Method and apparatus for communications with carrier aggregation

A method at a user equipment comprising:

• transmitting Hybrid Automatic Repeat reQuest, HARQ feedback to a base station in a communications system supporting carrier aggregation of at least one first carrier on which a short Transmission Time Interval, TTI, is applied and at least one second carrier on which a long TTI is applied;
• receiving downlink data transmission from the base station in a data transmission region of a short TTI on a first carrier and in the data transmission region of a long TTI on a second carrier;
• and
• transmitting HARQ feedback for the received downlink data transmission towards the base station in an uplink control region of at least one of a short TTI on the first carrier and a long TTI on the second carrier;
• wherein the HARQ feedback for the downlink data transmission received on the second carrier is transmitted on the second carrier in a long TTI immediately following or two long TTIs later than the long TTI where the downlink data transmission is received;
• and
• the HARQ feedback for the downlink data transmission received on the first carrier is transmitted on the second carrier in a long TTI whose index nlong and the index nshort of the short TTI where the downlink data transmission is received have a relationship of nlong=floor(nshort/2)+1, wherein nshort is an integer.

A method at a user equipment comprising:

• performing data transmission to a base station in a communications system supporting carrier aggregation of at least one first carrier on which a short Transmission Time Interval, TTI is applied and at least one second carrier on which a long TTI is applied;
• receiving at least one uplink scheduling grant for data transmission to the base station in a downlink control region of at least one of a short TTI on a first carrier and a long TTI on a second carrier;
• and
• performing uplink data transmission towards the base station in a data transmission region of a short TTI on the first carrier and in the data transmission region of a long TTI on the second carrier as indicated by the at least one uplink scheduling grant;
• said receiving at least one uplink scheduling grant for data transmission to the base station comprises receiving, in the downlink control region of a short TTI on the first carrier, an uplink scheduling grant for data transmission on the first carrier and receiving, in the downlink control region of a short TTI on the first carrier, an uplink scheduling grant for data transmission on the second carrier;
• the uplink data transmission on the first carrier is performed in a short TTI immediately following the short TTI where the corresponding uplink scheduling grant is received;
• and
• the uplink data transmission on the second carrier is performed in a long TTI whose index nlong and the index nshort of the short TTI where the corresponding uplink scheduling grant is received have a relationship of nlong=nshort/2, wherein nshort is an even integer or in a long TTI whose index nlong and the index nshort of the short TTI where the corresponding uplink scheduling grant is received have a relationship of nlong=1+nshort/2 wherein nshort is an even integer.