# Evolution and Testing of NB-IoT Solutions
## 4 NB-IoT Evolution  
In Release 13, NB-IoT was specified as a new radio access which addressed the main requirements for covering the low-end segment of the use cases considered in IoT and, as shown in Figure 3, it has been evolving and including new features to support additional uses.  
Release 14 (March 2017) added support for more LTE features to increase functionality and the number of use cases covered by NB-IoT. Features in Release 14 include support for the ECID (Enhanced Cell Identifier) and OTDOA (Observed Time Difference of Arrival) positioning method based on NPRS (Narrowband Positioning Reference Signal), mobility and service continuity enhancements, new power class with a reduced output power of 14 dBm, Single-cell Point-to-Multipoint (SC-PTM) for broadcast/multicast services based on MBMS architecture, peak throughput improvement in the downlink (144 kbps) and in the uplink (142.5 kbps), and a new device category Cat-NB2 with higher values of TBS (Transport Block Size) in the uplink and in the downlink.  
Release 15 introduced TDD (Time Division Duplexing) support, higher spectral efficiency, early data transmission, wake-up mechanism and on demand network access for UE power saving, NPRACH (NB-IoT physical random access channel) reliability and range enhancement, small cell support and LTE Device to Device, and UE to Network Relays for IoT and wearables.  
Some of the latest additions to Release 15 (December 2018) were the coexistence of NB-IoT with 5G NR and the coexistence of NB-IoT with eMTC. As many NB-IoT devices are expected to live more than ten years after being deployed, they are expected to be compatible with future 3 GPP releases. In addition, as suggested by multiple 3 GPP contributions [12], both NB-IoT and eMTC are also expected to coexist and converge in the future towards mMTC, but that does not mean that every new feature will be added to both eMTC and NB-IoT. Instead, quite likely, a decision should be taken case by case depending on the needs of the specific use cases.  
From this listing, arguably the two most important features, from the point of view of the potential to cover new use cases and increase the number of NB-IoT devices, are OTDOA (Observed Time Difference Of Arrival) positioning (Release 14) and Device-to-Device (D2D) communication (Release 15). These new features are introduced in detail next.  
The introduced improvements in Release 16 (June 2020) are related on enhancements of previous features: improved DL/UL transmission efficiency and UE power consumption, scheduling  
Figure 3: NB -IoT Evolution.  
enhancement, network management enhancement, improved multi-carrier operation, mobility enhancements, and the study of the coexistence with NR.  
Finally, the planned features for Release 17 (standard freeze scheduled for late 2021) are to increase the peak data rate introducing the support of a higher modulation (16 QAM) in downlink and also in uplink, reduce RRC reestablishment time to another cell defining specific signaling for neighbor cell measurements and the corresponding measurement triggering before radio link failure, and support NB-IoT carrier selection depending on the coverage level and specific carrier configurations.