Telecom Informer

    

by The Prophet

Hello, and greetings from the Central Office!

Fall has turned to winter here in Beijing, and the temperature continues to drop every day.  In the waning days of fall, my neighborhood suddenly turned upscale.  This, as is often the case in Beijing, happened virtually overnight.  My modest hutong apartment is now surrounded by swanky cafés, high-end spas with names like "Zen" and - in the only development I personally consider an improvement - a nice whiskey bar.  In any event, it's a good thing that my contract is ending here, because the landlord is raising the rent by 40 percent.  I am moving away next week.

Leaving Beijing has given me a lot of time to think about wide open spaces.  Although I haven't completely decided what I am doing for the next stage of my career (any thoughts of future retirement have been eviscerated by the (((Wall Street))) collapse), I do plan to live somewhere less crowded.  The problem with rural places is that it's sometimes hard to get traditional telephone service, and wireless service can be spotty.  Often only one wireless carrier is available, and what passes for coverage may be a spotty signal - only working outdoors - from a tower ten or more miles away.

Meanwhile, mobile phones are increasingly designed for dense, urban places.  External antennas have disappeared from phones sold today, and transmission power is a maximum of 0.6 watts.  Modern phones (especially smartphones) often transmit at lower power than is allowed under the specification to save battery life.  Some phones allow you to control this yourself through power management settings, but other phones don't permit the same degree of control.

For these types of situations, the solution used to be relatively simple.  You'd just get an AMPS bag phone, which operates at up to 3 watts, and attach a good-quality antenna in a location where signal was available.  AMPS had no distance limitation for effective operation, so it didn't matter how far away you were from the nearest tower.  A group of hobbyists at the Burning Man festival using a bag phone connected to a Yagi antenna were routinely able to use AMPS towers over 80 miles away.  This configuration, unfortunately, is no longer an option.  The FCC stopped requiring carriers to offer AMPS service on February 18, 2008, and most carriers shut it down immediately.  Today, only a handful of small carriers in extremely remote areas still offer AMPS.  Virtually no handsets made after 2007 have AMPS functionality either.  All in all, AMPS is effectively dead.

So, what do you do when your phone has both a weak amplifier and a lousy antenna, the signal from your carrier is weak and spotty, and coverage is effectively available within a few square meters on the roof of your house?  A wide variety of products are available, each of which promises solutions while sometimes creating additional problems.

Femtocells

The preferred solution of wireless carriers because they completely control the user experience, hardware, and billing, a femtocell is roughly the same size and shape as a wireless router.

You plug it into your home broadband service, configure it for your handset (typically, femtocells are limited to serving only registered phones), and it happily provides you with a good quality wireless signal.  Behind the scenes, the device routes calls (typically using SIP) via your home broadband service.  Your carrier, meanwhile, bills you as if you were using your service normally (although depending on the carrier, different plans may be available).  Some carriers sell you a femtocell and charge to use it as if you were using ordinary plan minutes and data (even though any data usage is over your own Internet connection), but others (such as Sprint) also require a monthly fee.  Occasionally, these devices are given away for free as a customer retention tool.  It doesn't really make sense to me that you should have to pay a mobile carrier extra money because their service is lousy - in particular when you're providing your own backhaul - but the world of mobile phone billing is a strange and wonderful one disconnected from all forms of usual reality.

Femtocells can be really useful in some scenarios, but they have limited power and usually only cover registered handsets on a particular mobile carrier.  Accordingly, they are not well suited to places like shopping malls or parking garages where you don't know who the subscribers are and you need a larger coverage area.  Also, since they rely on a broadband connection, they are really only useful in places that already have broadband coverage.  For a family whose house is in an urban area "dead zone," this isn't necessarily a problem.  However, broadband is either unavailable or unsuitable in many rural areas.

Microcells

Ever walk inside a mall or office building and watch your mobile phone signal completely disappear?

This isn't something most carriers want to see happen, and it's not something that building managers want to see happen either.  In large buildings with signal problems, mobile carriers will typically install a microcell.

This is an actual full-featured cellular tower that is fully integrated into the rest of the carrier's wireless network, but it operates at low power with the intention of providing only in-building coverage.  Microcells are also generally compact, usually the size of a small form factor PC with a 6 to 12 inch antenna.  Large buildings may contain more than one microcell.

Repeaters, Amplifiers, and Signal Boosters

Up until now, we've been talking about solutions provided by the carriers themselves.

However, these solutions are only useful in limited scenarios.  There are plenty of places without broadband and with poor to nonexistent wireless coverage.  For scenarios like these, repeaters and signal boosters can be used.

When you buy a "signal booster," it will typically come in one of two forms.  The most common form is a repeater, which does exactly what the name implies: takes a signal from an area where it is available, and repeats it over a separate antenna into an area where it is not available.

This could, for example, bring a weak (but working) cellular signal from a directional antenna on your rooftop and rebroadcast it inside your house, where there is no signal.  Obviously, this isn't a one-way proposition; for transmission, the same thing happens in reverse.

Repeaters are typically coupled with an amplifier, which amplifies the transmission from your mobile phone and juices it up to an appropriate power level for the distant cellular tower to receive.  Cheaper and simpler "signal boosters" only consist of an amplifier and a single antenna.

My friend Andy works in network quality for a Canadian wireless carrier.  In his line of work, these devices are the bane of his existence, because improperly installed or poorly configured ones can cause severe interference that is almost impossible to track down.  Both types of devices are capable of causing significant interference when failing or improperly configured.

There are three basic types of interference:

Oscillating CW Spike:  You can think of this type of interference as similar to feedback on a microphone.  When it occurs, it essentially creates a lot of background noise in the radio spectrum and can cause other calls to drop.  This problem is generally caused when antennas are improperly installed on repeaters.

Improper Power Regulation:  Some amplifiers broadcast at the full maximum three watts all the time, either by (poor) design or because their control circuitry has failed.  This causes the amplifier to drown out other traffic on a cell tower, or even multiple towers if you do this in an urban area.  One of Andy's subscribers had a full-powered 3W amplifier installed in a boat.  This was just fine when he was out on the water ten miles from shore, but when he pulled into the marina, calls all around him would drop.  In a variation on the same theme, some amplifiers are configured to use a more remote tower than necessary, thus operating at higher power.  This can similarly cause interference to nearby towers and everyone using them.

Out of Band Transmission:  When they begin to fail, some amplifiers begin splattering on channels where they don't belong, causing interference and dropped calls.

Interference from these devices is a real problem, and carriers spend real money dealing with it.

In 2010, the CTIA (a wireless carrier lobbying group) petitioned the FCC to ban them entirely.  Most carriers enthusiastically jumped on board the petition, but Verizon Wireless was noticeably absent.  Instead, they separately petitioned the FCC along with Wilson Electronics, a major manufacturer of repeaters and amplifiers.

Wilson and Verizon suggested that interference could be mitigated through more rigid certification and technical standards, and (correctly) suggested that the real problem was substandard and improperly installed gear.

T-Mobile later agreed, and participated in a joint filing of proposed technical standards.  In a startling burst of rationality, the FCC rejected the CTIA's petition, while adopting the T-Mobile/Verizon/Wilson proposal for further study.

While technical standards are likely to become more rigid (and correctly so), it appears that repeaters and amplifiers are here to stay.

And with that, it's time for me to finish packing my apartment.  Beijing has been amazing, and I can't wait for whatever is next!

References

Shout Outs

Thanks to DJ Bolivia for the connection and Andy for the details.  And Kaizoku, Beijing is in your blood!
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