CDMA: Code Division Multiple Access
Code Division Multiple Access is a channel access method used by several radio communication technologies. It is a digital cellular technology and an example of multiple access. It is generally used for mobile communication.
Multiple access means that several transmitters can send information simultaneously over a single communication channel. In this system, different CDMA codes are assigned to different users and the user can access the whole bandwidth for the entire duration. It optimizes the use of available bandwidth as it transmits over the entire frequency range and does not limit the user’s frequency range.
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Thus, CDMA allows several users to share a band of frequencies without undue interference between the users. It is used as a access method in many mobile phone standards.
CDMA technology was developed during World War II. It was developed by English allies to protect their wireless transmissions from jamming. When the war ended, Qualcomm patented this technology and made it commercially available. The first CDMA system was launched in September 1995 in Hong Kong by Hutchison Telephone Co.
- It is used in the Global Positioning System (GPS).
- It is used by several mobile phone companies (e.g. Qualcomm standard IS-2000 also known as CDMA2000)
- W-CDMA is used in UTMS 3G mobile phone standard.
- CDMA has been used in OmniTRACS satellite system for transportation.
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Categories of CDMA
- Synchronous CDMA (orthogonal codes)
- Asynchronous CDMA (pseudorandom codes)
Difference between CDMA and GSM
The major difference between CDMA and GSM are given below.
|CDMA is based on spread-spectrum technology which makes the optimum use of available bandwidth.
|GSM operates on the wedge spectrum. it uses both time division multiple access (TDMA) and frequency division multiple access (fdma). TDMA provide multi-user access by cutting up the channel into different time slice and fdma provides the multi-user access by separating the used frequency.
|CDMA is more secure than GSM.
|GSM is less secure than CDMA.
|CDMA is used in usa and some part of canada and japan. CDMA is used only by 24% of the users worldwide.
|GSM is used over 80% of the world network in over 210 countries.
GSM is used 76% of the users worldwide.
|Data Transfer Rate
|CDMA has faster data transfer as compared to GSM.
|GSM has slower data transfer as compared to CDMA.
|CDMA phones emits less radiation than GSM phones.
|GSM phones emits continuous wave pulses and emits almost 28 times more radiation than CDMA phones.