Development and Field Testing of a DSP-Based Dual-Frequency Software GPS Receiver
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A real-time software GPS receiver for the L1 C/A and L2 C codes has been implemented on a Digital Signal Processor (DSP) and tested in both scintillating and nonscintillating environments. This receiver is being developed as a low-cost space weather instrument with improved tracking robustness in comparison to a traditional semi-codeless dual-frequency receiver and with flexibility in its choices of signal tracking algorithms and data outputs. The receiver is capable of continuous background signal acquisition and utilizes the L1 C/A code to assist in acquisition of the L2 C signal. Efficient on-the-fly generation of oversampled PRN code replicas for the L2 CM and CL codes, which are required for real-time software radio signal processing, has been implemented to ensure a manageable requirement for memory. Bit-wise parallel correlation techniques have been implemented to reduce the number of operations needed for correlation. The receiver currently tracks both the L2 CL and CM codes for the purpose of calculating TEC. Results are presented based on data generated by a signal simulator, on real data taken in Ithaca, NY (42.44 N, 76.48W), and on real data taken during ionospheric scintillation in Natal, Brazil (5.8S, 35.2W) in January 2009. Position and velocity solution accuracy is evaluated using both real and simulated data.