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Sunday, January 24, 2016

CDMA

CDMA

Full form of cdma :-

CDMA- CODE DIVISION MULTIPLE ACCESS 

Now all time the questions arrive 

-> What is CDMA ?

-> GSM vs CDMA 

-> Which one is better GSM or CDMA ?

-> CDMA and 3G ?

These following are the top asked questions from users .
  
Now First of all 

Dafination -

where several transmitters can send information simultaneously over a single communication channel.


Introduction -

Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. 
 Channerl access 

  • 1 Fundamental types of channel access schemes
    • 1.1 Frequency Division Multiple Access (FDMA)
    • 1.2 Time division multiple access (TDMA)
    • 1.3 Code division multiple access (CDMA) / Spread spectrum multiple access (SSMA)
    • 1.4 Space division multiple access (SDMA)
 W-CDMA or WCDMA (Wideband Code Division Multiple Access)

Code Division Multiple Access communication networks have been developed by a number of companies over the years, but development of cell-phone networks based on CDMA (prior to W-CDMA) was dominated by Qualcomm, the first company to succeed in developing a practical and cost-effective CDMA implementation for consumer cell phones and its early IS-95 air interface standard has evolved into the current CDMA2000 (IS-856/IS-2000) standard. Qualcomm created an experimental wideband CDMA system called CDMA2000 3x which unified the W-CDMA (3GPP) and CDMA2000 (3GPP2) network technologies into a single design for a worldwide standard air interface. Compatibility with CDMA2000 would have beneficially enabled roaming on existing networks beyond Japan, since Qualcomm CDMA2000 networks are widely deployed, especially in the Americas, with coverage in 58 countries as of 2006. However, divergent requirements resulted in the W-CDMA standard being retained and deployed globally. W-CDMA has then become the dominant technology with 457 commercial networks in 178 countries as of April 2012. Several CDMA2000 operators have even converted their networks to W-CDMA for international roaming compatibility and smooth upgrade path to LTE.





What CDMA vs. GSM Means to You

For call quality, the technology you use is much less important than the way your carrier has built its network. There are good and bad CDMA and GSM networks, but there are key differences between the technologies. Here's what you, as a consumer, need to know.
It's much easier to swap phones on GSM networks, because GSM carriers put customer information on a removable SIM card. Take the card out, put it in a different phone, and the new phone now has your number. What's more, to be considered GSM, a carrier must accept any GSM-compliant phone. So the GSM carriers don't have total control of the phone you're using.
That's not the case with CDMA. In the U.S., CDMA carriers use network-based white lists to verify their subscribers. That means you can only switch phones with your carrier's permission, and a carrier doesn't have to accept any particular phone onto its network. It could, but typically, U.S. carriers choose not to.
Many Sprint and Verizon phones now have SIM cards, but that isn't because of CDMA. The SIM cards are generally there for Sprint's and Verizon's 4G LTE networks, because the LTE standard also uses SIM cards. The phones may also have SIM slots to support foreign GSM networks as "world phones." But those carriers still use CDMA to authenticate their phones on their own home networks.
3G CDMA networks (known as "EV-DO" or "Evolution Data Optimized") also, generally, can't make voice calls and transmit data at the same time. Once more, that's an available option (known as "SV-DO" for "Simultaneous Voice and Data Optimization"), but one that U.S. carriers haven't adopted for their networks and phones.
On the other hand, all 3G GSM networks have simultaneous voice and data, because it's a required part of the spec. (3G GSM is also actually a type of CDMA. I'll explain that later.)
So why did so many U.S. carriers go with CDMA? Timing. When Verizon's predecessors and Sprint switched from analog to digital in 1995 and 1996, CDMA was the newest, hottest, fastest technology. It offered more capacity, better call quality and more potential than the GSM of the day. GSM caught up, but by then those carriers' paths were set.
It's possible to switch from CDMA to GSM. Bell and Telus in Canada have done it, to get access to the wider variety of off-the-shelf GSM phones. But Verizon and Sprint are big enough that they can get custom phones built for them, so they don't see the need to waste money switching 3G technologies when they could be building out their 4G

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