• E.coli chromogenic reagent selection based on user perception for use in field based water quality tests

      Ajmal, Tahmina; Scott-Samuel, N.E.; Magro, Germinal; Bain, Robert Edward Shenton; Matthews, R.L.; Gundry, Stephen; Woodall, C.A.; Jeffreys, H.J.; Davies, A.P. (American Science Press, 2010)
    • Edge and motion-adaptive median filtering for multi-view depth map enhancement

      Ekmekcioglu, Erhan; Velisavljević, Vladan; Worrall, Stewart T. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009)
      The authors present a novel multi-view depth map enhancement method deployed as a post-processing of initially estimated depth maps, which are incoherent in the temporal and inter-view dimensions. The proposed method is based on edge and motion-adaptive median filtering and allows for an improved quality of virtual view synthesis. To enforce the spatial, temporal and inter-view coherence in the multiview depth maps, the median filtering is applied to 4-dimensional windows that consist of the spatially neighbor depth map values taken at different viewpoints and time instants. These windows have locally adaptive shapes in a presence of edges or motion to preserve sharpness and realistic rendering. We show that our enhancement method leads to a reduction of a coding bit-rate required for representation of the depth maps and also to a gain in the quality of synthesized views at an arbitrary virtual viewpoint. At the same time, the method carries a low additional computational complexity.
    • Edge-preservation resolution enhancement with oriented wavelets

      Velisavljević, Vladan (ie, 2008)
      A novel directionally adaptive image resolution enhancement method is proposed. The method uses a multiple-direction wavelet transform, called directionlets, to efficiently extract edge information along different directions, not necessarily horizontal or vertical, from the low-resolution image. Then, the high-resolution image is synthesized using the extracted information to preserve sharpness of edges and texture. The novel algorithm provides the interpolated images at a higher resolution that are better than the images obtained by the state-of-the-art methods in terms of both numeric and visual quality
    • Editorial: antenna systems and propagation for future wireless communications

      Malik, Wasim Q.; Allen, Ben; Edwards, David J.; Brown, Anthony (IET, 2007-12)
    • Editorial: ultra wideband systems technologies and applications

      Rashvand, Habib F.; Allen, Ben; Ghavami, Mohammad (IET, 2006-02)
      Orthogonal technological competition allows the introduction of constructive new products that will allow a minimum interaction with those already in use. Radio technology has the potential for making use of unlimited untapped frequency resources up to terahertz level. The radio technology behind this Special Issue, so called impulse radio (IR) or ultra-wideband (UWB) is approaching its prime and will compete with narrowband RF technology in wireless communications. This will also enable us to make use of traditional pulse techniques to devise suitable solutions for new civil and commercial applications. It is expected that the UWB market for shortrange applications will grow to a quarter of a billion units in the next 5 years.
    • Effect of time-correlated errors on power saving mechanisms for IEEE 802.11 Infrastructure networks

      Safdar, Ghazanfar Ali; Scanlon, W.G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2005)
    • Effects of antenna impulse response on wideband wireless channel

      Sipal, Vit; Allen, Ben; Edwards, David J.; University of Oxford; University of Bedfordshire (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010-11)
      This paper presents wideband measurements in a laboratory environment. These measurements provide further evidence in support of the previously published hypothesis that the clusters within the Saleh-Valenzuela propagation model are manifestations of antenna impulse responses. The issue caused by frequency variations of the antenna radiation pattern of wideband antennas and by the selection of antenna type are discussed. It is shown that due to limited movement in target applications of extremely wideband systems, the variation of antenna impulse responses due to the change of mutual antenna position does not significantly change. Thus, the deterministic nature of the antenna impulse responses can be exploited in the design of more efficient receivers.
    • Effects of human body interference on the performance of a GPS antenna

      Ur-Rehman, Masood; Gao, Yue; Chen, Xiaodong; Parini, Clive G.; Ying, Zhinong; Queen Mary University, London (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007)
    • 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.
    • Efficient bit allocation for multiview image coding & view synthesis

      Cheung, Gene; Velisavljević, Vladan (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010)
      In this paper, the authors address the problem of efficient bit allocation among texture and depth maps of multi-view images. We pose the following question: for chosen (1) coding tool to encode texture and depth maps at the encoder and (2) view synthesis tool to reconstruct uncoded views at the decoder, how to best select captured views for encoding and distribute available bits among texture and depth maps of selected coded views, such that visual distortion of a “metric” of reconstructed views is minimized. We show that using the monotonicity assumption, suboptimal solutions can be efficiently pruned from the feasible space during parameter search. Our experiments show that optimal selection of coded views and associated quantization levels for texture and depth maps can outperform a heuristic scheme using constant levels for all maps (commonly used in the standard implementations) by up to 2.0dB. Moreover, the complexity of our scheme can be reduced by up to 66% over full search without loss of optimality.
    • Efficient discovery and recovery of common control channel in cognitive radio wireless ad-hoc networks

      Shah, Munam Ali; Zhang, Sijing; Maple, Carsten (River Publishers, 2013)
      The most important aspect of cognitive radio (CR) networks is to search, scan, and access the control channel to advertise the free channel list (FCL)amongst the participating CR nodes. Subsequent communication could not take place until there is an access to a well-known and agreed upon control channel to dialogue the initial configuration. In this paper, a novel protocol for searching, scanning, and accessing the control channel is proposed. The protocol consists of two levels of selection: rapid channel accessing and reliable channel accessing. In rapid channel accessing, nodes quickly and efficiently converge to a newly found control channel. In reliable channel accessing, switching to the backup control channel is performed when necessary. Furthermore, our reliable channel accessing allows CR nodes to access more than one control channel simultaneously. We evaluate the performance of the proposed approach through analytical modelling. The performance results show that our protocol can achieve efficient channel access time and fairness
    • Efficient edge, motion and depth-range adaptive processing for enhancement of multi-view depth map sequences

      Ekmekcioglu, Erhan; Velisavljević, Vladan; Worrall, Stewart T. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2009)
      The authors present a novel and efficient multi-view depth map enhancement method proposed as a post-processing of initially estimated depth maps. The proposed method is based on edge, motion and scene depth-range adaptive median filtering and allows for an improved quality of virtual view synthesis. To enforce the spatial, temporal and inter-view coherence in the multi-view depth maps, the median filtering is applied to 4-dimensional windows that consist of the spatially neighboring depth map values taken at different viewpoints and time instants. A fast iterative block segmentation approach is adopted to adaptively shrink these windows in the presence of edges and motion for preservation of sharpness and realistic rendering and for improvement of the compression efficiency. We show that our enhancement method leads to a reduction of the coding bit-rate required for representation of the depth maps and also leads to a gain in the quality of synthesized views at arbitrary virtual viewpoints.
    • Efficient image compression using directionlets

      Velisavljević, Vladan; Beferull-Lozano, Baltasar; Vetterli, Martin (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007)
      Directionlets are built as basis functions of critically sampled perfect-reconstruction transforms with directional vanishing moments imposed along different directions. We combine the directionlets with the space-frequency quantization (SFQ) image compression method, originally based on the standard two-dimensional wavelet transform. We show that our new compression method outperforms the standard SFQ as well as the state-of-the-art image compression methods, such as SPIHT and JPEG-2000, in terms of the quality of compressed images, especially in a low-rate compression regime. We also show that the order of computational complexity remains the same, as compared to the complexity of the standard SFQ algorithm.
    • Efficient node discovery in mobile wireless sensor networks

      Dyo, Vladimir; Mascolo, Cecilia; University College London; University of Cambridge (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008)
      In this paper we propose an algorithm for energy efficient node discovery in sparsely connected mobile wireless sensor networks. The work takes advantage of the fact that nodes have temporal patterns of encounters and exploits these patterns to drive the duty cycling. Duty cycling is seen as a sampling process and is formulated as an optimization problem. We have used reinforcement learning techniques to detect and dynamically change the times at which a node should be awake as it is likely to encounter other nodes. We have evaluated our work using real human mobility traces, and the paper presents the performance of the protocol in this context.
    • Efficient zerotree-based image compression with directionlets

      Velisavljević, Vladan; Beferull-Lozano, Baltasar; Vetterli, Martin (EURASIP, 2007)
      Directionlets are built as basis functions of critically sampled perfect-reconstruction transforms with directional vanishing moments (DVMs) imposed along different directions. Here, we combine the directionlets with the spacefrequency quantization (SFQ) image compression method, originally based on the standard two-dimensional (2-D) wavelet transform (WT). We show that our new compression method outperforms the standard SFQ as well as the stateof-the-art image compression methods, such as SPIHT and JPEG-2000, in terms of the quality of compressed images, especially in a low-rate compression regime. We also show that the order of computational complexity remains the same, as compared to the complexity of the standard SFQ algorithm.
    • Elements reviews-new books

      Wilkinson, T.; Malik, Wasim Q.; Allen, Ben (IET, 2007)
      Network convergence is the topic in the telecommunications arena both from a commercial management and technological perspective. How to combine many different services in one single network is a very strong motivational direction for both research and development. This book provides a very thorough and surprisingly readable guide to the many different subtleties of network convergence. Moreover, it applies its perspective in a very unbiased way, focusing on the technological, historical and standardisation issues
    • 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.
    • Energy efficient distributed index for large scale sensor networks

      Dyo, Vladimir; Mascolo, Cecilia (National eScience Centre, Edinburgh, 2005)
    • An enhanced cross-layer routing protocol for wireless mesh networks based on received signal strength

      Amusa, Ebenezer Olukayode (University of BedfordshireUniversity of Bedfordshire, 2010-11)
      The research work presents an enhanced cross-layer routing solution for Wireless Mesh Networks (WMN) based on Received Signal Strength. WMN is an emerging technology with varied applications due to inherent advantages ranging from self-organisation to auto-con guration. Routing in WMN is fundamen- tally achieved by hop counts which have been proven to be de cient in terms of network performance. The realistic need to enhance the link quality metric to improve network performance has been a growing concern in recent times. The cross-Layer routing approach is one of the identi ed methods of improving routing process in Wireless technology. This work presents an RSSI-aware routing metric implemented on Optimized Link-State Routing (OLSR) for WMN. The embedded Received Signal Strength Information (RSSI) from the mesh nodes on the network is extracted, processed, transformed and incorporated into the routing process. This is to estimate efficiently the link quality for network path selections to improved network performance. The measured RSSI data is filtered by an Exponentially Weighted Moving Average (EWMA) filter. This novel routing metric method is called RSSI-aware ETT (rETT). The performance of rETT is then optimised and the results compared with the fundamental hop count metric and the link quality metric by Expected Transmission Counts (ETX). The results reveal some characteristics of RSSI samples and link conditions through the analysis of the statistical data. The divergence or variability of the samples is a function of interference and multi-path e effect on the link. The implementation results show that the routing metric with rETT is more intelligent at choosing better network paths for the packets than hop count and ETX estimations. rETT improvement on network throughput is more than double (120%) compared to hop counts and 21% improvement compared to ETX. Also, an improvement of 33% was achieved in network delay compared to hop counts and 28% better than ETX. This work brings another perspective into link-quality metric solutions for WMN by using RSSI to drive the metric of the wireless routing protocol. It was carried out on test-beds and the results obtained are more realistic and practical. The proposed metric has shown improvement in performance over the classical hop counts metric and ETX link quality metric.