• 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)
    • Invited session 2: medical and healthcare applications of microwave, mm-waves and THz

      Allen, Ben; Craddock, Ian; Chen, Xiaodong; Cook, Greg (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008)
    • Joint source / channel coding forwwan multiview video multicast with cooperative peer-to-peer repair

      Liu, Zhi; Cheung, Gene; Velisavljević, Vladan; Ekmekcioglu, Erhan; Ji, Yusheng (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010)
      WWAN video multicast is challenging because of unavoidable packet losses, and inability to perform retransmission per packet for every user due to the NAK implosion problem. Previously proposed cooperative peer-to-peer repair (CPR) strategy, leveraging on the broadcast nature of wireless transmission and “uncorrelatedness” of receivers' channels, calls for peers with good WWAN channels to streaming server (rich peers) to locally relay packets lost to peers with bad WWAN channels (poor peers) over a secondary ad-hoc WLAN network. In the interactive multiview video streaming (IMVS) scenario, however, where users can each periodically select one out of many available views for decoding and display, a poor peer may not have a neighboring rich peer watching the same view for packet recovery via CPR. In this paper, we propose a new CPR strategy for peers to repair lost packets to neighbors watching different views. The key idea is for server to transmit depth maps in addition to texture maps, so that lost frames in a different view can be reconstructed using depth-image-based rendering (DIBR). Like Forward Error Correction (FEC) packets, encoded depth maps incur an overhead in redundant information transmission to counter network losses, and we allocate optimal amount of bits for FEC packets (for same-view direct path protection via WWAN source) and depth map encoding (for different-view indirect path via CPR peers) to minimize expected distortion. Experimental results show our proposed CPR scheme offers a 3.4dB PSNR improvement over a non-CPR scheme that relies on FEC only.
    • Joint source and channel coding of view and rate scalable multi-view video

      Chakareski, Jacob; Velisavljević, Vladan; Stankovic, Vladimir; University of Alabama; University of Bedfordshire; Strathclyde University (IEEE, 2014-10)
      We study multicast of multi-view content in the video plus depth format to heterogeneous clients. We design a joint source-channel coding scheme based on view and rate embedded source coding and rateless channel coding. It comprises an optimization framework for joint view selection and source-channel rate allocation, and includes a fast method for separate optimization of the source and channel coding components, at a negligible performance loss wrt the joint solution. We demonstrate performance gains over a state-of-the-art method based on H.264/SVC, in the case of two client classes.
    • Keyless security in wireless networks

      Albermany, Salah A.; Safdar, Ghazanfar Ali (Springer Verlag, 2014)
      Security in mobile wireless networks is difficult to achieve because of vulnerability of the links, inadequate physical protection, dynamically changing topology and the sporadic nature of the connectivity. The change in topology results in the change of trust relationships among the communicating nodes and as a consequence any security solution with a static configuration will not suffice. Key management and related protocols play a vital role and are the basis of security in many distributed systems. Cryptographic keys require dedicated mechanisms in place for their exchange before substantial security can be achieved; subsequently this exchange results in additional overhead and is prone to serious compromise of the security. The drawbacks of key oriented cryptographic techniques have resulted in the demand to develop keyless security schemes. This paper presents a novel keyless security scheme Reaction Automata Direct Graph (RADG), which is based on automata direct graph and reaction states. The novelty of RADG lies in the fact that it does not require any key to perform the cryptographic operations thus making it a feasible scheme for large wireless systems. Paper presents implementation of RADG and the results have shown that the hamming distance between individual cipher texts differ significantly a lot making the process of code breaking within the large systems very difficult compared to the schemes that rely on classical cryptography. The Security analysis of RADG proves that it is cryptographically sound in terms of confidentiality, integrity and non-repudiation.
    • 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.