A spread spectrum communication system without reference signal for frequency-selective fading channel

The RAKE receiver for spread spectrum communication is a countermeasure against frequency-selective fading. In order to operate the RAKE receiver, the impulse response of the fading channel must be sounded. For this purpose, some reference signal is transmitted together with the information signal in conventional systems. A method in which no reference signal is required is proposed. In this method, different codes are assigned corresponding to input binary data. Techniques are proposed which reduce the harmful effects of residual autocorrelation and cross-correlation of the spectrum-spreading code. In this method, a threshold value is used, and the residual response of autocorrelation and cross-correlation is subtracted from the matched filter output signal determining the channel impulse response. Computer simulation results under a two-path fading model are shown. Bit error rate performance of the RAKE receiver is improved with the proposed channel estimation method