Changes In Received Signal Strength Research Articles

Vehicle-to-vehicle communication channel measurements on a vertical curve road

Vehicle-to-Vehicle (V2V) communication channel measurements were carried out in different environments such as urban, suburban, rural, highway, tunnel, and overpass. The roads in these environments have generally flat terrain. However, there are horizontal or vertical curve roads that have been little focused in the literature. In this study, we performed two V2V measurements on a vertical-curve road in a rural environment to show how received signal strength changes with the distance between the transmitter and the receiver. The path loss exponent of log-distance path loss model was calculated by using the least-square method. According to the results, the path loss exponents were estimated as 7.53 and 7.61 with 78% and 83% fitting performances for two measurements. In literature, however, the path loss exponent for different propagation environments was obtained up to 6.13, especially in the straight road. Thus, our findings show that the vertical curve roads cause 15-20 dB more attenuation in the received signal strength than the straight roads. As a result, the vertical curve roads should be investigated and included in existing wireless communication simulators to better model real measurements. The authors contend that this study will aid in improving the channel modeling of V2V communication.

An enhanced RSS-distance-angle weighted geometric filter for device-free localization

Device-free localization and tracking as an emerging technology has attracted substantial research attention in wireless sensor networks. However, there is much room for improvement in localization and tracking accuracy. In this paper, by using received signal strength (RSS) measurements we propose an enhanced geometric filter which consists of a series of weights corresponding to RSS, distance, and angle, respectively. Specifically, RSS-based weights are dependent on the change in RSS of communication links to remove improbable target locations. To ensure robust tracking performance, distance-based weights are assigned to probable target locations. Angle-based weights are used to ensure the correct direction of motion. Experimental results demonstrate that the proposed geometric filter could improve the accuracy of positioning by up to 50.8% for non-straight path and 48.3% for straight path over some state-of-the-art methods.

Wireless Localization Method Based on AHP-WKNN and Amendatory AKF

In this paper, we propose an AHP-WKNN method for indoor localization which combines the Analytic Hierarchy Process (AHP) technique and the Weighted K -nearest Neighbor (WKNN) algorithm. AHP serves to assign weights when WKNN is employed to select fingerprints for indoor positioning. The AHP technique can reasonably enlarge the influence that the received signal strength (RSS) gap between reference points has on the weights, achieving better performance in positioning. This paper also modifies the adaptive Kalman filter (AKF) noise reduction method by correcting the output based on the error between the RSS measurement and the expected output. The modified AKF can track the changes of RSS more effectively and achieve better performance of noise reduction. The simulation result shows that the proposed AHP-WKNN method and the modified AKF can improve positioning accuracy effectively.

Simultaneous Material Identification and Target Imaging with Commodity RFID Devices

Material identification and target imaging play an important role in many applications. This paper introduces TagScan, a system that can identify the material type and image the horizontal cut of a target simultaneously with cheap commodity Radio-Frequency IDentification (RFID) devices. The key intuition is that different materials and/or target sizes cause different amounts of phase and RSS (Received Signal Strength) changes, when radio frequency (RF) signal penetrates through the target. Multiple challenges need to be addressed before we can turn the idea into a functional system, including (i) indoor environments exhibit rich multipath which breaks the linear relationship between the phase change and the propagation distance inside a target; (ii) without knowing either material type or target size, trying to obtain these two information simultaneously is challenging; and (iii) stitching pieces of the propagation distances inside a target for an image estimate is non-trivial. We propose solutions to all the challenges and evaluate the system's performance in three different environments. TagScan is able to achieve higher than 94 percent material identification accuracies for 10 liquids and differentiates even very similar objects such as Coke and Pepsi. TagScan can accurately estimate the horizontal cut images of more than one target behind a wall.

Quantifying Interference-Assisted Signal Strength Surveillance of Sound Vibrations

A malicious attacker could, by taking control of internet-of-things devices, use them to capture received signal strength (RSS) measurements and perform surveillance on a person's vital signs, activities, and sound in their environment. This article considers an attacker who looks for subtle changes in the RSS in order to eavesdrop sound vibrations. The challenge to the adversary is that sound vibrations cause very low amplitude changes in RSS, and RSS is typically quantized with a significantly larger step size. This article contributes a lower bound on an attacker's monitoring performance as a function of the RSS step size and sampling frequency so that a designer can understand their relationship. Our bound considers the little-known and counter-intuitive fact that an adversary can improve their sinusoidal parameter estimates by making some devices transmit to add interference power into the RSS measurements. We demonstrate this capability experimentally. As we show, for typical transceivers, the RSS surveillance attacker can monitor sound vibrations with remarkable accuracy. New mitigation strategies will be required to prevent RSS surveillance attacks.

Automatic Detection of Changes in Signal Strength Characteristics in a Wi-Fi Network for an Indoor Localisation System.

This paper faces the issue of changing the received signal strength (RSS) from an observed access point (AP). Such a change can reduce the Quality of Service (QoS) of a Wi-Fi-based Indoor Localisation System. We have proposed a dynamic system based on an estimator of RSS using the readings from other APs. Using an optimal threshold, the algorithm recognises an AP that has changed its characteristics. Next, the system rebuilds the localisation model excluding the changed AP to keep QoS. For the tests, we simulated a change in the analysed Wi-Fi network by replacing the measured RSS by an RSS obtained from the same AP model that lies in another place inside the same multi-floor building. The algorithm was evaluated in simulations of an isolated single-floor building, a single-floor building and a multi-floor building. The mean increase of the localisation error obtained by the system varies from 0.25 to 0.61 m after the RSS changes, whereas the error increase without using the system is between 1.21 and 1.98 m. The system can be applied to any service based on a Wi-Fi network for various kinds of changes like a reconfiguration of the network, a local malfunction or ageing of the infrastructure.

MUSIC Algorithm for Respiratory Rate Estimation Using RF Signals

DOI: 10.26650/electrica.2018.03405 Continuous monitoring of respiratory rate (cycle) during sleep for diseases such as sleep apnea and sudden infant death syndrome (SIDS) can be lifesaving. Wireless radio communications signals are everywhere and can be harnessed for contactless monitoring of the respiratory rates. The amplitude of the received signal strength changes periodically depending on the exhalation and inhalation of the subject. In this paper, subspace-based multiple signal classification (MUSIC) algorithm is applied to estimate the respiratory rate for better results. The proposed method and the other power spectral density (PSD) methods for respiratory estimations are compared with the real laboratory measurements. It is demonstrated that the proposed method estimates the respiratory rate with high accuracy and outperforms the other PSD-based methods which are commonly used in the literature.

Finding Near-Optimal Regularization Parameter for Indoor Device-free Localization

Device-free Localization (DfL) systems offer real-time indoor localization of people without any electronic devices attached on their bodies. The human body influences the radio wave propagation between wireless links and changes the Received Signal Strength (RSS). Wireless Sensor Networks (WSNs) nodes easily measure these RSS changes and appropriate Radio Tomographic Imaging (RTI) algorithms can then process the RSS data and allow human localization. This paper investigates how to choose near-optimal regularization parameter during the regularization process for indoor DfL and describes an experimental indoor DfL setup realized with a Sun SPOT based WSN. The work elaborates on the numerical calculation of the near-optimal regularization parameter by usage of the trade-off curve criterion. The calculated parameter enables conclusive RTI image with sufficient localization precision for eHealth or other ambient-assisted-living applications where the error tolerance is at a scale of several tens of centimeters. The value for the regularization parameter matches the empirical derived value obtained in the authors'previous work.

An Experimental Comparison of Radio Transceiver and Transceiver-Free Localization Methods

This paper presents an experimental performance assessment for localization systems using received signal strength (RSS) measurements from a wireless sensor network. In this experimental study, we compare two types of model-based localization methods: transceiver-based localization, which locates objects using RSS from transmitters to receivers at known locations; and transceiver-free localization, which estimates location by using RSS changes on known-location nodes caused by objects. We evaluate their performance using three sets of experiments with different environmental conditions. Our performance analysis shows that transceiver-free localization methods are generally more accurate than transceiver-based localization methods for a wireless sensor network with high node density.

Transferring Compressive-Sensing-Based Device-Free Localization Across Target Diversity

Device-free localization (DFL) plays an important role in many applications, such as wildlife population and migration tracking. Most of current DFL systems leverage the distorted received signal strength (RSS) changes to localize the target(s). However, they assume a fixed distribution of the RSS change measurements, although they are distorted by different types of targets. It inevitably causes the localization to fail if the targets for modeling and testing belong to different categories. This paper presents TLCS-a transferring compressive sensing based DFL approach-which employs a rigorously designed transferring function to transfer the distorted RSS changes across different categories of targets into a latent feature space, where the distributions of the distorted RSS change measurements from different categories of targets are unified. A benefit of this approach is that the same transferred sensing matrix can be shared by different categories of targets, leading to a substantial reduction in the human efforts. The results of experiments illustrate the efficacy of the TLCS.