2.4 GHz radio use
[4] Wi-Fi (/ˈwaɪfaɪ/)[5] is technology for radio wireless local area networking of devices based on the IEEE 802.11 standards.
[6] Devices that can use Wi-Fi technologies include desktops and laptops, video game consoles, smartphones and tablets, smart TVs, digital audio players, cars and modern printers.
Hotspot coverage can be as small as a single room with walls that block radio waves, or as large as many square kilometres achieved by using multiple overlapping access points.
Many common materials absorb or reflect them, which further restricts range, but can tend to help minimise interference between different networks in crowded environments.
To guarantee no interference in any circumstances the Wi-Fi protocol requires 16.25 (11b) or 22 MHz (11g/n) of channel separation (as shown below).
While overlapping frequencies can be configured and will usually work, it can cause interference resulting in slowdowns, sometimes severe, particularly in heavy use.
Certain subsets of frequencies can be used simultaneously at any one location without interference (see diagrams for typical allocations): However, the exact spacing required when the transmitters are not colocated depends on the protocol, the data rate selected, the distances and the electromagnetic environment where the equipment is used.
[11][12][13] Most domestic microwave ovens operate by emitting a very high power signal in the 2.4 GHz band.
Older devices have poor shielding,[14] and often emit a very "dirty" signal over the entire 2.4 GHz band.
[a] This can cause considerable difficulties to Wi-Fi and video [16] transmission, resulting in reduced range or complete blocking of the signal.
The IEEE 802.11 committee that developed the Wi-Fi specification conducted an extensive investigation into the interference potential of microwave ovens.
However, some devices, especially wireless cameras, operate with (often unauthorized) high power levels, and have high-gain antennas.
Continuous transmissions interfere with these, causing "patterning" on the picture, sometimes a dark or light shift, or complete blocking of the signal.
This causes a very intense signal as viewed on a spectrum analyser, and completely obliterates over half a channel.
The result of this, typically in a Wireless Internet service provider-type environment, is that clients (who cannot hear the video sender due to the "hidden node" effect) can hear the Wi-Fi without any issues, but the receiver on the WISP's access point is completely obliterated by the video sender, so is extremely deaf.
Furthermore, due to the nature of video senders, they are not interfered with by Wi-Fi easily, since the receiver and transmitter are typically located very close together, so the capture effect is very high.
[citation needed] Many video senders on the market in the UK advertise a 100 mW equivalent isotropically radiated power (EIRP).
[citation needed] USB 3.0 devices and cables, if not shielded properly, may introduce noise to the 2.4 GHz band.
Products are coming onto the market cheaply which act as spectrum analyzers and use a standard USB interface into a laptop, meaning that the interference source can be fairly easily found with a little work, a directional antenna and driving around to find the interference.
It is better to use Ethernet or maybe PLC when Wi-Fi can be avoided (but beware of power surges, they may happen through any conductive cable).
In extreme cases, where the interference is either deliberate or all attempts to get rid of the offending device have proved futile, it may be possible to look at changing the parameters of the network.
Deploying additional base stations around the coverage area of a network, particularly in existing areas of poor or no coverage, reduces the average distance between a wireless device and its nearest access point and increases the average speed.
However, there is a maximum number of base stations that can be added, after which they disrupt the network more than that they help: any additional capacity is then sapped by control traffic.
[22] The alternative of increasing coverage by adding an RF power amplifier to a single base station can bring similar improvements to a wireless network.
However, care must be taken to use a highly linear amplifier in order to avoid adding excessive noise to the signal.
Wireless clients then automatically select the strongest access point from all those with the specified SSID, handing off from one to another as their relative signal strengths change.
On many hardware and software implementations, this hand off can result in a short disruption in data transmission while the client and the new base station establish a connection.
