研究目的
To analyze the behavior of successive interference cancellation (SIC) scheme and its ability to mitigate multiple access interference in optical PPM-CDMA systems, and to compare performance using different optical codes.
研究成果
The SIC scheme effectively mitigates multiple access interference in optical PPM-CDMA systems, significantly improving bit error rate performance and increasing user capacity. Systems using modified quadratic congruence codes with SIC show better performance than those using modified prime codes, contrary to conventional receivers. Higher M-ary PPM levels further enhance performance. The scheme is a low-complexity suboptimal multiuser detector suitable for optical networks.
研究不足
The analysis is theoretical and simulation-based, lacking experimental validation with real-world equipment. It assumes ideal synchronous conditions and specific code properties, which may not hold in practical implementations. The study focuses on specific code families (MPC and MQC) and may not generalize to other codes or varying network conditions.
1：Experimental Design and Method Selection:
The study uses a theoretical analysis approach for an incoherent, direct sequence Optical PPM-CDMA system with N users. Successive interference cancellation (SIC) scheme is employed to suppress multiple access interference (MAI) by subtracting the strongest user signals sequentially. Mathematical models and probability of bit error calculations are derived based on Q functions and signal correlations.
2：Sample Selection and Data Sources:
Simulations are conducted with parameters such as prime number p=11 for codes, M-ary PPM values (e.g., 16, 64), effective power of -11.3 dBm, channel length of 50 km, and fiber transmission losses of 0.25 dB/km. Modified prime codes (MPC) and modified quadratic congruence codes (MQC) are used as signature sequences for comparison.
3：3 dBm, channel length of 50 km, and fiber transmission losses of 25 dB/km. Modified prime codes (MPC) and modified quadratic congruence codes (MQC) are used as signature sequences for comparison.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: No specific equipment or materials are mentioned; the analysis is theoretical and simulation-based.
4：Experimental Procedures and Operational Workflow:
The process involves encoding data using PPM modulation, spreading with signature codes, transmission through an optical channel, reception with photodetection, application of SIC by ordering users by signal strength, regenerating and subtracting signals iteratively, and decoding to obtain data. Bit error rate (BER) is calculated and compared for different scenarios.
5：Data Analysis Methods:
Data analysis includes numerical simulations to compute BER performances. Equations for probability of symbol error and bit error are derived and evaluated using Q functions, with comparisons made between systems with and without SIC and between different code types.
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