Poor Voice Quality of CDMA is GSM Better?

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playbirdiegolf - 21 Jan 2004 18:12 GMT

I am currently debating to switch from T-Mobile to Verizon. The only
reason I am considering switching is the dropped calls or no signals
from using T-mobile. I currently could not have 5 minute conversation
while at my APT. But works (Nokia 6610) great on the ground floor. I
had tried everything.... new phones, external antennas, service
requests... nothing works.
So I got the new LG VX6000 from Verizon and it works 90% better. Only
one dropped call since using it for a week.
My only complaint... besides not using the Nokia 6610 phone is that I
get complaints from the people I talk to that the sound quality of my
voice is digitized or sounds digital (like I am talking on a cell
phone) where my voice will break up or cut of the end or beginning of
words. And I NEVER HAD THAT HAPPEN WITH T-MOBLILE TO THEIR CREDIT.
I too have noticed this too when talking to Verizon Customers. Call
Quality on my end hearing the conversation is great.. (if they are
not a cell phone or Verizon Wireless) I can hear them great with no
distortion. I did some testing with a friend of mine and the voice
quality on the T-Mobile Network does not do that (when I have a good
signal), and is hard to tell the diff. between a regular phone and a
cell.
Anyone else noticed this? And how can I correct it? Or is this just
the diff. in voice quality from CDMA and GSM. Or is it the LG VX6000
or is the Nokia 6610 a better voice quality phone.
Of course when this occurs I have FULL signal strength and no back
ground noise. I am talking directly into the phone (no headset).

I have the current phone and doubled check the bios\HW\SW versions all
are current.

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James Calivar - 22 Jan 2004 20:15 GMT

> I am currently debating to switch from T-Mobile to Verizon. The only
> reason I am considering switching is the dropped calls or no signals
[quoted text clipped - 9 lines]
> phone) where my voice will break up or cut of the end or beginning of
> words. And I NEVER HAD THAT HAPPEN WITH T-MOBLILE TO THEIR CREDIT.

The voice codecs for CDMA are different than the ones for GSM, and hence
will have different characteristics. The codec you're using in your Verizon
system is probably either the Enhanced Variable Mode Codec (EVRC) or the
Selectable Mode Vocoder (SMV), but it is possible that you're using the
older (and inferior) QCELP13K codec. Some good information on these codecs
can be found at
http://www.commsdesign.com/printableArticle/;jsessionid=VENQN1U0VCWCOQSNDBCS
KHQ?articleID=16500249 .

> I too have noticed this too when talking to Verizon Customers. Call
> Quality on my end hearing the conversation is great.. (if they are
> not a cell phone or Verizon Wireless) I can hear them great with no
> distortion.

Voice codecs used in CDMA systems can have variable rates at which they can
operate. Typically, the higher the data rate it which the codec operates,
the better the voice quality (but of course, this reduces capacity of the
cell in which you're in). Since it is to the cellular operator's advantage
to maximize the capacity of the cell (more paying customers = more revenue),
if you get a lot of users concentrated in one area, the average rate (and
hence the perceived ulaity per user) will decrease. That said, also note
that the radio channel used in the to-user direction is separate from the
radio channel used in the from-user direction - so it is certainly possible
that the rate at which you are *receiving* speech information is higher than
the rate at which you are *tranmsitting*. The net effect is that you hear
high quality voice, but the person on the opposite side of the converstaion
hears "canned" voice.

> I did some testing with a friend of mine and the voice
> quality on the T-Mobile Network does not do that (when I have a good
> signal), and is hard to tell the diff. between a regular phone and a
> cell.

GSM networks allocate a fixed 8 users per cell, and the codecs they use are
fixed-rate. Thus, the quality is always going to be the same, assuming
you're stationary. I've also noticed that the GSM codecs (FR and EFR) are
pretty high-quality.

> Anyone else noticed this? And how can I correct it? Or is this just
> the diff. in voice quality from CDMA and GSM. Or is it the LG VX6000
> or is the Nokia 6610 a better voice quality phone.

It's not the phone - the cellular specifications dictate how a certain codec
will be implemetned, so there should be no difference in the voice quality
using a particular codec from one phone vendor to another. It is simply a
characteristic of the network.

> Of course when this occurs I have FULL signal strength and no back
> ground noise. I am talking directly into the phone (no headset).
>
> I have the current phone and doubled check the bios\HW\SW versions all
> are current.

Hey, at least your calls aren't being dropped! The variable capacity of
CDMA networks is one of its main advantages, and allows for adapting to
users constantly entering and leaving cells without denying or cutting off
calls (albeit at a price, of course - that price being perceived voice quali
ty).

Regards

J

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matt weber - 23 Jan 2004 03:59 GMT

>GSM networks allocate a fixed 8 users per cell, and the codecs they use are
>fixed-rate. Thus, the quality is always going to be the same, assuming
>you're stationary. I've also noticed that the GSM codecs (FR and EFR) are
>pretty high-quality.

Huh...
Each cell phone for voice in a GSM system gets to transmit 217 times
with FR or EFR vocoding per second, and each channel has 8 x 217 time
slots. The number of calls a cell can handle is channels X 8
usually. A channel is 200 Khz, and each cell usually has a number of
channels. a 900 Mhz EGSM system would have 165 channels in each
direction

GSM supports, and many GSM cell phones support the HFR (Half Rate)
Vocoder, which would raise the number of calls per channel to 16, but
I don't know of any service provider using the feature.

In general if there is a voice quality problems when using the EFR
Vocoder, it is either outside the Cell network, or a major screw up by
service provider. The voice quality from the EFR Vocoder is generally
regarded as excellent, and it is fixed bandwidth, so it doesn't
degrade because the service provider cannot crank it down to squeeze
more calls in.

GSM other advantage is that it treats existing calls much better than
CDMA does. In a CDMA system, when the energy in the channel gets too
high, calls start randoming dropping. When you run out of capacity in
GSM, calls aren't dropped unless they are handed off. If you have a
connection, you don't suddenly lose it. You just may not be able to
make any calls when the cell capacity is reached.

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Brian Oakley - 24 Jan 2004 04:07 GMT

> > I am currently debating to switch from T-Mobile to Verizon. The only
> > reason I am considering switching is the dropped calls or no signals
[quoted text clipped - 16 lines]
> older (and inferior) QCELP13K codec. Some good information on these codecs
> can be found at

http://www.commsdesign.com/printableArticle/;jsessionid=VENQN1U0VCWCOQSNDBCS

> KHQ?articleID=16500249 .
>
[quoted text clipped - 51 lines]
>
> J

Whats the use of holding up a call when you cant get all the conversation?
My suggestion is go with Cingular.
B.

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James Calivar - 24 Jan 2004 23:50 GMT

> Whats the use of holding up a call when you cant get all the conversation?
> My suggestion is go with Cingular.
> B.

You can still hear the other person, it's just that the quality of the voice
is lesser. What would you rather have, and entire conversation at a low
quality of voice, or a dropped call in the middle of a high-quality voice
conversation? I would go with the provider that has the best coverage and
lowest % of dropped calls.

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