• Exploration of Nakagami fading in ultra-wideband wireless channels

      Sipal, Vit; Allen, Ben; Edwards, David J. (IET, 2011-04-14)
    • Fade depth scaling with channel bandwidth

      Malik, Wasim Q.; Allen, Ben; Edwards, David J. (IET, 2007-11)
      The dependence of small-scale fading on bandwidth is quantified experimentally in the 3.1–10.6 GHz band for indoor channels. The fade depth converges to 4 dB at 1 GHz bandwidth, with little reduction for further increase in bandwidth. A simple yet accurate empirical fade depth model is developed, enabling convenient evaluation of the link budget for a channel with given bandwidth.
    • A fibre optic tiltmeter [for volcano monitoring]

      Ur-Rehman, Masood; Ahmed, W.; Ajmal, Tahmina (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 1996)
      A simple, rugged and highly sensitive fibre optic tiltmeter has been designed and its prototype model tested. The sensor intensity modulates the light with the change in the level of Hg surface with tilt. Hence, producing a detector output proportional to the tilt angle. The most important attribute of the tiltmeter is its ability to measure tilts of the order of microradians with a high degree of precision, hence making it an important tool for geophysical monitoring. Besides, the dielectric construction and inherent compatibility with fibre optic telemetry make the sensor suitable for monitoring the conditions of hostile and remote sites of volcanoes. The prototype model has been developed using rugged and easy to handle plastic fibres and the results obtained were satisfactory with a sensitivity of approximately 1.0 mV/μrad
    • Fountain coding in ad hoc wireless networks

      Allen, Ben; Dyo, Vladimir; University of Bedfordshire, UK (University of Bedfordshire, 2011)
      The aim of this PhD is to investigate innovative means of achieving real-time communications over an ad hoc wireless network by using Fountain coding, and more specifically as a novel means of message routing.
    • Frequency band sharing in CDMA-based micro/macro-cellular systems

      Ghorashi, S.A.; Said, F.; Dohler, Mischa; Allen, Ben; Aghvami, A.Hamid; King's College London (IEEE, 2005-09)
      A novel approach is proposed and analysed in this paper, where the micro-cell utilises the same frequency band as the macro-cell to transmit non-real time data. The main idea is that, whenever the macro-cell interference falls below a given threshold, the micro-cell schedules data with a transmission rate dependent on the micro-cell signal strength and the macro-cell interference level. We prove analytically that utilizing the hence created micro-cell transmission scheme non-real time data can be transmitted at micro-cells. We also derive the average duration and the frequency of transmit event for non-real time data transmission at micro-cells, all of which is verified by means of a dynamic CDMA system level simulator.
    • Frequency selectivity in confined environments

      Sipal, Vit; Gelabert, Javier; Stevens, Christopher; Allen, Ben; Edwards, David J.; University of Oxford (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011-04)
      This paper explores the wireless channel propagation properties in confined environments from the resonator perspective. The relationship between the performance of a communication system and the combination of the environment's size, system frequency, and system bandwidth are analysed. The conclusions of the analysis are supported by simulation and measurement results. The impact of frequency selectivity on communication systems is discussed and approaches to alleviate this issue are evaluated.
    • Frequency-selective fading of ultrawideband wireless channels in confined environments

      Sipal, Vit; Gelabert, Javier; Allen, Ben; Stevens, Christopher; Edwards, David J. (2011-08)
    • A generalized analysis of three-dimensional anisotropic scattering in mobile wireless channels-part I: theory

      Karadimas, Petros; Zhang, Jie (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011)
    • Generation of OAM radio waves using circular time-switched array antenna

      Tennant, Alan; Allen, Ben; University of Sheffield (IET, 2012-10)
      A circular time-switched array (TSA) is analysed and configured to radiate radio waves which correspond to the modes associated with orbital angular momentum (OAM) theory. Results are presented to show that the harmonic frequencies radiated by the circular TSA directly correspond to OAM modes of progressive order, including negative modes.
    • Generation of orbital angular momentum (OAM) radio beams with phased patch array

      Qiang Bai; Tennant, Alan; Allen, Ben; Rehman, Masood Ur; University of Sheffield; University of Bedfordshire (IEEE, 2013-11)
      This paper describes the design of an 8-element circular phased patch array antenna which can generate radio beams carrying orbital angular momentum at 10 GHz. Realistic antenna design issues are discussed, including mutual coupling and the array performance when operating in different OAM states.
    • Generation of radio frequency OAM radiation modes using circular time-switched and phased array antennas

      Tennant, Alan; Allen, Ben; University of Sheffield (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012-11)
      A circular array antenna is used to generate radiation modes which correspond to the modes associated with Orbital Angular Momentum (OAM) theory. Initially the circular array is used to generate OAM radiation by configuring it as a conventional phased array system with appropriate phase excitation. The array is then configured to operate as a time-switched array (TSA). The OAM modes generated by the TSA are compared to those obtained from the phased array system. Results are presented to show that the TSA radiates simultaneous multiple OAM modes at the harmonic frequencies generated by time switching the array.
    • Generic stochastic modeling of vehicle-to-vehicle wireless channels

      Karadimas, Petros; Matolak, David; University of Bedfordshire; University of South Carolina (Elsevier, 2014-08)
      We present a generic statistical characterization of the vehicle-to-vehicle (V–V) wireless channel by adopting a stochastic modeling approach. Our approach is based on the doubly underspread (DU) property of non-wide sense stationary uncorrelated scattering (non-WSSUS) wireless channels, with V–V channels pertaining to this category. DU channels exhibit explicit frequency and time intervals over which they are approximated as WSSUS. We call these intervals restricted time interval (RTI) and restricted bandwidth (RBW), and variations taking place inside them are characterized as small scale variations. Large scale variations take place outside RTI and RBW. In this paper, we focus on small scale variations, thus, our modeling finds its applicability within RTI and RBW. As practical V–V channels exhibit rapid temporal fluctuations due to the inherent mobility of transmitter (Tx), receiver (Rx) and surrounding scatterers (e.g., other vehicles), we analyze the relevant second order statistics characterizing temporal variability, namely, the a) temporal correlation function (CF) (or autocorrelation function (ACF)), b) power spectral density (PSD) (or Doppler spectrum), c) level crossing rate (LCR) and d) average fade duration (AFD). Our analysis considers three-dimensional (3-D) scattering at the Tx and Rx together with random scatterers' mobility. Illustrative examples demonstrate the usefulness and flexibility of our analysis, which is further validated by fitting the theoretical LCR to an empirical, obtained at a US interstate highway. We show that significant Doppler frequencies can arise due to scatterers' mobility exceeding the respective maximum and minimum values when considering only Tx and Rx mobility. Also scatterers' mobility causes more rapid temporal variations when it becomes more intense. The latter is also true when 3-D scattering at the Tx and/or Rx spreads over a greater range of angular sectors and becomes less directional.
    • Genetic algorithms with immigrants and memory schemes for dynamic shortest path routing problems in mobile ad hoc networks

      Yang, Shengxiang; Cheng, Hui; Wang, Fang (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2010-01)
    • GMZRP: Geography-aided Multicast Zone Routing Protocol in Mobile Ad Hoc Networks

      Cheng, Hui; Cao, Jiannong; Fan, Xiaopeng (SpringerLink, 2009-04)
    • GrLS: Group-Based Location Service in Mobile Ad Hoc Networks

      Cheng, Hui; Cao, Jiannong; Chen, Hsiao-Hwa; Zhang, Hongke (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2008)
    • Guaranteeing hard real-time traffic with legitimately short deadlines with the timed token protocol

      Wang, Jun; Zhang, Sijing; Maple, Carsten; Zhao, Zhengxu (Elsevier, 2009-03)
      Synchronous bandwidth, defined as the maximum time a node is allowed to send its synchronous messages while holding the token, is a sensitive parameter for deadline guarantees of synchronous messages in any timed token network. In order to offer such guarantees, synchronous bandwidth has to be allocated carefully to each individual node. This paper studies the synchronous bandwidth allocated to those synchronous message streams whose deadlines are less than twice the Target Token Rotation Time (TTRT). A new approach for allocating synchronous bandwidth to such streams, which can be used with any previously published local synchronous bandwidth allocation (SBA) for guaranteeing a general synchronous message set with its minimum deadline (D"m"i"n) no less than 2.TTRT, is proposed. The proposed scheme can be applied efficiently in practice to any general synchronous message set with D"m"i"n>TTRT. Numerical examples are presented to demonstrate the enhanced performance of this new local scheme over any of the previously published local SBA schemes.
    • Guaranteeing the timely transmission of periodic messages with arbitrary deadline constraints using the timed token media access control protocol

      Wang, Jun; Zhang, Sijing; Maple, Carsten (IET, 2011-03)
      Synchronous bandwidth, defined as the maximum time a node is allowed to send its synchronous messages while holding the token, is a sensitive parameter for deadline guarantees of synchronous messages in a timed token network. In order to offer such guarantees, synchronous bandwidth has to be allocated carefully. The allocation of synchronous bandwidths to a general synchronous message set with the minimum message deadline (Dmin) larger than the target token rotation time is studied. A new approach for allocating synchronous bandwidth, which can be easily implemented in practice, is proposed. It is demonstrated, through simulations and numerical examples, that the proposed approach performs better than any of previously proposed local synchronous bandwidth allocation schemes, in terms of its ability in guaranteeing hard real-time traffic.