| Summary: | 碩士 === 國立中正大學 === 通訊工程研究所 === 90 === In recent years, wireless communication systems are growing up rapidly. Researches are devoted to increase the system capacity. The spread spectrum technique based on code division multiple access (CDMA) has played a significant role in cellular and personal communications. The CDMA has been found to be attractive because of its characteristics, such as potential capacity increase over other competing multiple-access methods, anti-multipath capabilities, soft capacity and soft hand-off. The Direct Sequence-CDMA (DS-CDMA) is the most popular one among all of the CDMA techniques. The DS-CDMA transmitter multiplies each user’s signal with a distinct code waveform. In a conventional DS-CDMA system, a particular user’s signal is detected by correlating the entire received signal with the user’s code waveform.
The multiple access interference (MAI) is a factor that limits the capacity and performance of DS-CDMA systems. The MAI is known as the interference between direct-sequence users [1]. Although, the MAI caused by any user is generally small, however, as the number of interferers or the power increases, it becomes substantial.
In Verdú’s research work, an optimal multiuser detector was proposed and analyzed. This is known as the maximum likelihood sequence detector. Unfortunately, the complexity for the detector is too high to be implemented. Therefore, most of the researchers focus on finding the solutions of realizable sub-optimal multiuser detector [2] [3]. Among all of the sub-optimal detector researches, the successive interference cancellation (SIC) and the parallel interference cancellation (PIC) appear to be the most attractive.
The Fuzzy-based Partial Parallel Interference Cancellation (FBPPIC) was proposed by Wen and Huang in 2000 [7]. The major concept is based on the principle of Fuzzy logic to infer adequate cancellation weights for each interferer, and then the inferred weights are further used to perform the PIC scheme. This multiuser detector obtains excellent performance as a near-optimum multiuser detector.
In this paper, the DSP-based architecture is used to implement the FBPPIC for DS-CDMA systems. For further consumer’s application, promising results indeed have been observed by simulated image experiments to confirm the effectiveness of this implementation.
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