A method of processing a signal in a wireless digital communications system, wherein a source of disturbance affects differently at least first and second portions of a received signal carrying user data and/or control data, the method comprising: identifying the second portion of the received signal, most affected by the source of disturbance; generating a first estimate of the disturbance (PI) for received samples in the first, less affected portion of the received signal; generating a second estimate of the disturbance (PI(SCH)) for received samples in the second portion of the received signal; and using the first and second disturbance estimates to generate reliability information for the data bits corresponding to the received signal samples, for use in a decoding process to estimate the transmitted data bits.