One or more computer-readable media comprising instructions that, when executed by one or more processors of a mobile device, cause the mobile device to: establish communications with one or more base stations through a primary serving cell, PCell, and a secondary serving, SCell, the PCell being established with a first time-division duplexing, TDD, configuration, the SCell being established with a second TDD configuration; receive downlink data through the SCell and the PCell; select a reference TDD configuration based on the first and second TDD configurations; and transmit acknowledgement information associated with the downlink data of the SCell according to a hybrid automatic repeat request, HARQ, timing of the reference TDD configuration wherein acknowledgement information includes HARQ-acknowledgement, HARQ-ACK, signals, wherein only HARQ-ACK signals associated with the downlink data of the SCell are transmitted according to the HARQ timing of the reference TDD configuration, wherein HARQ-ACK signals associated with downlink data of the PCell are transmitted only according to the HARQ timing of the first TDD configuration; wherein the instructions are further to: select TDD downlink/uplink, DL/UL, configuration 4 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 1 and the second TDD configuration is TDD DL/UL configuration 3; select TDD DL/UL configuration 5 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 2 and the second TDD configuration is TDD DL/UL configuration 3; and select TDD DL/UL configuration 5 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 2 and the second TDD configuration is TDD DL/UL configuration 4. establish communications with one or more base stations through a primary serving cell, PCell, and a secondary serving, SCell, the PCell being established with a first time-division duplexing, TDD, configuration, the SCell being established with a second TDD configuration; receive downlink data through the SCell and the PCell; select a reference TDD configuration based on the first and second TDD configurations; and transmit acknowledgement information associated with the downlink data of the SCell according to a hybrid automatic repeat request, HARQ, timing of the reference TDD configuration wherein acknowledgement information includes HARQ-acknowledgement, HARQ-ACK, signals, wherein only HARQ-ACK signals associated with the downlink data of the SCell are transmitted according to the HARQ timing of the reference TDD configuration, wherein HARQ-ACK signals associated with downlink data of the PCell are transmitted only according to the HARQ timing of the first TDD configuration; wherein the instructions are further to: select TDD downlink/uplink, DL/UL, configuration 4 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 1 and the second TDD configuration is TDD DL/UL configuration 3; select TDD DL/UL configuration 5 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 2 and the second TDD configuration is TDD DL/UL configuration 3; and select TDD DL/UL configuration 5 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 2 and the second TDD configuration is TDD DL/UL configuration 4. select TDD downlink/uplink, DL/UL, configuration 4 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 1 and the second TDD configuration is TDD DL/UL configuration 3; select TDD DL/UL configuration 5 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 2 and the second TDD configuration is TDD DL/UL configuration 3; and select TDD DL/UL configuration 5 as the reference TDD configuration, if the first TDD configuration is TDD DL/UL configuration 2 and the second TDD configuration is TDD DL/UL configuration 4.