ABSTRACT
Since J. Mitola III proposed the concept of cognitive radio (CR) [1], cognitive radio technology with federal communication commission (FCC) endorsement has been widely considered as an emerging solution of crowded spectrum for future wireless communications. Haykins’ classic paper in 2005 [2] summarized important tasks to facilitate CRs. Particularly, the CR-transmitter (CR-Tx) shall identify the spectrum hole or white space in the spectrum for primary system (PS), such that CR-Tx can take this opportunity to transmit its message or packet(s) to the CR-receiver (CR-Rx). We may name such a link-level transportation of packets between CR-Tx and CR-Rx as a sort of opportunistic transmission. However, another major challenge arises to deal with multiuser opportunistic transmissions and to network CRs through opportunistic transmissions into the multihop cognitive radio network (CRN). This chapter therefore summarizes state-of-the-art CRN technology and its research opportunities at the horizon.
