Research On CDMA Systems Combined With MIMO Technology And CC Spreading

With the rapid development of mobile communication and the emerging of new wireless services, high data rate transmission is required to achieve with the limited spectral resource. CDMA systems based on orthogonal complementary code (CC) spreading (CC-CDMA) and multiple input multiple output (MIMO) technology have recently been proposed as two important means to achieve higher spectral efficiency. CC possesses ideal auto-correlation and cross-correlation properties. As spreading codes, it can effectively suppress multipath interference (MI) and multiple access interference (MAI) in current CDMA systems and thus greatly improve system performances. Employing multiple antennas at transmitter and receiver, MIMO technology has enormous potential to increase system capacity and thus improve spectral efficiency.The definitions of complementary code, complete complementary code and orthogonal complementary code are introduced. Correlation property and code set of CC is presented. After CC-CDMA systems are briefly illustrated, CC-CDMA systems with Offset-Stack spreading and high order modulation are analyzed. In the precondition of achieving the same capacity with equal wireless resource, the BER performances of CC-CDMA and DS-CDMA systems are compared. Both numerical and simulation results reveal that the performance of CC-CDMA is much better, especially at high Eb/N0.Combined with MIMO technology, two Offset-Stack CC-CDMA systems are proposed. From the scheme of space-time block code (STBC) and the structure of current STBC-CDMA systems, the design conception of STBC and the principle of achieving transmitter diversity are analyzed and an STBC CC-CDMA system is presented. Using Offset-Stack spreading, STBC and CC-CDMA systems can be integrated to obtain both transmitter diversity and multipath diversity to combat fading channels. Then MIMO-CDMA system with VBLAST structure is introduced. Based on it, a MIMO CC-CDMA systems are proposed. With the perfect correlation property of CC, the system performance can be greatly improved. Therefore, high order modulations become applicable to increase system capacity.A novel MIMO CC-CDMA system are proposed in the final part. The system utilizes a novel transmitter structure, which combines CC spreading and spatial delay multiplexing technique. Therefore, at the receiver only simple correlation operation is needed to resist interference caused by multipath propagation effect, and maximum-ratio-combination (MRC) can be employed to further resist channel fading. The proposed system provides higher BER performance and lower hardware complexity. Mathematical expressions and theoretical analysis are presented. Simulation results validate the perfect anti-interference properties of the proposed system.