Triple multiplexing spread spectrum receiver

Abstract

A GPS car navigation system permits single satellite navigation by representing the x and y unknowns with on-track and cross track vectors and estimating the z and t unknowns. An estimate of the y unknown, representing the maximum width of the track or roadway, is thereby combined with altitude and clock hold estimates to derive GPS position information along the predicted track. Turns along the track are detected when they actually occur and are compared with the predicted turns so that the time and position at the actual turn can be used to update the then current GPS derived position of the vehicle. Updating position information with actual turn data improves the accuracy of GPS navigation especially when using single satellite navigation. Multiple, parallel correlations of data in a wide capture window extending, at 1/2 chip width intervals or less from the predicted prompt correlation delay of a previously tracked satellite, permits seamless tracking and rapid reacquisition at speeds sufficient to permit position information updates during momentary view available of satellites in intersections. The satellite tracking and data processing is implemented in an ASIC which is configured to use a minimum number of gates. The received data is processed in 11 bit samples, for a total of 186 time segments per 1 msec code period, which are each doppler shifted and multiplexed into 12 channels. The code correlations are performed 22 times per channel by shifting the 11 bit locally generated code by one bit each correlation. The chip rate of the incoming data is 2f.sub.0 and the correlations are performed at 48f.sub.0 providing a time magnification advantage of 24.