Dac-Binh Ha

Symbol Error Probability of Distributed-Alamouti Scheme in Wireless Relay Networks

In this paper, we analyze the maximum likelihood decoding performance of non-regenerative cooperation employing Alamouti scheme. Specifically, we derive two closed-form expressions for average symbol error probability (SEP) when the relays are located near by the source or destination. The analytical results are obtained as a single integral with finite limits and an integrand composed solely of trigonometric functions. Assessing the asymptotic (high signal-to-noise ratio) behavior of SEP formulas, we show that the distributed-Alamouti codes achieves a full diversity order. We also perform Monte-Carlo simulations to validate the analysis.

On The Symbol Error Probability of Distributed-Alamouti Scheme

Taking into account the relay’s location, we analyze the maximum likelihood (ML) decoding performance of dualhop relay network, in which two amplify-and-forward (AF) relays employ the Alamouti code in a distributed fashion. In particular, using the well-known moment generating function (MGF) approach we derive the closed-form expressions of the average symbol error probability (SEP) for M-ary phase-shift keying (M-PSK) when the relays are located nearby either the source or destination. The analytical result is obtained as a single integral with finite limits and the integrand composed solely of trigonometric functions. Assessing the asymptotic characteristic of SEP formulas in the high signal-to-noise ratio regime, we show that the distributed-Alamouti protocol achieves a full diversity order. We also perform the Monte-Carlo simulations to validate our analysis. In addition, based on the upper bound of SEP we propose an optimal power allocation between the first-hop (the source-to-relay link) and second-hop (the relay-to-destination link) transmission. We further show that as the two relays are located nearby the destination most of the total power should be allocated to the broadcasting phase (the first-hop transmission). When the two relays are placed close to the source, we propose an optimal transmission scheme which is a non-realtime processing, hence, can be applied for practical applications. It is shown that the optimal power allocation scheme outperforms the equal power scheme with a SEP performance improvement by 2-3 dB.

Physical layer secrecy performance over Rayleigh/Rician fading channels

In this paper, we investigate the physical layer secrecy performance of a single-input single-output system that consists of single antenna devices and operates in the presence of a single antenna passive eavesdropper over dissimilar fading channels. In particular, we consider two scenarios in terms of dissimilar fading channel arrangements: the legal/illegal channels are subject to Rayleigh/Rician fading, respectively; and the legal/illegal channels are subject to Rician/Rayleigh fading, respectively. Specifically, analytical expressions for the probability of the existence of a non-zero secrecy capacity and the secrecy outage probability are derived by using statistical characteristics of the signal-to-noise ratio. Numerical results are provided for selected scenarios to illustrate applications of the developed analytical expressions.

Green two-tiered wireless multimedia sensor systems: an energy, bandwidth, and quality optimisation framework

In wireless multimedia sensor systems (WMSSs), the devices are equipped with multiple energy-constrained camera sensors (CSs) distributed over bandwidth-constrained and lossy wireless channels, in catastrophe-prone areas. Meanwhile, multimedia applications, e.g. video streaming, require considerable energy and bandwidth resources to gain long lifetime and high streaming quality. This study proposes an energy, bandwidth, and quality (EBQ) optimisation framework for green two-tiered WMSSs. The first tier contains the CSs and the second tier includes cluster heads (CHs) selected from the CSs with higher available energy and processing capacity. In the EBQ optimisation framework, a rate allocation optimisation problem is formulated under given constraints of available backhaul bandwidth of the CHs and quality of received videos at base stations (BSs). This problem is solved for optimal encoding rates to packetise each video captured from different environments into multiple descriptions for transmission. Consequently, the average energy consumption per CS is minimised for long lifetime while conserving the bandwidth of the CHs and guaranteeing high quality of received videos for the purpose of monitoring at the BSs. Simulations demonstrate that the proposed EBQ optimisation framework can efficiently enhance the performance of green two-tiered WMSSs in terms of minimum energy consumption, bandwidth efficiency, and high quality.

Physical Layer Secrecy Performance of Multi-hop Decode-and-Forward Relay Networks with Multiple Eavesdroppers

Today, wireless networks become the most popular way to communicate. However, information can be easily eavesdropped or extracted by eavesdroppers due to the broadcast nature of wireless communication. Multi-hop relay communication systems provide for higher secrecy performance than direct transmission techniques. In this paper, the physical layer secrecy performance of multi-hop decode-and-forward (DF) relay network is investigated in the presence of multiple passive eavesdroppers over Nakagami-m fading channels. To do so, we find out the exact closed-form expressions of existence probability of secrecy capacity and secrecy outage probability by using statistical characteristics of signal-to-noise ratio (SNR). Importantly, these expressions are in more general forms compared to other results in the literature. The proposed results show a quite agreement between numerical analysis and equivalent Monte-Carlo simulations.

Time Reversal SWIPT Networks with an Active Eavesdropper: SER-Energy Region Analysis

This paper analyzes a novel multiple-input single- output (MISO) simultaneous wireless information and power transfer (SWIPT) system model in the presence of an active eavesdropper over the frequency-selective fading channel. In this model, a transmitter applies the time reversal (TR) beamforming technique to combat the fading effects whereas a legitimate user employs a power splitter to jointly receive information and energy, and the active eavesdropper jams the user. Given the system model, the system performance in terms of symbol error rate (SER) and energy harvesting (EH) is analyzed. In particular, we devise a SER-energy region, instead of the conventional rate-energy region, to evaluate system performance of the SWIPT model. A moment generating function (MGF)-based method is presented to exactly derive the average SER analysis. Moreover, the closed-form expression of average effective harvested energy is then provided to complete SERenergy region analysis. Finally, analytical results confirmed by numerical simulations show that the TR technique can support the SWIPT system to notably improve the SER performance whereas the jamming signal can enhance the EH performance.

Cognitive Heterogeneous Networks with Unreliable Backhaul Connections

To enhance the spectrum scarcity of cooperative heterogeneous networks (HetNets) with unreliable backhaul connections, we examine the impact of cognitive spectrum sharing over multiple small-cell transmitters in Nakagami-m fading channels. In this system, the secondary transmitters are connected to macro-cell via wireless backhaul links and communicate with the secondary receiver by sharing the same spectrum with the primary user. Integrating cognitive radio (CR) network into the system, we address the combined power constraints: 1) the peak interference power at the primary user and 2) the maximal transmit power at the secondary transmitters. In addition, to exclude the signaling overhead for exchanging channel-state-information (CSI) at the transmitters, the selection combining (SC) protocol is assumed to employ at the receivers. To evaluate the performance, we first derive the closed-form statistics of the end-to-end signal-to-noise (SNR) ratio, from which the exact outage probability, ergodic capacity and symbol error rate expressions are derived. To reveal further insights into the effective unreliable backhaul links and the diversity of fading parameters, the asymptotic expressions are also attained. The two interesting non-cooperative and Rayleigh fading scenarios are also investigated. Numerical results are conducted to verify the performance of the considered system via Monte-Carlo simulations.

Secrecy Performance Analysis of Energy Harvesting Wireless Sensor Networks With a Friendly Jammer

The broadcast nature of energy harvesting wireless sensor networks (EH-WSNs) allows sensor nodes (SNs) within the coverage range of a transmitter to capture its signals. However, an EH-WSN is vulnerable to eavesdropping and signal interception; therefore, security in the EH-WSNs is of significant interest, and this issue has been addressed over many years. However, no work has studied the existence of a friendly jammer to mitigate the security impact. Thus, this paper proposes a model and optimization scheme that uses a wirelessly powered friendly jammer to improve secrecy in EH-WSNs. The considered EH-WSN model includes multiple power stations, multiple SNs (sources) and their base station, a friendly jammer, and multiple passive eavesdroppers. We divide the model into two phases: 1) the power stations transfer RF energy to the source SNs and 2) the source SNs transmit information to their base station, while a friendly jammer generates jamming signals against multiple eavesdroppers. Using statistical characteristics of the signal-to-noise ratio, the closed-form expressions of the existence probability of the secrecy capacity and secrecy outage probability are derived. We also propose an optimal sensor scheduling scheme to enhance physical layer secrecy (i.e., best-node scheduling), and we demonstrate our method’s superior performance compared with a conventional round-robin scheduling scheme. The analysis of the simulation results supports our hypothesis, which is in line with Monte Carlo simulations.

Secure Cognitive Relay Network: Joint the Impact of Imperfect Spectrum Sensing and Outdated Feedback

In this paper, we consider cognitive relay networks with Nth best relay and beamforming schemes under the joint impact of imperfect spectrum sensing and outdated channel feedback. Specifically, we examine the secrecy performance by deriving the exact and asymptotic analytical expressions for the secrecy outage probability. Based on the analysis, we observe that these two types of channel impairments, i.e., imperfect spectrum sensing and outdated channel feedback, greatly affect the system performance. Particularly, the outdated channel feedback (i.e., the outdated coefficient