A 12 channel real-time GPS L1 C/A-code software receiver has been implemented on a Desktop with 1.84GHz Intel CPU. The software receiver has the capability to acquire new satellites coming in, keep tracking of satellites in view and give a user solution accuracy of 30 meters. This study also explores a real-time correlator for the GLONASS L1 signals. This software receiver is going to be used for scientific research and education. This work is a part of the ongoing effort to develop a low-cost, flexible, and capable GNSS receiver for use as a scientific instrument and for GNSS receiver technology development. The software receiver developed here makes use of a reconfigurable RF front end called the Universal Software Radio Peripheral (USRP) with a maximum real sampling frequency of 8MHz of complex samples. The USRP uses interchangeable daughter boards to down-convert and digitize RF signals in the range of DC to 2.9GHz, where each daughterboard covers an overlapping subset of this range. This RF front end was chosen for its flexibility and ease of use. The output of the RF front end is 8-bit complex I/Q samples output via a USB cable. The software receiver processing of the RF front-end outputs is accomplished by using bit-wise parallelism, as described in References [1] and [2]. In order to process the incoming RF data in this manner, the 8-bit complex I/Q samples are quantized to two bits. This is performed in the software receiver prior to signal correlation. In-phase and quadrature accumulations are computed using bit-wise parallel techniques, and these accumulations are used to drive code tracking delay-lock loops (DLLs) and carrier tracking phase-lock loops(PLLs). The computation of accumulations and the implementation of DLLs and PLLs for the GNSS ranging signals are detailed in the thesis. The software receiver is developed by C++. It consists of two parts: the software receiver core program and a simple interface. The current software receiver runs under Ubuntu Linux systems, but it is convenient to implement on other Linux systems. The software prerequisites for the software receiver are GNUradio and QT4.0. GNUradio is an open source program which provides the driver for the USRP board. The current version used by the software receiver is GNUradio-3.1.3. The user interface program is developed by using the classes provided by QT4.0. The hardware of the whole system consists of computer with intel 1.84 GHz CPU and 2GHz RAM, GPS and GLONASS antenna, USRP, and analogue signal generator. One problem with the USRP is that its on-board oscillator is not particularly stable in terms of frequency and phase. One solution to this problem is to use a high-quality external oscillator. An Agilent N5181A MXG Analog Signal Generator configured to output a 64MHz signal has been used as an external input clock to the USRP. This oscillator has a stated frequency error of 1 ppm/yr, has decent short-term frequency stability, and has a reasonably low phase noise at 64MHz. The outputs of the USRP board are 8 bits complex data with 4MHz sampling frequency with an intermediate frequency of zero. The input data are re-quantized and pack into 32-bit of integers. The total CPU usage of the software receiver is about 30 ~ 40% of the 1.84GHz CPU. The software receiver is started with a FFT based acquisition. The acquisition results are then used to initialize the receiver. The background search of satellites is accomplished by a serial search of PRN code replicas. The novelty of the the software receiver developed in this study is as follows: first, a reconfigurable RF front end is used which makes the software receiver extendable.Second, The software is developed with C++ in the general Linux system; This will make the software receiver easy to maintain and update. Third, the current software receiver also explores the process of GLONASS L1 signals with bit-wise parallel correlation. / Master of Science

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Off-line software based signal analysis can be a valuable tool for detailed examination of transmitter signal characteristics. This paper describes the Advanced Range Telemetry (ARTM) Constant Envelope (CE) offset quadrature phase shift keying (OQPSK) modulation analyzer. It was developed expressly for evaluation of FQPSK-B^(1), FQPSK-JR and shaped OQPSK transmitter signals. Rationale for its creation, underlying assumptions, computation methods, and examples of its data products are presented.

No description available.

Ionospheric scintillations can cause significant amplitude and/or phase fluctuations of GNSS signals. This work presents analysis results of scintillation effects on the new GPS L5 signal based on data collected using a real-time scintillation monitoring and data collection system at HAARP, Alaska. The data collection setup includes a custom narrow band front end that collects GPS L1, L2 IF samples and two reconfigurable USRP2 based RF front ends to collect wideband GPS L5 and GLONASS L1 and L2 signals. The results confirm that scintillation has a stronger impact on GPS L2 and L5 signals than on the L1 signal. Our preliminary results also show that carrier phase and amplitude scintillations on each signal are highly correlated. The amplitude and carrier phase scintillation are also correlated among the three signals. In this study, a multi-constellation multi-band GNSS software receiver has been developed based on USRP2, a general purpose radio platform. The C++ class-based software receiver were developed to process the IF data for GPS L1, L2C, and L5 and GLONASS L1 and L2 signals collected by the USRP2 front end. The front end performance is evaluated against the outputs of a high end custom front end driven by the same local oscillator and two commercial receivers, all using the same real signal sources. These results demonstrate that the USRP2 is a suitable front end for applications, such as ionosphere scintillation studies. Another major contribution of this work is the implementation of a Vector tracking loop (VTL) for robust carrier tracking. The VTL is developed based on the extended Kalman filter (EKF) with adaptive covariance matrices. Both scalar tracking loop (STL) and VTL are implemented. Once an error in the scalar loop is detected, the results from the VTL are used to assist the STL. The performance of the VTL is compared with the traditional STL with three different data sets: raw GPS RF data with short signal outages, RF data with strong scintillation impacts collected during the last solar maximum, and high dynamic data with long interval signal outages from a GPS simulator. The results confirm the performance improvement of the VTL over scintillation impacts and show that the VTL can maintain signal lock during long intervals of signal outage if the satellite ephemerides are available and the pseudorange estimation is within one code chip accuracy. The dynamic performance improvement of the VTL is verified as well. The results show the potential of robust tracking based on VTL during scintillation and interference. / Ph. D.

No description available.

Global Positioning System (GPS) is a satellite-based navigation system that has been used widely both in civilian and military for positioning, navigation, timing and other position related applications. The hardware-based GPS receivers provide the least user flexibility. Thus, it is necessary to have Software-based GPS receivers for easy and quick implementation, simulation and analysis of algorithms. Software-based GPS receiver processes the GPS signal at the radio frequency or intermediate frequency depending on the hardware configuration of the receiver. In this development of the acquisition and tracking processes of the software receiver, the front-end device that converts the radio frequency signal from the antenna to an intermediate frequency is the Mitel 2021 GPS receiver board. An analog-to-digital (A/D) converter then digitizes the output signal from the RF front-end. The data is then processed using MATLAB programs to achieve acquisition and tracking of the GPS signals. The software GPS receiver can perform acquisition and tracking using different parameters and threshold values. This flexibility of operation allows weaker signals to be tracked and processed. In this software receiver design, the focus is on the acquisition and tracking of L1 band C/A code GPS signals used by most civilian applications. The purpose of this thesis is to develop the acquisition and tracking algorithms to extract the navigation data bits from the raw GPS signals. The navigation data bits provide all the necessary information to compute the pseudorange between the receiver and the visible satellites and determine the receiver location. Both MATLAB simulated GPS data and realistic GPS signals from a GSS 6560 simulator are used to verify the performance of the acquisition and tracking programs. The acquisition program is capable of locating the beginning of the C/A code and the carrier frequency to within the desired accuracy. From the output of the acquisition program, the tracking program can decode the navigation data bits. The tracking algorithm implemented is based on the block adjustment of synchronizing signal (BASS) method. / Master of Science