An Improved Structure of STS-CDMA System

Under the environments of multiuser and multipath, the performance of space-time spreading (STS) CDMA systems will decline. To solve the problem, this paper develops an improved structure of STS-CDMA system with complementary matching filters and Hamming orthogonal interleavers. In this improved STS-CDMA system, base station assigns two orthogonal codes and two Hamming orthogonal interleavers for each mobile user. The data flow transmitted to one mobile user is interleaved by two hamming orthogonal interlevers and then spread by two orthogonal codes respectively. The spread data flows are sent to two transmit antennas at base station, while the mobile user despreads and deinterleaves the data flow by two matching filters and two deinterleavers respectively. Since the received data streams of the mobile user are orthogonal each other in space and time, the system performances (BER and SINR) can be improved remarkably. The paper analyzes the performance of STS-CDMA systems theoretically and experimentally under such conditions of multiuser and multipath. The simulation results show that the STS-CDMA systems can be of better performance than the conventional CDMA systems based on single transmit antenna at a base station