Anytime there are too many WiFi networks in the same proximity it’s inevitable to have contention between networks. Such contention will cause a WiFi network to slow down since the current WiFi standards tells a WiFi device to back-off whenever it sees interference, meaning that two neighboring WiFi networks will both back off when there is contention. People with slow WiFi tend to blame their router for their problems, but often it is this contention that is slowing them down.
Using research first done at MIT and recently revived at Northwestern University, engineers have figured out a way to greatly reduce the contention between neighboring WiFi networks using a technology they are dubbing as Wi-FM since it uses a tiny slice of FM frequency to resolve conflicts.
It’s not hard to imagine situations where WiFi can become congested. For instance, consider somebody living in an apartment building who has other WiFi routers over, under and on all sides, all relatively close. We tend to think of WiFi as being a pretty reliable transmission medium, but when there are many networks all trying to work at the same time there can be a tremendous amount of interference, and a major degradation of throughput.
The Wi-FM technology uses the tiny slice of FM radio spectrum that is reserved for the Radio Data System (RDS). This is the spectrum that is used to transmit the content information about the FM radio programming and is used in your car radio, for example, to tell you the name of the song and the artist you are listening to.
Along with the broadcast information the RDS system also utilizes a time slot technology that allows it to sync up the broadcast information with songs as they change. The Wi-FM technology takes advantage of these time slots and uses the quiet times when there is no broadcast information being sent to monitor the WiFi signals and to direct packets so that they don’t interfere.
WiFi utilizes multiple channels, and if all channels are used efficiently then much of the interference between neighboring networks can be avoided. But there are no techniques that can direct WiFi to change channels on the fly that can be done easily from inside the WiFi spectrum without eating up a lot of the available spectrum in the effort. Using the slice of FM frequency as an external traffic cop allows for the rapid routing of contentious packets to different channels and can greatly reduce contention and interference.
This technology would probably be best used today in places like apartment buildings where there are multiple WiFi networks. But we are moving into a future where there is likely to be a lot more WiFi interference. For example, there are plans to use a continuous WiFi signal to power cellphones and small IoT sensors. And the cellular industry wants to use WiFi as overflow for LTE calls.
So however busy WiFi is today, the chances are that it’s going to get a lot busier in the future. And that means there will be lot more interference between packets. Wi-FM is just one of many techniques that are probably going to be needed if we want to keep the public spectrum usable in busy places. Otherwise, the interference will just accumulate to shut the spectrum down at the busiest times of the day.