A Feasibility Study of RIP Using 2.4 GHz 802.15.4 Radios

This paper contains a feasibility study of Radio Interferometric Positioning (RIP) implemented on a widely used 2.4 GHz radio (CC2430). RIP is a relatively new localization technique that uses signal strength measurements. Although RIP outperforms other RSS-based localization techniques, it imposes a set of unique requirements on the used radios. Therefore, it is not surprising that all existing RIP implementations use the same radio (CC1000), which operates below the 1 GHz range. This paper analyzes to what extent the CC2430 complies with these requirements. This analysis shows that the CC2430 platform introduces large and dynamic sources of errors. Measurements with a CC2430 test bed in a line-of-sight indoor environment verify this. The measurements indicate that the existing RIP algorithm cannot cope with these types of errors, and will incur a relatively low accuracy of 3.1 meter. Based on these results, we made an initial implementation of a new algorithm, which can cope with these errors, and decreases this positioning error by a factor of two to 1.5 meter accuracy

A review of RFI mitigation techniques in microwave radiometry

Radio frequency interference (RFI) is a well-known problem in microwave radiometry (MWR). Any undesired signal overlapping the MWR protected frequency bands introduces a bias in the measurements, which can corrupt the retrieved geophysical parameters. This paper presents a literature review of RFI detection and mitigation techniques for microwave radiometry from space. The reviewed techniques are divided between real aperture and aperture synthesis. A discussion and assessment of the application of RFI mitigation techniques is presented for each type of radiometer.Peer ReviewedPostprint (published version

inTrack: High Precision Tracking of Mobile Sensor Nodes

Radio-interferometric ranging is a novel technique that allows for fine-grained node localization in networks of inexpensive COTS nodes. In this paper, we show that the approach can also be applied to precision tracking of mobile sensor nodes. We introduce inTrack, a cooperative tracking system based on radio-interferometry that features high accuracy, long range and low-power operation. The system utilizes a set of nodes placed at known locations to track a mobile sensor. We analyze how target speed and measurement errors affect the accuracy of the computed locations. To demonstrate the feasibility of our approach, we describe our prototype implementation using Berkeley motes. We evaluate the system using data from both simulations and field tests

SIGINT: The Mission CubeSats are Made For

The collection of radio frequency (RF) signals by means of interferometry is an area that shows great promise for small satellite applications and is a shared interest of business and the scientific and military community. SIGnals INTelligence or SIGINT is one of the oldest missions for satellites, especially for its subfield, ELectronic INTelligence (ELINT), the analysis and localization of RF-signals. Unfortunately, the accuracy that customers demand from such systems in order to merit their costs is often incongruent with detection techniques that rely on single nanosatellites (such as Angle of Arrival methods). Accuracy is strongly related to aperture size; rigid antennas are therefore limited to the available surface area of small satellites. Typical accuracies that can be expected of AOA-techniques range from 0.1° – 1°1. Factoring in orbital altitude, this results in geolocation accuracies of 10 km or more for RF-sources close to the satellite’s nadir, increasing rapidly with distance from nadir for missions in LEO. Using a single CubeSat solution with rigid antenna systems limits the type of RF-emitters that can be geolocated with high accuracy (\u3c 0.1°) to X-band (or shorter wavelengths). Deployable structures and small satellites that do not adhere to the CubeSat standard offer a limited solution as there is limited volume available for deployment mechanisms. One of the key benefits of using CubeSats is their lower unit and launch cost. This enables technical solutions that depend on distributing the desired functionality over many satellites, instead of investing in highly sophisticated single satellite payloads. This approach has in the past been studied for space-based interferometers like Orbiting Low Frequency Antennas for Radio Astronomy (OLFAR) enabling far larger diameter “apertures” than could be fitted on a single satellite while at the same time simplifying the development and deployment2. The same technologies that enable these scientific missions are at the heart of satellite formations for the purpose of identifying and geolocating RF-emitters on the Earth’s surface, such as inter-satellite datalinks, station-keeping systems and precise avionics. The overlap is not limited to these enabling technologies but also extends to system level characteristics. One of the big obstacles for CubeSat missions beyond LEO is their reliability. CubeSat missions beyond LEO face two hurdles that amplify each other, on the one hand the radiation environment becomes significantly more hostile, complicating the use of COTS components and on the other hand the cost of replenishment increases drastically with distance from Earth. Missions such as OLFAR thus require a step change in the reliability of the subsystems in order for them to be affordable and cost effective. At the same time these same reliability improvements would further decrease the cost of ownership of LEO spectrum monitoring (or SIGINT) constellations

Strong RFI impact mitigation in the synthetic aperture interferometric radiometer

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Radio Frequency Interference (RFI) is one of the problems causing the performance degradation in passive microwave radiometry. Especially, Synthetic Aperture Interferometric Radiometer (SAIR) is quite vulnerable to strong RFI. The Soil Moisture Ocean Salinity (SMOS) brightness temperature images show serious contamination by the RFI. The RFI affection in SAIR images should be mitigated or filtered out to retrieve the geophysical parameters. This work presents a method to RFI mitigation/filtering for SAIRs. Different from the existing method processing the brightness temperature image directly, RFI filtering of the subspace of covariance matrix is introduced, and the results are shown. The proposed method shows decent results for strong RFI with efficiency compared to the existing methods. © 2018 IEEE.Peer ReviewedPostprint (published version

TechSat 21 and Revolutionizing Space Missions using Microsatellites

The Air Force Research Laboratory (AFRL) TechSat 21 flight experiment demonstrates a formation of three microsatellites flying in formation to operate as a “virtual satellite.” X-band transmit and receive payloads on each of the satellites form a large sparse aperture system. The satellite formation can be configured to optimize such varied missions as radio frequency (RF) sparse aperture imaging, precision geolocation, ground moving target indication (GMTI), single-pass digital terrain elevation data (DTED), electronic protection, single-pass interferometric synthetic aperture radar (IF-SAR), and high data-rate, secure communications. Benefits of such a microsatellite formation over single large satellites include unlimited aperture size and geometry, greater launch flexibility, higher system reliability, easier system upgrade, and low cost mass production. Key research has focused on the areas of formation flying and sparse aperture signal processing and been sponsored and guided by the Air Force Office of Scientific Research (AFOSR). The TechSat 21 Program Preliminary Design Review (PDR) was held in April 2001 and incorporated the results of extensive system trades to achieve a light-weight, high performance satellite design. An overview of experiment objectives, research advances, and satellite design is presented

Phase and Amplitude Interferometry Based Radio Frequency Direction Finder

Direction finding (DF) systems have been around for decades, preceding WWII. The main function of these systems is to calculate the direction of arrival of an electromagnetic wave. There are many real-world applications which utilize direction finders and direction-finding techniques, from recreational “fox hunts” to military geolocation systems. The following approach for implementing a direction finding system revolves around the phase and amplitude of a signal that is being radiated at an unlicensed frequency of 2.45Ghz by an RF source. The system is comprised of an antenna array of 4 antennas which can be used receive the radiated signal. By comparing the amplitudes of the signal received by each antenna relative to each other, the quadrant from which the RF source is located in can be identified. By comparing the phase difference, 0° to +/- 180°, of the signal received by each antenna relative to each other, four possible directions can be calculated, one in each quadrant. Using the information discovered from comparing the phase and the amplitudes of the received signal at each antenna, the direction of the RF source can be found. The system runs the direction finding algorithm when the user commands it to from the graphical user interface (GUI), iterates it hundreds of times per second, and averages the found direction to reduce the effects of noise. The direction is then displayed on the GUI

In-depth verification of Sentinel-1 and TerraSAR-X geolocation accuracy using the Australian Corner Reflector Array

This article shows how the array of corner reflectors (CRs) in Queensland, Australia, together with highly accurate geodetic synthetic aperture radar (SAR) techniques—also called imaging geodesy—can be used to measure the absolute and relative geometric fidelity of SAR missions. We describe, in detail, the end-to-end methodology and apply it to TerraSAR-X Stripmap (SM) and ScanSAR (SC) data and to Sentinel-1interferometric wide swath (IW) data. Geometric distortions within images that are caused by commonly used SAR processor approximations are explained, and we show how to correct them during postprocessing. Our results, supported by the analysis of 140 images across the different SAR modes and using the 40 reflectors of the array, confirm our methodology and achieve the limits predicted by theory for both Sentinel-1 and TerraSAR-X. After our corrections, the Sentinel-1 residual errors are 6 cm in range and 26 cm in azimuth, including all error sources. The findings are confirmed by the mutual independent processing carried out at University of Zurich (UZH) and German Aerospace Center (DLR). This represents an improve�ment of the geolocation accuracy by approximately a factor of four in range and a factor of two in azimuth compared with the standard Sentinel-1 products. The TerraSAR-X results are even better. The achieved geolocation accuracy now approaches that of the global navigation satellite system (GNSS)-based survey of the CRs positions, which highlights the potential of the end-to-end SAR methodology for imaging geodesy