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

In a spread spectrum communication system (SS), RAKE reception is effective 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 under fast fading. This paper proposes a scheme that does not use the reference signal by allocating different codes to information signals. In addition, a channel‐estimation scheme that alleviates effects of undesired autocorrelation values or cross‐correlation values of spreading codes is proposed. This scheme subtracts cross‐correlation values or excess autocorrelation values from a matched filter (MF) in measuring a channel impulse response and eliminates responses lower than a given threshold. Computer simulations under two‐path fading were performed. the error characteristics were improved with the proposed channel‐estimation scheme. It is shown that the proposed scheme is better than the scheme using a reference signal.