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Quoth · 07-21-2020, 04:48 AM

"CDMA" is a generic term in the USA. It covers two kinds of US only 2G services that don't use a SIM. Technically 3G does also use a form of CDMA (Because of Qualcomm, a retrograde step), but outside the USA it's never called CDMA. There are three main variations of 3G data: Original 245K and various faster modes such as HSPA.
The USA only CDMA (US 2G) was never in Europe I think. The European 2G is using GSM, which always has a SIM. Apple wants SIMs to be software rather than a small card so they can have more control. Like the 3.5mm jack it's not actually about cost or space. The USA also has GSM, but on a different band to the original European GSM.
Later 1.8 GHz was added for GSM in Europe and in some places that's migrated to 3G.
Ironically GSM is the most reliable at long distance with low usage for voice. USA 2G CDMA and all 3G suffer cell breathing where calls are dropped as more users connect and further out users can't connect. The GSM doesn't breathe, the 4G mostly doesn't.
For 1 to 4 users the 4G and 5G are no faster at all in the same size channel. At 10 users the 4G supports twice the speed as 3G in the same channel, because CDMA is rubbish for mobile. Only because of Qualcomm wanting to dip their 2G CDMA patents it was used in 3G. CDMA was invented for secure two user half duplex military communication. It's always been a rubbish solution as more users are added on WiFi or Mobile.
Also 4G has NO voice mode. Voice calls have to use the data mode and VOIP which uses far more channel capacity than GSM or 3G. USA 2G CDMA is inefficient for voice.

I suspect some of the "CDMA" closures announced in the USA are not GSMA 3G, but the early 2G CDMA.
The 4G really needs 20 MHz channels to have a x4 performance boost over 5MHz channels. Some places only have 5MHz channels, and with small numbers of users there is little difference between 3G and 4G.
Also the word "cellular" is a clue. You need an absolute minimum of 3 channels, and ideally 9 channels to build a cellular network as the masts typically divide the area into 3 overlapping beams around the circle and any phone/modem has to pick up one mast much stronger than a further away one on the same channel. The reasonably received masts need to be on different channels.

You add more capacity by dividing a cell into 3 or 9 smaller cells.

07-21-2020, 04:48 AM	#428
Quoth Still reading Posts: 14,420 Karma: 107078855 Join Date: Jun 2017 Location: Ireland Device: All 4 Kinds: epub eink, Kindle, android eink, NxtPaper	"CDMA" is a generic term in the USA. It covers two kinds of US only 2G services that don't use a SIM. Technically 3G does also use a form of CDMA (Because of Qualcomm, a retrograde step), but outside the USA it's never called CDMA. There are three main variations of 3G data: Original 245K and various faster modes such as HSPA. The USA only CDMA (US 2G) was never in Europe I think. The European 2G is using GSM, which always has a SIM. Apple wants SIMs to be software rather than a small card so they can have more control. Like the 3.5mm jack it's not actually about cost or space. The USA also has GSM, but on a different band to the original European GSM. Later 1.8 GHz was added for GSM in Europe and in some places that's migrated to 3G. Ironically GSM is the most reliable at long distance with low usage for voice. USA 2G CDMA and all 3G suffer cell breathing where calls are dropped as more users connect and further out users can't connect. The GSM doesn't breathe, the 4G mostly doesn't. For 1 to 4 users the 4G and 5G are no faster at all in the same size channel. At 10 users the 4G supports twice the speed as 3G in the same channel, because CDMA is rubbish for mobile. Only because of Qualcomm wanting to dip their 2G CDMA patents it was used in 3G. CDMA was invented for secure two user half duplex military communication. It's always been a rubbish solution as more users are added on WiFi or Mobile. Also 4G has NO voice mode. Voice calls have to use the data mode and VOIP which uses far more channel capacity than GSM or 3G. USA 2G CDMA is inefficient for voice. I suspect some of the "CDMA" closures announced in the USA are not GSMA 3G, but the early 2G CDMA. The 4G really needs 20 MHz channels to have a x4 performance boost over 5MHz channels. Some places only have 5MHz channels, and with small numbers of users there is little difference between 3G and 4G. Also the word "cellular" is a clue. You need an absolute minimum of 3 channels, and ideally 9 channels to build a cellular network as the masts typically divide the area into 3 overlapping beams around the circle and any phone/modem has to pick up one mast much stronger than a further away one on the same channel. The reasonably received masts need to be on different channels. You add more capacity by dividing a cell into 3 or 9 smaller cells.