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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.

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.

© 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.

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

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.

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.

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.