• Spatial channel characterisation of FDD wireless links

      Allen, Ben; Beach, Mark; Karlsson, Peter; University of Bristol (IET, 2001)
      For smart antenna deployments in frequency division duplex (FDD) applications the downlink weight vector can be derived from the uplink steering vector. However, this assumes a degree of correlation between these channels. It is shown here that de-correlation between uplink and downlink power azimuth spectrums (PAS) is significant for frequency offsets as small as 5 MHz in urban environments, with this increasing to 15 MHz when long term averaging is applied. Results reported here are computed from measured data taken within the UMTS (Universal Mobile Telecommunications System) frequency band for a cluttered urban environment
    • Spatial channel characterization for smart antenna solutions in FDD wireless networks

      Beach, Mark; Allen, Ben; Karlsson, Peter (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004-01)
      This paper introduces a novel metric for determining the spatial decorrelation between the up- and down-link wireless bearers in frequency division duplex (FDD) networks. This metric has direct relevance to smart or adaptive antenna array base-station deployments in cellular networks, which are known to offer capacity enhancement when compared to fixed coverage solutions. In particular, the results presented were obtained from field trial measurement campaigns for both urban and rural scenarios, with the observations having a direct impact on the choice of down-link beamforming architecture in FDD applications. Further, it is shown that significant spatial decorrelation can occur in urban deployments for bearer separations as small as 5 MHz. Results are presented in terms of both instantaneous characteristics as well as time averaged estimates, thus facilitating the appraisal of smart antenna solutions in both packet and circuit switched networks
    • Spatial de-correlation of the UTRA-FDD radio channel

      Allen, Ben; Beach, Mark; Karlsson, Peter; University of Oxford (2000)
      For smart antenna deployment in Frequency Division Duplex (FDD) applications the downlink weight vector can be derived from the uplink steering vector, assuming a degree of correlation between these channels. It is shown here that de-correlation between uplink and downlink power azimuth spectrums (PAS) is significant for frequency offsets as small as 5MHz in urban environments. Results reported here are computed from measured data taken within the UTRA (UMTS Terrestrial Radio Interface) frequency band for cluttered urban
    • Spatial decorrelation of frequency division duplex links

      Beach, Mark; Allen, Ben; Karlsson, Peter (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2000-10)
      It is shown that decorrelation between power azimuth spectrums for incremental duplex separation becomes significant for frequency offsets as small as 5 MHz. The results reported are computed from measured data taken within the UMTS frequency band
    • Spatial diversity for wireless LANs

      Brito, Rodrigo; Allen, Ben; Dohler, Mischa; Aghvami, A.Hamid; University of Bristol (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2004-05)
      Wireless local area networks (W-LAN) are widely used as a means of providing broadband access for high-speed wireless data services. The maximization of the system performance independent of the transceiver technology and the operating environment is of utmost importance to the hotspot system designer. This paper reports on the performance of single input and multiple output (SIMO) W-LAN systems and shows that a circular array topology located at the access point provides the best performance improvement compared to other candidate technologies when operating in an indoor office environment.
    • Spectrally efficient transmit diversity scheme for differentially modulated multicarrier transmissions

      Allen, Ben; Said, F.; Bauch, G.; Auer, G.; Aghvami, A.Hamid (IET, 2005-08)
      Cyclic delay diversity is a simple, yet effective, transmit diversity scheme for multicarrier based transmissions employing coherent digital linear modulation schemes. It is shown that, for satisfactory operation, the scheme requires additional channel estimation overhead compared to single antenna and traditional space–time coded transmissions owing to the inherent increase in frequency selective fading. The authors analyse the additional channel estimation overhead requirement for a Hiperlan #2 style system with two transmit antennas operating in a NLOS indoor environment. The analysis shows that an additional overhead of 500% is required for the candidate system compared to a single antenna system. It is also shown that by employing differential modulation the channel estimation overhead can be eliminated with significant performance improvement compared to a system employing a practical channel estimation scheme. This novel combination, termed ‘differentially modulated cyclic delay diversity, is shown to yield a highly spectral efficient, yet simple transmit diversity solution for multi-carrier transmissions.
    • Spectrum sharing security and attacks in CRNs: a review

      Alhakami, Wajdi; Mansour, Ali; Safdar, Ghazanfar Ali; University of Bedfordshire (SAI Organization, 2014)
      Cognitive Radio plays a major part in communication technology by resolving the shortage of the spectrum through usage of dynamic spectrum access and artificial intelligence characteristics. The element of spectrum sharing in cognitive radio is a fundament al approach in utilising free channels. Cooperatively communicating cognitive radio devices use the common control channel of the cognitive radio medium access control to achieve spectrum sharing. Thus, the common control channel and consequently spectrum sharing security are vital to ensuring security in the subsequent data communication among cognitive radio nodes. In addition to well known security problems in wireless networks, cognitive radio networks introduce new classes of security threats and challenges, such as licensed user emulation attacks in spectrum sensing and misbehaviours in the common control channel transactions, which degrade the overall network operation and performance. This review paper briefly presents the known threats and attacks in wireless networks before it looks into the concept of cognitive radio and its main functionality. The paper then mainly focuses on spectrum sharing security and its related challenges. Since spectrum sharing is enabled through usage of the common control channel, more attention is paid to the security of the common control channel by looking into its security threats as well as protection and detection mechanisms. Finally, the pros and cons as well as the comparisons of different CR - specific security mechanisms are presented with some open research issues and challenges.
    • Stacked patch circular polarized antenna for GPS/Galileo receiver applications

      Falade, Oluyemi Peter; Ur-Rehman, Masood; Gao, Yue; Chen, Xiaodong; Parini, Clive G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012)
    • A statistical framework for channel availability modelling in the polarisation domain

      Velisavljević, Vladan; Allen, Ben; Chatziantoniou, Eleftherios; University of Bedfordshire (IET, 2014-03)
      Cognitive radio has been proposed as a means of improving the spectrum utilisation and increasing spectrum efficiency of wireless systems. This can be achieved by allowing cognitive radio terminals to monitor their spectral environment and opportunistically access the unoccupied frequency channels. Due to the opportunistic nature of cognitive radio, the overall performance of such networks depends on the spectrum occupancy or availability patterns. Appropriate knowledge on channel availability can optimise the sensing performance in terms of spectrum and energy efficiency. This work proposes a statistical framework for the channel availability in the polarization domain. A Gaussian Normal approximation is used to model real-world occupancy data obtained through a measurement campaign in the cellular frequency bands within a realistic scenario.
    • Statistical modeling and characterization of wireless channels with multi-clustered scattering

      Allen, Ben; Karadimas, Petros; University of Bedfordshire (University of Bedfordshire, 2012)
      The proposed research will focus on statistically modeling of small scale and large scale variations in wireless channels, both separately and jointly. Focus will be given on multi-clustered channel modeling, which is more evident when the frequency of operation increases, making the proposed research particular useful for extremely high frequency bands (e.g., 60GHz band).
    • Stokes encrypted secure communication over optically amplified links

      Ajmal, Tahmina; Lepley, Jason J.; Walker, Stuart D. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2006)
      The authors describe an innovative polarization-based optical fibre physical layer cryptography technique capable of highly secure data transmission over amplified optical links. It offers completely opaque communication over trans-oceanic distances, gigabit date rates and multiple wavelengths
    • Study of a miniaturized circular patch diversity antenna for mobile terminals

      Gao, Yue; Falade, Oluyemi Peter; Ur-Rehman, Masood; Wang, Shihua; Chen, Xiaodong; Parini, Clive G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010)
    • A study of cross ring antenna for UWB applications

      Guo, Lu; Ur-Rehman, Masood; Liang, Jianxin; Chen, Xiaodong; Parini, Clive G. (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2007)
    • Study of human body exposure to RF signal at UHF frequencies

      Ur-Rehman, Masood; Alfadhl, Yasir; Wang, Z.; Chen, Xiaodong; Tattersall, J.; Inns, R.H. (Curran Associates, Inc, 2009)
    • Subcarrier fading in UWB OFDM symbols

      Sipal, Vit; Edwards, David J.; Allen, Ben; University of Oxford (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012-07)
      This paper studies the correlation between subcarriers in ultrawideband OFDM symbols. It is shown that because the channel impulse response can be assumed identical for all subcarriers within the OFDM symbol, the correlation remains strong throughout the symbol. This can be used to determine the probability distribution function of subcarrier fading within the OFDM symbol. These statistics are used for more accurate Bit-Error-Rate (BER) estimation than the standard approach using the assumption of independent BER for each subcarrier.
    • A survey of QoS-aware web service composition techniques

      Shehu, Umar Galadima; Epiphaniou, Gregory; Safdar, Ghazanfar Ali; University of Bedfordshire (Foundation of Computer Science, 2014-03)
      Web service composition can be briefly described as the process of aggregating services with disparate functionalities into a new composite service in order to meet increasingly complex needs of users. Service composition process has been accurate on dealing with services having disparate functionalities, however, over the years the number of web services in particular that exhibit similar functionalities and varying Quality of Service (QoS) has significantly increased. As such, the problem becomes how to select appropriate web services such that the QoS of the resulting composite service is maximized or, in some cases, minimized. This constitutes an NP-hard problem as it is complicated and difficult to solve. In this paper, a discussion of concepts of web service composition and a holistic review of current service composition techniques proposed in literature is presented. Our review spans several publications in the field that can serve as a road map for future research.
    • Threshold optimization for energy detection-based spectrum sensing over hyper-Rayleigh fading channels

      Chatziantoniou, Eleftherios; Allen, Ben; Velisavljević, Vladan; University of Bedfordshire (IEEE, 2015-06)
    • Tuning of plasmonic nanoparticle and surface enhanced wavelength shifting of a nanosystem sensing using 3-D-FDTD method

      Bouali, A.; Haxha, Shyqyri; AbdelMalek, Fathi; Dridi, M.; Bouchriha, Habib; Carthage University; University of Bedfordshire (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2014)
      In this paper, we have used in-house the 3-D finite-difference time-domain method to analyze a novel design of metallic nanoparticles based on a sensing nanosystem. The proposed structure is composed of two gold-nanocylinders of finite height with varying radii separated by a nanogap. We have demonstrated that tunable plasmonic nanoparticles can be controlled by varying the size of the interparticles separation distance. By engineering the nanogaps, it is shown that a strong enhancement of the electric field is achieved. Our simulations show a pronounced wavelength shift for small nanogaps. In addition, the influence of the refractive index of the surrounding medium is presented.
    • Twenty years of ultrawideband: opportunities and challenges

      Sipal, Vit; Allen, Ben; Edwards, David J.; Honary, Bahram; University of Oxford; University of Bedfordshire; Lancaster University (IET, 2012-07)
      It has been 20 years since the word ultrawideband (UWB) has first been used in the open literature. In these 20 years, ideas have been transformed into real products. Yet, some might object that UWB has not yet lived upto the promises of gigabit wireless. This review shows that despite some drawbacks, UWB is not only needed because of the spectrum gridlock but it can still deliver its promises, including gigabit wireless. To do so, the gap between the potential, which is achievable, and the current performance must be closed. Thus, this review identifies some main issues of UWB (range, bit error rate performance, data rate, chip complexity and issues associated by strong narrowband interference). It shows that their reasons are well understood and addressed by erudite research, which includes low complexity chip design, alternative modulation schemes, multiple antenna systems, UWB radio-over-fibre, higher band UWB and interferer detection and suppression techniques. A specific feature of this review is the cross-layer approach. The latest findings from different system layers, for example, wave propagation, are linked to the system performance or complexity.