A cellular repeater (also known as cell phone signal booster or amplifier) is a type of bi-directional amplifier used to improve cell phone reception and address coverage issues. Both indoor and outdoor cellular repeater deployments are possible, but a majority of deployments occur inside buildings where coverage is weakened by attenuation from building materials. A typical repeater system consists of a donor antenna that receives and transmits signal from nearby cell towers, coaxial cables, a signal amplifier, and an indoor rebroadcast antenna.
Typical 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. Donor antennas can be of multiple types, but are typically categorized as either directional or omnidirectional. Omnidirectional antennas, which broadcast in all directions, are typically used for repeater systems that amplifier coverage for all cellular carriers. Directional antennas are used when a particular tower or carrier needs to be isolated for improvement. The use of highly directional antenna can help improve the donor's signal-to-noise ratio, thus improving the quality of signal redistributed inside the building.
Indoor antenna
The better systems will generally include an internal monopole antenna (although the type of antenna is far from standardized) for rebroadcasting the signal internally - the advantage of using a mono-pole antenna is that the signal will be equally distributed in all directions (subject, of course, to attenuation from obstacles). Because all radio antennas are intrinsically polarized, cell phones perform best when their antennas are oriented parallel to the booster's antenna - although within reasonable proximity to the booster's signal, it will be strong enough that the orientation of the cell phone's antenna will not make a significant difference in usability.
Signal amplifier
All models will include a signal amplifier. Even the cheaper home-use models (typically band selective) now provide 20Â dB - 50Â dB gain and many of the more expensive models provide over 50Â dB. Excellent high-power models (used for by commercial operators) offer a gain of around 100Â dBm (Interference cancellation equipment function is an improvement of the radio isolation between donor and service antenna). However, since decibels are logarithmic a 30Â dB gain represents a one thousandfold signal power increase - meaning the total amplification of a repeater with greater than around 50Â dB is likely to be useless without a good, well aligned antenna. This is due to the difficulty of filtering the correct signal out from the background noise, which will be amplified equally, and the limiting maximum signal power of the amplifier (for picorepeaters typically from around 5 dBm (3.2Â mW)). Standard GSM channel selective repeaters (operated by telecommunication operators for coverage of large areas and big buildings) have output power around 2Â W, high power repeaters (e.g., NodeG from Andrew) have output power around 10Â W. The power gain is calculated by the following equation:
A repeater is needed to secure sufficient isolation between donor and service antenna. When the isolation is lower than actual gain + reserve (typically 5-15Â dB) then the repeater is in loop oscillation and this oscillation can cause serious interference to the cellular network outside the building.
Also, cheap models are equipped with automatic gain reduction in case of poor or weak isolation. In case of poor isolation the device works but with low gain, and coverage is poor.
The isolation may be improved by antenna type selection in a macro environment: by 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 => prox. +5 us up to standard rep. delay) and consequently a shorter radius from donor site, where a repeater could be used.
Amplification and filtration introduce a delay (typically between 5 and 15 us), depending on the type of repeater and features used. Additional distance adds propagation delay. Because of the cellular network has form principle reduced cell size (depends on the technology and activated features typically X*10Â km (for standard GSM 35Â km), urban FDD/TDD network 20Â km), usage of repeater virtually moves the user to a bigger distance: radio distance = real distance + (repeater delay in us) *0.3Â km (delay of RF signal in air is 3.3us/km). This is reason why, with sufficient levels, a repeater doesn't work. After repeating there will be better (or excellent) coverage, but the network can not be accessed. The user, from network point of view, is too far.
There is also problem with noise amplification (especially in UL) and desensitization of the donor site.
Reasons for weak signal
Rural areas
In many rural areas the housing density is too low to make construction of a new base station commercially viable. In these cases it is unlikely that the service provider will do anything to improve reception, due to the high cost of erecting a new tower. As a result, the only way to obtain strong cell phone signal in these areas is usually to install a home cellular repeater. In flat rural areas the signal is unlikely to suffer from multipath interference, so it will just be heavily attenuated by the distance. In these cases the installation of a cellular repeater will generally massively increase signal strength just due to the amplifier, even with a great distance from the broadcast towers.
Building construction material
Some construction materials rapidly attenuate cell phone signal strength. Older buildings, such as churches, which may use lead in their roofing material, will very effectively block any signal. Any building which 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 massively decrease signal strength.
Building size
Large buildings, such as warehouses, hospitals, and factories, often have no cellular reception further than a few meters from the outside wall. Low signal strength is also often the case in underground areas, such as basements, and in shops and restaurants located towards the centre of shopping malls. This is caused by both the fact that the signal is attenuated heavily as it enters the building and the interference as the signal is reflected by the objects inside the building. For this reason, in these cases, an external antenna is usually desirable.
Multipath interference
Even in urban areas, which usually have strong cellular signals throughout, there are often dead zones caused by destructive interference of waves which have taken different paths (caused by the signal bouncing off buildings etc.). 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 is because the different wavelengths of the different frequencies interfere destructively at different points. Directional antennas are very helpful at overcoming this since they can be placed at points of constructive interference and aligned so as not to receive the destructive signal. See Multipath interference for more details.
Diffraction and general attenuation
The longer wavelengths have the advantage of being able to diffract to a greater degree, so are less reliant on line of sight to obtain a good signal, but still attenuate significantly. Because the frequencies which cell phones use are too high to reflect off the ionosphere as shortwave radio waves do, cell phone waves cannot travel via the ionosphere.
See Diffraction and Attenuation for more details.
Different operating frequencies
Repeaters are available for all the different GSM frequency bands. Some repeaters will handle different types of networks, such as multi-mode GSM and UMTS, repeaters however dual- and tri-band systems cost significantly more. Repeater systems are available for certain Satellite phone systems, allowing the satphones to be used indoors without a clear line of sight to the satellite.
Regulation and sales in Australia
General
A cellular repeater is referred to as a mobile phone repeater or mobile repeater, and communicated in that way by Regulators.
A mobile phone repeater operates within apparatus or spectrum licensed radio-frequency bands. Mobile repeaters are also used and managed by mobile carriers as part of their general network, and authorised under its PMTS licence.
Subscribers (mobile phone end users) wanting to use a mobile repeater must (with the exception of a passive mobile repeater) obtain permission from the mobile carrier under a third-party arrangement. Subscribers that operate a mobile repeater without the mobile carrier’s permission, runs the risk of causing harmful interference to the mobile network, and a number of contraventions to the Radiocommunications Act 1992 such as Unlicensed Operation and Possession. Section 474.6 of the Criminal Code Act 1995 may apply as the person unlawfully operates the mobile repeater in the carriers network which can be taken to be an act of tamper or interference. Absolute liability applies to the physical element of circumstance of the offence, that the facility is owned or operated by a carrier, a carriage service provider or a nominated carrier.
Allowed Repeaters
The Australian Carriers have agreed to authorise the Cel-Fi Brand Smart Repeater. These smart repeaters are network specific. For example, a 3G repeater will scan their specific allocated network and then select to amplify signals from their relevant base stations that have the best signal quality. The quality calculations are based on repeating signals with the best ec\lo. Therefore, if a repeater received three signals from three different macro cells, the one with the best ec\lo will be repeated.
Analog and other smart repeaters that do not have the network friendly cognitive functions to safely repeat mobile phone signals will not be authorised. Analog and other smart repeaters are general broadband amplifiers that boost mobile signals of all base stations without control. For example, signals are boosted from these base stations, which cause uncontrolled signal levels on the down-link and up-link. Phone signals on the up-link may be over amplified which cause high levels of Gaussian noise and/or inter-modulation which causes the base station/s capacity to severely drop or fail.
Suppliers
Australian Suppliers of Mobile Repeaters are now required to maintain records of repeater sales and location information to assist the ACMA in its investigation of interference complaints by being able to access detailed information about those devices supplied.
The amendment to the Regulations, Regulation 38B specifies the ‘particulars’ which the supplier is required to record under paragraph 301(1)(b) of the Act. In summary, the ‘particulars’ include: licence holder or authorisation agreement details (for example the licence number, date of issue and expiry, full name of the licensee or a duplicate of the licence) repeater device details (for example the device’s serial or model number) and information concerning the actual transaction (for example, the date of supply, particulars regarding the identity of the recipient, such as photo identification).
Illegal supply of repeaters
The changes to legislation has not stopped the supply and proliferation of unauthorised Mobile Phone repeaters into Australia. There is ongoing misleading information from overseas sellers continuing to target Australian Consumers, and they're using search engine advertised marketing such as Google Adwords, to entice consumers to purchase and use their mobile repeaters that are illegal to possess or operate under Australian Law. The changes has only affected Australian Suppliers that can be directly governed under Australian Jurisdiction. The ACMA and Australian carriers reported a number of instances of illegal mobile repeaters they found which caused interference, through Twitter feeds and online news services.
- Mobile Repeaters Australia (MRA) told to stop selling
On 16 April 2015 NSW Fair Trading served a cease and desist order on the largest internet supplier of repeaters, Mobile Repeaters Australia (MRA). ‘Traders like MRA are keeping consumers in the dark and misinformed about the necessary licensing requirements for using mobile repeater devices,’ said NSW Fair Trading Commissioner Rod Stowe.
MRA and others selling these second-rate mobile phone repeaters, are putting at risk the whole community for the sake of their own financial gain.’ Mobile phone repeaters cannot be used in Australia without written authorisation from the carrier.
- Other online traders selling similar questionable product as MRA are
signalboostersaustralia.com
boosteraustralia.com
amplifyaustralia.com
- eBay
eBay list thousands of mobile repeaters to the Australian buyers. The online sellers use fake Australian Addresses such as Regents Park NSW to pose as a local seller and sell similar repeaters listed by the other online sellers such as MRA. Despite complaints to eBay regarding the unauthorised sales, eBAY appears to not police and remove these repeaters.
eBay could restrict the sales of Mobile Repeaters by forcing the sellers to show documentary evidence that the repeater shall be authorised, however eBay shopping continues to be a buyer beware platform until such time.
Google marketing platforms such as Google Adwords enables online sellers such as MRA and MRA like sellers to continue selling unauthorised repeaters without any intervention, repercussion and any sort of policing. Google has enabled thousands of illegal repeaters to be marketed and sold though its Google Adwords platform for many years. Google takes no responsibility for misleading ads. It is a buyer beware platform.
- Legitimate Channels
There is difficulty in contacting the correct person from one of the three carriers (Optus Telstra and Vodafone)that can provide information or web links regarding legitimate repeater (repeaters that are authorised either through them or a third party supplier).
Below lists the carriers and help with purchasing an authorised repeater.
- Optus
Optus provide a web page that links back to Cel-Fi.com.au. A web site by Powertec Telecommunications. The page is used to inform end users of the legitimate arrangement to get an authroised repeater. Optus use Powertec Telecommunications as the third Party to supply and authorise repeaters.
- Telstra
Imports their own Cel-Fi Repeaters under the 'Smart Antenna' brand and use Powertec Telecommunications as a third party vendor to supply and authorise repeaters.
Telstra customers can call on the following numbers below to query about the legitimacy of the repeaters below: • Residential customers call 13 2200 (say 'coverage')
• Business customers call 13 2000 (say 'coverage') or contact your account executive.
- Vodafone
Currently - Vodafone do not disclose any information about legitimate Mobile Phone Repeaters. They do not sell any repeater to end users, and their converge tech support team cannot provide any comment.
Legitimate suppliers
At the time of writing this literature, there was only one known importer that has agreements with all three Australian Carriers, other than the mobile carriers themselves (Optus Telstra and Vodafone), that supply Mobile Phone repeaters that can be authorised under a third party agreement. The repeaters are manufactured by Nextivity Inc. The mobile repeaters are imported by Powertec Telecommunications Australia Ltd and distributed by a number of retailers and installers across the country. The repeaters are sold under the Cel-Fi brand to subscribers.
- Applicable Standards
At the time of writing this literature, there were no Regulatory Australian Telecommunications Standards applicable to mobile repeaters. However the 3rd Generation Project Partnership (3GPP) developed technical specification TS25.143 to allow manufacturers to assess performance of the repeaters against the specification as a benchmark.
Other applicable standards that may apply are the Radiocommunications EMC Standard 2008 for external power supplies, and ARPANSA standard relates to the electromagnetic radiation exposure to humans.
- The Regulator links
The Australian Communications and Media Authority (ACMA) published information to help consumers in their quest in obtaining a legitimate mobile phone repeater. Mobile Phone Repeaters Information for Consumers
Approval in the USA 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, the 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. It is widely considered a landmark decision which was many years in the making. Only a few companies have a product compatible with the new FCC report and order.
The FCC has defined two types of repeaters:
1. 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 70Â dB (for the low LTE 700Mhz bands) to 72Â 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.
2. 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 100Â 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.
The new rules from the FCC should start on March 1, 2014. Here are the rules.
Approval in the UK by Ofcom and the UK market
Many websites and forums state Ofcom have banned the use of mobile boosters. This does not appear to be the case and in May 2011 Ofcom provided clarification. This was stated as follows:
Installation or use of repeater devices (as with any radio equipment) is a criminal offence unless two conditions are satisfied:
1. That the equipment is CE marked, indicating that the manufacturer has declared it complies with all relevant EU regulatory requirements, including the Radio equipment and Telecommunications Terminal Equipment (R&TTE) Directive;
2. 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.
Possible Clarification due late 2015.
The wireless act also allows under WT Act 2006 section 1.15 an exemption if the device does not "involve undue interference with wireless telegraphy" They have entered into a discussion with www.mobilerepeatergermany.com to give guidelines after an EU case was brought against Ofcom claiming exemption under WT Act 2006 section 1.15 and Ofcom lost and has to undergo a review of the guidelines. See EU case summary here. http://www.monckton.com/publication/recall-support-services-limited-et-al-v-secretary-state-culture-media-sport/
It is expected to follow the US style regulations where a mobile repeater must have protection built in against interference and will allow people install quality units but put cheaper ones out of business.
Ofcom states 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."
This has not deterred the UK market for signal boosters with an explosion of web retailers offering a wide range of solutions from DIY installs to installations. This has largely been driven by the tightening of energy efficiency regulations in building construction. The use of materials that mitigate heat loss such as metallic foil laminated insulation board and energy efficient glazing with a metallic anodised coating also have high signal attenuation properties.
The window for regulation of the UK market, as in the US, is likely passed as the quantity of repeaters already shipped and in place in the UK is estimated at the tens of thousands. Repeaters operating in rural and less densely populated areas do not pose a quantifiable problem. However, in cities and areas where many cells exist from each operator, the use of devices ranging from small mobile signal boosters to high power repeaters can cause loss of coverage through interference and desensitisation of the cells. Most installations are simply 'plug and play' and have been installed by non technical persons who have no appreciation or understanding of even the most basic RF principles.
There are well established vendors who have worked for some time in this area who work for, and with the networks to provide in building coverage solutions. Ofcom suggest that "Anyone wishing to improve coverage in a particular area is advised to contact their network provider." At present, the willingness and capability of network operators to initiate the process to providing an in building solution varies greatly. Some network operators have dedicated teams that will visit a customers site to assess the cause of the problems experienced and offer to put in place a solution provided by a third party vendor. However this is generally limited to large corporates and the public sector, with the expense being borne by the client. The disparity in approach and the lack of a cross network operator working group means that sites requiring a 'wideband' coverage solution for all networks is not currently possible.
References
See also
- Base Station Subsystem
- Femtocell - type of cellular repeater
- Home Node B - a femtocell
- Coverage noticer
- Dead zone (cell phone)
- Waves
- Cel-Fi Signal Booster
- Repeater