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LoRa – Could this Proprietary Standard Deliver the Bandwidth

lora Why LoRa by Semtech

LoRa is a system finding some uses in Amateur Radio, but this is limited to operation over poor links and lower bandwidths. It does seem a good fit for point-to-point links on the 920MHz. band where its spread spectrum potential can be used.

LoRa (from "long range") is a proprietary low-power wide-area network modulation technique that is popular for connecting the IoT. It is patented and was acquired by Semtech Corporation in 2012. They went on to form the LoRa Alliance who now manage the standard. Primarily designed for use on the unlicensed bands throughout the world, low-cost hardware versions are available for the following bands: 433-435MHz, 863–873 MHz, 915–928 MHz and as a special version for the 2.4GHz band. Extreme noise immunity and long range is achieved using spread spectrum and error correcting coders, low power is achieved by compromising duty cycle and versatility. The output power of the available hardware is between 2-20dBm, throughput between 0.3 kbit/s and 27 kbit/s and range between 3-10 miles.

Some of the available bands overlap the licensed amateur bands which allow for spread spectrum communications. It is possible to turn off any encryption within LoRa which means the available devices could be used. There are some examples of using LoRa on 70cm for troposcatter and old (2016-2018) examples of making 70cm packet transmissions but little current development. A recent article demonstrating moon-bounce on 70cm was published in Dec 2021 suggesting LoRa is still under active experimentation.

The available LoRa embedded radio hardware can be configured for different bandwidths and data rates, to meet the 100KHz limit on 70cm the data rate has to be low. Using the LoRa Calculator you can calculate the highest achievable rates. This comes out to a low 4600bps using a bandwidth of 62.5KHz. If we stretch the amateur licensed bandwidth to be 125KHz, then things improve to give a data rate of 9300bps which is still a low data rate. A comparable 2GFSK modulation system is specified at a usable 65000bps while still meeting the CFR 47 Part 97.3 requirements.

Things could be improved on the 920MHz band where the licensed bandwidth can be much higher. The highest data rate specified for LoRa hardware is with minimal spreading, then at a bandwidth of 500KHz is 37000bps. This is still less than modes like 2GFSK or 4GFSK but LoRa has a much better link bandwidth and so will require much less power and quality of link.

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Monday, 20 May 2024