Performance Evaluation and Improvement of Wireless Amplify-and-Forward Cooperative-Based Systems under Nodes Mobility and Imperfect CSI Estimation Impacts

Cooperative communication techniques have been introduced in wireless networks to achieve spacial diversity-gain via the readiness of multiple users (via relays) to assist a source forwarding its data to a final destination. Cooperative communication techniques have shown their capability in improving system reliability and extending coverage area, and hence, it is believable that they will act as a promising technology for the coming fifth-generation (5G). Nevertheless, most existing work reported in literature on performance studies of wireless cooperative-based systems are based on the assumptions that the multipath fading channels among systems cooperating nodes are quasi-static (i.e., fading channels coefficients are constant over a number of consecutive signaling periods) and channel-state-information (CSI) estimation processes at systems receivers are perfect. Nowadays, however, there is an increased number of users riding high-speed public transportation vehicles and demanding wireless data services through their own terminals. As a result of such high mobility wireless terminals, the assumption of time-selective (i.e., non quasi-static) fading is more realistic. This time-selective fading environment would severely deteriorate the performance of existing wireless cooperative systems that have been already designed based on the assumption of quasi-static fading (low users speeds). Further, due to impairments associated with practical receiver tracking-loops implementation issues, it is more general to assume that CSI estimations at systems receiving sides are imperfect. The scope of this dissertation is to provide comprehensive performance evaluation study for several emerging models of wireless amplify-and-forward (AF) cooperative-based communication systems that operate under the effects of the more general scenarios of high nodes mobility (time-selective fading) and imperfect channel estimations. This performance evaluation study is conducted by deriving closed-form expressions for different performance metrics; including error probability, outage probability and channel capacity. Monte Carlo simulations are also provided to complement and validate the analytical analyses. All of the obtained results in this dissertation are novel and general for mobile as well as non-moving nodes and for imperfect as well as perfect CSI estimations. Moreover, in this dissertation we develop innovative and applicable solutions and receiver designs that are capable of mitigating the detrimental impacts of the high nodes mobility on the performance of the cooperative system models under study

Revisiting Lightweight Encryption for IoT Applications: Error Performance and Throughput in Wireless Fading Channels with and without Coding

© 2013 IEEE. Employing heavy conventional encryption algorithms in communications suffers from added overhead and processing time delay; and in wireless communications, in particular, suffers from severe performance deterioration (avalanche effect) due to fading. Consequently, a tremendous reduction in data throughput and increase in complexity and time delay may occur especially when information traverse resource-limited devices as in Internet-of-Things (IoT) applications. To overcome these drawbacks, efficient lightweight encryption algorithms have been recently proposed in literature. One of those, that is of particular interest, requires using conventional encryption only for the first block of data in a given frame being transmitted. All the information in the remaining blocks is transmitted securely without the need for using heavy conventional encryption. Unlike the conventional encryption algorithms, this particular algorithm achieves lower overhead/complexity and higher data throughput. Assuming the additive white Gaussian noise (AWGN) channel, the performance of the lightweight encryption algorithm under study had been evaluated in literature in terms of throughput under the assumption that the first block, that undergoes conventional encryption, is free of error, which is practically unfeasible. In this paper, we consider the AWGN channel with Rayleigh fading and assume that the signal experiences a certain channel bit error probability and investigate the performance of the lightweight encryption algorithm under study in terms of bit error probability and throughput. We derive analytical expressions for these performance metrics considering modulated signals with and without coding. In addition, we propose an extension to the lightweight encryption algorithm under study by further enhancing its security level without significantly affecting the overhead size and processing time. Via numerical results we show the superiority of the lightweight encryption algorithm under study over the conventional encryption algorithms (like the AES) and the lightweight encryption algorithms proposed in literature in terms of error and throughput performance