Rohde & Schwarz: NB-IoT (Narrow Band IoT) Devices Focus on Machine-type Terminals

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Machine type communications (MTC) are distinguished as wireless technology devices that operate with little or no human intervention. They feature fully automatic generation, exchange and processing of data. MTC is being used in applications where smart services are needed, such as utilities, manufacturing and transportation. It is estimated that as many as 50 billion such wireless devices will be in service by 2020, communicating much more often with other machines and devices than with humans.

Machine Type Communications

MTC were introduced as a major aspect of 3GPP Release 12. Such devices offer machine-to-network types of communication, and include tools such as sensors, actuators, sniffers and detectors. The main motivations for developing these devices includes a reduction in signaling overhead, less complex (and therefore less expensive) hardware, enhanced coverage, and energy savings.

For machine type communications, LTE has introduced several protocol features for less frequent data communication between the network and the device, all of which extend battery life. A very long paging cycle allows the device to be in idle mode for extended periods of time, until it needs to awaken to see if there is any new data for it to process. DRX (discontinuous reception) means that there may be a lengthy delay when such a device receives new data, as it may have been in an idle state when the data arrives. Finally, a reduction in signaling permits location updates or periodic tracking to take place only every few days. This protocol feature is especially useful for a machine-type terminal that is stationary, where mobility tracking is unnecessary. The reduced complexity of these devices relative to human-controlled devices saves energy in terms of electricity cost and battery life.

NB-IoT (Narrow Band IoT) devices focus on machine-type terminals and communications. These devices use many of the protocol features discussed earlier to help establish a long battery life (several years, in many cases).

Enhancements to Machine Type Communications

Several enhancements to MTC, especially for Narrow Band IoT, were introduced in Release 13. The motivation for developing NB-IoT is improved coverage in those areas where coverage might otherwise be difficult. It was designed for maximum acceptable path loss so that it can be used deep indoors – NB-IoT sensors may be placed inside buildings, in basements and behind concrete walls or metal doors. Very narrow band subcarriers and power density are needed to achieve this extended indoor coverage. Also, NB-IoT uses repetition of the data packets for better coverage.

NB-IoT technology uses a 200 KHz bandwidth and a 15 KHz sub-carrier spacing. It is important to note that due to its very narrow bandwidth, an NB-IoT device is not able to connect to an existing LTE base station. It will be necessary to develop an NB-IoT specific synchronization method.

Although NB-IoT devices do not operate in the LTE bandwidth, it does inherit several LTE aspects such as the EPC (Evolved Packet Core) network architecture and protocol flow. While NB-IoT does inherit much of its functionality and features from LTE technology, it has some of its own profile features. For example, NB-IoT uses only one resource block, while standard LTE uses six resource blocks to send synchronization signals such as PSS (primary synchronization signal), SSS (secondary synchronization signal) or PBCH (physical broadcast channel).

NB-IoT uses single tone operation. Its bandwidth can cover only one resource block (12 subcarriers), but it can use six subcarriers, three subcarriers, one subcarrier, or just a single tone, which is a 3.75 KHz subcarrier.

One important goal of NB-IoT is the ability to talk to a large number of devices. For example, in a skyscraper or tall building there could be thousands to tens of thousands of devices. The base station must be able to address and talk to all of them. NB-IoT’s narrow bandwidth and single tone operation helps to accommodate this goal.

For security, NB-IoT may be able to send its own encapsulated protocol inside an LTE-controlled SMS (short message service) message. This makes such devices especially good and advantageous for non-standard or proprietary protocol systems.

NB-IoT uses many of the Release 12 protocol features for less frequent data communication to extend battery life. A battery life of more than 10 years can be expected in some cases.

In 3GPP Release 13, an enhancement of the protocol features introduced the Power Saving Mode (PSM). PSM was designed specifically for the requirements of IoT and machine-to-machine communications. It uses extremely long stand-by cycles and power-off cycles to significantly reduce power consumption in certain types of machine type communications. For example, devices that do not move (such as smart gas and water meters), devices that need uplink capability only (such as alarm systems) and devices that a network needs to talk to only rarely are all good candidates for this Power Saving Mode, which improves battery time substantially.

NB-Iot In Action

Singapore was among the first countries to deploy a nationwide narrowband Internet of Things (NB-IoT) network in 2018. Learn more about NB-IoT field test procedure, including results from NB-IoT measurements underground here.

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