In the first embodiment, UE1 sends the second feedback information to the BS through a newly defined MAC CE (e.g. which may be referred to as PC5 feedback MAC CE). The PDU (Protocol Data Unit) containing the PC5 feedback MAC CE also contains the LCD (Logical Channel ID) for indicating the MAC CE type. A MAC PDU may contain feedback information for one or more remote UEs. In one example, a PC5 feedback MAC CE can contain a list of feedback messages for multiple remote UEs. In another example, a PC5 feedback MAC CE contains only one remote UE feedback information, and a MAC PDU can contain a list of PC5 feedback MAC CEs corresponding to one or more remote UEs. The BS may schedule resources, adjust the transmission parameters, or perform other adjustments as listed in FIG. 5, for at least one of UE1, UE2 and UE3, based on the second feedback information.

In a second embodiment, UE1 receives first feedback information from UE2 through sidelink; and UE1 transmits second (processed) feedback information to the BS. The first feedback information includes at least one of the following: process numbers, HARQ ACK/NACK information; the second (processed) feedback information includes: statistics of ACK feedback ratio received by the relay UE over a period of time from the remote UE, and the corresponding remote UE IDs. The ACK feedback ratio is a ratio between a total number of ACK feedback received from the remote UE and a total number of sidelink transmissions to the remote UE during the period of time.