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Comment by mchannon | Hacker News Reader

Simple- it inhabits the same band almost everything else inhabits- 2.4GHz. To an extent, the reason Bluetooth is unreliable is the same reason most Wifi is unreliable in crowded areas. There's a lot of appliances that use that bandwidth over incompatible standards.

Even worse are the "spark" kind of 2.4GHz appliances that don't play nice, like wireless camera systems and baby monitors. If your strong-signal wifi or bluetooth keeps dropping, it's far more likely to be one of those at fault than anything else.

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I am currently in the process of developing a BT based embedded system, and in my experience Bluetooth is extremely resilient to the crowded 2.4 GHz space. It has very good and fast frequency hopping, so it maintains a connection even in the presence of several WiFi access points covering all but a small portion of the 2.4 GHz band. We ran a test in our office which has many access points and laptops/phones, and even an alarm system that uses 2.4 GHz. At a distance of 10m between central and peripheral (with several dry-walls in between) we didn't lose a single bit over a full week of continuous data transmission at several 100 kbit/s.

There are limits of course. At some point the 2.4 GHz band is so saturated nothing low power gets through. But so far, I am pleasantly surprised by the reliability.

All this was done using BT 4.2 though, so maybe that helps.

I did some similar experiments with the original Ericsson Bluetooth development kits and got the same results, BT won over WiFi.

Yes. This is why I stopped using wireless keyboard and mouse. Despite the fact that they are within close proximity to their receivers, there is frequent signal instability, resulting in spikes in input lag and outright input loss.

Why is that range so popular? When presented with what appears (perhaps naively) to be a vast range of frequencies to use, why do so many wireless specs settle on the same thing?

Its an ISM band and not heavily regulated. There are only a few such bands.

It's unlicensed worldwide -- free and easy to use. Same as the 900MHz and 5GHz bands. It's a political/regulatory decision, not technical.

(And the higher the frequency, generally the more bandwidth is available, but chipsets are a little more expensive.)

The technical reason is they do not travel through walls that well, so they would make very bad bands for things like radio stations or cell phones.. so why not give it to people to use for local devices.

Actually, 900MHz ISM band exists only in ITU Region 2 (ie. Americas), in rest of the world it is usually allocated to GSM and some IIRC aviation related use in the middle of GSM up-down guard band, both are things that you don't want to interfere with, because somebody will care and come after you. 5.8GHz is universally accepted as ISM, but sometimes shared with licensed users (eg. weather radars), who have priority.

Fun fact: It's available worldwide because they wanted to use Microwaves on ships and planes. https://www.indiegogo.com/projects/why-2-4ghz-chasing-wirele...

Because it's unlicensed. It's unlicensed because it's close to the frequency designated for household microwave ovens.

Much of the EM spectrum is licensed. 2.4GHz is one of the 'unlicensed' bands set aside for consumer electronics, meaning no special permit is required to create something that uses radio within it. That's the gist of it.

Different radio frequencies have different ranges and propogation effects depending on local weather conditions, absorbtion by humidity etc. Generally high-frequency radio is short range but high bandwidth, which is perfectly suited to what consumers want.

To add, the US Department of Commerce puts out a great graphic [1] showing how the spectrum is split up. The only bands available are labeled "Amateur" in a greenish box.

https://upload.wikimedia.org/wikipedia/commons/c/c7/United_S...

The green amateur bands are in no way "available". Those are the Amateur (Ham) Radio bands.

N9NAY

The bands typically thought of as "available to electronics" (meaning available without a license) are designated on that chart as ISM bands. (https://en.wikipedia.org/wiki/ISM_band)

This doesn't seem to be a hard and fast rule all the time (eg some wireless runs at 5Ghz I believe, a bit off from the 5.8Ghz ISM band.) I believe WiGig is roughly centered around the ISM 61Ghz band though.

Use of the radio spectrum is regulated (e.g. by the FCC in the US). Different things are allowed or not, depending on the frequency. 2.4GHz is one of the few frequencies which are allowed for consumer use without much restriction; hence that's what everything uses.

There's a fair amount of restriction, the difference being if you agree to operate within the restrictions you don't need a license.

The FCC and other government bodies (ITU) in other countries tightly control the radio spectrum to prevent interference. There are a few bands that are set aside for general use called the ISM bands (industrial, scientific, medical). In those bands you can emit RF that might interfere with other devices. So you can run stuff like wifi, cordless phones, induction heaters, and microwaves that emit RF energy that can cause interference without a license (subject to some restrictions).

https://en.wikipedia.org/wiki/ISM_band

AFAIK, there are not so much unlicensed frequency ranges that are available almost worldwide. 2.4 GHz was initially reserved to use in microwave ovens that can cause interference in that range, then spread-spectrum technologies (such as used in wifi) that are not sensitive to noise from ovens became cheap so this frequency range became useful for that.

Other popular unlicensed range - 443 Mhz has much lesser bandwidth so it's popular for slower data transfers, i.e. in doorbells and temperature sensors. Also AFAIK it requires larger antennas because of longer wavelength.

5 GHz wifi is only recently started to become popular because, I think, there are some problems in implementing such high frequencies, or because it's more affected by walls and furniture.

As a general rule, high-frequency transmissions suffer from short range, particularly in an atmosphere. 5GHz was implemented in 802.11a in the early days of wifi, but suffered shorter range than 802.11b despite its higher bit rate. However, as it's not used as much by consumer devices, the spectrum is generally clearer so you get more consistent data rates.

802.11n and 802.11ac get around this by dynamically hopping between the two bands as necessary to get the clearest signal at the current distance.

> 802.11n and 802.11ac get around this

11n is available on both 2.4GHz and 5GHz. 11ac is 5GHz only.

I don't think there's any specific hopping thing in n/ac. It's just normal roaming between APs with the same SSID, if you use the same SSID for both frequencies. Same roaming would happen with just 11a and 11g.

Because it is the resonant frequency of water. Early microwave ovens polluted that frequency band so heavily that no other service used it. Nowadays, microwave ovens don't send out radio waves any more, so the frequencies are available for other services.

Which is a bit of a shame, since the resonant frequency of water is, by definition, absorbed by water, like wet walls or walking water-bags like you and me. Other frequencies would be much better-suited for human cohabitation, but that's historical evolution for you.

"Nowadays, microwave ovens don't send out radio waves any more"

Every microwave oven I've ever had, including name-brand ones purchased in the last year, sent out loads of interference on one or more wifi channels.

This morning I noticed that my connection at the breakfast table was really crappy. The upstairs hotspot likes to change channels every few days, and it had picked 11. When the microwave stopped, everything cleared up, so I forced it to channel 1 and tested with the microwave again. No problems there.

Every single sentence in your post is incorrect. https://www.indiegogo.com/projects/why-2-4ghz-chasing-wirele...

My guess is because most ranges are already reserved for other types of devices. I think the 2.4GHz spectrum is one of the few open for general consumer use.

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