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The impact of transceiver hardware impairments on the accuracy of spectrum sensing cannot be ignored in low-cost and high data rate cognitive radio systems. Nevertheless, ideal hardware for spectrum sensing is widely assumed in the technical literature. This paper presents a novel method for evaluating the improved energy detector (IED) statistics using α-µ distribution over additive white Gaussian noise (AWGN) and Nakagami-m fading channel by considering transceiver hardware imperfections. Moreover, the performance of the IED over AWGN channel is highlighted by the area under the receiver operating curve. Furthermore, the average probability of detection is evaluated for both fading and non-fading environments. An asymptotic analysis studies detection probability over fading channels at a low average signal-to-noiseratio region. Moreover, p-order law combining and p-order law selecting diversity techniques are proposed to increase the performance of the detector. Our simulation results demonstrate that the diversity techniques significantly improve the detector performance. INDEX TERMS Area under the ROC curve (AUC), α-µ distribution, false alarm probability, improved energy detector, Nakagami-m fading channel, probability of detection, receiver operating characteristic (ROC) curve, transceiver hardware impairments.

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This work elaborates the analysis on ergodic capacity, coverage probability, and average throughput for multi-user non-orthogonal multiple access (NOMA) based device-to-device communication networks, which operate in the millimeter-wave spectrum range and are constrained by practical system imperfections such as residual transceiver hardware impairments, imperfect channel state information, and non-ideal successive interference cancellation. More importantly, we consider that the proposed network model is limited by independent and non-identically distributed interference noises emerging from neighboring device nodes. Computationally effective and comprehensive closed-form expressions are delivered to evaluate the ergodic capacity with its upper and lower bounds, as well as coverage probability and average throughput expressions. Furthermore, the asymptotic analysis of ergodic capacity and coverage probability at high and low signal-to-noise-ratio regimes are analyzed and the corresponding closed-form expressions are presented. Valuable discussions on the fairness-based power allocation scheme for NOMA users have been provided. Moreover, a thorough Monte Carlo simulation is carried out to validate the corresponding analytical findings. Finally, simulation results have revealed that the system impairments aforementioned herein cause an ergodic capacity saturation phenomenon. Especially, interference plays a significant role as a performance limitation factor for the ergodic capacity and coverage probability.INDEX TERMS Average throughput, coverage probability, device-to-device (D2D) communications, ergodic capacity, imperfect channel state information (CSI), successive interference cancellation (SIC), millimeter-wave (mmWave), non-orthogonal multiple access (NOMA), residual transceiver hardware impairment (RTHI).