A method is presented for enhancing the narrowband interference rejection capability of direct-sequence spread-spectrum systems employing an adaptive notch filter. The method, based on projection onto convex sets, restores that part of the spread-spectrum signal distorted by the filter. Simulation results are presented which show the output bit-error rate (BER) improvement gained by using the s...

This paper reports on the development of an authentication watermark for digital video that is based on the principles of direct sequence and time-hopping spread spectrum. The watermark is identifiable in the presence hostile and benign intensity attacks. In addition, the explicit timing structure of the proposed watermark indexes video frames in such a way that re-indexing attacks, such as fra...

Closed-form expressions for the performance of radio networks are generally not available. For spread spectrum networks, it is not even clear how to represent the underlying network, since the existence of links is heavily dependent on activity in other parts of the network. We have developed a set of computer-based modeling tools to help understand the performance and behavior of these network...

Frequency hopping spread spectrum and direct sequence spread spectrum are two main spread coding technologies. Frequency hopping sequences are needed in FH-CDMA systems. In this paper, a construction of optimal sets of frequency hopping sequences is presented via cyclotomy. The construction is based on the set-theoretic characterization of an optimal set of FH sequences. As a consequence, new o...

Direct sequence spread spectrum transmissions (DSSS) are now widely used for secure communications, as well as for multiple access. They have many interesting properties, including low probability of interception. Indeed, DS-SS transmitters use a periodical pseudo-random sequence to modulate the baseband signal before transmission. A receiver which does not know the sequence cannot demodulate t...

The paper aim was an investigation on use of chaotic sequence in DS-CDMA. The DS-CDMA systems offer physical layer security without the need for a significant increase in computation or power requirements. Nowadays, DSCDMA has been used widely. These systems suffers from multiple access interference because of other users transmitting in the cell, channel inter symbol interference and additive ...

Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping (FHSS) techniques are widely used to implement code-division multiple access (CDMA) in wireless communication systems. Both DSSS FHSS systems help reducing the effects of interference on transmitted information making it robust against channel impairments. uses a signal bandwidth that is much broader than bandwidth. Traditionally, wid...