A communication device comprises a storage device for storing instructions of receiving a semi-persistent scheduling (SPS) uplink (UL) grant in a transmission time interval (TTI) from a base station (BS), wherein the SPS UL grant indicates a UL frequency resource periodically allocated to the communication device; storing the SPS UL grant as a configured UL grant; initializing the configured UL grant to start in an earliest TTI after the first TTI and applying the configured UL grant to a plurality of TTIs after the earliest TTI; transmitting at least one first repetition of a UL transmission by using a hybrid automatic repeat request (HARQ) process according to the configured UL grant; starting a UL HARQ round trip time (RTT) timer for the HARQ process in response to the UL transmission; and starting a drx-ULRetransmissionTimer for the HARQ process, when the UL HARQ RTT timer expires.