Abstract: In TV band, adopting the current cognitive radio schemes, the cognitive user (CU) will face the problem of TV signals. In order to solve this problem, this paper proposes a novel interference cancellation scheme based on protograph LDPC codes and virtual MIMO for cognitive radio system in television band.
Protograph LDPC codes are applied to virtual MIMO cognitive radio system in the proposed scheme, and by encoding transmitting data and MIMO space-time processing, it can cancel TV signal interference and channel noise. The core idea of the proposed scheme is that, depending on the difference of channel fading between the CUs and TV station’s transmitter, the TV signal interference and channel noise are looked as a new interference at the CU receiver. By decoding received signal using protograph LDPC, the CU receiver can cancel the TV signal interference from the TV station. In an optimal situation, the proposed approach can increase about 0.620.76 times of communication capacity for the proposed cognitive radio system. Comparing with the approach of directly extracting user information, the proposed scheme obtained about 12 dB coding gain in Rayleigh flat-fading channel, and it can cancel the TV signal interference efficiently.

Key words: cognitive radio system, virtual MIMO, television band, interference cancellation, protograph LDPC codes