| Michael D. Sullivan 2007-03-13, 4:33 am |
| On 3/12/2007 4:03 PM, John R. Copeland wrote:
> "baumgrenze" <baumgrenze@yahoo.com> wrote . . .
& #91;snip][color=dark
red]
As John Copeland indicates below, the bars don't correspond to the
number of towers. In fact, they provide a pretty gross approximation of
the tower's signal strength. Your phone may have a diagnostic or test
mode that allows it to display the received signal strength in dBm and
identifiers of multiple towers.
If the bars did correspond to towers, and if you were receiving plain
old FM signals, yes. With CDMA, no. A CDMA network allows your phone
to receive, and transmit to, multiple cells operating on the same
channel. The network decides which tower will establish communications
with your handset, and it changes that decision as traffic demands.
This is known as "soft handoff".
[color=darkred]
One problem with your proposal is that the power transmitted from CDMA
towers varies continuously. Your phone may be within easy
communications range of two towers, but both towers power down because
they are carrying a large number of conversations from subscribers close
in. As a result, the phone shows only one bar and can't make a call.
Later, the same phone in the same location may show five bars and can
make calls without any problem.
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> First, I was amazed that you had signal problems with 5 *towers*.
> It's a little unusual to be served simultaneously by five cell towers.
> Later, I realized you meant *bars* of signal strength on your display.
> Possibly you are getting services from a single cell tower.
>
> Next, forget about the destructive interference idea.
> That's a discrete-frequency phenomenon caused by multi-path propagation.
> CDMA is a wide-spectrum signal, and multi-path signals do not kill it.
> Even better, your handset uses multiple correlators in a "Rake Receiver"
> which has the effect of receiving multi-path signals separately,
> and combining them so as to actually *improve* reception, not degrade it.
>
> Finally, locate the actual cell tower(s) serving your area,
> and check for possible shadowing of the area where you lose signal.
> Perversely, some of the shadowed areas can be filled in by signals
> reflected from houses and buildings, so some places which seem ought
> to be in shadow, may in fact have useful coverage by reflections.
>
> And one added item about the handset's display of bars.
> Some handsets possibly still show the signal strength per se,
> but there's been a trend toward showing signal-to-noise ratio instead.
> If your LG shows S/N ratio, then you'd see fewer bars in high-noise areas,
> even if the actual signal *strength* remained constant.
Actually, in CDMA S/N ratio is pretty much irrelevant. The factor used
in determining call quality is Eb/N0. Damned if I know what it stands
for, though.
--
Michael D. Sullivan
Bethesda, MD (USA)
(To reply, change example.invalid to com in the address.)
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