Current long term evolution (LTE)/LTE-A frequency division duplex (FDD) networks may be unable to support half-duplex (HD)-FDD wireless transmit/receive unit (WTRU) if the HD-FDD WTRU simply follows regular FDD WTRUs. The LTE/LTE-A may support both FDD and time division duplex (TDD) together. TDD operation may be similar to half-duplex FDD, such that a WTRU may perform either uplink transmission or downlink reception at one time. Because a TDD uplink (UL)/downlink (DL) subframe configuration is reused for HD-FDD WTRU in FDD network and all TDD-specific functions are supported, the scheduling flexibility may still be restricted, as few subframe configurations were defined in TDD. Similar to FD-FDD, HD-FDD may use at least two separate frequency bands for UL and DL transmissions, but UL and DL transmissions may not be supported simultaneously. In other words, HD-FDD may suffer from spectral inefficiency due to incomplete frequency band usage. Meanwhile, HD-FDD operation may be scheduled in the same manner as a TDD system, and may operate asymmetric DL-UL or UL-DL data requirements in a manner similar to TDD networks. Furthermore, in either DL or UL transmission, there may be a need for corresponding acknowledgement/non-acknowledgement (A/N) feedback.
In FD-FDD, in order to minimize the control signaling overhead, UL hybrid automatic repeat request (HARQ) may be synchronized so that UL retransmission occurs 8 subframes after the previous transmission of the same HARQ process, which may not give the UL scheduling flexibility to the WTRU. In HD-FDD, DL and UL transmission may be scheduled by eNB to avoid the conflict transmission. However, for some situations, there may be no available or scheduled source for a scheduling request (SR) or for when the WTRU has a SR to be transmitted but may be preempted by DL data reception.