What is Interference Cancellation

In this chapter, the authors discuss the design of precoders in cognitive multi-user multi-way relay systems. When multiple secondary users intend to communicate with each other using the spectrum licensed to the primary user, how to manage the interference between primary and secondary networks as well as among multiple secondary users becomes an important design issue. They discuss one possible solution of using a relay station as well as multiple antenna techniques. Precoding design in such a relay supported multiple antenna secondary network is presented based on the Mean Square Error (MSE) design criterion. The joint design of precoding matrices at all the secondary nodes is a non-convex problem. Therefore, an iterative algorithm is proposed to iteratively optimize the precoding matrices at secondary transmitters, the precoding matrix at the secondary relay, and decoding matrices at secondary receivers. Other non-iterative solutions are also presented to strike a balance between performance and complexity.