Wavelet-based multiple access technique for mobile communications

Abstract

Wavelet theory has emerged as a new mathematical tool that can be applied in many fields such as image processing, biomedical engineering, radar, physics, control systems and communication systems. The important area of application of wavelets in communication: multiple accesses. Among the multiple access applications one of the most notable work is wavelet packet-based multiple access communication. The two new multiple access systems are Scale-Time-Code Division Multiple Access (STCDMA) and Scale-Code Division Multiple Access (SCDMA). In a STCDMA system, Direct-Sequence (DS) Code-Division Multiple Access (CDMA) is used in each time slot to identify multiple users. If time division multiplexing is excluded in each scale, SCDMA, which is a multimedia system, is obtained. These systems are analyzed over a synchronous Additive White Gaussian Noise (AWGN) by using a conventional detector and a multiuser detector based on decorrelating detector for real and complex-valued PN sequences. These systems have better performance for complex-valued sequences compared to real-valued sequences. SCDMA can also be analyzed over an asynchronous AWGN by using a conventional detector for real-valued sequences. SCDMA is attractive compared to DS-CDMA, because it is capable of transmitting different rates of information messages. To be more specific, STCDMA is user-advantageous and SCDMA is information-advantageous. In STCDMA and SCDMA good PN sequences such as Kasami sequences are required because of the reuse capability while DS-CDMA has only limited number of them. Kasami sequences are optimal since the maximum cross correlation value achieves the Welch Lower Bound. The main purpose of using Kasami sequences is that, it decreases the multiple access interference. These PN sequences are very useful for multipath, jamming environments and synchronization purposes.