Browsing by Author "Sofotasios, P. C."

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Open Access
Capacity analysis of NOMA-enabled underwater VLC networks
(IEEE, 2021) Elamassie, Mohammed; Bariah, L.; Uysal, Murat; Muhaidat, S.; Sofotasios, P. C.; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Visible light communication (VLC) has recently emerged as an enabling technology for high capacity underwater wireless sensor networks. Non-orthogonal multiple access (NOMA) has been also proven capable of handling a massive number of sensor nodes while increasing the sum capacity. In this paper, we consider a VLC-based underwater sensor network where a clusterhead communicates with several underwater sensor nodes based on NOMA. We derive a closed-form expression for the NOMA system capacity over underwater turbulence channels modeled by lognormal distribution. NOMA sum capacity in the absence of underwater optical turbulence is also considered as a benchmark. Our results reveal that the overall capacity of NOMA-enabled Underwater VLC networks is significantly affected by the propagation distance in underwater environments. As a result, effective wireless transmission at high and moderate spectral efficiency levels can be practically achieved in underwater environments only in the context of local area networks. Moreover, we compare the achievable capacity of NOMA system with its counterpart, i.e., orthogonal frequency division multiple access (OFDMA). Our results reveal that NOMA system is not only characterized by achieving higher sum capacity than the sum capacity of its counterpart, OFDMA system. It is also shown that the distances between sensor nodes and the clusterhead for achieving the highest sum capacity in these two multiple access systems are different.
Open Access
Coordinated beamforming design for multi-user multi-cell MIMO VLC networks
(IEEE, 2022-06) Naser, S.; Bariah, L.; Jaafar, W.; Muhaidat, S.; Al-Qutayri, M.; Uysal, Murat; Sofotasios, P. C.; Electrical & Electronics Engineering; UYSAL, Murat
Inter-cell interference (ICI) and inter-user interference (IUI) constitute a major issue towards achieving the optimum spectral efficiency (SE) and energy efficiency (EE) performance in multi-cell visible light communication (VLC) networks. Hence, advanced multiple access techniques need to be leveraged in order to improve the provided service to the users of such interfering networks. To this end, the present contribution proposes the integration of coordinated beamforming (CB) with rate-splitting multiple access (RSMA) in multi-cell VLC systems. Specifically, we consider the design of beamformers for the common and private streams in a coordinated manner between different attocells, which is shown to provide efficient mitigation of the incurred interference. Additionally, the formulated optimization problem aims to minimize the sum of the mean squared error across all attocells in order to jointly determine the optimum receive filters and coordinated transmit beamformers for RSMA streams. In this context, we illustrate through extensive computer simulations, which are carried out in a realistic setup that assumes noisy channel state information acquisition, the distinct flexibility and robustness of CB-based RSMA in mitigating the incurred interference. Finally, the offered results demonstrate the superiority of CB-based RSMA in terms of achievable SE and EE performance in multi-cell VLC networks compared to the conventional CB-based space division multiple access counterpart.
Metadata only
Interference management strategies for multiuser multicell MIMO VLC systems
(IEEE, 2022-09) Naser, S.; Bariah, L.; Muhaidat, S.; Al-Qutayri, M.; Uysal, Murat; Sofotasios, P. C.; Electrical & Electronics Engineering; UYSAL, Murat
This paper investigates different precoding strategies for rate splitting multiple access (RSMA) in the downlink of multi-cell visible light communication (VLC) networks. Since classical Shannon capacity formula does not hold for VLC, we first provide a lower bound on the channel capacity for RSMA in such interfering networks. Then, we formulate a spectral efficiency maximization problem to jointly find the optimal rate-splitting and transmit precoding. Beside that, since cell-edge users suffer from additional inter-cell interference, we propose to design the precoders of different RSMA signals utilizing coordinated beamforming (CB). Subsequently, aiming to improve the performance of the CB design for RSMA, while maintain a reduced complexity, we introduce two enhanced precoding strategies for RSMA. To the best of the authors' knowledge such a contribution has not been considered before in the open literature. It is shown in the paper that the formulated optimization problem is non-convex and a sub-optimal, yet, a low complexity solution can be obtained efficiently using semi-definite relaxation combined with successive convex approximation. Through analytical results, we illustrate the flexibility and superiority of the proposed precoding strategies for RSMA over conventional coordinated space division multiple access and non-orthogonal multiple access for different scenarios and network loads.
Metadata only
Non-orthogonal multiple access-based underwater VLC systems in the presence of turbulence
(IEEE, 2022-02) Bariah, L.; Elamassie, Mohammed; Muhaidat, S.; Sofotasios, P. C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; ELAMASSIE, Mohammed
The promising potential of underwater applications in visible light communication (VLC) systems has recently gained considerable research attention, as an efficient technology for enabling high data rate, massive connectivity, and ultra-low latency. Different from indoor VLC, underwater wireless communications experience harsh environmental challenges, yielding a degraded performance. Non-orthogonal multiple access (NOMA) was introduced to enhance spectral efficiency and connectivity of underwater VLC communications. In this paper, we develop a mathematical framework to evaluate the performance of NOMA-enabled underwater VLC systems in the presence of turbulence. Specifically, we derive a closed-form expression for the outage probability of NOMA over lognormal channels, while considering the effect of path loss and turbulence. The derived analytical results with the corresponding numerical results demonstrate that the transmission distance between laser diode and sensor nodes (SNs) has a high impact on the outage performance of the SNs, due to the increased turbulence level with increased distance. Moreover, the presented results show the effect of the water type on the outage performance of the SNs and on the optimum values of the power coefficients.