3,041 research outputs found

    Optical Non-Orthogonal Multiple Access for Visible Light Communication

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    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

    Performance Evaluation of Non-Orthogonal Multiple Access in Visible Light Communication

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    Resource allocation for 5G technologies under statistical queueing constraints

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    As the launch of fifth generation (5G) wireless networks is approaching, recent years have witnessed comprehensive discussions about a possible 5G standard. Many transmission scenarios and technologies have been proposed and initial over-the-air experimental trials have been conducted. Most of the existing literature studies on 5G technologies have mainly focused on the physical layer parameters and quality of service (QoS) requirements, e.g., achievable data rates. However, the demand for delay-sensitive data traffic over wireless networks has increased exponentially in the recent years, and is expected to further increase by the time of 5G. Therefore, other constraints at the data-link layer concerning the buffer overflow and delay violation probabilities should also be regarded. It follows that evaluating the performance of the 5G technologies when such constraints are considered is a timely task. Motivated by this fact, in this thesis we explore the performance of three promising 5G technologies when operating under certain QoS at the data-link layer. We follow a cross-layer approach to examine the interplay between the physical and data-link layers when statistical QoS constraints are inflicted in the form of limits on the delay violation and buffer overflow probabilities. Noting that wireless systems, generally, have limited physical resources, in this thesis we mainly target designing adaptive resource allocation schemes to maximize the system performance under such QoS constraints. We initially investigate the throughput and energy efficiency of a general class of multiple-input multiple-output (MIMO) systems with arbitrary inputs. As a cross-layer evaluation tool, we employ the effective capacity as the main performance metric, which is the maximum constant data arrival rate at a buffer that can be sustained by the channel service process under specified QoS constraints. We obtain the optimal input covariance matrix that maximizes the effective capacity under a short-term average power budget. Then, we perform an asymptotic analysis of the effective capacity in the low signal-to-noise ratio and large-scale antenna (massive MIMO) regimes. Such analysis has a practical importance for 5G scenarios that necessitate low latency, low power consumption, and/or ability to simultaneously support massive number of users. Non-orthogonal multiple access (NOMA) has attracted significant attention in the recent years as a promising multiple access technology for 5G. In this thesis, we consider a two-user power-domain NOMA scheme in which both transmitters employ superposition coding and the receiver applies successive interference cancellation (SIC) with a certain order. For practical concerns, we consider limited transmission power budgets at the transmitters, and assume that both transmitters have arbitrarily distributed input signals. We again exploit the effective capacity as the main cross-layer performance measure. We provide a resource management scheme that can jointly obtain the optimal power allocation policies at the transmitters and the optimal decoding order at the receiver, with the goal of maximizing the effective capacity region that provides the maximum allowable sustainable arrival rate region at the transmitters' buffers under QoS guarantees. In the recent years, visible light communication (VLC) has emerged as a potential transmission technology that can utilize the visible light spectrum for data transmission along with illumination. Different from the existing literature studies on VLC, in this thesis we consider a VLC system in which the access point (AP) is unaware of the channel conditions, thus the AP sends the data at a fixed rate. Under this assumption, and considering an ON-OFF data source, we provide a cross-layer study when the system is subject to statistical buffering constraints. To this end, we employ the maximum average data arrival rate at the AP buffer and the non-asymptotic bounds on buffering delay as the main performance measures. To facilitate our analysis, we adopt a two-state Markov process to model the fixed-rate transmission strategy, and we then formulate the steady-state probabilities of the channel being in the ON and OFF states. The coexistence of radio frequency (RF) and VLC systems in typical indoor environments can be leveraged to support vast user QoS needs. In this thesis, we examine the benefits of employing both technologies when operating under statistical buffering limitations. Particularly, we consider a multi-mechanism scenario that utilizes RF and VLC links for data transmission in an indoor environment. As the transmission technology is the main physical resource to be concerned in this part, we propose a link selection process through which the transmitter sends data over the link that sustains the desired QoS guarantees the most. Considering an ON-OFF data source, we employ the maximum average data arrival rate at the transmitter buffer and the non-asymptotic bounds on data buffering delay as the main performance measures. We formulate the performance measures under the assumption that both links are subject to average and peak power constraints

    Secrecy Design of Indoor Visible Light Communication Network under Downlink NOMA Transmission

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    In this work, we investigate the transmission sum rate as well as the secrecy sum rate of indoor visible light communication (VLC) networks for mobile devices with the power domain non-orthogonal multiple access (NOMA) transmission, where multiple legitimate users are equipped with photodiodes (PDs). We introduce a body blockage model of the legitimate users as well as the eavesdropper to focus on the case where the communications from transmitting light-emitting diodes (LEDs) to receiving devices are blocked by the bodies of receiving users. Furthermore, in order to improve the secrecy without any knowledge of the channel state information (CSI) of the eavesdropper, a novel LED arrangement is introduced to reduce the overlapping area covered by LED units supporting different users. We also propose two LED operation strategies, called simple and smart LED linking, and evaluate their performance against the conventional broadcasting in terms of transmission sum rate and secrecy sum rate. Through computer simulations, the superiority of our proposed strategies is demonstrated.Comment: 30 pages, 13 figures. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

    Hybrid Free-Space Optical and Visible Light Communication Link

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    V součastnosti bezdrátové optické komunikace (optical wireless communication, OWC) získávají širokou pozornost jako vhodný doplněk ke komunikačním přenosům v rádiovém pásmu. OWC nabízejí několik výhod včetně větší šířky přenosového pásma, neregulovaného frekvenčního pásma či odolnosti vůči elektromagnetickému rušení. Tato práce se zabývá návrhem OWC systémů pro připojení koncových uživatelů. Samotná realizace spojení může být provedena za pomoci různých variant bezdrátových technologií, například pomocí OWC, kombinací různých OWC technologií nebo hybridním rádio-optickým spojem. Za účelem propojení tzv. poslední míle je analyzován optický bezvláknový spoj (free space optics, FSO). Tato práce se dále zabývá analýzou přenosových vlastností celo-optického více skokového spoje s důrazem na vliv atmosférických podmínek. V dnešní době mnoho uživatelů tráví čas ve vnitřních prostorech kanceláří či doma, kde komunikace ve viditelném spektru (visible light communication, VLC) poskytuje lepší přenosové parametry pokrytí než úzce směrové FSO. V rámci této práce byla odvozena a experimentálně ověřena závislost pro bitovou chybovost přesměrovaného (relaying) spoje ve VLC. Pro propojení poskytovatele datavých služeb s koncovým uživatelem může být výhodné zkombinovat více přenosových technologií. Proto je navržen a analyzovám systém pro překonání tzv. problému poslední míle a posledního metru kombinující hybridní FSO a VLC technologie.The field of optical wireless communications (OWC) has recently attracted significant attention as a complementary technology to radio frequency (RF). OWC systems offer several advantages including higher bandwidth, an unregulated spectrum, resistance to electromagnetic interference and a high order of reusability. The thesis focuses on the deployment and analyses of end-user interconnections using the OWC systems. Interconnection can be established by many wireless technologies, for instance, by a single OWC technology, a combination of OWC technologies, or by hybrid OWC/RF links. In order to establish last mile outdoor interconnection, a free-space optical (FSO) has to be investigated. In this thesis, the performance of all-optical multi-hop scenarios is analyzed under atmospheric conditions. However, nowadays, many end users spend much time in indoor environments where visible light communication (VLC) technology can provide better transmission parameters and, significantly, better coverage. An analytical description of bit error rate for relaying VLC schemes is derived and experimentally verified. Nonetheless, for the last mile, interconnection of a provider and end users (joint outdoor and indoor connection) can be advantageous when combining multiple technologies. Therefore, a hybrid FSO/VLC system is proposed and analyzed for the interconnection of the last mile and last meter bottleneck
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