Search

Cubesats have been effective at lowering the barriers for entry to space for educational institutions and small private players resulting in new and innovative missions and concepts. Novel, potentially powerful, space science projects such as QB50 can now be undertaken with limited budgets and resources. However, the failure rate of Cubesats has been quite high with many failing to establish any communications at all, leaving little opportunity for teams to debug and recover the satellite. Due to the time and cost restrictions faced by Cubesat projects, traditional verification and validation testing processes are not feasible, giving rise to the high failure rate. In this paper, we describe the experience gained during the development, launch and operation of the UNSW-EC0 Cubesat, which was deployed in 2017 as part of the QB50 mission. In particular, we present a robust framework derived from Failure Mitigation Effects and Criticality Analysis (FMECA) for Cubesat testing that is practical for typically resource and time constrained missions. We also describe robustness testing performed during development combined with additional functionality that was built into the satellite, which allowed in-orbit troubleshooting and mission recovery. Following its recovery, UNSW-EC0 was able to perform nominally for the remaining duration of its lifetime. Some preliminary in orbit mission results are also described in the paper. Two UNSW-built Single Event Upset (SEU) resistant experiments as well as the RAMSES payload successfully demonstrated long endurance operations in orbit.

This paper proposes a hybrid cooperative positioning (CP) algorithm suitable for vehicular network applications which can fuse the measurements from global navigation satellites, ground stations, signals of opportunity, inter-node ranging from neighbouring vehicles and onboard inertial navigation systems (INS). By applying the framework of generalized approximate message passing (GAMP), the complex CP problem is transformed into an iterative yet lower computational load process. In each iteration, the time recurrence of navigation states and initialization of GAMP computation are conducted based on Kalman filter. The proposed algorithm guarantees the overall positioning performance of multiple vehicles in a hybrid navigation scenario, and improves the robustness and accuracy of CP navigation systems. Simulation results show that the proposed algorithm has better estimation accuracy than traditional CP algorithms, and has 20 times less computational load than the best existing algorithm with equivalent accuracy.

We demonstrate a single layer of terahertz sub-wavelength fibers can act as an electromagnetic mirror due to the excitation of Mie-resonances and the lattice coupling. This opens up new avenues in developing simple terahertz metadevices for beam manipulation.

Due to proliferation of Personal Privacy Devices (PPDs), it has become imperative for safety-critical GNSS users (such as airports and marine ports) to be situationally aware of local GNSS interference. It is the aim of this paper to propose and validate an enhanced method for geolocating GNSS interference sources so that PPDs can be found and disabled. A requirement for geolocating a narrowband transmitting source is to have a sparsely spread network of three or more stations equipped with an RF phased array. However, when a sufficiently wideband transmitting source is present, two techniques are now available for geo-localisation: Angle of Arrival (AOA) methods and Time Difference of Arrival (TDOA) methods. In this situation, it becomes useful to combine both AOA and TDOA information from all stations to compute the best possible geo-localisation estimate of the source location. This paper proposes an iterative least squares method to combine AOA and TDOA measurements for joint localisation. We then derive the Cramer Rao Bounds of geo-localisation for the joint AOA/TDOA estimation which we further show to be approximated by the performance of our proposed method. We also analyse how the proposed method compares against conventional AOA-only and TDOA-only methods in a three-station network as a case study. This paper also verifies the proposed method against data collected from the GRIFFIN open area calibrated test range. The range is an approved site in southern Australia that permits actively monitored and controlled transmissions of weak signal GNSS jamming & spoofing for experimental purposes. The 1 km2 range consists of three passive sensor arrays (each with a circular concentric array of eight element antenna), multiple GNSS interference simulators and the accompanying ground truth capability. As the sensor arrays operate in the GNSS band, it uses beam-steering to exploit the GNSS signal for calibration without being affected by the interference. From both th

It has been demonstrated that delay-Doppler (DD) maps (DDMs) retrieved from spaceborne Global Navigation Satellite Systems Reflectometry missions contain sea clutter and also potential sea targets. Examples of sea targets include sea ice, oil rigs, and oil slicks. To distinguish sea targets from sea clutter, one can estimate the sea clutter and subtract it from the DDM, leaving behind only the sea target's signature on the DDM. This is computationally expensive and will not be robust when the sea clutter estimate is poor or if there are DD tracking errors. This article presents two blind methods for the suppression of sea clutter: first, an adaptive filter and second, an infinite impulse response low-pass filter. We use real DDMs collected by TechDemoSat-1 to show the autoregressive, hence temporally correlated nature of the DDM time series, and present evidence that two blind methods can suppress clutter at least as effectively as the existing method, albeit at a fraction of its computational cost.

Global navigation satellite system (GNSS) signal is vulnerable and easily interfered by spoofing because of its opening signal structure and weak signal power. A signal quality monitoring (SQM) technique has been shown to be viable to detect spoofing attacks on GNSS signals. However, the effectiveness of spoofing detection employing a single SQM metric alone is limited and conditional upon the features extracted of that specific SQM metric. The complementary features among various SQM metrics can be exploited to implement joint detection to overcome the deficiency of the individual SQM metric. Motivated by this idea, this paper investigates the multi-metric joint detection technique, which combines various SQM metrics into a composite SQM metric to detect spoofing attacks. This paper proposes two combination strategies, namely amplitude combination mode and probability of false alarm combination mode (PfaM). The overall performance of different metric combinations was verified using simulations and the Texas Spoofing Test Battery dataset. Results show that the PfaM detector outperforms all single SQM metric detectors under various scenarios.

Signal quality monitoring (SQM) techniques, originally designed for multipath detection, were recently found to be useful to identify underway spoofing attacks. Conventional SQM-based methods directly employ the values of the SQM metrics to monitor spoofing attacks. They have good feasibility with simple structures but suffer from significant performance loss for frequency unlocked spoofing cases due to the drift of the relative carrier phase. We developed an enhanced SQM technique for detecting an onset of spoofing. It is known that the value of the SQM metric fluctuates significantly during the interaction stage between the counterfeit signal and authentic signal. As the variance of metric can better reflect this fluctuation, we choose the moving variance (MV) of the SQM metric as a new metric to detect the occurrence of spoofing. The basic principle of the proposed method is introduced. Its ability to detect spoofing has been validated using the Texas Spoofing Test Battery dataset and compared with the classic SQM methods and a moving average-based method. The results show that the proposed MV-based SQM method is advantageous in the detection of an onset of a frequency unlocked spoofing attack.

Synchronisation of the received Pseudorandom (PRN) code and its locally generated replica is fundamental when estimating user position in Global Navigation Satellite System (GNSS) receivers. It has been observed through experiments that user position accuracy decreases if sampling frequency is an integer multiple of the nominal code rate. This paper provides an accuracy analysis based on the number of samples and the residual code phase of each code chip. The outcomes reveal that the distribution of residual code phases in the code phase range [0, 1/n s), where n s is the number of samples per code chip, is the root cause of accuracy degradation, rather than the ratio between sampling frequency and nominal code rate. Doppler frequencies, coherent integration periods, front-end filter bandwidths and received Carrier to Noise ratios (C/N 0) also influence receiver accuracy. Also provided are a sampling frequency selection guideline and new proposed estimates of the correlation output and the Delay Locked Loop (DLL) tracking error, which can be applied to precisely model GNSS receiver baseband signal processing.

© Springer Nature Singapore Pte Ltd. 2018. Intermediate spoofing, identified as an efficient spoofing attack method, can launch a spoofing attack without interrupting the regular functioning of Global Navigation Satellite System (GNSS) receivers. GNSS is vulnerable and easily interfered by spoofing because of its opening signal structure and low signal power, and this threatens the security and integrity of GNSS, especially for the safety critical applications such as maritime and aviation. Signal Quality Monitoring (SQM) techniques, originally designed for multipath detection, are recently found to be useful to identify the deformation on the correlation function of a GNSS signal due to an intermediate spoofing attack. Conventional SQM-based methods directly employ the values of the SQM metric to detect spoofing attacks. In this paper, we develop an enhanced SQM technique for spoofing detection. It is known that the value of SQM metric fluctuates significantly during the interaction between the counterfeit signal and authentic signal. As the variance of metric can better reflect this fluctuation of metric, we choose the moving variance (MV) of the SQM metric as a new “metric” to detect the occurrence of spoofing. The basic principle of the proposed method is well introduced and tested on four different SQM metrics. Its ability to detect spoofing has been validated using the dataset collected using our SPIRENT simulators. The results show that the proposed moving variance-based SQM method is advantageous in the detection of spoofing attacks.

Ground-based pseudolite navigation systems have several limitations, such as low vertical accuracy, susceptibility to multipath effects, and near-far signal problems. These limitations could be addressed with an airborne pseudolite system. However, to ensure high user positioning accuracy the aerial signal transmitters have to be accurately positioned. Commonly used methods are based on the “inverted GNSS” principle, with ground stations monitoring the pseudolites, or the differential GNSS (DGNSS) technique with one or more reference stations. However, the inverted GNSS method introduces delay for user positioning, while DGNSS has stringent requirements that include simultaneous measurements made by both the pseudolite(s) and the reference station(s), and a limitation on the distance between pseudolite(s) and reference station(s). To address such problems the authors propose an airborne pseudolite system, where the pseudolites are positioned using the GNSS Precise Point Positioning (PPP) technique. To enhance the pseudolite positioning performance, inter-pseudolite range measurements could be used as additional observations. The performance of the proposed system is validated using simulation tests. The results show that A-PL achieves the best positioning accuracy with measurements from both G-PLs and limited GNSS satellites or only from G-PLs where no satellite signals are available.

The Australian Centre for Space Engineering Research (ACSER) at the University of New South Wales has developed a 2U Cubesat named 'Educational Cubesat 0 (EC0)' to participate in the QB50 project. QB50 is a constellation of 50 Cubesats developed by various universities to perform in-situ scientific experiments in the largely unexplored thermosphere. The Cubesats will be launched to the International Space Station (ISS) for deployment in mid 2016. This paper details the software and hardware integration and testing of EC0. The findings cover the functionality of the system, as well as a discussion of testing methods selected for subsystem verification and the lessons learnt in developing and integrating ACSER's first CubeSat. The primary payload of EC0 is the INMS (Ion/Neutral Mass Spectrometer), which will measure the mass of ions and neutral atoms. In addition, EC0 features four other UNSW experiments; the Kea GPS Board for navigation and remote sensing experiments, the seL4 board for testing of its formally verified microkernel experiment, the RUSH FPGA for testing a radiation tolerant FPGA to mitigate SEU failures, and finally, RAMSES, a rapidly manufactured Cubesat structure using selective laser sintering of high temperature 3D-printing. The EC0 was developed by a diverse team that integrated the payloads, support structures and core subsystems. An Electrical Ground Support Equipment (EGSE) was implemented, allowing for core subsystems and payload integration testing with the On-Board Computer (OBC) in the loop. The EGSE allows the OBC to be controlled and programmed, with each satellite resource accessible. Various electrical power conditions can be simulated. The EGSE can be accessed remotely to facilitate off-site code development and testing work. The development of EC0 follows the agile methodology and strict version control via the use of a GIT repository. A magnetically actuated, Attitude Determination and Control System (ADCS) was designed and implement

The continuing expansion of available GNSS signals is an increasingchallenge for receiver designers. New signals with expandedbandwidths are demanding greater sampling rates that require carefuldesign of the receiver RF section to maximise performance tradeoffs. Ahigh level of integration is required to preserve signal path integrity andminimise noise while keeping power consumption to a minimum. Thedesign of the frequency plan and the choice of IF bandwidth are criticalto overall receiver performance. This paper describes the developmentof the monolithic RF front end chips used in the new Namuru multi-GNSS receivers at UNSW. Analysis of the system requirements andarchitecture design are discussed including the LNA, Mixer, IFAmplifier through to the A/D converter. The re-configurable designprovides frequency plan and signal selection flexibility using anintegrated synthesiser and programmable bandwidth filter. The designchallenges of the new front end chips are discussed including featuresaimed at delivering greater performance and flexibility.

Accurate and precise frequency references and timekeeping systems are required for a wide range of applications, such as stock market trading, power generation and distribution, and telecommunications. Over the years, the Global Positioning System (GPS) has become the “go-to” solution for time transfer. This paper details the initial time transfer capabilities of Locata, a localized GPS-like technology. In order to investigate this capability, two time transfer experiments were conducted using two configurations of LocataNets. A LocataNet consists of a single master LocataLite transceiver and one or more slave LocataLites. The process by which the slaves are synchronized to the master (or other slaves) is known as TimeLoc. he first experiment, demonstrating external time transfer, consisted of a master and two slave LocataLites. Each LocataLite was located at an independent site. The master was synchronized to GPS Time (GPST) via the pulse per second (PPS) signal output by a co-located GPS receiver. The first slave was TimeLoc’d to the master with a site separation of 45km. The second slave was TimeLoc’d to the first slave with a site separation of 28km, providing a total time transfer distance of 73km. The time difference between the PPS signals output by the second slave and an independent, but co-located GPS receiver was measured. The mean and standard deviation of the time difference were both on the order of a few nanoseconds. The frequency difference, as derived from the time difference, had a standard deviation of approximately 1 part per billion (ppb). The second experiment, demonstrating internal time transfer, also consisted of a master and two slave LocataLites, albeit in a different configuration. The first slave was TimeLoc’d to the master with a site separation of 28 km and the second slave was adjacent to the master, though TimeLoc’d to the first slave 28 km away, providing a total time transfer distance of 56 km. The time difference between the PPS s

This study investigates identifying forest condition changes using Global Navigation Satellite System (GNSS) signal measurements obtained in a recently conducted airborne experiment. Received signal strength (i.e. the peak correlation power) of the reflected signal is used to distinguish ground surfaces or forest conditions from each other. A simple threshold based method is developed to perform the identification of forest condition change. Through processing the logged airborne experimental data, it is observed that GNSS signal power can be used to reliably and accurately identify abnormal conditions in a forest.

In late 2010 the Garada project., funded by the Australian Space Research Program, was launched at the Australian Centre for Space Engineering Research (ACSER). This collaborative project aims to develop the design, technologies and business case for an Earth observation Synthetic Aperture Radar (SAR) satellite mission, known as “Garada”. The objectives of the mission include developing the capabilities to acquire images of the Earth day or night and in any weather for multiple applications, including soil moisture measurement, biomass estimation, and flood mapping. The mission concept involves two identical satellites that will orbit at a nominal altitude of 612km in a Sun-synchronous orbit with a 6 day repeat cycle. The two satellites will fly in the same orbital plane half an orbit apart. This configuration is capable of acquiring SAR interferometric data pairs with a 3 day period. Each satellite’s primary payload is an L-band radar sensor with a range of different modes of operation, allowing it to record images with different swath widths, resolutions and polarisations. This paper describes the orbit and attitude determination system that could provide inputs to determining imaging system performance, as well as the methodology and algorithms that could be employed for the orbit and attitude determination system. The preliminary design of the orbit and attitude determination system and the navigation sensors are presented for the Garada mission. Their performance was investigated and has confirmed their compliance with the scientific requirements of Garada.

This paper presents field test results from a prototype GPS interference localisation system that uses spatially separated sensor nodes containing antenna arrays to localise interference using both Direction of Arrival (DOA) at each array and Time Difference of Arrival (TDOA) measurements between arrays. The synergy between antenna arrays and TDOA systems are explored and it is found that antenna arrays bring many important benefits to TDOA systems. They can be used to improve time synchronisation between nodes by steering a null at the interference and beams at GPS satellites. They can also be used to steer a beam at the interference to improve its Signal-to-Noise Ratio (SNR) when estimating the TDOA between nodes. Finally the DOA measurements themselves can be used to localise the interference even for very narrowband signals for which TDOA becomes unusable. In this paper the use of the GPS signals themselves for array calibration is also explored, and the GPS signals are used to estimate the orientation of each antenna array, calibrate the phase errors in each antenna array and improve the synchronisation between spatially separated nodes. The experimental antenna array nodes developed are intended for integration into the GNSS Environment Monitoring System (GEMS) developed by GPSat Systems which consists of a number of low-cost sensor nodes that comprehensively monitor GNSS system performance in a given area.

In this paper the performance of GPS timing under jamming conditions is evaluated in the context of a GPS jammer localization system that uses the Time-Difference-Of-Arrival (TDOA) technique. To investigate the performance of GPS timing receivers under jamming conditions, jammer signals of different types and powers were combined with real GPS signals and input into two timing receivers and the response of the PPS and frequency outputs measured. It was found that for at least 3 seconds after the jammer was turned on there was no noticeable drift. This is long enough to switch to a backup timing source or to perform a number of TDOA measurements. The implementation of post-processed time synchronization based on common-view satellite time transfer was also explored to examine the performance that can be expected when using the GPS signals embedded in the data captured for TDOA localization. The relative clock drift between two GPS receivers was then measured for 11 hours to see how Temperature Compensated Crystal Oscillators (TCXOs) behave over time. Using a linear fit to the relative clock drift values before simulated GPS outages, it was found that in the worst case a similar amount of holdover could be achieved as the timing receivers before the drift became significant. The performance of the timing receivers during a jammer localization field-trial was then analyzed. It was found that the TDOA localization could be improved significantly by correcting for timing offsets detected using the post-processing technique.

The use of magnetic field variations for positioning and navigation has been suggested by several researchers. In most of theapplications, the magnetic field is used to determine the azimuth or heading. However, for indoor applications, accurate headingdetermination is difficult due to the presence of magnetic field anomalies. Here location fingerprinting methodology can take advantageof these anomalies. In fact, the more significant the local anomalies, the more unique the magnetic “fingerprint”. In general, in eachfingerprint, the more elements, the better for positioning. Unfortunately, magnetic field intensity data only consists of threecomponents. Since true north (or magnetic north) is unknown, even with help of the accelerometer to detect the direction of the gravity,only two components can be extracted, i.e. the horizontal intensity and the vertical intensity (or total intensity and inclination).Furthermore, moving objects containing ferromagnetic materials and electronic devices may affect the magnetic field. Tests werecarried out to investigate the feasibility of using magnetic field alone for indoor positioning. Possible solutions are discussed.

This paper focuses on sea surface height (SSH)estimation using GNSS direct and reflected signals observed viaan airborne receiver. A power-ratio-based method is presented tocompute the relative delay of the reflected signal, which is thenused to estimate the SSH. The power ratio is defined as the ratioof the correlation power at the code phase over the peakcorrelation power. Preliminary results from processing airborneexperimental data collected over a duration of 1 minutedemonstrate that the mean power ratios associated with foursatellites are very similar. When such a single constant meanpower ratio is used to estimate the relative delay and the SSH, themean of the SSH estimation errors is 4.5cm and the errorstandard deviation (STD) is 1.08m in the presence of significantwave height of about 4 metres.

Australia is presently investigating the design of an earth observation SyntheticAperture Radar (SAR) satellite mission, known as “Garada”, optimised to collect SAR imagesover Australia’s huge land mass for a variety of applications using several small satellitesflying in formation. This paper describes some aspects of the mission design, including themission objectives and the satellite orbit design. It presents the requirements andconsiderations regarding the choice of satellite orbits. The orbit design is mainly driven by therevisit performance, the SAR imaging performance and the solar power requirements. Theresults shows that two identical satellites in the same 613km repeating Sun-synchronous orbitcould meet the user’s 3-day revisit requirement.

Australia is presently investigating the design of an earthobservation Synthetic Aperture Radar (SAR) satellitemission, known as “Garada”, optimised to collect SARimages over Australia’s huge land mass for a variety ofapplications using several small satellites flying information. The Australian Centre for Space EngineeringResearch (ACSER) is funded by a grant from theAustralian Space Research Program to conduct andcoordinate project research activities across severalacademic and industry partners. The applications ofinterest for this proposed mission are flood and disastermonitoring, and early warning deforestation detection fortropical forests. This paper describes some aspects of themission design, including the mission objectives and thebrief satellite design. It presents the requirements andconsiderations regarding the choice of satellite orbits. Theorbit design is mainly driven by the SAR imagingperformance, the lifetime of the satellites, and coveragerequirements such as revisit time. The area of interest isthe Australian continent. In order to achieve a rapid revisittime a satellite constellation is proposed.

This paper introduces the concept of Global Navigation Satellite System (GNSS) receiver design based on the principles derived from the cognitive radio (CR) technology. The receiver so designed is referred to as “cognitive GNSS receiver (CGR)”. The ontology and its rationale for CGR are described by defining different layers of cognition in GNSS receivers. The architecture of the cognition/decision module is presented, and the incremental differences with respect to existing receiver design methodologies are described. Two “use cases” are studied with cost (such as resource utilisation and power consumption) per fix and the usual GNSS performance parameters (such as the Time-to-First-Fix (TTFF), the acquisition/tracking sensitivity and the solution accuracy) as metrics, and the challenges in realising a full-fledged CGR are identified. It is shown that the CGR has the potential to replace the existing GNSS receiver architectures, especially in the multi-frequency and multi-system context.

This paper proposes a new modulation for a Global NavigationSatellite System (GNSS) to efficiently utilize a givenbandwidth. This modulation, referred to as Time-MultiplexedMulti-Carrier (TMMC), divides the available bandwidth intoN sub-bands such that each sub-band resembles a QuadraturePhase Shift Keying (QPSK) modulation and at the same timeallows the receiver to exploit the benefits of a widebandsignal. The generation of the new signal and its propertiesare described and the performance of TMMC is compared tothe other existing modulation schemes. The benefits of usingTMMC modulation for wideband signals in terms of overcomingthe errors due to propagation channel impairments,continuous wave (CW) interference mitigation and receiverdesign complexity is discussed.

Wi-Fi positioning has found favour in environments which are traditionally challenging for GPS. The currently used method of Wi-Fi fingerprinting assumes that the devices used for training and locating perform identically. We have undertaken an experiment to determine how different devices behave in an empirical controlled test to identify the challenges and limitations which Wi-Fi fingerprinting positioning systems will face when deployed across many devices. We found that they performed significantly differently in respect to the mean reported signal strength — even those which came from the same vendor. We also found that multiple samples of the same device do not perform identically. Furthermore, it was found that certain devices were entirely unsuitable for positioning as they reported signal strength values uncorrelated with distance from the transmitter. Some other devices behaved in a way that made them poor candidates for use in fingerprinting. Temporal patterns were found in some wireless cards which suggest that filtering should be used. The tests also found that the use of 5GHz band signals had the potential to improve the accuracy of Wi-Fi location due to its higher stability compared to 2.4GHz. Ultimately however, the accuracy of Wi-Fi fingerprinting is limited due to many factors in the hardware and software design of Wi-Fi devices which affect the reported signal strength.

GPS is the popular positioning technology widely used formany applications. However, many GPS receivers havedifficulty tracking signals in harsh environments such asurban canyons or indoors. So-called “high sensitivity” GPS(HSGPS) receivers have been developed to address thisproblem, and nowadays many different models of HSGPSreceivers can be found in the market. For example, thelatest mobile phones typically have built-in HSGPSchipsets. In addition, many HSGPS receivers accept“assisted GPS” (A-GPS) messages to reduce the time-tofirst-fix (TTFF) and possibly increase the sensitivity evenfurther. However, the performance of these receivers interms of TTFF and accuracy does vary.This paper evaluates several HSGPS receivers: ubloxLEA-4P, Navman Jupiter 32, ublox EVK-5H and SiRFGSCI-5000. Several mobile phones, such as the Nokia N95and iPhone models were also tested. Several experimentswere conducted. One is a static test for a standalone GPSreceiver. Four A-GPS tests were also conducted using anOpen Source GNSS Reference Server to provide the AGPSassistance messages. The TTFF, positioning accuracyand the sensitivity to weak signals has been investigated. Akinematic test was also carried out. Several scenarios wereutilised in order to test all HSGPS devices.

Carrier phase positioning is a reliable approach that offersbetter accuracies than pseudorange-based positioning. Itrelies on carrier phase measurements that originate fromthe carrier tracking loop. The performance of this loopdictates the quality of the phase measurements andconsequently the quality of the final positioning solution.Carrier phase jitter, which is the metric of carrier loop’sperformance, needs to be reduced to improve carrierphase measurement quality. This paper first analyses thecarrier phase jitter and provides rationales for itsreduction. It then discusses four jitter reductiontechniques that could be adapted to improve the situationfor low as well as high Carrier-to-Noise- and Interfernce-Ratio (CNIR) signals. A performance comparison ispresented and the trade-offs involved in the selection ofeither of these schemes are discussed.

Global Navigation Satellite Systems (GNSS) are comprehensively used for navigation in vehicular environments. However, the limited accuracy of GNSS for civilian use makes it unsuitable for some safety applications such as collision avoidance. Cooperative positioning in vehicular networks is a relatively new concept for positioning enhancement in a group of vehicles capable of communicating with each other. In addition to data communication, estimation of the distance between the nodes of a vehicular network is one the most challenging issues in cooperative positioning. Radio ranging methods such as Received Signal Strength (RSS), Time of Arrival (TOA), and Time Difference of Arrival (TDOA) are the most common techniques which are referred to in the literature for distance estimation without considering the poor accuracy of these methods for positioning accuracy improvement purposes, especially in vehicular environments. In this article, two methods for positioning enhancement and distance estimation are proposed that do not rely on common radio ranging techniques. The independence from radio ranging is one of the main contributions of this work. The proposed techniques are solely based on communicating data among the vehicular network nodes through Dedicated Short Range Communication (DSRC). The proposed solutions are suitable for suburbs and open space areas such as highways with less multipath error and at least four common visible satellites. The key idea is elimination of common errors of pseudorange estimates among the nodes of the vehicular network in a cluster of vehicles or between vehicles and roadside units. This looks similar to Differential GPS (DGPS) but the approach is different. The other advantage of the proposed methods is the low minimum possible number of participating nodes required by the algorithms, which is useful for saving communications bandwidth. Some experiments were conducted to verify the performance of the proposed algorithms. Results

Wi-Fi fingerprinting is a technique which can providelocation in GPS-denied environments, relying exclusively on Wi-Fi signals. It first requires the construction of a database of“fingerprints”, i.e. signal strengths from different access points(APs) at different reference points in the desired coverage area.The location of the device is then obtained by measuring thesignal strengths at its location, and comparing it with thedifferent reference fingerprints in the database. The maindisadvantage of this technique is the labour required to build andmaintain the fingerprints database, which has to be rebuilt everytime a significant change in the wireless environment occurs,such as installation or removal of new APs, changes in the layoutof a building, etc. This paper investigates a new method to utiliseuser feedback as a way of monitoring changes in the wirelessenvironment. It is based on a system of “points” given to each APin the database. When an AP is switched off, the number ofpoints associated with that AP will gradually reduce as the usersgive feedback, until it is eventually deleted from the database. If anew AP is installed, the system will detect it and update thedatabase with new fingerprints. Our proposed system has twomain advantages. First it can be used as a tool to monitor thewireless environment in a given place, detecting faulty APs orunauthorised installation of new ones. Second, it regulates thesize of the database, unlike other systems where feedback is onlyused to insert new fingerprints in the database.

This paper reviews computer vision and image analysis studies aiming at automated diagnosis or screening of malaria infection in microscope images of thin blood film smears. Existing works interpret the diagnosis problem differently or propose partial solutions to the problem. A critique of these works is furnished. In addition, a general pattern recognition framework to perform diagnosis, which includes image acquisition, pre-processing, segmentation, and pattern classification components, is described. The open problems are addressed and a perspective of the future work for realization of automated microscopy diagnosis of malaria is provided. © 2009 Tek et al; licensee BioMed Central Ltd.

Locata is a Pseudolite-based Positioning System (PPS) operating in thelicence-free 2.4GHz Industrial Scientific and Medical (ISM) frequencyband. Unlike its predecessors, Locata utilises time-diversity methods toovercome the near-far problem. Therefore Locata is able to operate overlarger regions than previous PPSs. Since the School of Surveying & SpatialInformation Systems (SSIS) at the University of New South Wales (UNSW)has considerable experience in designing GNSS receivers, the integration ofPPS signal processing within its own GNSS receiver (known as “Namuru”)is currently being investigated. Research into Locata’s signal structure isaimed at gaining insight and detailed technical knowledge to supportalternate receiver designs for processing terrestrial PPS-type signals.In this investigation, several important signal variables were identified viacoaxially connecting the Locata transmitter to a Radio Frequency (RF)down-converter, high speed digitiser and signal recorder. Using spectralanalysis methods, and having apriori knowledge of the signal’s operatingfrequency range (i.e. the ISM band), the centre frequency of the signal wasfound. It was assumed that the signal has CDMA-type characteristics. Thiswas further verified by fine tuning the centre frequency, and sampling thedown-converted signal at very high frequency. Exploiting its autocorrelationfunction, the code sequence and code period was also deciphered. Othersignal parameters (e.g. code chipping rate, code sequence generator, andTime Hopping sequence) were then progressively discovered using varioussignal processing/diagnostic methods.

Carrier tracking in GNSS receivers suffers in environments whereplatform dynamics, received noise and interference are expectedsimultaneously. Similar is the case of a Locata receiver which operateson the same basic principles as GNSS receivers. A reduction in trackingloop bandwidth may offer noise rejection, but at the same time it makestracking more vulnerable to oscillator and platform dynamics. Thispaper aims to stabilise Locata receiver tracking in the presence ofreceived noise and interference in a dynamic environment. It firstcompares two existing solutions: Adaptive Loop Aiding and the use ofKalman filters for noise reduction. It then proposes a Kalman filterbased loop aiding scheme for further reduction in noise without makingtracking more vulnerable to signal dynamics and loss of lock. It isshown that the proposed scheme offers reductions of 93% and 85% inerror for static and dynamic platform cases respectively, as compared toadaptive loop aiding without a Kalman filter.

GNSS is undoubtedly the most popular and widelyused 3D positioning technology today, providing24/7 position, velocity and timing (PVT), withaccuracies ranging from the 10 metre-level (usingstandard pseudorange single point positioning) tothe centimetre-level (using differential carrierphasedbased positioning techniques). Despite thisversatility, GNSS cannot satisfy the positioningrequirements for all applications in engineering andmining, surveying, machine guidance/control,structural monitoring and indoor positioning.Locata’s positioning technology solution has beenproposed as an alternative to GNSS in ‘difficult’GNSS environments. A network of ground-basedtransceivers (LocataLites) transmit positioningsignals. These transceivers form a positioningnetwork (LocataNet) that can operate incombination with GNSS, or entirely independent ofGNSS. One special property of the LocataNet is thatit is time-synchronous, allowing single pointpositioning with potentially cm-level accuracy usingcarrier phase measurements. The LocataLitestransmit their own proprietary signal structure in the2.4GHz ISM (licence-free) band. This allows forconsiderable flexibility in system design due tothere being complete control over both the signaltransmitters and the user receiver.

Locata’s positioning technology was designed to be used as analternative to GNSS in classically-difficult GNSS signalenvironments. A network of time-synchronized terrestrial transceivers(LocataLites) forms a positioning network (LocataNet) that canoperate entirely independent of GNSS. Operating in the 2.4GHz ISMlicence-free band, the Pseudolite Positioning System (PPS) is immuneto the near-far problem due to the usage of TH/DS-CDMA signal.Conversely, the use of such signals results in the degradation of codetracking performance in comparison to an equivalent DS-CDMAsystem. The relative performance degradation is proven viatheoretical derivation and simulation to be directly related to the dutyfactor of the TH/DS-CDMA signal. The transient behavior of thesignal is also observed and compared to the conventional DS-CDMAsignal. This type of signal provides an efficient way to track multipletransmitter using only one tracking loop.

The requirement that signals must be continuously repeated in the time domain for the Fast Fourier Transform(FFT)-aided correlation to function results in considerable correlation loss when it is used on the Time Hopping / Direct Sequence – Code Division Multiple Access (TH/DS-CDMA) type signals. A proposed correlation technique utilising the Digital Passive Matched Filter (DPMF) based technique eliminates correlation losses due to TH/DS-CDMA’s non-timerepetitive property. However, direct implementation of DPMF is computationally expensive. A FFT-based overlap-add filtering technique is shown to overcome the shortcomings of the primitive FFT-based correlation technique. Also, an acquisition method for the time-hopping domain is presented, adapted from the concept of exhaustive search. The method is modified to take into account undetected ‘CDMA bursts’ in the code phase and frequency search process. As the exhaustive search requires signal acquisition to be performed continuously in time as new samples arrive, a large computational load is required. In the time-hopping domain search, a simplification to the DPMF-based acquisition is made in order to reduce the computational load by gradually reducing the Doppler frequency uncertainty range for each successful acquisition in the code phase and frequency search domains. Experimental results show that the peak-to-subpeak ratio was sustained at high values despite various delays being introduced. Successful acquisition of the signal collected via an over-the-air transmission demonstrates the viability of the algorithms presented. The paper comprises five sections. It begins with an introduction to the general concepts relevant to Pseudolite Positioning Systems, followed with an introduction to the TH/DS-CDMA signal. The third section describes the proposed acquisition model and compares it with an existing method. The last two sections describe the Time Hopping frame Starting Index (THSI) search methods and the experime

Dedicated Short Range Communication (DSRC) technology protocols form a platform for vehicle to vehicle communications. This communication platform will enable Vehicular Adhoc NETworks (VANTEs) through which many Intelligent Transport Systems applications including cooperative positioning of vehicles become possible. Cooperative positioning integrates the on board GPS information of vehicles in one-hop neighbourhood and the measurements of inter-vehicle distances (dissimilarities) that are measured by means independent from GPS. The performance of cooperative positioning can be characterized by Cramar Rao Lower Bound (CRLB) analysis. However, the communication constraints, resulting from the adhoc nature of communication in vehicular networks and packet collisions, affect the calculation of the CRLB; since the number of active one-hop neighbours that each vehicle detects, depending on the network density, can effectively be lower than the real number of one-hop neighbours. Simulating the packet delivery failure rate for a cooperative positioning communication protocol under various network conditions, the CRLB is calculated. It is shown that CRLB increases, on average, up to one meter for dense traffic conditions.

Operation of GNSS receivers in noise- and interferencedominated environments results in degraded solution accuracy and precision. Locata, working on similar principles to the Global Positioning System (GPS) and using single point carrier phase positioning, can suffer from similar issues. This paper considers a variety of schemes to address these problems. It is established, using simulation results that, for single point positioning, the widely accepted Carrier-to-Noise and Interference Ratio (CNIR) based carrier phase measurement weighting scheme can degrade the solution quality rather than improve it. It is also established that the tracking loop’s bandwidth in addition to CNIR must be considered when generating correct weights for pseudorange measurements. Using a theoretical analysis of carrier phase measurements, a hybrid scheme is suggested for solution quality improvement. It is shown that the proposed scheme, suggesting the use of an adaptive bandwidth tracking loop architecture and total phase jitter based carrier phase measurement weighting, can offer excellent improvement in performance. Implementation results are presented which show that solution accuracy and precision improvements of up to 48% and 37% respectively can be achieved using the proposed scheme.

Due to their structure, Galileo E5 signals offer anumber of ways to synchronise the signal and todemodulate the data. In this paper the authorsdescribe the architectures required, and discuss thepros and cons of several of these methods, fortracking the E5 signal. It is shown that the trade-offsin tracking individual components of the E5 signalcan be converted to advantages thereby improvingthe tracking jitter performance in low signal strengthenvironments.

Reliable and continuous navigation in GPS-challenged environments is only possible with integrated systems that include self-contained sensors, which facilitate independent navigation during GPS outages. Traditionally, an inertial navigation system (INS) has been integrated with GPS to allow bridging during GPS gaps. The recently developed RF-based navigation and positioning system “Locata” offers an attractive augmentation alternative in situations where GPS satellite geometry is poor or the signal availability is limited. In cooperation with Locata Corporation, a Canberra-based company, School of Surveying and Spatial Information Systems (at the University of New South Wales - UNSW), and the Satellite Positioning and Inertial Navigation (SPIN) Laboratory (of The Ohio State University - OSU), have assembled a working prototype of a hybrid system based on GPS, inertial navigation and Locata receiver technology to provide seamless and reliable navigation to support vehicle guidance and control for mining, construction, mobile and GIS mapping, and industrial applications. For experimental purposes, a dual IMU system, based on the navigation grade H764G and a tactical grade CMIGITS2, were used. In addition, a Locata receiver and a dual-frequency GNSS receiver, the Leica System 1200, were used on a test vehicle at the Locata’s Numerella Test Facility, near Canberra, Australia. This test site features areas of both open sky as well as moderate to dense foliage. The test was repeated by mounting the devices on an autonomous electric car, operated on the UNSW campus. The GPS and Locata data were processed separately (for testing the internal consistency) as well in a hybrid solution, resulting in few centimetre-level accuracy for each coordinate component, depending primarily on GPS availability and the geometry between the test vehicle and the LocataLites, as well as the level of multipath.

Classically difficult positioning environments have always called for some augmentation technology to assist the Global Positioning System (GPS). "Locata" offers augmentation, and even replacement, to GPS in such environments. However, like any other system relying on wireless technology, a Locata positioning network faces issues in the presence of RF interference (RFI). This problem magnifies due the fact that Locata operates in the licence-free 2.4GHz ISM band. WiFi devices operating in this band have been identified as the most likely potential interferer, due partially to their use of the whole ISM band. This paper evaluates the performance of Locata in the presence of WiFi interference. A comparison of Version 2 and Version 3 devices is presented. Evidently very significant advances and improvements have been made in Version 3 for rejecting RF interference (RFI). Test results presented in this paper give an insight into this situation. Also, Locata characteristics have been identified which can be exploited to mitigate RFI issues.

In GNSS, longer integrations are required to obtain better signal-to-noise ratio during the signal synchronization process. However the presence of secondary codes on the top of primary codes puts a constraint on the coherent integration duration for pilot channels in a similar way to the effect of data bits in data-carrying channels. In this paper we explore the problem of coherent integration over periods longer than one primary code length and the acquisition of secondary code chip position. We propose an acquisition engine architecture which can handle both these problems together.

In this paper the authors analyze the effect of signal precorrelationfiltering in the ¿BOC-Gated-PRN¿ (¿BOCGPRN¿)discriminator technique, recently proposed foruse within Global Navigation Satellite System receiversto handle the new signal modulation scheme). Theproposed discriminator is introduced to eliminate thetracking ambiguity for Delay Locked Loops andstrengthen multipath resistance for precise GNSSapplications. In practice, a pre-correlation filter withinsufficient bandwidth can, in general, increase the errordue to multipath and noise. However, it is preferred thatthe bandwidth of the front end filter is kept as narrow aspossible for other limitation. Hence focusing on thetracking performance, measured in terms of multipatherror and discriminator gain optimization of the DLLtracking performance with the BOC-GPRN discriminatoris investigated by adjusting the parameters of theproposed discriminator and the pre-correlation filter(e.g. the double-sided bandwidth and transitionbandwidth). The relationship among those parameters isdiscussed.

This paper describes the design, analysis and testing of two methods that can be used to bridge GPS outages during an agricultural row cropping operation when using an integrated INS and code-based GPS system. The use of integrated systems in agricultural operations has become of increasing importance in recent years as farming operators are looking at combining different technologies to increase efficiency and to reduce the environmental `footprint` of farming operations. Integrated GPS and INS systems are used to provide good long term stability through the GPS system, with higher data rates and reliability from the INS system. However these systems can still suffer from degradation during GPS blockages and increasing the availability of a position solution is one of the key challenges to improving the use of integrated systems in agricultural applications. The `virtualite` concept is a new method that involves the transformation of INS measurements into simulated GPS signals via the creation of virtual satellites (`virtualites`) that can be processed alongside real GPS measurements. In this paper two methods to bridge situations where operating tractors experience low GPS visibility by using virtualite measurements with the available GPS satellites were examined. The first method used virtualite measurements processed alongside real GPS measurements within a single receiver. The second method transformed the INS output into virtualite measurements and then constructed double-differenced code measurements for processing with double-differenced measurements formed from the visible GPS satellites. This method was used in order to obviate the need to simulate the receiver clock bias in the virtualite measurement simulation process. The effect on the position accuracy of placing the imaginary virtual satellites in different orbital positions was also examined. The two methods were compared in a real world test.

An algorithm to estimate reflection coefficient propertiesof materials based on code multipath errors is developedand tested in two urban environments. The algorithmextends an existing model that integrates 3D structuremodels, electromagnetic ray-tracing algorithms, antennapattern measurements, and receiver tracking loop modelsto simulate code multipath errors. Instead of using theFresnel equations to compute reflection coefficients, weutilize a simplified, fixed reflection coefficient modelwith no incident/reflection angle dependence. In previousmodel validation work these coefficients were adjustedmanually to fit to experimental data. Herein, a minimumleast-squares (LS) filter is used to improve upon initialreflection coefficient estimates by comparingexperimental and simulated multipath errors. Themodeled environments are the University of Colorado(CU) Engineering Center rooftop and the campus of thePresented at the Institute of Navigation 63rd Annual Meeting 2007, April 23-25, Cambridge, MA 2University of New South Wales (UNSW). For both,simulations that mimic open-air experiments are run toprovide information on multipath ray paths, geometricdelays, interaction types, and the receiving antennaresponse. The LS filter then adjusts the reflection andphase coefficients for materials that produce reflections inthe model. Short segments of experimental data withdistinct multipath signatures are used to update reflectioncoefficients for the concrete walls of the CU rooftop andconcrete sidewalks at UNSW, with estimated values of0.42 and 0.48, respectively. In addition, a hill coveredwith foliage is estimated to have a reflection coefficient of0.1.