The Centre for Wireless Research brings together expertise in the areas of mobile and wireless sensor networks. The breadth and depth of the expertise make the Centre rich with research and innovation potential.

Recent Submissions

  • On statistical characterization of EESM effective SNR over frequency selective channels

    Hui Song; Kwan, R.; Jie Zhang; University of Bedfordshire (IEEE, 2009-08)
    A novel expression of the moment generating function (MGF) of the exponential effective SNR mapping (EESM) signal-to-noise ratio (SNR) over two correlated but not necessarily identically distributed Nakagami-m fading channels is presented. Based on the MGF, a novel expression for the average effective SNR is also presented. Numerical evaluation of these expressions shows that the proposed approach can be a useful and efficient analytical tool in analyzing the characteristics of EESM over correlated Nakagami-m fading channels.
  • Approximations of EESM effective SNR distribution

    Song, Hui; Kwan, Raymond; Zhang, Jie; University of Bedfordshire (IEEE, 2011-02)
    The Probability Density Function (PDF) or Cumulative Distribution Function (CDF) of the effective Signal to Noise Ratio (SNR) is an important statistical characterization in the performance analysis of an Orthogonal Frequency Division Multiple Access (OFDMA) system using Exponential Effective SNR Mapping (EESM). However, the exact closed form of PDF is extremely difficult to obtain. A general approximation method known as Moment Matching Approximating (MMA) is used to approximate the distribution of effective SNR by a simple expression. In this paper, the approximation by Gaussian, Generalized Extreme Value (GEV) and Pearson distribution are studied. Results show that Gaussian approximation is very useful when the number of sub-carriers is sufficiently large. Both GEV and Pearson approximation are accurate enough in approximating the distribution of effective SNR in a general case.
  • Disparity map compression for depth-image-based rendering

    Cheung, Gene; Ortega, Antonio; Kim, Woo-Shik; Velisavljević, Vladan; Kubota, Akira; National Institute of Informatics, Japan; University of Southern California; Texas Instruments; University of Bedfordshire; Chuo University (Springer, 2012-03)
  • 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.
  • Scalable user-adaptive multiview video coder

    Velisavljević, Vladan; Chakareski, Jacob; Stankovic, Vladimir; University of Bedfordshire; University of Alabama; Strathclyde University (IEEE, 2013-07)
    We derive an optimization framework for joint view and rate scalable coding of multi-view video content represented in the texture plus depth format. The optimization enables the sender to select the subset of coded views and their encoding rates such that the aggregate distortion over a continuum of synthesized views is minimized. We construct the view-rate scalable bitstream such that it delivers optimal performance simultaneously over a discrete set of transmission rates. In conjunction, we develop a user interaction model that characterizes the view selection actions of the client as a Markov chain over a discrete state-space. Our scheme outperforms the state-of-the-art H.264 SVC codec as well as a multi-view wavelet-based coder equipped with a uniform rate allocation strategy, across all scenarios studied. Finally, we observed that the interactivity-aware coding delivers superior performance over conventional allocation techniques that do not anticipate the client's view selection actions in their operation.
  • 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.
  • 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, 2015-04)
  • 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)
  • 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)
  • 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.
  • Centralized and interactive compression of multiview images

    Gelman, Andriy; Dragotti, Pier Luigi; Velisavljević, Vladan; Imperial College London; Deutsche Telekom Laboratories (SPIE, 2011-09-08)
  • 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.
  • Keyless security in wireless networks

    Albermany, Salah A.; Safdar, Ghazanfar Ali (Springer Verlag, 2014)
    Security in mobile wireless networks is difficult to achieve because of vulnerability of the links, inadequate physical protection, dynamically changing topology and the sporadic nature of the connectivity. The change in topology results in the change of trust relationships among the communicating nodes and as a consequence any security solution with a static configuration will not suffice. Key management and related protocols play a vital role and are the basis of security in many distributed systems. Cryptographic keys require dedicated mechanisms in place for their exchange before substantial security can be achieved; subsequently this exchange results in additional overhead and is prone to serious compromise of the security. The drawbacks of key oriented cryptographic techniques have resulted in the demand to develop keyless security schemes. This paper presents a novel keyless security scheme Reaction Automata Direct Graph (RADG), which is based on automata direct graph and reaction states. The novelty of RADG lies in the fact that it does not require any key to perform the cryptographic operations thus making it a feasible scheme for large wireless systems. Paper presents implementation of RADG and the results have shown that the hamming distance between individual cipher texts differ significantly a lot making the process of code breaking within the large systems very difficult compared to the schemes that rely on classical cryptography. The Security analysis of RADG proves that it is cryptographically sound in terms of confidentiality, integrity and non-repudiation.
  • 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 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.
  • Dynamic adjustment of weighting and safety factors in playout buffers for enhancing VoIP quality

    Syed, Tazeen S.; 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.
  • 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.
  • Shared-key based secure MAC protocol for CRNS

    Alhakami, Wajdi; Mansour, Ali; Safdar, Ghazanfar Ali; University of Bedfordshire (IEEE, 2014)
  • 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.
  • Spectrum sharing security and attacks in CRNs: a review

    Alhakami, Wajdi; Mansour, Ali; Safdar, Ghazanfar Ali; University of Bedfordshire (SAI Organization, 2014)
    Cognitive Radio plays a major part in communication technology by resolving the shortage of the spectrum through usage of dynamic spectrum access and artificial intelligence characteristics. The element of spectrum sharing in cognitive radio is a fundament al approach in utilising free channels. Cooperatively communicating cognitive radio devices use the common control channel of the cognitive radio medium access control to achieve spectrum sharing. Thus, the common control channel and consequently spectrum sharing security are vital to ensuring security in the subsequent data communication among cognitive radio nodes. In addition to well known security problems in wireless networks, cognitive radio networks introduce new classes of security threats and challenges, such as licensed user emulation attacks in spectrum sensing and misbehaviours in the common control channel transactions, which degrade the overall network operation and performance. This review paper briefly presents the known threats and attacks in wireless networks before it looks into the concept of cognitive radio and its main functionality. The paper then mainly focuses on spectrum sharing security and its related challenges. Since spectrum sharing is enabled through usage of the common control channel, more attention is paid to the security of the common control channel by looking into its security threats as well as protection and detection mechanisms. Finally, the pros and cons as well as the comparisons of different CR - specific security mechanisms are presented with some open research issues and challenges.

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