Indian Journal of Science and Technology

Abstract

Objectives: The protection of signal against jamming is accomplished using Spread Spectrum (SS) techniques. In this research paper, noise rejecting property of the matched filter and Binary Phase Shift Keying (BPSK) modulation is used in Direct Sequence Spread Spectrum (DSSS) system for secure communication. Methods/Statistical Analysis: Here, DSSS system has been developed and simulated using C-programming language on windows platform. In order to perform the simulation, different parameters are initialized and message bits are generated by random function. With the help of binary message signal and PN sequence, a SS signal is generated which is modulated using BPSK modulation technique at the transmitter side. In the channel, noise/jamming signal is added to the transmitted signal. Then the received signal is demodulated using coherent BPSK receiver (i.e., correlation receiver) and matched filtering is followed by despreading the demodulated signal at the receiver side. Finally, the received binary message bits are detected by threshold detector and various parameters such as input SNR, output SNR, probability of error are calculated. Findings: It has been found that matched filter is a linear filter which has a noise rejection property (means jamming signals can be treated just like other random noise) and hence provides signal security. This particular property of matched filter is used in DSSS communication. As far as matched filter is concerned, it cannot remove the total effect of interference but still the waveforms can be detected in the presence of noise/jamming signal. So, a matched filter receiver is supposed to be an ideal receiver for a signal which is corrupted by AWGN/jamming signal. Here, an average probability of symbol error decreases because it maximizes the output signal to noise ratio. These parameters are supposed to be the most important factors that determine the efficiency of performance of the system. Applications: DSSS systems using matched filter are strong contender for mobile and personnel communications, due to their very large user handling capacity. They also have better transmission quality and capability by incorporating wireless services such as data, short transaction messages, and multimedia etc.

Keywords: Signal Security,Matched filter, DSSS, PN Sequence, SNR, Probability of Error.