Cognitive transmissions under a primary ARQ process via backward interference cancellation

In this work, we address the problem of the coexistence of Primary and Secondary Users (PU and SU, respectively) in a wireless network, where the PU employs a retransmission based error control technique (ARQ). This mechanism offers the SU a non trivial opportunity: by decoding the Primary Message (PM), the Secondary Receiver (SR) can perform interference cancellation during the whole primary ARQ window, thus enhancing its own outage performance. In particular, we investigate a Back- ward Interference Cancellation (BIC) mechanism: the SR buffers the secondary transmissions that underwent outage due to primary interference, and attempts to recover them once the knowledge about the PM becomes available due to decoding operation in a future instant. We present analytical results for the scenario where the primary ARQ process is limited to one retransmission, and show by numerical results the throughput benefit of BIC, over other techniques investigated in the literature.