Method and apparatus for communications with carrier aggregation

1. A method at a base station comprising:

performing data transmission to a user equipment 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;

transmitting at least one downlink scheduling grant corresponding to data transmission to the user equipment 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 downlink data transmission towards the user equipment 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 downlink scheduling grant;

wherein said transmitting at least one downlink scheduling grant corresponding to data transmission to the user equipment comprises transmitting, in the downlink control region of a short TTI on the first carrier, a downlink scheduling grant corresponding to data transmission on the second carrier and transmitting, in the downlink control region of a short TTI on the first carrier, a downlink scheduling grant corresponding to data transmission on the first carrier;

the downlink data transmission on the first carrier is performed in the short TTI where the corresponding downlink scheduling grant is transmitted or in a short TTI immediately following the short TTI where the corresponding downlink scheduling grant is transmitted; and

the downlink data transmission on the second carrier is performed in a long TTI whose index n long and the index n short of the short TTI where the corresponding downlink scheduling grant is transmitted have a relationship of n long =n short /2, wherein n short is an even integer.

2. The method according to claim 1 , wherein

said transmitting at least one downlink scheduling grant corresponding to data transmission to the user equipment comprises transmitting, in the downlink control region of a short TTI on the first carrier, a downlink scheduling grant corresponding to data transmission on the first carrier and transmitting, in the downlink control region of a long TTI on the second carrier, a downlink scheduling grant corresponding to data transmission on the second carrier;

the downlink data transmission is performed on the first carrier in the short TTI where the corresponding downlink scheduling grant is transmitted or in a short TTI immediately following the short TTI where the corresponding downlink scheduling grant is transmitted; and

the downlink data transmission is performed on the second carrier in the long TTI where the corresponding downlink scheduling grant is transmitted or in a long TTI immediately following the long TTI where the corresponding downlink scheduling grant is transmitted.

3. The method according to claim 1 , wherein

said transmitting at least one downlink scheduling grant corresponding to data transmission to the user equipment comprises transmitting, in the downlink control region of a long TTI on the second carrier, a downlink scheduling grant corresponding to data transmission on the second carrier and a downlink scheduling grant corresponding to data transmission on the first carrier;

the downlink data transmission on the second carrier is performed in the long TTI where the corresponding downlink scheduling grant is transmitted or in a long TTI immediately following the long TTI where the corresponding downlink scheduling grant is transmitted; and

the downlink data transmission on the first carrier is performed in a short TTI whose index n short and the index n long of the long TTI where the corresponding downlink scheduling grant is transmitted have a relationship of n long =floor(n short /2), wherein n short is an integer; or

the downlink data transmission on the first carrier is performed in a short TTI whose index n short and the index n long of the long TTI where the corresponding downlink scheduling grant is transmitted have a relationship of n long =floor((n short −1)/2, wherein n short is an integer.

4. 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 n long and the index n short of the short TTI where the downlink data transmission is received have a relationship of n long =floor(n short /2)+1, wherein n short is an integer.

5. The method according to claim 4 , wherein

the HARQ feedback for the downlink data transmission received on the first carrier is transmitted on the first carrier in a short TTI immediately following or two short TTIs later than the short TTI where the downlink data transmission is received.

6. The method according to claim 5 , 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.

7. The method according to claim 5 , wherein

the HARQ feedback for the downlink data transmission received on the second carrier is transmitted on the first carrier in either of the following:

a short TTI whose index n short and the index n long of the long TTI where the downlink data transmission is received have a relationship of n short =2*(n long +1)+1, wherein n long is an integer; and

a short TTI whose index n short and the index n long of the long TTI where the downlink data transmission is received have a relationship of n short =2*(n long +1), wherein n long is an integer.

8. The method according to claim 4 , wherein

the HARQ feedback for the downlink data transmission received on the first carrier is transmitted on the first carrier in the short TTI where the downlink data transmission is received.

9. The method according to claim 8 , wherein

the HARQ feedback for the downlink data transmission received on the second carrier is transmitted on the second carrier in the long TTI where the downlink data transmission is received; or

the HARQ feedback for the downlink data transmission received on the second carrier is transmitted on the first carrier in a short TTI whose index n short and the index n long of the long TTI where the downlink data transmission is received have a relationship of n short =2*n long +1, wherein n long is an integer.

10. The method according to claim 4 , wherein

the HARQ feedback for the downlink data transmission received on the second carrier is transmitted on the second carrier in 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 n long and the index n short of the short TTI where the downlink data transmission is received have a relationship of n long =floor((n short −1)/2)+1, wherein n short is an integer.

11. 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 n long and the index n short of the short TTI where the corresponding uplink scheduling grant is received have a relationship of n long =n short /2, wherein n short is an even integer or in a long TTI whose index n long and the index n short of the short TTI where the corresponding uplink scheduling grant is received have a relationship of n long =1+n short /2 wherein n short is an even integer.

12. The method according to claim 11 , wherein

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 long TTI on the second carrier, an uplink scheduling grant for data transmission on the second carrier;

the uplink data transmission is performed on the first carrier in a short TTI immediately following the short TTI where the corresponding uplink scheduling grant is received; and

the uplink data transmission is performed on the second carrier in a long TTI immediately following the long TTI where the corresponding uplink scheduling grant is received.

13. The method according to claim 11 , wherein

said receiving at least one uplink scheduling grant for data transmission to the base station comprises receiving, in the downlink control region of a long TTI on the second carrier, an uplink scheduling grant for data transmission on the first carrier and 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 whose index n short and the index n long of the long TTI where the corresponding uplink scheduling grant is received have a relationship of n long =floor((n short −1)/2), wherein n long is an integer; and

the uplink data transmission on the second carrier is performed in a long TTI immediately following the long TTI where the corresponding uplink scheduling grant is received.