Full-duplex (FD) wireless communication systems have become an important research issue since it can increase spectral efficiency through higher spectrum utilization. The main challenge in achieving FD is the cancellation of strong interference at the received interface from the transmitted interface of a node, namely, self-interference (SI). Therefore, a technique for SI cancellation using an oblique projection-based postcoding (OPP) scheme is proposed in this paper. The major merit of the proposed OPP method is the non-necessity of SI channel estimation, which can reduce the signaling overhead and can be adopted even when the SI channel distribution is unknown. Simulation results show that the proposed OPP scheme can achieve significant performance gain in terms of signal-to-interference-plus-noise ratio (SINR) compared to conventional method.