Passive radars using illuminators of opportunity have attracted much attention in the international radar community. One existing radio transmission system that may be utilised for this purpose is the Global System for Mobile communication (GSM). The paper presents a study showing the feasibility of using a GSM signal for passive radar. The analysis of the GSM waveform, and any significance or influence it has with respect to the passive radar design considerations are investigated in detail. The paper describes fully the design and implementation of a low-cost GSM-based passive radar prototype in addition to the associated signal processing scheme. Numerous measurements for various ground-moving targets were investigated extensively. The preliminary processing results demonstrate the feasibility of using GSM signals as a radar waveform and have the potential capability to detect and track different types of ground-moving targets.

Passive radar using Global System for Mobile communication signal: theory, implementation and measurements

In this paper, we investigate the feasibility of uncooperatively and covertly detecting people moving behind walls using passive bistatic WiFi radar at standoff distances. A series of experiments was conducted which involved personnel targets moving inside a building within the coverage area of a WiFi access point. These targets were monitored from outside the building using a 2.4-GHz passive multistatic receiver, and the data were processed offline to yield range and Doppler information. The results presented show the first through-the-wall (TTW) detections of moving personnel using passive WiFi radar. The measured Doppler shifts agree with those predicted by bistatic theory. Further analysis of the data revealed that the system is limited by the signal-to-interference ratio (SIR), and not the signal-to-noise ratio. We have also shown that a new interference suppression technique based on the CLEAN algorithm can improve the SIR by approximately 19 dB. These encouraging initial findings demonstrate the potential for using passive WiFi radar as a low-cost TTW detection sensor with widespread applicability.

Through-the-Wall Sensing of Personnel Using Passive Bistatic WiFi Radar at Standoff Distances

This paper compares two algorithms for three-dimensional target localization from passive radar measurements. The algorithms use bistatic range measurements from multiple transmitter-receiver pairs to calculate the target position. The algorithms derived are based on the methods known for time-difference-of-arrival (TDOA) systems, namely spherical interpolation (SI) and spherical intersection (SX). Both algorithms rely on closed-form equations. A theoretical accuracy analysis of the algorithms is provided. This analysis is verified with Monte-Carlo simulations and a real-life example is presented.

Two Methods for Target Localization in Multistatic Passive Radar

The practical feasibility of a WiFi transmissions based passive bistatic radar (PBR) is analyzed here. The required data processing steps are described including the adopted techniques for 1) the control of the signal autocorrelation function (ACF) usually yielding a high sidelobe level, and 2) the removal of the undesired signal contributions which strongly limit the useful dynamic range. The performance of the proposed techniques is firstly evaluated against simulated data generated according to the IEEE 802.11 Standards. Moreover the results are presented against a real data set collected by an experimental setup when using the conventional dual (reference and surveillance) channels PBR receiving scheme. This allows us to demonstrate the potentialities of a WiFi-based PBR for local area surveillance applications, where vehicles and people can be detected and tracked. Based on the digital nature of the exploited signals of opportunity, the attractive possibility is also investigated of avoiding the use of a dedicated receiving channel for the reference signal, by synthesizing it from the surveillance channel. This approach is shown to yield comparable performance with respect to the conventional PBR approach while yielding a remarkable saving in terms of system complexity.

WiFi-Based Passive Bistatic Radar: Data Processing Schemes and Experimental Results

We investigate the use of WiFi Received Signal Strength Information (RSSI) at a mobile phone for the recognition of situations, activities and gestures. In particular, we propose a device-free and passive activity recognition system that does not require any device carried by the user and uses ambient signals. We discuss challenges and lessons learned for the design of such a system on a mobile phone and propose appropriate features to extract activity characteristics from RSSI. We demonstrate the feasibility of recognising activities, gestures and environmental situations from RSSI obtained by a mobile phone. The case studies were conducted over a period of about two months in which about 12 hours of continuous RSSI data was sampled, in two countries and with 11 participants in total. Results demonstrate the potential to utilise RSSI for the extension of the environmental perception of a mobile device as well as for the interaction with touch-free gestures. The system achieves an accuracy of 0.51 while distinguishing as many as 11 gestures and can reach 0.72 on average for four more disparate ones.

The telepathic phone: Frictionless activity recognition from WiFi-RSSI

Passive radar using GSM cellular mobile communication signal had been demonstrated to be feasible for short-range moving target measurements. This paper presents some new results of aircraft measurements with enhanced performance. It is shown that the operation range of GSM-based passive radar can be substantially larger than the coverage of one normal base station cell that is allocated for mobile communication service. In addition, based on the signals received by passive radar, the target RCS is estimated and a reliable performance prediction is performed for different operating conditions.

Aircraft target measurements using A GSM-based passive radar

The networks of cell phone base stations not only provide continuous service for mobile communications users but also offer abundant illuminator resources for passive surveillance radar systems. This extensively explores the potential applications of passive surveillance radar using cell phone base station signals for various scenarios such as ground traffic monitoring, coastal and air surveillance, and through-the-wall motion detections. These promising experimental results demonstrated that such systems can be an attractive, low-cost alternative solution for various applications and prospectively as a complement to traditional active radar systems.

Applications of passive surveillance radar system using cell phone base station illuminators

Passive radar makes use of an 'illuminator of opportunity' already present in the environment for other purposes (TV transmission, broadcast systems, etc) to detect targets as well as estimating target parameters. This radar has the merit of being a completely covert radar system, which does not advertise the presence of either the receivers or transmitting stations. One such existing radio transmission that may be utilize for this purpose is that of the GSM system. This paper is intended to access the feasibility and suitability of using the GSM downlink signals from the GSM base station as the 'transmissions of opportunity' in an experimental passive radar system. The analysis of the GSM signal as a radar waveform for the passive radar systems design and its associate signal processing scheme is investigated. Simulations and preliminary experimental results demonstrate that the detection of ground moving targets can be indeed be achieved, affirming that this system is indeed viable and for certain does offer a novel and unique kind of passive detection that is outside the scope of other current approaches.

Feasibility analysis of GSM signal for passive radar

This study presents the space-time snapshot models for the interfering passive signals received by the airborne passive radar which uses a ground-based stationary non-cooperative transmitter. The random range sidelobes couplings of the direct path and of the strong clutter signals into further range cells are major concerns in moving target detection performance. The least squares-based adaptive interference cancellation technique is proposed to efficiently suppress the direct path, strong clutter and Doppler-shifted strong clutter signals present at each antenna element prior to matched filter processing. In mitigating the interfering signals, their corresponding random range sidelobes will also be suppressed by the same amount. Ground-based moving passive radar trials were conducted to validate and ascertain the effectiveness of the proposed adaptive interference cancellation algorithm.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-rsn.2013.0190

Danny Kai Pin Tan

Papers

Passive radar using Global System for Mobile communication signal: theory, implementation and measurements

Aircraft target measurements using A GSM-based passive radar

Applications of passive surveillance radar system using cell phone base station illuminators

Feasibility analysis of GSM signal for passive radar

Space–time interference analysis and suppression for airborne passive radar using transmissions of opportunity