• 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.
    • 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.