| 摘要 |
In LTE TDD with Carrier Aggregation (CA), a two bit sequence number or downlink assignment indicator (DAI) can be attached to downlink control information (DCI) messages relating to packets transmitted on some or all of successive carrier frequencies in a given subframe. The numerical progression of the sequence numbers can be used to determine the number of ACK/NACK bits (ACK/NACK codebook size) needed to acknowledge reception of the packets. The receiver determines the ACK/NACK codebook size to within a certain granularity or other constraints, depending on the received sequence of DAI values. The granularity or constraint(s) may be pre-determined, configured or indicated by the sequence. This allows a more accurate and reliable common understanding between the transmitter and receiver concerning the number of DCI messages transmitted. This is useful, for example, if the format of transmission of ACK/NACK information relating to the DCI messages depends on the number of messages transmitted, since the most likely cases of failed detection of a DCI message can be detected and corrected. |
