A novel downlink signaling method for OFDM based cognitive radio system

The Cognitive radio (CR) is an efficient approach for future wireless communication system. In CR system the rental users can identify the spectrum information and access the unoccupied spectrum hole under the interference constraint to the licensed users. The spectrum is allocated and utilized dynamically nearly without adjusting of existing systems. Orthogonal frequency division multiplexing (OFDM) is a good candidate technology for rental users in CR system especially in the system with a base station. The spectrum assignment can be realized easily through sub-carrier allocation. The interference constraint can be fulfilled by sub-carrier and power allocation. The resource allocation scheme should vary corresponding to the variation of the environment. So the signaling method takes very important role in the resource allocation which guarantees the realization and efficiency. Traditional signaling message is usually transmitted through high layer packet. It is error-prone and low efficient. In this paper a novel downlink signaling method for OFDM based CR system is proposed. It is based on low density parity check (LDPC) codes and constellation rotation. It can transmit the sub-carrier allocation message reliably without extra difficulty for the resource allocation scheme. The method also adapts to different transmit power on sub-carrier.