• 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.
    • Beamforming

      Allen, Ben (Wiley, 2006)
    • Bit allocation and encoded view selection for optimal multiview image representation

      Cheung, Gene; Velisavljević, Vladan (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010)
      Novel coding tools have been proposed recently to encode texture and depth maps of multiview images, exploiting inter-view correlations, for depth-image-based rendering (DIBR). However, the important associated bit allocation problem for DIBR remains open: for chosen view coding and synthesis tools, how to allocate bits among texture and depth maps across encoded views, so that the fidelity of a set of V views reconstructed at the decoder is maximized, for a fixed bitrate budget? In this paper, we present an optimization strategy to select subset of texture and depth maps of the original V views for encoding at appropriate quantization levels, so that at the decoder, the combined quality of decoded views (using encoded texture maps) and synthesized views (using encoded texture and depth maps of neighboring views) is maximized. We show that using the monotonicity property, complexity of our strategy can be greatly reduced. Experiments show that using our strategy, one can achieve up to 0.83dB gain in PSNR improvement over a heuristic scheme of encoding only texture maps of all V views at constant quantization levels. Further, computation can be reduced by up to 66% over a full parameter search approach.
    • Bit allocation for multiview image compression using cubic synthesized view distortion model

      Velisavljević, Vladan; Cheung, Gene; Chakareski, Jacob (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011)
      "Texture-plus-depth" has become a popular coding format for multiview image compression, where a decoder can synthesize images at intermediate viewpoints using encoded texture and depth maps of closest captured view locations via depth-image-based rendering (DIBR). As in other resource-constrained scenarios, limited avail able bits must be optimally distributed among captured texture and depth maps to minimize the expected signal distortion at the decoder. A specific challenge of multiview image compression for DIBR is that the encoder must allocate bits without the knowledge of how many and which specific virtual views will be synthesized at the decoder for viewing. In this paper, we derive a cubic synthesized view distortion model to describe the visual quality of an interpolated view as a function of the view's location. Given the model, one can easily find the virtual view location between two coded views where the maximum synthesized distortion occurs. Using a multi view image codec based on shape-adaptive wavelet transform, we show how optimal bit allocation can be performed to minimize the maximum view synthesis distortion at any intermediate viewpoint. Our experimental results show that the optimal bit allocation can outperform a common uniform bit allocation scheme by up to 1.0dB in coding efficiency performance, while simultaneously being competitive to a state-of-the-art H.264 codec.
    • Calibration of smart antenna systems: measurements and results

      Tyler, Neville; Allen, Ben; Aghvami, A.Hamid; King's College London; University of Oxford (IET, 2007-06)
      Smart antennas (SAs) are viewed as a candidate enabling technology for modern wireless communication systems to increase network capacity and facilitate location-based services. By conducting measurements on an SA test-bed, the signal distortion introduced by the implementation of a practical system can be analysed. This distortion can have significant impact on the estimation of signal wavefronts. Measurements have been conducted at the system, sub-system and component levels, using an SA developed for this purpose and employing a uniform circular array. This has enabled the error introduced by an implemented system to be examined. Calibration procedures are developed to overcome these implementation limitations. The cause and effects of these errors are examined, and system manufacturing tolerances and temporal thermal effects on the analogue sub-systems are shown to be the major contributor to this error; these results are presented and analysed.
    • Centralized and interactive compression of multiview images

      Gelman, Andriy; Dragotti, Pier Luigi; Velisavljević, Vladan; Imperial College London; Deutsche Telekom Laboratories (SPIE, 2011-09-08)
    • Characterisation of system performance of GPS antennas in mobile terminals including environmental effects

      Ur-Rehman, Masood; Gao, Yue; Chen, Xiaodong; Parini, Clive G.; Ying, Zhinong (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009)
    • Code orthogonality for wideband CDMA systems with multiple transmit antennas

      Hunukumbure, Mythri; Allen, Ben; Beach, Mark; Fujitsu Laboratories of Europe Limited, Uxbridge (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007-11)
      Code orthogonality is a useful indicator in determining the performance of the synchronous downlink of third generation Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access systems. In this paper, previous work on quantifying code orthogonality for single-antenna [or single-input single-output (SISO)] links is extended to fixed beamforming and transmit diversity schemes. Code orthogonality estimates from real measured channel data are extracted for typical outdoor radio environments. The results indicate that the spatial conditioning of fixed beamforming radio channels generally improves code orthogonality. In contrast, full code-rate transmit diversity schemes degrade code orthogonality.
    • Common control channel security framework for cognitive radio networks

      Safdar, Ghazanfar Ali; O'Neill, M. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009)
    • A compact multi-band slot-ring microstrip patch antenna for wireless applications

      Ur-Rehman, Masood; Allen, Ben; University of Bedfordshire (IEEE, 2013-11)
      Design of a printed microstrip patch antenna operating at multiple frequency bands is presented in this paper. The antenna has a very simple structure combining a microstrip patch, two rings and a slot. The antenna covers GPS (1.575 GHz), 4G/LTE/CDMA (2.1 GHz), and Wi-Fi (3.6/5.3 GHz) frequency bands with good impedance matching (2:1 VSWR) and radiation pattern performance. It has an omni-directional radiation pattern at most of the desired frequencies of operation. The antenna has good efficiency ranging from 60% to 98% and exhibits high peak gain values of 4.1 dBi, 5.7 dBi, 5.1 dBi and 7.9 dBi at 1.575 GHz, 2.1 GHz, 3.68 GHz and 5.37 GHz, respectively.
    • Comparison of coherent and differential space-time block codes over spatially correlated channels

      Allen, Ben; Kuroda, Y.; Said, F.; Aghvami, A.Hamid; King's College London (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004-11)
      This paper compares the performance of coherent, differential and differential unitary space-time block codes operating over spatially correlated Rayleigh fading channels with up to four transmit antennas, ft is shown that, when operating over spatially correlated channels, the relative performance of all candidate codes is improved when the number of transmit antennas is kept low. Improved performance is also observed when differential STBC are used compared to coherent STBC.
    • Comparison of differential space-time block codes and differential cyclic delay diversity for a multi-carrier wireless system

      Hashim, W.; Said, F.; Allen, Ben; Aghvami, A.Hamid; King's College London (IET, 2005-11)
      Differential transmit diversity is an attractive alternative to its coherent counterpart, especially for multiple antenna systems where channel estimation is more difficult to attain compared to that of single antenna systems. In this paper we compare two different types of differential transmit diversity techniques for a multi-carrier based transmissions in particular OFDM. The first technique uses Differential Space-time Block Codes from orthogonal designs and the second uses Differential Cyclic Delay Diversity. The results present the bit error performance for several transmit antenna configurations. The results show that DCDD offers close performance to that of DSTBC with the advantage of simplified receiver.
    • Constraint-based planning of mobile communication networks: optimisation models and constraint algorithms

      Allen, Ben; Wei, Huang; University of Bedfordshire (University of Bedfordshire, 2011)
      The constraint-based approach is effective at solving complex problems with many parameters and constraints. It is fast, practical and significantly different from existing research in mobile network planning. An in-depth investigation is needed to enable the full potential of this approach to be explored and applied in mobile telecommunication network planning. The key ideas created in this project are also expected to be useful to the 4th generation wireless network design.
    • Content adaptive enhancement of multi-view depth maps for free viewpoint video

      Ekmekcioglu, Erhan; Velisavljević, Vladan; Worrall, Stewart T. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011-04)
    • Correlation-based double-directional stochastic channel model for multiple-antenna ultra-wideband systems

      Hong, Xuemin; Wang, C.-X.; Allen, Ben; Malik, Wasim Q. (IET, 2007-12)
      A correlation-based double-directional stochastic channel model for indoor multiple-input multiple-output (MIMO) ultra-wideband (UWB) propagation channels is proposed. The proposed model extends the IEEE 802.15.3a standard model to spatially correlated MIMO channels. Both angular and temporal statistics are taken into account in the modelling procedure. Spatial correlation is introduced into the multipath amplitude and time-of-arrival (ToA) matrices of the channel model. Each amplitude matrix consists of entries of correlated lognormal random variables, whereas each ToA matrix is obtained as the sum of a reference matrix and a difference matrix. The frequency-dependent spatial correlation function is derived to give an insight of model properties. Model parameters are determined based on well-known measurement campaigns. In addition, simulation-based analysis indicates that this model has desirable spatial correlation properties in both the time and frequency domains. The ToA correlation matrix was also found to have dominant effects on the correlation characteristics. This suggests that future research into spatial correlation properties of MIMO-UWB channels should focus on ToA correlation characteristics, rather than amplitude correlation characteristics, which are the current focus of narrowband and wideband MIMO channel research.
    • Cost-variant sage: field trails and results

      Tyler, Neville; Allen, Ben; Aghvami, A.Hamid; King's College, London (IEEE, 2007)
      By extending the Space-Alternating Generalised Expectation-Maximisation (SAGE) parameter estimation algorithm to include a novel cost variant process, the robustness of Direction of Arrival (DoA) estimation from the SAGE algorithm is shown here to improve. A novel extension to the standard SAGE algorithm that enhances the parameter estimation process is first introduced. Field trials that have been conducted using an adaptive antenna to verify the performance of this algorithm are presented. Results show the extended SAGE algorithm improves DoA performance compared to standard SAGE by 5deg when operating in an urban environment.
    • Creativity or process?

      Goffin, Keith; Allen, Ben (IET, 2008-09)
      Managing new product development effectively is a trade-off between process and innovation. Keith Goffin and Ben Allen look at the steps engineering managers can take to make sure that the customer's 'hidden needs' are met.
    • Data Compression by using bit stuffing with threshold criteria in run length encoding scheme

      Qureshi, Faisal Fayyaz; Asghar, Muhammad Nabeel; Hussain, Fiaz; Safdar, Ghazanfar Ali; Shah, Syed Stiwat (IADIS, 2012)