Direct sequence spread spectrum communication simulation system

The purpose of this work is to develop a fast, dynamic, and menu driven direct sequence spread spectrum communication simulation system for the Digital Equipment Corporation's VAX VMS line of computers. This software breaks the system down into two sections, the transmitter and the receiver. Each of the blocks that comprise the system is user definable in order to program the desired conditions. The input data and spreading data located within the transmitter are generated by a maximal length sequence generator, up to the tenth order. Encoding of the data is achieved by using an (n,k) cyclic code. A level shifter and pulse shaper may be implemented prior to modulation to improve the system signal-to-noise ratio. The filter can be used after modulation to emulate channel bandwidth limitations. The input to the receiver is the sum of the transmitted wave, with White Gaussian noise, and hostile jamming capability. A coherent oscillator is available at the receiver to obtain the demodulated signal; this signal is then compared against a preset threshold level. The output from the comparator is then unspread by the correlator using an acquisition sequence to lock-in a duplicate of the spreading sequence generator. Once unspread, the signal is then decoded with a syndrome calculator routine that detects and/or corrects single bit errors.