SBIR-STTR Award

The global positioning system (gps) satellites transmit information on two frequencies in the l-band: l(1) at 1575.42 mhz and l(2) at 1227.6 mhz. These two transmissions are phase-coherent since they are derived from a common oscillator. Both of these frequencies are modulatedby a p-code consisting of pseudo-radom one's and zero's. The transmission rate is 10.23 mhz and the code on both the transmissions is coherent. The importance of gpc satellites for ionospheric research is in the dual coherently transmitted frequencies designed for the navigation user to correct for ionospheric errors. Since the p-code has limitedaccessibility, it is proposed to analyze and optimize two simpler receiver designs which do not require the knowledge of the p-code. One system is more accurate but requires somewhat complex circuitry to determine the differential group delay. The second system proposed is muchsimpler and cheaper to implement but of adequate accuracy to determine the differential group delay to calibrate the differential carrier phase for absolute value of electron content. In both systems, the differential carrier phase and signal amplitudes are also measured. The parameters provide necessary information on ionospheric irregularities and disturbances

A receiver design has been developed during Phase I for Code-Free Dual-Frequency (CFDF) GPS receiver to measure 1) the differential carrier phase, 2) differential group delay and 3) amplitudes on the L(1) and L(2) GPS frequencies. This design does not require access to the P-code and enables the determination of the differential group delay hence the absolute value of the Total Electron Content (TEC). During Phase II the receiver design will be hardware implemented and trade-offs in antenna gain, processing gain and integration time will be optimized. A prototype receiver will be built and tested to demonstrate the realization of the design objectives. Necessary tests and calibration will be made on the receiver and it will be used with the antenna design chosen to receive GPS signals and the receiver performance will be demonstrated to achieve the design goals. Two additional receivers will be fabricated so that the three receivers are deployed in actual geographical environments, namely, in equatorial, middle and high latitudes. The field test data would be evaluated to determine the receiver performance. Based on this experience, adjustment will be made on the receivers to realize the original design objectives. SAM