A SPREAD-SPECTRUM COMMUNICATION-SYSTEM WITHOUT A REFERENCE SIGNAL FORA FREQUENCY-SELECTIVE FADING CHANNEL

In a spread spectrum communication system (SS), RAKE reception is effe ctive as a measure against frequency-selective fading. Channel impulse response should be known for RAKE reception. In a conventional system where a reference signal is added to a transmission signal to obtain an impulse response, a decrease in transmission efficiency occurs unde r fast fading. This paper proposes a scheme that does not use the refe rence signal by allocating different codes to information signals. In addition, a channel-estimation scheme that alleviates effects of undes ired autocorrelation values or cross-correlation values of spreading c odes is proposed. This scheme subtracts cross-correlation values or ex cess autocorrelation values from a matched filter (MF) in measuring a channel impulse response and eliminates responses lower than a given t hreshold. Computer simulations under two-path fading were performed. T he error characteristics were improved with the proposed channel-estim ation scheme. It is shown that the proposed scheme is better than the scheme using a reference signal.