I. Introduction
A variety of new technologies have been / will be introduced in 5G /beyond and 6G communications [1]. Small cell network operated by non-legacy micro operators like industrial company, local government, and so on, is considered as one of important topics [2] regarding its flexibility, robustness, and low deployment cost. In Japan, local 5G small cell system has recently started licensing assuming operation within limited area, but it still requires further investigations for fully invoking its potential. For example, because of the cohabitation of small cells in a small area, interference mitigation with energy saving is an important problem to realize broadband communication under efficient resource sharing [3]–[6].