Superposition data transmission for cognitive radios: Performance and algorithms

For improvement of achievable rate region in cognitive radio channels, a transmission method for secondary users is proposed. At first, the rate region of the sensing based cognitive radio scheme in which secondary users access the channel based on their channel sensing results with sensing error is analyzed. In the multiuser information theory, it is well-known that interference channel cases where both users transmit their own signal simultaneously achieve better rate region than the time-sharing method based on sensing outcomes. Based on this theoretical result, we propose the new transmission scheme in which a secondary transmitter relays primary userpsilas signal with a full-duplex amplify and forward (AF) manner while transmitting its own data at the same time. In the proposed method, we take account of practical implementation issues which are ignored in the theoretical method guaranteeing an upper bound of a rate region. With different geometric locations and power ratios between the relaying signal and the secondary userpsilas one, we evaluate the achievable rate region of the proposed method and compare with those of the conventional ones.