|I've been taken to task by
some GSM advocates regarding the alleged superiority of GSM voice
quality. One gentleman stated, "Voice quality is not a minor
thing when you spend several hours a day on the phone."
I don't dispute his contention. But here's the reality of the situation:
- I can't find a single real-life study
or survey that proclaims that GSM voice quality is better than CDMA
voice quality. Every study points to the opposite conclusion, or is
too close to call. I am talking about surveys and studies by
independent entities. I can easily find studies at both the GSM and
CDMA trade organizations, each of which claim superior voice
quality; in my view these studies are too biased to be taken
- The quality (or lack thereof) of the
GSM networks in the U.S. masks the fact that GSM is actually capable
of providing better voice quality than CDMA. In other words, all
things being equal, GSM will sound better than CDMA, but all
things are not equal.
- In a perfect world, with 800 Mhz CDMA
on an uncongested network versus 800 Mhz GSM on an uncongested
network, GSM will indeed sound better than CDMA. If the GSM
advocates are saying that GSM in Europe and Asia sounds better than
CDMA in the U.S., I'll agree completely, as I've experienced it
personally. When the U.S. GSM networks sound better than the U.S.
CDMA networks, and I believe that this will eventually be the case,
I will certainly change the voice quality ratings for GSM in the
technology comparison table from "Good" to
- The comparisons put forward by GSM
advocates invariably compare a congested CDMA network to a GSM
network; indeed, under this scenario there will be a very big
difference in voice quality.
- There are not many places where CDMA
congestion is actually a problem. At special events, where network
congestion is a real possibility, both the CDMA and the TDMA/GSM
carriers roll in mobile cells to handle it. These mobile cells
prevent deterioration of the CDMA voice quality and prevent
"system busy" problems on TDMA and GSM networks.
- Both CDMA and GSM are
"improving" their vocoders in order to increase capacity.
Both camps claim that the vocoders with lower bit rates sound the
same or better than the higher rate vocoders they are replacing.
CDMA is further along in reducing the bit rates than GSM. CDMA
networks are switching from the QCELP-13 vocoder (13kb/s) to
EVRC vocoders with an 8kb/s coding rate. GSM networks are switching
from a 13kb/s EFR vocoder to an AMR (adaptive multi-rate) vocoder.
AMR vocoders vary their bit rate based on network quality. There was
an attempt by Vodafone to use half-rate GSM vocoders but the poor
voice quality resulted in so many complaints that they dropped it.
Next, the CDMA networks are going to deploy SMV (selectable
mode vocoder) vocoders. Naturally, the CDMA lobbying group claims
that the SMV vocoder is better than the AMR vocoder (and has posted
the results of listening tests). It is safe to say that the CDMA
EVRC vocoder is worse than the GSM AMR vocoder, but it is also
likely that the SMV vocoder will improve CDMA voice quality to equal
or better than the GSM AMR vocoder. SMV vocoders still give the CDMA
carriers the ability to trade capacity for quality. Note that a
handset with an older, higher bit-rate vocoder will continue to work
just fine on networks with the "improved" vocoders, and it
may be a bad decision to "upgrade" your handset to one
that has an "improved" vocoder.
- People will put up with different
things based on their being mobile or stationary, and based on
whether they are making calls or receiving calls. The result of
Vodafone's failed attempt to use half-rate GSM vocoders in Europe
showed that users valued voice quality over the ability to make a
call at all. If a user is stationary they would probably be willing
to hit re-dial a few times (or a few dozen times) to get a
dedicated GSM slot that is of discernibly higher voice quality than
CDMA. If they are mobile, they would likely prefer not having the
call drop as they move from cell to cell, even at the expense of
lower voice quality. The big difference is for incoming calls.
Subscribers don't want to miss calls, especially emergency calls
(knock on wood), because there are no free GSM slots; yet this is exactly
what I've experienced with GSM in its current state in the U.S..
- This debate reminds me of the
Ethernet/Token Ring debate of a decade ago. In a very heavily loaded
network it is possible for Ethernet to be slower than Token Ring.
But the reality was that this did not happen because if the network
became too congested it was simply split into segments. Similarly,
if a CDMA cell is consistently congested then another cell will be
added; it is even possible to add more cells to one cell site via
directional antennas. Wow, CDMA has a lot in common with CSMA/CD.