No-line-of-sight Research Articles

Integration of GNSS observations with volunteered geographic information for improved navigation performance

Abstract Pedestrian and vehicular navigation relies mainly on Global Navigation Satellite System (GNSS). Even if different navigation systems are integrated, GNSS positioning remains the core of any navigation process as it is the only system capable of providing independent solutions. However, in harsh environments, especially urban ones, GNSS signals are confronted by many obstructions causing the satellite signals to reach the receivers through reflected paths. These No-Line of Sight (NLOS) signals can affect the positioning accuracy significantly. This contribution proposes a new algorithm to detect and exclude these NLOS signals using 3D building models constructed from Volunteered Geographic Information (VGI). OpenStreetMap (OSM) and Google Earth (GE) data are combined to build the 3D models incorporated with GNSS signals in the algorithm. Real field data are used for testing and validation of the presented algorithm and strategy. The accuracy improvement, after exclusion of the NLOS signals, is evaluated employing phase-smoothed code observations. The results show that applying the proposed algorithm can improve the horizontal positioning accuracy remarkably. This improvement reaches 10.72 m, and the Root Mean Square Error (RMSE) drops by 1.64 m (46 % improvement) throughout the epochs with detected NLOS satellites. In addition, the improvement is analyzed in the Along-Track (AT) and Cross-Track (CT) directions. It reaches 6.89 m in the AT direction with a drop of 1.076 m in the RMSE value, while it reaches 8.64 m with a drop of 1.239 m in the RMSE value in the CT direction.

Analysis of Ultra Wide Band OFDM Communication System through IEEE802.15.4a in Wireless Communication

This paper uses simulation to evaluate the performance of a UWB communication system with an accurate channel model. A cost-effective prototype model of a real-time UWB communication system. This paper presents a UWB multiband OFDM system for various frequency ranges.Channel subgroups provide various models for the various frequency ranges of IEEE 802.15.4a. The UWB frame repeats from 2 to 10 GHz and provides 8-channel models for indoor and outdoor LOS (line-of-sight) and NLOS (no-line-of-sight) environmental conditions.The uniqueness of Task Group 4a channel models and UWB-enabled frameworks are reviewed and evaluated against a number of channel models.

Detection of GNSS no-line of sight signals using LiDAR sensors for intelligent transportation systems

The reliability and robustness of positioning systems in urban and suburban environments are intrinsic. This is obvious following the continuous increase of Intelligent Transportation Systems (ITS) applications in such challenging environments. Global Navigation Satellite Systems (GNSS) represent the primary positioning technique used for navigation purposes in these applications, which can be satisfying in open-sky areas. However, GNSS cannot provide the same level of navigation performance in urban environments. One of the main reasons for this is the No-Line of Sight (NLOS) signals. In this study, the integration of GNSS and Light Detection and Ranging (LiDAR) sensors is exploited, and a new algorithm is proposed for the detection of NLOS signals. Real field data are used to test and validate the proposed strategy and algorithm. Phase-smoothed code observations are employed to evaluate the accuracy improvement after excluding the NLOS observations. The results show that the horizontal direction's positional accuracy can be improved significantly after applying the proposed algorithm. This improvement reaches 10.403 m with a mean value of 2.162 m (62.2% improvement) over all epochs with detected NLOS signals. After analysing this improvement in the Cross-Track (CT) and Along-Track (AT) directions, it is found that the accuracy improvement reaches 8.641 m with a mean value of 1.699 m in the CT direction and 6.879 m with a mean value of 1.303 m in the AT direction.

Fog-IoT-Based Slope Monitoring (FIoTSM) System With LoRa Communication in Open-Cast Mine

Personal safety of mine professionals in open-cast (OC) mines is a critical concern in mines management and administrative agencies. Miners are required to perform many mining activities and hence are prone to unexpected calamities such as slope failure which is a frequently occurring catastrophe in OC mines. With emerging technologies like wireless sensor network (WSN), fog computing (FC), Internet of Things (IoT), and low-power technologies like long-range (LoRa), the task of monitoring OC mines has become more feasible, cost-effective, and efficient. In this research work, a novel real-time fog-IoT slope monitoring (FIoTSM) system is developed to monitor OC mines. Performance of LoRa coverage is assessed in line of sight (LoS) and no line of sight (NLoS) scenarios. Due to an uncertain condition of mine, where slope failure can occur anytime, latency-free data transmission and processing are required. Thus, IoT is applied to deploy LoRa modules for wireless communication under FC, boosting the monitoring system with the power of LoRa and FC. The data transmitted are permanently stored in cloud servers making it ubiquitously available to users for analytics. The experimental outcome projects the system to be up-and-coming for smart real-time monitoring of slope of OC mines and thereby alert the miners of any failure.

Research on Node localization Algorithm in WSN Based on TDOA

Many applications of wireless sensor networks (WSN) require nodes to know their location information. Monitoring data without node location information is meaningless in many situations. Since the node positioning efficiency of WSN directly affects the performance of the network, designing an efficient positioning algorithm is the focus of WSN research. Based on the principle of TDOA positioning in WSN, it studies two main positioning algorithms: Chan and Taylor algorithm. Meanwhile the least square (LS) method is used to provide the initial position for Taylor algorithm and the first calculation result for Chan algorithm. Simulation results under different conditions show that the Chan algorithm has a good positioning accuracy and less computation than that of Taylor algorithm in the line of sight (LOS) environment. However, under the actual channel, due to the influence of No Line of Sight (NLOS), the positioning accuracy of Taylor algorithm is better than that of Chan algorithm, but its computation is large.

Analysis of channel correlation and channel capacity for indoor MIMO visible light communication systems.

In indoor multi-input-multi-output (MIMO) visible light communication (VLC) systems, spatial multiplexing (SMP) is employed to improve spectral efficiency. However, the performance of SMP in an indoor VLC system depends on a low channel correlation. In this paper, a receiver model with angular diversity detectors is considered. The objective is to reduce the channel correlation and hence the system performance in terms of bit error rate (BER) and channel capacity compared to vertically oriented detectors under no-line-of-sight (NLOS) channel conditions. For a vertical detector setup, the results show that the channel correlation cannot be further reduced by varying the transmitter separation, transmitter semi-angle, or field of view of the receiver in NLOS conditions due to the design of receiver separation being very small in small mobile devices. In comparison to vertical detector setups, by varying the detector axis of each photodetector (PD) detector axis in angular diversity detector setups, the channel matrix rank is improved under LOS conditions, and the channel correlation is effectively reduced under NLOS conditions without requiring any implementation complexity at the receiver. Therefore, it is found that the angular diversity detector setup can substantially improve the BER performance of SMP, since it makes each PD more spatially separated to improve channel conditions. Notably, we deduce the channel capacity expression to approximate the capacity of the indoor highly correlated MIMO channel and verify the theoretical analysis by numerical simulations. The results show that the angular diversity detector setup provides capacity improvement when compared with the vertical detector setup. Even though it diminishes the received power when the elevation angle exceeds the optimal elevation angle, it outweighs this degradation by providing reduced channel correlation.

Modeling and measurements for wireless communication networks in underground mine environments

One of the crucial problems being faced by wireless system designers is experimental understandings of the electromagnetic (EM) wave propagation in high stress environments, such as underground mines and tunnels, so that reliable performance can be achieved. This is driven by the fact of limited availability of real-time data of operational underground mines with different measurement considerations. This paper reports extensive experimental studies and proposes a modified multimode based channel model for wireless communication networks in underground mine environments. The experimental campaigns were carried out in an underground coal mine considering significant use cases viz. line of sight (LOS), no line of sight (NLOS), across the curves and bends, in noisy environments, straight tunnels, and near the face (extraction area). We then validated the proposed channel model with the experimental measurements. The validation results showed reliably a good agreement with a model accuracy of 94.60%, 91%, 90.98% for the straight tunnel, along the belt conveyor and near face respectively. The proposed model outperforms the state-of-the-art channel model for mine workings with model accuracy differences of 60.1%, 60.45% and 58.56% for straight tunnel, along the belt conveyor and near face respectively. A model accuracy of 78.31% is achieved across the curvature measurement scenario. Hence, the proposed channel model can be accepted for wireless communication system design and deployment planning in underground mines to provide a reliable two-way wireless communication and coverage. Furthermore, detailed link analysis of wireless sensor networks in mine workings is also discussed considering packet reception rate with respect to distance and received signal strength.

Analysis of UWB MB-OFDM Communication System through IEEE802.15.4a Channel Models using Matlab Simulink

This paper evaluates the performance of the UWB communication system with an accurate channel model using simulation. In real time a prototype model of UWB communication system is cost effective. This paper UWB Multiband-Orthogonal Frequency Division Multiplexing System is provided for various range of frequency. In various frequency range of IEEE 802.15.4a channel subgroup provides a several model. Ultra wideband frame work recurrence ranges from 2 to 10 GHz, and provides eight different models of channel for both Line-of-Sight (LOS) and No-line-of- Sight (NLOS) environment circumstances of both indoor as well as outdoor. The uniqueness of task group 4a Channel Models and UWB correspondence framework are confirmed and evaluated for numerous channel models.

An Improved Algorithm for TDOA Trajectory Tracking

In a precision positioning system, one important source of positioning error is the clock synchronization problem, which is caused by multiple base stations. Therefore, eliminating the clock synchronization problem in a no-line-of-sight (NLOS) environment plays an important role in reducing errors in a positioning system. To address this problem, this study designs a practical experimental environment and proposes the concepts of Time Difference of Arrival (TDOA) and non-line-of-sight-Time Difference of Arrival (N-TDOA). First, the improved TDOA algorithm is used to determine the tag’s position; second, the tag’s trajectory is drawn at different times; then, a map of the monitored area is loaded, and the tag trajectory is displayed in the actual experimental environment. The experimental results show that the N-TDOA algorithm synchronizes the base stations at the algorithmic layer; thus, deploying network cables or wires to achieve clock synchronization is unnecessary: wireless deployment can be used. In an NLOS environment, the N-TDOA method significantly improves the positioning accuracy compared with that of other algorithms, which facilitates further trajectory tracking research. Overall, the proposed approach improves both the accuracy and stability of trajectory tracking.

Effect of Doppler Shift frequency on the performance of 2x2 OSTBC-OFDM System

In this paper the effect of the Doppler shift frequency on the performance of the 2x2 MIMO system has been studied and presented. A system with two transmits antennas and two receive antennas has been used. Accurate and efficient channel estimation which plays a key role in MIMO-OFDM communication system has been implemented using pilots and training sequences. To guarantee a much more reliable and robust transmission over a hostile wireless channel, a convolutional codes have been added to the 2x2 MIMOOSTBC-OFDM system as a Forward Error Correction (FEC) codes. Two types of convolutional code rate have been used (1/2 and 2/3) depending on the type of modulation. To make this code more robustness against channel impairments; interleaving has been used with the convolutional code. The system has been evaluated for four types of QAM modulation (4-QAM, 8-QAM, 16-QAM, and 64-QAM) as a baseband modulation. The system has been evaluated for three different values of Doppler Shift frequency (5, 50, and 100) Hz. The simulation results demonstrated the performance of the systems over Flat and multi-path Frequency-Selective fading channels, assuming the channels are with No Line Of Sight (NLOS), so the channels are Rayleigh fading channels. The results show that when the Doppler Shift Frequency increased the BER also increases and when Doppler Shift Frequency is 5Hz, the performance of the system is better for four types of QAM modulation and in the two cases of Flat and multi-path Frequency-Selective fading.

Guest Editorial

Guest Editorial

A Localization Algorithm Research to Eliminate the Indoor NLOS Error

Currently, there is an urgent need for indoor positioning technology. Considering the complexity of indoor environment, this paper proposes a new positioning algorithm (N-CHAN) via the analysis of the error of arrival time positioning (TOA) and the channels of S-V model. It overcomes an obvious shortcoming that the accuracy of traditional CHAN algorithm effected by no-line-of-sight (NLOS). Finally, though MATLAB software simulation, we prove that N-CHAN’s superior performance in NLOS in the S-V channel model, which has a positioning accuracy of centimeter-level and can effectively eliminate the influence of NLOS error on positioning accuracy. Moreover, the N-CHAN can effectively improve the positioning accuracy of the system, especially in the conditions of larger NLOS error.

Multi-channel access technology based on wavelength division multiplexing in wireless UV communication mesh network

In this paper, the multi-channel access technology of wavelength division multiplexing (WDM) in the wireless ultraviolet (UV) scattering communication is studied. A multi-interface and multi-channel device is deployed in each UV transceiver node. The band-pass filter is configured in the receiving node so as to realize the multi-channel access by use of the UV WDM technology. Both the UV communication node model and the UV channel model are established. Three types of UV no-line-of-sight (NLOS) multi-channel communications are simulated in the mesh topologies with NS2. The results show that the UV multi-channel access technology can increase network throughput effectively with using WDM.

APPLYING COMBINATORIAL OPTIMIZATION HEURISTICS FOR ENHANCING THE PERFORMANCE OF TH-PPM UWB SYSTEMS: CHAOTIC VERSUS CLASSICAL CODE SEQUENCES

In this article, we propose a process to minimize the Multi-User Interference (MUI) caused by Multiple Access (MA) in a Time Hopping Ultra Wide Band (TH-UWB) system with No Line-Of-Sight (NLOS) multipath channel in a residential environment IEEE 802.15.4a Channel Model 2 (CM2). We discuss both synchronous and asynchronous channels with an Additive White Gaussian Noise (AWGN). The choice of codes allowing multiple access is crucial for minimizing the MUI and to improve the system performance. Recently much works has been done in order to optimize performance by code selection [Bravo et al., 1999; Moreno & Marić, 2000; Guvenc & Arslan, 2004]. This paper is a contribution to this research axis. The minimization of the MUI is formulated as a Combinatorial Optimization Problem (COP) and solved by means of an efficient generic optimization method called Guided Local Search (GLS) [Voudouris, 1997]. In this context, we exploit the richness of chaotic sequences with respect to topologic properties. Simulation results based on the Binary Error Rate (BER) show that optimized chaotic sequences outperforms the classical code sequences.

Monte Carlo simulations for non-line-of-sight ultraviolet scattering coverage area

In this paper, the Monte Carlo method is employed to simulate the ultraviolet light scattering transmission. The three modes of ultraviolet (UV) no-line-of-sight (NLOS) communication are analyzed. The UV NLOS transmission model based on the Monte Carlo method is proposed. The path losses of single and multiple scatterings and the coverage area of three UV NLOS modes are simulated by using the Monte Carlo method. Finally, we obtain the conclusion that multiple scattering and single scattering basically have the same path loss. The coverage of NLOS (a) is smallest, but omni-direction is good. The coverage of NLOS (b) is larger, but it is directional. The coverage of NLOS (c) is largest, but it is strongly directional.

Experimental Characterization of an UWB Propagation Channel in Underground Mines

An experimental characterization of the ultrawideband (UWB) propagation channel in an underground mine environment over the frequency range from 3 GHz to 10 GHz is reported in this paper. Two kinds of antennas, directional and omnidirectional, were used to investigate the effect of the antenna directivity on the path loss propagation and on the time dispersion parameters in both line-of-sight (LOS) and no-line-of-sight (NLOS) underground galleries. The measurement and simulation results show that the path loss exponents in an underground environment are larger than their counterparts in an indoor environment. In NLOS, the directional-directional (Direct-Direct) antenna combination showed better radiation efficiency for reducing the time dispersion parameters while the omnidirectional-omni directional (Omni-Omni) case resulted better performance in term of path loss. After extracting the channel parameters, a statistical modeling of the UWB underground channel based on data measurements was conducted.