Date: Sun, 01 Feb 2009 08:16:08 -0700
>From: Robert Neville
>To: snipped-for-privacy@invalid.telecom.csail.mit.edu
>Subject: Re: nano cell site
>Message-ID:
>
> snipped-for-privacy@panix.com (Scott Dorsey) wrote:
>
>>No, the device talks to your phone and it also talks to a local
>>cell tower. It acts effectively as a repeater.
>
>There are two types of devices. One is a true repeater, where you install an
>antenna on a roof or tower to pick up the cell signal, then rebroadcast it on
>another antenna inside the building. These work for any cell company and any
>number of users.
>
>The devices being discussed are femtocells. These are restricted to a specific
>company, plug into a broadband connection and act as mini cell towers. The
>communicate back to the cell network over your broadband connection, not
through the cell company air network.
>AIUI, the femtocells allow you to restrict the number of users by specific
>phone. At least one model restricts originating calls to within 15' of the
>femtocell. Whether you can leave them open to all phones, I don't know. They
>also have a GPS receiver embedded that prevents them from being used outside the US.
I don't know the specific details about how the "femtocell" base station which connects via a broadband internet connection works, but Robert Neville has done a good job at explaining the difference between this device and the cellular "boosters" (repeaters) which use a high gain antenna to provide a connection to the existing wireless cellular network.
I tried one of these repeater devices made by Zboost
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because my home is poorly served by AT&T's wireless signal. (There are three AT&T towers nearby, but because of a strange quirk of geography and fate, my location is shielded from each by relatively a small rock out-cropping, dense forest, and the shadow of a hillside. For that reason, I am now using Verizon -- without the Zboost -- because it has one tower which is just high enough to provide a signal over the intervening hillside.)
Quoting from the Zboost manual:
Before installing zBoost in your home, make sure that you can place calls
>on the outside of your home or in the attic or at roof level where you
>will install the signal antenna. The zBoost Series can only bring cell
>phone signals into your home if cell phone signals are reaching the
>outside of your home, your attic or at roof level.
>
>Using your cell phone, place a call from an outdoor location to confirm
>that enough signal is present to complete the call. If a weak signal is
>available at ground level, check the signal strength in an attic or roof
>level location where the signal antenna could be installed for best >performance.
>
>If you can reliably make and receive calls outside your home, then zBoost
>can bring the signal into your home.
>
>The Zboost YX500/510 Series is designed to cover multiple signals
>simultaneously and will allow multiple users to operate at the same time.
>For example, if there were 8 people in the same room then the system
>would help each of them.
(The full manual for this device is may be found online in PDF format at
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)
Worth noting is that the Zboost does some clever stuff in choosing which frequencies to use so that it minimizes the likelihood that it will feedback its own signal. That means that if it is communicating with the local cell tower one channel, it will use a different channel to communicate with your handset. This gets even more interesting, because the Zboost will also try to confirm that the channel is available and not it use by your next door neighbor communicating directly with the cell tower -- something which would cause an obvious conflict.
It would seem that any "femtocell" device would need to do similar signal processing to assure that it was not stepping on a channel in use by another nearby femtocell device (say, your upstairs neighbor in an apartment building) or on a signal from the phone company's own cell towers in the area.
In other words, the problem of integrating femtocells into an existing cellular network is not trivial and is more complicated than just connecting a cordless phone base station to a VoIP interface device.
I'd also be curious to know if one can set up a femtocell device to recognize only one's own handset(s) or if the femtocell is promiscuous and available for use by anyone within its range. Specific situations might determine how one would want one's femtocell configured: to keep one's neighbors from using one's limited backhaul bandwidth or to allow friends to be able to make and receive calls using their own handsets when visiting.
Just some thoughts.
Regards, Will