A radio communications link is established between radio stations, and a semi-persistent radio resource is allocated to support data transmission over the communications link. The semi-persistent radio resource is associated with a corresponding automatic repeat request (ARQ) process identifier. Non-limiting examples of a semi-persistent radio resource include a regularly scheduled transmission time interval, frame, subframe, or time slot during which to transmit a data unit over the radio interface. Retransmission is requested of a data unit transmitted using the semi-persistent radio resource. The ARQ process identifier associated with the semi-persistent resource is used to match a retransmission of a data unit dynamically scheduled on the communications link with the requested data unit retransmission. In a preferred example embodiment, the ARQ process identifier is a hybrid ARQ (HARQ) process, where a retransmitted data unit is combined with a previously-received version of the data unit.