A method is provided of evaluating the frame error probability (FER) of a selected communications link in a telecommunications network. The link is that between a MIMO transmitter comprising one of a base station or mobile user terminal, and MIMO receiver comprising the other of the base station or mobile user terminal. The method comprises determining values of instantaneous channel capacity of a MIMO channel of a mobile user terminal at multiple time instants over a predetermined time, processing the values to determining a level of channel capacity which any of the instantaneous channel capacity values has a predetermined probability of being less than, and looking up said level in predetermined calibration data of FER versus the channel capacity level so as to provide an FER value.