Unsourced Random Access with Authentication and Joint Downlink Acknowledgements

In massive access scenarios, an unknown subset of a very large number of wireless devices transmit small packets to the base station (BS) in an uncoordinated manner. These scenarios have been a hot research topic in the context of 5G/Beyond-5G as they pose many challenges and require the design of highly efficient and lightweight communication protocols. This has inspired the paradigm of unsourced random access (U-RA) as a way to simplify multi-user decoding and reduce overhead in the uplink. However U-RA, being mainly a physical layer approach, lacks the ability to identify and authenticate users, which needs to be taken into account. Another important functionality is the transmission of acknowledgements (ACK) in the downlink. The naïve method of sending a dedicated message to each user may not be feasible in the massive random access scenario, thus a solution is to provide jointly encoded ACKs, which can achieve much higher efficiency at the cost of introducing false positives. In this paper we consider a system that combines U-RA with joint ACKs transmitted in the downlink. We focus on the systematic description and analysis of the false positives, as well as the design options, and the associated trade-offs among reliability, rate of retransmissions and power efficiency.