1. Introduction
NB-IoT is a product of both technological evolution and market competition. Because the future market outlook is generally optimistic, device vendors competed intensely for market share during the standards process; however, the expected performance targets were largely consistent and standardization has continued to accelerate.
2. Background of NB-IoT Technology
2.1 Classification of IoT Communication Technologies
There are many IoT communication technologies. Based on transmission range, they can be divided into two categories:
One category is short-range communication technologies, represented by Zigbee, Wi-Fi, Bluetooth, Z-wave, etc., with typical applications such as smart home.
The other category is wide-area network technologies, commonly referred to as LPWAN (low-power wide-area network), with typical applications such as smart metering.
LPWAN technologies can be further divided into two types: one type operates in unlicensed spectrum, such as Lora and Sigfox; these are often proprietary or custom implementations.
The other type operates in licensed spectrum, such as mature 2G/3G cellular technologies GSM, CDMA, and WCDMA, and LTE and its evolutions that are being deployed and support different terminal categories. These technologies are generally standardized by international bodies such as 3GPP (which defines standards for GSM, WCDMA, LTE and their evolutions) or 3GPP2 (which focuses on CDMA-related standards).
NB-IoT was proposed and initiated in 3GPP in September 2015 as a new narrowband cellular LPWAN technology.
2.2 Development of 3GPP MTC Technologies
Before NB-IoT was proposed, the industry broadly recognized the trend toward ubiquitous IoT connectivity. 3GPP viewed the prospects for M2M communication as a significant opportunity for standards ecosystems, and LPWAN technologies with low cost, low power consumption, wide coverage, and low data rate characteristics were expected to play an important role. Accordingly, 3GPP has been promoting the development of machine-type communication (MTC) technologies along two main directions.
Direction one: In response to challenges from non-3GPP technologies, pursue further evolution of GERAN/GSM and study new access technologies.
For many years, 3GPP-based network operators relied on low-cost GPRS modules for IoT services. However, the emergence of technologies such as Lora and Sigfox threatened GPRS modules' traditional advantages in cost, power consumption, and coverage. At the GERAN #62 meeting in March 2014, 3GPP proposed a new study item "FS_IoT_LC" to investigate the feasibility of evolving GERAN and new access systems to support lower complexity, lower cost, lower power consumption, and enhanced coverage.
Direction two: Study low-cost, evolutionary LTE-MTC technologies as potential replacements for 2G/3G IoT modules.
As LTE and its evolutions progressed, 3GPP defined many terminal categories to meet different IoT service needs. Rel-8 already defined category 1–5 terminals at different rates; later releases added higher-bandwidth categories such as category 6 and category 9, and also defined lower-cost, lower-power categories such as category 0 (Rel-12). Building on Cat.0, at RAN #65 in September 2014 3GPP established a study item "LTE_MTCe2_L1" to further investigate lower-cost, lower-power, and enhanced-coverage LTE-MTC solutions.
NB-IoT originated from the study of new access technologies in the first direction. In addition to these two directions, 3GPP has continued work on power-saving techniques and updates to system architecture and the network side to support these evolutions.
3. International Standardization of NB-IoT Technology
3.1 NB-IoT Project Initiation Process
In 3GPP standardization, adding a new technology typically starts with a study item (SI), which produces a technical report. Based on the study report, a work item (WI) is created within the same Release or the next Release to produce technical specifications. The NB-IoT development followed this process.
In the GERAN study "FS_IoT_LC", three technologies were proposed: Extended Coverage-GSM (EC-GSM), NB-CIoT, and NB-LTE.
NB-CIoT was jointly proposed by Huawei, Qualcomm, and Neul (Neul was a UK IoT company acquired by Huawei in September 2014), while NB-LTE was proposed by vendors such as Ericsson, ZTE, and Nokia. After intensive discussion at the RAN#69 plenary in September 2015, the parties negotiated and unified on a single technology solution, named NB-IoT.
Compared with NB-LTE, NB-CIoT proposed a largely new air interface relative to legacy LTE, which could introduce compatibility issues and require larger theoretical changes on the network side; NB-LTE aimed to be as compatible as possible with existing LTE networks.
NB-CIoT met the study objectives for enhanced indoor coverage, support for massive low-rate terminals, reduced terminal complexity, lower power consumption and latency, coexistence and interference management with GSM/UMTS/LTE, and limited hardware impact on GSM/EDGE base stations. A critical point was that NB-CIoT module cost estimates could even be lower than GSM modules, while NB-LTE costs, though lower than eMTC, were expected to remain higher than GSM modules.
A more detailed comparison between NB-CIoT and NB-LTE is available in 3GPP document RP-151550.
3.2 Standardization Progress of NB-IoT
The core 3GPP specifications for NB-IoT were scheduled to be frozen in June 2016, with performance-related standards completed by September 2016, and conformance test specifications completed by December 2016.
