Abstract: Space-Time Block Coding (STBC) is a promising spatial diversity technique for future wireless communications systems. The combination of STBC and Code Division Multiple Access (CDMA) technology has the potential to increase the users performance in wireless communication networks. Space Time Transmit Diversity (STTD) is the extension of Space-Time Block Coding (STBC) to code division multiple access (CDMA) systems. To date, most discussions of STTD either assumed flat fading or ignored the Inter-Symbol and Multi-Access Interference (ISI and MAI) induced by frequency selective fading. MAI and ISI can pass an unacceptable break down in STTD performance with conventional; interference is limited only by channel estimation. RAKE receiver is used in the CDMA system to gain the multipath diversity. In this study, we combine the new orthogonal polynomial based on STBC extended with CDMA 2000(STTD), so as to avoid ISI and MAI. Simulation results show that the increased accuracy of the channel estimation schemes significantly improves the Bit Error Rate (BER) performance.