Holiday comes to us: SCRF doubled the ISM band of 868 MHz

Published on October 10, 2018

Holiday comes to us: SCRF doubled the ISM band of 868 MHz

    A short but important news for those involved in IoT: GKRCH officially expanded the unlicensed 868 MHz band, in which networks such as LoRaWAN, Strizh / Waviot, Sigfox and others traditionally live.

    Officially, this is called "non-specialized devices of small radius of general use", and the changes are fixed in Appendix 12 to the Decision of the State Committee for Emergencies No. 18-46-03-1 of September 11, 2018.

    It was:

    • 864.0 - 865.0 MHz - power up to 25 mW, duty cycle up to 0.1% or LBT *, use at airports is prohibited
    • 868.7 - 869.2 MHz - power up to 25 mW, duty cycle without restrictions, use without restrictions

    It has become (changes are marked in bold):

    • 864.0 - 865.0 MHz - power up to 25 mW, duty cycle up to 0.1% or LBT *, use at airports is prohibited
    • 866.0 - 868.0 MHz - power up to 25 mW, duty cycle up to 1% or LBT *, use at airports is prohibited, power spectral density up to 1000 mW / MHz
    • 868.7 - 869.2 MHz - power up to 100 mW, duty cycle up to 10% or LBT * , unlimited use

    * Listen Before Talk. True, no one knows what this means, since in Russian legal acts the technical essence of LBT is not deciphered anywhere. And, in fact, no one uses it.

    What does this mean specifically for LoRaWAN networks?

    Firstly, the possibility of leaving the 864-865 MHz band to the new 866-868 MHz band. The old range is inconvenient for two reasons - both because of the duty cycle of only 0.1%, and because of the obstruction of the frequency response of existing base stations by 2-3 dB in its lower half.

    A typical LoRaWAN base station can serve 8 frequency channels in 200 kHz increments - that is, with the old regulation, 2 channels in the upper range and 5 channels in the lower range were obtained, total 7. New regulation allows you to deploy all 8 channels in the upper and middle ranges, necessary (using a BS with two radio blocks) - as many as 16 channels. This does not require changing the current LoRaWAN standard, since the base station can transmit to the device a list of channels available to it when it is registered on the network.

    Secondly, at base stations, it is possible to increase the exhaust air power to 100 mW in order to more easily reach the end devices in the downstream channel. This allows you to organize the RX2 downlink with a higher speed than the upstream, and reduce the load of ether with a large number of devices that use the downlink.

    Thirdly, in all ranges there was a restriction on the duty cycle. It’s now impossible to put a piece of iron that will poison everyone’s life, continuously radiating something to the ether. On the other hand, this imposes restrictions on the operation of the base station - now it cannot occupy one channel more than 10% of the time.

    However, restrictions on the base station can be circumvented by the network settings - in the downstream channel, the base station can respond to the device either at the same frequency on which the latter itself went on the air, or at a fixed frequency RX2. Actively using a combination of them, you can “smear” the airtime of the base station on different frequency channels - taking into account that RX2 can now be done faster by four times the power, this generally solves the problem.

    Fourthly, in the new range there is a restriction on the power spectral density - 1000 mW / MHz. This means that UNB systems with their bands of 100-200 Hz cannot work in it - with an output power of 25 mW and a band of 100 Hz, the spectral density will greatly exceed the allowed one. Simply put, this range is completely at the mercy of broadband systems - LoRa and mesh networks on 802.15.4.

    Fifthly, it is tempting to increase the number of standard device registration channels - these are the channels on which the BS must listen to the broadcast, when you turn on or reboot, the device may exit on any of them. At the moment there are two such channels, both in the upper range, and one of them coincides with the RX2 channel.

    The new regulation allows you to redraw the channels according to the European model - to highlight three full-fledged device registration channels, none of which overlap with RX2. Unfortunately, this will require the adoption of a new regional standard (LoRaWAN Regional Parameters) for Russia, which, in turn, will require flashing devices and reconfiguring base stations. However, there remains a variant of adding one new registration channel - then devices already made under RU864-870 will continue to work normally. On the third hand, there are still few such devices (although for now new RPs will be accepted there ...). Fourth, the current channels allow you to use devices at airports without changing their firmware - the base station simply does not have to give them additional channels when registering on the network, and that’s all.

    In general, the question is debatable, so I summarize briefly: there will be no changes in the LoRaWAN Regional Parameters for the range RU864-870.

    The firmware of the devices does not need to be changed, you can add new ranges to the network settings right now, if you wish. They will be distributed automatically to the devices (but since the device that has already been registered already works on the old frequency grid, in practice the new one will be introduced either in addition to the old one to increase the total number of channels or in newly deployed networks).

    Fourth, we still do not have harmonization with Europe, the use of European devices and European settings is still illegal and may result in confiscation of equipment. The European channels - 868.1, 868.3, 868.5 MHz and 869.525 MHz - still do not fall into any of the allowed bands in Russia.

    PS If we talk about purely amateur radio devices, then you have every right to do whatever you want for the range 866-868 MHz, subject to three conditions - power limits of 25 mW, duty cycle of 1% (this is 36 seconds per hour) and using a broadband signal. If you have devices broadcasting in the range of 868.7-869.2 MHz for more than 360 seconds per hour, now they should be limited.