A user equipment, UE, apparatus, the apparatus comprising: processing circuitry and memory, the processing circuitry being adapted to: decode downlink control information signaling that identifies a shortened transmission time interval, xTTI, length configuration for a time division duplexing, TDD, component carrier, CC, the xTTI length configuration comprising a length in time or a length in orthogonal frequency division multiplexing, OFDM, symbols, wherein a legacy LTE transmission time interval is partitioned into a plurality of xTTIs; decode a physical downlink control channel, PDCCH, to identify scheduling timing and hybrid automatic repeat request, HARQ, timing of a physical downlink shared channel, PDSCH, and physical uplink shared channel, PUSCH, on the TDD CC based on the identified xTTI length configuration; and characterized by the processing circuitry further to: determine a self-contained HARQ-ACK window in xTTI based on the identified scheduling timing of the PDSCH and PUSCH, the self-contained window comprising a downlink transmission burst period, a guard period, GP, and an uplink transmission period; and transmit HARQ acknowledgement, HARQ-ACK, bits for one or more PDSCH transmissions in the self-contained HARQ-ACK window to an evolved NodeB, eNB, based at least on the HARQ timing and based on the identified xTTI length configuration; wherein HARQ-ACK bits for the one or more PDSCH transmissions in the self-contained HARQ-ACK window are transmitted within a subset of the GP in the self-contained HARQ-ACK window. decode downlink control information signaling that identifies a shortened transmission time interval, xTTI, length configuration for a time division duplexing, TDD, component carrier, CC, the xTTI length configuration comprising a length in time or a length in orthogonal frequency division multiplexing, OFDM, symbols, wherein a legacy LTE transmission time interval is partitioned into a plurality of xTTIs; decode a physical downlink control channel, PDCCH, to identify scheduling timing and hybrid automatic repeat request, HARQ, timing of a physical downlink shared channel, PDSCH, and physical uplink shared channel, PUSCH, on the TDD CC based on the identified xTTI length configuration; and characterized by the processing circuitry further to: determine a self-contained HARQ-ACK window in xTTI based on the identified scheduling timing of the PDSCH and PUSCH, the self-contained window comprising a downlink transmission burst period, a guard period, GP, and an uplink transmission period; and transmit HARQ acknowledgement, HARQ-ACK, bits for one or more PDSCH transmissions in the self-contained HARQ-ACK window to an evolved NodeB, eNB, based at least on the HARQ timing and based on the identified xTTI length configuration; wherein HARQ-ACK bits for the one or more PDSCH transmissions in the self-contained HARQ-ACK window are transmitted within a subset of the GP in the self-contained HARQ-ACK window. determine a self-contained HARQ-ACK window in xTTI based on the identified scheduling timing of the PDSCH and PUSCH, the self-contained window comprising a downlink transmission burst period, a guard period, GP, and an uplink transmission period; and transmit HARQ acknowledgement, HARQ-ACK, bits for one or more PDSCH transmissions in the self-contained HARQ-ACK window to an evolved NodeB, eNB, based at least on the HARQ timing and based on the identified xTTI length configuration; wherein HARQ-ACK bits for the one or more PDSCH transmissions in the self-contained HARQ-ACK window are transmitted within a subset of the GP in the self-contained HARQ-ACK window.