Multipath Model Research Articles

A geometry-free and ionosphere-free multipath mitigation method for BDS three-frequency ambiguity resolution

Because of the unknown systematic errors and special satellite constellations in the Beidou system (BDS), it is difficult to quickly and reliably determine the ambiguity over long-range baselines in continuously operating reference station (CORS) network. This study seeks to improve the effectiveness and reliability of BDS ambiguity resolution (AR) by combining the geometry-free and ionosphere-free (GFIF) combination and multipath mitigation algorithm. The GFIF combination composed with three-frequency signals is free of distance-dependent errors and can be used to determine the narrow lane ambiguity. The presence of multipath errors means that not all ambiguities can be correctly achieved by rounding the averaged GFIF ambiguity series. A multipath model of the single-differenced (SD) GFIF combination from the previous period is established for each individual satellite. This model is subtracted from the SD GFIF combination for the current day to remove the effects of multipath errors. Using three triangle networks with lengths of approximately 120, 80 and 50 km, we demonstrate that the proposed method improves the AR performance. The ambiguity averaged first fixing time is typically less than 1801 s for inclined geosynchronous orbit (IGSO) and medium earth orbit (MEO) satellites and less than 2007 s for the \(\sim \)42\(^{\circ }\) elevation geostationary earth orbit (GEO) C02 satellite. However, it is more time consuming for the low-elevation GEO satellites C04 (\(\sim \)18\(^{\circ }\)) and C05 (\(\sim \)28\(^{\circ }\)). Kalman filtering is used to estimate the troposphere delays and two unfixed ambiguities by employing the ionosphere-free observations of all ambiguity-fixed/unfixed satellites. The experimental results show that only tens of seconds are required for AR in around 90 km baselines.

Multipath ghost elimination for through‐wall radar imaging

In through-wall radar imaging, the multipath echoes caused by specular reflections at interior walls of an enclosed room will lead to multipath ghosts in the resulting image. The ghosts appear like the true targets and therefore tend to increase the number of false alarms. To solve this problem, a new ghost elimination method that removes multipath echoes from the raw radar data is proposed in this study. With a priori knowledge of the room, a concise multipath model is first developed, based on which the locations of the multipath echoes can be determined. Then, a cancellation process that consists of two steps is performed wherein the multipath echoes are cancelled in a specific order depending on the positions of the targets they correspond to. The major advantage of this method is that it can preserve the true targets while eliminating the ghosts even if the targets overlap with those ghosts. The effectiveness of the proposed method is validated by the processed imaging results using both the finite-difference time-domain-simulated data and the real experimental data.

Ship-to-Ship Radiocommunication Trial by Using Wireless LAN

Seamless transfer of electronic information/data between ship-to-shore and vice versa and between ship-to-ship and shore-to-shore is being developed in the IMO e-Navigation strategy implementation plan (SIP). We have been focused on wireless LAN for ship-to-ship radiocommunication.In a former field radiocommunication trial, omni-directional antennas were used and a few hundred kbps throughput between two ships was measured, which was not enough for our research target (over 1Mbps). In order to get faster throughput, a field radiocommunication trial was carried out again with a few types of directional antennas and RSSI (Received Signal Strength Indication) and the throughput between two ships was measured simultaneously. As a result, multi-path (2-path) model affected by the reflection of the sea surface was confirmed and also the characteristics of the directional antennas such as half-power angle were confirmed, but the measured throughput was fast enough to meet our expectation.

Exploring the effect of diffuse reflection on indoor localization systems based on RSSI-VLC.

This work explores and evaluates the effect of diffuse light reflection on the accuracy of indoor localization systems based on visible light communication (VLC) in a high reflectivity environment using a received signal strength indication (RSSI) technique. The effect of the essential receiver (Rx) and transmitter (Tx) parameters on the localization error with different transmitted LED power and wall reflectivity factors is investigated at the worst Rx coordinates for a directed/overall link. Since this work assumes harsh operating conditions (i.e., a multipath model, high reflectivity surfaces, worst Rx position), an error of ≥ 1.46 m is found. To achieve a localization error in the range of 30 cm under these conditions with moderate LED power (i.e., P = 0.45 W), low reflectivity walls (i.e., ρ = 0.1) should be used, which would enable a localization error of approximately 7 mm at the room's center.

Asymmetrical Multi-path Selection Game for Wireless Overlay Networks

In order to transfer the increasing big data we need to make use of multiple wireless paths. Overlay networks provide the possibility of taking advantage of multiple available routing paths to realize the bandwidth aggregating. We present a game-theoretic study of the selfish strategic collaboration of multiple heterogeneous overlays when they are allowed to use massively-multipath transfer. Overlays are modeled as players in this multipath selection game model, we discuss the asymmetric case where all overlays have the different round trip times (RTT) and different wastefulness level, and demonstrate the existence and uniqueness of Nash equilibrium (NE). Then we find overlays differing only in their RTTs still receive equal throughput shares and utilities at the NE. However, if overlays differ only in their wastefulness levels, a more wasteful overlay has a larger utility and a larger throughput (bandwidth) share than a less wasteful overlay.

Multi-Path Model and Sensitivity Analysis for Galvanic Coupled Intra-Body Communication Through Layered Tissue.

New medical procedures promise continuous patient monitoring and drug delivery through implanted sensors and actuators. When over the air wireless radio frequency (OTA-RF) links are used for intra-body implant communication, the network incurs heavy energy costs owing to absorption within the human tissue. With this motivation, we explore an alternate form of intra-body communication that relies on weak electrical signals, instead of OTA-RF. To demonstrate the feasibility of this new paradigm for enabling communication between sensors and actuators embedded within the tissue, or placed on the surface of the skin, we develop a rigorous analytical model based on galvanic coupling of low energy signals. The main contributions in this paper are: (i) developing a suite of analytical expressions for modeling the resulting communication channel for weak electrical signals in a three dimensional multi-layered tissue structure, (ii) validating and verifying the model through extensive finite element simulations, published measurements in existing literature, and experiments conducted with porcine tissue, (iii) designing the communication framework with safety considerations, and analyzing the influence of different network and hardware parameters such as transmission frequency and electrode placements. Our results reveal a close agreement between theory, simulation, literature and experimental findings, pointing to the suitability of the model for quick and accurate channel characterization and parameter estimation for networked and implanted sensors.

Symbol Synchronization for OFDM Receivers with FFT Transport Delay Compensation

This paper proposes a new blind approach for time synchronization of orthogonal frequency division multiplexing (OFDM) receivers (RX). It is largely known that the OFDM technique has been successfully applied to a wide variety of digital communications systems over the past several years — IEEE 802.16 WiMax, 3GPP-LTE, IEEE 802.22, DVB T/H, ISDB-T, to name a few. We focus on the synchronization for the ISDB-T digital television system, currently adopted by several South American countries. The proposed approach uses the coarse synchronization to estimate the initial time reference and then, the fine synchronization keeps tracking the transmitter (TX) time reference. The innovation on the proposed approach regards to the closed loop control stabilization of the fine synchronization. It uses a smith predictor and a differential estimator, which estimates the difference between TX and RX clock frequencies. The proposed method allows the RX to track the TX time reference with high precision ([Formula: see text] sample fraction). Thus, the carriers phase rotation issue due to incorrect time reference is minimized, and it does not affect the proper RX IQ symbols demodulation process. The RX internal time reference is adjusted based on pilot symbols, called scattered pilots (SPs) in the context of the ISDB-T standard, which are inserted in the frequency domain at the inverse fast Fourier transform (IFFT) input in the TX. The averaged progressive phase rotation of the received SPs at the fast Fourier transform (FFT) output is used to compute the time misalignment. This misalignment is used to adjust the RX fine time synchronism. Furthermore, the proposed method has been implemented in an ISDB-T RX. The FPGA-based receiver has been evaluated over several multipath, Doppler and AWGN channel models.

Analytical bit error rate performance evaluation of an orthogonal frequency division multiplexing power line communication system impaired by impulsive and Gaussian channel noise

An analytical approach is presented to evaluate the bit error rate (BER) performance of a power line (PL) communication system considering the combined influence of impulsive noise and background PL Gaussian noise. Middleton class-A noise model is considered to evaluate the effect of impulsive noise. The analysis is carried out to find the expression of the signal-to-noise ratio and BER considering orthogonal frequency division multiplexing (OFDM) with binary phase shift keying modulation with coherent demodulation of OFDM sub-channels. The results are evaluated numerically considering the multipath transfer function model of PL with non-flat power spectral density of PL background noise over a bandwidth of 0.3–100 MHz. The results are plotted for several system and noise parameters and penalty because of impulsive noise is determined at a BER of 10−6. The computed results show that the system suffers significant power penalty because of impulsive noise which is higher at higher channel bandwidth and can be reduced by increasing the number of OFDM subcarriers to some extent. The analytical results conform well with the simulation results reported earlier.

A New Statistical WRELAX Algorithm Under Nakagami Multipath Channel Based on Delay Power Spectrum Characteristic

Multipath delay estimation plays an important role in wireless channel estimation, equalization, and synchronization. Weighted Fourier transform and relaxation (WRELAX) algorithm is frequently used for its high resolution and good convergence property. However, the WRELAX algorithm is prone to false estimated delays and irregular multipath sorting under Nakagami-based multipath channel, which is a more practical model than the traditional Rice or Rayleigh-based multipath model, because of the oscillatory cost function property between the received and the known transmitted signals. Given relatively stable characteristics and delay power spectrum distribution characteristics of the wireless channel, together with the principle that the statistical probability of the true estimated delays is larger than that of the false ones through statistical detection, this study proposes a delay power spectrum characteristic-based statistical WRELAX time delay estimation algorithm. The improved algorithm excludes false estimated paths and sorts the delays in size order simultaneously by establishing a two-dimensional relation graph composed of the superposition value of estimated attenuation coefficient and their response-estimated delays. Simulation under three typical Nakagami-based slow fading multipath channels shows that the proposed algorithm has good accuracy and robustness, and the cost of complexity increased by only a few times.

Range impairments of multi-band OFDM UWB communication systems in the presence of OFDM-based WLAN interference

In this paper, a closed form expression for the bit error rate performance of the multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) communication system in the presence of interference is analytically analysed. The considered channel is the Saleh-Valenzuela multipath fading channel model. The interference is modelled as the OFDM-based IEEE802.11n wireless local area networks (WLANs). The dependence of the bit error rate performance of the MB-OFDM UWB communication system on the transmission range along with the impact of interference is also analytically investigated. Numerical results are validated with the aid of simulations. It is shown that the range performance of the MB-OFDM UWB communication system is severely deteriorated due to the presence of such interference.

Target Detection in Low Grazing Angle with Adaptive OFDM Radar

Multipath effect is the main factor of deteriorating target detection performance in low grazing angle scenario, which results from reflections on the ground/sea surface. Amplitudes of the received signals fluctuate acutely due to the random phase variations of reflected signals along different paths; thereby the performances of target detection and tracking are heavily influenced. This paper deals with target detection in low grazing angle scenario with orthogonal frequency division multiplexing (OFDM) radar. Realistic physical and statistical effects are incorporated into the multipath propagation model. By taking advantage of multipath propagation that provides spatial diversity of radar system and frequency diversity of OFDM waveform, we derive a detection method based on generalized likelihood ratio test (GLRT). Then, we propose an algorithm to optimally design the transmitted subcarrier weights to improve the detection performance. Simulation results show that the detection performance can be improved due to the multipath effect and adaptive OFDM waveform design.

Optimal Congestion Control and Routing for Multipath Networks with Random Losses

In this paper we consider optimal congestion control and routing schemes for multipath networks with non-congestion related packet losses which can be caused by, for example, errors on links on the routes, and develop a relaxed multipath network utility maximization problem. In order to obtain the optimum, we present a primal algorithm which is shown to be globally stable in the absence of round-trip delays. When round-trip delays are considered, decentralized sufficient conditions for local stability of the algorithm are proposed, in both continuous-time and discrete- time forms. Finally, a window-flow control mechanism is presented which can approximate the optimum of the multipath network utility maximization model.

Phase Errors Simulation Analysis for GNSS Antenna in Multipath Environment

High-precision GNSS application requires the exact phase center calibration of antenna. Various methods are published to determine the locations of the phase center. In the outfield, when the phase errors that arose by multipath exceed the phase center variations (PCV) tolerance, the calibration values may be not useful. The objective of this paper is thus to evaluate the phase errors that arose by multipath signals. An improved model of antenna receiving signal is presented. The model consists of three main components: (1) an antenna model created by combination of right hand circular polarization (RHCP) and left hand circular polarization (LHCP), (2) a multipath signals model including amplitude, phase, and polarization, and (3) a ground reflection model applying to circular polarization signals. Based on the model, two kinds of novel up-to-down(U/D)ratios are presented. The performance of the model is assessed against the impact of up-to-down ratio of antenna on phase errors.

Modelling Transmission Lines for the Purpose of Data Transmission over Power Lines

The aim of the article is to create two models of power line communication. First model is called Multipath model and It is based on identifying the transfer function based on the measured values. Second model is called Transmission line model and It is useful if the topology of the network under consideration is known. Both models are useful to obtain information of the operation of outdoor networks.

Stochastic Analysis of Scattered Field by Building Facades Using Polynomial Chaos

This paper presents a statistical assessment of scattered field from a building facade having rando m physical and geometrical parameters. A simple inhomogeneous model is considered for the building and the calculation met hod is based on Green's functions. The basis of polynomial chaos expansion method is explained and applied to estimate the sca ttered electric field from a building facade having 8 random parameters, in specular and non-specular scenarios. Uncertainty analysis and total output distribution are discussed in differen t diffraction zones of the building. IRELESS communications, particularly mobile networks, experienced a great expansion worldwide. These networks are very dense in urban areas and th e electromagnetic field distribution is highly depend ent on city structures. It is essential to have predictive tool s to assess as accurately as possible the distribution of electrom agnetic fields in order to enable optimized implementation of base stations and respect the constraints regarding huma n exposure. Wave propagation simulators are based on different models of urban environment with different assumptions on the building architectural details. Given the adopted model, the y incorporate appropriate calculation methods. We can mention empirical, statistical, theoretical, site-specific models or a combination of them to generate a hybrid model (1). Empirical models (2) are based on the extensive measurement campaigns and are highly related to the structure of the city . Statistical models (3) are also based on measurements and are u sed to give wide band multipath model of the environment. Theoretical (physical) (4) models are obtained by i mposing some general idealized conditions on the geometry. They usually use physical optics with or without diffrac tion phenomena. Site-specific models (5) depend on a lar ge number of parameters which are related to a given s ite and their computing time, depending on the complexity o f the environment, can be long. These models usually employ ray

Inverse Modeling of GPS Multipath for Snow Depth Estimation—Part I: Formulation and Simulations

Snowpacks provide reservoirs of freshwater. The amount stored and how fast it is released by melting are vital information for both scientists and water supply managers. GPS multipath reflectometry (GPS-MR) is a new technique that can be used to measure snow depth. Signal-to-noise ratio data collected by GPS instruments exhibit peaks and troughs as coherent direct and reflected signals go in and out of phase. These interference fringes are used to retrieve the unknown land surface characteristics. In this two-part contribution, a forward/inverse approach is offered for GPS-MR of snow depth. Part I starts with the physically based forward model utilized to simulate the coupling of the surface and antenna responses. A statistically rigorous inverse model is presented and employed to retrieve parameter corrections responsible for observation residuals. The unknown snow characteristics are parameterized, the observation/parameter sensitivity is illustrated, the inversion performance is assessed in terms of its precision and its accuracy, and the dependence of model results on the satellite direction is quantified. The latter serves to indicate the sensing footprint of the reflection.

A novel hybrid CDL-based multipath propagation model for the high-speed railway at 2.35 GHz

In this study, based on the actual channel measurements of the high-speed railway (HSR) in a viaduct scenario at 2.35 GHz, a hybrid cluster delay line (CDL) channel modeling technology which combines a statistical model and a theoretical model is proposed. This novel channel-characterization approach is used to reveal the statistical properties for “random” scattering and to provide a geometric mechanism for computing the time-variant paths for “periodically moving” scattering. Using a modified clustering algorithm in the delay domain, the inter-cluster and intra-cluster characteristics against the distance between the transmitter and the receiver were extracted and analyzed. In addition, the measurement results were compared with some conclusions from other measurement studies, and the proposed channel model was validated by comparing the simulated results with the measurement data. The study results provide a useful technique for the evaluation and verification of wireless communications in the HSR environment.

Impact of Multipath Effect on Low-Altitude Elevation Measurement of Radar

The main impact of multipath effect on low-altitude radar measurement is elevated in this paper. The influence of multipath effect on monopulse radar measurement of elevation is analyzed. Examples suggest that the multipath error caused by the signals from pattern main lobe of radar antenna should be mainly considered in the actual project. According to the three elevation range of reflected signal entering the radar beam area, the multipath error model of elevation is established. The problem of anti-multipath interference for low-altitude target tracking with radar is solved by analyzing the error source which causes multipath effect.

Statistical independence of reflection and transmission coef-ficients on PLT due to system loads

This paper presents the theoretical development of the covariance between reflection and transmission coefficients caused by system loads in electric grids. This result allows the calculation of the expected value and covariance of the channel response; these parameters can be used as design criteria in telecommunication networks over power lines in in-home environments. Additionally, the product of these variables is encountered commonly in the channel transfer function, whereby it can be determined if the calculation of these parameters can be simplified when this product is on a given path. For this purpose, the random behavior of the channel response caused by human activity is represented by a multipath model with a stochastic addition, where the reflection coefficient is treated as a random complex variable, providing more information compared to the real field.

On Energy Consumption of Network Coding Based Reliability Transmission Mechanism

Network coding based multipath routing (NCMR) transmission mechanism is interpreted. Introduced the energy model into research, the transmission reliability and energy consumption of NCMR is analyzed with quantitative analysis on a braided multipath network model. A source controlling strategy is proposed for optimizing the energy consumption with transmission reliability requirement.