The NB-IoT standard — its benefits and test challenges
With more than 10 standards already being proposed for low-power applications related to the Internet of Things, it seems reasonable to ask why we might need another one. Yet NarrowBand IoT (NB-IoT), which forms part of the LTE-Advanced Pro (3GPP Release 13) standard that was finalised in June 2016, is perhaps the most eagerly-anticipated new protocol to join the ranks of those addressing this application. What are its benefits, and how can we ensure its smooth deployment and interoperability?
The advantages of the NB-IoT standard are perhaps best appreciated by first looking at some of the other contenders and their respective strengths and weaknesses. Some machine-type communications (MTC) standards are either local area networks (LAN) such as Wi-Fi 802.11ah (also known as HaLow) or personal area networks (PAN), like ZigBee or Bluetooth, and these require the use of a gateway using another comms technology in order to actually connect to the IoT. Several of the new Low Power Wide Area (LPWA) technologies – whether they are open standards like Weightless, or proprietary ones like LoRa, Telensa and SigFox – need a whole new network to be deployed, distinct from existing cellular infrastructure.
The main advantage of 3GPP-standardised, cellular LPWA solutions is that they have the support of a huge existing ecosystem, and can therefore both be deployed and scale up more rapidly, as well as having a single regulatory body that enforces the standard and controls interoperability across vendors and mobile operators. The LPWA standards supported by 3GPP now include the low-power LTE variants Cat-0 and Cat-1, and LTE eMTC, as well as NB-IoT. There is also a 2G-based standard, EC-GSM-IoT (Extended Coverage GSM IoT).
The earlier LTE-based standards (Cat-0 and Cat-1) that were proposed as solutions for MTC prior to Release 13 failed to secure a significant share of the IoT market. Unlike these, however, NB-IoT aims to meet the stringent targets for both low device modem cost of below $5 and long battery life in excess of 10 years, which are likely to make it much more successful.
Characteristics cited by the GSM Association as making NB-IoT particularly attractive to users include:
- Low power consumption: current consumption of the order of 1nA enables devices to operate for up to 10 years on a single charging cycle
- Low device unit cost
- Improved outdoor and indoor penetration coverage compared with existing wide area technologies
- Secure connectivity and strong authentication
- Optimised data transfer, supporting small, intermittent blocks of data
- Simplified network topology and deployment
- Ability to integrate into a unified IoT/MTC platform
- Network scalability to increase capacity
It is crucial that operators modify their current business models in order to capitalise on this opportunity and to fully exploit the huge market potential offered by IoT. Leading network operators are already going on record to say that NB-IoT promises to be a ‘game-changer’.
The NB-IoT technology can either be deployed ‘in-band’ in LTE spectrum – utilising resource blocks within a normal LTE carrier, or in the unused resource blocks within a LTE carrier’s guard-band – or ‘standalone’ for deployments in dedicated spectrum. The latter deployments mainly target the re-farming of GSM spectrum. Although encapsulated in the LTE-A Pro standard, NB-IoT requires a radical change to the physical and protocol layers in order to meet the specific requirements of the IoT. The channel bandwidth is 200 kHz (180 kHz plus guard bands), which also makes it suitable for GSM channel re-farming because it allows one GSM/GPRS channel to be replaced with a single NB-IOT channel. This narrow bandwidth makes it possible for LTE networks to accommodate a huge number of IoT devices without compromising the performance of regular mobile devices connected to the network. Some sources regard NB-IoT as a stepping stone towards the massive IoT use cases planned for 5G.
The NB-IoT devices can be flexibly deployed and scheduled within any legacy LTE system, sharing capacity and cell-site resources with other connected devices. This flexibility gives the mobile operator significant scope in order to make the best choice to suit the particular network scenarios they are designing. However, this same versatility – being able to re-use existing spectrum, in particular GSM carriers, or to work within an LTE band or in the gaps between existing spectrum allocations – also introduces new test challenges because of the diverse frequencies and the potential to interfere with other LTE traffic.
A further test challenge is the ability to ensure that the network can actually cope with the anticipated volume of attached devices, potentially exceeding that of current networks by an order of magnitude or more. A proliferation of IoT device types with very different traffic and application profiles is expected, which further adds to the complexity of validation. A scalable, proven LTE network test solution such as the VIAVI TM500 can provide this assurance.
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