1. A method comprising:transmitting during a first subframe, by a base station, an uplink grant triggered in response to transmitting a trigger during a validation duration, the uplink grant indicating resource blocks;
transmitting, during the validation duration, the trigger indicating an uplink subframe for reception via the resource blocks; and
receiving, during the uplink subframe and via the resource blocks, a power headroom value determined for a reference subframe, wherein the reference subframe:is after the first subframe; and
is before the uplink subframe.