15

The Wi-Fi Alliance's relatively new Wi-Fi HaLow (802.11ah) specification seems to be ideal in some characteristics for IoT devices:

Wi-Fi HaLow will enable a variety of new power-efficient use cases in the Smart Home, connected car, and digital healthcare, as well as industrial, retail, agriculture, and Smart City environments.

Wi-Fi HaLow extends Wi-Fi into the 900 MHz band, enabling the low power connectivity necessary for applications including sensor and wearables. Wi-Fi HaLow’s range is nearly twice that of today’s Wi-Fi, and will not only be capable of transmitting signals further, but also providing a more robust connection in challenging environments where the ability to more easily penetrate walls or other barriers is an important consideration.

However, as mentioned in the linked source, HaLow operates in the 900MHz frequency, which, according to eWeek, is an unlicensed frequency:

Unfortunately, the new HaLow standard doesn't have its frequencies to itself. Because the 900MHz band is shared with other licensed services, the new WiFi band is subject to interference from other users and there is no remedy when that interference happens.

For example, if a ham radio operator next door goes on the air with a powerful signal that wipes out your smart thermostat, you're out of luck. Because you're an unlicensed service, you're required to accept that interference.

However, if your smart thermostat happens to cause interference to that ham radio operator next door, then you're required to stop doing it. As an unlicensed user, you have few rights to the spectrum if someone else wants to use it.

Presumably this is related to the FCC rules which are commonly seen on RF products:

This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

Does this make HaLow too problematic for use as a communication method, since my transmissions could easily be forced to stop if someone else was transmitting in that frequency? If I wished to design a device using HaLow, how could I avoid interference which would require me to stop broadcasting?

  • 2
    There are 900 MHz GSM frequency bands as well which can interfere. – Bence Kaulics Dec 10 '16 at 12:16
  • 1
    Possibly it makes more problematic to use it as GSM traffic can be pretty intense IMO. – Bence Kaulics Dec 10 '16 at 12:21
  • 1
    I'd need to check, but I believe a licensed amateur can transmit the equivalent of 400 W isotopic. A GSM handset is closer to 2 W. – Sean Houlihane Dec 10 '16 at 21:08
  • 1
    Also, wifi is a pretty robust protocol -- if you live in an apartment building, you could easily be within range of a dozen different routers, but this does not stop everyone from using it, and presumably at reasonable performance level for essentially infinite streams of data (think of movie time...). A "harsh environment" in which data is often lost/corrupted will just hamper performance (there's parity checks, back-off algorithms, etc. and it does not give up easily). This doesn't answer the other half of the problem, but I suspect interfering w/ GSM won't be...so it's just ham... – goldilocks Dec 10 '16 at 21:18
  • 1
    The part I'm missing is to what extent the methodologies used to prevent nodes on the same wifi network from interfering with one another would mitigate the effect of interference generally. Some of them will I think help (back-off, error/parity checks), some not at all (time division), but I don't know anything about about the physics of radio interference, which is what I think you need to answer this effectively. – goldilocks Dec 19 '16 at 16:45
6

The WiFi we know and use now also share the 2.4 GHz frequency range with a lot of other technologies and applications which might interfere. If we have a look on the list of 2.4 GHz radio usage, a couple of items are there beside WiFi.

  • Many cordless telephones and baby monitors in the United States and Canada use the 2.4GHz frequency, the same frequency at which Wi-Fi standards 802.11b, 802.11g and 802.11n operate.

  • Bluetooth devices intended for use in short-range personal area networks operate from 2.4 to 2.4835 GHz.

  • Certain car manufacturers use the 2.4 GHz frequency for their car alarm internal movement sensors. These devices transmit on 2.45 GHz (between channels 8 and 9) at a strength of 500 mW.

  • ZigBee

  • My wireless mouse and keyboard.

Moreover the 2.4 GHz band has the following licensed users:

FIXED, MOBILE, RADIOLOCATION, Amateur & Amateur-satellite service

So accepting interference is pretty much the case right now too.

From The Verge's article, "There's a new type of Wi-Fi, and it's designed to connect your smart home":

It'll be in the 900MHz range, which has better reach and penetration than the 2.4GHz and 5GHz range that existing Wi-Fi operates in. (But, like existing Wi-Fi, it'll be in operating in unlicensed spectrum, so there may be interferences.) There does, of course, have to be a downside. And there is: HaLow isn't going to be as good at quickly transferring data. This isn't Wi-Fi for browsing the web; it's for transferring small bits of data on infrequent occasions. Device manufacturers can, to some extent, customize HaLow to their needs to get faster transfers, but that'll happen at the expense of battery life.

So as WiFi HaLow is designed for lower bandwidth and for battery saving low-power applications it might a be better solution if we are already talking about interference. As it is intended to transfer less data then original WiFi.

| improve this answer | |
  • 1
    That's very reassuring if it's not going to be any worse than the current Wi-Fi performance characteristics. Thanks a lot! – Aurora0001 Dec 21 '16 at 10:21
6

There are two aspects to this regulatory regime which you need to understand the impact of.

  1. Accept interference. One of the constraints of an amateur license is that continuous transmission is restricted. The underlying assumption is of a 2-way human-to-human conversation, so transmit time is unlikely to be longer than 15 minutes continuous. Beacons and similar are permitted, but there are restrictions. The impact of this is that maybe you will be denied connectivity for short periods, but this is unlikely to persist for a long period. There are very few ways of getting any guaranteed bandwidth without paying lots of money, so its a trade off.

  2. Not interfere. This is generally easier to comply with - Keep your transmissions narrow and clean so that there is space in the band for other users. A noisy transmitter could wipe out the whole band, and this would be unreasonable.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.