| Interference has been the core issue of the wireless communication technology. As the key technologies of the third generation (3G) wireless system, the multiple antennas technique and spreading spectrum technique are influenced by kinds of interference problems. The interference cancellation technology is studied worldwide, which has theoretical and practical significance.In the multiple antennas system, the existing serial interference cancellation (SIC) technology has high complexity and long process delay problems, and it is not conducive to the actual realization, meanwhile, the parallel interference cancellation (PIC) has poor performance. The complexity of channel coding joint interference cancellation is higher than the previous techniques. Therefore, low-complexity high-performance interference suppression technology becomes the new needs. Existing spread spectrum communication interference suppression technology is main for narrowband interference suppression, therefore a low-complexity high-performance suppression technology is also need for wideband interference.In this paper, for multi-antenna system and spread spectrum communication system, the idea of the iteration is used in the multi-antenna and the same frequency interference suppression. For each interference situation, different iterative method is used for interference suppression, which improves BER performance.First, the power spreading is used in asynchronous V-BLAST, an iterative parallel interference cancellation algorithm based on power spreading transform is proposed. Meanwhile, the performance and complexity of proposed algorithm is analyzed as well. Compared with linear method and ordered successive interference cancellation (OSIC) method, the performance improvement is verified by analysis and simulation, and the complexity of proposed algorithm is as O(N3) as the linear method. Under the condition of8transmit antennas and4receive antennas at the BER of10-3, about7dB gain is offered by proposed algorithm compared with traditional ordered successive interference cancellation algorithm.Second, the power spreading is used in asynchronous MIMO-OFDM, an iterative parallel interference cancellation algorithm based on single subcarrier is proposed. This method based on power spreading relives the error propagation effectively. Compared with conventional iterative parallel interference cancellation and time domain iterative interference cancellation method, the proposed algorithm improves the performance remarkably, which has linear complexity relation with linear detection methods. The performance improvement is verified by simulation, when there are4transmitters2receivers and the BER is10-3,SNR is improved about4.5dB compared with the traditional iterative parallel interference cancellation algorithm.Finally, consider the CDMA system under the broadband interference, an optimized iterative interference cancellation algorithm is proposed by using the bandwidth and power information of interference, which cognized by the receiver. The order of iteration is optimized by comparing the cognized SIR and critical point. The performance and complexity improvement of proposed algorithm is verified by simulation, when the spread gain is63, SNR and SIR are-5dB and-12dB respectively, the BER is improved from4×10-3to1×10-4.The research in this thesis explores the problem of interference cancellation techniques for MIMO and CDMA systems, which extends the existing researches and has some theoretical and practical values. The research results can be applied for the3G and next generation mobile communication systems. |
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