[Show abstract][Hide abstract] ABSTRACT: Dynamic power allocation and power splitting, in a multicarrier two-hop link with a wireless powered relay, is investigated. We first formulate the corresponding optimization problem, which consists of the joint optimization -in terms of achievable rate- of, 1) the dynamic power allocation among multiple channels and, 2) the selection of the power splitting ratio between information processing and energy harvesting at the relay, when amplify-and-forward is applied. This is a non-convex optimization problem, which is mapped to a convex one and optimally solved using one-dimensional search and dual decomposition, while a suboptimal efficient iterative method is also proposed. Simulations reveal a significant increase in the throughput, when comparing the proposed approach with two alternative power allocation schemes, while they verify the effectiveness of the fast-converging iterative solution.
IEEE Wireless Communication Letters 08/2015; 4(4):1-1. DOI:10.1109/LWC.2015.2424237
[Show abstract][Hide abstract] ABSTRACT: This paper presents an adaptive approach to address the two main problems associated with the time varying Doppler shift, the first being the acceleration effects on the cyclic-prefix (CP) correlation and the second, the effect of a sudden change in the velocity direction between packets on the entire orthogonal frequency division multiplexing (OFDM) symbols. In addition, this paper considers the residual Doppler shift or carrier frequency offset (CFO) that was estimated iteratively within a range according to a design based on the sub-carrier spacing using pilots, which are basically utilized for the purpose of channel estimation. Furthermore, the proposed algorithm adopts three estimations of the symbol timing offset. These estimations are centroid-based localization over an anticipated CP window, first order expectation and autocorrelation of the received CP with its replica. Subsequently, a penalization algorithm is applied in order to drop the anomalous parameter among them. Therefore, the consequences of the inflection point that accompanies the abrupt change in the velocity are mitigated and a reliable time varying Doppler shift is obtained. This Doppler shift is fine tuned in an iterative manner. Compared with the block-based Doppler compensation approach, the proposed technique works with variable speed during packet duration. In addition, it exploits the available bandwidth more efficiently by utilizing a single preamble of linear-frequency-modulation (LFM) to detect the start of the packet. The proposed receiver was evaluated through simulations and sea trials conducted over 500 m and 1000 m channel ranges. In simulations, a model was designed to imitate the time varying Doppler shift with two scenarios (expansion/compression) in combination with a various multipath delay spread. The simulation results confirm that the proposed system accommodates an acceleration up to m/s2 during the packet time.
[Show abstract][Hide abstract] ABSTRACT: Novel analytic solutions are derived for integrals that involve the
generalized Marcum Q-function, exponential functions and arbitrary powers.
Simple closed-form expressions are also derived for the specific cases of the
generic integrals. The offered expressions are both convenient and versatile,
which is particularly useful in applications relating to natural sciences and
engineering, including wireless cpmmunications and signal processing. To this
end, they are employed in the derivation of the channel capacity for fixed rate
and channel inversion in the case of correlated multipath fading and switched
[Show abstract][Hide abstract] ABSTRACT: Energy harvesting has been recognized as a key technique for improving the performance of energy constrained networks. In this paper, the application of wireless information and power transfer, an emerging concept of energy harvesting, to wireless cooperative networks is considered. Particularly the focus is on a cooperative network in which a source communicates with a destination with the help of relays and the relays are randomly deployed according to homogeneous Poisson point process. According to the available channel state information, three different strategies to use the available relays are studied, and their impact on the outage probability and diversity gain is characterized by applying stochastic geometry. Particularly the developed analytical results demonstrate that the use of energy harvesting relays does not degrade the achievable diversity gain of cooperative protocols, but has a deteriorating effect on the outage performance. Simulation results are provided to confirm the accuracy of the developed analytical results and facilitate a better performance comparison.
ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
[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: 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: 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: Physical layer network coding (PNC) is a novel technique that allows two users to exchange messages in a wireless network. The most significant feature of PNC is the exploitation of interference at a relay due to incoming signals from two users, allowing an increase in throughput. In this paper, Extrinsic Information Transfer (ExIT) charts are employed to evaluate the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) combined with PNC. We address critical design issues to enhance decoding performance and provide analytical bounds on the performance. The analysis is extended for PNC employing Turbo and Low-Density Parity-Check (LDPC) codes to compare the performance with BICM-ID on the AWGN channel. Our results show that BICM-ID with PNC performs very similarly to a turbo-coded PNC scheme but, surprisingly, it outperforms a LDPC-coded PNC scheme, due to the Sum-Product decoding algorithm, which is less robust to unreliable symbols broadcast from the relay and needs more iterations to reach convergence. This shows that when considering trade-offs between performance and complexity, BICM-ID is an attractive coding scheme for wireless relay networks employing PNC.
2013 IEEE 20th International Conference on Electronics, Circuits, and Systems (ICECS); 12/2013
[Show abstract][Hide abstract] ABSTRACT: Resource allocation for a downlink orthogonal frequency division multiple access (OFDMA) system ensures that capacity and throughput are maximized. In the literature, either channel coding is not considered or only a fixed code rate is specified. To overcome this problem, an optimized cross-layer resource allocation strategy that distributes the user, bit and power optimally has been proposed for adaptive modulation and coding (AMC) based single-cell downlink OFDMA systems. The proposed strategy, which is referred to as optimized user, bit and power allocation (OUBPA), considers throughput as a new cost function in terms of spectral efficiency and bit-error rate (BER) to allocate the available resources. An optimized approach is presented for solving the throughput maximization problem and simulation results demonstrating that the throughput performance of the OFDMA-AMC system using OUBPA strategy outperforms conventional techniques.
2013 IEEE 20th International Conference on Electronics, Circuits, and Systems (ICECS); 12/2013
[Show abstract][Hide abstract] ABSTRACT: The exploitation of already deployed wireless local area networks
(WLAN)s (e.g., WiFi access points (AP)s) has attracted considerable
attention, as an efficient and practical method to improve the
performance of beyond 4G wireless networks. In this paper, we propose a
novel communication paradigm to satisfy the performance demands of
future wireless networks: a hybrid Cellular/WLAN network architecture
with wireless offloading. In contrast to the commonly adopted practice
of WiFi offloading, where the WLAN APs have a wired backhaul (e.g.,
Digital Subscriber Line), we propose a wireless offloading approach,
where the WLAN APs will share their wireless cellular broadband
connection with other users. These users will select their serving node,
i.e., the macro-cell eNodeB or a WLAN AP, based on a certain selection
criterion. Thus a challenging research field is originated, where
interfering effects and wireless resources limitations play a dominant
role. Important performance metrics of the proposed hybrid scheme,
including the bit error probability, the ergodic capacity and the
average signal-to-interference-plus noise ratio, are theoretically
studied and closed form expressions are derived for the single-user case
with multiple interferers, for both identical and non-identical fading
conditions. Also, based on the general multi-cellular hybrid
WLAN-Cellular concept, we first propose a intercell interference
minimization approach. Then we present a novel scheme for achieving
frequency reuse equal to one within a single macro-cell, under specific
performance criteria and constraints, that guarantee the overall cell or
the individual user QoS requirements.
[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. DOI:10.1109/TTHZ.2013.2271833 · 2.18 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.
[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 05/2013; 19(3):9000208-9000208. DOI:10.1109/JSTQE.2012.2227686 · 2.83 Impact Factor
[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: This chapter highlights the history of optical and infrared antennas for solar rectennas and mentions the important contributions made in this field. Moreover, it demonstrates the versatility of solar rectennas over the traditional solar cells. The structure and the operation theory of solar rectennas have also been presented in this chapter. The main part of this chapter focuses on the antenna types utilized in solar rectenna systems such as: dipole, bowtie and spiral nanoantennas in both single and array forms. A comparison between these types has been made based on the captured electric field and the area under curve which were computed by the aid of numerical analysis.
Rectenna Solar Cells, 01/2013: pages 231-256; Springer.