[opendtv] Re: Will Femtocells Save LTE?
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 27 Apr 2011 06:52:43 -0400
At 3:27 PM -0500 4/26/11, Manfredi, Albert E wrote:
Sorry, Craig, but you misunderstand the problem.
It may even be true that femtocells are most useful indoors, because
it is probably true that indoors is where most people are busiest
with their smartphones. But the idea of femtocells is simply to
create, in a *compatible* with regular-sized outdoor cells, a much
more dense set of cells. You are simply reducing the RF link length,
in order to greatly increase spectrum reuse.
This is not WiFi!
Yes, I understand that femtocells use the 3G radio today. But you are
the one who did not understand. So once again...
Voice traffic is not the major problem, although the quality of voice
service could certainly be improved. The point is that it is high
priority but rather low bandwidth traffic. The primary purpose of
femtocells is to move your voice traffic off of the cellular network.
These cells are also capable of handing off data traffic to the wired
network, but this just duplicates the functionality of the OTHER
radio in the smart phone.
WiFi plays an important role as well. A smart phone will attempt to
use WiFi rather than cellular broadband when it is available. Thus in
my house or the brewery my phone ALREADY moves any data traffic off
of the cellular network. IF no WiFi is available then a femtocell can
be used for data.
I've been reading detailed reports about the data files that Apple is
storing on iPhones, which some reports have incorrectly assumed are
tracking your location. In reality Apple is downloading a database of
local cell towers and WiFi hot spots to the phone to assist with
staying connected and to support location based services. Other
reports yesterday suggest that Apple and Google are constantly
building and updating a massive database of cell towers and Wi-Fi
hotspots.
The underlying philosophy is the same - move the mobile traffic to a
wired network when possible. And yes, using local RF links to
maximize spectrum reuse.
Remember when radio telephones depended on perhaps one operator in
every city? Well, cellular telephony got away from that, allowing
the spectrum to be reused over and over again, within that city. And
femtocells take it another step further.
Did you pay attention to their mention of cell antennas on light
poles, for example?
Yes, I even joked about putting antennas at intersections instead of
red light cameras.
This is already happening in some cities with WiFi.s a
But it does not work as well when there is a mix of higher and lower
powered signals using the same spectrum. If there is a "high powered"
cellular tower using that frequency, you cannot reuse that spectrum
with an overlaid network of femtocells on the same frequency.
As I pointed out, these lower powered devices are best for filling in
holes, especially in buildings where the signals from the cell towers
are blocked. AND they are useful in locations where there is very
high traffic like train stations, since the tiny RF footprint allows
spectrum reuse within that location.
When I am at home and work (or in the hotel where I am currently staying)
my cellphone ALREADY uses WiFi for data.
That's not femtocells. That's perhaps picocells. Femtocells are
standard 3G or 4G cells, only a lot smaller in area of coverage.
Yes Bert. You are ignoring the point. Smartphones ALREADY use WiFi to
take traffic off of the cellular network. And when the carriers move
to VOIP instead of dedicated voice channels, then the voice traffic
can also move to WiFi 0 you would not even need a femtocell. So in
essence femtocells are a temporary solution - something ELSE the
telcos can sell you to help them manage their voice networks.
When we move to 4G LTE networks with VOIP, your smartphone will
constantly be looking for WiFi hot spots to take traffic off of the
expensive telco networks.
Just like regular cells, they use exactly the same spectrum assigned
to that service provider. They simple REUSE the spectrum more
effectively.
EXACTLY, but only in areas where their low power levels exceed the
levels of the signals from the cell towers.
This does a whole lot more for personal wireless comms than adding
maybe four 20 MHz slices, by grabbing all that TV spectrum. But, as
I said, it doesn't have the same dramatic feel. Still, it is the
FCC's job to understand these tradeoffs. Their advisory council
figured it out. Will the FCC listen? Or will they charge along, come
hell or high water?
In reality BOTH are necessary. There are many areas where you can
off-load traffic to WiFI, and there are some areas where you can use
micro, pico and femtocells to achieve improved spectral reuse. But
there are many other areas where the only solution is more spectrum
to handle the rapidly increasing demand for mobile broadband. Tiny
cell footprints are not going to help much along the Interstate
highways unless you place them at 200-500 meter intervals.
You can only push spectral re-use so far. At some point you need more
frequencies to handle more traffic.
Regards
Craig
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