Measuring up to the NB-IoT revolution

Dr. Stamatis Georgoulis
Product Director
Measuring up to the NB-IoT revolution
There is a rapidly growing demand for making connections to all kinds of devices as the Internet of Things (IoT) starts to become a reality. Well over 10 different standards are already being proposed for these low-power machine-type communications (MTC) applications.

Some of the 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 a different wired or wireless communications technology in order to actually connect to the IoT. Others are Low Power Wide Area (LPWA) technologies, where the network covers a much larger area. The optimum choice of technology will depend on the details of the precise use case, whether dense sets of similar connections, or more sparsely distributed terminals that need long distance wireless connections.

Some of the available 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. But the standard that has been most eagerly-anticipated, and is currently generating a lot of interest, is NarrowBand IoT (NB-IoT), which will use the existing LTE infrastructure. In its November 2016 Mobility Report Ericsson forecast that there will be 1.5 billion IoT devices with cellular connections by 2022, representing 70% of all LPWA connections.

The main advantage of using 3GPP-standardised cellular LPWA technology is that it has the support of a huge existing ecosystem, and can therefore both be deployed and scaled up more rapidly. Having a single regulatory body that enforces the standard and controls interoperability across vendors and mobile operators is also an advantage. NB-IoT forms part of the LTE-Advanced Pro (3GPP Release 13) standard that was finalised in June 2016. Other LPWA standards supported by 3GPP include the low-power LTE variants Cat-0 and Cat-1, and LTE eMTC (also known as Cat-M1). There is also a 2G-based standard, EC-GSM-IoT (Extended Coverage GSM IoT).

Cat-0 and Cat-1 were introduced as early LTE-based standards solutions for MTC prior to Release 13, but failed to secure a significant share of the IoT market. In contrast, NB-IoT aims to meet more stringent targets for low unit cost and battery life, which are likely to make it much more successful. Current consumption for devices working to the NB-IoT standard (also being called Cat-NB1) is of the order of 1nA, which enables devices to operate for up to 10 years on a single charging cycle, and the device modem cost is below $5. Higher protocols, signalling, and physical-layer processing requirements have all been simplified in order to reduce power consumption and complexity.

Other characteristics cited by the GSM Association as improving the attractiveness of NB-IoT to users include improved outdoor and indoor penetration coverage compared with existing wide area technologies, and secure connectivity with strong authentication. The simplicity of its network topology, and the ability to integrate NB-IoT into a unified IoT/MTC platform, are further advantages, as is the ease with which the network can be scaled to increase capacity.

Leading network operators are already going on record to say that NB-IoT promises to be a ‘game-changer’. Tier 1 operators have announced plans to commercialis NB-IoT during the later months of 2017, and although LTE licensed LPWA currently lags proprietary LPWA such as SigFox and LoRa it is expected to grow at a much faster rate. In order to capitalise on this opportunity and to fully exploit the huge market potential it offers, operators will need to modify their current business models and introduce creative charging structures which some believe may be based on blockchain technology. Some sources also regard NB-IoT as an important stepping stone towards the massive IoT use cases planned for 5G.

Spectrum usage

There are two ways that NB-IoT technology can be deployed. The first, known as ‘in-band’, uses resource blocks within a normal LTE carrier, or in the unused resource blocks within a LTE carrier’s guard-band. A second ‘standalone’ mode can be used for deployments in dedicated spectrum, and mainly targets 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 is what 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.

The technology supports two modes for uplink: a single tone with 15 kHz and/or 3.75 kHz tone spacing, or multiple tone transmissions with 15 kHz tone spacing. The PHY is simplified by not supporting turbo code for the downlink, while radio protocol features a single HARQ process and simplified status reporting. Key specification characteristics are summarized in Table 1.

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.

Test challenges

It is the versatility of NB-IoT – its ability to re-use existing spectrum, especially GSM carriers, or to work within an LTE band or in the gaps between existing spectrum allocations – which makes it challenging to test because the diverse frequencies give it the potential to interfere with other LTE traffic. Interoperability validation will be a key part of device testing, but will need to be performed rapidly and economically because of the constraints of high volume, low cost production.

The ability to ensure that the network can actually cope with the anticipated volume of attached devices, which potentially exceeds that of current networks by an order of magnitude or more, will pose an additional test challenge. A proliferation of IoT device types with very different traffic and application profiles (e.g. ranging from short, bursty data to continuous video streaming) is expected, which further adds to the complexity of validation. A scalable, proven LTE network test solution that uses real-life data usage, traffic and mobility scenarios, and which incorporates emulation of both conventional cellular user equipment and IoT devices, will be able to provide this assurance.

 

Deployment

  • In-band LTE
  • Guard-band LTE
  • Standalone

Downlink

OFDMA, 15 kHz

Downlink Peak Rate

250 kbps

Uplink

Single tone, 15 kHz  and 3.75 kHz spacing
SC-FDMA, 15kHz tone spacing, turbo code

Uplink Peak Rate

250 kbps (multi-tone)
20 kbps (single-tone)

Duplex Mode

Half Duplex, FDD

Bandwidth

180 kHz

Device Transmit Power

+23 dBm

 

Table 1: Key specification parameters for NB-IoT (Source: 3GPP)

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