CDMA stands for code division multiple access. As the name suggests the CDMA wireless technology is able to accommodate multiple users at the same time using the same spectrum with each user having a digital random encoding to access the system. This technology like many other important ones traces its roots to the military during the second world war when the British and their allies are reported to have used the technology to confuse the Germans. Since it is allows many channels at the same time, the Germans were unable to intercept the messages.
CDMA Technical Details
CDMA works by converting analogue to digital signals using the spread spectrum technology to increase the number of connections to multiple signals. The sent signal is given a defined code which can only be received by someone on the other side with the exact code. This makes CDMA the most secure wireless technology since it is not possible to intercept because there are millions of possible combination codes to use.
When a call is made on a CDMA line, it is first transmitted to the nearest base station, from the base station it goes to the mobile switching center, the mobile switching center modulates and encodes the particular signal. It is then routed to the call processing system through a high speed interconnection router.
From there it is connected to the base trans receiver system where through the mobile switching center using the same code it is connected to the receiver on the other side from the nearest base station. CDMA uses the standard IS-95A with a 45MHz separation between the uplink and the downlink. Each CDMA channel has a bandwith of 1.25MHz.
CDMA phones are usually given a code which represents their number unlike GSM phones which have a sim card.It is therefore not possible to unlock then from the network provider who issued them. The only exception would be if one were to manage to get the provider themselves to release the code.
The current CDMA standards have incorporated 3G therefore the technology is able to deliver data, MMS, SMS and other related services faster. The differences between CDMA and GSM for the end consumer also depend on the network and the infrastructure of each company. There may be companies offering a superior GSM service while others a better CDMA technology. Again for a consumer, a GSM phone is better because they can switch networks simply by changing a SIM card.However most networks in the US use CDMA technology so you may not have much of a choice. The two standards have also merged in a way since 3G GSM actually uses CDMA technology.
When it comes to Multi Media Messaging Services and SMS most providers use CDMA technology since it is able to carry a lot more data including pictures due to its capabilities of many combinations. Like mentioned above this is the reason GSM networks now use CDMA for their data and messaging services.
In terms of technology, it looks like a merge of the two technologies is the best way forward so as to maximize on the benefits associated with each. The stability and security of CDMA means that the technology will continue to be used in the future unless a newer more secure one is developed.