Alternate waveforms for a low-cost civil GPS receiver
April 14, 1980
This report examines the technical feasibility of alternate waveforms to perform the GPS functions and to result in less complex receivers than is possible with the GPS C/A waveform. The approach taken to accomplish this objective is (a) to identify, after a quick broad overview, a few promising waveforms, (b) to complete the architectural synthesis of a GPS system based on the new waveforms, (c) to analyze the performance of these systems in providing ranging and communication capability and (d) to assess the impact on receiver hardware and software. One conclusion is that the class of pulsed waveform, when combined with emerging matched filter technology, permits the use of a greatly simplified receiver design. Although very specific, the design was intended as a vehicle for performance analysis only and many refinements and alternatives within the same class are possible. Other classes of waveforms such as tome ranging and chirped FM waveforms, although adequate, do not seem superior to the present PN encoded CW waveform for GPS. Finally, if the "alternate" waveform is simply the present C/A waveform but with substantially increased power level, it is shown that with the present designs the performance will be greatly increased or, alternatively, performance margin can be traded for a simplified receiver implementation.