Optical Asymmetric Modulation for VLC Systems

The explosive growth of connected devices and the increasing number of broadband users have led to an unprecedented growth in traffic demand. To this effect, the next generation wireless systems are envisioned to meet this growth and offer a potential data rate of 10 Gbps or more. In this context, an attractive solution to the current spectrum crunch issue is to exploit the visible light spectrum for the realization of high-speed commutation systems. However, this requires solutions to certain challenges relating to visible light communications (VLC), such as the stringent requirements of VLC-based intensity modulation and direct detection (IM/DD), which require signals to be real and unipolar. The present work proposes a novel power-domain multiplexing based optical asymmetric modulation (OAM) scheme for indoor VLC systems, which is particularly adapted to transmit high-order modulation signals using linear real and unipolar constellations that fit into the restrictions of IM/DD systems. It is shown that the proposed scheme provides improved system performance that outperforms alternative modulation schemes, at no extra complexity

Optical Non-Orthogonal Multiple Access for Visible Light Communication

The proliferation of mobile Internet and connected devices, offering a variety of services at different levels of performance, represents a major challenge for the fifth generation wireless networks and beyond. This requires a paradigm shift towards the development of key enabling techniques for the next generation wireless networks. In this respect, visible light communication (VLC) has recently emerged as a new communication paradigm that is capable of providing ubiquitous connectivity by complementing radio frequency communications. One of the main challenges of VLC systems, however, is the low modulation bandwidth of the light-emitting-diodes, which is in the megahertz range. This article presents a promising technology, referred to as "optical- non-orthogonal multiple access (O-NOMA)", which is envisioned to address the key challenges in the next generation of wireless networks. We provide a detailed overview and analysis of the state-of-the-art integration of O-NOMA in VLC networks. Furthermore, we provide insights on the potential opportunities and challenges as well as some open research problems that are envisioned to pave the way for the future design and implementation of O-NOMA in VLC systems

Macrocell-femtocells resource allocation with hybrid access motivational model

Femtocell technology has emerged as an efficient cost-effective solution not only to solve the indoor coverage problem but also to cope with the growing demand requirements. This paper investigates two major design concerns in two tier networks: resource allocation and femtocell access. Base station selection together with dual bandwidth and power allocation among the two tiers is investigated under shared spectrum usage. To achieve fair and efficient resource optimization, our model assumes that the hybrid access mode is applied in the femtocells. The hybrid access mode is beneficial for system performance as (1) it lessens interference caused by nearby public users, (2) it allows public users to connect to near femtocells and get better Quality of Service (QoS) and (3) it increases system capacity as it allows the macrocell to serve more users. However, femtocells’ owners can behave selfishly by denying public access to avoid any performance reduction in subscribers’ transmissions. Such a problem needs a motivation scheme to assure the cooperation of femtocells’ owners. In this paper, we propose a game-theoretical hybrid access motivational model. The proposed model encourages femtocells’ owners to share resources with public users, thus, more efficient resource allocation can be obtained. We optimize the resource allocation by means of the Genetic Algorithm (GA). The objective of the formulated optimization problem is the maximization of network throughput that is calculated by means of Shannon’s Capacity Law. Simulations are conducted where a modified version of the Weighted Water Filling (WWF) algorithm is used as a benchmark. Our proposed model, compared to WWF, achieves more efficient resource allocation in terms of system throughput and resources utilization

Multi-user techniques in visible light communications: A survey

Visible light communication (VLC) is a recent proposed paradigm of optical wireless communication, in which the visible electromagnetic radiation is used for data transmission. The visible part of the spectrum occupies the frequency range from 400 THz to 800 THz, which is 10,000 times greater than the radio frequency (RF) band. Therefore, its exceptional characteristics render it a promising solution to support and complement traditional RF communication systems, and also overcome the currently witnessed scarcity of radio spectrum resources. To this end, in the last few years, there has been a rapid interest in multi-user processing techniques in VLC. Motivated by this, in this paper, we present a comprehensive and up-to-date survey on the integration of multiple-input multiple-output systems, multi-carrier modulations and multiple access techniques in the context of VLC

Genetic Algorithm Based Resource Allocation and Interference Mitigation for OFDMA Macrocell-femtocells Networks

In this paper, we propose a base station selection and resource allocation model for OFDMA macro-femtocell networks. Dense deployment of femtocells can cause severe interference for femto and macro users alike. Our framework assumes hybrid-access femtocells to grant access to public user in their vicinity and to reduce interference perceived by femto users. Full spectrum sharing is investigated for the purpose of increasing system capacity. The proposed model aims to maximize the network throughput for a given interference threshold. To do so, the model determines the best serving base station based on link conditions. Genetic Algorithm is used to solve the resource optimization problem by finding the appropriate bandwidth and power assignments for each user. Simulations were conducted and a comparison with a modified version of the Weighted Water Filling algorithm is presented

Realistic framework for resource allocation in macro–femtocell networks based on genetic algorithm

In this paper, we consider the problem of resource allocation in non-dense macrocell–femtocell networks. We build a comprehensive realistic framework that overcomes the limitations of previous research work such as (1) resources underutilization due to the equal transmitted power per subcarrier in macrocell, (2) lack of femtocells selection mechanism that grant access to public users without depriving their own subscribers. Orthogonal Frequency Division Multiple Access is a promising candidate for efficient spectrum sharing techniques as it eliminates intracell interference. We propose a base station selection and resource allocation model for two-tier networks that is able to: (i) maximize the overall network throughput, (ii) find the appropriate serving base station for each mobile user, and (iii) jointly assign bandwidth and power to each user. The proposed approach is based on Genetic Algorithm (GA) technique since this technique allows to find a near optimal solution and to speed up the optimization process. Simulations are conducted under realistic scenarios where user mobility and resource reservation are taken into account. The performance of the proposed approach is compared with a Mixed Integer Linear Programming (MILP) approach and the Weigthed Water Filling (WWF) algorithm

Resource Allocation in Macrocell-femtocell Network Using Genetic Algorithm

In this paper, we consider the problem of resource allocation in two-tier networks taking into consideration nondense femtocell deployments. The following limitations can be remarked from the prior work in the field of resource allocation: (1) resources are underutilized due to the equal power distribution in macrocell, (2) access to public users in femtocells is restricted to avoid depriving own subscribers transmissions, and (3) degradation of signal-to-noise ratio due to noise effects has not been evaluated. To overcome these limitations, we propose a joint power and bandwidth allocation among two tiers together with base station selection using genetic algorithm. Our solution is able to: (1) maximize the overall system throughput, (2) find an appropriate serving base station for each user, and (3) bandwidth and power assigned to each user. Simulations were conducted and a comparison with a Weighted Water Filling algorithm is carried out

On the performance of visible light communication systems with non-orthogonal multiple access

Visible light communication (VLC) has been proposed as a promising and efficient solution to indoor ubiquitous broadband connectivity. In this paper, non-orthogonal multiple access, which has been recently introduced as an effective scheme for fifth generation (5G) wireless networks, is considered in the context of VLC systems under different channel uncertainty models. To this end, we first derive a novel closed-form expression for the bit-error-rate (BER) under perfect channel state information (CSI). Capitalizing on this, we then quantify the effect of noisy and outdated CSI by deriving a simple and accurate approximation for the former and a tight upper bound for the latter. The offered results are corroborated by respective results from extensive Monte Carlo simulations and assist in developing useful insights on the effect of imperfect CSI knowledge on the overall system performance. Furthermore, it was shown that while noisy CSI leads to slight degradation in the BER performance, outdated CSI can cause considerable performance degradation, if the order of the users' channel gains change due to the involved mobility

Error performance of NOMA VLC systems

Visible light communication (VLC) systems are expected to provide remarkably high speed indoor communications and effective ubiquitous connectivity. However, the key limitation of such systems is the narrow modulation bandwidth of the light sources. Based on this, non-orthogonal multiple access (NOMA) has been recently proposed as an effective method that can enhance considerably the spectral efficiency of indoor downlink VLC systems. In this context, the present work is devoted to the evaluation of the bit-error-rate (BER) performance of NOMA-based VLC systems. Specifically, a novel closed-form expression is first derived for the BER of the considered set up, by also taking into account the realistically incurred cancellation errors and interference terms. The validity of the derived expressions is verified through extensive comparisons with respective results from Monte Carlo simulations, while their algebraic representation is relatively simple, which renders them convenient to handle both analytically and numerically. This leads to meaningful insights on the behavior and performance gains achieved, thanks to the adoption of NOMA, which are particularly useful in future design and deployment of VLC systems