• Laboratory measurement campaign of DVB-T signal with transmit delay diversity

      Di Bari, R.; Bard, M.; Zhang, Yue; Nasr, K.M.; Cosmas, John; Kok-Keong Loo; Nilavalan, R.; Shirazi, H.; Krishnapillai, K. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008-09)
      The requirements for future DVB-T/H networks demand that broadcasters design and deploy networks that provide ubiquitous reception in challenging indoors and other obstructed situations. It is essential that such networks are designed cost-effectively and with minimized environmental impact. The EC funded project PLUTO has since its start in 2006 explored the use of diversity to improve coverage in these difficult situations. The purpose of this paper is to investigate the performance of Transmit Delay Diversity (DD) with two antennas to improve the reception of DVB-T/H systems operating in different realistic propagation conditions through a series of tests using a SPIRENT SR5500 dual channel emulator. The relationship between correlation coefficient between channels, receiver velocity and diversity gain is investigated. It is shown that transmit delay diversity significantly improves the quality of reception particularly in simulated fast fading mobile broadcasting applications. This paper documents research conducted by Brunel University and Broadreach Systems.
    • LAPC conference committee

      Provides a listing of current committee members.
    • Large‐and medium‐scale propagation modelling

      Allen, Ben; Dohler, Mischa; Liu, Junsheng; Venkatesh, Swaroop; Buehrer, R. Michael (John Wiley & Sons, 2007)
    • Layer based multi-view image compression

      Gelman, Andriy; Dragotti, Pier Luigi; Velisavljević, Vladan (ICST, 2009)
      The authors propose a compression algorithm for an array of multiview images. First, we apply a segmentation algorithm to partition the data into coherent layers and significantly reduce the number of images required for artifact-free rendering. Then, we exploit the coherence in each layer by applying a 1D disparity compensated wavelet transform across the views followed by a 2D SA-DWT on each of the spatial subbands. Finally, the data is entropy coded using a modified version of EBCOT. Experimental results show that our coder outperforms state-of-the-art H.264/AVC at low bit-rates and intra-image JPEG-2000 over the complete range of bit-rates. Furthermore, unlike other multi-view image compression techniques, our implementation does not rely on estimating a 3D geometric model of the scene.
    • Limitations of existing wireless networks authentication and key management techniques for MANETs

      Safdar, Ghazanfar Ali; McGrath, Clare; McLoone, Maire (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2006)
    • Low complexity free space impedances measurement of UWB antennas

      Sipal, Vit; Gelabert, Javier; Stevens, Christopher; Edwards, David J.; Allen, Ben; University of Oxford (IEEE, 2012-03)
      This work discusses the standard algorithm for measurement of free-space antenna reflection coefficient in a reverberation chamber. This algorithm is explored in the time domain and it is shown that the bandwidth of ultrawideband antennas allows a significant reduction of the number of measurements required. This is because the ultrawideband bandwidth allows us differentiating between the free space antenna reflection coefficient and the backscattering of the environment. The limits on the minimum bandwidth, the distance to the nearest object, and the number of measurement points are discussed and experimental results confirm the methodology. The proposed methodology significantly reduces the duration of the measurement and it is believed to be of interest for industrial production and testing of ultrawideband antennas.
    • Low complexity MIMO for WiMedia UWB

      Sipal, Vit; Edwards, David J.; Allen, Ben; University of Oxford (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012-03)
      This article explores and quantifies the correlation of adjacent subcarriers in WiMedia UWB MB OFDM symbols. It is shown that in 70% of cases the energy of adjacent subcarriers differs by less than 3 dB. This finding is considered in the design of a novel antenna selection algorithm. The classical algorithm performs antenna selection for individual subcarriers, which is associated with high complexity. This paper proposes a method with reduced complexity by performing joint selection for groups of subcarriers. This proposal is evaluated for a 1 × 1 system, a 2 × 1 system with optimum antenna selection, and with a 2 × 1 with antenna selection for bundles of 2, 4, and 8 subcarriers for broadside and end-fire arrays. It is shown that optimum antenna selection can significantly enhance the range of WiMedia OFDM systems. Furthermore, antenna selection for groups of two subcarriers is shown to provide almost optimum performance whilst the complexity of the algorithm is reduced by 50%.
    • Low power transmission efficient medium access control protocol for IEEE 802.11 infrastructure networks

      Safdar, Ghazanfar Ali; Scanlon, W.G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004)
    • Low-complexity iris coding and recognition based on directionlets

    • Low-complexity iris recognition with oriented wavelets

      Iris recognition recently became an active field of biometric security because of reliability and easy non-invasive acquisition of the data. The randomness and stability of the iris textures allow for a convenient application in personal authentication and identification. In a novel iris recognition method presented here, the iris features are extracted using the oriented separable wavelet transforms (directionlets) and they are compared in terms of a weighted Hamming distance. The feature extraction and comparison are shift, size and rotation-invariant to the location of iris in the acquired image. The generated iris code is binary, whose length is fixed (and therefore commensurable), independent of the iris image, and comparatively short. The novel method shows a good performance when applied to a large database of irises and provides reliable identification and verification. At the same time, it preserves conceptual and computational simplicity and allows for a quick analysis and comparison of iris samples.
    • Low-rate reduced complexity image compression using directionlets

      Velisavljević, Vladan; Beferull-Lozano, Baltasar; Vetterli, Martin; Dragotti, Pier Luigi (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2006)
      The standard separable two-dimensional (2-D) wavelet transform (WT) has recently achieved a great success in image processing because it provides a sparse representation of smooth images. However, it fails to capture efficiently one-dimensional (1-D) discontinuities, like edges and contours, that are anisotropic and characterized by geometrical regularity along different directions. In our previous work, we proposed a construction of critically sampled perfect reconstruction anisotropic transform with directional vanishing moments (DVM) imposed in the corresponding basis functions, called directionlets. Here, we show that the computational complexity of our transform is comparable to the complexity of the standard 2-D WT and substantially lower than the complexity of other similar approaches. We also present a zerotree-based image compression algorithm using directionlets that strongly outperforms the corresponding method based on the standard wavelets at low bit rates
    • LTE-A advanced and next generation wireless networks: channel modeling and propagation

      De La Roche, Guillaume; Alayon-Glazunov, Andres; Allen, Ben; University of Bedfordshire; Royal Institute of Technology, Sweden (Wiley, 2012)
      LTE- A and Next Generation Wireless Networks: Channel Modeling and Performance describes recent advances in propagation and channel modeling necessary for simulating next generation wireless systems. Due to the radio spectrum scarcity, two fundamental changes are anticipated compared to the current status. Firstly, the strict reservation of a specific band for a unique standard could evolve toward a priority policy allowing the co-existence of secondary users in a band allocated to a primary system. Secondly, a huge increase of the number of cells is expected by combining outdoor base stations with smaller cells such as pico/femto cells and relays. This evolution is accompanied with the emergence of cognitive radio that becomes a reality in terminals together with the development of self-organization capabilities and distributed cooperative behaviors.
    • Managing threats by the use of visualisation techniques

      Viduto, Valentina; Maple, Carsten; Huang, Wei (Inderscience, 2011)
      Identification of threats in networked systems is one of the important risk management processes that should be followed in order to be aware of all risks. In general, risk assessment guidelines for threat analysis propose to use historical organisation's data, thus, novel and unheard threats often are skipped from an analysis. In this paper, we propose a novel onion skin model (OSM) which consists of visualisation techniques, such as attack graphs, often applied for qualitative and quantitative risk assessment analyses. The model can be used to facilitate in threat identification and decision-making process by focusing on attack scenarios that illustrate vulnerable nodes, threats and shortest attack paths to the attacker's goal. The model can be used as part of risk management practices to improve security awareness through different attack scenarios and manage all system risks.
    • Minimum energy wireless sensor networks

      Allen, Ben; Safdar, Ghazanfar Ali; University of Bedfordshire, UK (University of Bedfordshire, 2011)
      Here, on-off keying modulation is used as a means of reducing the transmit energy requirements whilst exploiting inherent channel coding, which sets the scene of this PhD study.
    • Mobile terminal GPS antennas in multipath environment and effects of human body presence

      Ur-Rehman, Masood; Gao, Yue; Chen, Xiaodong; Parini, Clive G.; Ying, Zhinong (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009)
    • Mode converter optical isolator based on dual negative refraction photonic crystal

      Aroua, Walid; AbdelMalek, Fathi; Haxha, Shyqyri; Tesfa, Sintayehu; Bouchriha, Habib; University of Bedfordshire; El Manar University (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2014)
      A new design of an optical isolator based on photonic transitions in the interbands of a honeycomb structure that generates a dual negative refraction in a photonic crystal is presented. The involved photonic transition is associated to the perturbation of the dielectric constant of the medium. The band structure is determined using the plane wave method where the transmission spectra, field profile, and mode amplitudes are obtained by applying the finite difference time domain method. Due to the time-dependent perturbation of the refractive index of the medium that constitutes the dual negative refraction, asymmetric transmission mechanism is achieved for one of the desired modes, demonstrating optical isolation. Using the dual negative refraction effect in photonic crystal structure, the optical isolation is reported for only one of the desired optical modes. It is anticipated that the proposed mode conversion mechanism can be employed for designing ultrahigh-speed optical interconnections. The proposed optical isolator model is expected to have a significant impact on designing ultrahigh-speed integrated optical platforms.
    • A modified Loo model with partially blocked and three dimensional multipath scattering: analysis, simulation and validation

      Karadimas, Petros; Kotsopoulos, Stavros A.; University of Patras (Springer, 2009)
      This paper presents a novel mobile fading channel model, belonging to the class of Loo models, in which the multipath power arrives both in three dimensions (3-D) and in two angular sectors at the azimuth receiver's plane. Moreover shadowing affects the amplitude of the line of sight (LOS) component, making it time varying and following a lognormal distribution, as required for a Loo model. The Doppler power spectral density (PSD) is analytically calculated, after Fourier transforming the closed form autocorrelation function. Afterwards exact solutions for the probability density function (PDF) of the envelope and phase are presented. What follows are approximate solutions for the second order statistics, i.e. the level crossing rate (LCR) and the average duration of fades (ADF's). A new, appropriate for 3-D scattering cases, deterministic simulation scheme is developed, which implements the analytical model on a digital computer and is used to test the validity of the approximate solutions. Moreover the deterministic model is thoroughly investigated for all the possible cases, in terms of its convergence to the analytical one. Finally a curve fitting of the LCR to real world data, drawn from channel measurements, will demonstrate the flexibility and usefulness of the modified Loo model.
    • Multi objective resource scheduling in LTE networks using reinforcement learning

      Comşa, Ioan-Sorin; Aydin, Mehmet Emin; Zhang, Sijing; Kuonen, Pierre; Wagen, Jean–Frédéric (IGI Global, 2012)
      The use of the intelligent packet scheduling process is absolutely necessary in order to make the radio resources usage more efficient in recent high-bit-rate demanding radio access technologies such as Long Term Evolution (LTE). Packet scheduling procedure works with various dispatching rules with different behaviors. In the literature, the scheduling disciplines are applied for the entire transmission sessions and the scheduler performance strongly depends on the exploited discipline. The method proposed in this paper aims to discuss how a straightforward schedule can be provided within the transmission time interval (TTI) sub-frame using a mixture of dispatching disciplines per TTI instead of a single rule adopted across the whole transmission.
    • Multi-element antenna systems for wireless communications with multi-clustered scattering

      Allen, Ben; Karadimas, Petros; University of Bedfordshire (University of Bedfordshire, 2012)
      the proposed research will focus on analyzing and evaluating MEA systems based on new theoretical, realistic though, multi-clustered scattering models for the directional statistics of the propagating multipath power and using several well-known signal processing techniques (e.g., MRC, SC).