A method for adaptive transmission time intervals, TTI, wherein the method is characterized by comprising: receiving, by a user equipment, UE, time division duplexing, TDD, TTI configuration information from a communications controller, wherein the TDD TTI configuration information includes the uplink and downlink direction patterns and configuration of different TTIs based on traffic types; receiving, by the UE, a first higher layer signaling indicating a feedback slot configuration information from the communications controller, wherein the feedback slot configuration information comprises information on which TTI lengths in the system are configured with feedback slot and a hybrid automatic repeat request, HARQ feedback delay between a downlink transmission and a HARQ feedback corresponding to the downlink transmission; receiving, by the UE, feedback slot switching flags from the communications controller, wherein the feedback slot switching flags indicate whether feedback slots are turned on or turned off for a period of time; transmitting and receiving, by the UE, data in TDD TTI intervals in units of frames, multiple frames, or other larger interval, wherein the TDD TTI configuration of a frame is based on the TDD TTI configuration received from the communications controller; and transmitting, by the UE based on data received the in TDD TTI intervals, HARQ feedback on TTIs of the TDD TTI interval to the communications controller, wherein when the data is successfully received, an ack is transmitted, and when the data is not successfully received, a nack is transmitted, wherein the HARQ ack/nack is transmitted based on the feedback slot configuration information; wherein the HARQ feedback delay is explicitly indicated in the first higher layer signaling; and wherein the HARQ feedback delay is provided in units of TTIs. receiving, by a user equipment, UE, time division duplexing, TDD, TTI configuration information from a communications controller, wherein the TDD TTI configuration information includes the uplink and downlink direction patterns and configuration of different TTIs based on traffic types; receiving, by the UE, a first higher layer signaling indicating a feedback slot configuration information from the communications controller, wherein the feedback slot configuration information comprises information on which TTI lengths in the system are configured with feedback slot and a hybrid automatic repeat request, HARQ feedback delay between a downlink transmission and a HARQ feedback corresponding to the downlink transmission; receiving, by the UE, feedback slot switching flags from the communications controller, wherein the feedback slot switching flags indicate whether feedback slots are turned on or turned off for a period of time; transmitting and receiving, by the UE, data in TDD TTI intervals in units of frames, multiple frames, or other larger interval, wherein the TDD TTI configuration of a frame is based on the TDD TTI configuration received from the communications controller; and transmitting, by the UE based on data received the in TDD TTI intervals, HARQ feedback on TTIs of the TDD TTI interval to the communications controller, wherein when the data is successfully received, an ack is transmitted, and when the data is not successfully received, a nack is transmitted, wherein the HARQ ack/nack is transmitted based on the feedback slot configuration information;