Toward the Standardization of Grant-Free Operation and the Associated NOMA Strategies in 3GPP

The dramatic increase in Internet traffic to and from wireless devices poses significant challenges for network operators. While the current growth of traffic is mostly due to consumers communicating more frequently and larger amounts of data over the wireless infrastructure, much of the future growth is predicted to originate from non-human-operated devices or so-called IoT communication. The 3GPP standardization activities toward 5G cellular systems envisages two IoT-centric scenarios: mMTC and URLLC. In this article, we quantify the advantages of grant-free operation for 5G mMTC using latency, signaling overhead, and power consumption aspects. We propose the high-level design of a new grant-free state of operation and explain its interaction with the legacy LTE operating states. We also describe promising grantfree NOMA solutions with respect to synchronization and HARQ, and resource collision handling procedures. Our discussion and proposal relate closely to the current 5G standardization activities in 3GPP and highlight solutions that can easily be integrated into the current LTE framework.