In a communications system including a transmitter for transmitting signals over a transmission channel and a receiver for receiving the signals, the transmitter includes: a filter for filtering a modulated signal to modify amplitude and phase characteristics of the modulated signal; and a first processor for performing interleaving process and/or scrambling process for the filtered signal. On the other hand, the receiver includes: a second processor for performing deinterleaving process and/or descrambling process for a received signal; and an inverse filter for filtering a signal supplied from the second processor.