TECHNOLOGY USED IN CDMA
Basically, both CDM and GSM technologies address differently the same fundamental problem of mobile communication, how to divide the finite frequency of air waves between multiple users at the same time. In CDMA it uses a special type of digital modulation called Spread Spectrum, which takes the user's voice stream bits and splatters them across a very wide channel in pseudo-random fashion.
Code-division multiple access is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. CDMA uses following Technology and standards:
IS 95 :
The CDMA technology based on the IS-95 protocol standard .The CDMA technology, used in the Interim Standard IS-95, maximizes spectrum efficiency and enables more calls to be carried over a single. In a CDMA system each digitized voice is assigned a binary sequence that directs the proper response signal to the corresponding user. The receiver demodulates the signal using the appropriate code. The resulting audio signal will contain only the intended conversation, eliminating any background noise.
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CDMA employs analog to digital signal conversion in combination with spread spectrum technology. In this technology audio is first digitized (ADC) into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern, so it can be intercepted only by a receiver whose frequency response is programmed with the same code.
CDMA is form of multiplexing (access to the same resource will be given to the more than one user) which allows the use of a particular frequency of a number of signals, optimizing the use of available bandwidth. It is a cellular technology that uses the spread spectrum technology. In CDMA technology every channel uses the full available spectrum.
CDMAONE technology improves quality of service through the use of soft handoffs, which greatly reduce the number of dropped calls and ensure a smooth transition between cells. CDMAONE technology also takes advantage of multipath fading to enhance communications and voice quality.
Optical multimedia CDMA system with novel multiplexing techniques
Four novel multiplexing techniques are VSM, PSM, RPM, OIM. PSM and VSM have the advantages of easily adding and controlling the inserting code system, but with a limited successful number. RPM can dynamically add the inserting codes into the original codes at the price of a complicated algorithm and lower multiplexing speed.
The W-CDMA system is a new design by NTT DoCoMo, and it differs in many aspects from CDMA2000. From an engineering point of view, W-CDMA provides a different balance of trade-offs between cost, capacity, performance, and density; it also promises to achieve a benefit of reduced cost for video phone handsets.
High Speed Packet Access:
HSPA is a collection of two mobile telephony protocols, HSDPA and HSUPA. HSPA improves the end-user experience by increasing peak data rates up to 14 Mbit/s in the downlink and 5.8 Mbit/s in the uplink. It also reduces latency and provides up to five times more system capacity in the downlink and up to twice as much system capacity in the uplink, reducing the production cost per bit compared to original WCDMA protocols.
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The successor to CDMA2000 is LTE, part of the competing 3GPP family.
Spatial multiplexing is a transmission technique in MIMO (multiple-input and multiple-output) wireless communication to transmit independent and separately encoded data signals. Therefore, the space dimension is reused, or multiplexed, more than one time.
Its characteristics are:
Several different data bits are transmitted via several independent (spatial) channels.
Always on Time
Marked to Standard
No bandwidth expansion.
Space-time equalization needed in the receiver.
it is a way to fight against fades. If a radio signal is received through one channel in a deep fading environment then there is a possibility of losing that signal, if lost then there is nothing that can be done to recover. That is why diversity technique is used to improve system performance in the presence of fading channel. In this technique, signals are transmitted and received through a number of channels instead of only one channel http://hubpages.com/hub/spatial-multiplexing-spatial-diversity
IMPLEMENTATION OF CDMA TECHNOLOGY
As a security view we know that it is very secure and when we look its history it was used for the military operation in second world war. CDMA uses spread spectrum technique to increase spectrum efficiency over current FDMA and TDMA systems. This covers high range and delivers secure communication. So there is a chance of CDMA in Military and marines areas. CDMA provide fast and secure communication, it cannot be hacked easily due to its nature. So it can be implemented in security area where secure communication is required.
This technology can be implemented in those areas where Population density is too low. We know CDMA technology provide signal in high range. So implementing CDMA technology, we can save cost in order to stand this technology. It saves costs of calls so it can be implemented in those area and locality where people are too poor and unable to bear out so many expanses on mobile phones. CDMA covers large geographical area so it can be implemented in Desert areas, hill Areas, Seas etc. In this area CDMA will save costs as well as provide a clear communication to the users.
CDMA technology is best suited in Developing Country, where people are not economically well and those localities where people are not more literate. They have a single purpose to use mobile phones that is Communication.