Direct P(Y) Code Acquisition Using An Electro- Optic Correlator

Modern military GPS receivers adopt a digital architecture to facilitate direct P(Y) code signal processing using high speed VHDL electronics. NAVSYS has developed a buffered digital receiver architecture that optimizes the GPS direct acquisition process by operating in the frequency domain. The effectiveness of acquisition in the frequency domain is dictated by the speed of the Fourier Transform implementation. High speed DSPs can perform a 1024 point Fourier Transform in less than 128 microseconds. The Fourier Transform approach can be dramatically improved by using an electro-optic correlator. Digital Spatial Light Modulators (SLM) are under development that can perform 1000 x 1000 2-dimensional correlations at kHz rates, which is equivalent to over 10 parallel digital correlations. This paper describes an electo-optic correlator integrated with a GPS receiver, which was developed and tested to demonstrate the massive parallelism possible using modern electro-optic correlation techniques. This design performs the Fourier Transforms optically. A combination of simulation and live satellite test data was used to demonstrate the search and acquisition of the GPS P(Y) code signals. This paper includes test results showing the predicted performance of the direct P(Y) code acquisition using an optical correlator.