Now showing items 21-40 of 267

    • 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.
    • Ultra Wideband Systems and MIMO

      Sipal, Vit; Allen, Ben; Edwards, David J.; Malik, Wasim Q.; University of Bedfordshire (CRC Press, 2014-06)
    • 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.
    • A compact multi-band slot-ring microstrip patch antenna for wireless applications

      Ur-Rehman, Masood; Allen, Ben; University of Bedfordshire (IEEE, 2013-11)
      Design of a printed microstrip patch antenna operating at multiple frequency bands is presented in this paper. The antenna has a very simple structure combining a microstrip patch, two rings and a slot. The antenna covers GPS (1.575 GHz), 4G/LTE/CDMA (2.1 GHz), and Wi-Fi (3.6/5.3 GHz) frequency bands with good impedance matching (2:1 VSWR) and radiation pattern performance. It has an omni-directional radiation pattern at most of the desired frequencies of operation. The antenna has good efficiency ranging from 60% to 98% and exhibits high peak gain values of 4.1 dBi, 5.7 dBi, 5.1 dBi and 7.9 dBi at 1.575 GHz, 2.1 GHz, 3.68 GHz and 5.37 GHz, respectively.
    • 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.
    • 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.
    • Novel method for improving the capacity of optical MIMO system using MGDM

      Baklouti, F.; Dayoub, I.; Haxha, Shyqyri; Attia, R.; Aggoun, Amar; University of Bedfordshire (2014)
      In current local area networks, multimode fibers (MMFs), primarily graded index (GI) MMFs, are the main types of fibers employed for data communications. Due to their enormous bandwidth, it is considered that they are the main channel medium that can offer broadband multiservices using optical multiplexing techniques. Amongst these, mode group diversity multiplexing (MGDM) has been proposed as a way to integrate various services over an MMF network by exciting different groups of modes that can be used as independent and parallel communication channels. In this paper, we study optical multiple-input–multiple-output (O-MIMO) systems using MGDM techniques while also optimizing the launching conditions of light at the fiber inputs and the spot size, radial offset, angular offset, wavelength, and the radii of the segment areas of the detectors. We propose a new approach based on the optimization of launching and detection conditions in order to increase the capacity of an O-MIMO link using the MGDM technique. We propose a (3 $times$ 3) O-MIMO system, where our simulation results show significant improvement in GI MMFs' capacity compared with existing O-MIMO systems.
    • A novel birefrigent photonic crystal fiber surface plasmon resonance biosensor

      Otupiri, R.; Akowuah, Emmanuel K.; Haxha, Shyqyri; Ademgil, H.; AbdelMalek, Fathi; Aggoun, Amar; Kwame Nkrumah University of Science & Technology, Ghana; University of Bedfordshire (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2014)
      A numerical analysis of a novel birefringent photonic crystal fiber (PCF) biosensor constructed on the surface plasmon resonance (SPR) model is presented in this paper. This biosensor configuration utilizes circular air holes to introduce birefringence into the structure. This PCF biosensor model shows promise in the area of multiple detection using HEx11 and HEy11 modes to sense more than one analyte. A numerical study of the biosensor is performed in two interrogation modes: amplitude and wavelength. Sensor resolution values with spectral interrogation yielded 5 × 10-5 RIU (refractive index units) for HEx11 modes and 6 × 10-5 RIU for HEy11 modes, whereas 3 × 10-5 RIU for HEx11 modes and 4 × 10-5 RIU for HEy11 modes are demonstrated for the amplitude interrogation.
    • Mode converter optical isolator based on dual negative refraction photonic crystal

      Aroua, Walid; AbdelMalek, Fathi; Haxha, Shyqyri; Tesfa, Sintayehu; Bouchriha, Habib; University of Bedfordshire; El Manar University (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2014)
      A new design of an optical isolator based on photonic transitions in the interbands of a honeycomb structure that generates a dual negative refraction in a photonic crystal is presented. The involved photonic transition is associated to the perturbation of the dielectric constant of the medium. The band structure is determined using the plane wave method where the transmission spectra, field profile, and mode amplitudes are obtained by applying the finite difference time domain method. Due to the time-dependent perturbation of the refractive index of the medium that constitutes the dual negative refraction, asymmetric transmission mechanism is achieved for one of the desired modes, demonstrating optical isolation. Using the dual negative refraction effect in photonic crystal structure, the optical isolation is reported for only one of the desired optical modes. It is anticipated that the proposed mode conversion mechanism can be employed for designing ultrahigh-speed optical interconnections. The proposed optical isolator model is expected to have a significant impact on designing ultrahigh-speed integrated optical platforms.
    • 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.
    • Design and optimisation of integrated hybrid surface plasmon biosensor

      Gorman, T.; Haxha, Shyqyri; University of Bedfordshire; University of Greenwich (Elsevier, 2014)
      In this paper we present a novel idea for an integrated surface plasmon biosensor. The proposed hybrid sensor aims to couple the high sensitivity of the well known Kretchmann prism excitation design with the more robust integrated waveguide design. The sensor is modelled and simulated using a 2D Finite Element Method (FEM) in order to establish the devices sensitivity, resolution and signal-to-noise-ratio.
    • Design of a ferrite rod antenna for harvesting energy from medium wave broadcast signals

      Dyo, Vladimir; Allen, Ben; Jazani, David; Ivanov, Ivan; Ajmal, Tahmina; University of Bedfordshire (Institution of Engineering and Technology, 2014)
      Radio frequency (RF) energy harvesting is an emerging technology that has the potential to eliminate the need for batteries and reduce maintenance costs of sensing applications. The antenna is one of the critical components that determines its performance and while antenna design has been well researched for the purpose of communication, the design for RF energy harvesting applications has not been widely addressed. The authors present an optimised design for such an antenna for harvesting energy from medium wave broadcast transmissions. They derive and use a model for computing the optimal antenna configuration given application requirements on output voltage and power, material costs and physical dimensions. Design requirements for powering autonomous smart meters have been considered. The proposed approach was used to obtain the antenna configuration that is able to deliver 1 mW of power to 1 kΩ load at a distance of up to 9 km, sufficient to replace batteries on low-power sensing applications. Measurements using a prototype device have been used to verify the authors simulations.
    • 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
    • Wireless data encoding and decoding using OAM modes

      Tennant, Alan; Chatziantoniou, Eleftherios; Allen, Ben; Bai, Qiang; University of Bedfordshire; University of Sheffield (IET, 2014-01)
    • Experimental circular phased array for generating OAM radio beams

      Bai, Qiang; Tennant, Alan; Allen, Ben; University of Bedfordshire; University of Sheffield (IEEE, 2014-09)
      A circular phased array antenna that can generate orbital angular momentum (OAM) radio beams in the 10 GHz band is described. The antenna consists of eight inset-fed patch elements and a microstrip corporate feeding network. A full-wave electromagnetic simulator is used to aid the antenna design and theoretical simulations are confirmed by measurements
    • Design and optimisation of compact RF energy harvesting device for smart applications

      Allen, Ben; Jazani, David; Dyo, Vladimir; Ajmal, Tahmina; Ivanov, Ivan; University of Bedfordshire (IEEE, 2014-01)
      An optimised design of a radio frequency energy harvesting antenna is presented. The antenna is based on a compact ferrite rod which, together with the electronics, can directly replace batteries in suitable applications. The antenna is optimised such that the energy available for the applications is maximised, while considering constraints such as the device geometry and the Q-factor. That the antenna can power a wireless sensor node is shown from the ambient medium wave transmissions.
    • 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.
    • User-action-driven view and rate scalable multiview video coding

      Chakareski, Jacob; Velisavljević, Vladan; Stankovic, Vladimir (IEEE, 2013-09)
      We derive an optimization framework for joint view and rate scalable coding of multi-view video content represented in the texture plus depth format. The optimization enables the sender to select the subset of coded views and their encoding rates such that the aggregate distortion over a continuum of synthesized views is minimized. We construct the view and rate embedded bitstream such that it delivers optimal performance simultaneously over a discrete set of transmission rates. In conjunction, we develop a user interaction model that characterizes the view selection actions of the client as a Markov chain over a discrete state-space. We exploit the model within the context of our optimization to compute user-action-driven coding strategies that aim at enhancing the client's performance in terms of latency and video quality. Our optimization outperforms the state-of-the-art H.264 SVC codec as well as a multi-view wavelet-based coder equipped with a uniform rate allocation strategy, across all scenarios studied in our experiments. Equally important, we can achieve an arbitrarily fine granularity of encoding bit rates, while providing a novel functionality of view embedded encoding, unlike the other encoding methods that we examined. Finally, we observe that the interactivity-aware coding delivers superior performance over conventional allocation techniques that do not anticipate the client's view selection actions in their operation.
    • Directional wavelet transforms and frames

      Velisavljević, Vladan; Dragotti, Pier Luigi; Vetterli, Martin (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2002)
      The application of the wavelet transform in image processing is most frequently based on a separable transform. Lines and columns in an image are treated independently and the basis functions are simply products of corresponding one-dimensional functions. Such a method keeps simplicity in design and computation. A new two-dimensional approach is proposed, which retains the simplicity of separable processing, but allows more directionalities. The method can be applied in many areas like denoising, nonlinear approximation and compression. The results on nonlinear approximation and denoising show interesting gains compared to the standard two-dimensional analysis.
    • Discrete directional wavelet bases for image compression

      Dragotti, Pier Luigi; Velisavljević, Vladan; Vetterli, Martin; Beferull-Lozano, Baltasar (SPIE, 2003)
      The application of the wavelet transform in image processing is most frequently based on a separable construction. Lines and columns in an image are treated independently and the basis functions are simply products of the corresponding one dimensional functions. Such method keeps simplicity in design and computation, but is not capable of capturing properly all the properties of an image. In this paper, a new truly separable discrete multi-directional transform is proposed with a subsampling method based on lattice theory. Alternatively, the subsampling can be omitted and this leads to a multi-directional frame. This transform can be applied in many areas like denoising, non-linear approximation and compression. The results on non-linear approximation and denoising show very interesting gains compared to the standard two-dimensional analysis.