Like all spectrum, WiFi is subject to interference. Most licensed spectrum has strict rules against interference and there are generally very specific rules about how to handle contention if somebody is interfering with a licensed spectrum-holder. But WiFi is the wild west of spectrum and it’s assumed there is going to be interference between users. There is no recourse to such interference – it’s fully expected that every user has an equal right to the spectrum and everybody has to live with the consequences.
I look at all of the different uses for WiFi and it’s not too hard to foresee problems developing in real world deployments. Consider some of the following:
- Just about every home broadband connection now uses WiFi as the way to distribute data around the house between devices.
- Comcast has designed their home routers to have a second public transmitter in addition to the home network, so these routers initiate two WiFi networks at the same time.
- There is a lot of commercial outdoor WiFi being built that can bleed over into home networks. For example, Comcast has installed several million hotspots that act to provide convenient connections outside for their landline data customers.
- Many cities are contemplating building citywide WiFi networks that will provide WiFi for their citizens. There are numerous network deployments by cities, but over the next few years I think we will start seeing the first citywide WiFi networks.
- Cable companies and other carriers are starting to replace the wires to feed TVs with WiFi. And TVs require a continuous data stream when they are being used.
- Virtual reality headsets are likely to use WiFi to feed the VR headsets. There are already game consoles using WiFi to connect to the network.
- There is a new technology that will use WiFi to generate the power for small devices like cellphones. For this technology to be effective the WiFi has to beam continuously.
- And while not big bandwidth user at this point, a lot of IoT devices are going to count on WiFi to connect to the network.
On top of all of these uses, the NCTA sent a memo to the FCC on June 11 that warned of possible interference with WiFi spectrum from outside through the LTE-U or LAA spectrum used for cellphones. Outside interference is always possible, and in a spectrum that is supposed to have interference this might be hard to detect or notice for the average user. There is generally nobody monitoring the WiFi spectrums for interference in the same ways that wireless carriers monitor their licensed spectrum.
All of these various uses of the spectrum raise several different concerns:
- One concern is just plain interference – if you cram too many different WiFi networks into one area, each trying to grab the spectrum, you run into traditional radio interference which cuts down on the effectiveness of the spectrum.
- WiFi has an interesting way of using spectrum. It is a good spectrum for sharing applications, but that is also its weakness. When there are multiple networks trying to grab the WiFi signal, and multiple user streams within those networks, each gets a ‘fair’ portion of the spectrum which is going to somehow be decided by the various devices and networks. This is a good thing in that it means that a lot of simultaneous streams can happen at the same time on WiFi, but it also means that under a busy load the spectrum gets chopped into tiny little steams that can be too small to use. Anybody who has tried to use WiFi in a busy hotel knows what that’s like.
- All WiFi is channelized, or broken down into channels instead of being one large black of spectrum. The new 802.11ac that is being deployed has only two 160 MHz channels and once those are full with a big bandwidth draw, say a virtual reality headset, then there won’t be room for a second large bandwidth application. So forget using more than one VR headset at the same time, or in general trying to run more than one large bandwidth-demanding application.
It’s going to be interesting to see what happens if these problems manifest in homes and businesses. I am imagining a lot of finger-pointing between the various WiFi device companies – when the real problem will be plain old physics.