Craig Tong

Planning and design phases of a commensal radar system in the FM broadcast band

We refer to radars that depend on transmitters of opportunity while having no impact on the systems that the transmitters are serving, as commensal radars. Other researchers refer to such systems as passive bistatic radar (PBR) [5], [26], [18]. The word passive refers only to the receivers; since, no radar system can be passive. Our system is multistatic, so the term PBR is not appropriate. Another term used in open literature is, passive coherent location [5], [23], [9]. This nomenclature is closer to our system, except that the system is not passive, so we believe that commensal is the best descriptor of this class of radar, while ours is specifically, a multistatic FM broadcast band commensal radar. An overview of a multistatic system is shown in Figure 1. For simplicity, we shall refer to commensal multistatic radar (CMR) when referring to our system here. We will explain in the following why our system must be multistatic, with few transmitter sites and many receivers, due to its intended deployment in developing nations.

Processing design of a networked passive coherent location system

This paper outlines the design of a bistatic passive coherent location radar receiver system using Software Defined Radio (SDR) techniques. The receiver of the bistatic system is made up of a RF front-end, digitisation section, digital signal processing section and user interface. The integration of various components of the system are discussed. The digital signal processing stages of the system are implemented using general purpose computing hardware in an attempt to keep development costs to a minimum. The design is then elaborated to form a multi-static system which consists of several receiver nodes and multiple illuminators of opportunity.

Commensal radar: Range-Doppler processing using a recursive DFT

Commensal radar [1] is an attractive solution to low-cost air-traffic surveillance. This paper proposes an alternative approach using a recursive Fourier transform for Doppler processing for computing amplitude-range-Doppler (ARD) data. At present, the full FFT is utilsed, however, at the cost of unnecessary channel decomposition, excess memory, and high-overhead for the required sampling window lasting 1-4s. This work proposes the use of a recursive Fourier technique which allows select channels to be computed, introduces significant memory savings, and offers very fine time frequency decomposition.

A minimal architecture for real-time, medium range aircraft detection using FM-band illuminators of opportunity

This paper details the architecture for a minimal commensal radar system which makes use of commercial FM broadcast band transmitters for the detection of aircraft. The architecture, consisting of a RF front-end, digital acquisition and radar signal processing up to the detection stage (after CFAR on a Range-Doppler plot), is intended to be small, easily portable, low power, and yet able to operate in real-time. The system is based mostly on low cost commercial off-the-shelf (COTS) components. To this end, an Ettus Research USRP board, a NVIDIA Jetson TK1 computing board and connectorised RF components are exploited. It is shown that the presented system is able to detect commercial airliners in excess of 100 km from the receiver while providing output in a real-time streaming manner.

FM band commensal radar technology used for the detection of small aircraft and the measurement of propeller modulation

Commensal radars (CR) depend on transmitters of opportunity whilst having no impact on the systems the transmitters are serving. This paper presents initial trials conducted to investigate the performance of an FM radio band based CR system against smaller aircraft. We present the detection range results and also demonstrate that we could accurately determine the rotation rate of the aircrafts propeller.

ComRad3, a multichannel direct conversion receiver for FM Broadcast Band Radar

FM Broadcast Band Radar, based on the commensal use of the narrow band emissions of the FM broadcast band (88-108 MHz) is highly attractive for developing nations. We report on a direct sampling, multichannel receiver designed to exploit the entire FM broadcast band. To allow for applications such as angle of arrival (AoA) measurements, 3 receiver channels are provided, i.e. 3 analogue stages each driving a coherently clocked analogue to digital converter (ADC). The receiver allows for the continuous, simultaneous and coherent channelisation using 16 digital down converters (DDCs). Up to 8 FM band channels can therefore be digitised simultaneously when using 2 receiver channels or up to 5 FM band channels when using 3 receiver channels. This provides redundancy against the time-fluctuating modulation bandwidth of FM broadcast band channels as well as potential robustness against undesirable propagation effects such as multipath, achievable as a result of the concurrent exploitation of multiple carrier frequencies. Application of Compressive Sensing techniques are also allowed by the multichannel architecture, spread over the whole band. The architecture, test results, and demonstration of aircraft detection are presented.

Performance improvements using the separated reference configuration for a multi-static FM broadcast band radar system

A Commensal Radar (CR) uses the transmissions from radiators to detect and track targets. Since there is no requirement for dedicated spectrum allocation, Commensal Radars are gaining interest as an alternative to conventional, monostatic, active radar for applications such as air traffic control. Moves by governments to charge for spectrum usage is a growing concern for operators. Commensal radars have, until recently, been crippled by direct signal interference, limiting dynamic range [1]. Traditionally the CR system will produce bistatic detections by recording the reference and surveillance channels together at the same site with a multi-channel receiver. The multi-channel receiver ensures relative phase stability and inherent synchronicity between the 2 channels for the purpose of cross-correlation, to recover time delay and Doppler shift of the target(s). This configuration makes it difficult to use site selection to reduce the interference in the surveillance channel (e.g. by means of terrain shielding) as the reference antenna always needs to have Line of Site (LoS) to the illuminator. The “Separated Reference” [2] configuration was thus developed to allow the reference and surveillance antennas to be placed at widely separated sites (10s to 100s of km). Each receiver is equipped with a Global Navigation Satellite Systems (GNSS) stabilised oscillator to maintain relative channel synchronicity and provide accurate time stamping to allow the combing of many bistatic baselines. The separated reference configuration allows each antennas location to be optimised purely for the detection function. This paper reports on some of the results and performance improvements obtained with field testing the separated reference configuration, beyond what was initially published [2].