Electromagnetic interference at 2.4 GHz
Encyclopedia
Electromagnetic interference
at 2.4 GHz
can affect various devices.
This article details the different users of the 2.4 GHz band, how they cause interference to other users and how they are prone to interference from other users.
s and baby monitor
s in the United States
and Canada
use the 2.4 GHz frequency, the same frequency at which Wi-Fi
standards 802.11b, 802.11g and 802.11n operate. This can cause a significant decrease in speed, or sometimes the total blocking of the Wi-Fi signal when a conversation on the phone takes place. There are several ways to avoid this though, some simple, and some more complicated.
The last will sometimes not be successful, as numerous cordless phones use a feature called Digital Spread Spectrum. This technology was designed to ward off eavesdroppers, but the phone will change channels at random, leaving no Wi-Fi channel safe from phone interference.
devices intended for use in short-range personal area network
s operate from 2.4 to 2.4835 GHz. To reduce interference with other protocols that use the 2.45 GHz band, the Bluetooth protocol divides the band into 79 channels (each 1 MHz wide) and changes channels up to 1600 times per second. Newer Bluetooth versions also feature Adaptive Frequency Hopping which attempts to detect existing signals in the ISM band
, such as Wi-Fi
channels, and avoid them by negotiating a channel map between the communicating Bluetooth devices.
internal movement sensors. These devices broadcast on 2.45 GHz (between channels 8 and 9) at a strength of 500 mW. Because of channel overlap, this will cause problems for channels 6 and 11 which are commonly used default channels for Wi-Fi connections. Because the signal is transmitted as a continuous tone, it causes particular problems for Wi-Fi traffic. This can be clearly seen with spectrum analysers. These devices, due to their short range and high power, are typically not susceptible to interference from other devices on the 2.4 GHz band.
s operate by emitting a very high power signal in the 2.4 GHz band. Older devices have poor shielding, and often emit a very "dirty" signal over the entire 2.4 GHz band.
This can cause considerable difficulties to Wi-Fi
and Video senders, 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. A typical microwave oven uses a self-oscillating vacuum power tube
called a magnetron and a high voltage power supply
with a half wave rectifier (often with voltage doubling
) and no DC filtering
. This produces an RF pulse train
with a duty cycle
below 50% as the tube is completely off for half of every AC mains
cycle: 8.33 ms in 60 Hz countries and 10 ms in 50 Hz countries.
This property gave rise to a Wi-Fi "microwave oven interference robustness" mode that segments larger data frames into fragments each small enough to fit into the oven's "off" periods.
The 802.11 committee also found that although the instantaneous frequency of a microwave oven magnetron varies widely over each half AC cycle with the instantaneous supply voltage, at any instant it is relatively coherent
, i.e., it occupies only a narrow bandwidth. The 802.11a/g
signal is inherently robust against such interference because it uses OFDM with error correction information interleaved across the carriers; as long as only a few carriers are wiped out by strong narrow band interference, the information in them can be regenerated by the error correcting code from the carriers that do get through.
s typically operate using an FM
carrier
to carry a video signal from one room to another (for example, satellite TV or closed-circuit television
). These devices typically operate continuously but have low (10 mW) transmit power. However, some devices, especially wireless cameras, operate with (often unauthorized) high power levels, and have high-gain antenna
s.
Although the transmitter of some video cameras appears to be fixed on one frequency, it has been found in several models that the cameras are actually frequency agile, and can have their frequency changed by disassembling the product and moving solder links or dip switches inside the camera.
These devices are prone to interference from other 2.4 GHz devices, due to the nature of an analog video
signal showing up interference very easily. A carrier to noise ratio of some 20 dB is required to give a "clean" picture.
Continuous transmissions interfere with these, causing "patterning" on the picture, sometimes a dark or light shift, or complete blocking of the signal.
Non-continuous transmissions, such as Wi-Fi, cause horizontal noise bars to appear on the screen, and can cause "popping" or "clicking" to be heard on the sound.
Video senders are a big problem for Wi-Fi networks. Unlike Wi-Fi they operate continuously, and are typically only 10 MHz in bandwidth. 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. Wi-Fi also has a very wide spectrum, so only typically 30% of the peak power of the Wi-Fi actually affects the video sender. Wi-Fi is not continuous transmit, so the Wi-Fi signal interferes only intermittently with the video sender. A combination of these factors - low power output of the Wi-Fi compared to the video sender, the fact that typically the video sender is far closer to the receiver than the Wi-Fi transmitter and the FM capture effect means that a video sender may cause problems to Wi-Fi over a wide area, but the Wi-Fi unit causes few problems to the video sender.
802.11n Wi-Fi networks are proving to be a source of interference for other wireless data networks operating at 2.4 GHz.
(EIRP). However, the UK market only permits a 10 mW EIRP limit. These devices cause far more interference across a far wider area, due to their excessive power. Furthermore, UK video senders are required to operate across a 20 MHz bandwidth (not to be confused with 20 MHz deviation). This means that some foreign imported video senders are not legal since they operate on a 15 MHz bandwidth or lower, which causes a higher spectral power density, increasing the interference. Furthermore, most other countries permit 100 mW EIRP for video senders, meaning a lot of video senders in the UK have excessive power outputs.
/ IEEE 802.15.4
-based wireless data networks operate in the 2.45–2.4835 GHz band, and so are subject to interference from other devices operating in that same band. To avoid interference from IEEE 802.11
networks, an IEEE 802.15.4 network can be configured to only use channels 15, 20, 25, and 26, avoiding frequencies used by the commonly used IEEE 802.11 channels 1, 6, and 11.
s 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.
s, whereby plugging in the receiver with no transmitter attached will let you "see" the neighbour's video sender, this technique is considered part of the "Installation process". Where the channel of one system, such as a Wireless ISP cannot be changed, and it is being Interfered with by something such as a video sender, the owner of the video sender is normally very happy to assist with doing this, providing it is not too much work. However the problem comes when the interference is something such as a wireless CCTV camera which is mounted on a chimney and requires a long ladder to access. Such cameras, due to their height, cause serious problems across a wide area.
Yet another cure is to move from 2.4 GHz to another frequency which lacks the vulnerability to interference inherent at that frequency, for example the 5 GHz frequency for 802.11a/n.
have sharp "nulls" in their vertical pattern, so changing the tilt angle of sector antennas with a spectrum analyzer connected to monitor the strength of the interference can place the offending device within the null of the sector. High gain antennas on the transmitter end can "overpower" the interference, although their use may cause the effective radiated power
(ERP) of the signal to become too high, and so their use may not be legal.
The alternative of increasing coverage by adding an RF power amplifier to a single base station can bring similar improvements to a wireless network. The additional power offered by a linear amplifier will increase the signal-to-noise ratio at the client device, increasing the data rates used and reducing time spent transmitting data. The improved link quality will also reduce the number of retransmissions due to packet loss, further reducing channel occupancy. However, care must be taken to use a highly linear amplifier in order to avoid adding excessive noise to the signal.
All of the base stations in your network should be set to the same SSID (which must be different from all of your neighbors) and plugged into the same logical Ethernet segment (one or more hubs or switches directly connected without IP routers). 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. This potential disruption should be factored in when designing a network for low-latency services such as VoIP.
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
at 2.4 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
can affect various devices.
This article details the different users of the 2.4 GHz band, how they cause interference to other users and how they are prone to interference from other users.
Phone
Many cordless telephoneCordless telephone
A cordless telephone or portable telephone is a telephone with a wireless handset that communicates via radio waves with a base station connected to a fixed telephone line, usually within a limited range of its base station...
s and baby monitor
Baby monitor
A baby monitor, also known as a baby alarm, is a radio system used to remotely listen to sounds made by an infant. The transmitter unit, equipped with a microphone, is placed near to the child. It transmits the sounds the baby makes by radio waves to a receiver unit with a speaker carried by, or...
s in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
use the 2.4 GHz frequency, the same frequency at which Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
standards 802.11b, 802.11g and 802.11n operate. This can cause a significant decrease in speed, or sometimes the total blocking of the Wi-Fi signal when a conversation on the phone takes place. There are several ways to avoid this though, some simple, and some more complicated.
- Buy/Use wired phones.
- Buy DECT 6.0 (1.9 GHz), 5.8 GHz or 900 MHz phones, commonly available today.
- Use VoIP/Wi-Fi phones; these share the Wi-Fi base stations and participate in the Wi-Fi contention protocols.
- Test several different Wi-Fi channels to avoid the phone channels.
The last will sometimes not be successful, as numerous cordless phones use a feature called Digital Spread Spectrum. This technology was designed to ward off eavesdroppers, but the phone will change channels at random, leaving no Wi-Fi channel safe from phone interference.
Bluetooth
BluetoothBluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
devices intended for use in short-range personal area network
Personal area network
A personal area network is a computer network used for communication among computer devices, including telephones and personal digital assistants, in proximity to an individual's body. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters...
s operate from 2.4 to 2.4835 GHz. To reduce interference with other protocols that use the 2.45 GHz band, the Bluetooth protocol divides the band into 79 channels (each 1 MHz wide) and changes channels up to 1600 times per second. Newer Bluetooth versions also feature Adaptive Frequency Hopping which attempts to detect existing signals in the ISM band
ISM band
The industrial, scientific and medical radio bands are radio bands reserved internationally for the use of radio frequency energy for industrial, scientific and medical purposes other than communications....
, such as Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
channels, and avoid them by negotiating a channel map between the communicating Bluetooth devices.
Car alarm
Certain car manufacturers use the 2.4 GHz frequency for their car alarmCar alarm
A car alarm is an electronic device installed in a vehicle in an attempt to discourage theft of the vehicle itself, its contents, or both. Car alarms work by emitting high-volume sound when the conditions necessary for triggering are met, as well as by flashing some of the vehicle's...
internal movement sensors. These devices broadcast on 2.45 GHz (between channels 8 and 9) at a strength of 500 mW. Because of channel overlap, this will cause problems for channels 6 and 11 which are commonly used default channels for Wi-Fi connections. Because the signal is transmitted as a continuous tone, it causes particular problems for Wi-Fi traffic. This can be clearly seen with spectrum analysers. These devices, due to their short range and high power, are typically not susceptible to interference from other devices on the 2.4 GHz band.
Microwave oven
Microwave ovenMicrowave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
s operate by emitting a very high power signal in the 2.4 GHz band. Older devices have poor shielding, and often emit a very "dirty" signal over the entire 2.4 GHz band.
This can cause considerable difficulties to Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
and Video senders, 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. A typical microwave oven uses a self-oscillating vacuum power tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
called a magnetron and a high voltage power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
with a half wave rectifier (often with voltage doubling
Voltage doubler
A voltage doubler is an electronic circuit which charges capacitors from the input voltage and switches these charges in such a way that, in the ideal case, exactly twice the voltage is produced at the output as at its input....
) and no DC filtering
Electronic filter
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
. This produces an RF pulse train
Pulse wave
A pulse wave or pulse train is a kind of non-sinusoidal waveform that is similar to a square wave, but does not have the symmetrical shape associated with a perfect square wave. It is a term common to synthesizer programming, and is a typical waveform available on many synths. The exact shape of...
with a duty cycle
Duty cycle
In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration....
below 50% as the tube is completely off for half of every AC mains
Mains electricity
Mains is the general-purpose alternating current electric power supply. In the US, electric power is referred to by several names including household power, household electricity, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power...
cycle: 8.33 ms in 60 Hz countries and 10 ms in 50 Hz countries.
This property gave rise to a Wi-Fi "microwave oven interference robustness" mode that segments larger data frames into fragments each small enough to fit into the oven's "off" periods.
The 802.11 committee also found that although the instantaneous frequency of a microwave oven magnetron varies widely over each half AC cycle with the instantaneous supply voltage, at any instant it is relatively coherent
Coherence (physics)
In physics, coherence is a property of waves that enables stationary interference. More generally, coherence describes all properties of the correlation between physical quantities of a wave....
, i.e., it occupies only a narrow bandwidth. The 802.11a/g
IEEE 802.11g-2003
IEEE 802.11g-2003 or 802.11g is an amendment to the IEEE 802.11 specification that extended throughput to up to 54 Mbit/s using the same 2.4 GHz band as 802.11b. This specification under the marketing name of Wi-Fi has been implemented all over the world...
signal is inherently robust against such interference because it uses OFDM with error correction information interleaved across the carriers; as long as only a few carriers are wiped out by strong narrow band interference, the information in them can be regenerated by the error correcting code from the carriers that do get through.
Video devices
Video senderVideo sender
A video sender is a device for transmitting domestic video signals wirelessly from one room to another, as for example sending the output of a satellite TV decoder located in the lounge, to a television set in the bedroom....
s typically operate using an FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
carrier
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
to carry a video signal from one room to another (for example, satellite TV or closed-circuit television
Closed-circuit television
Closed-circuit television is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors....
). These devices typically operate continuously but have low (10 mW) transmit power. However, some devices, especially wireless cameras, operate with (often unauthorized) high power levels, and have high-gain antenna
High-gain antenna
A high-gain antenna is an antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signal - also known as a directional antenna...
s.
Although the transmitter of some video cameras appears to be fixed on one frequency, it has been found in several models that the cameras are actually frequency agile, and can have their frequency changed by disassembling the product and moving solder links or dip switches inside the camera.
These devices are prone to interference from other 2.4 GHz devices, due to the nature of an analog video
Analog video
Analog video is a video signal transferred by an analog signal. An analog color video signal contains luminance, brightness and chrominance of an analog television image...
signal showing up interference very easily. A carrier to noise ratio of some 20 dB is required to give a "clean" picture.
Continuous transmissions interfere with these, causing "patterning" on the picture, sometimes a dark or light shift, or complete blocking of the signal.
Non-continuous transmissions, such as Wi-Fi, cause horizontal noise bars to appear on the screen, and can cause "popping" or "clicking" to be heard on the sound.
Wi-Fi networks
Video senders can, in some areas, have interference from Wi-Fi networks. Particularly in the UK, whereby most broadband providers are giving away free routers with wireless built in and enabled by default, it is possible that no clear channel can be found for the video sender, and that it is not possible to make it work.Video senders are a big problem for Wi-Fi networks. Unlike Wi-Fi they operate continuously, and are typically only 10 MHz in bandwidth. 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. Wi-Fi also has a very wide spectrum, so only typically 30% of the peak power of the Wi-Fi actually affects the video sender. Wi-Fi is not continuous transmit, so the Wi-Fi signal interferes only intermittently with the video sender. A combination of these factors - low power output of the Wi-Fi compared to the video sender, the fact that typically the video sender is far closer to the receiver than the Wi-Fi transmitter and the FM capture effect means that a video sender may cause problems to Wi-Fi over a wide area, but the Wi-Fi unit causes few problems to the video sender.
802.11n Wi-Fi networks are proving to be a source of interference for other wireless data networks operating at 2.4 GHz.
EIRP
Many video senders on the market in the UK advertise a 100 mW equivalent isotropically radiated powerEquivalent isotropically radiated power
In radio communication systems, Equivalent isotropically radiated power or, alternatively, Effective isotropically radiated power is the amount of power that a theoretical isotropic antenna would emit to produce the peak power density observed in the direction of maximum antenna gain...
(EIRP). However, the UK market only permits a 10 mW EIRP limit. These devices cause far more interference across a far wider area, due to their excessive power. Furthermore, UK video senders are required to operate across a 20 MHz bandwidth (not to be confused with 20 MHz deviation). This means that some foreign imported video senders are not legal since they operate on a 15 MHz bandwidth or lower, which causes a higher spectral power density, increasing the interference. Furthermore, most other countries permit 100 mW EIRP for video senders, meaning a lot of video senders in the UK have excessive power outputs.
ZigBee / IEEE 802.15.4 Wireless Data Networks
Many ZigBeeZigBee
ZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on an IEEE 802 standard for personal area networks. Applications include wireless light switches, electrical meters with in-home-displays, and other consumer and industrial...
/ IEEE 802.15.4
IEEE 802.15.4
IEEE 802.15.4 is a standard which specifies the physical layer and media access control for low-rate wireless personal area networks . It is maintained by the IEEE 802.15 working group....
-based wireless data networks operate in the 2.45–2.4835 GHz band, and so are subject to interference from other devices operating in that same band. To avoid interference from IEEE 802.11
IEEE 802.11
IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent...
networks, an IEEE 802.15.4 network can be configured to only use channels 15, 20, 25, and 26, avoiding frequencies used by the commonly used IEEE 802.11 channels 1, 6, and 11.
Resolving interference
Normally interference is not too hard to find. Products are coming onto the market cheaply which act as spectrum analyzerSpectrum analyzer
A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals...
s and use a standard USB interface into a laptop
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
, meaning that the interference source can be fairly easily found with a little work, a directional antenna and driving around to find the interference.
Channel change
Often solving interference is as simple as changing the channel of the offending device. Particularly with video senderVideo sender
A video sender is a device for transmitting domestic video signals wirelessly from one room to another, as for example sending the output of a satellite TV decoder located in the lounge, to a television set in the bedroom....
s, whereby plugging in the receiver with no transmitter attached will let you "see" the neighbour's video sender, this technique is considered part of the "Installation process". Where the channel of one system, such as a Wireless ISP cannot be changed, and it is being Interfered with by something such as a video sender, the owner of the video sender is normally very happy to assist with doing this, providing it is not too much work. However the problem comes when the interference is something such as a wireless CCTV camera which is mounted on a chimney and requires a long ladder to access. Such cameras, due to their height, cause serious problems across a wide area.
Alternative product
Another cure is to offer an alternative product to the owner free of charge. Typically this would be a wired camera, which normally have far better performance than wireless cameras anyway, a cable to replace the video sender, or an alternative video sender which has been hard-wired to an alternative channel, with no means of changing it back to the offending frequency.Yet another cure is to move from 2.4 GHz to another frequency which lacks the vulnerability to interference inherent at that frequency, for example the 5 GHz frequency for 802.11a/n.
Parameter change
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. Changing collinear antennas for high gain directional dishes normally works very well, since the narrow beam from a high gain dish will not physically "see" the interference. Often sector antennaeSector antenna
A sector antenna is a type of directional microwave antenna with a sector-shaped radiation pattern. The word "sector" is used in the geometric sense; some portion of the circumference of a circle measured in degrees of arc...
have sharp "nulls" in their vertical pattern, so changing the tilt angle of sector antennas with a spectrum analyzer connected to monitor the strength of the interference can place the offending device within the null of the sector. High gain antennas on the transmitter end can "overpower" the interference, although their use may cause the effective radiated power
Effective radiated power
In radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
(ERP) of the signal to become too high, and so their use may not be legal.
Adding base stations
It may seem counter intuitive, but you can reduce the interference your Wi-Fi network causes your neighbors by adding more base stations to your own network. Every Wi-Fi standard provides for automatic adjustment of the data rate to channel conditions; poor links (usually those spanning greater distances) automatically operate at lower speeds. Deploying additional base stations around your home or office, 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. The same amount of data takes less time to send, reduces channel occupancy, and gives more idle time to your neighbors. And it improves the performance of your own network.The alternative of increasing coverage by adding an RF power amplifier to a single base station can bring similar improvements to a wireless network. The additional power offered by a linear amplifier will increase the signal-to-noise ratio at the client device, increasing the data rates used and reducing time spent transmitting data. The improved link quality will also reduce the number of retransmissions due to packet loss, further reducing channel occupancy. However, care must be taken to use a highly linear amplifier in order to avoid adding excessive noise to the signal.
All of the base stations in your network should be set to the same SSID (which must be different from all of your neighbors) and plugged into the same logical Ethernet segment (one or more hubs or switches directly connected without IP routers). 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. This potential disruption should be factored in when designing a network for low-latency services such as VoIP.