The Performance comparison of Minimum Mean Square Error-based Adaptive Multi-User Detection (MUD) of Direct Sequence-Code Division Multiple Access (DS-CDMA) signals is considered. DS-CDMA is a popular multiple-access technology for wireless communication. But its performance is limited by multiple-access interference (MAI) and multipath distortion. Adaptive techniques, such as least mean squares (LMS) algorithm is employed for detection of DS-CDMA signals which improves the performance of the CDMA system by reducing interference among users. In this paper the diversity scheme called maximum ratio combining (MRC) as preprocessor to the adaptive MMSE detector of DS-CDMA system in frequency-selective multipath channel is introduced and compare the complexities of adaptive techniques. The performance of the proposed detector for frequency-selective multipath channel is simulated. Simulations in frequency-selective multipath channels have proved its better performance compared with the conventional Match Filter detector, and it is performing nearly as well as single user case.

1. J. G. Proakis, Digital Communication, 4th Ed. , McGraw Hill, New York, 2001.
2. S. Moshavi, "Multi-User Detection for DS-CDMA Communication," IEEE Communication Magazine, Vol. 34, pp. 124-136, Oct. 1996.
3. A Duel-Hellen, J. Holtzman and Z. Zvonar, "Multiuser detection for CDMA systems", IEEE Personal commun. Mag. , pp46-58, Apr. 1995
4. G. Woodward and B. S. Vucetic, "Adaptive detection for DS_CDMA", Proceedings of the IEEE, Vol. 86, pp. 1413-1434, Jul. 1998.
5. M. Ghotbi & M. R. Soleymani, "MMSE-Based Adaptive Multiuser Detection of DS-CDMA Signals," CCECE/CCGEL IEEE, May 2005.
6. Wei Li, Hong-Chuan Yang and T. Aaron Gullver, "A Practical Rake Combining Scheme For Synchronous CDMA Systems", IEEE Communications Society / WCNC 2005.
7. Chetan Mahendra and Sadasivan Puthusserypady, "Multiuser Receiver for DS-CDMA Signals in Multipath Channels: in Enhanced Multisurface Method", IEEE Transactions on Neural Networks, Vol. 17, No. 6, November 2006.
8. Aditya Dua, Uday B. Desai,and Ranjan K. Mallik, "Minimum Probability of Error-Based Methods for Adaptive Multiuser Detection in Multipath DS-CDMA Channels", IEEE transaction on Wireless Communications, Vol. 3, No. 3, May 2004.
9. Khuram Waheed and Fathi M Salem, "Blind Information-Theoretic Multi-User Detection Algorithms for DS-CDMA and WCDMA Downlink Systems", IEEE transaction on Neural Networks, Vol. 16, No. 4, July 2005.
10. Pickholtz R. L. , Milstein L. B. , and Schilling D. L. , "Spread Spectrum for Mobile Communications," IEEE Transactions on Vehicular Technology, Vol. 40, No. 2, , pp. 313-322, May 1991.
11. Kamil Sh. Zigangirov, "Theory of Code Division Multiple Access Communication", IEEE Press, e-Book, April 2004.
12. M. K. Tsatsanis, ``Inverse filtering criterion for CDMA systems,'' IEEE Trans. on Signal Processing, vol. 45, no. 1, pp. 102-12, Jan. 1997.
13. Tan-Hsu Tan, Yung-Fa Huang, Chung-Weng Lin, and Ray-Hsiang Fu "Performance Improvement of Multiuser Detection Using a Genetic Algorithm in DS-CDMA UWB Systems over an Extreme NLOS Multipath Channel", IEEE International Conference on Systems, Man, and Cybernetics October 8-11, 2006, Taipei, Taiwan.
14. M. Z. Win and R. A. Scholtz, "Ultra-wide Bandwidth Time-hopping Spread Spectrum Impulse Radio for Wireless Multiple-access Communications," IEEE Transactions on Communications, vol. 48, no. 4, pp. 679-689, April 2000.
15. R. Lupas, S. Verdu, "Linear multiuser detectors for synchronous code-division multiple access channels," IEEE Trans. Information Theory, vol. 35, no. 1, pp. 123-136, Jan. 1989.
16. M. Shakhsi Dastgahian, H. Khoshbin, S. Shaerbaf, A. Seyedin, "DS-CDMA Blind Detection for Frequency-Selective Multipath Channels by Neural Networks", IEEE International Symposium on Telecommunications, pages 53-58, 2010.

Direct-sequence Code-division Multiple Access (ds-cdma) Multipath Channel Minimum Mean Square Error (mmse) Lms (least Mean Square) Algorithms