[Show abstract][Hide abstract] ABSTRACT: In this paper, the application of wireless information and power transfer to
cooperative networks is investigated, where the relays in the network are
randomly located and based on the decode-forward strategy. For the scenario
with one source-destination pair, three different strategies for using the
available relays are studied, and their impact on the outage probability and
diversity gain is characterized by applying stochastic geometry. By using the
assumptions that the path loss exponent is two and that the relay-destination
distances are much larger than the source-relay distances, closed form
analytical results can be developed to demonstrate that the use of energy
harvesting relays can achieve the same diversity gain as the case with
conventional self-powered relays. For the scenario with multiple sources, the
relays can be viewed as a type of scarce resource, where the sources compete
with each other to get help from the relays. Such a competition is modeled as a
coalition formation game, and two distributed game theoretic algorithms are
developed based on different payoff functions. Simulation results are provided
to confirm the accuracy of the developed analytical results and facilitate a
better performance comparison.
[Show abstract][Hide abstract] ABSTRACT: This paper studies different secrecy rate optimization problems for a multiple-input–multiple-output (MIMO) secrecy channel. In particular, we consider a scenario where a communication through a MIMO channel is overheard by a multiple-antenna eavesdropper. In this secrecy network, we first investigate two secrecy rate optimization problems: 1) power minimization and 2) secrecy rate maximization. These optimization problems are not convex due to the nonconvex secrecy rate constraint. However, by approximating this secrecy rate constraint based on Taylor series expansion, we propose iterative algorithms to solve these secrecy rate optimization problems. In addition, we provide the convergence analysis for the proposed algorithms. These iterative optimization approaches are developed under the assumption that the transmitter has perfect channel state information. However, there are practical difficulties in having perfect channel state information at the transmitter. Hence, robust secrecy rate optimization techniques based on the worst-case secrecy rate are considered by incorporating channel uncertainties. By exploiting the S-Procedure, we show that these robust optimization problems can be formulated into semidefinite programming at low signal-to-noise ratios (SNRs). Simulation results have been provided to validate the convergence of the proposed algorithms. In addition, numerical results show that the proposed robust optimization techniques outperform the nonrobust schemes in terms of the worst-case secrecy rates and the achieved secrecy rates.
[Show abstract][Hide abstract] ABSTRACT: A new cost efficient automated planning and optimization method is proposed for OFDMA future-generation cellular networks targeting throughput maximization. The mathematical formulation is a non-linear multi-objective optimization problem subject to minimum interference, cost and similar resource constraints at each cell within a defined heterogeneous traffic environment. The fundamental objective is to maximize the individual cell throughput without deteriorating it over other cells, which results in a throughput equilibrium maximization over multiple cells. This implicitly implies traffic and co-channel interference congestion avoidance across the network whilst maintaining both cost efficiency and quality of service (QoS) policies. Optimal solution existence is subject to the network size, traffic and computational complexity constraints which converges to a throughput equilibrium or alternatively to the well known Nash Equilibrium (NE).
[Show abstract][Hide abstract] ABSTRACT: In this paper, an investigation is presented into nanogap-based bowtie nanoarrays for THz energy detection, with the aim of optimizing their geometrical parameters utilizing finite-element method (FEM) based simulations. The bowtie elements of the array are connected by feeding lines, which are used to transfer the captured electric field away from the antenna's center to a common feeding gap. The performance of the bowtie nanoarray has been compared with a single bowtie element constructed using the same device area. The obtained results demonstrated that the array outperforms the single element bowtie. Subsequently, a parametric study is carried out on important geometrical parameters of the array to optimize its performance. The results demonstrate that the optimum spacing between array elements is 2.9 m, whereas the best line width of the feeding lines is 50 nm. Additionally, it has been found that a 25 nm gap offers the highest electric field at resonance. Furthermore, a bowtie nanoarray is designed based on the optimized parameters of the parametric study. Finally, the effects of the incident angle and curvature of the edges of the array elements and feeding lines have also been studied and their impact on the overall performance is presented in this paper.
IEEE Transactions on Terahertz Science and Technology. 09/2013; 3(5):524-531.
[Show abstract][Hide abstract] ABSTRACT: There is considerable interest in the use of wireless sensor networks (WSNs) for distributed sound capture and acoustic source localisation (ASL) where array elements are spaced over a large area. High sampling rates, such as digital audio at 44.1 kHz, pose a major challenge for efficient wireless personal area network (WPAN) standards such as IEEE 802.15.4 (Zigbee) with an absolute maximum data throughput of 250 kbps. This paper investigates the effect of sampling frequency on the accuracy of time delay estimation using different algorithms in the time domain, such as basic cross correlation (BCC) and generalised cross correlation (GCC), frequency and content based features such as envelope, including generalised phase spectrum (GPS) and envelope-GPS (EGPS). Experimental and simulation studies have been undertaken which show that frequency domain and content based features algorithms can achieve more accurate time delay estimation at low sampling frequencies than time domain algorithms if the appropriate signal contents are extracted. Therefore they are more appropriate for wireless ASL applications.
[Show abstract][Hide abstract] ABSTRACT: In this paper, a study is conducted into optimization of quantum and coupling efficiency of solar rectennas. The optical antenna impedance is calculated using Method of Moment, whereas the Metal/Insulator/Metal (MIM) diode characteristics are calculated using Simmons' formula of tunneling current. The diode resistance and the responsivity have been determined based on the I–V characteristics of the MIM diode. Additionally, the quantum and coupling efficiency have been calculated from the diode and antenna resistances as well as the diode responsivity. Furthermore, both efficiencies have been optimized by finding the optimum values of the insulator layer thickness and the metal work function difference.
Antennas and Propagation Conference (LAPC), 2013 Loughborough; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Physical layer network coding (PNC) is a novel technique that allows two users to exchange messages in a wireless network. PNC takes place at a relay node and exploits the interference caused by incoming signals from the two users to increase throughput. In this paper, the performance of a two-way relay network employing PNC is evaluated with three types of error-correcting codes used at the source and destination nodes, namely low-density parity-check codes, turbo codes and bit-interleaved coded modulation with iterative decoding (BICM-ID). All three coding schemes perform similarly in a single user system on the AWGN channel with no relay, but results obtained when employing PNC show that although there is an overall degradation in their performance of all three codes, the LDPC code performance is more seriously affected due to the Sum-Product decoding algorithm being less robust to unreliable symbols broadcast from the relay.
Wireless and Mobile Networking Conference (WMNC), 2013 6th Joint IFIP; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Throughput maximization is generally the major objective when allocating resources in orthogonal frequency division multiple access (OFDMA)networks. Traditionally, dynamic allocation methods were developed to exploit multi-user diversity in these networks. These techniques achieved significant gain in throughput by adopting relaxed convex models to define system upper bound capacity. Frequency diversity, on the other hand, is only considered to a certain extent in order to meet user service constraints. The vast majority of existing research relies on these techniques. Separately, research considering combining frequency diversity and multi-user diversity in full has been scarce. The results of our research in this paper show that using this dual diversity combining can substantially maximize system capacity and resource efficiency, and minimize outage probability whilst users' quality of service (QoS) demands are maintained.
[Show abstract][Hide abstract] ABSTRACT: In this work, a new low complexity linear precoded orthogonal frequency division multiplexing (LP-OFDM) system, called Haar-OFDM (H-OFDM), is proposed. The proposed system employs a fast precoder, denoted as inverse D-precoder (IDP), which is derived by merging the operations of the fast Haar precoder (FHP) and inverse fast Fourier transform (IFFT) as one transform. Interestingly, the number of arithmetic operations required by the H-OFDM system are noticeably smaller than the conventional OFDM. Furthermore, extensive simulation results demonstrate that the H-OFDM system is robust against the frequency-selectivity of the channel.
Communications (ICC), 2013 IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: In this paper, an investigation is presented into infrared nanoantennas for solar energy harvesting at 10-μm wavelength, where considerable solar energy is available. These antennas have been modeled using both the integral equation model and the circuit model. The method of moments has been utilized to solve Hallen's and Pocklington's integral equations to find the current distribution over the antenna surface by considering the conductivity and the dielectric properties of gold at this wavelength, as well as its effect on the antenna performance. For verification of the obtained results, this antenna has been simulated using a finite element method-based electromagnetic simulator and both results were found to be consistent. In addition, the metal/insulator/metal (MIM) diode has been studied and its equivalent circuit is presented. Furthermore, a solar rectenna has been constructed by overlapping the antenna arms over a small area to incorporate the MIM diode. The circuit of the solar rectenna, with mathematical expressions for the elements of the equivalent circuit, is demonstrated. Finally, a parametric study into the effect of the MIM diode on the captured voltage is conducted.
IEEE Journal of Selected Topics in Quantum Electronics 01/2013; 19(3):9000208-9000208. · 4.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this letter, a Sum-Product algorithm (SPA) utilizing soft distances is shown to be more resilient to impulsive noise than conventional likelihood-based SPAs, when the noise distribution is unknown. An efficient version of the soft distance SPA is also developed but with half the storage requirements and running time.
IEEE Transactions on Communications 01/2013; 61(6):2113-2116. · 1.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This letter presents an efficient technique to reduce the impact of nonlinear power amplifiers on the bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems. The proposed technique is based on the well-established Partial Transmit Sequence (PTS), a power amplifier model, and a simple single point cross correlator. Unlike the conventional PTS, the optimum phase sequence in the proposed system is selected by maximizing the correlation between the input and output of the power amplifier model. Simulation results have confirmed that the BER using the proposed technique is almost identical to the state-of-the-art while the complexity of the proposed optimization metric is significantly reduced.
[Show abstract][Hide abstract] ABSTRACT: In this paper, a novel adaptive detector for uplink interleaved division multiple access (IDMA) transmissions is proposed. The conventional IDMA receiver mitigates multiple access interference (MAI) and inter-symbol interference (ISI) by exchanging iteratively extrinsic soft log-likelihood ratio (LLR) information between the Elementary Signal Estimation (ESE) and the a posteriori probability decoder (APP-DEC). In contrast, the proposed receiver jointly removes MAI and ISI effects by utilizing an adaptive, chip-level, centralized decision feedback equalizer (CDFE). The CDFE equalizer iteratively exchanges data symbols with the DEC. In decision-directed mode, for efficient estimation of the transmitted symbols, the CDFE equalizer depends on both a priori information of the user's information symbols, which are fed back from the decoders, and the estimated channel impulse response. Simulation results using experimentally obtained shallow water impulse responses demonstrate the superior performance of the proposed CDFE receiver over the decentralized decision feedback equalizer (DDFE) and linear equalizer (LE).
Sensor Signal Processing for Defence (SSPD 2012); 01/2012
[Show abstract][Hide abstract] ABSTRACT: This paper presents a proof-of-concept for a short range underwater optical wireless communication system. It investigates of the use of Optical Orthogonal Frequency Division Multiplexing (OOFDM) as a modulation scheme and presents the characteristics of the underwater propagation channel for amplitude modulated optical waves. Although system under investigation utilizes a data rate of 1 Mbpsm, it is evident that higher data rates are possible with minor changes in the optical front-end hardware and the signal processing chain. To evaluate the system performance, tests were conducted in clear water for distances up to three meters and in three simulated scenarios of dirty water (deep, medium and shallow) for a distance of half a meter. All test were performed in a controlled laboratory environment using a water tank. The performance of the system has been evaluated using offline processing of the received OOFDM symbols. The Bit-Error Rate (BER) performance of the system is investigated as function of bandwidth, distance of transmission, and Signal-to-Noise Ratio (SNR). Additionally, the transfer function of the optical underwater channel characteristics are presented along with measured statistics of delay spread of the channel to show the presence or absence of multi-path effects. It should be noted that the intended application of this system is docking of remotely operated and autonomous underwater vehicles, where high speed data transfers are essential. Another possible application is data collection from deployed sensors gathering data over a long periods of time.
[Show abstract][Hide abstract] ABSTRACT: In this paper, a new and simple actuation system based on a magnetic levitation is proposed to move a small permanent magnet embedded in a Wireless Capsule Endoscope (WCE) for inspection of the colon. This study focuses on the design of a PID linear controller to hold the WCE and maintain it at a desired position relative to the robotic movable frame so that it can navigate the bowel by moving this frame and/or the patient. The controller output in the form of pulse width modulation (PWM) is based on position feedback from magnetic sensors. A realistic simulation model is designed and implemented in Matlab/Simulink to validate the proposed controller. To verify the effectiveness of the proposed system, the controller is implemented, based on the TMS320F2812 digital signal processor (DSP). The real-time tracking performance of the control system is evaluated based on step and square reference trajectories. Simulation and experimental results are included showing the performance of the proposed controller for capsule actuation.
Robotic and Sensors Environments (ROSE), 2012 IEEE International Symposium on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: This work addresses specific challenges posed by wireless communications for a Micro-Remotely Operated Vehicle (ROV). The majority of research within this field has primarily focussed on reliable acoustic links for navigation purposes and low data rate communications for critical status updates (
[Show abstract][Hide abstract] ABSTRACT: This paper explores possible approaches to very low power, environmentally friendly underwater acoustic communications with signals that are well disguised in the background noise. While the underwater acoustic spectrum is currently not regulated, it is likely that it will be in the future, both to ensure human activities have minimal impact on marine wildlife and to minimise interference with other acoustic systems. Two variations on a low bit rate spread spectrum modulation scheme using multiple pseudo-noise codes are compared, the first using conventional BPSK modulation and the second using “carrierless” modulation (bandlimited noise). Simulation shows that for a given time-bandwidth product and data rate, the carrierless modulation outperforms the BPSK system. Additional benefits from the carrierless approach are a simpler transmitter and receiver structure, reduced cost of implementation and better noise-like statistics for blending into background noise. The carrierless system is tested in recent trials in the North Sea and was effective for communication at ranges up to 4km with only 0.1W of acoustic power transmitted (160 dB re 1 μPa at 1m). The maximum bit rate tested for systems using length 4095 PN codes was 70bps, while for a system with length 8191 codes 35bps, with the latter system being capable of 48bps if it's full codebase capacity is used. The authors conclude that this is a potentially powerful technique that, combined with advanced error correction codes and Doppler compensation methods, could form the basis of very robust, long range, environmentally friendly acoustic modems for a variety of command/control and low volume sensor data gathering applications.