Method and apparatus for communications with carrier aggregation

A method at a base station for 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, the method comprising:

• 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
• the downlink data transmission on the second carrier is performed in a long TTI which is determined depending on a ratio of a length of the long TTI to a length of the short TTI and the short TTI where the corresponding downlink scheduling grant is transmitted;
• or
• transmitting, in the downlink control region of a long TTI on the second carrier, a downlink scheduling grant corresponding to data transmission on the first carrier;
• and
• the downlink data transmission on the first carrier is performed in a short TTI which is determined depending on a ratio of a length of the short TTI to a length of the long TTI and the long TTI where the corresponding downlink scheduling grant is transmitted.