Abstract-The main limitation of visible light communication (VLC) is the narrow modulation bandwidth, which reduces the achievable data rates. In this paper, we apply the nonorthogonal multiple access (NOMA) scheme to enhance the achievable throughput in high-rate VLC downlink networks. We first propose a novel gain ratio power allocation (GRPA) strategy that takes into account the users' channel conditions to ensure efficient and fair power allocation. Our results indicate that GRPA significantly enhances system performance compared to the static power allocation. We also study the effect of tuning the transmission angles of the light emitting diodes (LEDs) and the field of views (FOVs) of the receivers, and demonstrate that these parameters can offer new degrees of freedom to boost NOMA performance. Simulation results reveal that NOMA is a promising multiple access scheme for the downlink of VLC networks.Index Terms-Multiple access, NOMA, power allocation, power domain multiple access, visible light communication.

The smart electricity grid enables a two-way flow of power and data between suppliers and consumers in order to facilitate the power flow optimization in terms of economic efficiency, reliability and sustainability. This infrastructure permits the consumers and the micro-energy producers to take a more active role in the electricity market and the dynamic energy management (DEM). The most important challenge in a smart grid (SG) is how to take advantage of the users' participation in order to reduce the cost of power. However, effective DEM depends critically on load and renewable production forecasting. This calls for intelligent methods and solutions for the real-time exploitation of the large volumes of data generated by a vast amount of smart meters. Hence, robust data analytics, high performance computing, efficient data network management, and cloud computing techniques are critical towards the optimized operation of SGs. This research aims to highlight the big data issues and challenges faced by the DEM employed in SG networks. It also provides a brief description of the most commonly used data processing methods in the literature, and proposes a promising direction for future research in the field.Comment: Published in ELSEVIER Big Data Researc

Monotonicity criteria are established for the generalized Marcum Q-function, Q M (α, β), the standard Nuttall Qfunction, Q M,N (α, β), and the normalized Nuttall Q-function, QM,N (α, β), with respect to their real order indices M, N . Besides, closed-form expressions are derived for the computation of the standard and normalized Nuttall Q-functions for the case when M, N are odd multiples of 0.5 and M ≥ N . By exploiting these results, novel upper and lower bounds for Q M,N (α, β) and QM,N (α, β) are proposed. Furthermore, specific tight upper and lower bounds for Q M (α, β), previously reported in the literature, are extended for real values of M . The offered theoretical results can be efficiently applied in the study of digital communications over fading channels, in the informationtheoretic analysis of multiple-input multiple-output systems and in the description of stochastic processes in probability theory, among others. Index Terms-Closed-form expressions, generalized Marcum Q-function, lower and upper bounds, monotonicity, normalizedNuttall Q-function, standard Nuttall Q-function. † This work is dedicated to the memory of Marvin K. Simon. 1 We adopt the term "standard" for the Nuttall Q-function in order to avoid ambiguity with its normalized version to be introduced later.

In this paper, we present a novel low-complexity scheme, which improves the performance of single-antenna multi-carrier communication systems, suffering from in-phase and quadrature (I/Q)-imbalance (IQI) at the receiver. We refer to the proposed scheme as I/Q-imbalance self-interference coordination (IQSC). IQSC does not only mitigate the detrimental effects of IQI, but, through appropriate signal processing, also coordinates the self-interference terms produced by IQI in order to achieve second-order frequency diversity. However, these benefits come at the expense of a reduction in transmission rate. More specifically, IQSC is a simple transmit diversity scheme that improves the signal quality at the receiver by elementary signal processing operations across symmetric (mirror) pairs of subcarriers. Thereby, the proposed transmission protocol has a similar complexity as Alamouti's space-time block coding scheme and does not require extra transmit power nor any feedback. To evaluate the performance of IQSC, we derive closed-form expressions for the resulting outage probability and symbol error rate. Interestingly, IQSC outperforms not only existing IQI compensation schemes but also the ideal system without IQI for the same spectral efficiency and practical target error rates, while it achieves almost the same performance as ideal (i.e., IQI-free) equal-rate repetition coding. Our findings reveal that IQSC is a promising low-complexity technique for significantly increasing the reliability of low-cost devices that suffer from high levels of IQI.Comment: Published in IEEE Transactions on Wireless Communication

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