Real-time dual frequency software receiver

A software based, real time, navigational receiver is described. This provides high-accuracy and flexible operation using C/A, P and M codes. The receiver has improved dynamic performance and anti-jam capabilities. It allows incorporation of novel architectures such as those using Ultra Tight Coupling, RTK type processing, etc. New and future signals (such as Galileo) can be easily incorporated. The block processing architecture enables improved dynamic performance, anti-jam capability, faster acquisition, less susceptibility to multipath, robust performance, easy transition to GPS/INS integration, and RTK processing. The flexible, re-configurable, software based, real time receiver will allow test and measurement of a variety of receiver architectures. These in conjunction with the data recorder will allow both real-time and off-line test of new signals and performance of receivers under difficult conditions. 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.