• 1.562 Gb/s phase-encrypted secure communication

      Ajmal, Tahmina; Walker, Stuart D. (IET, 2008-10)
    • 2007 Index IEEE Transactions on Vehicular Technology Vol. 56

      Allen, Ben (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007)
      This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author's name. The primary entry includes the coauthors' names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author's name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index.
    • 60 GHz time-domain propagation measurement system

      Karadimas, Petros; Allen, Ben; Okon, Ernest; University of Bedfordshire (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012-11)
      We present a measurement system and method for characterising the 60 GHz time-domain wireless propagation channel using commercially available and cost effective equipment. Our measurements campaign focuses on characterizing shadowing attenuation due to human activity when intercepting the line-of-sight (LOS) path in indoor environments. Such characterization, accompanied by a statistical description of the received power levels, validates our measurement configuration and depicts its potentials for deriving novel research results in the 60 GHz band.
    • Adaptive antennas: the calibration problem

      Tyler, Neville; Allen, Ben; Aghvami, A.Hamid (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004-12)
      Adaptive antennas are recognized as a means of increasing the performance of communications systems. However, practical realization of such systems relies on suitable calibration of distortion effects caused by the circuitry and antenna structures. This work presents a detailed analysis of the classes of distortion that degrade the performance of adaptive antennas. This uses the results of an adaptive antenna testbed employing an eight-element circular array to illustrate the impact of temperature on performance. Design techniques that aid calibration are then described. In particular, digital downconversion, array design, harmonic sampling, sample clock dither, and clock management are discussed as a means of designing an adaptive array with the calibration problem in mind.
    • Adaptive array systems: fundamentals and applications

      Allen, Ben; Ghavami, Mohammad (Wiley-Blackwell, 2005-02)
      Adaptive Array Sensors: Fundamentals and Applications provides a fundamental and basic introduction to the broad aspects of array processing within a general framework. Authors Mohammad Ghavami and Ben Allen explain smart antennas, narrowband, wideband, multi-band beamforming, and a new method employing a rectangular array. Provides a comprehensive introduction to the entire field of adaptive array sensors. Presents smart antennas, narrowband, wideband and multi-band beamforming and a new method employing a rectangular array is explained. Discusses how adaptive arrays are a key technique for maximizing the capacity of wireless multimedia. CDMA networks and transmission beamforming is also discussed along with some of the associated practical constraints. Discusses numerous applications, such as spatial channel modelling and equalization, source separation, space-time coding and processing for communications, radar and sonar array processing, and highlights their operational benefits. Features chapter summaries and problems at the end of each chapter to aid understanding.
    • Adaptive distributed indexing for spatial queries in sensor networks

      Dyo, Vladimir; Mascolo, Cecilia (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2005)
    • Analysis and mitigation of antenna effects on wideband wireless channel

      Sipal, Vit; Allen, Ben; Edwards, David J. (IET, 2010-08-05)
    • Analysis of DVB-H network coverage with the application of transmit diversity

      Zhang, Yue; Zhang, Chunhui; Cosmas, John; Kok-Keong Loo; Owens, T.; Di Bari, R.; Lostanlen, Y.; Bard, M. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008-09)
      This paper investigates the effects of the cyclic delay diversity (CDD) transmit diversity scheme on DVB-H networks. Transmit diversity improves reception and quality of service (QoS) in areas of poor coverage such as sparsely populated or obscured locations. The technique not only provides robust reception in mobile environments thus improving QoS, but it also reduces network costs in terms of the transmit power, number of infrastructure elements, antenna height and the frequency reuse factor over indoor and outdoor environments. In this paper, the benefit and effectiveness of CDD transmit diversity is tackled through simulation results for comparison in several scenarios of coverage in DVB-H networks. The channel model used in the simulations is based on COST207 and a basic radio planning technique is used to illustrate the main principles developed in this paper. The work reported in this paper was supported by the European Commission IST project - PLUTO (physical layer DVB transmission optimization).
    • Analysis of GPS antenna performance in a multipath environment

      Ur-Rehman, Masood; Gao, Yue; Chen, Xiaodong; Parini, Clive G.; Ying, Zhinong (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008)
    • Analysis of smart antenna outage in UTRA FDD networks

      Allen, Ben; Beach, Mark; Karlsson, Peter; University of Bristol; Telia Research (IET, 2002-01)
      The outage occurring from beamformer-based smart antennas is analysed for an antenna array deployed in an urban macro-cell environment. Spatio-temporal channel data obtained from a small, urban cell and from within the UTRA frequency allocation has enabled beamforming performance to be determined from the measured uplink and downlink frequency bands. The analysis shows a sub-optimum uplink beamformer performance is observed for 8% of occasions and a 25% downlink beamforming outage for an eight-element uniformly spaced linear array.
    • Analysis of time correlated channel model for simulation of packet data networks

      Safdar, Ghazanfar Ali (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011)
      Performance of any communication system is ultimately determined by the characteristics of the medium, i.e., the channel utilized. A communication channel may be wired, where there is a constrained physical connection between the transmitter and receiver, or wireless where the physical constraint is missing. Wired channels differ significantly from wireless channels which can change their state in very short time span and are thus unreliable in behaviour. Wireless network protocol simulators that operate at a packet level are computationally intensive and the addition of accurate channel fading models must add as little complexity as possible. The need for channel modelling is emphasized in this paper whereas as limitations of uncorrelated channel models have been highlighted. Paper describes benefits of time correlated channel modelling and provides validation of such a model for simulation of burst errors. Results presented also prove that both Doppler frequency and velocity are inversely proportional to channel invariance for small scale fading models.
    • Antenna technology - demystifying MIMO

      Allen, Ben; Malik, Wasim Q.; Smith, P.J.; Edwards, David J. (IET, 2006-12)
      This paper deals with the MIMO (multiple- input multiple-output) wireless communication system, and how it relates to spatial diversity and WLANs. MIMO relies on multipath propagation for capacity benefit. The aim is to build a multiple antenna system in which as many as possible of the transmitting and receiving antenna-pairs are able to carry independent information channels within the same bandwidth. The system is able to distinguish the fading channels which are sharing the band
    • Antennas for global navigation satellite systems

      Chen, Xiaodong; Parini, Clive G.; Collins, Brian; Yao, Yuan; Ur-Rehman, Masood (Wiley, 2012)
    • Apparatus for testing the quality of a fluid sample

      Ajmal, Tahmina; Bain, Robert Edward Shenton; Gundry, Stephen; Walsh, Philip; Wightman, Craig Ian (2010-11-04)
      Apparatus for testing the quality of a fluid sample comprising a body defining an interior space including a primary chamber and one or more secondary chambers, the apparatus having a first configuration in which it is arranged to hold at least some of the fluid sample in the primary chamber and a second configuration in which it is arranged to isolate a first portion of the fluid sample within the one or more secondary chambers whilst retaining a second portion of the fluid sample in the primary chamber
    • Application of directionlets in video coding

      Velisavljević, Vladan; Mrak, Marta; Kondoz, A. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008)
      The goal of the presented work is to apply a directionally-adaptive two-dimensional separable wavelet transform, called directionlets, in common wavelet-based video coders. So far, directionlets have been used only in still image coding, where they have provided a sparser representation of images in the transform domain and a better compression performance. We apply directionlets to frames of video sequences in the video coding scheme based on the Dirac video codec. The novel method outperforms the traditional non-adaptive method based on the standard wavelet transform in terms of both the rate-distortion performance and the visual quality of reconstructed sequences
    • Approximation power of directionlets

      Velisavljević, Vladan; Beferull-Lozano, Baltasar; Vetterli, Martin; Dragotti, Pier Luigi (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2005)
      In spite of the success of the standard wavelet transform (WT) in image processing, the efficiency of its representation is limited by the spatial isotropy of its basis functions built in only horizontal and vertical directions. One-dimensional (1-D) discontinuities in images (edges and contours), which are very important elements in visual perception, intersect too many wavelet basis functions and reduce the sparsity of the representation. To capture efficiently these anisotropic geometrical structures, a more complex multi-directional (M-DIR) and anisotropic transform is required. We present a new lattice-based perfect reconstruction and critically sampled anisotropic M-DIR WT (with the corresponding basis functions called directionlets) that retains the separable filtering and simple filter design from the standard two-dimensional (2-D) WT and imposes directional vanishing moments (DVM). Further-more, we show that this novel transform has non-linear approximation efficiency competitive to the other previously proposed over-sampled transform constructions.
    • 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.
    • Bandwidth requirement for suppression of grating lobes in ultrawideband antenna arrays

      Sipal, Vit; Edwards, David J.; Allen, Ben; University of Oxford (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012-09)
      Sparse ultrawideband antenna arrays suppress the grating lobes due to the fact that the duration of pulses processed by individual antenna elements is too short to constructively superpose them in the time domain. Such arrays represent an attractive option for design of many low-comlexity low-cost ultrawideband systems, where narrow beamwidth is achieved by increase of element spacing. This paper empirically explores the minimum bandwidth required for suppression of the grating lobes. It is found that the relative bandwidth required to suppress grating lobes is independent on the centre frequency, element spacing, and number of elements. There is a weak dependency of the bandwidth on the type of the pulse used, but the general conclusion is that the relative bandwidth has to exceed 100% in order to suppress the grating lobes. It is, however, noted that whilst sparse array with a low number of antenna elements can suppress the grating lobes and posses a narrow beam, the compromise for this feature is a reduction of the level of spatial filtering between the main lobe and other directions, when compared to arrays where grating lobes are suppressed by dense spacing.
    • Bandwidth-dependent modelling of small-scale fade depth in wireless channels

      Malik, Wasim Q.; Allen, Ben; Edwards, David J. (IET, 2008-09)
      In this paper, the relation between small-scale fade depth and channel bandwidth in an indoor environment is investigated. The fade depth, a measure of the signal power variability over a local region in space, is evaluated for arrowband, wideband and ultrawide-band channels. The experimental analysis is based on frequency-domain measurements in the 3.1–10.6 GHz microwave band. Physical insight into the fading process is provided, and the effect of increasing bandwidth and temporal resolution is discussed. A dual-slope empirical model is developed, which accurately describes the relationship between fade depth and channel bandwidth. It is demonstrated that the fade depth, considered at the three standard deviation values, converges to about 4 dB at 1 GHz bandwidth, and a further increase in bandwidth yields only a marginal improvement in fade mitigation.