Three NB-IoT deployment models – and why NB-IoT performance is not what it should be
Narrowband IoT (NB-IoT) is a cellular-based low-power wide-area (LPWA) technology. Specified in Release 13 of the 3GPP in June 2016, it coexists with GSM and LTE in licensed frequency bands.
NB-IoT is associated with simple sensor applications, which make up most of the burgeoning internet-of-things (IoT) space. It is considered a rival to proprietary LPWA networking technologies like LoRaWAN and Sigfox, and tends to be paired with LTE-M, another cellular LTE-based solution.
In fact, all four offer different capabilities within the LPWA space, and are increasingly serving different business cases. NB-IoT provides a low-cost, long-lasting, high density solution, with good penetration, including hard-to-reach indoor coverage.
It uses a 200 KHz frequency band, which corresponds to one resource block in GSM and LTE transmissions. It uses orthogonal frequency-division multiplexing (OFDM) modulation for downlink communication and the single-carrier frequency-division multiple access (SC-FDMA) scheme for uplink communications.
NB-IoT data rates are limited to 200 kbps for the downlink and to 20 kbps for the uplink. The maximum payload size for each message is 1,600 bytes. NB-IoT technology can achieve 10 years of battery lifetime when transmitting 200 bytes per day on average. The latest Release 15 version of NB-IoT introduces localisation methods, multi-cast services, and mobility.
NB-IoT can be deployed in three ways: in stand-alone operation, guard-band operation, and in-band operation.
Stand-alone operation describes a deployment where NB-IoT is used exclusively within a spectrum holding, whether in a private or public network arrangement. This implementation gives the best performance – and, in fact, the type of performance claimed by cellular operators deploying NB-IoT in the guard band.
The world’s first standalone private NB-IoT network launched in Florida last month, using upper 700 MHz A-Block spectrum. The operator, San Francisco-based startup Puloli, is targeting utilities and other critical infrastructure industries.
Puloli claims a distance of up to 25 miles from its tower sites, making it “one of the most capital efficient” ways for utilities to connect industrial assets, run process analytics, and drive digital change, it says.
Every other NB-IoT network that has been launched to date has has been deployed by a cellular operator using the LTE guard band, designed as a buffer between strips of spectrum carrying mobile broadband services. The GSMA counts 82 operator-run NB-IoT networks, as of May 2019.
All of these utilise the unused resource blocks within an LTE carrier’s guard band, which impacts performance. Guard bands are there for a reason: to stop roll-off of output power from base stations into adjacent LTE channels. The signal-to-noise ratio increases for NB-IoT if it co-exists with roll-off from LTE channels – and performance suffers, and misses the levels typically claimed online.
“It is a great example of how this industry can be misleading,” said one sage industry source to Enterprise IoT Insights this week.
The third implementation mode, in-band operation, utilises, resource blocks (frequencies) within an LTE carrier that are otherwise used for mobile broadband resources. This method impacts both NB-IoT and LTE performance, as it bundles the former directly into the latter’s channels.