SigFox / LoraWAN

[robin]

Looking at it further with an isotropic antenna (uniform radiation in any direction) you're limited to 14dBm in the 868MHz spectrum, so there's no real reason for the antenna to be all that big ... in fact it could be tiny.

I guess the receivers must have fantastic sensitivity in order to get any sort of range!

Cheers,
Robin

[scott_e]

Thanks again for the reply Robin. You are spot on.

"The secret to LoRaWAN — the thing that allows it to achieve such incredible range with remarkably modest transmit power — is Semtech's LoRa modulation. A derivative of chirp spread spectrum (CSS), this takes advantage of the fact that by spreading a signal across a broader band of spectrum, a system can be made which will work with a far worse signal-to-noise ratio (SNR).The spreading in spread spectrum systems is generally achieved by multiplying the original data signal with a spreading code or chip sequence, that is at a much faster rate than the data signal and therefore spreads the resulting signal bandwidth beyond that of the original. With LoRa a chirp signal is generated that continuously varies in frequency and it is this onto which the spread/chipped data signal is then modulated. Given a fixed modulation bandwidth — amount of radio spectrum occupied by the transmitted signal — the amount of spreading can then be varied, in order to trade the available data throughput for greater range and resilience to interference. The spreading factors (SF) used are from 7 to 12 and with each increase comes a link budget gain of an additional 2.5dB, with Semtech modem ICs being specified to have a sensitivity of an impressive -134dBm at a spreading factor of 12. Furthermore, since these are orthogonal and minimally interfere at the receiver, the total radio channel capacity is the sum of that for each spreading factor. The modulation also includes provision for error correction. Beyond the noted low power and long range capabilities, other key properties include that it is relatively simple, multipath/fading and doppler shift resistant, and suited to use with low cost, high efficiency RF power amplifiers".

Licence-except spectrum and encryption too which is a big issue looming for field devices in the telematics / m2m / IoT industry.

Will ping you a couple of articles if you are interested.

[robin]

Looks interesting, though my understanding of these things is limited (I am no RF weenie!). I think the good news for you is that on private property you'll need no planning permission - the transmit power levels are so low and the aerial so small that no-one will even know you're running it

Cheers,
Robin

[fd]

Came across this as a fluke . . .

I've been using LORA RF tech recently, very impressive, super low power, very impressive range compared to more common FSK/narrow band transceivers. Antenna on 868MHz is tiny, 1/4 wavelength is quite sufficient, even 400oddMHz are only twice the size - still tiny. Have been using the transceivers raw rather than as an internet connected thang . . . however for max range (as usual) your effective bitrate over the air is very low . . . itro <1Kbit. I can easily achieve >5K range LOS, 2K NLOS with legal 868MHz kit. Lots of very cheap dev kit around . . . http://www.rocketscream.com/blog/produc ... ith-radio/ for example . . . spec an RF95 LORA xceiver. Get yourself a cheap 20 quid SDR to understand how it all works . . . easy . . . connecting it to some internet peesh megaframework is the easy bit

Fd

[graeme]

We're using the kit from Multitech for our trials. Conduit gateway has modular radio slots so you can add cellular or wifi backhaul for example, and mdots, which are mbed-programmable transmitters, but you can ditch the mbed world very quickly and use anything you like). Makes for nice tech demos.

It's good stuff, nicely packaged. They have an IP67 gateway too which we're going to stick on the roof. We're also looking for sites in Aberdeen, planning city-wide LoRaWAN coverage in 2017.