Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005)

Cross correlations caused by the limited dynamic range of the GPS Gold codes represent a significant problem in the observation of weak GPS signals. This is of particular concern in applications such as assisted GPS for E911 and in the use of GPS for remote sensing where the presence of a single strong GPS signal can make observation of other weaker signals difficult. A number of different techniques have been developed to deal with the ‘near-far’ problem ranging from cancellation (subtraction) methods through to subspace-projection techniques. This paper provides a brief review of the cross correlation problem followed by a description of a new a sub-optimal approach to dealing with the ‘near-far’ problem. The new technique is similar in approach to the subspace projection techniques already described in the literature, but is realizable in hardware or software, thereby making the method applicable for real receivers. Simulations showing the performance of the method under various scenarios are given and the advantages and limitations of the technique are discussed

Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006)

Many spread spectrum systems that employ Direct Sequence/Code Division Multiple Access (DS/CDMA) techniques suffer from cross correlation or ‘Near-Far’ problems if the spreading codes have a relatively short length, as is the case for CDMA cellular communications and C/A code GPS receivers. One class of methods available for cross correlation mitigation (CCM) includes Subspace Projection, although such methods have typically not been employed due to computational complexity. This paper describes a sub-optimal subspace projection approach to CCM that uses constraints to construct despreading codes that are exactly orthogonal to signals being received by the GPS receiver. Application of the technique using a software GPS correlator written in C and run within a Matlab environment are described and results presented based on realistic datasets acquired using hardware GPS simulators. The effectiveness of the method compared to other more traditional CCM methods is also discussed

Proceedings of the 2011 International Technical Meeting of The Institute of Navigation January 24 - 26, 2011

Japan.s first Quasi-Zenith Satellite (QZS-1) "Michibiki" has began transmissions in the last quarter of 2010. This has provided an opportunity across South-East Asia and Australia to investigate live QZSS signals. QZS-1 transmits 6 signals across 4 frequency bands, most of which are compatible with current and modernised GPS signal structures. Michibiki is the first satellite to transmit GPS-like L1C/A, L1C, L2C, L5 and the SBAS signals from a single transmitter. This paper reports on architecture options for a hardware correlator and acquisition schemes that support the acquisition and processing of QZSS signals. Focusing on the QZS-L1C signal in particular, design ideas and trade-offs are investigated along with practical implementation issues on a Field Programmable Gate Array (FPGA) development platform

Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting

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 signals output by the master and the adjacent second slave was measured. The mean and standard deviation of the time difference were on the order of a few nanoseconds and a couple of hundred picoseconds, respectively. The frequency difference, as derived from the time difference, had a standard deviation of less than 0.1 ppb. The purpose of the external and internal synchronization experiments was to demonstrate the absolute and relative time transfer performance of Locata, respectively.Publications Article Search Browse Publications Journal Proceedings Newsletter Other Publications Download Subscriptions Buy Publication

IGNSS Society 2013 Symposium Proceedings

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

An autonomous satellite time synchronization system using remotely disciplined VC-OCXOs

© 2015 by the authors; licensee MDPI, Basel, Switzerland. An autonomous remote clock control system is proposed to provide time synchronization and frequency syntonization for satellite to satellite or ground to satellite time transfer, with the system comprising on-board voltage controlled oven controlled crystal oscillators (VC-OCXOs) that are disciplined to a remote master atomic clock or oscillator. The synchronization loop aims to provide autonomous operation over extended periods, be widely applicable to a variety of scenarios and robust. A new architecture comprising the use of frequency division duplex (FDD), synchronous time division (STDD) duplex and code division multiple access (CDMA) with a centralized topology is employed. This new design utilizes dual one-way ranging methods to precisely measure the clock error, adopts least square (LS) methods to predict the clock error and employs a third-order phase lock loop (PLL) to generate the voltage control signal. A general functional model for this system is proposed and the error sources and delays that affect the time synchronization are discussed. Related algorithms for estimating and correcting these errors are also proposed. The performance of the proposed system is simulated and guidance for selecting the clock is provided