Study On The Iterative Detection Of MC-CDMA Systems

Sensor networks have been used more and more widely. This paper investigates the iterative detection of Multi-Carrier Code-Division-Multi-Access (MC-CDMA) system with the aim to meet the demand of the high data rate and high system load in the CDMA wireless sensor network. This paper discusses four aspects of the iterative detection of the MC-CDMA system, including equalization, feedback, channel estimation and the density evolution analysis of the MC-CDMA system.In the uplink of the synchronized MC-CDMA system, four equalization approaches of the iterative detection have been studied, which are ORC(O rthogonality Restoring Combining), EGC(Equal Gain Combining), MRC(Maximum Ratio Combining), MMSEC(Minimum Mean Square Error Combining). The MMSEC method has the best performance among the four approaches but it demands complicated calculation. While MRC has the good performance and low calculation complexity at the same time, so MRC is the most appropriated equalization method to the practical systems.Different feedback methods have been discussed of the iterative detection. The improved feedback methods, such as soft feedback, partial hard feedback, hard feedback with threshold have the better performance than the directly hard feedback. The comparisons of bias, MSE and SIR performance of the PIC output of a posteriori information feed back and extrinsic information feedback also been studied. The extrinsic information feedback has the better bias performance, which is appropriated to the high load systems. The a posteriori information feed back has the better MSE performance, which is appropriated to the not very high load systems and the MMSE filtered systems.The time domain and the frequency domain channel estimation methods are compared in the paper. With the same received data, to estimating channel response inthe time domain needs fewer variables than estimating in frequency domain, so the time domain estimation has better performance. An EM based estimation approach is derived in the MC-CDMA system, which has lower calculation complexity with the same performance to the time domain LS estimation.Finally, an improved gauss-approximation density evolution method is presented to analyze the iterative detection performance of random channel response phase one path DS-CDMA system and the multi paths MC-CDMA system. The performance improvement of the iterative detection to the multi user detection with no decoding is also provided with the density evolution method.Through the discussion of the paper, we can see the iterative detection of the MC-CDMA can meet the high data rate and high system load demands of the CDMA wireless sensor network.