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In this paper, we consider a unified approach to model wireless channels by a mixture of Gaussian (MoG) distributions. The proposed approach provides an accurate approximation for the envelope and the signal-to-noise ratio (SNR) distributions of wireless channels. Simulation results have shown that our model can accurately characterize multipath fading and composite fading channels. We utilize the well known expectation-maximization algorithm to estimate the parameters of the MoG distribution and further utilize the Bayesian information criterion to determine the number of mixture components automatically. We employ the Kullback-Leibler divergence and the mean square error criteria to demonstrate that our distribution provides both high accuracy and low computational complexity. Additionally, we provide closed-form expressions or approximations for several performance metrics used in wireless communication systems, including the moment generating function, the raw moments, the amount of fading, the outage probability, the average channel capacity, and the probability of energy detection for cognitive radio. Numerical Analysis and Monte-Carlo simulation results are presented to corroborate the analytical results.

Direct-conversion architectures can offer highly integrated low-cost hardware solutions to communication transceivers. However, it has been demonstrated that radio frequency (RF) impairments such as amplifier nonlinearities, phase noise and in-phase/quadrature-phase imbalances (IQI) can lead to a severe degradation in the performance of such systems. Motivated by this, the present work is devoted to the quantification and evaluation of the effects of RF IQI on wireless communications in the context of cascaded fading channels for both single-carrier and multi-carrier systems. To this end, closed form expressions are firstly derived for the outage probability (OP) over N *Nakagami−m channels for the cases of ideal transmitter (TX) and receiver (RX), ideal TX and IQI RX, IQI TX and ideal RX, and joint TX/RX IQI. The offered expressions along with several deduced corresponding special cases are subsequently employed in the context of vehicular-tovehicular (V2V) communications to justify their importance and practical usefulness in the context of emerging communication systems. We demonstrate that considering non-ideal RF frontends at the TX and/or RX, introduces non-negligible errors in the OP performance that can exceed 20% in several communication scenarios. We further demonstrate that the effects by cascaded multipath fading conditions are particularly detrimental, as they typically result in considerable performance losses of around or over an order of magnitude.

This paper investigates non-orthogonal multiple access (NOMA), cooperative relaying, and energy harvesting to support device-to-device (D2D) transmission. In particular, we deploy multiple relay nodes and a cell-center D2D device which can operate in full-duplex (FD) or half-duplex (HD) mode to communicate with a cell-edge D2D device. In this context, there are two possible signal transmission paths from the base station (BS) to the far D2D user either through multiple decode-and-forward (DF) relay nodes or through a near D2D user. Consequently, we propose three schemes to support D2D-NOMA systems, namely non-energy harvesting relaying (Non-EHR), energy harvesting relaying (EHR) and quantize-mapforward relaying (QMFR) schemes. For each of the proposed schemes, closed-form expressions of the outage probabilities of both D2D users are derived. Extensive Monte-Carlo simulation results are provided to validate the derived analytical expressions. The study results show that the proposed schemes can improve the outage performance compared to conventional orthogonal multiple access (OMA) schemes. Moreover, it is shown that the Non-EHR scheme achieves the best outage performance among the three considered schemes.

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