Analyzing And Simulating The Performance Of The Wavelet Packet Multicarrier Modulation In CDMA System

For the multi-rate and wideband signal transmission in mobile environment, now many people keep close watch on the Multi-carrier CDMA which bases on FFT operators, which is effective in suppressing interference caused by multi-path fading and using spectrum. But it has a disadvantage. When the modulation and demodulation are implanted by means of IFFT and FFT operators, the input data bits are actually truncated by a rectangular window and the envelope of the spectrum takes the form of sin(w)/w which attenuates slowly. Multi-path fading or synchronization error will cause severe degradation due to inter-subchannel-interference, inter symbol interference and multiple access interference. In fact, people use additional time and band to suppress the ISI and ICI. Adding the time of a frame will decrease data rate. Only in the linear channel, adding the band of signal will increase the performance of the system. Really the condition of linear channel always isn't tenable. So we must search for other means to settle the two problem. Wavelet packet functions have many attractive properties such as time-frequency localization, self-orthogonality in the same wavelet packet space and inter-orthogonality in the different wavelet packet space , the multi-carrier system has the capability of suppressing multi-access interference. When we take for the wavelet packet functions as the sub-carrier. In the AWGN channel, we analyze and simulate the wavelet packet modulation multi-carrier CDMA, and compare with the BPSK modulation .In the end, we validate the capability of suppressing multi-access interference.