Wireless communication systems have been recognized as one of the fastest-growing technologies in recent times. Wireless researchers look for viable solutions to meet higher data rates required by evolving applications. One solution is to use a dedicated ultra-high frequency (UHF) spectrum instead of the almost exhausted radio-frequency band.

Emerging millimeter-wave (mmWave) band, terahertz (THz) band, femtocell, and wireless powered communication (WPC) systems are relatively new research areas, which can provide the needed solution to the rapidly growing need for higher data rates. However, there are unresolved challenges. A foremost challenge is the need for a suitable channel model to adequately characterize transmission environments. Channel modeling is a preliminary step for the successful design and deployment of any communication system;​ hence, channel modeling is the main focus of this thesis. This thesis presents detailed work on the newly-introduced Beaulieu-Xie (BX) distribution as a useful channel model, with extensive performance analyses.

First, we analyze the BX fading model's second-order statistics for both single and diversity receptions using the probability density function (PDF) and characteristic function (CHF) methods, respectively. Our result provides insight into a communication system's dynamic performance operating on the BX fading model. Next, we carry out a robust performance analysis of correlated BX fading channels using bounds. Here, tractable analytical bit-error rate (BER) and outage probability (OP) expressions are derived using a newly-developed bounding technique that involves transforming correlated BX random variables (RVs) to correlated Gaussian RVs. Our results present insights into the primary factors affecting emerging communication systems' performance utilizing massive multiple-input and multiple-output technologies.

Subsequently, we present performance analyses of the BX fading channels in the presence of interfering signals for diversity receptions of the maximal-ratio combining technique. Tractable expressions of the average BER and OP are derived and used to show the effect of interference on the communication systems' performance. The results provide insight into the performance of short-range communication systems where interference is prominent. Furthermore, we develop a new composite model, which we refer to as the shadowed Beaulieu-Xie (SBX). We derive the SBX's PDF, CHF, cumulative distribution function, and moment generating function in closed-form. Then, we carry out a detailed performance analysis of this new distribution and ultimately fit it to published experimental data obtained from fading measurements in 28 gigahertz outdoor mmWave channels. The goodness-of-fit demonstrates that our model yields far more accurate characterizations of new emerging wireless systems' communication environment than other existing unimodal and composite distributions.

Finally, we apply the BX fading model to the performance analyses of WPC. We establish the validity of the BX fading model by the possible presence of multiple line-of-sight components in such communication environments. Here, we introduce two new nonlinear energy harvesters and fit them to measured data obtained from a communication system operating in a UHF band. Our fits are improved over those of existing nonlinear energy harvesters that apply the same set of measured data.