| With the developments in mobile communications, to provide the high-rate and high-quality transmissions more effectively to meet requirements of people, it is essential to develop more efficient spread spectrum techniques, modulation schemes and signal processing technologies so as to improve the spectrum efficiency. Used as the spreading sequences in code-division multiple-access system, orthogonal complementary code (OCC) can eliminate the interference among multiple users and paths due to its auto-and cross-correlation properties and can improve the spectrum efficiency when combined with new modulation schemes. Meanwhile, the spectrum efficiency can be enhanced through multiple input multiple output (MIMO) technology which uses multiple transmit and receive antennas to take the full advantage of the spatial resources.Starting with the introduction to the correlation properties sequences, the thesis presents the definition of OCC and the discussions on multicarrier direct-spreading code division multiple access (MC-DS-CDMA) system based on OCC, as well as the analysis of offset-stacked modulation (OSM) scheme. Further, the structure of RAKE receiver and the OCC MC-OSM-CDMA system are provided and the performance evaluation of OCC MC-OSM-CDMA system is derived. Also, the circular shift OCC is proposed to enlarge the capability in OCC MC-OSM-CDMA system. Under the same channel conditions, the MC-OSM-CDMA system is compared with the DS-CDMA system via simulation. The simulation results indicate that the performance of MC-OSM-CDMA system is better than that of DS-CDMA system. And better performance of MC-OSM-CDMA system can be obtained with the increasing SNR. Moreover, simulating results obtained for different shift intervals and number of users show that no interference exists in the MC-OSM-CDMA system and those obtained for different number of paths show that the multipath diversity can be realized through RAKE receiver. The final simulation results obtained for the circular shift OCC show that the system with circular shift OCC can provide capability against multipath and multiuser interferences.Based on space time block code CDMA (STBC-CDMA) system, the structure of STBC MC-OSM-CDMA system is presented in the thesis. In STBC OCC MC-OSM-CDMA system, the circular shift OCC is used as spread spectrum, which can not only improve the system capacity but also suppress the multipath and multiuser interference. The structure of VBLAST (vertical Bell laboratories layered space time) and two encoding algorithms, ZF (Zero Forcing) and MMSE (Minimum Mean-Squared Error), is introduced in the thesis, on the basis of which, a solution for VBLAST MC-OSM-CDMA system is presented to use multiple antennas to obtain larger system capacity. A novel spatial time delay MIMO MC-DS-CDMA system with satisfactory performance is introduced, which deals with the multipath signals through RAKE receiver to obtain diversity. |
PDF Full Text Request