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Apr. 16, 2008

For many years now, wireless repeater stations have been around since the first days of commercial cellular service back in mid-1986.

In those days, wireless base station were few and sometimes very far between. Even in large cities, repeaters were used to good advantage for filling in coverage gaps caused by various terrain and urban clutter.

However, as wireless networks grew faster and faster, additional base repeater stations were deployed to increase overall capacity and improve service quality.

In other parts of the world, particularly in Asia, low-powered repeater stations gained acceptance for solving indoor coverage problems. However, such applications have yet to be widely embraced in North America.

Most U.S. wireless carriers surveyed don’t appear to be interested in repeater stations, even though there are still plenty of coverage problems they could help resolve with the use of repeaters.

Two main reasons wireless carriers are ambivalent about repeaters are:

But here comes R.F. Window, a company that offers over-the-air repeater stations it claims will eliminate such problems, making repeater engineering much simpler and less risky for network operators.

Such a breakthrough is possible with the help of R.F. Window’s patented Interference Cancellation System or ICS. To appreciate what ICS can do, you must first consider how typical over-the-air repeaters work.

Reduced to their simplest form, a repeater station simply consists of two antennas, one pointing toward the donor base station and the other toward the area to be covered.

In between is a bi-directional RF (radio frequency) amplifier that boosts the downlink and uplink signals so they can be retransmitted at a far higher level. To provide much coverage benefit, the gain of this amplifier generally has to be quite large, at least 65 dB or more.

And therein lies the whole problem. In order to keep the repeater operating in a very stable manner, the isolation between its two antennas has to be greater than its amplifier gain. With a small safety margin thrown in, the isolation between the two antennas typically has to be at least 80 dB, meaning that the signal transmitted by one antenna must be reduced by at least 80 dB before it finds its way into the other antenna.

R.F. Window claims that its proprietary ICS technology addresses these repeater issues by simply reducing the amount of RF isolation needed between the two antennas. By using sophisticated DSP (digital signal processing) technology, ICS senses the signals leaking from one antenna to the other and injects equal, but 180 degrees out of phase, signals to cancel them out.

The end result is that repeater stations with a higher gain can be easily installed with little regard for antenna isolation.

RF Window says the ability to operate at high amplifier gain means that repeaters can put out much higher transmit power. One RF Window repeater model has a total downlink power capacity of 20 Watts, rivaling that of regular base stations.

To this date, RF Window repeaters have been deployed in Asia, South America, and Europe, but not in North America. If ICS provides the technology breakthrough that RF Window claims, that could soon change however.

Correctly analyzing in order to accurately obtain sufficient RF isolation with a practical installation is the main reason repeaters can be difficult to engineer in the first place. However, the real problem is that if isolation is inadequate – that is, less than the repeater’s gain – the repeater can go out of control.

If that happens, not only will the repeater fail to enhance coverage, it also may generate significant RF interference that can potentially disrupt operation of the entire network over a large area.

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    This article was featured on Business 5.0.

Source: RF Window.