The near-far effect occurs when radio signals are received at different distances from the receiver. This effect is known, among other things, from the CDMA method, Code Division Multiple Access (CDMA).
The near-far problem can be described as follows: If a CDMA receiver receives two transmit signals with different field strengths, then the stronger signal will outshine the weaker one and the receiver will not be able to detect the weaker one. If two transmitters located at different distances from the receiver transmit at the same power level, then the signal-to- noise ratio( SNR) of the more distant transmitter will degrade, depending on the distance, to the point where it cannot be selected by the receiver.
The near-far problem is relevant for the reception of mobile stations because they can be located anywhere in a radio cell, and in the case of large radio cells there may well be greater distances to the access point( AP).