Impact of Beacon Interval on the performance of WiFi-based passive radar against human targets
01 May 2018-
TL;DR: The results of a dedicated acquisition campaign show that both the detection capability and the localization accuracy progressively degrade as the BI increases due to both the reduction of the received beacons and to the intrinsic undersampling of the target motion.
Abstract: The capability of WiFi-based passive radar to detect, track and profile human targets in both indoor and outdoor environment has been widely demonstrated This paper investigates the impact of the Beacon Interval (BI) on the passive radar performance The results of a dedicated acquisition campaign show that both the detection capability and the localization accuracy progressively degrade as the BI increases due to both the reduction of the received beacons and to the intrinsic undersampling of the target motion Limit values are suggested for practical applications
Citations
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TL;DR: Experimental data is presented which verifies the proposed methods for using any type of signal transmission from a standalone WiFi device, and demonstrates the capability for human activity sensing.
Abstract: Human sensing using WiFi signal transmissions is attracting significant attention for future applications in e-healthcare, security, and the Internet of Things (IoT). The majority of WiFi sensing systems are based around processing of channel state information (CSI) data which originates from commodity WiFi access points (APs) that have been primed to transmit high data-rate signals with high repetition frequencies. However, in reality, WiFi APs do not transmit in such a continuous uninterrupted fashion, especially when there are no users on the communication network. To this end, we have developed a passive WiFi radar system for human sensing which exploits WiFi signals irrespective of whether the WiFi AP is transmitting continuous high data-rate Orthogonal Frequency-Division Multiplexing (OFDM) signals, or periodic WiFi beacon signals while in an idle status (no users on the WiFi network). In a data transmission phase, we employ the standard cross ambiguity function (CAF) processing to extract Doppler information relating to the target, while a modified version is used for lower data-rate signals. In addition, we investigate the utility of an external device that has been developed to stimulate idle WiFi APs to transmit usable signals without requiring any type of user authentication on the WiFi network. In this article, we present experimental data which verifies our proposed methods for using any type of signal transmission from a standalone WiFi device, and demonstrate the capability for human activity sensing.
66 citations
Cites background from "Impact of Beacon Interval on the pe..."
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01 Oct 2019
TL;DR: In this paper, a modified cross-ambiguity function (CAF) has been proposed to reduce redundant samples and an external device has been developed to send WiFi probe request signals which stimulates an idle AP to transmit WiFi probe responses, thus generate usable transmission signals for sensing applications without the need to authenticate and join the network.
Abstract: WiFi signals for physical activity sensing show great practical potentials for pervasive healthcare applications due to the widespread WiFi deployments and high levels of public acceptance of such systems. Traditionally, WiFi-based sensing uses the Channel State Information (CSI) from an off-the-shelf WiFi Access Point (AP) which transmits signals that have high pulse repetition frequencies. However, when there are no users on the local network only beacon signals are transmitted from the WiFi AP which significantly deteriorates the sensitivity and specificity of such systems. Surprisingly, WiFi based sensing under these conditions have received little attention given that WiFi APs are frequently in idle state. This paper presents a practical system based on passive radar techniques which does not require any special setup or firmware changes to be able to work with any commercial WiFi device. To cope with the low duty cycles associated with beacon signal transmissions, a modified Cross Ambiguity Function (CAF) has been proposed to reduce redundant samples. In addition, an external device has been developed to send WiFi probe request signals which stimulates an idle AP to transmit WiFi probe responses, thus generate usable transmission signals for sensing applications without the need to authenticate and join the network. Detection performance shows that the proposed concept can significantly improve activity detection and is a viable candidate in future healthcare applications.
9 citations
05 Oct 2020
TL;DR: The comparison between the use of the sensor fusion approach and the localization based on a single sensor (PBR or PSL) shows the benefits coming from the exploitation of multiple sensors.
Abstract: This paper investigates the joint exploitation of Wi-Fi based Passive Bistatic Radar (PBR) and Wi-Fi based Passive Source Location (PSL) for drone localization. The inherent features of the two strategies and the results obtained from their comparison on experimental data show an interesting complementarity between them. Following this consideration, a proper sensor fusion strategy combining these two methodologies is investigated in order to achieve improved results in terms of positioning capability. The three strategies (PBR, PSL and sensor fusion) are evaluated against experimental data. The comparison between the use of the sensor fusion approach and the localization based on a single sensor (PBR or PSL) shows the benefits coming from the exploitation of multiple sensors.
6 citations
Cites background from "Impact of Beacon Interval on the pe..."
...This can be achieved by setting the AP to transmit with a high transmission rate ([11], [14]), i....
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22 Apr 2019
TL;DR: W WiFi activity classification is investigated using just WiFi probe response signals which can be generated using a low-cost off-the-shelf secondary device (Raspberry Pi) eliminating the requirement to actually connect to the WiFi network.
Abstract: Passive WiFi radar shows significant promise for a wide range of applications in both security and healthcare owing to its detection, tracking and recognition capabilities. However, studies examining micro-Doppler classification using passive WiFi radar have relied on manually stimulating WiFi access points to increase the bandwidths and duty-cycles of transmissions; either through file-downloads to generate high data-rate signals, or increasing the repetition frequency of the WiFi beacon signal from its default setting. In real-world scenarios, both these approaches would require user access to the WiFi network or WiFi access point through password authentication, and therefore involve a level of cooperation which cannot always be relied upon e.g. in law-enforcement applications. In this research, we investigate WiFi activity classification using just WiFi probe response signals which can be generated using a low-cost off-the-shelf secondary device (Raspberry Pi) eliminating the requirement to actually connect to the WiFi network. This removes the need to have continuous data traffic in the network or to modify the firmware configuration to manipulate the beacon signal interval, making the technology deployable in all situations. An activity recognition model based on a convolutional neural network resulted in an overall classification accuracy of 75% when trained from scratch using 300 measured WiFi probe-response samples across 6 classes. This value is then increased to 82%, with significantly less training when adopting a transfer learning approach: initial training using WiFi data traffic signals, followed by fine-tuning using probe response signals.
5 citations
TL;DR: The design process of a simplified harvesting circuit for WiFi at the 2.4 GHz frequency band based on the analysis of the environment available signals is shown, allowing to devise a novel switching scheme that employs two units that favor energy use and speed up the recharging process.
Abstract: This paper shows the design process of a simplified harvesting circuit for WiFi at the 2.4 GHz frequency band based on the analysis of the environment available signals. Those signals and their power level define an antenna design to maximize captured energy and select the proper number of stages for a voltage multiplier so that an impedance matching network is no longer required. With this, it is possible to maintain the harvester architecture simple without sacrificing performance. The use of supercapacitors is preferred over batteries due to their high-power capacity, the ability to deliver high peak currents, long-life cycle size, and low cost. Hence, supercapacitor availability allows to devise a novel switching scheme that employs two units that favor energy use and speed up the recharging process. The built harvester exhibits a power conversion efficiency greater than 50% under an incident signal of 0 dBm in the rectenna. The tests are carried out in an academic environment using a multi SSID router, collecting 494 mJ without requiring special modifications in the router used as an energy source.
2 citations
References
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10 May 2010
TL;DR: In this paper, the practical feasibility of a WiFi transmissions based passive bistatic radar (PBR) is analyzed with reference to typical signals broadcasted by a IEEE 802.11 access point exploiting an OFDM modulation.
Abstract: In this paper the practical feasibility of a WiFi transmissions based passive bistatic radar (PBR) is analyzed. The required data processing steps are described there including the adopted techniques for: (i) the control of the signal Ambiguity Function usually yielding a high sidelobe level and (ii) the removal of the undesired signal contributions which strongly limit the useful dynamic range. The performance of the conceived system is evaluated with reference to typical signals broadcasted by a IEEE 802.11 access point exploiting an OFDM modulation. The achievable results are presented against a real data set collected by an experimental setup. This allowed us to preliminarily demonstrate the potentialities of a WiFi-based PBR for local area surveillance applications.
82 citations
"Impact of Beacon Interval on the pe..." refers background in this paper
...In the past, a few research groups developed WiFi-based passive radar [1]-[5], which performs the localization and tracking of moving targets....
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TL;DR: This study investigates the two-dimensional target localisation capabilities of a passive radar system based on WiFi transmissions and compares different target localisations strategies based on subsets of the available measurements to understand the localisation accuracies achievable using the different combinations of measurements.
Abstract: In this study the authors investigate the two-dimensional target localisation capabilities of a passive radar system based on WiFi transmissions. It is well known that the most straightforward way to achieve the target position estimation in the horizontal plane with a passive radar exploits the measurements either of a single bistatic range plus a direction of arrival (DoA) or of two bistatic ranges collected by two separate receivers. However, for a practical application it is interesting to clearly define which one of the two approaches provides the passive radar target localisation with a higher accuracy and whether combining both multiple bistatic range plus DoA measurements provides a further advantage. A multistatic configuration is considered which allows to collect a set of range/Doppler/angle measurements for a given target. Different target localisation strategies are devised and compared, based on subsets of the available measurements with the aim of understanding the localisation accuracies achievable using the different combinations of measurements. Experimental results are shown based on a passive radar prototype developed and fielded at the DIET Department - Sapienza University of Rome. This will contribute to demonstrate the fruitful application of the passive radar concept for short range surveillance.
62 citations
"Impact of Beacon Interval on the pe..." refers methods in this paper
...The passive radar processing scheme developed at Sapienza University of Rome ([3]-[4]) was applied....
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...To obtain 2D localization, [4], in addition to bistatic range, the target AoA, θ, is estimated from the phase difference, Δφ, between the signals collected by RX2 and RX3, as = ⋅ 2 (1)...
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TL;DR: An effective signal processing scheme to track moving vehicles and to obtain their cross-range profiles with a passive bistatic radar (PBR) based on the signals of opportunity emitted by a WiFi router is presented.
Abstract: This paper presents an effective signal processing scheme to track moving vehicles and to obtain their cross-range profiles with a passive bistatic radar (PBR) based on the signals of opportunity emitted by a WiFi router. While the target detection using WiFi-based PBR has already been studied by the authors, this paper focuses on the targets moving with a low radial velocity component. These are especially interesting since they might have a reasonable cross-range velocity component, which allows us to apply inverse synthetic aperture radar (ISAR) techniques to provide a high-resolution cross-range profile. A specific problem for these targets is the presence of possibly strong echoes from the stationary background (clutter), which tend to mask their contributions. In such cases, the standard Doppler processing does not help in separating the targets from this clutter. Therefore, appropriate clutter cancellation schemes are applied, and their effectiveness and impact are analyzed both on the tracking and on the ISAR profiling. An appropriate ISAR scheme for cross-range profiling is introduced, tailored for the typical short-range and possibly bistatic surveillance scenarios of the WiFi-based PBR; this scheme comprises the automatic estimation from the data of the target motion components up to a higher order than in usual long-range imaging and their compensation. The reliability of the obtained profiles is also investigated, for both the monostatic and bistatic cases, which is essential both for the vehicle size/characteristics estimation and for the automatic recognition schemes based on vehicle databases. The results obtained using an experimental setup developed and fielded at the University of Rome “La Sapienza,” Rome, Italy, show that the considered approach is effective and that the obtained cross-range profiles achieved by ISAR processing with WiFi-based passive radar are quite reliable both in the monostatic and bistatic cases.
55 citations
"Impact of Beacon Interval on the pe..." refers background in this paper
...In contrast, good Doppler frequency resolution is available, which provides good localization performance when the target is well separated in Doppler from the other targets and even allows to obtain cross-range profiles, [7]....
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17 Oct 2014
TL;DR: The design and implementation of a real-time passive high Doppler resolution radar system is described and it is shown that the proposed system can be used in a range of application scenarios such as eHealth, human-machine interaction and high accuracy indoor target tracking.
Abstract: The design and implementation of a real-time passive high Doppler resolution radar system is described in this paper Batch processing and pipelined processing flow are introduced for reducing the processing time to enable real-time display The proposed method is implemented on a software defined radio (SDR) platform Two experiments using this system are described: one based on small human body motions and another one on hand gesture detection The results from these experiments show that the proposed system can be used in a range of application scenarios such as eHealth, human-machine interaction and high accuracy indoor target tracking
55 citations
"Impact of Beacon Interval on the pe..." refers background in this paper
...In the past, a few research groups developed WiFi-based passive radar [1]-[5], which performs the localization and tracking of moving targets....
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23 Apr 2012
TL;DR: In this paper, an effective cancellation strategy is introduced to cope with the target signal distortion at the output of the cancellation stage which might be responsible of severe target profile degradation, which allows an effective removal of the undesired contributions while preserving the quality of the target cross-range profile.
Abstract: The application of Inverse Synthetic Aperture Radar (ISAR) techniques to WiFi-based passive radar is investigated in this paper with the purpose of obtaining high resolution cross-range profiling of moving targets. It is firstly shown that the ISAR processing must follow the typical disturbance cancellation stage required in passive radar to remove undesired contributions from the stationary scene which are likely to mask the target returns. Thus the attention is focused on the analysis of the impact of the disturbance cancellation stage on both the autofocus (i.e. the target motion parameters estimation) and the target profiling stages. An effective cancellation strategy is introduced to cope with the target signal distortion at the output of the cancellation stage which might be responsible of severe target profile degradation. The reported experimental results show that the proposed technique allows an effective removal of the undesired contributions while preserving the quality of the target crossrange profile.
46 citations