• Harvesting energy from ambient radio signals: a load of hot air?

      Allen, Ben; Ajmal, Tahmina; Dyo, Vladimir; Jazani, David; University of Bedfordshire (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012-11)
      Harvesting energy from ambient radio signals is claimed to hold much innovation potential. Advances in ultra-low power electronics, an appetite for reducing the environmental footprint of technology and the business need for enabling new applications such as sensing in inaccessible locations are widely believed to be drivers. We review these drivers, and recent technological advances to reveal what potential there is by harvesting energy from ambient radio signals. Particular attention is given to the possibility of powering smart meters in this way.
    • An HMM-based spectrum occupancy predictor for energy efficient cognitive radio

      Chatziantoniou, Eleftherios; Allen, Ben; Velisavljević, Vladan; University of Bedfordshire (IEEE, 2013-09)
      Spectrum sensing is the cornerstone of cognitive radio technology and refers to the process of obtaining awareness of the radio spectrum usage in order to detect the presence of other users. Spectrum sensing algorithms consume considerable energy and time. Prediction methods for inferring the channel occupancy of future time instants have been proposed as a means of improving performance in terms of energy and time consumption. This paper studies the performance of a hidden Markov model (HMM) spectrum occupancy predictor as well as the improvement in sensing energy and time consumption based on real occupancy data obtained in the 2.4GHz ISM band. Experimental results show that the HMM-based occupancy predictor outperforms a kth order Markov and a 1-nearest neighbour (1NN) predictor. Our study also suggests that by employing such a predictive scheme in spectrum sensing, an improvement of up to 66% can be achieved in the required sensing energy and time.
    • Hotflashes: thumbnailing videos of social gatherings by detecting camera flash illuminated frames

      Sundaram, Shiva; Velisavljević, Vladan; Qin, Yujie (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011)
      Automatic annotation of video clips is desired to efficiently thumbnail user generated content available in the Internet. Automatic techniques typically focus on a selected set of inherent video features (such as scene-cut or shot boundaries) that are deemed to be salient. Along this line, the presence of camera flash light illumination is a feature of interest. This event is usually triggered manually (by a photographer) within a scene and the selected frame(s) they occur in are deemed to be interesting in the recording: for instance, the appearance of a celebrity in a party. In this paper we present a method to detect video frames that contain flashes originating from still cameras in user generated video clips. We focus on designing features for flash illumination detection using various measures of luminance change within video sequences. Using the proposed method, we obtain detection performance of approximately 89% which is 8% absolute improvement over the baseline method that uses only change in average illumination. We also illustrate a case where flashes are automatically detected in video clips of social gatherings that can be used for thumbnailing and browsing.
    • Human body shadowing characterization for 60-GHz indoor short-range wireless links

      Karadimas, Petros; Allen, Ben; Smith, Peter; University of Bedfordshire (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2013)
      We statistically characterize received signal power variations in the time domain caused by human activity affecting 60-GHz indoor short-range wireless links. Our approach is based on propagation measurements in indoor environments considering human activity intercepting the line-of-sight (LOS) path. It has been previously shown that the ensemble of received power levels in decibel (dB) scale cannot be modeled by a Gaussian distribution, as is the case for spatial shadowing variations. In this letter, we present a theoretical stochastic approach showing that received power variations can follow a Gaussian statistical model when considered within the time intervals of similar shadowing processes. Our model is shown to have good comparison to experimental data
    • A 'human-in-the-loop' mobile image recognition application for rapid scanning of water quality test results

      Loudon, Melissa; Ajmal, Tahmina; Rivett, Ulrike; De Jager, Dirk; Bain, Robert Edward Shenton; Matthews, Robert; Gundry, Stephen (British Computer Society, 2009)
      This paper describes an interactive system for drinking water quality testing in small community supplies, particularly in the developing world. The system combines a low-cost field test (the Aquatest field kit), a mobile phone for data processing and communications, and a human operator who is able to react immediately to a test result. Once a water sample has been collected and incubated, the mobile phone camera is used to 'scan' the test and obtain the result, which is displayed to the user along with information about the health implications of the water quality. Initial prototypes, while not yet sufficiently robust for real-world use, demonstrate that the system is technically feasible. This opens up interesting possibilities for wider use of 'human-in-the-loop' sensor systems in environmental monitoring.
    • Hybrid model for throughput evaluation of OFDMA networks

      Mahato, Shyam Babu; Allen, Ben; Liu, Enjie; Zhang, Jie; University of Bedfordshire; Budapest University of Technology and Economics; University of Sheffield (IET, 2013-12)
      Data throughput is an important metric used in the performance evaluation of the next generation cellular networks such as Long-Term Evolution (LTE) and LTE-Advanced. To evaluate the performance of these networks, Monte Carlo simulation schemes are usually used. Such simulations do not provide the throughput of intermediate call state, instead it gives the overall performance of the network. We propose a hybrid model consisting of both analysis and simulation. The benefit of the model is that the throughput of any possible call state in the system can be evaluated. Here, the probability of possible call distribution is first obtained by analysis, which is used as input to the event-driven based simulator to calculate the throughput of a call state. We compare the throughput obtained from our hybrid model with that obtained from event-driven based simulation. Numerical results are presented and show good agreement between both the proposed hybrid model and the simulation. The maximum difference of relative throughput between our hybrid model and the simulation is found in the interval of(0.04%;1.06%) over a range of call arrival rates, meanholding times and number of resource blocks in the system.
    • Hyperband wireless

      Allen, Ben; Zhang, Yue; University of Bedfordshire (University of Bedfordshire, 2011)
      Research at Oxford University is currently exploring the feasibility of this concept with a focus on examining the fundamental aspects such as signal propagation and waveform design. The objective of research proposed here is to compliment the work at Oxford University through addressing ways of managing interference from other spectrum users. This PhD will have collaborative aspects with the Oxford University.
    • Identity based Public Key Exchange (IDPKE) for wireless ad hoc networks

      McGrath, Clare; Safdar, Ghazanfar Ali; McLoone, Maire (INSTICC Press, 2007)
    • Image interpolation using oriented wavelet transforms

      Velisavljević, Vladan (EURASIP, 2008)
      A novel directionally adaptive image interpolation method based on the oriented wavelet transforms is proposed. The method uses the wavelet transforms built along multiple di- rections (directionlets) to e±ciently capture directional features and to extract edge information 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 interpolation algorithm outperforms the state-of-the-art methods in terms of both numeric and visual quality of the interpolated image.
    • Image interpolation with directionlets

      Velisavljević, Vladan; Coquoz, Raphael (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008)
      We present a novel directionally adaptive image interpolation based on a multiple-direction wavelet transform, called directionlets. The algorithm uses directionlets to efficiently capture directional features and to extract edge information along different directions from the low-resolution image. Then, the high-resolution image is generated using this information to preserve sharpness of details. Our interpolation algorithm outperforms the state-of-the-art methods in terms of both numeric and visual quality of the interpolated image.
    • Image representation and compression using directionlets

      Velisavljević, Vladan; Beferull-Lozano, Baltasar; Vetterli, Martin; Luigi Dragotti, Pier; Van De Ville, Dimitri; Goyal, Vivek K.; Papadakis, Manos (SPIE, 2007)
      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 or contours. These features, being elongated and characterized by geometrical regularity along different directions, intersect and generate many large magnitude wavelet coefficients. Since contours are very important elements in visual perception of images, to provide a good visual quality of compressed images, it is fundamental to preserve good reconstruction of these directional features. We propose a construction of critically sampled perfect reconstruction transforms with directional vanishing moments (DVMs) imposed in the corresponding basis functions along different directions, called directionlets. We also demonstrate the outperforming non-linear approximation (NLA) results achieved by our transforms and we show how to design and implement a novel efficient space-frequency quantization (SFQ) compression algorithm using directionlets. Our new compression method beats the standard SFQ both in terms of mean-square-error (MSE) and visual quality, especially in the low-rate compression regime. We also show that our compression method, does not increase the order of computational complexity as compared to the standard SFQ algorithm.
    • Impact of bandwidth on small-scale fade depth

      Malik, Wasim Q.; Allen, Ben; Edwards, David J. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007-11)
      This paper investigates the impact of channel bandwidth on fading in wireless channels using indoor measurements. The variation of channel energy over a local region is examined for narrowband, wideband and ultrawideband (UWB) channels, and the corresponding fade depth is evaluated. The relation between bandwidth and fade depth is then captured with a simple dual-slope model. The effect of antenna polarization and line-of- sight blockage is also investigated. We observe that the fade depth initially falls rapidly with bandwidth, reaching 4 dB at 1 GHz, but further reduction in fading with bandwidth is much slower.
    • Impact of confined environments on WiMedia UWB systems

      Sipal, Vit; Gelabert, Javier; Stevens, Christopher; Allen, Ben; Edwards, David J.; University of Oxford (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011-11)
      This paper explores the performance of a commercial WiMedia Multi-Band OFDM Ultrawideband development kit in a confined environment. It confirms previous predictions that the forward error correction schemes of WiMedia systems might not be sufficient for confined environments with a high number of multipaths. A carefully designed environment is shown to be able to alleviate the issue and improve the performance by reducing the packet-error rates. Analysis of packet-error-rates obtained for various antenna orientations and polarisations enables us to propose design rules to assist deployment of WiMedia Multi-Band OFDM Ultrawideband wireless systems in confined environments.
    • Impacts of human body on built-in GPS antennas for mobile terminal in multipath environment

      Ur-Rehman, Masood; Ghao, Y.; Chen, Xiaodong; Parini, Clive G.; Ying, Zhinong (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010)
      .
    • Improved power-saving medium-access protocol for IEEE 802.11e QoS-enabled wireless networks

      Safdar, Ghazanfar Ali; Scanlon, W.G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007)
      The performance of a new pointer-based medium-access control protocol that was designed to significantly improve the energy efficiency of user terminals in quality-of-service-enabled wireless local area networks was analysed. The new protocol, pointer- controlled slot allocation and resynchronisation protocol (PCSARe), is based on the hybrid coordination function-controlled channel access mode of the IEEE 802.11e standard. PCSARe reduces energy consumption by removing the need for power-saving stations to remain awake for channel listening. Discrete event network simulations were performed to compare the performance of PCSARe with the non-automatic power save delivery (APSD) and scheduled-APSD power- saving modes of IEEE 802.11e. The simulation results show a demonstrable improvement in energy efficiency without significant reduction in performance when using PCSARe.
    • Indoor-indoor and indoor-outdoor propagation trial results at 2.6 GHz

      Fang, Cheng; Allen, Ben; Liu, Enjie; Karadimas, Petros; Zhang, Jie; Glazunov, Andres Alayon; Tufvesson, Fredrik; University of Bedfordshire (IEEE, 2012-11)
      This paper presents delay spread, coherence bandwidth, and angle-of-arrival statistics derived from an extensive MIMO channel measurement campaign carried out at a central frequency of 2.6GHz. The measurement scenarios include indoor-indoor, indoor-outdoor and indoor-outdoor-indoor. The results are useful for analytical and performance studies of post-3G wireless communication systems such as femtocell design and deployment.
    • Interactive multiview image coding

      Gelman, Andriy; Dragotti, Pier Luigi; Velisavljević, Vladan (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011)
      The authors propose a novel multiview compression method for multiview images. The algorithm supports random access for interactive applications and has low storage requirements. The fundamental component of the method is the layer-based representation, which partitions the dataset into redundant layers characterized by a constant depth value. We exploit the redundant property of each layer and remove the side information uncertainty using Distributed Source Coding (DSC) principles. In comparison to independent coding, our method achieves a PSNR improvement of 3dB. Furthermore, we present a rate-distortion (RD) analysis which demonstrates that the proposed algorithm can achieve a better performance in comparison to independent coding.
    • Interference mitigation in Cognitive Radio based Femtocells

      Kpojime, Harold Orduen; Safdar, Ghazanfar Ali (IEEE, 2014)
      Femtocell architecture involves the use of two separate layers – the macrocell and femtocell layers. In this architecture, the former is the conventional cellular network whereas the latter incorporates a range of shorter range cells. Femtocells are designed to co-exist alongside macrocells providing spatial frequency reuse, higher spectrum efficiency and cover areas where macrocells cannot. Femtocells positioned in the macrocell considerably improve the indoor coverage and provide better user experience. However, interference between the two layers is imminent; therefore ways to manage it must be employed to efficiently avoid problems such as coverage holes in the macrocells. Essential limits of capacity and attainable data rates also mainly depend on the interference faced by a femtocell network. Recently, Cognitive Radio (CR) which has the ability to sense its environment and accordingly alter its characteristics, e.g. transmission parameters, has been merged with femtocells to exploit the capabilities of the former in the latter. CR enabled femtocells in a two tier network can sense the environment and opportunistically allocate both licensed and unlicensed frequency bands to user equipments to avoid interference. This paper examines interference mitigation in femtocells using CR and provides comprehensive survey of different CR enabled interference mitigation schemes. Presented schemes such as power control, spectrum access, antenna and joint schemes are classified before they are compared for pros and cons. Finally tradeoffs and cost of using CR in femtocells are highlighted with some insight into future research issues and challenges.
    • Introduction to Part III

      Dohler, Mischa; Allen, Ben (Wiley, 2006)
      Ultra-wideband (UWB) is predicted to emerge as a fundamental technology for the home entertainment, security, tracking and high data rate wireless transmission markets. It will be a viable part of future wireless personal area networks (WPANs), wireless body area networks (WBANs) and sensor networks, among others.
    • 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)