• Threshold optimization for energy detection-based spectrum sensing over hyper-Rayleigh fading channels

      Chatziantoniou, Eleftherios; Allen, Ben; Velisavljević, Vladan; University of Bedfordshire (IEEE, 2015-06)
    • View-popularity-driven joint source and channel coding of view and rate scalable multi-view video

      Chakareski, Jacob; Velisavljević, Vladan; Stankovic, Vladimir; University of Alabama; University of Bedfordshire; Strathclyde University (IEEE, 2015-02-11)
      We study the scenario of multicasting multi-view video content, recorded in the video plus depth format, to a collection of heterogeneous clients featuring Internet access links of diverse packet loss and transmission bandwidth values. We design a popularity-aware joint source-channel coding optimization framework that allocates source and channel coding rates to the captured content, such that the aggregate video quality of the reconstructed content across the client population is maximized, for the given packet loss and bandwidth characteristics of the clients and their view selection preferences. The source coding component of our framework features a procedure for generating a view and rate embedded bitstream that is optimally decodable at multiple data rates and accounts for the different popularity of diverse video perspectives of the scene of interest, among the clients. The channel coding component of our framework comprises an expanding-window rateless coding procedure that optimally allocates parity protection bits to the source encoded layers, in order to address packet loss across the unreliable client access links. We develop an optimization method that jointly computes the source and channel coding decisions of our framework, and also design a fast local-search-based solution that exhibits a negligible performance loss relative to the full optimization. We carry out comprehensive simulation experiments and demonstrate significant performance gains over competitive state-of-the-art methods (based on H.264/AVC and network coding, and H.264/SVC and our own channel coding procedure), across different scenario settings and parameter values.
    • Introduction to the issue on visual signal processing for wireless networks

      Velisavljević, Vladan; Pesquet-Popescu, Beatrice; Vucetic, Branka; Reibman, Amy R.; Yang, Chenyang; University of Bedfordshire; ParisTech Telecom; University of Sydney; Purdue University; Beihang University (IEEE, 2015-02)
    • Performance analysis of energy detection over hyper-Rayleigh fading channels

      Chatziantoniou, Eleftherios; Allen, Ben; Velisavljević, Vladan; University of Bedfordshire (IET, 2015-01-01)
      This study investigates the performance of energy detection (ED)-based spectrum sensing over two-wave with diffused power (TWDP) fading channels, which have been found to provide accurate characterisation for a variety of fading conditions. A closed-form expression for the average detection probability of ED-based spectrum sensing over TWDP fading channels is derived. This expression is then used to describe the behaviour of ED-based spectrum sensing for a variety of channels that include Rayleigh, Rician and hyper-Rayleigh fading models. Such fading scenarios present a reliable behavioural model of machine-to-machine wireless nodes operating in confined structures such as in-vehicular environments.
    • Dynamic adjustment of weighting and safety factors in playout buffers for enhancing VoIP quality

      Syed, Tazeen Shabana; Epiphaniou, Gregory; Safdar, Ghazanfar Ali; University of Bedfordshire (IEEE, 2014-10)
      The quality of Voice over Internet Protocol (VoIP) calls is highly influenced by transmission impairments such as delay, packet loss and jitter, with jitter being manifested as one of the deleterious effects affecting its quality. A jitter buffer is usually employed at the receiver side to mitigate its effects by adapting its parameters in a trade-off between delay and packet loss. This paper proposes a novel de-jitter algorithm that adaptively changes the size of the playout buffer depending on the network states, in order to effectively handle the packet loss and delay, whereas E-model is used to quantify speech quality. Based on the statistics of the received packets, the adaptive playout buffer algorithm dynamically adjusts the weighting factor (α) and the safety factor (β) for regulating the delay and trade-off loss, thus maximizing the quality for VoIP.
    • Joint source and channel coding of view and rate scalable multi-view video

      Chakareski, Jacob; Velisavljević, Vladan; Stankovic, Vladimir; University of Alabama; University of Bedfordshire; Strathclyde University (IEEE, 2014-10)
      We study multicast of multi-view content in the video plus depth format to heterogeneous clients. We design a joint source-channel coding scheme based on view and rate embedded source coding and rateless channel coding. It comprises an optimization framework for joint view selection and source-channel rate allocation, and includes a fast method for separate optimization of the source and channel coding components, at a negligible performance loss wrt the joint solution. We demonstrate performance gains over a state-of-the-art method based on H.264/SVC, in the case of two client classes.
    • A secure MAC protocol for Cognitive Radio Networks (SMCRN)

      Alhakami, Wajdi; Mansour, Ali; Safdar, Ghazanfar Ali; Albermany, Salah A.; University of Bedfordshire (IEEE, 2014-10)
      In addition to standard authentication and data confidentiality requirements, Cognitive Radio Networks (CRNs) face distinct security issues such as primary user emulation and spectrum management attacks. A compromise of these will result in a denial of service, eavesdropping, forgery, or replay attack. These attacks must be considered while designing a secure media access control (MAC) protocol for CR networks. This paper presents a novel secure CR MAC protocol: the presented protocol is analysed for these security measures using formal logic methods such as Burrows-Abadi-Needham (BAN) logic. It is shown that the proposed protocol functions effectively to provide strong authentication and detection against malicious users leading to subsequent secure communication.
    • Experimental circular phased array for generating OAM radio beams

      Bai, Qiang; Tennant, Alan; Allen, Ben; University of Bedfordshire; University of Sheffield (IEEE, 2014-09)
      A circular phased array antenna that can generate orbital angular momentum (OAM) radio beams in the 10 GHz band is described. The antenna consists of eight inset-fed patch elements and a microstrip corporate feeding network. A full-wave electromagnetic simulator is used to aid the antenna design and theoretical simulations are confirmed by measurements
    • An empirical polarisation domain channel availability model for cognitive radio

      Chatziantoniou, Eleftherios; Allen, Ben; Velisavljević, Vladan; University of Bedfordshire (IEEE, 2014-09)
      In dynamic spectrum access networks, cognitive radio terminals monitor their spectral environment in order to detect and opportunistically access unoccupied frequency channels. The overall performance of such networks depends on the spectrum occupancy or availability patterns. Accurate knowledge on the channel availability enables optimum performance of such networks in terms of spectrum and energy efficiency. This work proposes a novel probabilistic channel availability model that can describe the channel availability in different polarizations for mobile cognitive radio terminals that are likely to change their orientation during their operation. A Gaussian approximation is used to model the empirical occupancy data that was obtained through a measurement campaign in the cellular frequency bands within a realistic operational scenario.
    • Generic stochastic modeling of vehicle-to-vehicle wireless channels

      Karadimas, Petros; Matolak, David; University of Bedfordshire; University of South Carolina (Elsevier, 2014-08)
      We present a generic statistical characterization of the vehicle-to-vehicle (V–V) wireless channel by adopting a stochastic modeling approach. Our approach is based on the doubly underspread (DU) property of non-wide sense stationary uncorrelated scattering (non-WSSUS) wireless channels, with V–V channels pertaining to this category. DU channels exhibit explicit frequency and time intervals over which they are approximated as WSSUS. We call these intervals restricted time interval (RTI) and restricted bandwidth (RBW), and variations taking place inside them are characterized as small scale variations. Large scale variations take place outside RTI and RBW. In this paper, we focus on small scale variations, thus, our modeling finds its applicability within RTI and RBW. As practical V–V channels exhibit rapid temporal fluctuations due to the inherent mobility of transmitter (Tx), receiver (Rx) and surrounding scatterers (e.g., other vehicles), we analyze the relevant second order statistics characterizing temporal variability, namely, the a) temporal correlation function (CF) (or autocorrelation function (ACF)), b) power spectral density (PSD) (or Doppler spectrum), c) level crossing rate (LCR) and d) average fade duration (AFD). Our analysis considers three-dimensional (3-D) scattering at the Tx and Rx together with random scatterers' mobility. Illustrative examples demonstrate the usefulness and flexibility of our analysis, which is further validated by fitting the theoretical LCR to an empirical, obtained at a US interstate highway. We show that significant Doppler frequencies can arise due to scatterers' mobility exceeding the respective maximum and minimum values when considering only Tx and Rx mobility. Also scatterers' mobility causes more rapid temporal variations when it becomes more intense. The latter is also true when 3-D scattering at the Tx and/or Rx spreads over a greater range of angular sectors and becomes less directional.
    • Ultra Wideband Systems and MIMO

      Sipal, Vit; Allen, Ben; Edwards, David J.; Malik, Wasim Q.; University of Bedfordshire (CRC Press, 2014-06)
    • Prevention against threats to self co-existence - a novel authentication protocol for cognitive radio networks

      Safdar, Ghazanfar Ali; Albermany, Salah A.; Aslam, Nauman; Mansour, Ali; Epiphaniou, Gregory; University of Bedfordshire (IEEE, 2014-05)
      Cognitive radio networks are intelligent networks that can sense the environment and adapt the communication parameters accordingly. These networks find their applications in co-existence of different wireless networks, interference mitigation, and dynamic spectrum access. Unlike traditional wireless networks, cognitive radio networks additionally have their own set of unique security threats and challenges, such as selfish misbehaviours, self-coexistence, license user emulation and attacks on spectrum managers; accordingly the security protocols developed for these networks must have abilities to counter these attacks. This paper presents a novel cognitive authentication protocol, called CoG-Auth, aimed to provide security in cognitive radio networks against threats to self co-existence. CoG-Auth does not require presence of any resource enriched base stations or centralised certification authorities, thus enabling it to be applicable to both infrastructure and ad hoc cognitive radio networks. The CoG-Auth design employs key hierarchy; such as temporary keys, partial keys and session keys to fulfil the fundamental requirements of security. CoG-Auth is compared with IEEE 802.16e standard PKMv2 for performance analysis; it is shown that CoG-Auth is secure, more efficient, less computational intensive, and performs better in terms of authentication time, successful authentication and transmission rate.
    • Efficacy of coverage radius-based power control scheme for interference mitigation in femtocells

      Kpojime, Harold Orduen; Safdar, Ghazanfar Ali; University of Bedfordshire (IEEE, 2014-04)
      A novel coverage radius-based downlink power control scheme to mitigate interference in densely deployed femtocells is presented. A femtocell access point (FAP) self-update algorithm is implemented, which determines the coverage radius of the femtocell with respect to its farthest served femtocell user equipment (FUE). Based on varying coverage radii, a max/min function is used to adjust the downlink transmit power value of a FAP. System-level simulations are performed to compare the performance of the presented scheme with the existing fixed coverage radius schemes. Even though the proposed scheme results in better cross-tier signal to interference plus noise ratio (SINR) values, due to a low co-tier SINR it is found that the efficacy of adaptive power control schemes based on the pilot power of a FAP is less significant if FUEs are located close to the neighbouring FAPs in densely deployed urban femtocells.
    • A statistical framework for channel availability modelling in the polarisation domain

      Velisavljević, Vladan; Allen, Ben; Chatziantoniou, Eleftherios; University of Bedfordshire (IET, 2014-03)
      Cognitive radio has been proposed as a means of improving the spectrum utilisation and increasing spectrum efficiency of wireless systems. This can be achieved by allowing cognitive radio terminals to monitor their spectral environment and opportunistically access the unoccupied frequency channels. Due to the opportunistic nature of cognitive radio, the overall performance of such networks depends on the spectrum occupancy or availability patterns. Appropriate knowledge on channel availability can optimise the sensing performance in terms of spectrum and energy efficiency. This work proposes a statistical framework for the channel availability in the polarization domain. A Gaussian Normal approximation is used to model real-world occupancy data obtained through a measurement campaign in the cellular frequency bands within a realistic scenario.
    • A survey of QoS-aware web service composition techniques

      Shehu, Umar Galadima; Epiphaniou, Gregory; Safdar, Ghazanfar Ali; University of Bedfordshire (Foundation of Computer Science, 2014-03)
      Web service composition can be briefly described as the process of aggregating services with disparate functionalities into a new composite service in order to meet increasingly complex needs of users. Service composition process has been accurate on dealing with services having disparate functionalities, however, over the years the number of web services in particular that exhibit similar functionalities and varying Quality of Service (QoS) has significantly increased. As such, the problem becomes how to select appropriate web services such that the QoS of the resulting composite service is maximized or, in some cases, minimized. This constitutes an NP-hard problem as it is complicated and difficult to solve. In this paper, a discussion of concepts of web service composition and a holistic review of current service composition techniques proposed in literature is presented. Our review spans several publications in the field that can serve as a road map for future research.
    • Wireless data encoding and decoding using OAM modes

      Tennant, Alan; Chatziantoniou, Eleftherios; Allen, Ben; Bai, Qiang; University of Bedfordshire; University of Sheffield (IET, 2014-01)
    • Design and optimisation of compact RF energy harvesting device for smart applications

      Allen, Ben; Jazani, David; Dyo, Vladimir; Ajmal, Tahmina; Ivanov, Ivan; University of Bedfordshire (IEEE, 2014-01)
      An optimised design of a radio frequency energy harvesting antenna is presented. The antenna is based on a compact ferrite rod which, together with the electronics, can directly replace batteries in suitable applications. The antenna is optimised such that the energy available for the applications is maximised, while considering constraints such as the device geometry and the Q-factor. That the antenna can power a wireless sensor node is shown from the ambient medium wave transmissions.
    • Design and optimisation of integrated hybrid surface plasmon biosensor

      Gorman, T.; Haxha, Shyqyri; University of Bedfordshire; University of Greenwich (Elsevier, 2014)
      In this paper we present a novel idea for an integrated surface plasmon biosensor. The proposed hybrid sensor aims to couple the high sensitivity of the well known Kretchmann prism excitation design with the more robust integrated waveguide design. The sensor is modelled and simulated using a 2D Finite Element Method (FEM) in order to establish the devices sensitivity, resolution and signal-to-noise-ratio.
    • Novel method for improving the capacity of optical MIMO system using MGDM

      Baklouti, F.; Dayoub, I.; Haxha, Shyqyri; Attia, R.; Aggoun, Amar; University of Bedfordshire (2014)
      In current local area networks, multimode fibers (MMFs), primarily graded index (GI) MMFs, are the main types of fibers employed for data communications. Due to their enormous bandwidth, it is considered that they are the main channel medium that can offer broadband multiservices using optical multiplexing techniques. Amongst these, mode group diversity multiplexing (MGDM) has been proposed as a way to integrate various services over an MMF network by exciting different groups of modes that can be used as independent and parallel communication channels. In this paper, we study optical multiple-input–multiple-output (O-MIMO) systems using MGDM techniques while also optimizing the launching conditions of light at the fiber inputs and the spot size, radial offset, angular offset, wavelength, and the radii of the segment areas of the detectors. We propose a new approach based on the optimization of launching and detection conditions in order to increase the capacity of an O-MIMO link using the MGDM technique. We propose a (3 $times$ 3) O-MIMO system, where our simulation results show significant improvement in GI MMFs' capacity compared with existing O-MIMO systems.
    • Design of a ferrite rod antenna for harvesting energy from medium wave broadcast signals

      Dyo, Vladimir; Allen, Ben; Jazani, David; Ivanov, Ivan; Ajmal, Tahmina; University of Bedfordshire (Institution of Engineering and Technology, 2014)
      Radio frequency (RF) energy harvesting is an emerging technology that has the potential to eliminate the need for batteries and reduce maintenance costs of sensing applications. The antenna is one of the critical components that determines its performance and while antenna design has been well researched for the purpose of communication, the design for RF energy harvesting applications has not been widely addressed. The authors present an optimised design for such an antenna for harvesting energy from medium wave broadcast transmissions. They derive and use a model for computing the optimal antenna configuration given application requirements on output voltage and power, material costs and physical dimensions. Design requirements for powering autonomous smart meters have been considered. The proposed approach was used to obtain the antenna configuration that is able to deliver 1 mW of power to 1 kΩ load at a distance of up to 9 km, sufficient to replace batteries on low-power sensing applications. Measurements using a prototype device have been used to verify the authors simulations.