Survey on Cell-Free Massive MIMO with Limited Fronthaul

User Centric Cell-Free massive MIMO is a technology that ensures uniform service for users located at cell boundaries and interference control when multiple APs are densely deployed to support services. At this time, the Cell-Free MIMO system requires the CPU to control the simultaneous transmission of multiple APs and determine which APs will communicate with each user by estimating channel between the user and the base station. And it greatly increases the bandwidth requirement for fronthaul uplink to deliver state information, resulting in performance constraints according to fronthaul capacity. This paper investigates the research trends in Cell-Free massive MIMO considering fronthaul capacity.