ROBUST HARQ-ACK DESIGN FOR MF-HSDPA

When a UE (12) is configured with MF-HSDPA and HARQ-ACK information associated with cells (14, 16) (characterized by potentially different downlink timing) is jointly encoded, only part of the existing Rel-9 HARQ-ACK codebook is reused. In one embodiment, only the codebook conflict arising from reuse of encodings is resolved. This is achieved by introducing a new codeword for at least one of the HARQ-ACK code words that are used multiple times in the existing Rel-9 codebook. In another embodiment, all codewords in the Rel-9 HARQ-ACK codebook having a Hamming distance smaller than a predetermined value (but not all codewords) are replaced. In yet another embodiment, all codewords in the Rel-9 HARQ-ACK codebook having a Hamming distance smaller than a predetermined value (but not all codewords) that would cause ambiguity at the NodeB receiver (i.e. where the interpretation of the HARQ-ACK information for one cell (14) depends on the number of streams transmitted at the other cell (16)) are replaced.