How does Cel-Fi differ from a broadband repeater?

Cel-Fi does several things:
1. A Cel-Fi device only boosts specific UMTS carrier frequencies (5MHz channels, up to 3) and not the whole band.
2. Cel-Fi will only boost the pre-configured UMTS carrier frequencies if they actually contain a valid UMTS signal and are for the correct network (i.e. the Cel-Fi device can lock onto the UMTS pilot channel, like a phone, and read broadcast information, such as the network identity or ‘PLMN-ID’ then determine what to boost)
3. Cel-Fi automatically limits its boost when close to the base station (based on a calculation of the actual RF path-loss) and so will never boost thermal noise to a level where the base station’s uplink performance will be damaged
4. Cel-Fi is unconditionally stable and will never oscillate – oscillation is usually a common and serious problem with traditional repeaters which causes power spikes that degrade the base station’s uplink performance.

What’s the radiation level of Cel-Fi RS2?

So is the Cel-FI RS2 Signal booster safe? We actually test the Cel-Fi units like a phone for a SAR rating. Anything with a SAR rating of less than 2.0 is defined as ‘touch safe’. Both the Cel-fi window unit and coverage unit have a SAR rating below 2.0.

Technically measuring SAR is usually only done for hand-held or body worn devices so WiFi routers generally don’t have a SAR rating. In any case the power we emit is no greater in general than other consumer wireless networking devices and smart phones.

Many boosters providers claim that there’s a loophole in the Ofcom policy stating that signal boosters are legal if they don’t interfere with other networks and their boosters abide that rule. Is it true?

The Ofcom rules are:

1)The boosters must not interfere with other networks.

2)The boosters remain within the license conditions of the mobile network which they boost – this means that the mobile network must be able to control them (turn them on and off) and the boosters must automatically configure themselves so as to never cause harm to the network.

Some products may claim to meet (1) but no product other than Cel-Fi can meet (2).  Incidentally you may not have been aware, but all Cel-Fi RS2 devices sold in the UK can be turned off by the network if they set certain parameters to be sent over the air.

The loophole in the Ofcom policy is that it is not illegal to sell mobile phone signal boosters that meet only (1) however it is definitely illegal to actually use them!

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How to boost mobile phone signal indoors?

The simple answer to improving indoor coverage would be to deploy hundreds (or thousands) of new base stations and build taller towers in all sectors of a community — but this strategy is neither likely nor cost effective.

In the residential market, there are several approaches to addressing indoor coverage. Two competing technology approaches that you may be aware of are working their way towards market acceptance. These are Femtocells and UMA (Unlicensed Mobile Access)

Femtocells are miniature base stations that are placed in the residence and connected back to the core network via a high speed internet connection. The air interface between the Femtocell and the handset is the same as with the macro mobile network. Implementation of this system requires significant upgrades to the carrier network and back office systems, but it does offer the advantage of being able to work in areas where there is no mobile coverage.

Unlicensed Mobile Access (UMA) according to Wikipedia is a telecommunication system allowing seamless roaming and handover between local area networks and wide area networks using the same dual-mode mobile phone. The local network could be based on private unlicensed spectrum technologies like Bluetooth or 802.11. The wide network is alternatively GSM/GPRS or UMTS mobile services. It lets mobile operators deliver voice, data and IMS/SIP (IP Multimedia Subsystem/Session Initiation Protocol) type applications to mobile phones on local networks. Its ultimate goal is the convergence of mobile, fixed and Internet telephony (Fixed Mobile Convergence).

On the mobile network, the mobile handset communicates over the air with a base station through a base station controller, to servers in the core network of the carrier. Under the GAN system, when the handset detects a LAN, it establishes a secure IP connection through a gateway to a server called a GAN Controller (GANC) on the carrier’s network. The GANC translates the signals coming from the handset to make it appear to be coming from another base station. Thus, when a mobile moves from a GSM to a Wi-Fi network, it appears to the core network as if it is simply on a different base station.

The UMA concept is a few years more mature than the Femto approach, but the requirement for dual-mode handsets means that consumers have a smaller population of phones to choose from if they would like to adopt a UMA-based plan. Those who experience poor indoor coverage and want to take advantage of a UMA solution often find that the coolest, smallest phones don’t yet feature dual mode (Wi-Fi and mobile) chipsets.

Repeater technology has been used since the early days of wireless communications. Its premise is fairly straightforward. A wireless signal is received over the air by a donor antenna which is connected to a signal amplifier. The amplifier sends the signal  to

an indoor server antenna. From here, it is redistributed throughout the room or building that was not able to obtain a sufficiently strong signal from the operator’s base station. These products have been called boosters, bi-directional amplifiers or repeaters — the terms are often used synonymously. By using a bi-directional amplifier (BDA) approach, the mobile signal is amplified on both the downlink path (to the mobile device) and on the uplink path (back to the base station antenna). By increasing the gain of the re-transmission, the user experiences a stronger connection.

Traditional analog repeaters and boosters designed to serve single family homes or apartments have not been embraced by mobile network operators. In fact, consumers are forbidden from using them in most countries since they transmit on frequencies that are the exclusive domain of a licensed operator. While they can prove effective in amplifying signals to and from an individual subscriber, their basic operation is crude and they are prone to over-amplifying signals on the outbound link and lowering the quality of service that neighbouring subscribers expect. Their potential for raising the noise floor and creating harmful interference has always outweighed their potential for solving the in-home coverage challenge.

Traditional bi-directional amplifier (BDA) products have been promoted for in-home use by electronics vendors outside the walled garden of licensed operators with limited success. These analog repeater products require a fairly complicated outdoor (and indoor) installation procedure that often involves drilling through walls and powering amplifier units from attics or other inconspicuous locations. Due to the nature of their directional antennas, which must be mounted outdoors and precisely aimed at a nearby base station in order to be most effective, the opportunities for installer error and unintentional interference with the macro network are numerous. Once installed, these point-and-mount antenna approaches cannot react to environmental changes or network upgrades (such as new base stations) in their service areas. Individuals who install off-the-shelf consumer repeaters without the knowledge of their operator can rob their neighbours of network capacity and cause an overall reduction in the coverage area of the local cell. In some countries, mobile network operators have been known to employ Repeater Referral Programs for customers in remote or unserviceable areas, but only with their authorization and under their strict guidance.

Perhaps you are aware of instances where your company’s subscribers have installed rogue repeater devices. Your network planning department would not be pleased to find that unauthorized devices were in operation since they often degrade the performance that neighbouring subscriber’s experience.

Nextivity Cel-Fi RS2 is the newest entry into the indoor coverage market. Cel-Fi systems are carrier-grade devices that are designed to eliminate indoor dead zones and work in harmony with the mobile macro network. Designed with smart antenna technology and onboard intelligence, Cel-Fi Systems continually seek out the best available signal and automatically adjust to any changes in the RF (Radio Frequency) environment in order to maximize the signal gain to the user. Cel-Fi Systems are designed to protect the integrity of the wireless network while increasing the effective RF capacity of each base station.

Cel-Fi Systems can more than triple the data rates experienced by wireless subscribers in their homes. Even the most non-technical subscriber can install a Cel-Fi System in a matter of minutes. No cables. No ladders. No drilling, No interference. No burden on network provisioning, management or support. None of the potential, for degrading the wireless network that traditional analog repeater products have become infamous for. The Cel-Fi system will only operate on the mobile frequencies that are licensed to the wireless carrier offering the device. Since the Cel-Fi  Systems are approved by an operator for use on their frequency spectrum, each device is fully compliant with the spectrum licensing conditions and will not radiate outside a designated frequency band.

A Cel-Fi system consists of two devices. The Window Unit (WU) is placed in the area with the strongest received signal from the carrier network. The WU contains a transmitter and receiver which communicate with the cell tower. The Coverage Unit (CU) is placed in the centre of the home and communicates wirelessly with the WU to “light up” the interior of the house with significantly enhanced signal levels. The result is better quality calls and greater data throughput.

Why do I lose 3G signal as soon as I enter the building?

I’m sure it happened to you more than once. You entered the building and couldn’t make a single phone call. Whether it is at the airport, in the club or shopping centre, at work or simply at home it is frustrating that you need to press your head against the ceiling or lean over the window not to mention going outside when it’s absolutely miserable out there, just to get a signal. You’d ask why is that? Especially if you live in the area with great coverage with no blank spots. Well let me answer this question for you.

Building materials and wireless signals have always had an uneasy relationship. Wireless signals get weaker, or dissipate, as they travel over long distances to reach subscriber homes and pass through and around obstacles. Degradation of wireless signals is often the result of Radio Frequency path loss, which can be greatly impacted by common architectural and construction elements. These might include: metal roofs, garage doors, aluminium siding, thermal insulation boards, refrigerators, plaster walls, reinforced concrete, double pane windows or Low-E glass.

These are just few of the unfriendly barriers that keep people from enjoying five bars of signal strentgh inside the building they are in. Atmospheric conditions (such as the amount of moisture in the air) combined with dense building materials can further reduce the connection speeds of the user significantly. These factors are perhaps as significant as distance from the base station - at least in terms of perceived service quality.

Network planners often find that the most ideal locations for masts are not viable due to opposition from city councils, government agencies, property owners and neighborhood advocates who oppose the construction of new towers within their neighborhoods. In these cases planners are required to build around the contentious areas and find creative ways to optimize their network. They often rely on smaller mobile base stations and/or specially designed Distributed Antenna Systems to serve densely populated buildings and well-traveled indoor areas such as airports and shopping centers that would otherwise suffer from poor coverage.

Unfortunately the cost of supplementing coverage to individual residences with these macro network approaches would be prohibitive.

Challenges from the physical world extend beyond construction material and masts design. When people are indoors or among obstacles and there is more than one route for a Radio Frequency signal to propagate, the phenomenon of multipath occurs. A signal can be scattered, reflected or diffracted on its path to the user. Any and all of the re-directions of a wireless signal will diminish the quality of an indoor connection.

As a result, dropped calls, straight-to-voicemail messages and missed texts are often experienced by wireless users inside their home and in the workplace.