• On dependent bit allocation for multiview image coding with depth-image-based rendering

      Cheung, Gene; Velisavljević, Vladan; Ortega, Antonio (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011-11)
    • On space–frequency correlation of UWB MIMO channels

      Hong, Xuemin; Wang, Cheng-Xiang; Thompson, John; Allen, Ben; Malik, Wasim Q.; Ge, Xiaohu (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010-11)
    • On statistical characterization of EESM effective SNR over frequency selective channels

      Hui Song; Kwan, R.; Jie Zhang; University of Bedfordshire (IEEE, 2009-08)
      A novel expression of the moment generating function (MGF) of the exponential effective SNR mapping (EESM) signal-to-noise ratio (SNR) over two correlated but not necessarily identically distributed Nakagami-m fading channels is presented. Based on the MGF, a novel expression for the average effective SNR is also presented. Numerical evaluation of these expressions shows that the proposed approach can be a useful and efficient analytical tool in analyzing the characteristics of EESM over correlated Nakagami-m fading channels.
    • On the analysis of switched-beam antennas for the W-CDMA downlink

      Smart antennas are widely recognized as an enabling technology for addressing the demand of future wireless network capacity when employed in place of traditional fixed-coverage sector antennas. Furthermore, switched-beam antenna systems offer a robust implementation against multipath propagation effects and reduced complexity that is inherent with fully adaptive implementations. This paper introduces a simple closed-form expression for evaluating the capacity increase of W-CDMA cellular networks employing switched-beam antennas. The expression incorporates the effect of practical antenna patterns and the impact of multipath scattering on code orthogonality, as well as that of pilot signal power. The results show that a reduction in downlink interference of approximately 6 dB can be achieved by installing an eight-beam antenna system in a 120° sector configuration when representative values of these parameters are taken into account.
    • On the complexity of routing in wireless multihop network

      Waharte, Sonia; Golynski, Alexander; Boutaba, Raouf; University of Bedfordshire; Google Inc.; University of Waterloo (IEEE, 2012-08)
      Wireless backbone networks represent an attractive alternative to wired networks in situations where cost, speed of deployment, and flexibility in network design are important. In typical configurations, users connect to wireless routers of the backbone network, which then redirect the traffic to one of the existing network gateways. To improve the network performance, wireless backbone routers redirect their traffic to the network gateways so as to maximize amount of traffic that can be sup- ported by the network. In this paper, we prove that this problem is NP-hard as a result of the wireless interference that is created between geographically close transmission links. We consequently design and investigate the performance of interference-aware algorithms suitable for multi-channel environments against more traditional routing approaches. We evaluate their performance in simulated environments based on data taken from existing networks, and show that interference-based heuristics exhibit advantageous performance in non-uniform deployment.
    • On the range of Wimedia OFDM UWB wireless

      Sipal, Vit; Edwards, David J.; Allen, Ben; University of Oxford (IEEE, 2012-09)
      We show a significant discrepancy between the range estimates and the actual performance of an ultrawideband wireless system based on the Wimedia standard. We also show this discrepancy to be linked to the combination of frequency selectivity of the ultrawideband channel and the low dynamic range available to ultrawideband receiver. We propose an alternative means of range estimation combining the statistics of frequency selective fading and the path-loss and we show that this algorithm provides significantly more accurate estimation.
    • On the scatterers' mobility and second order statistics of narrowband fixed outdoor wireless channels

      Karadimas, Petros; Vagenas, Efstathios D.; Kotsopoulos, Stavros A. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010)
      In this paper, we study the temporal behavior of narrowband fixed outdoor wireless channels by modeling the impact of scatterers' mobility on the second order statistics of such channels. We show that the Nakagami-m, gamma, Weibull and lognormal probability density functions (PDFs) can adequately approximate the scatterers' mobility at outdoor environments by comparing the theoretically derived autocorrelation functions (ACFs) with measured ACFs. These theoretical ACFs arise after considering several candidate PDFs for the impact of scatterers mobility. We select that PDF whose ACF provides the best fitting to measurements. The modeling of scatterers' mobility lead us to present analytical expressions for the level crossing rate (LCR) and average fade duration (AFD) together with an exact expression for the power spectral density (PSD).
    • On-body bluetooth link budget: effects of surrounding objects and role of surface waves

      Ur-Rehman, Masood; Gao, Yue; Chen, Xiaodong; Parini, Clive G.; Ying, Zhinong; Bolin, Thomas; Zweers, J. W. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008)
    • Optimal rate allocation for view synthesis along a continuous viewpoint location in multiview imaging

      Velisavljević, Vladan; Cheung, Gene; Chakareski, Jacob (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010)
      The authors consider the scenario of view synthesis via depth-image based rendering in multi-view imaging. We formulate a resource allocation problem of jointly assigning an optimal number of bits to compressed texture and depth images such that the maximum distortion of a synthesized view over a continuum of viewpoints between two encoded reference views is minimized, for a given bit budget. We construct simple yet accurate image models that characterize the pixel values at similar depths as first-order Gaussian auto-regressive processes. Based on our models, we derive an optimization procedure that numerically solves the formulated min-max problem using Lagrange relaxation. Through simulations we show that, for two captured views scenario, our optimization provides a significant gain (up to 2dB) in quality of the synthesized views for the same overall bit rate over a heuristic quantization that selects only two quantizers - one for the encoded texture images and the other for the depth images.
    • Optimisation of low power Radio-over-fibre links for UWB systems

      Sipal, Vit; Edwards, David J.; Allen, Ben; University of Oxford (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011-09)
      This paper focuses on the design of Radio-over-fibre (ROF) links for ultrawideband (UWB) applications. Due to strict regulations, network architecture and technical feasibility, UWB ROF links must have 0 dB gain, low noise figure and low DC power dissipation. Due to the low power of UWB signals, pre-amplification is possible. Design rules for UWB ROF links with a pre-amplifier are presented. If followed, these rules enable design of links with a lower noise figure and power dissipation than previous design rules yield for general purpose ROF links. This is illustrated by a ROF link for UWB channel sounding that requires only 27.3% of DC power compared to a commercial link with similar gain and noise figure.
    • Optimizing readability of Escherichia coli selective fluorogenic assay for testing water quality

      Ajmal, Tahmina; Bain, Robert Edward Shenton; Matthews, R.L.; Gundry, Stephen (American Science Press, 2010)
    • Optimum receive antenna selection for transmit cyclic delay diversity

      Zhang, Fan; Zhang, Yangyang; Malik, Wasim Q.; Allen, Ben; Edwards, David J.; University of Oxford (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008-05)
      Cyclic delay diversity (CDD) is an attractive diversity scheme due to its low complexity and compatibility to the existing standard orthogonal frequency division multiplexing systems. This paper presents an novel receiver antenna selection criterion for transmit CDD systems to obtain the maximal diversity gain. The performance of the proposed system is very close to the corresponding orthogonal space-time block coding diversity schemes with optimum receiver antenna selection, but CDD has the advantages of much lower complexity and no data rate reduction. Moreover, in order to make the proposed system simpler for implementation, a low complexity antenna selection algorithm has been presented.
    • Outdoor channels

      Karadimas, Petros (Wiley, 2012)
    • An overview of MB-UWB OFDM

      Allen, Ben; Ghorashi, S. Ali; Ghavami, Mohammad; Aghvami, A.Hamid (IET, 2004-07)
      In Fehrualy 2002, the-FCC allowed.3.1 GHz to 10.6 GHz for use by Ultra Wide Band (UWB) devices. This ruling has generated lots of interest in developing UWB communication systems. UWB technology is highly anticipated because it provides the Wireless Personal Area Network (WPAN) connectivity of Bluetooth, but at speeds of up to 500 times faster or possibly even more. With this technology the energy is spread across an extremely large bandwidth to insure that the presence of the transmitted signal is virtually undetectable by traditional frequency-selective radio receivers. Other applications include: radar, sensor networks, hio-medical imaging. This paper focuses on WPAN applications.
    • Performance analysis of an improved power-saving medium access protocol for IEEE 802.11 point coordination function WLAN

      Safdar, Ghazanfar Ali; Scanlon, W.G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2006)
    • Performance analysis of energy detection over hyper-Rayleigh fading channels

      Chatziantoniou, Eleftherios; Allen, Ben; Velisavljević, Vladan; University of Bedfordshire (IET, 2015-01-01)
      This study investigates the performance of energy detection (ED)-based spectrum sensing over two-wave with diffused power (TWDP) fading channels, which have been found to provide accurate characterisation for a variety of fading conditions. A closed-form expression for the average detection probability of ED-based spectrum sensing over TWDP fading channels is derived. This expression is then used to describe the behaviour of ED-based spectrum sensing for a variety of channels that include Rayleigh, Rician and hyper-Rayleigh fading models. Such fading scenarios present a reliable behavioural model of machine-to-machine wireless nodes operating in confined structures such as in-vehicular environments.
    • Performance analysis of novel randomly shifted Certification Authority Authentication Protocol for MANETs

      Safdar, Ghazanfar Ali; O'Neill, M.P. (Hindawi, 2009-01)
      The provision of security in mobile ad hoc networks is of paramount importance due to their wireless nature. However, when conducting research into security protocols for ad hoc networks it is necessary to consider these in the context of the overall system. For example, communicational delay associated with the underlying MAC layer needs to be taken into account. Nodes in mobile ad hoc networks must strictly obey the rules of the underlying MAC when transmitting security-related messages while still maintaining a certain quality of service. In this paper a novel authentication protocol, RASCAAL, is described and its performance is analysed by investigating both the communicational-related effects of the underlying IEEE 802.11 MAC and the computational-related effects of the cryptographic algorithms employed. To the best of the authors' knowledge, RASCAAL is the first authentication protocol which proposes the concept of dynamically formed short-lived random clusters with no prior knowledge of the cluster head. The performance analysis demonstrates that the communication losses outweigh the computation losses with respect to energy and delay. MAC-related communicational effects account for 99% of the total delay and total energy consumption incurred by the RASCAAL protocol. The results also show that a saving in communicational energy of up to 12.5% can be achieved by changing the status of the wireless nodes during the course of operation.
    • Performance analysis of spectrum sensing techniques for cognitive radio

      Allen, Ben; Chatziantoniou, Eleftherios (University of Bedfordshire, 2006)
      Spectrum sensing is a key element for cognitive radio and is process of obtaining awareness about the radio spectrum in order to detect the presence of other users. In this paper we study the performance of different spectrum sensing techniques in terms of detection performance and required SNR, based on theoretical expressions. Keywords- cognitive radio; spectrum sensing; energy detection; matced filter detection; cyclostationary feature detection
    • Performance analysis of switched-sector antennas for indoor wireless LANs

      Pesik, L.J.; Beach, Mark; Allen, Ben; University of Bristol (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2001)
      Given the potential market for wireless LAN (WLAN) technology, capacity within the available 2 and 5 GHz frequency bands is likely to fall short of market demands. Multiple-sector antenna arrays are known to be able to provide capacity enhancement by means of interference reduction through spatial filtering. In this paper, the performance of an eight-element circular array acting as an Access Point (AP) in indoor wireless LAN environments is analysed. Spatial-temporal channel data used within the analysis were obtained from physical measurements within numerous indoor environments using a state-of-the-art wideband vector signal analyser. Performance analysis of the array employing a switched-sector controller within the Hiperlan/2 standard is appraised in terms of carrier-to-interference (C/I) ratios. Results show that an isolation of up to 15dB can be achieved between the two polarisations, by means of using an antenna array at the AP. It is shown that 54% of the time, 2 users per timeslot can be supported by the system