Digital DS-spread spectrum receiver with reduced computational cost

The design, develop and measurements of a digital receiver for an adaptive array that works with spread spectrum signals is addressed. Although the same structure might be used for any direct sequence (DS) spread spectrum system the prototype operates with GPS signals. An array of 6 elements equispaced over a circumference of radius ^λ /₂ is used. The received signals at each antenna element, with a carrier frequency of 1.575 GHz, is amplified, down converted in frequency and filtered to produce an IF signal centered at 4.3 MHz. Then a 2-bit analog to digital conversion is performed at a sampling rate of 5.71 MHz for each antenna. The bandwidth of the RF front-end is 2 MHz. At this point a microprocessor takes the digital signal, locks a Costas loop to the Doppler frequency and despread it with the appropriate code. The microprocessor combines the base-band processed signals from the six antennas to get an interference-free output. The digital process is described in detail. The overall goal of the DSP algorithms is to keep the computational cost as low as a low-cost midspeed microprocessor is able to accomplish it. Measurements and the simulation results are also provided