Method performed by a communication system comprising a serving base station, a first User Equipment, UE, and a second UE, the first and second UE's being comprised in a UE group comprising UEs having correlated mobility related parameters, the base station being associated with the UE group comprising UE's, the method comprising: - receiving, by the base station, from the first UE in the UE group, a mobility related parameter associated with the first UE, the first UE being associated with a first identifier identifying the UE group, the first identifier associated with the first UE comprises a group-ID part and an index indicating a group member number; - determining, by the base station, whether to initiate a mobility related procedure for the second UE in the UE group based on the received mobility related parameter, the second UE being associated with a second group identifier identifying the UE group, the second identifier associated with the second UE comprises a group-ID part and an index indicating a group member number; -initiating, by the base station, the mobility related procedure for the second UE when it is determined that the mobility related procedure is to be performed, wherein the mobility related procedure is initiated for a plurality of UEs in the UE group, said plurality comprising the second UE, and the initiating comprises sending, by the base station, a single mobility command to a plurality of UEs in the UE group, including the second UE, wherein the single mobility command comprises the second identifier; - receiving, by the first UE, the single mobility command comprising the second identifier, and determining whether the group-ID part of the first identifier corresponds to the group-ID part indicated in the second identifier; - determining, by the first UE, based on the first and second identifier, whether the first UE belongs to the UE group identified by the second identifier; and - responding, by the first UE, to the received command when it is determined that the first UE belongs to the UE group identified by the second identifier. - receiving, by the base station, from the first UE in the UE group, a mobility related parameter associated with the first UE, the first UE being associated with a first identifier identifying the UE group, the first identifier associated with the first UE comprises a group-ID part and an index indicating a group member number; - determining, by the base station, whether to initiate a mobility related procedure for the second UE in the UE group based on the received mobility related parameter, the second UE being associated with a second group identifier identifying the UE group, the second identifier associated with the second UE comprises a group-ID part and an index indicating a group member number; -initiating, by the base station, the mobility related procedure for the second UE when it is determined that the mobility related procedure is to be performed, wherein the mobility related procedure is initiated for a plurality of UEs in the UE group, said plurality comprising the second UE, and the initiating comprises sending, by the base station, a single mobility command to a plurality of UEs in the UE group, including the second UE, wherein the single mobility command comprises the second identifier; - receiving, by the first UE, the single mobility command comprising the second identifier, and determining whether the group-ID part of the first identifier corresponds to the group-ID part indicated in the second identifier; - determining, by the first UE, based on the first and second identifier, whether the first UE belongs to the UE group identified by the second identifier; and - responding, by the first UE, to the received command when it is determined that the first UE belongs to the UE group identified by the second identifier. - receiving, by the first UE, the single mobility command comprising the second identifier, and determining whether the group-ID part of the first identifier corresponds to the group-ID part indicated in the second identifier; - determining, by the first UE, based on the first and second identifier, whether the first UE belongs to the UE group identified by the second identifier; and - responding, by the first UE, to the received command when it is determined that the first UE belongs to the UE group identified by the second identifier.