To control allocation of a portion of a shared channel to use for control information, a base station determines an amount of resource elements of the shared channel to use for the control information in place of traffic data. The base station sends, to a mobile station, an indication relating to an offset parameter, where the indication is provided to allow the mobile station to compute a value for the offset parameter such that the mobile station can determine the amount of the resource elements of the shared channel to allocate for the control information.