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A cellular repeater (also known as cell phone signal booster or cell phone signal amplifier) is a type of
bi-directional amplifier A cellular repeater (also known as cell phone signal booster or cell phone signal amplifier) is a type of bi-directional amplifier used to improve cell phone reception. A cellular repeater system commonly consists of a donor Antenna (radio), anten ...
used to improve
cell phone A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This radio ...
reception. A cellular repeater system commonly consists of a donor antenna that receives and transmits signal from nearby cell towers, coaxial cables, a signal amplifier, and an indoor rebroadcast antenna.


Common components


Donor antenna

A "donor antenna" is typically installed by a window or on the roof a building and used to communicate back to a nearby cell tower. A donor antenna can be any of several types, but is usually directional or omnidirectional. An omnidirectional antenna (which broadcast in all directions) is typically used for a repeater system that amplify coverage for all cellular carriers. A directional antenna is used when a particular tower or carrier needs to be isolated for improvement. The use of a highly directional antenna can help improve the donor's
signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...
, thus improving the quality of signal redistributed inside a building.


Indoor antenna

Some cellular repeater systems can also include an omnidirectional antenna for rebroadcasting the signal indoors. Depending on attenuation from obstacles, the advantage of using an omnidirectional antenna is that the signal will be equally distributed in all directions.


Motor vehicle antenna

When it is raining and the motor vehicle windows are closed a cell phone could lose between 50% and 100% of its reception. To rectify the reception an antenna is placed outside the vehicle and is wired to the inside of the vehicle to another antenna and amplifier to transmit the mobile phone signal to the cell phone inside the vehicle.


Signal amplifier

Cellular repeater systems include a signal amplifier. Standard GSM channel selective repeaters (operated by telecommunication operators for coverage of large areas and big buildings) have output power around 2 W, high power repeaters have output power around 10 W. The power gain is calculated by the following equation: :: \quad P_\mathrm = 10 \log_ \left(\frac \right) \ A repeater needs to secure sufficient isolation between the donor and the service antenna. When the isolation is lower than actual gain plus a margin (of typically 5–15 dB), the repeater may go into in loop oscillation. This oscillation can cause interference to the cellular network. The isolation may be improved by antenna type selection in a macro environment, which involves adjusting the angle between the donor and service antennas (ideally 180°), space separation (typically the vertical distance in the case of the tower installation between donor and service antenna is several meters), insertion into an attenuating environment (e.g. installing a metal mesh between donor and service antennas), and/or reduction of reflections (no near obstacles in front of the donor antenna such as trees or buildings). Isolation can be also improved by integrated feature called ICE (interference cancellation equipment) offered in some products (e.g., NodeG, RFWindow). Activation of this feature has a negative impact on internal delay (higher delay => approximately +5 μs up to standard rep. delay) and consequently a shorter radius from donor site. Amplification and filtering introduce a delay (typically between 5 and 15 μs), depending on the type of repeater and features used. Additional distance also adds propagation delay.


Reasons for weak signal


Rural areas

In many rural areas the housing density is too low to make construction of a new
base station Base station (or base radio station, BS) is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a " land station in the land mobile service." A base station is called '' node B'' in 3G, '' eNB'' in L ...
commercially viable. Installing a home cellular repeater may remedy this. In flat rural areas the signal is unlikely to suffer from
multipath interference In radio communication, multipath is the radio propagation, propagation phenomenon that results in radio signals reaching the receiving antenna (electronics), antenna by two or more paths. Causes of multipath include atmospheric ducting, ionosph ...
.


Building construction material

Certain construction materials can attenuate cell phone signal strength. Older buildings, such as churches, often block cellular signals. Any building that has a significant thickness of concrete, or a large amount of metal used in its construction, will attenuate the signal. Concrete floors are often poured onto a metal pan, which completely blocks most radio signals. Some solid foam insulation and some fiberglass insulation used in roofs or exterior walls have foil backing, which can reduce transmittance. Energy efficient windows and metal window screens are also very effective at blocking radio signals. Some materials have peaks in their absorption spectra, which decrease signal strength.


Building size

Large buildings, such as warehouses, hospitals, and factories, often lack cellular reception. Low signal strength also tends to occur in underground areas (such as basements, and in shops and restaurants located towards the centre of
shopping mall A shopping mall (or simply mall) is a large indoor shopping center, usually Anchor tenant, anchored by department stores. The term ''mall'' originally meant pedestrian zone, a pedestrian promenade with shops along it, but in the late 1960s, i ...
s). In these cases, an external antenna is usually used.


Multipath interference

Even in urban areas (which usually have strong cellular signals throughout), there may be dead zones caused by
destructive interference In physics, interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have greater amplitude (constructive in ...
of waves. These usually have an area of a few blocks and will usually only affect one of the two frequency ranges used by cell phones. This happens because different wavelengths of the different frequencies interfere destructively at different points.
Directional antenna A directional antenna or beam antenna is an antenna that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain directio ...
s can be helpful at overcoming this issue since they may be used to select a single path from several (see
Multipath interference In radio communication, multipath is the radio propagation, propagation phenomenon that results in radio signals reaching the receiving antenna (electronics), antenna by two or more paths. Causes of multipath include atmospheric ducting, ionosph ...
for more details).


Diffraction and general attenuation

The longer
wavelengths In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same '' phase'' on ...
have the advantage of diffracting more, and so line of sight is not as necessary to obtain a good signal. Because the frequencies that cell phones use are too high to reflect off the
ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
as
shortwave radio Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the High frequency, high frequency band (HF), which extends from 3 to 30& ...
waves do, cell phone waves cannot travel via the ionosphere. (See
Diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...
and
Attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a Transmission medium, medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and ...
for more details).


Different operating frequencies

Repeaters are available for all of the
GSM frequency bands GSM frequency bands or frequency ranges are the cellular frequencies designated by the International Telecommunication Union, ITU for the operation of GSM mobile phones and other mobile devices. Frequency bands GSM frequency usage around th ...
. Some repeaters will handle different types of networks (such as multi-mode GSM and
UMTS The Universal Mobile Telecommunications System (UMTS) is a 3G mobile cellular system for networks based on the GSM standard. UMTS uses Wideband Code Division Multiple Access, wideband code-division multiple access (W-CDMA) radio access technolog ...
). Repeater systems are available for certain
Satellite phone A satellite telephone, satellite phone or satphone is a type of mobile phone that connects to other phones or the telephone network by radio link through satellites orbiting the Earth instead of terrestrial cell sites, as cellphones do. Therefo ...
systems, allowing these to be used indoors without a clear line of sight to the satellite.


Regional approval


Approval in the US by the FCC

It used to be legal to use the low power devices available for home and small scale use in commercial areas (offices, shops, bars, etc.). On February 20, 2013, th
FCC released a Report & Order
thus establishing two Safe Harbors and defining the use of "network safe" consumer boosters on licensed spectrum. The Safe Harbors represent a compromise solution between Technology Manufacturers and Wireless Operators. Only a few companies have a product compatible with the new FCC regulations. The FCC has defined two types of repeaters: # Wide-band (or broadband) signal boosters are usually repeaters that amplify all frequencies from cell phone carriers. Because interferences can be generated from such boosters, the manufacturers who apply to the FCC must limit their gain (among other things), to 65 dB (for the low LTE 700 MHz bands) to 72 dB (for higher frequencies such as AWS). By limiting the system gain, such boosters are only useful when the outdoor signal is relatively high, and need a complex outdoor installation of specific antennas. # Carrier specific (or provider specific) signal boosters. These boosters are only designed to boost those frequencies (and signal) that belong to a particular carrier. Usually, such carrier specific boosters do not produce interferences on other carrier's frequencies, and are allowed to have much larger system gains (sometimes 100 dB). In these conditions, such devices boost signal in a larger coverage area, and can still be efficient when outdoor carrier signals are weak, but are only boosting the signal for the carrier it is designed to operate. These new rules by the FCC were implemented on March 1, 2014.


Approval in the UK by Ofcom and the UK market

In May 2011,
Ofcom The Office of Communications, commonly known as Ofcom, is the government-approved regulatory and competition authority for the broadcasting, internet, telecommunications and mail, postal industries of the United Kingdom. Ofcom has wide-rang ...
stated the following: Installation or use of repeater devices (as with any radio equipment) is a criminal offence unless two conditions are satisfied: # That the equipment is
CE mark The presence of the logo on Product (business), commercial products indicates that the Manufacturing, manufacturer or importer affirms the goods' conformity with European Environment, health and safety, health, safety, and environmental prote ...
ed, indicating that the manufacturer has declared that it complies with all relevant EU regulatory requirements, including the Radio equipment and Telecommunications Terminal Equipment (R&TTE) Directive; # That the use of the equipment is specifically authorised in the UK, either via a licence or by regulations made by Ofcom to exempt the use from licensing. Under WT Act 2006 section 1.15, the wireless act also allows an exemption if the device does not "involve undue interference with wireless telegraphy". This is expected to follow the US-style regulations where a mobile repeater must have protection built in against interference.
Ofcom The Office of Communications, commonly known as Ofcom, is the government-approved regulatory and competition authority for the broadcasting, internet, telecommunications and mail, postal industries of the United Kingdom. Ofcom has wide-rang ...
stated that "Repeater devices transmit or re-transmit in the cellular frequency bands. Only the mobile network operators are licensed to use equipment that transmits in these bands. Installation or use of repeater devices by anyone without a licence is a criminal offence under Section 8 of the WT Act 2006." Repeaters operating in rural and less densely populated areas do not pose a quantifiable problem.


See also

* Base Station Subsystem *
Femtocell In telecommunications, a femtocell is a small, low-power cellular base station, typically designed for use in a home or small business. A broader term which is more widespread in the industry is ''small cell'', with ''femtocell'' as a subset. It t ...
– type of cellular repeater * Home Node B – a femtocell * Coverage noticer * Dead zone (cell phone) *
Wave In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from List of types of equilibrium, equilibrium) of one or more quantities. ''Periodic waves'' oscillate repeatedly about an equilibrium ...
s *
Repeater In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some ...


References


External links


Full Text of the FCC Report and Order on Use and Design of Signal Boosters
{{DEFAULTSORT:Cellular Repeater Radio electronics Mobile technology Telecommunications infrastructure