| A direct sequence spread spectrum multiple access system has been discussed, built and tested. A spread spectrum multiple access system is not only useful in military communications but also has varied commercial applications. The attractiveness of making such systems portable is the motivation for the integrated circuit implementations of a few parts carried out here. Essentially, two transmitters were built, one with voice capability. Gold codes were used for the spreading sequence and PN acquisition was accomplished using a serial search technique. PN tracking was achieved with a tau-dither loop. A squaring loop and a differential encoding scheme (for carrier phase ambiguity) was employed in the demodulation process, which was followed by conversion to a voice output when desired. The system was found to perform quite well under both single and multiple access conditions. As a demonstration of the feasibility of implementing the system on chips, a few small blocks were put on ICs (using CMOS technology); these performed as expected and clearly demonstrated both the feasibility and attractiveness of a VLSI implementation of the system. |
