Cell-Free Massive MIMO System With Dedicated Interference Cancellation Access Points.

A cell-free massive multiple-input multiple-output (mMIMO) system employs a large number of access points (APs). Since the APs collaboratively serve user equipments (UEs), its energy and spectral efficiency can be much higher than that of a conventional cellular system. Typically, the inter-user interference (IUI) is suppressed appropriately to improve performance, which usually results in high computational complexity. To reduce this computational complexity, we propose a new cell-free mMIMO architecture, called a dedicated AP-based interference cancellation (DAP-IC) architecture with two types of APs: DS-APs that transmit the data signal (DS) to UEs and IUI-APs that transmit the signal to eliminate the IUI. To this end, we first formulate an optimization problem of maximizing the spectral efficiency while ensuring the fairness of UEs by optimizing the precoding vectors of the APs. We then develop DAP-IC algorithm that solves this problem with a low computational complexity. The simulation results show that the DAP-IC algorithm provides good performance with much lower computational complexity, compared with the weighted minimum mean square error (WMMSE) algorithm for the conventional cell-free mMIMO architecture.