The present invention relates to transmitting data on a shared communication channel in a communication system supporting multiple hybrid automatic repeat request processes and configurable to apply a bundling of transmission time intervals. The data transmitting including mapping of TTIs of the HARQ processes cyclically onto subframes. In order to efficiently support dynamic bundle scheduling, when a grant is received during a bundle transmission, this grant becomes a shifting grant, according to which the bundle is transmitted and according to the location of which the timing of the grant reception and the data transmission is adapted. The transmission of the shifted bundle is performed in accordance with the state of its retransmission process, i.e. the bundle is either initially transmitted or retransmitted.