Teachings presented herein provide reduced computational complexity and/or memory requirements for a mobile terminal to determine the power backoff required for a multi-carrier uplink signal. In particular, the mobile terminal determines whether its power headroom falls below a pre-defined power headroom threshold, indicating that it is headroom limited. If so, it quantizes power allocated to each carrier of the multi-carrier uplink signal according to a pre-defined quantization policy. In doing so, the mobile terminal thereby reduces the possible configurations that may be selected for the multi-carrier uplink signal. Thus, in one embodiment, the mobile terminal stores the required backoff in a look-up table for only the configurations that may be selected when the mobile terminal is headroom limited. This relieves the memory requirements of the mobile terminal as compared to storing the required backoff for all possible configurations of the multi-carrier uplink signal.