5G NR Small Data Transmissions (SDT) Overview and Performance Evaluation

Optimising wide-area IoT connectivity in Long Term Evolution (LTE) lead to a mechanism that supported transmission of small, infrequent data packets during the random access procedure. This mechanism, which reduced the control signalling overhead, was introduced for LTE as Early Data Transmission (EDT) in 3GPP Release 15 and showed benefits in terms of User Equipment’s (UE’s) battery life and latency. The evolution of EDT feature into fifth generation New Radio (5G NR) has led to the introduction of Small Data Transmission (SDT) feature in 3GPP Release 17. The evolution continued in Release 18. This article provides an overview of SDT feature in Release 17 and 18, highlighting the aspects on which SDT differs from EDT. Most importantly, this article presents simulation results for Release 17 Mobile Originated (MO) SDT and Release 18 Mobile Terminated (MT) SDT, highlighting the performance impact for a range of different SDT data payload sizes. Our evaluations indicate that MO-SDT is beneficial even at 90000 bytes, offering tens of milliseconds of latency gains and up to 85% energy reduction for the UE. MT-SDT gains were restricted to data payloads below a few thousand bytes due to the limited link adaptation capability in the feature.