1. A method performed by a source base station in a wireless communication system, the method comprising:receiving, from a wireless device, user equipment (UE) assistance information for semi-persistent scheduling (SPS), the UE assistance information comprising a time offset of a packet for a transmission by the wireless device;
determining an adjusted time offset of a packet for a transmission by the wireless device based on the time offset reported by the wireless device and a timing difference between the source base station and a target base station; and
transmitting a message comprising the adjusted time offset to the target base station in a handover procedure,
wherein the UE assistance information for SPS is received from the wireless device upon a change of the time offset.