LPWAN and spectrum control


Low Power Wide Area Networks (LPWAN) for the Internet of Things use general authorisation spectrum (also known as the ISM band) in the 870-876 MHz, 915-921 MHz, 863-870 MHz bands, with no guaranteed interference protection. They are based on conditions of use that allow for spectrum sharing, but these conditions only operate within certain limits. They are predicated upon not exceeding a density level (number of devices per unit of volume, communication time of each device) considered plausible when the spectrum was opened up. These limits could be exceeded if the success of these applications exceeds the initial forecasts, as seems set to happen in the near future.

Business investment in these low-power networks is set to soar, and regulation must be put in place to protect their operation. Two phenomena related to the use of spectrum under general authorisation may entail risks for these networks. The first of these is non-compliance with the rules of spectrum use or interference created by other users. To protect the networks, ANFR should be required to ensure compliance with the rules of use and to deal with interference incidents. Its action could be envisaged as either preventive or corrective. Leverage for preventive action lies in market supervision, to ensure the compliance of devices offered for sale. Laboratory testing would be carried out to test compliance under normal operating conditions. Further development of test protocols would probably be required to make this possible. Corrective action would involve inspecting devices in situ in the event of interference.

The second risk for these networks is that, if the devices are deployed in great number, the density limits used to draw up the operating rules laid down as standards could be exceeded. Spectrum sharing only works well if the shared frequency remains operable without coordination between the various users, which supposes a limited call on resources by each of them for positive statistical effects. As with any other system (Internet, LAN, IT or road networks), if the utilisation rate exceeds forecasts, access to the resource is degraded. Above a certain threshold, the overall effective utilisation rate for each device will shrink rapidly or even collapse, because the collision rate will rise faster than the required utilisation rate. This outcome seems unavoidable if these low-power networks enjoy the success they envisage, and will probably occur by geographical area, starting with the most sensitive; at this stage of network deployment, this would be fraught with major economic consequences.
To avoid this risk, ANRF is proposing to contribute, in conjunction with ARCEP, to observation of general authorisation spectrum usage, putting the Agency in a position to intervene before the threshold of saturation is reached. This would then make it possible to define the actions required for the overall proper functioning of general authorisation spectrum, either by improving the spectrum utilisation rules to allow for a higher spectrum usage rate, or by increasing the frequency bands available whilst ensuring the proper distribution of usage by the various users.

Proposal 1

ANFR will monitor usage of general authorisation spectrum to ensure the economic development of low-power networks used for the Internet of Things, in order to improve resources and the rules of spectrum sharing (optimisation of spectrum usage).

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