilevel polarization-modulated signals. The analysis considers the wireline optical communication links, and it shows that the proposed modulation scheme achieves simultaneous improvements in the power and bandwidth efficiencies with low detection complexity by maintaining the noncoherent detection property at the receiver side. The final part of the dissertation presents new results for the average of higher-order powers of the one-dimensional Gaussian Q-function over Rayleigh and Nakagami-m fading channels employing linear diversity combining. Expressions are newly derived for i.i.d and i.n.d fading scenarios. The derived results are useful for several applications in the wireless communication theory, especially in evaluating the average error performance of various uncoded and coded communication systems over multi-branch fading channels.