Novel Channel Estimation for Non-orthogonal Multiple Access Systems

Non-orthogonal multiple access (NOMA) is a promising technology in future mobile communications. In this letter, we study the channel estimation and power allocation problem for the two-user NOMA downlink system with one strong user and one weak user. Firstly, we introduce a new type of linear estimator that aims at maximizing the average effective signal-to-interference-and-noise ratio (SINR) of the strong user with bounded average effective SINR guaranteed for the weak user. We propose a constrained concave convex procedure (CCCP)-based iterative algorithm to solve the estimation problem. Secondly, we also derive the maximum average effective SINR of the strong user under the traditional maximum-likelihood (ML)-based estimator and linear minimum-mean-square-error (LMMSE)-based estimator, respectively. Simulation results have shown that the proposed estimator outperforms the traditional ML and LMMSE estimators, indicating a new way of channel estimation and power allocation for the NOMA downlink systems.