This Book mainly concentrates on a direct sequence spread spectrum (DS/SS). A MATLAB - Simulink tool is used for designing DS/SS system to obtain system parameter and to test the influence of signals on the system. Two systems were designed, with data rate (100kb/s) and pseudo noise (PN) code with a code rate (4MHz),127 bits maximal linear code.Then, the performance evaluation was tested by simulating the design to get the received data which compared with transmitted data, and also to study the effect of additive white Gaussian noise (AWGN) and jamming to the DS/SS signal and calculate the bit error rate (BER).