Showing papers on "Multipath propagation published in 2012"

Cloud Transmission: A New Spectrum-Reuse Friendly Digital Terrestrial Broadcasting Transmission System

Abstract: This paper introduces a new transmission system—“Cloud Transmission (Cloud Txn)” for terrestrial broadcasting or point-to-multipoint multimedia services. The system is based on the concept of increasing the reception robustness, and using the spectrum more efficiently. As such, the system is designed to be robust to co-channel interference, immune to multipath distortion, and is highly spectrum reuse friendly. It can increase the spectrum utilization significantly (3 to 4 times) by making all terrestrial RF channels in a city/market available for broadcast service. The system has the robustness required for providing mobile, pedestrian and indoor reception. It can be used for both small and large cell applications. The receiver is simple and energy efficient. The proposed system is scalable and can be implemented progressively, i.e., providing an easy transition from the traditional systems to the new Cloud Txn system. It can also coexist with the existing DTV systems and their newer versions, such as DVB-T2 or Super Hi-Vision systems.

FM-based indoor localization

Abstract: The major challenge for accurate fingerprint-based indoor localization is the design of robust and discriminative wireless signatures. Even though WiFi RSSI signatures are widely available indoors, they vary significantly over time and are susceptible to human presence, multipath, and fading due to the high operating frequency. To overcome these limitations, we propose to use FM broadcast radio signals for robust indoor fingerprinting. Because of the lower frequency, FM signals are less susceptible to human presence, multipath and fading, they exhibit exceptional indoor penetration, and according to our experimental study they vary less over time when compared to WiFi signals. In this work, we demonstrate through a detailed experimental study in 3 different buildings across the US, that FM radio signal RSSI values can be used to achieve room-level indoor localization with similar or better accuracy to the one achieved by WiFi signals. Furthermore, we propose to use additional signal quality indicators at the physical layer (i.e., SNR, multipath etc.) to augment the wireless signature, and show that localization accuracy can be further improved by more than 5%. More importantly, we experimentally demonstrate that the localization errors of FM andWiFi signals are independent. When FM and WiFi signals are combined to generate wireless fingerprints, the localization accuracy increases as much as 83% (when accounting for wireless signal temporal variations) compared to when WiFi RSSI only is used as a signature.

Characterization of Reverberation Chambers for OTA Measurements of Wireless Devices: Physical Formulations of Channel Matrix and New Uncertainty Formula

Abstract: The paper deals with reverberation chambers for over-the-air (OTA) testing of wireless devices for use in multipath. We present a formulation of the S-parameters of a reverberation chamber in terms of the free space S-parameters of the antennas, and the channel matrix in the way this is known from propagation literature. Thereby the physical relations between the chamber and real-life multipath environments are more easily explained. Thereafter we use the formulation to determine the uncertainty by which efficiency-related quantities can be measured in reverberation chamber. The final expression shows that the uncertainty is predominantly determined by the Rician K-factor in the reverberation chamber rather than by the number of excited modes, assumed by previous literature. We introduce an average Rician K-factor that is conveniently expressed in terms of the direct coupling between the transmitting and receiving antennas (corresponding to a line-of-sight contribution) and Hill's transmission formula (corresponding to a multipath or non-line-of-sight contribution). The uncertainty is expressed in terms of this average K-factor and geometrical mode stirring parameters, showing strong reduction by platform and polarization stirring. Finally the formulations are verified by measurements, and the new understanding of uncertainty is used to upgrade an existing reverberation chamber to better uncertainty.

Magnetic Induction for Underwater Wireless Communication Networks

Abstract: Although acoustic waves are the most versatile and widely used physical layer technology for underwater wireless communication networks (UWCNs), they are adversely affected by ambient noise, multipath propagation, and fading. The large propagation delays, low bandwidth, and high bit error rates of the underwater acoustic channel hinder communication as well. These operational limits call for complementary technologies or communication alternatives when the acoustic channel is severely degraded. Magnetic induction (MI) is a promising technique for UWCNs that is not affected by large propagation delays, multipath propagation, and fading. In this paper, the MI communication channel has been modeled. Its propagation characteristics have been compared to the electromagnetic and acoustic communication systems through theoretical analysis and numerical evaluations. The results prove the feasibility of MI communication in underwater environments. The MI waveguide technique is developed to reduce path loss. The communication range between source and destination is considerably extended to hundreds of meters in fresh water due to its superior bit error rate performance.

Exploiting Channel Diversity in Secret Key Generation From Multipath Fading Randomness

Abstract: We design and analyze a method to extract secret keys from the randomness inherent to wireless channels. We study a channel model for a multipath wireless channel and exploit the channel diversity in generating secret key bits. We compare the key extraction methods based both on entire channel state information (CSI) and on single channel parameter such as the received signal strength indicators (RSSI). Due to the reduction in the degree-of-freedom when going from CSI to RSSI, the rate of key extraction based on CSI is far higher than that based on RSSI. This suggests that exploiting channel diversity and making CSI information available to higher layers would greatly benefit the secret key generation. We propose a key generation system based on low-density parity-check (LDPC) codes and describe the design and performance of two systems: one based on binary LDPC codes and the other (useful at higher signal-to-noise ratios) based on four-ary LDPC codes.

OTA Testing in Multipath of Antennas and Wireless Devices With MIMO and OFDM

Abstract: New over-the-air (OTA) measurement technology is wanted for quantitative testing of modern wireless devices for use in multipath. We show that the reverberation chamber emulates a rich isotropic multipath (RIMP), making it an extreme reference environment for testing of wireless devices. This thereby complements testing in anechoic chambers representing the opposite extreme reference environment: pure line-of-sight (LOS). Antenna diversity gain was defined for RIMP environments based on improved fading performance. This paper finds this RIMP-diversity gain also valid as a metric of the cumulative improvement of the 1% worst users randomly distributed in the RIMP environment. The paper argues that LOS in modern wireless systems is random due to randomness of the orientations of the users and their devices. This leads to the definition of cumulative LOS-diversity gain of the 1% worst users in random LOS. This is generally not equal to the RIMP-diversity gain. The paper overviews the research on reverberation chambers for testing of wireless devices in RIMP environments. Finally, it presents a simple theory that can accurately model measured throughput for a long-term evolution (LTE) system with orthogonal frequency-division multiplexing (OFDM) and multiple-input-multiple-output (MIMO), the effects of which can clearly be seen and depend on the controllable time delay spread in the chamber.

Bit Error Rate Performance of Generalized Frequency Division Multiplexing

Abstract: Generalized frequency division multiplexing is a non-orthogonal, digital multicarrier transmission scheme with attractive features that address the requirements of emerging applications of wireless communications systems in areas like cognitive radio and machine-to-machine communication. In this paper, first a linear system description is obtained for the transmitter by ordering data in a time-frequency block structure and representing the processing steps upconversion, pulse shaping and upsampling as matrix operations. Based on the transmitter, three standard ways of detecting the signal are derived and compared in terms of bit error performance in AWGN and Rayleigh multipath fading channels.

Delay-based congestion control for multipath TCP

Abstract: With the aid of multipath transport protocols, a multihomed host can shift some of its traffic from more congested paths to less congested ones, thus compensating for lost bandwidth on some paths by moderately increasing transmission rates on other ones. However, existing multipath proposals achieve only coarse-grained load balancing due to a rough estimate of network congestion using packet losses. This paper formulates the problem of multipath congestion control and proposes an approximate iterative algorithm to solve it. We prove that a fair and efficient traffic shifting implies that every flow strives to equalize the extent of congestion that it perceives on all its available paths.We call this result “Congestion Equality Principle”. By instantiating the approximate iterative algorithm, we develop weighted Vegas (wVegas), a delay-based algorithm for multipath congestion control, which uses packet queuing delay as congestion signals, thus achieving fine-grained load balancing. Our simulations show that, compared with loss-based algorithms, wVegas is more sensitive to changes of network congestion and thus achieves more timely traffic shifting and quicker convergence. Additionally, as it occupies fewer link buffers, wVegas rarely causes packet losses and shows better intra-protocol fairness.

Improving RF-based device-free passive localization in cluttered indoor environments through probabilistic classification methods

Abstract: Radio frequency based device-free passive localization has been proposed as an alternative to indoor localization because it does not require subjects to wear a radio device. This technique observes how people disturb the pattern of radio waves in an indoor space and derives their positions accordingly. The well-known multipath effect makes this problem very challenging, because in a complex environment it is impractical to have enough knowledge to be able to accurately model the effects of a subject on the surrounding radio links. In addition, even minor changes in the environment over time change radio propagation sufficiently to invalidate the datasets needed by simple fingerprint-based methods. In this paper, we develop a fingerprinting-based method using probabilistic classification approaches based on discriminant analysis. We also devise ways to mitigate the error caused by multipath effect in data collection, further boosting the classification likelihood. We validate our method in a one-bedroom apartment that has 8 transmitters, 8 receivers, and a total of 32 cells that can be occupied. We show that our method can correctly estimate the occupied cell with a likelihood of 97.2%. Further, we show that the accuracy remains high, even when we significantly reduce the training overhead, consider fewer radio devices, or conduct a test one month later after the training. We also show that our method can be used to track a person in motion and to localize multiple people with high accuracies. Finally, we deploy our method in a completely different commercial environment with two times the area achieving a cell estimation accuracy of 93.8% as an evidence of applicability to multiple environments.

Urban multipath detection and mitigation with dynamic 3D maps for reliable land vehicle localization

Abstract: Accurate and reliable positioning is an important prerequisite for numerous vehicular applications. Localization techniques based on satellite navigation systems are nowadays standard and deployed in most commercial vehicles. When such a standalone positioning is used in challenging environments like dense urban areas, the localization performance often dramatically degrades due to blocked and reflected satellites signals. In this paper, a general and lightweight probabilistic positioning algorithm with integrated multipath detection through 3D environmental building models is presented. It will be shown that the proposed system outperforms—in terms of accuracy and integrity—existing methods without introducing additional hardware sensors. Furthermore, a benefit analysis of the suggested 3D model for tightly and loosely coupled GPS/INS sensor integration schemas is provided. Finally, the algorithm will be evaluated with real-world data collected during an urban measurement campaign.

Physical Layer Authentication over MIMO Fading Wiretap Channels

Abstract: In a wide band and multipath rich environment, precise channel estimation allows authenticating the source and protecting the integrity of a message at the physical layer without the need of a pre-shared secret key. This allows also a reduction of the burden on the authentication protocols at higher layers. In this paper we develop an authentication scheme in the framework of hypothesis testing that suits a multiple wiretap channels environment with correlated fading, as is the case of multiple input multiple output (MIMO) systems and/or orthogonal frequency division multiplexing (OFDM) modulation. By allowing some degree of correlation among the channels, we formulate the optimal attack strategy for the cases of both single attempt and multiple repeated trials. For the latter scenario, due to the complexity of the optimal solution, we also develop a simpler suboptimal attack strategy. The performance of the proposed methods is evaluated in a MIMO/OFDM scenario and numerical results show the merits of the proposed approaches that can be adopted as a layer one authentication mechanism.

Cooperative Secret Key Generation from Phase Estimation in Narrowband Fading Channels

Abstract: By exploiting multipath fading channels as a source of common randomness, physical layer (PHY) based key generation protocols allow two terminals with correlated observations to generate secret keys with information-theoretical security. The state of the art, however, still suffers from major limitations,e.g., low key generation rate, lower entropy of key bits and a high reliance on node mobility. In this paper, a novel cooperative key generation protocol is developed to facilitate high-rate key generation in narrowband fading channels, where two keying nodes extract the phase randomness of the fading channel with the aid of relay node(s). For the first time, we explicitly consider the effect of estimation methods on the extraction of secret key bits from the underlying fading channels and focus on a popular statistical method - maximum likelihood estimation (MLE). The performance of the cooperative key generation scheme is extensively evaluated theoretically. We successfully establish both a theoretical upper bound on the maximum secret key rate from mutual information of correlated random sources and a more practical upper bound from Cramer-Rao bound (CRB) in estimation theory. Numerical examples and simulation studies are also presented to demonstrate the performance of the cooperative key generation system. The results show that the key rate can be improved by a couple of orders of magnitude compared to the existing approaches.

Multipath detection with 3D digital maps for robust multi-constellation GNSS/INS vehicle localization in urban areas

Abstract: Reliable knowledge of the ego position for vehicles is a crucial requirement for many automotive applications. In order to solve this problem for satellite-based localization in dense urban areas, multipath situations need to be handled carefully. This paper proposes a lightweight multipath detection algorithm which is based on dynamically built 3D environmental maps. The algorithm is evaluated with simulated and real-world data. Furthermore, it is applied to a combined GPS and GLONASS system in combination with a loosely coupled integration of odometry measurements from the vehicle.

Detection and Tracking of Mobile Propagation Channel Paths

Abstract: In dynamic channel sounder measurements with a moving receiver and/or moving transmitter, propagation paths' parameters show a time-variant behavior. This paper describes a novel algorithm which is able to both detect individual propagation paths and track how these paths evolve with time. The proposed algorithm is capable of estimating the paths' parameters and outperforms the standard snapshot-based algorithm in cases where low accuracy due to resolution limitations in the delay or angular domain is observed. An example based on channel sounder measurements with a moving receiver is given, showing that the algorithm is able to capture the dynamic behavior of the propagation channel.

Cellular broadband millimeter wave propagation and angle of arrival for adaptive beam steering systems (invited paper)

Abstract: The advent of inexpensive millimeter wave devices and steerable antennas will lead to future cellular networks that use carrier frequencies at 28 GHz, 38 GHz, 60 GHz, and above. At these frequencies, the available RF bandwidth is much greater than that of current 4G systems, and high gain millimeter wave steerable antennas can be made in much smaller form factor than current products. This paper presents an extensive measurement campaign and initial results for base-station - to - mobile propagation situations at 38 GHz carrier frequencies in an outdoor urban environment using directional, steerable antennas. This work provides angle of arrival (AOA) and RF multipath characteristics for highly directional antenna beams that may exploit non-line-of-sight propagation paths for futuristic channels at 38 GHz. This work yields data for a variety of antenna pointing and antenna beamwidth scenarios in line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios.

GPS snow depth meter with geometry-free linear combinations of carrier phases

Abstract: Multipath in global positioning system (GPS) is the interference of the microwave signals directly from satellites and those reflected before reaching the antenna, typically by the ground. Because reflected signals cause positioning errors, GPS antennas are designed to reduce such interference. Recent studies show that multipath could be utilized to infer the properties of the ground around the antenna. Here, we report one such application, i.e. a fixed GPS station used as a snow depth meter. Because the satellite moves in the sky, the excess path length of reflected waves changes at rates dependent on the antenna height. This causes quasi-periodic variations of the amplitude and phase of the received signals. Accumulation of snow reduces effective antenna heights, and we can see it by analyzing multipath signatures. Signal-to-noise ratios (SNR) are often used to analyze multipath, but they are not always available in raw GPS data files. Here, we demonstrate that the geometry-free linear combination (L4), normally used to study the ionosphere, can also be used to analyze multipath signatures. We obtained snow depth time series at a GPS station in Hokkaido, Japan, from January to April in 2009 using L4 and SNR. Then, we compared their precisions. We also discuss mechanisms responsible for the possible underestimation of the snow depth by GPS. Finally, we investigate the possibility of inferring physical conditions of the snow surface using amplitudes of multipath signatures.

Target Localization with a Single Sensor via Multipath Exploitation

Abstract: In urban sensing and through-the-wall (TTW) radar, the existence of targets inside buildings results in multipath returns. These multipath returns are exploited to achieve target localization with a single sensor. A time-of-arrival (TOA) wall association algorithm is derived to relate multipath returns to their respective walls and targets, followed by a nonlinear least squares (NLS) optimization to localize the targets. Simulations and experimental data are used to validate the proposed algorithms.

Dynamic subflow control for a multipath transport connection in a wireless communication network

Abstract: A multipath transport protocol such as multipath TCP can utilize metrics such as a wireless link condition corresponding to one or more paths as a parameter for controlling a dynamic allocation of data and control signaling over respective paths. Fault-tolerant control can enable retransmissions of packets already sent on a poor path, onto a good path. Further, the feedback, the retransmissions, and other control signaling can be provided on a separate subflow or on a UDP overlay. In this way, a multipath TCP connection can be more reliable and efficient as flow control and data flow are enhanced.

Development of Optically Transparent Ultrathin Microwave Absorber for Ultrahigh-Frequency RF Identification System

Abstract: The application of UHF radio-frequency identification (RFID) systems is rapidly increasing. However, the reliability of indoor telecommunication is adversely affected by multiple reflection interference. Consequently, to establish a highly reliable UHF-RFID system, it is essential to improve the multipath environment. This paper describes an ultrathin microwave absorber that is designed to improve the multipath environment of UHF-RFID systems. This absorber is optically transparent so that it does not create blind areas for surveillance cameras installed near an UHF-RFID system (e.g., at the entrance of an office or a warehouse). The improved tag identification probability using this absorber is demonstrated in an actual warehouse.

Modeling indoor TOA ranging error for body mounted sensors

Abstract: In Time of arrival (TOA) based indoor human tracking system, the human body mounted with the target sensor can cause non-line of sight (NLOS) scenario and result in significant ranging error. However, the previous studies on the behavior of indoor TOA ranging did not take the effects of human body into account. In this paper, we introduce a statistical TOA ranging error model for body mounted sensors based on the measurements in a typical office building. This model separates the ranging error into multipath error cased multipath combination and undetectable direct path (UDP) error derives from the body-caused NLOS. Both multipath error and UDP error are modeled as a Gaussian variable. The distribution of multipath error is relative to the bandwidth of the system and the distribution of UDP error is relative to the angle between the face direction and the direction of TX-RX, SNR and bandwidth of the system, clearly shows the effects of human body on TOA ranging.

Experimental Propagation Channel Characterization of mm-Wave Radio Links in Urban Scenarios

Abstract: The 71-76- and 81-86-GHz bands, which are a part of the millimeter-wave (mm-wave) E-band (60-90 GHz), are allocated worldwide for ultrahigh-capacity point-to-point communications. Here, a geometry-based single-bounce channel model is developed for E-band point-to-point link applications and is verified by channel measurements. A measurement campaign was performed in a street canyon scenario, which is one very interesting possible new usage environment for E-band radio links, where reflected signals can cause more severe multipath fading compared to traditional open environments. The measurement results and the geometry of the measurement locations were used to determine the parameters of the developed channel model. The model can be used to estimate the characteristics of the radio channel such as excess delay, power level, and angular distribution of the multipath components. The channel model was validated by comparing the measured and modeled root mean square (RMS) delay spread, which is an important parameter for very broadband radio systems. All the modeled and measured mean values of RMS delay spread were in the range of 0.089-0.125 ns, revealing a good agreement between the channel model and the measurements.

Industrial wireless sensor networks: channel modeling and performance evaluation

Abstract: A complete dynamic wideband channel model for industrial wireless sensor network is presented. The model takes into account the noise, interferences, and heavy multipath propagation effects present in harsh industrial environments. A first-order two-state Markov process is adopted to describe the typical bursty nature of the impulsive noise usually present in industrial environments. The interference effects are modeled as multiple narrowband signals operating on the same frequency band as the desired signal. The multipath propagation is described by assuming the scatterers to be uniformly distributed in space within an elliptical region where the transmitting and receiving nodes are located at the foci of the ellipse. Furthermore, performance evaluations of IEEE 802.15.4 in terms of bit error rate using the developed channel model are presented. The results show that in addition to spread spectrum techniques, link diversity can further improve the link quality in harsh industrial environments.

Doubly Selective Underwater Acoustic Channel Model for a Moving Transmitter/Receiver

Abstract: We propose a new method of modeling the signal transmission in underwater acoustic communications when the transmitter and receiver are moving. The motion-induced channel time variations can be modeled by sampling the transmitter/receiver trajectory at the signal sampling rate and calculating, for each position, the channel impulse response from the acoustic-field computation. This approach, however, would result in high complexity. To reduce the complexity, the channel impulse response is calculated for fewer (waymark ) positions and then interpolated by local splines to recover it at the signal sampling rate. To allow higher distances between waymarks and, thus, further reduction in the complexity, the multipath delays are appropriately adjusted before the interpolation. Because, for every time instant, this method only requires local information from the trajectory, the impulse response can recursively be computed, and therefore, the signal transmission can be modeled for arbitrarily long trajectories. An approach for setting the waymark sampling interval is suggested and investigated. The proposed method is verified by comparing the simulated data with data from real ocean experiments. For a low-frequency shallow-water experiment with a moving source that transmits a tone set, we show that the Doppler spectrum of the received tones is similar in the simulation and experiment. For a higher frequency deep-water experiment with a fast-moving source that transmits orthogonal frequency-division multiplexing (OFDM) communication signals, we investigate the detection performance of a receiver and show that it is similar in the simulation and experiment.

Multipathing with MPTCP and OpenFlow

Abstract: Data sets in e-science are increasing exponentially in size. To transfer these huge data sets we need to make efficient use of all available network capacity. This means using multiple paths when available. In this paper a prototype of such a multipath network is presented. Several emerging network technologies are integrated to achieve the goal of efficient high end-to-end throughput. Multipath TCP is used by the end hosts to distribute the traffic across multiple paths and OpenFlow is used within the network to do the wide area traffic engineering. Extensive monitoring is part of the demonstration. A website will show the actual topology (including link outages), the paths provisioned through the network and traffic statistics on all links and the end-to-end aggregate throughput.

MIMO-UWB Channel Characterization Within an Underground Mine Gallery

Abstract: Multiple input multiple output-ultrawide band (MIMO-UWB) systems are experimentally evaluated for underground mine high-speed radio communications. Measurement campaigns using two different antenna configurations have been made in an underground gold mine. Furthermore, two scenarios, which are the line of sight (LoS) and the non-LoS (NLoS), i.e., taking into account the mining machinery effect, are distinguished and studied separately. In fact, the channel is characterized in terms of coherence bandwidth, path loss, shadowing, channel correlation, and capacity. Results reveal how antenna array configuration affects main channel parameters and suggest that mining machinery presence substantially affects both received power and time dispersion parameters within the underground mine and should, therefore, be considered when assessing the performance of in-gallery wireless systems. Moreover, it is shown that the MIMO-UWB takes benefit of the large spreading bandwidth and the multipath propagation environment to increase the channel capacity.

Multipath-assisted single-anchor indoor localization in an office environment

Abstract: Multipath propagation is one of the key problems for indoor localization systems. Strong multipath components can cause range estimates to anchor nodes to be severely biased. If a floor plan is available, reflected signal paths can be used effectively by mapping them to virtual anchors. We show how to make use of the rich localization information provided by just one anchor node. Using tracking algorithms both with and without data association, we achieve accurate and robust localization, which is verified in an indoor environment using measured data at ultra-wide bandwidths. With an extended Kalman filter and data association, a position error of 22 cm is obtained for 90% of the estimates at a bandwidth of 2GHz.

Particle filter based positioning with 3GPP-LTE in indoor environments

Abstract: Global navigation satellite systems (GNSSs) can deliver very good position estimates under optimum conditions. However, especially in urban and indoor scenarios with severe multipath propagation and blocking of satellites by buildings the accuracy loss can be very large. Often, a position with GNSS is impossible in these scenarios. On the other hand, cellular wireless communication systems such as the third generation partnership project (3GPP) long-term evolution (LTE) provide excellent coverage in urban and most indoor environments. Thus, this paper researches timing based positioning algorithms, in this case time difference of arrival (TDoA), using 3GPP-LTE measurements. Several approaches and algorithms exist to solve the navigation equation for cellular systems, for instance Bayes filtering methods such as Kalman or particle filter. This paper specifically considers and develops a particle filter for 3GPP-LTE TDoA positioning. To obtain better positioning results, a 3GPP-LTE TDoA error model is derived. This error model is afterwards included in the likelihood function of the particle filter. The last part of this paper, evaluates the positioning performances of the developed particle filter in an indoor scenario. These evaluations show clearly the possibility of using 3GPP-LTE measurements for indoor positioning.

Evolutionary Algorithm Based Power Coverage Optimization for Visible Light Communications

Abstract: Inherent multipath diffuse channel characteristics inhibit visible light communications (VLC) system to provide uniform and satisfactory communication performance within the room domain. An evolutionary algorithm based optimization scheme is proposed to modify the optical intensity of LED transmitters for reducing the signal power fluctuation extent. Simulation results show that the proposed scheme can efficiently reduce the signal power dynamic range up to 26.5% while the SNR is still sufficient for keeping BER<;10-6 (using OOK-NRZ modulation format).

Tight Integration of GNSS and a 3D City Model for Robust Positioning in Urban Canyons

Abstract: Positioning and navigation by GNSS in urban context are always challenging tasks, because of signal propagation problems such as shadowing effects and multipath. When not enough GNSS signals are received in line-of-sight (LOS), classical approaches mitigating multipath effects become insufficient because there is not enough reliable information available. Consequently, positioning errors can be about tens of meters, especially in urban canyons. In this paper, we introduce a GNSS positioning approach that uses constructively non-line-of-sight (NLOS) signals in order to have enough information to compute the user’s position. In this work, we use the SE-NAV software to predict the geometric paths of NLOS signals using a high realistic 3D model of the environment. More precisely, we propose a new version of the extended Kalman filter augmented by the information provided by SE-NAV, referred to as 3D AEKF, for GNSS navigation in NLOS context. In the proposed approach, the measurement model traditionally based on the trilateration equations is constructed from the received paths estimated by SE-NAV. The Jacobian of the measurement model is calculated through knowledge of the objects on which the reflections have occured. To use even less reliable measurements, we propose a robust version of the 3D AEKF. Simulations conducted in realistic scenarios allow the performance of the proposed method to be evaluated.

Reliable and Energy-Efficient Multipath Communications in Underwater Sensor Networks

Abstract: Weak reliability and low energy efficiency are the inherent problems in Underwater Sensor Networks (USNs) characterized by the acoustic channels. Although multiple-path communications coupled by Forward Error Correction (FEC) can achieve high performance for USNs, the low probability of successful recovery of received packets in the destination node significantly affects the overall Packet Error Rate (PER) and the number of multiple paths required, which in turn becomes a critical factor for reliability and energy consumption. In this paper, a novel Multiple-path FEC approach (M-FEC) based on Hamming Coding is proposed for improving reliability and energy efficiency in USNs. A Markovian model is developed to formulate the probability of M-FEC and calculate the overall PER for the proposed decision and feedback scheme, which can reduce the number of the multiple paths and achieve the desirable overall PER in M-FEC. Compared to the existing multipath communication scheme, extensive simulation experiments show that the proposed approach achieves significantly lower packet delay while consuming only 20-30 percent of energy in multiple-path USNs with various Bit Error Rates (BER).