LTE-Advanced Pro and Massive MTC: NB-IoT

LTE-Advanced Pro¹ has addressed the needs of the massive MTC use cases under the Narrowband Internet-of-Things (NB-IoT)[1] feature². To address the IoT requirements in this segment, namely, support for: low throughput and sporadic transmission, limited mobility, large number of devices, low device cost, enhanced coverage – the PHY layer, protocol stack and signaling procedures have been simplified with respect to the LTE system design to support low-end devices and decrease the signaling load.

Narrowband-IoT (NB-IoT)

The key aspects of NB-IoT to support low-end IoT devices and services, while reusing LTE infrastructure include [2]:

• PHY layer which has been modified for coverage enhancements and power consumption reduction by: reduced system BW to 180kHz, reduction of transmission modes and number of antenna ports, reduced TB size, improved DRX cycles for both connected and idle modes, single HARQ process for both DL and UL, etc. Three operation modes have been specified: standalone 180kHz carrier, LTE guard-band and in-band LTE – using single LTE resource blocks. The DL supports multi-tone transmission with 12 subcarriers of 15kHz, while for UL both multi-tone and single-tone operation is possible with both 15kHz and 3.75kHz subcarrier separation.
• System aspects that have been modified with respect to LTE, include: lack of connected mobility support (assuming that majority of the NB-IoT applications will be used by stationary UEs) and system optimizations for efficient data transmission (also called Control Plane(CP)/User Plane(UP) CIoT EPS Optimization Solutions). The CP solution is based on the concept of UP data transmission over NAS signaling, without establishment of the Data Radio Bearer (DRBs) and is a mandatory solution for NB-IoT UEs. The UP solution on the other end is built upon the idea of holding the UE context at the eNB when the UE moves to RRC IDLE state, thus decreasing the signaling overhead when the UE is switching between IDLE and CONNECTED mode with the use of newly introduced RRC Resume/Suspend procedure.

Summary

As can be seen from the recent developments in the LTE domain, some of the 5G use case requirements are also heavily addressed with the use of legacy system support and infrastructure. In these considerations, eMTC corner of the “5G service triangle” is addressed by NB-IoT with:

• Air interface simplifications for coverage improvements, device simplification, battery consumption reduction etc.,
• System enhancements for enabling signaling reduction, UE operation simplification.

References:

[1] http://www.3gpp.org/news-events/3gpp-news/1785-nb_iot_complete

[2] 3GPP TS 36.300

¹ LTE-Advanced Pro has been addressed in these posts: https://www.grandmetric.com/blog/2016/04/07/lte-advanced-pro-what-is-this/ and https://www.grandmetric.com/blog/2015/12/15/lte-evolution-lte-lte-advanced-lte-advanced-pro/

² 3GPP Rel-13 has also specified the other 2 solutions for IoT, namely LTE-M (enhanced MTC) and EC-GSM