Shouhong Zhu

Bio: Shouhong Zhu is an academic researcher from Imperial College London. The author has contributed to research in topics: Code division multiple access & Relay. The author has an hindex of 6, co-authored 23 publications receiving 279 citations. Previous affiliations of Shouhong Zhu include Newcastle University & Lancaster University.

Joint synchronization and localization using TOAs: A linearization based WLS solution

Abstract: Joint synchronization and localization using time of arrival (TOA) measurements is a very important research topic for many wireless ad hoc sensor network applications. For such TOA based joint synchronization and localization, the least square (LS) criterion and its corresponding solution have been shown to exhibit optimum estimation performance but generally at a very high computational complexity. Due to its importance and difficulty, in this paper we consider the issue how to approach the estimation performance of such LS solution at low computational complexity: We propose a low-complexity algorithm, which is based on the linearized equations from TOA measurements and applies a weighted least square (WLS) criterion in a computationally efficient way to closely approach the LS solution in estimation performance; Via analyzing and simulating its estimation performance we evidently demonstrate the proposed algorithm of its superior trade-off between estimation performance and computational complexity. The proposed algorithm is also applicable to similar application areas involving TOA base joint timing and positioning.

Distributed Cooperative Localization of Wireless Sensor Networks with Convex Hull Constraint

Abstract: Localization of wireless sensor networks is aimed at determining the positions of all sensors in a network, usually given a few connected anchor nodes' positions and certain relative measurements, where the latter could be pairwise distance measurements among directly connected neighbors as considered in this paper. In this paper we investigate neighborhood collaboration based distributed cooperative localization of all sensors in a particular network with the so-called `convex hull constraint': all nodes in such a network are either position-known anchors or sensors to be localized, and every sensor is inside the convex hull of its neighbors. For such a practically widely seen thus important class of localizable wireless sensor networks, we propose three iterative self-positioning algorithms, for independent implementation at all individual sensors of the considered network. Analysis and simulation study show that when iteratively running at all sensors of the considered network, i) the first one of our proposed iterative self-positioning algorithms leads to global convergence, where the converged solution is the correct positions of all sensors in the absence of measurement error, but might not be optimum if there exist measurement errors; ii) the second algorithm suffers from local convergence, but once correctly converged the converged solution would be the least squares (LS) solution; iii) the third algorithm, a combined version that switches between the former two algorithms' iterations efficiently and independently at individual sensors based on locally collected information, globally converges to the LS solution, as long as the measurement errors are sufficiently small such that the converged solution by the first algorithm is well inside the correctly converging area of the second algorithm.

Distributed Cooperative Routing for UWB Ad-Hoc Networks

Abstract: This conference paper proposes and investigates a new distributed cooperative routing strategy that can be adopted to forward data in the ultra wide band (UWB) ad-hoc network via a multi-hop route with the best instantaneous quality. The strategy combines the physical (PHY) and medium-access-control (MAC) layer mechanisms to select the best route from available ones in a cooperative and distributed way. Using an example of the parallel two-hop relay network where data from a source node can be forwarded by several possible relays to the destination node, we study two related issues: First, we devise a new estimation algorithm for the UWB link received signal-to-noise ratio (SNR) that is used to determine the UWB link quality. The estimation algorithm is unbiased with estimation errors significantly lower than the reported algorithms in literature. Second, we propose a new distributed cooperative routing scheme. Each relay node uses an enhanced carrier sensing with deterministically mapped backoff period as the MAC protocol. The back-off period is chosen by each relay such that the higher the quality of the associated source-relay-destination route, the shorter the back-off time. Simulation results show that even without any feedback about the relay- destination link quality from the destination node to relays and using only its statistical information, the proposed scheme still has up to 3 dB improvement in performance as compared to the random routing. When having 1-bit such feedback, the proposed scheme can achieve full diversity and the overall performance is only 2 dB away from that with full-precision feedback.

A simple approach of range-based positioning with low computational complexity

Abstract: For range based positioning the least square (LS) criterion and its produced solution exhibit superb estimation performance, but generally at a very high computational complexity. In this letter we consider the issue how to approach such LS solution in estimation performance at low computational complexity. We propose a novel algorithm that is based on the equations linearized from range measurement equations and implements a weighted least square criterion in a computationally efficient way. The proposed algorithm involves a quadratic equation linking the linearization-caused extra variable and the position to be estimated, thus results in a closed form solution.We analyze and simulate its estimation performance, and evidently show that the proposed algorithm can very closely approach the LS solution in estimation performance at a significantly low computational complexity.

Cooperative Orthogonal MIMO-Relaying for UWB Ad-Hoc Networks

Abstract: This conference paper proposes and investigates the cooperative orthogonal multiple input multiple output (MIMO) relaying strategies that can be adopted to forward data within UWB ad-hoc networks. We study two related issues: We derive the formula for the cooperative orthogonal MIMO-relaying with all channels' information under the amplify-and-forward data relaying policy, and present the conditions for different data forwarding scenarios to realize orthogonal MIMO-relaying or that via own component suppression. Further, we propose three approaches to calculate the amplifying parameters at relays. Simulation studies show that for given data forwarding scenario if the relay number satisfies the least requested number, all three approaches can realize orthogonal MIMO-relaying or that via own component suppression. With the least requested number of relays, all three approaches exhibit the same diversity order (one), and that the seemingly best approach with channel-matched weights is worse than the other two approaches, i.e. the one with channel phase-matched weights and the one with all-equal weights.

On the study of network coding with diversity

Abstract: Recently proposed physical-layer network coding (PNC) has demonstrated the promise to significantly improve the throughput of wireless networks whose links can be modeled as additive white Gaussian noise (AWGN) channels. However, the extension to multipath channels is problematic, since the technique would then require both amplitude and phase compensation at each transmitter. Phase compensation requires accurate distributed phase tracking, whereas the required amplitude compensation is even more troubling, as it leads to an inefficient system that yields no diversity even in the presence of perfect channel estimates. Here, a system that avoids these limitations is obtained by reaching up one level higher in the network hierarchy and performing distributed relay selection with cognizance of the PNC technique that we will employ at the physical layer. Since the resulting scheme will achieve a form of selection diversity, we term it ldquonetwork coding with diversityrdquo (NCD). To facilitate performance evaluation, two information-theoretic metrics, the outage and ergodic capacity, are studied. Our analytical and simulation results show that the proposed protocol achieves more robust performance and higher system throughput than comparable schemes. Finally, the proposed network coding is extended to the context of cooperative multiple access channels, which yields a new cooperative protocol with larger outage and ergodic capacity compared with existing transmission schemes.

Radio Sleep Mode Optimization in Wireless Sensor Networks

Abstract: Energy efficiency is a central challenge in sensor networks, and the radio is a major contributor to overall energy node consumption. Current energy-efficient MAC protocols for sensor networks use a fixed low-power radio mode for putting the radio to sleep. Fixed low-power modes involve an inherent trade-off: deep sleep modes have low current draw and high energy cost and latency for switching the radio to active mode, while light sleep modes have quick and inexpensive switching to active mode with a higher current draw. This paper proposes adaptive radio low-power sleep modes based on current traffic conditions in the network. It first introduces a comprehensive node energy model, which includes energy components for radio switching, transmission, reception, listening, and sleeping, as well as the often disregarded microcontroller energy component for determining the optimal sleep mode and MAC protocol to use for given traffic scenarios. The model is then used for evaluating the energy-related performance of our recently proposed RFID impulse protocol enhanced with adaptive low-power modes, and comparing it against BMAC and IEEE 802.15.4, for both MicaZ and TelosB platforms under varying data rates. The comparative analysis confirms that RFID impulse with adaptive low-power modes provides up to 20 times lower energy consumption than IEEE 802.15.4 in low traffic scenario. The evaluation also yields the optimal settings of low-power modes on the basis of data rates for each node platform, and provides guidelines and a simple algorithm for the selection of appropriate MAC protocol, low-power mode, and node platform for a given set of traffic requirements of a sensor network application.

Non-Line-of-Sight Node Localization Based on Semi-Definite Programming in Wireless Sensor Networks

Abstract: An unknown-position sensor can be localized if there are three or more anchors making time-of-arrival (TOA) measurements of a signal from it. However, the location errors can be very large due to the fact that some of the measurements are from non-line-of-sight (NLOS) paths. In this paper, a semi-definite programming (SDP) based node localization algorithm in NLOS environments is proposed for ultra-wideband (UWB) wireless sensor networks. The positions of sensors can be estimated using the distance estimates from location-aware anchors as well as other sensors. However, in the absence of line-of-sight (LOS) paths, e.g., in indoor networks, the NLOS range estimates can be significantly biased. As a result, the NLOS error can remarkably decrease the location accuracy, and it is not easy to accurately distinguish LOS from NLOS measurements. According to the information known about the prior probabilities and distributions of the NLOS errors, three different cases are introduced and the respective localization problems are addressed. Simulation results demonstrate that this algorithm achieves high location accuracy even for the case in which NLOS and LOS measurements are not identifiable.

Non-line-of-sight node localization based on semi-definite programming in wireless sensor networks (アドホックネットワーク)

Abstract: An unknown-position sensor can be localized if there are three or more anchors making time-of-arrival (TOA) measurements of a signal from it. However, the location errors can be very large due to the fact that some of the measurements are from non-line-of-sight (NLOS) paths. In this paper, a semi-definite programming (SDP) based node localization algorithm in NLOS environments is proposed for ultra-wideband (UWB) wireless sensor networks. The positions of sensors can be estimated using the distance estimates from location-aware anchors as well as other sensors. However, in the absence of line-of-sight (LOS) paths, e.g., in indoor networks, the NLOS range estimates can be significantly biased. As a result, the NLOS error can remarkably decrease the location accuracy, and it is not easy to accurately distinguish LOS from NLOS measurements. According to the information known about the prior probabilities and distributions of the NLOS errors, three different cases are introduced and the respective localization problems are addressed. Simulation results demonstrate that this algorithm achieves high location accuracy even for the case in which NLOS and LOS measurements are not identifiable.