There is provided methods and associated base station and user equipment, for facilitating transmissions in a wireless communication system. The mapping between an index and its corresponding HARQ ID or HARQ ID & NDI pair can be done using one or more equations relating the two entities. The equations can be defined in two configurations, one for encoding HARQ ID or HARQ ID & NDI pair and a second for decoding the encoded HARQ ID or HARQ ID & NDI pair to determine the HARQ ID or HARQ ID and NDI.