3GPP Release-17 Physical Layer Enhancements for LTE-M and NB-IoT

The 3rd Generation Partnership Project (3GPP) introduced Long-Term Evolution (LTE) for Machine-Type Communications (LTE-M) and Narrowband Internet of Things (NB-IoT) in Release 13 (Rel-13) as part of the fourth generation LTE. Both technologies provide wide-area connectivity to “things” that benefit from being connected including sensors, machines, actuators, and so on. LTE-M and NB-IoT continued their evolution across successive 3GPP releases providing higher data rates, power saving features, coexistence with the fifth generation New Radio (NR), and so on. In Release-17 (Rel-17), 16-quadrature amplitude modulation (16-QAM) in uplink (UL) and downlink (DL) for NB-IoT, as well as the support of up to 14 hybrid automatic repeat request (HARQ) processes and a new maximum DL transporting block size (TBS) for half duplex frequency-division duplexing (HD-FDD) LTE-M devices were standardized. This article provides an overview of the Rel-17 physical layer enhancements according to the 3GPP specifications, including descriptions of their technical components, qualitative gains, and performance evaluations. For NB-IoT, 16-QAM in DL nearly doubles the peak data rate using a larger maximum DL TBS, whereas 16-QAM in UL allows transmitting the largest TBS available for quadrature phase shift keying using half of the resources in the time domain. For LTE-M, for HD-FDD Category M1 (Cat-M1) UEs, the 14 HARQ processes feature adds full support for handling the presence of invalid subframes and increases the DL peak data rate by 20 percent, whereas the introduction of a larger maximum DL TBS further increases the DL peak data rate by 73.6 percent.