Intelligent reflecting surfaces (IRSs) have emerged as a promising solution to mitigate line-of-sight (LoS) blockages and enhance signal coverage in optical wireless communication (OWC) systems with minimal additional power. In this work, we consider a mirror-based IRS to assist a dynamic indoor visible light communication (VLC) environment. We formulate an optimization problem that aims to maximize the sum rate by adjusting the orientation of the IRS mirrors. To enable real-time adaptability, the problem is modelled as a Markov decision process (MDP), and a deep reinforcement learning (DRL) algorithm is developed based on the deterministic policy gradient for real-time mirror-based IRS optimization in dynamic VLC networks. The proposed DRL is employed to optimize mirror orientation toward mobile users under blockage and mobility constraints. Simulation results demonstrate that our proposed DRL algorithm outperforms the conventional deep Q- learning (DQL) algorithm and achieves substantial improvements in sum rate compared to random-orientation IRS configurations

Intelligent reflecting surfaces (IRSs) technology has been considered a promising solution in visible light communication (VLC) systems due to its potential to overcome the line-of-sight (LoS) blockage issue and enhance coverage. Moreover, integrating IRS with a downlink non-orthogonal multiple access (NOMA) transmission technique for multi-users is a smart solution to achieve a high sum rate and improve system performance. In this paper, a dynamic IRS-assisted indoor NOMA-VLC system is modeled, and an optimization problem is formulated to maximize sum energy efficiency (SEE) and fairness among multiple mobile users under power allocation and IRS mirror orientation constraints. Due to the non-convex nature of the optimization problem and the non-linearity of the constraints, conventional optimization methods are impractical for real-time solutions. Therefore, a two-agent deep reinforcement learning (DRL) algorithm is designed for optimizing power allocation and IRS orientation based on centralized training with decentralized execution to obtain fast and real-time solutions in dynamic environments. The results show the superior performance in terms of SEE, sum rate and fairness index of the proposed DRL algorithm compared to standard DRL algorithms and conventional algorithms typically used for resource allocation in wireless communication. The results also show that the proposed two-agent DRL algorithm achieves higher performance compared to deployments without IRS and with randomly oriented IRS elements.

One of the crucial issues in indoor optical wireless communication (OWC) is service interruptions due to blockages that obstruct the line of sight (LoS) between users and their access points (APs). Recently, reflecting surfaces referred to as intelligent reflecting surfaces (IRSs) have been considered to provide improved connectivity in OWC systems by reflecting AP signals toward users. In this study, we investigate the integration of IRSs into an indoor OWC system to improve the sum rate of the users and to ensure service continuity. We formulate an optimization problem for the sum rate maximization, where the allocation of both APs and mirror elements of IRSs to users is determined to enhance the aggregate data rate. Moreover, reinforcement learning (RL) algorithms, specifically Q-learning and SARSA algorithms, are proposed to provide real-time solutions with low complexity and without prior system knowledge. The results show that using RL algorithms achieves near-optimal solutions that are close to the solutions of mixed integer linear programming (MILP). The results also show that the proposed scheme achieves a significant data rate increase compared to a traditional scheme that allocates the resources, APs and mirror elements, based on the distance.

In this paper, we put forward a proof of concept for sixth generation (6G) Terabit infrared (IR) laser-based indoor optical wireless networks. We propose a novel double-tier access point (AP) architecture based on anarray of arraysof vertical cavity surface emitting lasers (VCSELs) to provide a seamless grid-of-beam (GoB) coverage with multi-Gb/s per beam. We present systematic design and thorough analytical modeling of the AP architecture, which are then applied to downlink system modeling using non-imaging angle diversity receivers (ADRs). We propose static beam clustering with coordinated multi-beam joint transmission (CoMB-JT) for network interference management and devise various clustering strategies to address inter-beam interference (IBI) and inter-cluster interference (ICI). Non-orthogonal multiple access (NOMA) and orthogonal frequency division multiple access (OFDMA) schemes are also adopted to handle intra-cluster interference, and the resulting signal-to-interference-plus-noise ratio (SINR) and achievable data rate are derived. The network performance is studied in terms of spatial distributions and statistics of the downlink SINR and data rate through extensive computer simulations. The results demonstrate that data rates up to 15 Gb/s are achieved within the coverage area and a properly devised clustering strikes a balance between the sum rate and fairness depending on the number of users.

Optical wireless communication (OWC) has recently received massive interest as a new technology that can support the enormous data traffic increasing on daily basis. In particular, laser-based OWC networks can provide terabits per second (Tbps) aggregate data rates. However, the emerging OWC networks require a high number of optical access points (APs), each AP corresponding to an optical cell, to provide uniform coverage for multiple users. Therefore, inter-cell interference (ICI) and multi-user interference (MUI) are crucial issues that must be managed efficiently to provide high spectral efficiency. In radio frequency (RF) networks, rate splitting (RS) is proposed as a transmission scheme to serve multiple users simultaneously following a certain strategy. It was shown that RS provides high data rates compared to orthogonal and non-orthogonal interference management schemes. Considering the high density of OWC networks, the application of RS within each optical cell might not be practical due to severe ICI. In this paper, a novel strategy is derived, referred to as blind interference alignment-rate splitting (BIA-RS), to fully coordinate the transmission among the optical APs, while determining the precoding matrices of multiple groups of users formed beforehand. Therefore, RS can be implemented within each group to manage MUI. The proposed BIA-RS scheme requires two layers of power allocation to achieve high performance. Given that, a max-min fractional optimization problem is formulated to optimally distribute the power budget among the groups and the messages intended to the users of each group. Finally, a power allocation algorithm is designed with multiple Lagrangian multipliers to provide practical and sub-optimal solutions. The results show the high performance of the proposed scheme compared to other counterpart schemes.

This paper investigates the integration of Open Radio Access Network (O-RAN) within non-terrestrial networks (NTN), and optimizing the dynamic functional split between Centralized Units (CU) and Distributed Units (DU) for enhanced energy efficiency in the network. We introduce a novel framework utilizing a Deep Q-Network (DQN)-based reinforcement learning approach to dynamically find the optimal RAN functional split option and the best NTN-based RAN network out of the available NTN-platforms according to real-time conditions, traffic demands, and limited energy resources in NTN platforms. This approach supports capability of adapting to various NTN-based RANs across different platforms such as LEO satellites and high-altitude platform stations (HAPS), enabling adaptive network reconfiguration to ensure optimal service quality and energy utilization. Simulation results validate the effectiveness of our method, offering significant improvements in energy efficiency and sustainability under diverse NTN scenarios.

The ubiquitous deployment of Internet of Things (IoT) and the ever-evolving IoT services seek fully autonomous devices with no energy limitations. To fulfill this demand, we investigate the usage of unmanned aerial vehicles (UAVs) to overcome the limited battery constraint of IoT deployments in hard-to-reach locations. Specifically, we present a UAV-enabled wake-up radio (WuR) and data collection (U-WuRIoT) solution for future IoT networks. The proposed solution leverages UAVs to wake-up IoT devices from an ultralow power sleep mode by transmitting WuR signals. Upon successful wake-up, the devices use their batteries to transmit the collected data to the UAV. In this article, we present an overview of U-WuRIoT and its applications and discuss the challenges and enabling technologies toward realizing it. Candidate enablers, such as advances on wake-up receivers and UAV transmitters’ hardware, combined energy harvesting and WuR, new spectrum opportunities, energy beamforming, channel state information (CSI)-limited schemes, and UAV trajectory optimization, are outlined. A realistic experimental testbed, using a fully operational prototype implemented via off-the-shelf components, is constructed to validate the applicability of U-WuRIoT and its benefits compared to traditional duty cycling (DCY) solutions. Furthermore, a theoretical study is conducted to extrapolate the performance of U-WuRIoT in large-scale deployments. The obtained experimental and theoretical results demonstrate that U-WuRIoT can extend the lifetime of the IoT device up to three times the lifetime when DCY is applied and can reduce the false alarm rate to less than 10%. Finally, key research directions toward implementing U-WuRIoT in the 6G era are identified.

To achieve multi-Gb/s data rates in 6G optical wireless access networks based on narrow infrared (IR) laser beams, a high-speed receiver with two key specifications is needed: a sufficiently large aperture to collect the required optical power and a wide field-of-view (FOV) to avoid strict alignment issues. This paper puts forward the systematic design and optimisation of multi-tier non-imaging angle diversity receivers (ADRs) composed of compound parabolic concentrators (CPCs) coupled with photodiode (PD) arrays for laser-based optical wireless communication (OWC) links. Design tradeoffs include the gain-FOV tradeoff for each receiver element and the area-bandwidth tradeoff for each PD array. The rate maximisation is formulated as a non-convex optimisation problem under the constraints on the minimum required FOV and the overall ADR dimensions to find the optimum configuration of the receiver bandwidth and FOV, and a low-complexity optimal solution is proposed. The ADR performance is studied using computer simulations and insightful design guidelines are provided through various numerical examples. An efficient technique is also proposed to reduce the ADR dimensions based on CPC length truncation. It is shown that a compact ADR with a height of$\leq 0.5$cm and an effective area of$\leq 0.5$cm2 reaches a data rate of 12 Gb/s with a half-angle FOV of 30° over a 3 m link distance.

Recently, Optical wireless communication (OWC) have been considered as a key element in the next generation of wireless communications due to its potential in supporting unprecedented communication speeds. In this paper, infrared lasers referred to as vertical-cavity surface-emitting lasers (VC-SELs) are used as transmitters sending information to multiple users. In OWC, rate-maximization optimization problems are usually complex due to the high number of optical access points (APs) needed to ensure coverage. Therefore, practical solutions with low computational time are essential to cope with frequent updates in user-requirements that might occur. In this context, we formulate an optimization problem to determine the optimal user association and resource allocation in the network, while the serving time is partitioned into a series of time periods. Therefore, cooperative ANN models are designed to estimate and predict the association and resource allocation variables for each user such that sub-optimal solutions can be obtained within a certain period of time prior to its actual starting, which makes the solutions valid and in accordance with the demands of the users at a given time. The results show the effectiveness of the proposed model in maximizing the sum rate of the network compared with counterpart models. Moreover, ANN-based solutions are close to the optimal ones with low computational time.

The design of a compact high-speed and wide field of view (FOV) receiver is challenging due to the presence of two well-known trade-offs. The first one is the area-bandwidth trade-off of photodetectors (PDs) and the second one is the gain-FOV trade-off due to the use of optics. The combined effects of these two trade-offs imply that the achievable data rate of an imaging optical receiver is limited by its FOV, i.e., a rate-FOV trade-off. In this paper, we propose an imaging receiver design in the form of an array of (PD) arrays. To control the area-bandwidth trade-off, small PDs are used in an array of arrays structure instead of a single large PD. Moreover, to achieve a reasonable receiver FOV, we use an array of focusing lenses that focus the light individually on each inner PD array. The proposed array of arrays structure provides an effective method to control both gain-FOV trade-off (via an array of lenses) and area-bandwidth trade-off (via arrays of small PDs). We first derive a tractable analytical model for the signal-to-noise ratio (SNR) of an array of PDs that is equipped with a focusing lens assuming maximum ratio combining (MRC). Then, we extend the model to the proposed array of arrays structure and the accuracy of the analytical model is verified based on several Optic Studio-based simulations. Next, we formulate an optimization problem to maximize the achievable data rate of the imaging receiver subject to a minimum required FOV. The optimization problem is solved for two commonly used modulation techniques, namely, on-off keying (OOK) and direct current (DC) biased optical orthogonal frequency division multiplexing (DCO-OFDM) with variable rate quadrature amplitude modulation (QAM). Our results show the limits of high speed wide-FOV imaging receivers that can support mobility. For example, it is demonstrated that a data rate of$\sim 24$Gbps with a FOV of 15° is achievable using OOK with a total receiver size of 2 cm$\!\times \!\,\,2$cm.

Optical wireless communication offers unprecedented communication speeds that can support the massive use of the Internet on a daily basis. In indoor environments, optical wireless networks are usually multi-user multiple-input multiple-output (MU-MIMO) systems, where a high number of optical access points (APs) is required to ensure coverage. In this work, a laser-based optical wireless network is considered for serving multiple users. Moreover, blind inference alignment (BIA) is implemented to achieve a high degree of freedom (DoF) without the need for channel state information (CSI) at transmitters, which is difficult to provide in such wireless networks. Then, an objective function is defined to allocate the resources of the network taking into consideration the requirements of users and the available resources. This optimization problem can be solved through exhaustive search or distributed algorithms. However, a practical algorithm that provides immediate solutions in real time scenarios is required. In this context, an artificial neural network (ANN) model is derived in order to obtain a sub-optimal solution with low computational time. The implementation of the ANN model involves three important steps, dataset generation, offline training, and real time application. The results show that the trained ANN model provides a significant solution close to the optimal one.

Due to the emergence of new paradigms and services such as 5G/6G, IoT, and more, current deployed wired Data Center Networks (DCNs) are not meeting the required performance metrics due to their limited reconfigurability, scalability, and throughput. To that end, wireless DCNs using technologies such as Optical Wireless Communication (OWC) have become viable and cost-effective solutions as they offer higher capacity, better energy efficiency, and better scalability. This paper proposes an OWC-based spine and leafDCNs where the leaf switches are enabled with OWC transceivers, and the spine switches are replaced by Access Points (APs) in the ceiling connected to a backbone network. The APs are interconnected through a Passive Optical Network (PON) that also connects the architecture with upper network layers. An Infrared (IR) OWC system that employs Wavelength Division Multiplexing (WDM) is proposed to enhance the DCN downlink communication. The simulation (i.e., channel modeling) results show that our proposed data center links achieve good data rates in the data center up to 15 Gbps. For the PON, Arrayed Waveguide Grating Routers (AWGRs) that enable WDM are proposed to connect the APs. We evaluate the performance of the considered architecture in term of its power efficiency compared to traditional spine and leaf data centers. The results show that the OWC-enabled DCN reduces the power consumption by 42% compared to traditional the spine and leaf architecture.

Optical wireless Communication (OWC) is a strong candidate in the next generation (6G) of cellular networks. In this paper, a laser-based optical wireless network is deployed in an indoor environment using Vertical Cavity Surface Emitting Lasers (VCSELS) as transmitters serving multiple users. Specifically, a commercially available low-cost VCSEL operating at S50nm wavelength is used. Considering the confined coverage area of each VCSEL, an array of VCSELs is designed to transmit data to multiple users through narrow beams taking into account eye safety regulations. To manage multi-user interference (MUI), Zero Forcing (ZF) is implemented to maximize the multiplexing gain of the network. The energy efficiency of the network is studied under different laser beam waists to find the effective laser beam size that results in throughput enhancement. The results show that the energy efficiency increases with the laser beam waist. Moreover, using micro lenses placed in front of the VCSELs leads to significant increase in the energy efficiency.

The fourth call for papers of the Series on Machine Learning in Communications and Networks has continued to receive a great number of high-quality papers covering various aspects of intelligent communications, from which we have included 16 original contributions in this issue. In the following, we provide a brief review of these papers according to their topics.

The third call for papers of the Series on Machine Learning in Communications and Networks has continued to receive a great number of high-quality papers covering various aspects of intelligent communications, from which we have included 26 original contributions in this issue. In the following, we provide a brief review of key contributions of papers in this issue according to their topics.

The fourth (and final) call for papers of the Series on Machine Learning in Communications and Networks has continued to receive a great number of high-quality papers covering various aspects of intelligent communications. In addition to those published in the August issue, we include in this issue 16 articles submitted to the call. In the following, we provide a brief review of these articles according to their topics.

Light amplification by stimulated emission of radiation (laser) sources has many advantages for use in high-data-rate optical wireless communications (OWCs). In particular, the low-cost and high-bandwidth properties of laser sources, such as vertical-cavity surface-emitting lasers (VCSELs), make them attractive for future indoor OWCs. In order to be integrated into future indoor networks, such lasers should conform to eye safety regulations determined by the International Electrotechnical Commission (IEC) standards for laser safety. In this article, we provide a detailed study of beam propagation to evaluate the received power of various laser sources, based on which and the maximum permissible exposure (MPE) defined by the IEC 60825-1:2014 Standard, we establish a comprehensive framework for eye safety analyses. This framework allows us to calculate the maximum allowable transmit power, which is crucial in the design of a reliable and safe laser-based wireless communication system. Initially, we consider a single-mode Gaussian beam and calculate the maximum permissible transmit power. Subsequently, we generalize this approach for higher mode beams. It is shown that the$M$-squared-based approach for analysis of multimode lasers ensures the IEC eye safety limits; however, in some scenarios, it can be too conservative compared to the precise beam decomposition method. Laser safety analyses with consideration of optical elements, such as lens and diffuser, as well as for the VCSEL array, have been also presented. Skin safety, as another significant factor of laser safety, has also been investigated in this article. We have studied the impacts of various parameters, such as wavelength, exposure duration, and the divergence angle of laser sources on the safety analysis by presenting insightful results.

In this paper, the design of a multiple-input multiple-output (MIMO) optical wireless communication (OWC) link based on vertical cavity surface emitting laser (VCSEL) arrays is systematically carried out with the aim to support data rates in excess of 1 Tb/s for the backhaul of sixth generation (6G) indoor wireless networks. The proposed design combines direct current optical orthogonal frequency division multiplexing (DCO-OFDM) and a spatial multiplexing MIMO architecture. For such an ultra-high-speed line-of-sight (LOS) OWC link with low divergence laser beams, maintaining alignment is of high importance. In this paper, two types of misalignment error between the transmitter and receiver are distinguished, namely, radial displacement error and orientation angle error, and they are thoroughly modeled in a unified analytical framework assuming Gaussian laser beams, resulting in a generalized misalignment model (GMM). The derived GMM is then extended to MIMO arrays and the performance of the MIMO-OFDM OWC system is analyzed in terms of the aggregate data rate. Novel insights are provided into the system performance based on computer simulations by studying various influential factors such as beam waist, array configuration and different misalignment errors, which can be used as guidelines for designing short range Tb/s MIMO OWC systems.

A disaster may not necessarily demolish the telecommunications infrastructure, but instead it might affect the national grid and cause blackouts, consequently disrupting the network operation unless there is an alternative power source(s). In disaster-resilient networks, fiber cut, datacenter destruction, and node isolation have been studied before with different scenarios, but the power outage impact has not been investigated before. In this paper, power outages are considered, and the telecommunication network performance is evaluated during a blackout. A mixed Integer Linear Programming (MILP) model is developed to evaluate the network performance for a single node blackout under two scenarios: minimization of blocking and minimization of renewable and battery energy consumption. Insights analyzed from the MILP model results have demonstrated the trade-off between the two evaluated optimization cost functions and shown that the proposed scheme can extend the network lifetime while minimizing the required amount of backup energy.

Optical wireless communication provides data transmission at high speeds which can satisfy the increasing demands for connecting a massive number of devices to the Internet. In this paper, vertical-cavity surface-emitting(VCSEL) lasers are used as transmitters due to their high modulation speed and energy efficiency. However, a high number of VCSEL lasers is required to ensure coverage where each laser source illuminates a confined area. Therefore, multiple users are classified into different sets according to their connectivity. Given this point, a transmission scheme that uses blind interference alignment (BIA) is implemented to manage the interference in the laser-based network. In addition, an optimization problem is formulated to maximize the utility sum rate taking into consideration the classification of the users. To solve this problem, a decentralized algorithm is proposed where the main problem is divided into sub-problems, each can be solved independently avoiding complexity. The results demonstrate the optimality of the decentralized algorithm where a sub-optimal solution is provided. Finally, it is shown that BIA can provide high performance in laser-based networks compared with zero forcing (ZF) transmit precoding scheme.

Visible light communication (VLC) is considered a promising technology for providing high data rates in indoor environments. In this sense, each optical access point (AP) in a VLC network can be managed as a small cell usually referred to as attocell. Therefore, the received signal is subject to both multi-user interference (MUI) and inter-cell interference (ICI). In this work, we propose a user centric (UC) cell formation approach jointly with the use of blind interference alignment (BIA) in order to manage the interference. We formulate an optimization problem based on maximizing the sum utility of users rates for the sake of jointly finding the optimal cell formation and minimizing the limitations of BIA, i.e., the noise enhancement and the required coherence time given by the mobility of the users. This problem can be solved through exhaustive research, which involves an unpractical complexity. After that, we decouple the main problem into two sub-problems that may be solved separately. The simulation results show that the proposed schemes are more suitable for VLC networks than the considered benchmark schemes.

The rapid growth of time-sensitive applications and services has driven enhancements to computing infrastructures. The main challenge that needs addressing for these applications is the optimal placement of the end-users’ demands to reduce the total power consumption and delay. One of the widely adopted paradigms to address such a challenge is fog computing. Placing fog units close to end-users at the edge of the network can help mitigate some of the latency and energy efficiency issues. Compared to the traditional hyperscale cloud data centres, fog computing units are constrained by computational power, hence, the capacity of fog units plays a critical role in meeting the stringent demands of the end-users due to intensive processing workloads. In this paper, we first propose a federated fog computing architecture where multiple distributed fog cells collaborate in serving users. These fog cells are connected through dedicated Passive Optical Network (PON) connections. We then aim to optimize the placement of virtual machines (VMs) demands originating from the end-users by formulating a Mixed Integer Linear Programming (MILP) model to minimize the total power consumption. The results show an increase in processing capacity and a reduction in the power consumption by up to 26% compared to a Non-Federated fogs computing architecture.

In the era of the new generation of communication systems, data traffic is expected to continuously strain the capacity of future communication networks. Along with the remarkable growth in data traffic, new applications, such as wearable devices, autonomous systems, and the Internet of Things (IoT), continue to emerge and generate even more data traffic with vastly different requirements. This growth in the application domain brings forward an inevitable need for more intelligent processing, operation, and optimization of future communication networks.

The Second Call for Papers of the Series on Machine Learning in Communications and Networks has continued to receive a great number of high-quality papers covering various aspects of intelligent communication systems. In addition to 23 original contributions in response to the first call for papers, we include in this issue 5 articles submitted to the second call for papers. In the following, we provide a brief review of key contributions of papers in this issue according to their topics.

A system that employs wavelength division multiplexing (WDM) in conjunction with sub‐carrier multiplexing (SCM) tones is proposed to realise high data rate multi‐user indoor visible light communication (VLC). The SCM tones, which are unmodulated signals, are used to identify each light unit, to find the optimum light unit for each user and to calculate the level of the co‐channel interference (CCI). WDM is utilised to attain a high data rate for each user. In this study, multi‐colour (four colours) laser diodes are utilised as sources of lighting and data communication. One of the WDM colours is used to convey the SCM tones at the beginning of the connection to set up the connection among receivers and light units (to find the optimum light unit for each user). To evaluate the performance of the VLC system, two types of receivers are proposed: an array of non‐imaging receivers and an array of non‐imaging angle diversity receivers. In this study, the effects of diffuse reflections, CCI and mobility on the system performance are considered.

Currently, the world is witnessing a mounting avalanche of data due to the increasing number of mobile network subscribers, Internet websites, and online services. This trend is continuing to develop in a quick and diverse manner in the form of big data. Big data analytics can process large amounts of raw data and extract useful, smaller-sized information, which can be used by different parties to make reliable decisions. In this paper, we conduct a survey on the role that big data analytics can play in the design of data communication networks. Integrating the latest advances that employ big data analytics with the networks’ control/traffic layers might be the best way to build robust data communication networks with refined performance and intelligent features. First, the survey starts with the introduction of the big data basic concepts, framework, and characteristics. Second, we illustrate the main network design cycle employing big data analytics. This cycle represents the umbrella concept that unifies the surveyed topics. Third, there is a detailed review of the current academic and industrial efforts toward network design using big data analytics. Forth, we identify the challenges confronting the utilization of big data analytics in network design. Finally, we highlight several future research directions. To the best of our knowledge, this is the first survey that addresses the use of big data analytics techniques for the design of a broad range of networks.

In this paper, we study the impact of big data's volume and variety dimensions on energy efficient big data networks (EEBDN) by developing a mixed integer linear programming (MILP) model to encapsulate the distinctive features of these two dimensions. First, a progressive energy efficient edge, intermediate, and central processing technique is proposed to process big data's raw traffic by building processing nodes (PNs) in the network along the way from the sources to datacenters. Second, we validate the MILP operation by developing a heuristic that mimics, in real time, the behavior of the MILP for the volume dimension. Third, we test the energy efficiency limits of our green approach under several conditions where PNs are less energy efficient in terms of processing and communication compared to data centers. Fourth, we test the performance limits in our energy efficient approach by studying a “software matching” problem where different software packages are required to process big data. The results are then compared to the classical big data networks (CBDN) approach where big data is only processed inside centralized data centers. Our results revealed that up to 52% and 47% power saving can be achieved by the EEBDN approach compared to the CBDN approach, under the impact of volume and variety scenarios, respectively. Moreover, our results identify the limits of the progressive processing approach and in particular the conditions under which the CBDN centralized approach is more appropriate given certain PNs energy efficiency and software availability levels.

The need for high‐speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on visible light communication (VLC) systems. Although VLC systems provide lighting and communications simultaneously from light emitting diodes (LEDs), LEDs, the uplink channel design in such a system is a challenging task. In this study, the authors propose a solution in which the uplink challenge in indoor VLC is resolved by the use of an infrared (IR) link. The authors introduce a novel fast adaptive beam steering IR system (FABS‐IR) to improve the uplink performance at high data rates while providing security for applications. The goal of the authors’ proposed system is to enhance the received optical power signal, speed up the adaptation process and mitigate the channel delay spread when the system operates at a high transmission rate. The channel delay spread is minimised from 0.22 ns given by hybrid diffuse IR link to almost 0.07 ns. At 2.5 Gb/s, the authors’ results show that the imaging FABS‐IR system accomplished about 11.7 dB signal to noise ratio in the presence of multipath dispersion, receiver noise and transmitter mobility.

Cloud computing is expected to be a major factor that will dominate the future Internet service model. This paper summarizes our work on energy efficiency for cloud networks. We develop a framework for studying the energy efficiency of four cloud services in IP over WDM networks: cloud content delivery, storage as a service (StaaS), and virtual machines (VMS) placement for processing applications and infrastructure as a service (IaaS). Our approach is based on the co-optimization of both external network related factors such as whether to geographically centralize or distribute the clouds, the influence of users' demand distribution, content popularity, access frequency and renewable energy availability and internal capability factors such as the number of servers, switches and routers as well as the amount of storage demanded in each cloud. Our investigation of the different energy efficient approaches is backed with Mixed Integer Linear Programming (MILP) models and real time heuristics.

Environmental sustainability in high capacity networks and cloud data centers has become one of the hottest research subjects. In this paper, we investigate the effective use of renewable energy and hence resource allocation in core networks with clouds as a means of reducing the carbon footprint. We develop a Green Virtual Network Embedding (GVNE) framework for minimizing the use of non-renewable energy through intelligent provisioning of bandwidth and cloud data center resources. The problem is modeled as a mixed integer linear program (MILP). The results show that it is better to instantiate virtual machines in cloud data centers that have access to abundant renewable energy even at the expense of traversing several links across the network. The GVNE model reduces the overall CO2emissions by up to 32% for the network considering solar power availability and data center locations.

In this paper, we introduce an adaptive optical wireless system that employs a finite vocabulary of stored holograms. We propose a fast adaptation approach based on a divide and conquer methodology resulting in a number of adaptation algorithms: fast angle adaptive holograms (FAA-Holograms), fast power adaptive holograms (FPA-Holograms), and fast angle and power adaptive holograms (FAPA-Holograms) and evaluate these in mobile optical wireless (OW) systems in conjugation with imaging reception. The ultimate goal is to improve the signal-to-noise ratio (SNR), to reduce the effect of intersymbol-interference (ISI), to speed up the adaptation process, and to eliminate the need to calculate the hologram in real-time at each transmitter and receiver location. The system operates at high data rates under the impact of multipath dispersion, background noise and mobility. At a data rate of 2.5 Gb/s and under eye safety regulations, the proposed FAPA-Holograms offers around 20 dB SNR in the presence of background shot noise, receiver noise, multipath dispersion, and mobility. Simulation results show that the proposed system, FAPA-Holograms, can reduce the time required to identify the optimum hologram position from 80 ms in the original beam angle and power adaptive line strip multibeam system (APA-LSMS) to about 13 ms.

In this paper, we propose a beamforming-based dynamic spectrum leasing (DSL) technique to improve the spectral utility of bi-directional communication of the legacy/primary spectrum users through the help of colocated secondary users. The secondary users help for a time interval to relay the data between two primary terminals using physical layer network coding and beamforming to attain bi-directional communication with high spectral utility. As a reimbursement, the secondary users, cognitive radios (CRs) in our case, get exclusive access to the primary spectrum for a certain duration. We use Nash bargaining to determine the optimal division of temporal resources between relaying and reimbursement. Moreover, we consider that a fraction of secondary nodes can act selfishly by not helping the primary, yet enjoy the reimbursement time. We measure the utility of the DSL scheme in terms of a metric called time-bandwidth product (TBP) ratio quantifying the number of bits transmitted in direct communication versus DSL. We show that if all secondary nodes act honestly, more than 17-fold increase in the TBP ratio is observed for a sparse CR network. However, in such a network, selfish behavior of CR nodes can reduce the gain by more than a factor of 2.

Abstract This paper investigates optimum distributed storage techniques for data preservation, and eventual dissemination, in opportunistic heterogeneous wireless sensor networks where data collection is intermittent and exhibits spatio‐temporal randomness. The proposed techniques involve optimally sharing the sensor nodes' storage and properly handling the storage traffic such that the buffering capacity of the network approaches its total storage capacity with minimum energy. The paper develops an integer linear programming (ILP) model, analyses the emergence of storage traffic in the network, provides performance bounds, assesses performance sensitivities and develops quasi‐optimal decentralized heuristics that can reasonably handle the problem in a practical implementation. These include the Closest Availability (CA) and Storage Gradient (SG) heuristics whose performance is shown to be within only 10% and 6% of the dynamic optimum allocation, respectively. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper, we investigate maximizing the profit achieved by infrastructure providers (InPs) from embedding virtual network requests (VNRs) in IP/WDM core networks with clouds. We develop a mixed integer linear programming (MILP) model to study the impact of maximizing the profit on the power consumption and acceptance of VNRs. The results show that higher acceptance rates do not necessarily lead to higher profit due to the high cost associated with accepting some of the requests. The results also show that minimum power consumption can be achieved while maintaining the maximum profit

In this paper, we develop a Mixed Integer Linear Programming (MILP) model to study the impact of renewable energy availability, represented by wind farms, on the location of clouds and the content replication schemes of cloud content over IP/WDM networks. In our analysis, we assume that renewable energy is only available to power clouds while the IP/WDM network is powered by non-renewable energy. Our results show that popularity based replication in clouds is the most energy efficient content replication scheme when the clouds are powered only by non-renewable energy sources or when renewable energy availability is limited. With abundant renewable energy, a cloud with a full copy of the content can be built at each node. However, the model should achieve a trade-off between the transmission power losses to deliver renewable energy from wind farms to clouds and the non-renewable power consumption of the IP/WDM network. We discuss this trade-off and show how to optimize the transmission power losses of renewable energy while minimizing the non-renewable network power consumption.

Ultra‐wideband (UWB) is a very attractive technology for innovative in‐car wireless communications requiring high data rates. A designated antenna, which presents a reflection coefficient (S11) matched band comparable to the band‐pass filter (BPF) normally required at the transducers, plays a positive contribution in this in‐car application and was validated for the scenario. The inherited BPF‐like response of the antenna relaxes the specification of the front‐end BPF components of the transceivers. The in‐car propagation channel was modelled and used to validate the BPF‐like antenna. For the modelling, a comprehensive set of well‐defined measurements (using a standard antenna) were used to set‐up the in‐car channel simulator and simulated results were used to validate the BPF‐like antenna. In addition, the performance of the UWB radio system is studied and the probability of errors over the communication channel compared using the standard and the BPF‐like antenna by predictions.

In this paper, we present a novel licensed-shared access (LSA) spectrum-sharing scheme as an energy efficient way to increase the spectral utility of a network. We consider a two-tier network where a small cell network offers offloading services to a macro network to improve its quality of service. In return, the small cells are rewarded for their cooperation with a number of licenses to operate in the spectrum owned by the macro network. The short link distances and diversity offered by the small cell network to offload the macro user help enhance the total spectral and energy utilization of the network. For effective functioning of the scheme, it is important to determine the division between the fraction of small cells that provide offloading services and those which obtain the licenses. In this paper, we present a comprehensive mathematical model of this LSA-based offloading and evaluate the optimal division between the offloading and licensing small cells. Our analysis shows that such spectrum sharing can lead to commendable gains in the spectral utilization of the network while assuring the desired quality of service for both macro and small network. An intelligent determination of the fraction of offloading small cell network results in efficient energy use for offloading. We test our scheme within the network parameters of the city of Leeds, U.K. Our results indicate that the spectral utility of Leeds can be improved by more than 12×, and the energy efficiency by 16× through our proposed scheme.

In this paper, we investigate the joint optimization of power, electricity cost and propagation delay in IP over WDM networks employing renewable energy. We develop a mixed integer linear programming (MILP) model to jointly minimize the three parameters and compare its results to the results of optimizing these parameters individually. The models results show that the joint optimization maintains the power consumption and electricity cost savings obtained by the non-renewable power-minimized and the electricity cost-minimized models while hardly affecting the propagation delay. Compared to the delay-minimized model, the joint optimization model achieves power consumption and electricity cost savings of 73% and 74%, respectively under the non-bypass approach considering a unicasting traffic profile. The power and cost savings under an anycasting traffic profile increases to 82%.

Orthogonal Frequency Division Multiplexing (OFDM) has been proposed as an enabling technique for elastic optical networks to support heterogeneous traffic demands. In this paper, we investigate the energy efficiency of rate and modulation adaptive optical OFDM-based networks. A mixed integer linear programming (MILP) model is developed to minimize the total power consumption of optical OFDM networks. We differentiate between two optimization schemes: power-minimized and spectrum-minimized optical OFDM-based networks. The results show that while similar power consumption savings of up to 31% are achieved by the two schemes compared to conventional IP over WDM networks, the spectrum-minimized optical OFDM is 51% more efficient in utilizing the spectrum compared to the power-minimized optical OFDM.

In this paper, we propose dynamic spectrum leasing (DSL) for cognitive radio (CR) networks as an efficient alternative to two way direct communication for legacy/primary networks. We show that using physical layer network coding (PNC) and distributed beamforming, the CR nodes can relay the primary network data for some duration while the spectrum is leased to them. We demonstrate that in DSL operational mode, up to 20 times more data can be successfully exchanged between two primary sources as compared to direct two way communication. Also in DSL, as a reimbursement, the otherwise silent CR nodes that help in relaying can get a fraction of time during which they can carry out their own communication thereby increasing the spectral utilization.

The need for reducing the carbon footprint and reducing the operation expenditure (OPEX) in communication networks poses several challenges in the study, design and deployment of energy efficient networks in different environments. Recently there has been a considerable effort to green vehicular networks which is very challenging due to the very dynamic environment in which these networks operate. In this paper, we investigate the performance of the roadside units (RSUs) in a vehicular motorway network, and propose that these units are wind-powered and act as standalone entities. Real vehicular traffic profiles, reported data traffic measurements and reported wind measurements have been utilised to perform this study. We analyse the performance in several test cases and suggest an operational scenario. Both analytical and simulation results reveal that with the introduction of sleep cycles and a very small battery capacity (124 mAh), these RSUs are able to support quality of service (QoS) for video-related applications at each hour of the day in a motorway vehicular environment while increasing the energy efficiency by up to 32%.

In this paper, we evaluate the energy consumption of BitTorrent based peer to peer (P2P) content distribution systems in bypass IP/WDM core networks and compare it to client-server (C/S) systems. A Mixed Integer Linear Programming (MILP) model is developed to carry out the comparison. Our results for homogeneous peers with similar upload capacities show that the original BitTorrent, based on random peer selection, has comparable energy consumption to the C/S model. The results also reveal that the power-minimized BitTorrent model achieves 30% energy savings compared to the C/S model as it converges to locality. Furthermore, a heterogeneous BitTorrent system with two upload capacity classes is investigated and the results show a 50% reduction in energy consumption compared to a C/S model. For real-time implementation, we develop a simple heuristic based on the model insights. Comparable power savings are achieved with a reduction of only 13% in the download rate.

We propose a novel double cluster-head routing scheme for motorway vehicular networks which is generically modelled (can be applied o single or multiple cluster-head routing schemes) to save a significant amount of energy through adaptive sleep cycles while maintaining he required quality of service (QoS). Real vehicular and data traffic measurements are utilised o evaluate the performance of he double cluster-head (DCH) scheme and compare with he existing (a single cluster-head (SCH)) scheme. The results, also verified with he simulations, reveal that the DCH scheme is able to achieve 2× lower packet blocking probability compared o he SCH scheme. Furthermore, on an average energy saving of 94% with service-tolerant delay during the whole day is achieved. In addition, we found ha with a lower market penetration ratio (MPR), which represents he near future vehicular communication rend, more than 4× energy is saved during peak hours in a motorway vehicular environment.

Traditionally the locations of the base stations (BSs) in an indoor environment are optimised based on either traffic demand, signal to noise ratio (SNR), energy consumption or coverage area. However, considering only one of these parameters does not yield an optimum design, which is needed for efficient cost-effective planning with the required quality of service (QoS). Moreover, this problem becomes extremely challenging in highly dynamic environments such as airports, shopping malls and train stations where both spatial and temporal traffic variations are considerably high. Due to the continuous growth in international air traffic and the dynamic behaviour of passengers in an airport environment, providing reliable and cost-effective communication facilities to passengers and staff becomes even more difficult at different times and locations. Using data from Heathrow Terminal 4 (T4), we, in this paper, develop T4 passenger flow models which take both the spatial and temporal variations into account and help us accurately determine the traffic demand (TD), coverage area and path loss and thus outage and energy consumption. Moreover, we propose a multi-objective genetic algorithm (GA) which serves traffic demand and minimises both outage and energy consumption of the whole network. This eventually minimises the number of BSs while optimising their locations. The results reveal that only a few (i.e. 1-4) more base stations are required when we consider all three parameters together compared to the TD only. However our proposed GA, considering TD, outage and energy consumption, achieves lower outage and consumes almost 90% less transmission energy compared to the case of TD only while serving the same amount of traffic in such a dynamic environment.

In this paper, the antenna beam pattern modulation (ABPM) is presented as a transmission scheme which uses antenna patterns in addition to the conventional amplitude/phase modulation (APM) symbols to convey information and increase spectral efficiency. The transmitted bits per symbol period are divided into two blocks: the first block contains the antenna beam patterns and the second APM symbols. Then, the second block is mapped to an APM symbol, which is transmitted by the antenna pattern selected by the first block. The beam pattern and the transmitted symbol are detected using the maximum likelihood (ML) by the receiver, in order to de-map the block of information bits. The bit error rate (BER) performance of the proposed ABPM is evaluated over independent and identically distributed (iid) Rayleigh fading channel. The simulation results show that with appropriately designed beam patterns, the transmission scheme can provide a better performance and enhanced throughput when compared to conventional spatial modulation (SM) and APM.

Geographic routing (GR) algorithms are attractive in ad hoc wireless networks owing to their efficiency, scalability, and in particular energy efficiency. In a two-dimensional ad hoc wireless network, the authors propose the optimal range forward (ORF) algorithm, which is based on the optimal transmission range to reduce the energy consumption of the network. Furthermore, the energy balance of each node based on the ORF algorithm is considered, and an optimal forward with energy balance (OFEB) algorithm is proposed to balance the residual energy of each node and to prolong the network lifetime. The authors compare the proposed algorithms with the existing GR algorithms, such as the most forward within radius and the nearest forward progress algorithms. The network lifetime, the network throughput, the number of packets successfully received by the destination and the average energy cost of each successfully received packet, resulting from all the algorithms mentioned above, are compared based on different node densities. It is shown that the performance of the OFEB algorithm is significantly better than the others.

In this paper, we aim to present a cooperative relaying based two way wireless communication scheme which can provide both spectral and energy efficiency in future wireless networks. To this end, we propose a novel network coding based Dynamic Spectrum Leasing (DSL) technique in which the cognitive secondary users cooperatively relay the primary data for two-way primary communication. In exchange for the relaying services, the primary grants exclusive access to the secondary users for their own activity. We model the random geometry of the ad hoc secondary users using a Poisson point process. We devise a game theoretic framework for the division of leasing time between the primary cooperation and secondary activity phases. We demonstrate that under these considerations and employing network coding, DSL can improve the number of bits that are successfully transmitted by 54% as compared to un-coded direct two way primary communication. Also the energy costs of the proposed DSL scheme are more than 10 times lower. Employing DSL also enables the cognitive users to get reasonable time for their own transmission after increasing the primary spectral and energy efficiency.

Our research study in this paper focuses on supporting differentiated resilience services in IP/MPLS-over-WDM networks with minimum resources while guaranteeing the quality in provisioned services (QoS) for subscribers. This has been achieved through our multilayer scheme which supports dynamic traffic grooming associated with constrained differentiated resilience. This scheme incorporates an intelligent adaptive heuristic approach and other traffic management mechanisms which solve multiple challenging problems: Differentiated multilayer dynamic traffic grooming based on connections granularity and priority, and connection admission control and wavelength assignment subject to multiple QoS and resilience constraints. We have implemented this scheme to evaluate its performance through conducting simulation experiments. The results demonstrate that our multilayer scheme can enable a network operator to significantly improve the utilization of resources in WDM networks as well as reduce the connection and bandwidth blocking probabilities of all supported traffic classes while guaranteeing their requirements in terms of QoS, resilience and optical physical impairments.

In this paper, we propose a novel mobile optical wireless (OW) system that employs for the first time beam delay adaptation, and makes use of angle and power adaptation in a line strip multibeam spot diffusing configuration in conjunction with an imaging receiver (BDAPA-LSMS). Our ultimate goal is to improve the bandwidth, reduce the effect of inter-symbol-interference (ISI), and increase the signal to noise ratio (SNR) when the transmitter operates at a higher data rate under the impact of multipath dispersion, background noise and mobility. An increase in channel bandwidth from 36 MHz, typical in a conventional diffuse system (CDS), to about 9.8 GHz can be achieved when our methods of beam delay, angle and power adaptation coupled with an imaging receiver are employed. At a bit rate of 30 Mbit/s our proposed BDAPA-LSMS achieves about 50 dB signal-to-noise ratio gain over conventional diffuse non-imaging systems. Moreover, our simulation results show that the proposed BDAPA-LSMS at a bit rate of 10 Gbit/s achieves about 32.3 dB signal-to-noise ratio at the worst communication path in the presence of background noise and mobility thus achieving a BER below 10-9.

In this paper we propose the use of renewable energy in IP over WDM networks to reduce the non-renewable energy consumption and consequently the CO2emission. A Linear Programming (LP) model and a novel heuristic, REO-hop, are developed for improving renewable energy utilization. The results show that the non-renewable energy consumption can be reduced by up to 73%. We also study IP over WDM networks with data centres and investigate the problem of whether to locate data centres next to renewable energy or to transmit renewable energy to data centres. Taking into account the electrical power transmission losses the results show that by optimizing the data centre locations such that the network's power consumption is minimized up to 71% of the network's power consumption can be saved.

In this paper we study the quality of service (QoS) and energy performance of the carrier sense multiple access with collision avoidance (CSMA/CA) based 802.11p scheme, and our previously proposed modified version of packet reservation multiple access (M- PRMA) scheme for a vehicle-to-roadside (V2R) network in a motorway environment. The simulation results illustrate the deficiency of the 802.11p protocol in providing adequate QoS to support real-time communication for varying vehicular traffic loads expected on the motorway. The significant amount of energy required for carrier sensing in the 802.11p is realised when compared to the low listening energy expenditure levels of the M-PRMA protocol. We compare both protocols under realistic (experimental) vehicular flow in a motorway and show that power saving up to 12 x can be achieved if a time division multiple access (TDMA) approach such as M-PRMA is used or if the CSMA/CA listening power is reduced.

In this paper we propose a low carbon emission IP over WDM network where renewable energy is used to reduce the CO2emissions at a given energy consumption level. We develop a Linear Programming (LP) model to minimize the non-renewable energy consumption of the network and propose a novel heuristic for improving renewable energy utilization. Compared with routing in the electronic layer, the results show that routing in the optical layer coupled with renewable energy nodes significantly reduces the CO2emission of the IP over WDM network by up to 94%, and the new heuristic introduced has little impact on the QoS. In order to identify the impact of the number and the location of nodes that employ renewable energy on the non-renewable energy consumption of the whole network, we also build another LP model. The results show that the nodes at the centre of the network have more impact than other nodes if they use renewable energy sources.

This paper derives and evaluates mathematical models for supporting differentiated availability services in WDM networks protected by shared backup path protection (SBPP) schemes. These models aim to enable network operators to allocate working and backup resources for dynamic IP traffic connections based on their priority and availability requirements. The resource allocation process is based on optimal trade-off between the amount of allocated backup resources and degree of service availability (quality-of-recovery (QoR)) required for traffic connections arriving dynamically. Using a probabilistic approach based on Markov chain process, mathematical models have been conceived to quantify service availability, disruption rate and blocking probability of M:N and 1:N SBPP schemes in WDM networks. These models have been analytically and through simulation evaluated in terms of network service availability, disruption rate, network utilization and blocking probability.

In this paper, we propose a novel optical wireless (OW) system that employs beam delay and power adaptation in a line strip multibeam spot diffusing configuration in conjunction with an angle diversity receiver (BDPA-LSMS). Our ultimate goal is to improve the signal to noise ratio (SNR), reduce the delay spread and increase the received optical power under multipath dispersion, background noise and mobility. A significant reduction in delay spread from 2.4 ns (conventional diffuse system CDS) to about 0.11 ns can be achieved when our methods of beam delay and beam power adaptation coupled with an angle diversity receiver are employed. Our simulation results show that the proposed BDPA-LSMS at a bit rate of 30 Mbit/s achieves about 13 dB signal-to-noise ratio (SNR) gain over a line strip multibeam system (LSMS). At the worst case scenario our proposed (BDPA-LSMS) system offers SNR improvement of 20 dB over CDS and 10 dB SNR gain over LSMS.

This paper studies how Rayleigh flat fading causes partitioning of wireless ad-hoc networks which already satisfy the connectivity achieving conditions under macro-scale log-normal shadowing. The devolving effects of fading are investigated by analyzing the network-wide link outage, time-based connectivity, node degree loss and average lifetime of emergent connected components. The study reveals that fading severely impairs the connectivity of sparser networks where the network connectivity rate drops to below 40%. Shadowing is found to immunize the network against the devolving effects of fading by introducing a link-diversity gain. A slight tolerance to the spatial connectivity requirement yields considerable gains in the network robustness against further partitioning; 90% of the network can be kept connected at 50% less node density or shadowing. A high rate of change of the graph structure is observed. This results in short component lifetime that exponentially decays with component size.

In this paper, a generalized phase spatial shift keying (GPSSK) modulation is introduced as an improvement of the generalized space shift keying (GSSK) modulation which lays the concept of using the antenna indices to convey information. The idea behind the proposed scheme is to map the bit vector corresponding to one symbol in two information bit blocks: the first block selects the antennas used during the transmission and the second block chooses the transmitted symbols, which are distinguished by their phases. The receiver estimates the indices of the active antennas and the transmitted signal which are used to de-map the block of information bits. To validate the results, an upper bound on the bit error rate (BER) of GPSSK is derived. Both the analytical and simulation results show that the proposed scheme provides performance gain and improved spectrum efficiency over GSSK with low detection complexity.

Over the last two decades, indoor optical wireless (OW) systems have operated typically at 30 Mbit/s to 155 Mbit/s. Here, we propose and evaluate for the first time a mobile OW system that operates at 5 Gbit/s and 10 Gbit/s. The improvements in data rates and channel bandwidth are achieved through the introduction of three approaches: angle diversity, beam angle and beam power adaptation. We propose a mobile OW system that employs beam angle and beam power adaptation in a line strip multibeam spot diffusing system configuration in conjunction with an angle diversity receiver (APA-LSMS) to mitigate the degradation due to ambient light noise, multipath dispersion and mobility. The performance of our proposed system was investigated through channel and noise modelling. Our results show that the proposed APA-LSMS at a bit rate of 30 Mbit/s achieves about 45 dB signal-to-noise ratio (SNR) gain over a power adaptive line strip multibeam system (PA-LSMS) and offers 60 dB SNR gain over a conventional diffuse system (CDS) at a 6 m horizontal separation between the transmitter and the receiver. The SNR is independent of the transmitter location and when our methods (angle diversity, beam angle and beam power adaptations) are implemented, the SNR can be maximized at the receiver for every transmitter location. The results show an increase in channel bandwidth from 36 MHz (CDS) to approximately 7.2 GHz in our proposed system (APA-LSMS). These improvements enhance our system and enable it to operate at higher data rates of 5 Gbit/s and 10 Gbit/s.

The spot-diffusing geometry is one of the attractive configurations considered in the literature. It provides a better signal-to-noise ratio (SNR) than the conventional diffuse system (CDS), but its SNR can be degraded due to mobility. Three methods: imaging reception, beam angle and beam power adaptation are introduced to the design of spot-diffusing OW systems to effectively mitigate the degradation due to mobility in the presence of ambient light noise and multipath propagation. In an imaging spot-diffusing system, the SNR is independent of the transmitter position and can be maximized at all receiver locations when our new methods (beam angle and beam power adaptation) are implemented. Regardless of the transmitter position, beam angle adaptation can target the spots at the optimum location that yields the best SNR at the receiver. A significant SNR improvement of 36 dB in the imaging spot-diffusing performance can be achieved when angle adaptation is introduced. Further SNR gain of 4 dB can be obtained if the power is adaptively distributed among the spots. Furthermore, an increase in the channel bandwidth from 43 MHz (non-imaging CDS) to 8.19 GHz can be achieved through the combination of these methods. The increase in channel bandwidth and SNR can enable the OW system to achieve higher data rates and 2.5 Gbit/s and 5 Gbit/s mobile OW systems are shown to be feasible.

In this paper, a pico-cellular airport traffic model is proposed which supports Engset distributed fresh call arrival process and General distributed handoff process with Dynamic Channel Allocation (DCA). The proposed model enables load balancing using DCA and uses a three-dimensional Markov chain to compute traffic congestion and call congestion for any kind of traffic streams, including Pure Chance Type-I (PCT-I) or Pure Chance Type-II (PCT-II). The application of the proposed model is illustrated in assessing indoor mobility to evaluate QoS parameters. The proposed airport traffic model is fairly general in the sense that it is not restricted by number of users, user mobility or range of offered load, and can be reduced to predict congestion for Poisson distributed fresh call arrival processes and General distributed handoff processes.

Energy consumption is one of the active research areas in wireless communication due to the limited battery attached to mobile devices. This paper describes an energy efficient network architecture for infrastructured wireless networks. The contributions of this paper are the study of a distributed localized algorithm for constructing Voronoi diagram followed by a network architecture based on Voronoi diagrams. This architecture is not only energy efficient but also has lower latency and higher throughput. In addition, it provides the benefits of randomization and scalability to the network. The simulation work has been carried out using network simulator (ns2.28) and the results consolidate our claim.

Mobility can induce significant signal-to-noise ratio (SNR) performance degradation in optical wireless (OW) systems based on diffuse as well as spot diffusing configurations. Two methods (beam angle and beam power adaptation) are introduced to the design of OW multibeam systems to effectively mitigate the mobility based performance degradation in the presence of ambient light noise and multipath propagation. Simulation results indicate that in an angle diversity spot-diffusing system, the SNR is independent of the transmitter position and can be maximized at all receiver locations when our new methods are implemented. A multibeam power and angle adaptive system (MBPAAS) offers a significant SNR improvement of 29 dB over the traditional line strip multibeam system (LSMS) at a transmitter-receiver separation of 6 m, when both systems employ an angle diversity receiver and operate at 50 Mbit/s. This SNR improvement can be useful in transmit power reduction. Furthermore, an increase in the channel bandwidth from 647 MHz (LSMS) to 5.57 GHz can be achieved when the new MBPAAS is employed. The increase in channel bandwidth and SNR can enable the OW system to achieve higher data rates and a 2.5 Gbit/s mobile OW system was shown to be feasible.

The application of Radio-over-Fiber (RoF) technology in cellular systems has attracted considerable attention in recent time. Consequently, the indoor personal communication systems (PCS) using the RoF architecture needs reinvestigation in performance domain. In this paper, we investigate such a system, which uses tiny cells (pico-cells) with limited number of users. We develop a corresponding traffic model for state dependent fresh call requests (Engset distribution) from limited user population. The model, in addition, considers frequent handoffs of users, which is not necessarily a memoryless random process. The model has a provision of channel reservation for handoff calls thereby prioritize the handoff process. The proposed model is computationally efficient and simple to implement. Further, it is effective to determine the optimum level of reservation in system design.

This study introduces a new concept of using data and storage management techniques to boost the reliability of challenged ad hoc and sensor networks by mitigating the effects of link and graph connectivity outages. Novel distributed uniform and multi-rate storage management approaches are proposed and through proper modeling of the stochastic disconnectivity patterns, network heterogeneity degrees, data resolution thresholds and various network design parameters, this work shows how these techniques can improve the overall network performance. Both analytical and simulation results are presented and various sensitivities are thoroughly investigated to give the network designer solid guidelines.

To enable the evolving trend of ubiquitous computing and multi-service support of next generation ad hoc and sensor networks this paper proposes a new concept of static and dynamic application-based heterogeneity and introduces STEPS; a mathematically-based distributed multi-rate storage and data management mechanism that dynamically responds to the stochastic temporal networks' disconnectivity pattern in order to preserve the network's functionality and data under challenged conditions. Through a probabilistic analysis of collaborative storage provisioning the paper explores the performance of STEPS by investigating storage outage, weighted storage outage and storage traffic patterns. Through both analytical formulations and simulation results STEPS is confirmed to perform better than other mechanisms that have been recently proposed.

The authors develop an integrated scheme that supports differentiated resilience services (DiffResServ) for dynamic provisioning in heterogeneous IP-over- wavelength division multiplexing (WDM) networks. By integrated, the authors mean that the provisioning mechanism takes into account network topology, resource and resilience information in both the IP and WDM layers. By dynamic, the authors mean that the establishment process of connections and lightpaths is based on the fact that the arrivals and departures of IP traffic connections are not known in advance. By heterogenous, the authors mean that the state routing algorithms function on the fact that optical nodes in WDM network may support different switching capabilities. This has been achieved through our proposed scheme which operates based on a dual link metrics (bandwidth,delay)routing algorithm inter-operating with efficient connections and lightpaths rerouting algorithms. A genetic algorithm is introduced to operate based on the solution space generated by this scheme in order to minimise the total cost of network operation. The authors have conducted simulations, where the results show that this scheme enables IP-over-WDM networks to guarantee the quality-of-service and resilience required for heterogenous traffic classes with effective and efficient allocation of network resources.

The focus in Green ICT (information and communication technology) is on software and hardware solutions to reduce energy consumption. Here the authors consider the design of vehicular ad hoc networks (VANETs) to reduce energy consumption because of communications. Based on a realistic transport traffic scenario on a motorway, ‘M4’ in UK, this study computes the energy consumption in a motorway ad hoc wireless network. This is based on a geographical adaptive fidelity (GAF) topology management protocol, where the energy consumption has been analysed for equal-grid, adjustable-grid and genetic algorithm models. Considering nodes in the VANET network and their transmission ranges, this study provides a network model to compute the energy consumption of VANETs and compare their energy efficiency performance. As a result, the proposed genetic algorithm model has been found to be more energy efficient than the adjustable-grid model which is better than the equal-grid model.

Orthogonal frequency division multiplexing with code division multiplexing (OFDM-CDM) is attractive for the next generation high-speed wireless systems due to the fact that the performance of OFDM-CDM systems can be considerably improved by employing a joint detection scheme such as the maximum likelihood (ML) detector. However, the complexity of the ML detector increases rapidly as the number of orthogonal spreading codes and/or the number of bits per modulation symbol increase. In this study, the authors introduce a unified detection model and propose two hybrid detectors, which combine zero forcing (ZF) with successive interference cancellation (SIC) and sphere detection (SD) algorithms, respectively. After obtaining the initial solution from the front-end ZF receiver, the proposed back-end algorithms are adopted to extend the potential solution list and search for the final result. The objective is to utilise the combination of a simplified linear equaliser and a comprehensive detection scheme to achieve enhanced performance and offer alternatives to the more complex and channel-estimation-sensitive minimum mean squared error (MMSE) scheme. The results show that the proposed hybrid detectors are able to achieve superior performance compared to the MMSE scheme and provides a significant performance improvement compared to the conventional OFDM counterpart.

Mobility can induce significant signal-to-noise ratio (SNR) performance degradation in optical wireless (OW) systems based on diffuse as well as spot-diffusing configurations. Two methods (beam angle and beam power adaptation) are introduced to the design of OW multibeam systems to effectively mitigate the mobility-based performance degradation in the presence of ambient light noise, multipath propagation, and shadowing. Simulation results indicate that in an angle diversity multibeam system, the SNR is independent of the transmitter position and can be maximized at all receiver locations when our new methods are implemented. A multibeam power and angle adaptive system (MBPAAS) offers a significant SNR improvement of 29 dB over the traditional line strip multibeam system (LSMS) at a transmitter-receiver separation of 6 m, when both systems employ an angle diversity receiver and operate at 50 Mbit/s. This improvement comes at the cost of complexity. The complexity can be reduced by increasing the beam angle adaptation step size from 2.3° to 26.6° resulting in a typical search time reduction from 12.5 ms to 80 μs when our modified MBPAAS replaces the main MBPAAS. However, a power penalty of 11.7 dB at receiver locations near the room edges and 1.3 dB elsewhere can be induced. An increase in the channel bandwidth from 647 MHz (LSMS) to 5.57 GHz can also be achieved when the two new methods (beam angle and beam power adaptation) are implemented. The increase in channel bandwidth and SNR can enable the OW system to achieve higher data rates and 2.5 Gbit/s and 5 Gbit/s mobile OW systems are shown to be feasible. Furthermore, simulation results prove that our modified MBPAAS can sufficiently combat shadowing and signal blockage.

In this paper, a novel beam power adaptation method is proposed, studied and shown to be a desirable means for improving the performance of an optical wireless (OW) system that operates under the constraints of background noise, multipath dispersion, and mobility. We propose and evaluate a new OW configuration that employs an adaptive beam clustering method (ABCM) in conjunction with diversity detection. Our goal is to reduce the effect of transmitter/receiver mobility and the associated impacts in terms of a weak received optical power and reduction in bandwidth. Previous work has shown that multiple spot diffusing techniques suffer from these two fundamental limitations associated with mobility. Our new ABCM can help overcome the impairments introduced by mobility, introduce gain in the received optical power, and increase bandwidth even at large transmitter and receiver separations. Our results indicate that, at the least successful locations, the ABCM system can reduce the signal delay spread by nearly a factor of twenty and enhance the SNR by almost 15 dB over a line strip multibeam system (LSMS). We also incorporate the concept of relaying into the Adaptive line strip multibeam system and prove that this technique can lead to considerable performance improvements.

Abstract Due to the dynamic nature of vehicular networks, provisioning multimedia (triple play—video, voice and data) communications to motorway drivers with quality of service (QoS) is extremely challenging. To overcome the challenges in this scenario, substantial effort is required to analyse the characteristics of vehicular traffic profiles on motorways around a base station (BS). For this purpose, we first perform detailed analysis of real vehicular traffic data taken from inductive loops on a motorway, and then develop our own vehicular simulator to study real‐time vehicular traffic scenarios where a main BS is responsible for multimedia communication. To address the issue of maintaining QoS for different traffic classes in reservation‐based medium access control (MAC) protocols in high‐speed vehicles, a novel medium access control, PC‐MAC (pico cellular medium access control) protocol is introduced. The proposed PC‐MAC protocol is a combination of carrier sense multiple access (CSMA) and slotted time division multiple access (S‐TDMA) for multimedia communication with optimal utilization for a motorway environment. Finally, the access to the BS is managed by our proposed PC‐MAC protocol that we have integrated into the vehicular simulator. The results of this configuration have been compared with other protocols. Copyright © 2009 John Wiley & Sons, Ltd.

Nodes in energy-efficient ad-hoc wireless networks can benefit more of new ad-hoc services, as well as, can support better new emerging ad-hoc applications. In this paper, we introduce an approach to achieve the energy efficiency based on both optimal transmission range and topology management of ad-hoc wireless networks. We derive the relationship between the optimal transmission range (optimal grid length) and different intensities of static network traffic in the equal-grid rectangular GAF (the geographical adaptive fidelity topology management protocol) network and implement this result into dynamic network traffic scenario with adjustable-grid rectangular GAF network to achieve the energy efficiency. Then we compare the energy consumption result of adjustable-grid model to the result of traditional GAF model (equal-grid), which is derived in the same dynamic traffic scenario.Our results show that the adjustable-grid model saves 78.1% energy in comparison to the minimum energy consumption of equal-grid model.

For data dissemination using vehicular ad hoc networks (VANETs), it is essential to determine the end-to-end (e2e) delay, the packet dropping probability (PDP), the number of vehicles required, and the size of the vehiclespsila buffers needed to hold packets. In this paper, we study the impact of the above mentioned parameters and report original simulation results in a typical city scenario based on a 3x3 Manhattan grid. In addition, we also study the efficiency of our approach under varying degrees of market penetration of instrumented vehicles, hence establishing useful thresholds in realistic scenarios. Finally, by introducing different configurations of drop boxes, we show significant reduction in e2e delay and PDP.

In this paper, we propose and evaluate a novel optical wireless (OW) configuration that employs a two dimensional adaptive beam clustering method (2DABCM) in conjunction with imaging diversity receivers. Our goal is to reduce the effect of intersymbol interference and to improve the signal-to-noise ratio (SNR) when the system operates under the constraints of background noise (BN) and multipath dispersion. In the conventional diffuse system, an SNR improvement of 22 dB and an increase in the bandwidth from 38 MHz to 200 MHz approximately, is achieved when an imaging receiver is implemented. Furthermore, the new methods introduced (transmit power adaptation, beam clustering, and diversity imaging) increase the bandwidth from 38 MHz to 5.56 GHz. Previous optical wireless systems operated typically at 30 to 100 Mbit/s and here we report a system that operates at 2.5 Gbit/s. Our results indicate that the new 2.5 Gbit/s 2DABCM transmitter with a new imaging diversity receiver (with select best (SB)) demonstrates an SNR improvement of 16 dB over the non-imaging CDS system operating at 30 Mbit/s. The results also show that the proposed system (imaging 2DABCM at a bit rate of 2.5 Gbit/s) produces an SNR improvement of 10 dB when maximum ratio combining (MRC) replaces SB.

Most nodes of ad-hoc wireless networks are battery-powered, therefore the energy capacity limit is one of the critical constraints of ad-hoc wireless networks' development. This paper evaluates a rectangular network model that achieves energy efficiency by optimizing the node radio range based on the Geographical Adaptive Fidelity (GAF) topology management protocol [1]. For the first time we derive the optimal transmission range in a new adjustable-grid model and analyze both static and dynamic traffic scenarios in both equal-grid and adjustable-grid rectangular GAF models, where the results show that the adjustable-grid model is more energy efficient.

In order to provision data messages to vehicular drivers in an ad hoc network setting, it is essential to determine the end-to-end (e2e) delay, number of vehicles required, and the size of the vehicles' buffers needed to hold packets. In this paper, using vehicular ad hoc networks (VANETs) in a typical city scenario based on a 3x3 km Manhattan mobility model, we have studied the impact of the aforementioned parameters and original simulation results are reported. We have also studied the effectiveness of our approach under varying degrees of market penetration of instrumented vehicles, hence establishing useful thresholds in realistic scenarios. Furthermore, by introducing different configurations of drop boxes, we have shown that the packet dropping probability (PDP) and e2e delay can be significantly reduced.

Provisioning multimedia (triple play - video, voice and data) communications to motorway drivers with quality of service (QoS) is challenging due to the dynamic nature of the environment in which they operate. To overcome the challenges in this scenario, substantial effort is required to analyse the characteristics of vehicular traffic profiles on motorways around a base station (BS). For this purpose, we first perform an analysis of real vehicular traffic data taken from inductive loops on a motorway, and then develop our own vehicular simulator to study real-time vehicular traffic scenarios where a main BS is responsible for multimedia communication. To address the issue of maintaining QoS for different traffic classes in reservation-based medium access control (MAC) protocols in high-speed vehicles, a novel medium access control, PC-MAC (pico cellular medium access control) protocol is introduced. The proposed PC-MAC protocol is a combination of carrier sense multiple access (CSMA) and slotted time division multiple access (S-TDMA) for multimedia communication with optimal utilisation for a motorway environment. Finally, the access to the base station is managed by our proposed PC-MAC protocol that we have integrated into the vehicular simulator. The results of this configuration have been compared with the modified packet reservation multiple access (M-PRMA) protocol.

With multimedia (voice, video and data) services required irrespective of time, location and situation, airports are considered to be a major application area which require extremely advanced adaptive computing and communication systems. However, providing users with mobile, secure and reliable communication is extremely challenging due to the dynamic nature of the environment and travellers' own behaviour. The aim of The INtelligent Airport (TINA) project is to develop a new seamless wireless/wired infrastructure able to provide ubiquitous connectivity to users in this environment. In this paper, we model the teletraffic based on passenger flow and the number of users and their applications in each cell while considering both spatial and temporal traffic variations. Having base stations responsible for the access of the channel, we evaluate the performance of our airport model by using our proposed modified packet reservation multiple access (M-PRMA) protocol [1].

Multihomed vehicular mobile networks (NEMOs) require an intelligent route control (IRC) scheme which can enable them to select a routing path that guarantees high quality of communications with correspondent nodes, as well as use the maximum available bandwidth of wireless and radio technologies connecting them to Internet. In this paper, we develop a two-level intelligent route control scheme which enables multi-homed NEMOs to optimally distribute traffic among their mobile routers' egress interfaces based on a specific mobile routing policy, traffic connections scheduling and routing path performance metrics. The proposed IRC scheme is envisioned to be integrated in the control and management planes of mobile networks. Simulation experiments show that our proposed IRC scheme can improve the CWND of TCP and improve the e2e packet loss of video traffic despite network mobility.

Among the different wireless solutions, ultra-wide band (UWB) is a promising technology for in-car communications because of its high data rates. To optimise the UWB radio system design, knowledge of the propagation channel within the car is required. The performance of a high-speed 480 Mbps UWB radio system is studied within a real in-car environment measured under mobility. A comprehensive set of measurements is presented, including several possible non-line of sight scenarios while the vehicle is stationary and mobile, for open- and closed-window environments and with/without occupants. These measurements are used to characterise the in-car channel and evaluate the performance of a typical UWB radio system in this setting.

Previous indoor mobile optical wireless systems operated typically at 30 Mbit/s to 100 Mbit/s and here we report on systems that operate at 2.5 Gbit/s and 5 Gbit/s. We are able to achieve these improvements through the introduction of three new approaches: transmit beam power adaptation, a two dimensional beam clustering method (2DBCM), and diversity imaging. Through channel and noise modeling we evaluated the performance of our systems. The performance of a novel optical wireless (OW) configuration that employs a two dimensional adaptive beam clustering method (2DABCM) in conjunction with imaging diversity receivers is evaluated under multipath dispersion and background noise (BN) impairments. The new proposed system (2DABCM transmitter with imaging diversity receiver) can help reduce the effect of intersymbol interference and improve the signal-to-noise ratio (SNR) even at high bit rate. At a bit rate of 30 Mbit/s, previous work has shown that imaging conventional diffuse systems (CDS) with maximal ratio combining (MRC) offer 22 dB better SNR than the non-imaging CDS. Our results indicate that the 2DABCM system with an imaging diversity receiver provides an SNR improvement of 45 dB over the imaging CDS with MRC when both operate at 30 Mbit/s. In the CDS system, an increase in bandwidth from 38 MHz (non-imaging CDS) to 200 MHz approximately, is achieved when an imaging receiver is implemented. Furthermore, the three new methods introduced increase the bandwidth from 38 MHz to 5.56 GHz. At the least successful receiver locations, our 2.5 Gbit/s and 5 Gbit/s imaging 2DABCM systems with MRC offer significant SNR improvements, almost 26 dB and 19 dB respectively over the non-imaging CDS that operates at 30 Mbit/s.

Three methods (transmit power adaptation, imaging reception, and Multicarrier Code Division Multiple Access (MCCDMA)) are introduced to the optical wireless (OW) system and a significant improvement is achieved in the presence of very directive noise, multipath propagation, mobility, and shadowing typical in a real indoor environment. In the absence of shadowing, replacing a single non-imaging receiver by an imaging receiver with maximal ratio combining (MRC) improves the signal-to-noise ratio (SNR) by 20 dB in a conventional diffuse system (CDS) operating at 30 Mbit/s at a transmitter-receiver separation of 6 m in agreement with previous results in the field. Further SNR improvement of 24 dB is achieved when a line strip multi-beam system (LSMS) replaces the CDS when both systems employ an imaging MRC receiver. Furthermore, our new adaptive LSMS (ALSMS) system coupled with the imaging MRC receiver offers an SNR improvement of 23 dB over the imaging MRC LSMS illustrating the gain achieved through adaptation. The results also show that combining transmit power adaptation with spot diffusing (i.e. ALSMS) coupled with an imaging receiver based on select best (SB) increases the bandwidth from 46.5 MHz (non-imaging CDS) to 7.53 GHz thus enabling the OW system to achieve higher data rates and provide multi-user capabilities in our case by employing a MC-CDMA scheme. In a 10 user MC-CDMA OW system, a bit error rate (BER) improvement from 4.9 times 10-1to 2.1 times 10-5is achieved when the imaging MRC ALSMS system replaces the imaging CDS in a shadowed environment.

In this paper, we introduce a mobile optical wireless (OW) multicarrier - code division multiple access (MC-CDMA) system that employs a new adaptive line strip multibeam system (ALSMS) with diversity detection. Our results indicate that a significant improvement in the bit error rate (BER) can be obtained in the presence of very directive noise, multipath propagation and shadowing typical in a real indoor environment. With transmitter and/or receiver mobility, ALSMS can improve the BER performance by almost 10-5with 2 active users, and increase the signal-to-noise ratio (SNR) by more than 13 dB compared to the unadaptive LSMS.

We propose a novel optical wireless (OW) system based on power adaptive multi-beam spot diffusing transmitter serving multiple 7-segment MRC angle diversity receivers. A feedback link is assumed between the transceivers so that the receiver conveys to the multi-beam transmitter the new beams transmit power weights to be used in order to achieve the best signal quality at a given receiver location. The performance of a sample case of three receivers placed in different configurations in the room is evaluated in terms of signal-to-noise ratio (SNR) and is compared with the single receiver scenario with and without a power adaptation. In the presence of one receiver, the transmit spot powers can be adjusted for optimum performance at that receiver location. For multiple receivers, there is conflict and we propose spot power adaptation based on the average requirements (power distribution in spots), i.e., EGC of spot power or MRC combining of spot powers. The results showed that the three receivers benefit most from an adaptive transmitter when each is placed at a corner of the room. In this case, as much as 2.8 dB increase in SNR is achieved for all three receivers at the corners. Moreover, a considerable SNR gain (1.8 dB) is also obtained when all receivers lie directly under the line of diffusing spots. Although the performance of the collaborative transmitter when all three receivers were located near room wall produced very minimal improvement, none of the receivers suffered any decrease in SNR.

The received signal quality in indoor optical wireless (OW) systems is partly influenced by the change in receiver location relative to the optical transmitter. Employment of an angle diversity receiver counters signal degradation caused by background noise sources. While spot diffusing transmitters have been shown to produce better performance over the conventional full diffuse transmitters, transmit power distribution among the multiple beams, in studies to date, takes no account of the change in the transmitter-receiver separation especially when both are fully mobile. We investigate the performance of two new spot diffusing geometries based on clustering of spots on ceiling and walls. The performance is evaluated for both stationary and mobile transmitters in conjunction with diversity detection and is compared with that of the single line strip optical wireless system. Furthermore, single spot power adaptation is carried out on both systems and the discussion of the results highlights the signal-to-noise ratio (SNR) gain in comparison to the single line strip. The results show that while the adaptive transmit power approach achieved as much as 2dB increase in SNR for the single line, the one- plane configuration achieved a 5.7dB SNR gain near corners without power adaptation and 15.8dB with adaptation over the single line strip. The two-plane approach improved the SNR around the room centre (at the locations of the noise sources) by 5.2dB without adaptation and 11.6dB with the adaptive approach compared to the single line for both cases. Moreover, both configurations maintain the same improvement pattern when the transmitter is mobile.

Multicarrier code division multiple access (MC-CDMA) combines some of the desirable feature of orthogonal frequency division multiplexing (OFDM) and CDMA in that it offers multiple access facilities at a reduced channel rate. In this paper, the channel characteristics of mobile infrared links have been modelled in a highly impaired environment in the presence of windows, office cubicles, bookshelves, and shadowing. We introduce an adaptive line strip multibeam system (ALSMS) in conjunction with diversity detection and show that it dramatically improves the SNR performance of infrared links in the presence of very directive noise and shadowing. Our results indicate that, the mobile MC-CDMA ALSMS system with an angle diversity receiver offers a significant performance improvement including a reduction in the background noise (BN) effect, a strong received power, reduction in delay spread, and improvement in the SNR over the mobile MC-CDMA LSMS system in the poor communication environment considered. Furthermore, the OW MC-CDMA system operates at a channel rate lower than that associated with OW CDMA systems and we demonstrate the performance improvement obtained in a real OW environment in the presence of transmitter and receiver mobility.

To provision various multimedia communication services with guaranteed quality to motorway drivers and future autonomous vehicles, substantial work is required to analyze the characteristics of vehicular traffic profiles on the motorways. To this end, in this paper, we first analyze some real vehicular traffic data taken from an inductive loop on the motorway 'M4' in Wales over the last 5 years, and then developed our own simulator to simulate various vehicular traffic scenarios where vehicles access a wireless local area network (WLAN) base station (BS) to send or receive multimedia traffic. The access to the base station is managed by a modified version of the packet reservation multiple access (PRMA) protocol (Goodman, 1989) which we have integrated into the simulator. Finally we introduce an analytical model for this medium access control (MAC) protocol to evaluate the quality-of-service (QoS) required for multimedia traffic.

Multicarrier code division multiple access (MC-CDMA) is a transmission scheme that combines the robustness of orthogonal modulation with the flexibility of CDMA schemes. It can lower the symbol rate and is therefore suited to the bandwidth limited optical wireless indoor channel. In this paper, new work is presented for an optical wireless (OW) system that utilizes MC-CDMA to improve the bit error rate (BER) performance. Our results indicate that at a BER of 10-4a 7 dB SNR improvement is obtained by a 4 user MC-CDMA OW system compared to a single user OW OOK system. This improvement is obtained while enabling multi-user communication. The performance degrades gradually as the number of users increases due to the increase in multiple access interference (MAI). A consistent BER performance is achieved for all receiver positions in a line strip spot-diffusing transmitter system (LSMS) with an angle diversity receiver, whereas a fluctuating BER performance is obtained in a conventional diffuse optical wireless system (CDS).

The separating distance between the transceivers is one of the main factors that affect the quality of the received optical signal as the receiver changes locations in an optical wireless (OW) system. A beam clustering method was proposed to improve the indoor OW channel's performance by combating the degrading effects of multipath reflections. The method involved transmitting binary data bits over two other clusters of beams aimed at walls in addition to the one aimed at the ceiling. In this work, we investigate a novel approach to further improve the signal quality on reception using a proposed adaptive transmitter composed of three spot diffusing sub-transmitters aimed at the same three directions as in the beam clustering method. The receiver communicates with the transmitter and sends tap weights (for transmit powers) to be used by the sub-transmitters which optimises the signal reception based on the initial received pulses at different locations. Performance comparison with results of a non adaptive transmitter system is presented in terms of signal-to-noise ratio (SNR), delay spread (DS) and path loss distributions for two receiver types: 1) a single detector wide field-of-view (FOV) receiver and 2) a multi-detector angle diversity receiver. Our results show a significant improvement achieved with an SNR gain of 18 dB compared with the conventional diffuse system and a 6 dB SNR gain without transmitter adaptability. Therefore, at the expense of moderate computations, the use of an adaptive multi-beam clustering transmitter is promising and can enhance the optical signal reception to suit user mobility requirements.

In this paper, we discuss and evaluate our two metro wavelength division multiplexing (WDM) ring network architectures for variable-length packet traffic. The paper begins with a brief review of the relevant architectures and protocols in the literature. Subsequently, the network architectures along with their medium access control (MAC) protocols are described. Performance for the two network architectures is studied using both simulation and Markovian modeling approaches with the help of their results for queuing delay, node throughput and proportion of packet dropped. Performance for the network is evaluated under symmetric and asymmetric traffic scenarios with Poisson and self-similar traffic.

An adaptive transmission scheme using variable-length spreading sequences (VLSS) is proposed. The system is based on an impulse direct sequence ultra-wideband (DS-UWB) approach for wireless communication where the number of active users is variable. In contrast to the conventional DS-UWB system, which employs a fixed length spreading code, the proposed system changes the length of spreading code according to the system load adaptively, which is proven to be able to reduce the inter-chip interference, inter-symbol interference and multiple-access interference and thus improve the system performance in terms of bit error rate. The proposed system is simulated in multipath channels with a high level of multipath fragments, modelled by the standard IEEE 802.15.3a indoor channel model 1 (CM1) and channel model 2 (CM2). Numerical results demonstrate that when RAKE receivers are employed, the proposed VLSS DS-UWB system outperforms the conventional system by appropriately allocating the spreading sequences.

This paper proposes two metro Wavelength Division Multiplexing (WDM) ring network architectures for variable size packet traffic. Firstly, it presents the network architectures and describes their medium access control (MAC) protocol. Secondly, it evaluates and compares the performance of the modified and original architectures, presenting results for throughput, queuing delay, packet dropping probability and global delay. Finally, it analyses and explains the results.

As storage area networks (SANs) are increasingly replacing traditional direct-attached storage (DAS) in many large data centers, many studies are considering extending SANs over large distances. SANs in a metropolitan wavelength-division multiplexing (WDM) scenario create asymmetrical traffic and hot-node scenarios. This paper proposes a sectioned WDM metropolitan ring network as a suitable extension for SANs. Two node architectures are considered, one uses two fixed transmitters and the other uses a tuneable transmitter. A tunable receiver is used with both architectures. For the two fixed-transmitters node architecture, two versions of medium access control (MAC) protocol are introduced. Simulation is carried out under both symmetrical and asymmetrical traffic sources. Performance of the sectioned ring is compared with that of the SAN ring network architecture proposed in [1].

This paper considers the steady-state solution of Continuous Time Markov Chains (CTMCs). CTMCs are a widely used formalism for the performance analysis of computer and communication systems. A large variety of useful performance measures can be derived from a CTMC via the computation of its steady-state probabilities. However, CTMC models for realistic systems are very large. We address this largeness problem in this paper by considering parallelisation of implicit methods. In particular, we consider a modified form of Multi- Terminal Binary Decision Diagrams (MTBDDs) to compactly store CTMCs, and, using Jacobi iterative method, we present a parallel method for the CTMC steady-state solution. Employing a 24-node processor bank, we analyse our parallel implicit method using the experimental results for three widely used CTMC benchmark models, with well over a billion states and sixteen billion transitions.

Performance comparison and evaluations for indoor optical wireless systems in three different environments are carried out. Channel characteristics of infrared links have been evaluated under various conditions, including an empty room, a room with glass windows and a door, and a room that has very strong shadowing effects caused by mini cubical offices. The corresponding results have been analyzed and compared for conventional hybrid/diffuse systems (CDS/CHS) and line strip multibeam transmitter systems (LSMS) that use spot diffusing techniques. Eight directive lamps represented the ambient light noise and allowed further signal impairments to be taken into account. Under these conditions, our results indicate that LSMS can reduce pulse spread by a factor of 11 and 30 lower than the delay spread associated with CDS and CHS, respectively. Furthermore, LSMS links can increase the SNR by more than 50 dB and about 55 dB compared to the CDS and CHS, respectively.

The paper presents and evaluates a novel optical wireless configuration that employs multibeam transmitters in conjunction with direction diversity receivers. Such a configuration overcomes the drawbacks and combines the advantages of both types of optical wireless links including line-of-sight and diffuse links. We present an investigation of the effect of this configuration on the optical channel over the entire communication floor considering two important channel parameters, received power and delay spread. A multibeam transmitter placed on the communication floor was adopted to produce multiple diffuse spots in the middle of the ceiling in the form of a line strip. The results show that a high-received signal power, when the system operates under the constraints of background noise and multipath dispersion, can he obtained by using the proposed line strip multibeam transmitter (LSMT). Furthermore, with only three branch diversity, the proposed system gives about 23 dB SNR improvement over the conventional diffuse system.

Channel characteristics of mobile nondirected diffuse optical wireless communication under the constraints of multipath dispersion and ambient light noise have received little attention to date. This paper presents an original study of transmitter motion and diversity receivers and their effects on the system performance for both conventional diffuse systems (CDS) and line strip multispot diffusing systems (LSMS). Under these conditions, simulation results show that high-received signal power can be obtained by using a LSMS in conjunction with a composite receiver consisting of seven branches. Furthermore, under ambient noise corruption, LSMS provides signal-to-noise ratio (SNR) improvements of more than 30 dB over the conventional nondirected diffuse system at the worst communication link. Moreover, we evaluate the effect of path loss on the proposed system and it is confirmed that the path loss is reduced by more than 6 dB over the CDS.

High-speed nondirected optical wireless (OW) transmission is greatly desired for freedom of user mobility. In a mobile infrared wireless environment, it is difficult to maintain a signal-to-noise ratio (SNR) sufficient to support low error probability using the conventional diffuse optical wireless systems. We propose a novel beam clustering method (BCM) based on a line strip multibeam transmitter system (LSMS) combined with a diversity receiver and examine its performance under adverse conditions such as multipath dispersion and background noise. The BCM consists of three sets of spots aimed at different directions. BCM design, multipath dispersion, ambient light interference, and diversity receiver design are discussed. We investigate and compare the impact of user mobility on the performance of OW links for both BCM and conventional diffuse system (CDS). Simulation results for the BCM link characteristics are presented and comparison is made with CDS. Our results indicate that at the worst conventional communication link, BCM can substantially reduce the signal delay spread by nearly a factor of six and increase the SNR by more than 30 dB over the CDS.

In this letter, we propose and evaluate a novel optical wireless configuration that employs a multibeam transmitter in conjunction with a narrow field-of-view direction diversity receiver. Such a configuration overcomes the drawbacks and combines the advantages of both types of optical wireless links, including line-of-sight and diffuse transmission. A multibeam transmitter placed on the communication floor was adopted to produce multiple diffusing spots on the middle of the ceiling in the form of a line strip. The design goal is to reduce the effect of intersymbol interference and to improve the signal-to-noise ratio (SNR) when the system operates under the constraints of background noise and multipath dispersion. Simulation results show that our line strip multibeam transmitter (LSMT) with only three branches diversity gives about 23 dB SNR improvement over the conventional system. The results also show that the multipath dispersion, which induces pulse spread, is significantly reduced when the LSMT with diversity detection is used.

In this letter, the performance of an indoor optical wireless spot-diffusing system using various multibeam transmitter configurations, in association with direction diversity and combining techniques, is assessed and compared under the impact of multipath dispersion and ambient light noise through theoretical analysis and computer simulation. Computer simulation for three different multibeam transmitter configurations and a conventional diffuse transmitter is carried out. Diversity receiver and wide field-of-view (FOV) receiver configurations are evaluated in conjunction with the proposed configurations. For the diversity-detection case, a receiver comprising an array of narrow FOV detectors (three and seven segments) oriented in different directions is used to maximize the collected signals and minimize noise. A novel line-strip multibeam system (LSMS) is investigated with single and diversity receiver configurations, and is compared with other spot-diffusing methods. Combining schemes, including selection combining, maximum ratio combining, and equal gain combining are employed for the presented configurations. Our results indicate that the performance improvement obtained through the use of LSMS with a three-direction diversity receiver is about 20 dB signal-to-noise ratio enhancement over the conventional diffuse system, and 26 dB when combining techniques are used. Root mean square delay-spread performance for the proposed configurations, at different positions on the communication floor, are also evaluated and compared.

Background noise and multipath propagation are the major impairments in indoor optical wireless links. They can introduce heavy distortion in the received optical signal and can degrade the system performance. In this paper, we investigate these effects employing a novel triangular pyramidal fly-eye diversity receiver (PFDR). Original results for fully diffuse optical wireless links that utilize PFDR are presented. Impulse responses and background noise collected on the PFDR faces at various locations on communications floor are evaluated. It is demonstrated that through PFDR field-of-view optimization the directional background interference can be reduced and that the received pulse shape can be improved. Results show a marked improvement in the probability of error when the optimization is done. Moreover, system performance improvement over the conventional diffuse system can be achieved.

The paper proposes an original wavelength-division multiplexing slotted-ring network architecture with nodes that use one fixed transmitter and fixed receivers. It is shown, through theoretical predictions and simulation results, how a simple slotted medium access control protocol can be implemented to achieve fairness between access nodes and efficient bandwidth utilization when used in a metropolitan access network. Performance for both source and destination stripping schemes has been analytically derived and simulated with a realistic self-similar traffic model. A modified node architecture using a tunable receiver has also been considered and the impact of receiver collisions has been evaluated and analyzed. Finally, the effect of using unbalanced traffic sources has also been analyzed and simulated.

Optical wireless (OW) systems are generally impaired by multipath propagation and directional interference in the form of background noise. We present original results for a fully diffuse OW system that employs a novel triangular pyramidal fly-eye diversity receiver (PFDR). The received pulse shapes are evaluated at various locations on the communication floor and the background noise collected on the three faces of the pyramid is determined. It is demonstrated that, through optimization of the PFDR field-of-view, the directional background interference can be reduced and that the received pulse shape can be improved. The computed error probability shows a marked improvement when our optimized PFDR antenna is used instead of the conventional photodetector used in traditional diffuse optical wireless systems.

An estimation algorithm with improved robustness is presented for the class of linear channels that can be modelled by an autoregressive (AR) model. It combines features of two previously developed concepts: the finite correlation LMS (FCLS) and dynamic based deconvolution model (DBD). The new correlation DBD (CDBD) exploits the projection properties of the FCLS, leading to enhanced performance, as well as the FCLS correlation properties, leading to noise robustness, with the high adaptation performance of the DBD. Results are shown for uncoded and chaotic coded signals, where chaotic coding is achieved using the logistic map. The later is easy to implement in real time applications. The sensitivity of the CDBD to model uncertainties is addressed and it is shown that these do not influence its performance significantly.

This article proposes a WDM slotted-ring network architecture. Used as a metropolitan access network, it is shown through theoretical predictions and simulation results how a simple MAC protocol can be implemented to achieve fairness between access nodes and efficient bandwidth utilization. In the paper it is shown that the MAC protocol efficiency grows with the number of nodes in the network - a very attractive feature in the metropolitan market. Simple theoretical equations allow for easy provisioning of the network size and scalability. These were validated by discrete-event simulations using realistic traffic sources. The original set of simulation results using a source-stripping scheme are then compared with an improved implementation where destination-stripping is used. Finally, the impact of receiver collision is studied and a solution to this problem is presented.

A novel chaotic-based coding/decoding strategy that exploits radial basis function (RBF) artificial neural networks (ANNs) in a dynamic feedback (DF) configuration is reported. The ANNs are used as pseudochaotic carrier generators and as estimators for the received signal. The dynamics approximated were those of the logistic map (LM). This approach is compared with established methods that employ inversion, dynamic feedback, and least mean square (LMS) and recursive least squares (RLS) estimation. Our RBF-ANN-DF approach is shown to outperform these methods in terms of the recovered signal SNR at various channel SNRs with a speech information signal used as an example. In particular, the RBF-ANN-DF method is shown to outperform DF approaches by about 33 dB at all channel SNRs. Moreover, the proposed RBF-ANN-DF approach offers a recovered signal SNR improvement between about 15.1 and 27.4 dB for channel SNRs between 10 and 50 dB as compared to an LMS-based chaotic receiver. As a by-product, we have also shown that, for the logistic map, LMS- and RLS-based chaotic receivers are equivalent and, hence, the use of LMS-based receivers can result in implementation savings.

Wavelength conversion (WC) has recently emerged as an important technique that can be used to manage the spectacular increase of traffic in DWDM networks. WC is extremely useful for solving contention and reducing wavelength blocking and a wide range of WC methods have been reported. The optimum placement of these devices within a network remains an unexplored area and accurate models to measure the performance of the system are becoming vital. This paper presents an original noise characterisation of a class of WCs based on cross gain modulation (XGM) in semiconductor optical amplifiers (SOAs). A new expression for the error probability (P/sub e/) is presented offering considerable additional accuracy in sensitivity measurement compared with the Gaussian approach. Simulation comparisons are presented in different scenarios for a standard system working at 2.5 Gb/s in a metropolitan area network.

This article considers a WDM slotted-ring network architecture. Used as a metropolitan access network, it is shown through simulation results how a simple MAC protocol can be implemented to achieve fairness between access nodes. Excellent queuing delay and packet dropping probability results are obtained assuming that a maximum load threshold is not exceeded. Further developments are proposed to improve the efficiency, introduce congestion avoidance mechanisms and add QoS capabilities by implementing intelligence within the network access nodes.

The proposed system introduces a new approach to chaotic-based signal transmission and blind channel estimation. It is now well known that channel estimators based on FIR-digital adaptive-filters (FIR-DAF) approach the upper bound to their performance when driven by samples of chaotic signals. A fixed chaotic-system parameter is assigned to every m-valued information symbol and thus after symbol detection the chaotic sequence can be reconstructed. Assuming proper symbol synchronisation, the complete transmitted sequence (which is in general deteriorated by noise) can be reconstructed and employed as drive signal for the blind channel estimation algorithm. The performance of the proposed system is evaluated for a channel with low pass characteristics and a 10 MHz bandwidth. Channel estimation is carried out using the finite correlation least squares (FCSL) algorithm recently introduced by the authors.

Channel estimation is conventionally practically implemented using the least mean squares (LMS) algorithm due to its simplicity. This approach can significantly be impaired by channel noise and adaptation can be slow if the drive signal is correlated. We present a combined projection and correlation least mean squares (CPCLS) algorithm based on our former proposed finite correlation algorithm. These attributes speed up adaptation and result in robust estimation in the presence of noise respectively.

This paper proposes an efficient time-varying step-size adaptation algorithm implemented within an in-service non-intrusive measurement device (INMD) in public switched telephone networks (PSTNs). The adaptation step-size is obtained from the correlation of the input speech signal. The effect of the correlation method is described and the variable step-size is derived. The in-service non-intrusive measurement system of interest is used to monitor the delivered quality of service (QoS) by monitoring the echoes in the telephony network INMDs are usually based on a class of least mean square (LMS) digital adaptive filters (DAFs). The performance criterion is defined by the modelling convergence rate derived from the optimal Wiener weights, and the excitation for the DAFs is conversational speech. Experimental observations have shown that divergence occurs during the low energy unvoiced segments in high-noise environments. The optimum adaptation step-size minimises such divergence by using low step-sizes during unvoiced periods. This result is then compared with a perfect divergence detector (PDD), which employs the unknown Wiener weights, a technique applicable in simulations only. The optimal step-size method reported produces a significant improvement in the system's performance in a noise-impaired environment where the near-end speech and echo path speech are contaminated with noise. Original simulation results show a modelling misadjustment improvement of 30.3 dB and 11.9 dB for noise free and noisy (signal to noise ratio, S/N of 5 dB) near-end speech respectively, all at a far-end echo to noise ratio (E/N) of 0 dB over 1 second adaptation.

A novel linear whitening measurement device is presented in this paper that allows optimal echo path modelling using real time least mean square (LMS) system identification techniques. The device provides improved and accurate characterisation of the far-end echo path using only half-duplex speech during conversational calls. The in-service non-intrusive parallel digital adaptive filter measurement device (PDMD) is based on a class of in-service non-intrusive measurement devices (INMDs) for quality of service (QoS) assessment in public switched telephone networks (PSTNs). INMDs are usually based LMS digital adaptive filters (DAFs). The modelling convergence rate is derived from the optimal Wiener weights, which defines the performance criterion. The novel PDMD utilises a parallel additional FIR-DAF set which is driven by the input speech and the stochastic behaviour of the LMS upon convergence is used to provide a linear whitening function on the input speech's power spectral density (PSD). Whitening the input speech improves the convergence rate. Software simulation is reported for conversational speech realisation and it is shown that the proposed device significantly improve the convergence rate by 23.8 dB after 1 second adaptation.

This paper examines the potential merits of pre-distortion equalization as a novel measure to mitigate the distortion imposed by multipath dispersion in optical wireless communication links. It is demonstrated that the technique is able to reduce the required transmission power though, owing to a necessary signal content in the emitted zero-slot, this reduction is only possible when multipath dispersion has a significant influence. To attain the required transmission power, the authors propose a method that is based on a sensitivity assessment of the signal reception. Analytical details of this approach are provided demonstrating its ability to account for the received pulse shape which, in an optical wireless environment, is often irregular.

High QoS in communication demands channel estimation in real time. The normalized least mean squares (NLMS) algorithm is employed due to its simplicity. Several modifications have been considered to improve the adaptation performance based on the spectral properties of the driving signal including orthogonalisation procedures like the recursive LMS, the fast affine projection or frequency domain methods. These methods are extremely sensitive to observation noise. A new finite correlation LMS (FCLS) algorithm is proposed which yields increased noise robustness in noise contaminated environments. Under the set of conditions considered an adaptation improvement of about 23 dB is obtained by replacing NLMS by FCLS. Further improvements can be obtained if chaotic coding is used.

This paper analyses the merits of adaptive threshold detection (ATD) over fixed threshold detection (FTD) as a means to reduce the impact of ambient shot noise on wireless infrared communication links. Original analytic details are provided to allow for an accurate sensitivity account of an optical wireless receiver that employs either ATD or FTD. Proposals towards the implementation of adaptive threshold detection are outlined with considerations on their respective benefits and drawbacks.

This paper proposes new divergence detection techniques for implementation within in-service non-intrusive measurement devices (INMDs) in public switched telephone networks (PSTNs). The in-service non-intrusive measurement system of interest is used to monitor the delivered quality of speech (QoS) by monitoring the echoes in the telephony network. INMDs are usually based on a class of least mean square (LMS) digital adaptive filters (DAFs). The performance criterion is defined by the modelling convergence rate derived from the optimal Wiener weights, and the excitation for the DAFs is conversational speech. Four types of divergence detectors (DD) are proposed. These are energy divergence detectors (EDD), log energy divergence detectors (LDD), zero crossing divergence detectors (ZDD) and autocorrelation coefficient divergence detectors (ADD). The proposed DDs are based on the detection of voiced/unvoiced/silence periods and as such act as pattern classifiers. Experimental observations have shown that divergence occurs during the low energy unvoiced segments in high-noise environments. The tap-weight coefficients of the DAF are updated with the new value during the voiced segment while the update of the tap-weight coefficients during unvoiced segments of the speech is frozen. This result is then compared with the perfect divergence detector, which employs the Wiener weight theory. The DD techniques reported produce a significant improvement in the system's performance in a noise-impaired environment. Over one second adaptation (8000 samples) the energy divergence detector, the log energy divergence detector, the autocorrelation divergence detector and the zero crossing divergence detector gave model improvements of 16.93 dB, 15.81 db, 12.48 dB and 11.62 dB respectively at echo to noise ratio (e/N) of 0 dB. The proposed DDs compare well with the ideal (nonimplementable) Wiener DD which gives an improvement of 20.92 dB.

Two new chaotic based coding and decoding methods are introduced and discussed. Channel estimation is evaluated when chaotic coded sequences are employed. A speech transmission scenario using chaotic coded speech is considered and channel estimation is carried out. The results show that a modelling misadjustment improvement of 24 dB/100 iterations is achievable. This represents a 6 fold improvement compared to LMS adaptation for a 128 tap digital adaptive filter using a white noise process.

Code division multiple access (CDMA) allows simultaneous access to network facilities and enables independent and concurrent communication among the users. We propose a hybrid pulse position modulation (PPM) with CDMA. The hybrid can usefully be exploited in optical wireless and optical fibre networks. Original results are presented for the scheme under various coding schemes (optical orthogonal codes, prime codes and extended prime codes). The implications of using each coding scheme are evaluated in terms of error rate, number of users and bandwidth requirements.

Digital pulse position modulation (PPM) has been shown to be attractive for implementation over the optical fibre channel when the laser transmitters are average power limited and the channel bandwidth is abundant. The synchronization requirements for optical fibre PPM however have not yet been addressed. We present an original mathematical formulation for the problem of spectral prediction and synchronization in PPM based on the cyclostationary properties of the format. Further we predict the conditions required to achieve and optimize both slot and frame synchronization. The major system parameters including the modulation index, data probability distribution and pulse shape are catered for and used in the analysis. A novel technique, capable of coping with the different PPM word sizes, is presented and used to achieve frame phase extraction directly from the PPM stream. Appropriate mathematical models are developed and used to predict the spectral properties at the output of the frame phase synchronizer. Original practical results measured on a PPM system are presented and shown to agree with the theoretical models and predictions to within 1 dB.>

An optimum pre-synchronisation filtering strategy is proposed and analysed in the context of optical fibre pulse position modulation (PPM). Under Ideal synchronisation, the PPM system is shown to outperform the equivalent PCM system sensitivity. The PPM system performance penalty due to jitter is evaluated and an original expression is presented for the jittered PPM format power spectral density (PSD). The performance improvement obtained by using the proposed filtering is ascertained and the system parameters are specified for optimum performance.>

An original implementation for a PPM correlator-synchroniser is reported. The PPM frame synchronisation is achieved on both the frequency and phase levels. The proposed technique does not suffer any of the limitations of the previous methods such as the bit rate and sensitivity penalties. Original theoretical and practical results are reported for the synchroniser while a performance evaluation is carried out. An original method for pattern dependency elimination is proposed, implemented and characterised.>