MIMO cognitive radio system interference cancellation based on protograph LDPC codes

In the current MIMO cognitive radio system, the cognitive user (CU) and the primary user (PU) cannot communicate simultaneously in a channel. In order to solve this problem, this paper proposes a novel scheme for MIMO cognitive radio system based on protograph LDPC codes and interference cancellation. Protograph LDPC codes are applied to MIMO cognitive radio system in this approach, which can cancel multi-user interference and channel noise interference. The core idea of the proposed approach is that, depending on protograph LPDC codes and the difference of channel fading between the same type users (CU1 to CU2, PU1 to PU2) and different type users (CU1 to PU2, PU1 to CU2), the other co-channel user signals and channel noise are looked as a new interference at the given CU or PU receiver. By multiplying received signal with a zero forcing (ZF) interference cancellation matrix and decoding modified received signal, the CU or PU receiver can obtain the desired information from the same type user. The proposed approach can increase one time of communication capacity in MIMO cognitive radio system. Comparing with the approach of directly extracting user information, our approach obtained about 12dB coding gain in Rayleigh flat-fading channel.