Phuong T. Tran

Joint optimization of relay selection and power allocation in cooperative OFDM networks with imperfect channel estimation

We consider the wireless relay network in which a base station communicates with multiple subscribers, each of which has the ability to act as a relay to forward information to a base station. Here, we propose an algorithm for joint optimization of power allocation, time scheduling, and relay selection when there is imperfect channel state information (CSI). We show that the algorithm converges with probability one to the optimal solution when a condition is satisfied. Otherwise, it converges with probability one to a solution in some neighborhood of the optimal solution.

Joint optimization of power allocation and cooperation in wireless OFDM networks

In wireless communication networks more than one antenna can be used to enhance the quality of transmission with transmit diversity. However, wireless devices such as mobile phones cannot have more than one antenna because of limits on size and complexity. Recently, cooperative communications have been proposed to create virtual antenna systems for circumventing this problem. This technique achieves a diversity gain by using a combination of the relayed signal and the direct signal. Here, we use a dual optimization method for non-convex problems to jointly optimize the power allocation and the scheduling of wireless cooperative OFDM systems. We find the optimal solution, and confirm our analysis by numerical results.

Performance of time switching based energy harvesting for amplify-and-forward half-duplex relaying with hardware impairment

In this paper, we derive the formulas for outage probability and system throughput of an amplify-and-forward half-duplex relay network, in which the relay node is equipped with time switching based energy harvesting capability. It can be learnt from the analysis that the throughput performance of the system of interest is maximized only at an appropriate choice of the time-switching factor. This optimal value can be found by numerical algorithm. The analysis also clarifies the effect of other parameters such as transmitted-power-to-noise ratio and the data rate, to the system performance. All these above results are confirmed by Monte-Carlo simulation.

On the Performance of Decode-and-Forward Half-Duplex Relaying with Time Switching Based Energy Harvesting in the Condition of Hardware Impairment

In this paper, the outage performance and system throughput of a decode-and-forward half-duplex relay network, in which the relay node is equipped with time switching based energy harvesting capability, are derived rigorously. The analytical results provide theoretical insights into the effect of various system parameters, such as time switching factor, source transmission rate, transmitting-power-to-noise ratio to system performance. Our analysis is confirmed by Monte-Carlo simulation, and can serve as a guideline to design practical energy-harvested relaying systems.

Performance Enhancement for Energy Harvesting Based Two-Way Relay Protocols in Wireless Ad-hoc Networks with Partial and Full Relay Selection Methods

Abstract In this paper, we propose two relay selection methods to enhance system outage performance for energy harvesting (EH) based two-way relaying protocols in wireless adhoc networks. In the proposed protocol, two source nodes communicate with each other via the assistance of multiple decode-and-forward (DF) relays using three-phase digital network coding. At the first and second phases, two sources broadcast their data to the relays. Employing a power-splitting model, the relays would harvest energy from radio frequency (RF) signals of the sources to transmit the data at the third phase. We propose a simple partial relay selection (PRS) method and an opportunistic relay selection (ORS) method to enhance the reliability of data transmission at the cooperative phase. For performance evaluation, we derive exact and asymptotic expressions of the system outage probability (SOP) for the proposed protocols over block Rayleigh fading channels. Finally, Monte Carlo simulations are presented to verify the theoretical derivations as well as to compare the performance of the proposed protocols with that of the random relay selection protocol.

Adaptive Energy Harvesting Relaying Protocol for Two-Way Half-Duplex System Network over Rician Fading Channels

We investigate the system performance of a two-way amplify-and-forward (AF) energy harvesting relay network over the Rician fading environment. For details, the delay-limited (DL) and delay-tolerant (DT) transmission modes are proposed and investigated when both energy and information are transferred between the source node and the destination node via a relay node. In the first stage, the analytical expressions of the achievable throughput, ergodic capacity, the outage probability, and symbol error ratio (SER) were proposed, analyzed, and demonstrated. After that, the closed-form expressions for the system performance are studied in connection with all system parameters. Moreover, the analytical results are also demonstrated by Monte Carlo simulation in comparison with the closed-form expressions. Finally, the research results show that the analytical and the simulation results agree well with each other in all system parameters.

Energy harvesting over Rician fading channel: A performance analysis for half-duplex bidirectional sensor networks under hardware impairments

In this paper, a rigorous analysis of the performance of time-switching energy harvesting strategy that is applied for a half-duplex bidirectional wireless sensor network with intermediate relay over a Rician fading channel is presented to provide the exact-form expressions of the outage probability, achievable throughput and the symbol-error-rate (SER) of the system under the hardware impairment condition. Using the proposed probabilistic models for wireless channels between mobile nodes as well as for the hardware noises, we derive the outage probability of the system, and then the throughput and SER can be obtained as a result. Both exact analysis and asymptotic analysis at high signal-power-to-noise-ratio regime are provided. Monte Carlo simulation is also conducted to verify the analysis. This work confirms the effectiveness of energy harvesting applied in wireless sensor networks over a Rician fading channel, and can provide an insightful understanding about the effect of various parameters on the system performance.

Performance Analysis of General Hybrid TSR-PSR Energy Harvesting Protocol for Amplify-and-Forward Half-Duplex Relaying Networks

In this paper, we propose a hybrid protocol for energy harvesting in wireless relay networks, which combines the benefits of both time-switching relaying (TSR) and power-splitting relaying (PSR), which are two main protocols for energy harvesting. In TSR, a dedicated harvesting time in each time slot is allocated for energy harvesting, while the remaining time is used for information transmission. In PSR, a portion of received power is split for energy harvesting. TSR can simplify the hardware compared to PSR, but reduce the throughput or achievable rate of the system. Specifically, we conduct a rigorous analysis to derive the closed-form formulas for performance factors of the system. We deliver the analysis results for various transmission modes: instantaneous transmission, delay-limited transmission, and delay-tolerant transmission, which are different from each other on the availability of statistical information about the channels between source and relay nodes. The results are also confirmed by Monte Carlo simulation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Optimization of Mobility Control in Mobile Wireless Networks for Energy Saving

In this paper, we consider a multi-hop wireless relay neworks, in which the source node and destination node have fixed location while we can control the positions of the relay nodes. Some strategies to control positions of relay nodes to minimize energy consumption of transmission from sources to sinks is introduced and analyzed. Three different cases were investigated, including networks with single flow, networks with multiple flows, and networks with coverage constraints for the relay nodes. The most contribution of this paper is providing simple localized algorithms for relay nodes, yet optimize the energy consumption problem. The analysis is also confirmed by numerical results.

A Novel Compressed Sensing Approach to Speech Signal Compression

Compressed sensing (CS) is a technique to sample compressible signals below the Nyquist rate, whilst still allowing near optimal reconstruction of the signal. In this paper, we apply the iterative hard thresholding (IHT) algorithm for compressed sensing on the speech signal. The interested speech signal is transformed to the frequency domain using Discrete Fourier Transform (DCT) and then compressed sensing is applied to that signal. The compressed signal can be reconstructed using the recently introduced Iterative Hard Thresholding (IHT) algorithm and also by the tradditional \( \ell_{1} \) minimization (basic pursuit) for comparison. It is shown that the compressed sensing can provide better root mean square error (RMSE) than the tradition DCT compression method, given the same compression ratio.