Massive Grant-Free Access in Cell-Free Massive MIMO Networks

In this paper, a grant-free scheme is proposed for massive access from machine-type devices in cell-free massive MIMO networks. The proposed scheme, based on the coded random access approach, features transmission of multiple packet replicas per device and a distributed successive interference cancellation procedure across time slots and access points on the network side, generating very limited traffic on the fronthaul links. Its performance, in terms of packet loss rate versus the number of active devices, is analyzed from several perspectives including the device transmit power, the number of replicas per device, and the signal-to-interference-plus-noise ratio.