CDMA or GSM?

[Jake]

What is the real difference other than roaming in Europe about GSM or
CDMA? which would you reccomend?

[John Henderson]

Post by Jake
What is the real difference other than roaming in Europe
about GSM or CDMA? which would you reccomend?

2G GSM uses a form of "time division" (TDMA) to keep concurrent
calls from interfering with each other.

3G GSM (or "UMTS") uses a form of "code division" (CDMA) to
achieve the same end. UMTS is often referred to as W-CDMA to
distinguish it from the older CDMA systems.

CDMA systems are not distance-limited by timing constraints.
Normal 2G GSM cells have an absolute maximum range of 35 km
(regardless of signal strength). Because of the density of
cells in populated areas, this limit does not usually become
significant. But it can seriously affect ordinary GSM coverage
in sparsely-populated rural areas.

The best system will often come down to a matter of which system
has coverage in the region where you want to operate.

3G GSM (by whatever name: UMTS, W-CDMA) is the way of the
future. This is where the explosion in handset availability
and features will occur.

John

[Bert Hyman]

Post by Jake
What is the real difference other than roaming in Europe about GSM
or CDMA? which would you reccomend?

I like the fact that I'm free to use any unlocked phone with the SIM
for my account without any intervention by my carrier [assuming that
the phone operates on the bands my carrier uses].

[SMS]

Post by Jake
What is the real difference other than roaming in Europe about GSM or
CDMA? which would you reccomend?

In the U.S., if you're traveling to rural areas then go CDMA as you'll
get much better rural coverage than GSM because the maximum GSM distance
is limited to 35km.

Actually there's more to it than just GSM versus CDMA, you also have to
look at 800 MHz versus 1900 MHz. The best choice, in terms of the best
coverage, would be a carrier that is both 800 MHz and CDMA. This is why
Verizon and Alltel are consistently ranked as the best carriers in every
metropolitan area in the U.S..

[Andreas Wenzel]

Post by SMS

Post by Jake
What is the real difference other than roaming in Europe about GSM or
CDMA? which would you reccomend?

In the U.S., if you're traveling to rural areas then go CDMA as you'll
get much better rural coverage than GSM because the maximum GSM distance
is limited to 35km.[...]

This is often heard but has not been true for quite a while now.
Extended range GSM cells are available from many infrastructure vendors,
offering cell ranges of approx. 120km. The trick is to tell the mobile a
timing advance value that corresponds to the distance betweenn mobile
and base station modulo 35km, and then to expect to receive the signal
from the mobile by one or two timeslots late.

Full description here (but difficult to read):
http://www.freepatentsonline.com/6633559.html

Andreas

[John Henderson]

Post by Andreas Wenzel
This is often heard but has not been true for quite a while
now. Extended range GSM cells are available from many
infrastructure vendors, offering cell ranges of approx. 120km.
The trick is to tell the mobile a timing advance value that
corresponds to the distance betweenn mobile and base station
modulo 35km, and then to expect to receive the signal from the
mobile by one or two timeslots late.
http://www.freepatentsonline.com/6633559.html

Yes, but it is increasingly true that GSM is limited to 35 km.
The installed base of ER (Extended Range) GSM cells was always
very, very small (and non-existant in most countries). They
can handle only half the number of calls of standard cells
because half the available timeslots are sacrificed to the job
of extending Timing Advance on the other half.

More importantly, the only manufacturer of ER cells (Ericsson)
has not made any GPRS-compatible versions. With GPRS expected
as an important part of GSM coverage, ER cells are being
converted to standard cells rather than vice versa.

John

[Andreas Wenzel]

Post by John Henderson
[...]
Yes, but it is increasingly true that GSM is limited to 35 km.
The installed base of ER (Extended Range) GSM cells was always
very, very small (and non-existant in most countries). They
can handle only half the number of calls of standard cells
because half the available timeslots are sacrificed to the job
of extending Timing Advance on the other half.

The patent in the link claims to describe a method that works without
sacrificing half of the timeslots.

Post by John Henderson
More importantly, the only manufacturer of ER cells (Ericsson)
has not made any GPRS-compatible versions. With GPRS expected
as an important part of GSM coverage, ER cells are being
converted to standard cells rather than vice versa.

At least Motorola sells extended range BTSs as well. Do you have any
documentation that explays as to why GPRS and extended range should not
go together?

Andreas

[John Henderson]

Post by Andreas Wenzel

Post by John Henderson
[...]
Yes, but it is increasingly true that GSM is limited to 35
km. The installed base of ER (Extended Range) GSM cells was
always
very, very small (and non-existant in most countries). They
can handle only half the number of calls of standard cells
because half the available timeslots are sacrificed to the
job of extending Timing Advance on the other half.

The patent in the link claims to describe a method that works
without sacrificing half of the timeslots.

If that's the case, then this is a new development. That
wording is too obscure for me to put a firm interpretation onto
it without giving it a great deal of time and thought. Thanks
for the reference.

Post by Andreas Wenzel

Post by John Henderson
More importantly, the only manufacturer of ER cells
(Ericsson)
has not made any GPRS-compatible versions. With GPRS
expected as an important part of GSM coverage, ER cells are
being converted to standard cells rather than vice versa.

At least Motorola sells extended range BTSs as well. Do you
have any documentation that explays as to why GPRS and
extended range should not go together?

I had not heard of Motorola's entry into this market. Do you
have any references?

I understand the combination of GPRS and ER to be just "too
hard" (given the potential market), rather than impossible. If
GPRS ER develoment has been done recently, then it may be too
little, too late (with UMTS being pushed). Certainly the
number of ER cells in rural Australia was shrinking the last
time I was able to get any information (Vodafone used to
publish a list of cells which were not GPRS-compatible).

I quite like the guaranteed call quality from a TDMA-based
system like 2G GSM. CDMA-based systems can cram more data into
the available spectrum, but at the expense of call quality when
the system loads up heavily (especially for distant calls /
weaker signals).

John

[John Henderson]

Post by John Henderson
I had not heard of Motorola's entry into this market. Do you
have any references?
I understand the combination of GPRS and ER to be just "too
hard" (given the potential market), rather than impossible.
If GPRS ER develoment has been done recently, then it may be
too little, too late (with UMTS being pushed). Certainly the
number of ER cells in rural Australia was shrinking the last
time I was able to get any information (Vodafone used to
publish a list of cells which were not GPRS-compatible).

I see that Motorola were planning to sell Extended Range cells,
/with/ /GPRS/ from last year:

http://www.motorola.com/mot/doc/6/6679_MotDoc.pdf

John

[SMS]

Post by Andreas Wenzel

Post by SMS

Post by Jake
What is the real difference other than roaming in Europe about GSM or
CDMA? which would you reccomend?

In the U.S., if you're traveling to rural areas then go CDMA as you'll
get much better rural coverage than GSM because the maximum GSM
distance is limited to 35km.[...]

This is often heard but has not been true for quite a while now.
Extended range GSM cells are available from many infrastructure vendors,
offering cell ranges of approx. 120km. The trick is to tell the mobile a
timing advance value that corresponds to the distance betweenn mobile
and base station modulo 35km, and then to expect to receive the signal
from the mobile by one or two timeslots late.

They're available, but haven't been deployed in the U.S..