Anchor-Free Localization Method for Mobile Targets in Coal Mine Wireless Sensor Networks

Severe natural conditions and complex terrain make it difficult to apply precise localization in underground mines. In this paper, an anchor-free localization method for mobile targets is proposed based on non-metric multi-dimensional scaling (Multi-dimensional Scaling: MDS) and rank sequence. Firstly, a coal mine wireless sensor network is constructed in underground mines based on the ZigBee technology. Then a non-metric MDS algorithm is imported to estimate the reference nodes’ location. Finally, an improved sequence-based localization algorithm is presented to complete precise localization for mobile targets. The proposed method is tested through simulations with 100 nodes, outdoor experiments with 15 ZigBee physical nodes, and the experiments in the mine gas explosion laboratory with 12 ZigBee nodes. Experimental results show that our method has better localization accuracy and is more robust in underground mines

A Spectrum Efficient Secure Transmission Scheme Based on Directional Polarization Modulation for Wireless Communication Systems

In this paper, a spectrum efficient secure transmission scheme based on directional polarization modulation (DPM) is proposed. Specifically, the polarized signals are divided into two parts, i.e., I and Q, and a dual-polarized antenna array is designed to form beams to transmit these signals. Naturally, the constellation structure is associated with the beam gain, which can be controlled to make the constellation structure distort in undesired directions. Thus the security is enhanced for the symbol error rate performance deteriorates in undesired directions. Additionally, a kind of directional modulation technique is utilized to transform one component of the polarized signal into QPSK signal and thus improves the modulation order without extra transmitting power consummation. Finally, theoretical analysis and simulation results demonstrate that the proposed scheme can improve the transmission efficiency and provide a security transmission method for wireless communication systems

A Distributed Location Algorithm for Underground Miners Based on Rescue Robot and Coal-Mining Wireless Sensor Networks

Abstract-Rescue robot places an important role when any severe disaster in underground coal mine happens. To locate and keep a track of miners working in a well becomes an impossible completed mission once the well communication infrastructure is all destroyed due to the disasters such as fire damp explosion. Wireless sensor networks, together with underground mine rescue robot provide a potential solution for the challenges in terms of many unique advantages of the wireless sensor networks like random deployments of nodes and network self-organized multi-hops. In this paper, a new coal-mining wireless sensor network (C-WSN) is developed. We propose a distributed system architecture and an improved location algorithm for rescue robot based on radio signal strength indicator (RSSI). The experimental results are analyzed. Finally, we draw conclusion and address the future work

Polarization Filtering and WFRFT-Based Secure Transmission Scheme for Wireless Communications

In this paper, a transmission scheme based on polarization filtering and weighted fractional Fourier transform (PF-WFRFT) is proposed to enhance the transmission security in wireless communications. Indeed, the distribution of the transmit signals processed by WFRFT can be close to Gaussian, which can significantly improve the low detection probability. However, through scanning the WFRFT order with small step size, an eavesdropper can restore a regular constellation and crack the information. To overcome the problem, in the PF-WFRFT scheme, two polarized signals with mutually orthogonal polarization state are utilized to convey the information, which are processed by WFRFT separately and added up linearly before being transmitted by dual-polarized antennas. In this manner, even by scanning the WFRFT order, recovered signals are composite ones, which make the WFRFT order and the signals’ PSs difficult to crack, thus improving the security. In addition, the polarization-dependent loss (PDL) effect on the proposed scheme is discussed and a proprocessing matrix based on the channel information is constructed to eliminate this effect. Finally, numerical results are given to demonstrate the security performance of the proposed scheme in wireless communications

Secure Image Signal Transmission Scheme Using Poly-Polarization Filtering and Orthogonal Matrix

In this paper, a novel secure image signal transmission scheme was proposed in wireless systems, in which the poly-polarization filtering and the orthogonal matrix (PPF-OM) were combined to protect the image signal and eliminate the polarization dependent loss (PDL) at the same time, which was caused by the non-ideal wireless channel. This scheme divided the image information sequence into two parts in order to modulate and reshape the results into symbol matrices with the same size. Then, two sets of polarization states (PSs) and orthogonal matrices (OMs) were designed to process the symbols in order to enhance information protection and eliminate the PDL. Legitimate users were able to apply the shared PSs and OMs, step by step, so the information could be recovered. However, for eavesdroppers, the received signals were random symbols that were difficult to demodulate. Then, the bit error rate and the secrecy rate were derived to evaluate the performance of the PPF-OM scheme. Finally, the simulations demonstrated the superior performance of the PPF-OM scheme for enhancing the information security and eliminating the PDL

Highly Effective Proton-Conduction Matrix-Mixed Membrane Derived from an -SO₃H Functionalized Polyamide

Developing a low-cost and effective proton-conductive electrolyte to meet the requirements of the large-scale manufacturing of proton exchange membrane (PEM) fuel cells is of great significance in progressing towards the upcoming “hydrogen economy” society. Herein, utilizing the one-pot acylation polymeric combination of acyl chloride and amine precursors, a polyamide with in-built -SO3H moieties (PA-PhSO3H) was facilely synthesized. Characterization shows that it possesses a porous feature and a high stability at the practical operating conditions of PEM fuel cells. Investigations of electrochemical impedance spectroscopy (EIS) measurements revealed that the fabricated PA-PhSO3H displays a proton conductivity of up to 8.85 × 10−2 S·cm−1 at 353 K under 98% relative humidity (RH), which is more than two orders of magnitude higher than that of its -SO3H-free analogue, PA-Ph (6.30 × 10−4 S·cm−1), under the same conditions. Therefore, matrix-mixed membranes were fabricated by mixing with polyacrylonitrile (PAN) in different ratios, and the EIS analyses revealed that its proton conductivity can reach up to 4.90 × 10−2 S·cm−1 at 353 K and a 98% relative humidity (RH) when the weight ratio of PA-PhSO3H:PAN is 3:1 (labeled as PA-PhSO3H-PAN (3:1)), the value of which is even comparable with those of commercial-available electrolytes being used in PEM fuel cells. Additionally, continuous tests showed that PA-PhSO3H-PAN (3:1) possesses a long-life reusability. This work demonstrates, using the simple acylation reaction with the sulfonated module as precursor, that low-cost and highly effective proton-conductive electrolytes for PEM fuel cells can be facilely achieved