Performance Of LDPC-Coded IDMA System

In recent years, IDMA as the key technology in 4th mobile communication has been wildly studied. IDMA not only inherits many advantages from CDMA, especially diversity against fading, but also has some own advantages, such as a simple Chip by Chip iterative receiver structure, high spectral efficiency, and excellent performance of multi-user access. For making it closer to the multiple access channel (MAC) capacity limits, LDPC codes is applied to IDMA system, and LDPC-Coded IDMA system is presented in this paper.Though computer simulation, the performance of the designed system has been investigated and analyzed deeply. Further more, the optimal LDPC code rates of the designed system have been found and LDPC-Coded IDMA system is compared with IDMA system based on convolutional codes generally in different conditions. Simulation results indicate that LDPC-Coded IDMA system not only inherits many advantages from IDMA system, but also has its own predominance, such as closer to multiple access channel ( MAC ) capacity limits, obtains more coding gains, and supplies higher quality communication service. Furthermore, the middle LDPC code rates are the best choice for this system. Over AWGN channel, performance of the designed system with 16 users is about 2.6 dB away from the MAC capacity limits at bit error rate of 10-6, and 3.4 dB better than the system based on convolutional codes; the optimal LDPC code rates are between 0.4 and 0.5. In fast Rayleigh fading channel, even the coding length of the designed system is just 512 bits, it still has 3dB coding gains over the traditional coded system at bit error rate of 10-6. The results show that the designed system is very suitable for high-speed transmission operation and this work is of the far-reaching significance in future digital communication system.