Real-Time Dual Frequency Software Receiver

Software receivers provide flexibility, reconfigurability and high fidelity among many other advantages. There has been a variety of software based receiver architectures for GPS and other navigational systems. In general, the signals, after downconversion to a suitable frequency, are digitized and processed entirely in the digital domain. While C/A-code bandwidth is sufficiently low so that the processing can be performed in real-time, the other GPS codes such as P and emerging new military code will still have to wait for more powerful signal processors to achieve entirely software real-time processing. Still, one can utilize reprogrammable hardware devices to perform the most computationally intensive operation - the correlation of GPS signals. This paper describes the structure, operation and performance of a real-time dual frequency software GPS receiver. The receiver consists of the hardware front-end which downconverts and digitizes the signals from L1 and L2 frequencies, followed by the FPGA which performs signal correlation. The correlator output is fed to the PC which then continues signal processing entirely using software. The dual frequency processing is performed using semicodeless technique which provides independent carrier and code tracking of the L2 signal. Software processing of the signals has been extended to include advanced signal processing techniques such as beamforming, interference rejection, multipath mitigation etc. Addition of any novel type of processing using software approach is greatly simplified. This reduces development time and effort by an order of magnitude and at the same time allows the benefits of software receiver while achieving the real-time performance.