CDMA (Code Division Multiple Access) and GSM (Global System for Mobiles) are shorthand for the two major radio systems used in cell phones. Both acronyms tend to group together a bunch of technologies run by the same entities. In this story, I'll try to explain who uses which technology and what the real differences are.
Most of countries in the world uses GSM. The global spread of GSM came about because in 1987, Europe mandated the technology by law, and because GSM comes from an industry consortium. What we call CDMA, by and large, is owned by chipmaker Qualcomm. This made it less expensive for third parties to build GSM equipment.
CDMA is the Code Division Muitiple Access (code division Muitiple Access), which is a new and mature wireless communication technology developed on the branch of digital technology-spread spectrum communication technology. The principle of CDMA technology is based on spread spectrum technology, which is to transmit a certain signal bandwidth information data, and is modulated by a high-speed pseudo-random code whose bandwidth is much larger than the signal bandwidth, so that the bandwidth of the original data signal is expanded, and then modulated by carrier. Send it out. The receiving end uses the identical pseudo-random code to perform correlation processing with the received bandwidth signal, and the narrowband signal of the original information data is despreaded to realize information communication.
There are several classification methods for mobile communication systems. For example, according to the nature of the signal, it can be divided into analog and digital; according to the modulation method, it can be divided into frequency modulation, phase modulation and amplitude modulation; according to the multiple access connection method, it can be divided into frequency division multiple access (FDMA) and time division multiple access ( TDMA) and Code Division Multiple Access (CDMA). At present, the GSM mobile phone network used by China Unicom and China Mobile is a combination of FDMA and TDMA. GSM has great advantages over analog mobile phones, but it is only three times more spectrally efficient than analog systems, and its capacity is limited. It is also difficult to achieve wired telephone quality in terms of voice quality.
CDMA and GSM are both multiple access technologies. They're ways for people to cram multiple phone calls or Internet connections into one radio channel.
GSM came first. It's a "time division" system. Calls take turns. Your voice is transformed into digital data, which is given a channel and a time slot, so three calls on one channel look like this: 123123123123. On the other end, the receiver listens only to the assigned time slot and pieces the call back together.
The pulsing of the time division signal created the notorious "GSM buzz," a buzzing sound whenever you put a GSM phone near a speaker. That's mostly gone now, because 3G GSM (as I explain later) isn't a time division technology.
CDMA required a bit more processing power. It's a "code division" system. Every call's data is encoded with a unique key, then the calls are all transmitted at once; if you have calls 1, 2, and 3 in a channel, the channel would just say 66666666. The receivers each have the unique key to "divide" the combined signal into its individual calls.
Since its inception, GSM has evolved faster than CDMA. As I mentioned above, WCDMA is considered the 3G version of GSM technology. To further speed things up, the 3GPP (the GSM governing body) released extensions called HSPA, which have sped GSM networks up to as fast as 42Mbps, at least in theory.