Proceedings of the International Conference on Pattern Recognition, Informatics and Medical Engineering, March 21-23, 2012 978-1-4673-1039-0/12/$31.00 ©2012 IEEE Wavelet-Based Multiple Access Technique for Mobile Communications D.Parthiban, A. Jenifer Philomina, N. R. Raajan, B.Monisha, M.V. Priya, S. Suganya Department of Electronics and Communication Engineering School of Electrical and Electronics Engineering SASTRA University Thanjavur. Tamilnadu India 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. Keywords- Wavelet, STCDMA, SCDMA, Kasami, AWGN channel. I. INTRODUCTION In communication systems, mostly channel-access method is based on multiplexing. In channel-access method several streams of data share the same channel. FDMA which uses different frequency bands based on FDM and it uses guard- band to reduce the channel interference, but the spectrum utilization decreases. TDMA with different time-slots are based on TDM also uses guard band to mitigate the interference. These systems must be synchronized in order to reduce the interference. The use of guard band reduces the spectral efficiency. In data communication, many transmitters transmit data simultaneously in single channel. This concept is called multiple accesses. CDMA employs multiple users to be multiplexed over a same channel. Time division multiple access (TDMA) divides access by time, while frequency- division multiple access (FDMA) divides it by frequency. CDMA is a form of spread-spectrum signaling, because the modulated signal has higher bandwidth than the transmitted signal. CDMA uses different codes to modulate the signal, which decides the performance of the system. The performance is decided by the amount of separation between the signals of the original user and some other user. The separation is achieved by correlating the signal with the original signal. If the signal is same as the original signal then the correlation will be high and if it is not same, the correlation will be zero and it is called cross correlation. If the correlation is nearer to zero it is termed as auto-correlation. This type of correlation is used to decrease the multi-path interference. [1]. CDMA is classified as synchronous and asynchronous channels. In DS-CDMA, the users are allowed to transmit synchronously or asynchronously through the same channel, i.e., the signals of the users overlap in both time and frequency. The receiver receives a noisy version of the total aggregate transmitted waveforms and demodulates all (as in the case of the satellite channel) or a subset (as in multipoint to multipoint topologies) of the transmitted signals. In DS- CDMA, each user is assigned a fixed distinct PN sequence to modulate and spread its information signal, and then the spread signal is up-converted by a carrier to the desired frequency band. Then, the information signals transmitted asynchronously by each user can be demodulated by correlating the received signal with each of the signature waveforms, which are designed to exhibit relatively small cross correlations among themselves in order to minimize multiple access interference. If the decision is made directly based on the correlated outputs, the multiple access interference is neglected, i.e., the conventional single-user detector is employed. However, the conventional single-user detector is optimum in the absence of interfering users when the channel is corrupted by AWGN. Unlike the conventional single-user detector, multiuser detectors account for the multiple access interference existing at the outputs of the