What is the CDMA technology used in Mobile Communication?

Question

What is cdma?

Answer 1

Code division multiple access (CDMA) is a form of multiplexing (not a modulation scheme) and a method of multiple access that does not divide up the channel by time (as in time division multiple access), or frequency (as in frequency-division multiple access), but instead encodes data with a special code associated with each channel and uses the constructive interference properties of the special codes to perform the multiplexing. CDMA also refers to digital cellular telephony systems that make use of this multiple access scheme, such as those pioneered by Qualcomm, and W-CDMA by the International Telecommunication Union or ITU.

CDMA has since been used in many communications systems, including the Global Positioning System and in the OmniTRACS satellite system for transportation logistics.

Usage in mobile telephony

A number of different terms are used to refer to CDMA implementations. The original U.S. standard defined by QUALCOMM was known as IS-95, the IS referring to an Interim Standard of the Telecommunications Industry Association (TIA). IS-95 is often referred to as 2G or second generation cellular. The QUALCOMM brand name cdmaOne may also be used to refer to the 2G CDMA standard. The CDMA has been submitted for approval as a mobile air interface standard to the ITU International Telecommunication Union.

Whereas the Global System for Mobile Communications (GSM) standard is a specification of an entire network infrastructure, the CDMA interface relates only to the air interface—the radio part of the technology. For example GSM specifies an infrastructure based on internationally approved standard while CDMA allows each operator to provide the network features as it finds suited. On the air interface, the signalling suite (GSM: ISDN SS7) work has been progressing to harmonise these.

After a couple of revisions, IS-95 was superseded by the IS-2000 standard. This standard was introduced to meet some of the criteria laid out in the IMT-2000 specification for 3G, or third generation, cellular. It is also referred to as 1xRTT which simply means "1 times Radio Transmission Technology" and indicates that IS-2000 uses the same 1.25 MHz shared channel as the original IS-95 standard. A related scheme called 3xRTT uses three 1.25 MHz carriers for a 3.75 MHz bandwidth that would allow higher data burst rates for an individual user, but the 3xRTT scheme has not been commercially deployed. More recently, QUALCOMM has led the creation of a new CDMA-based technology called 1xEV-DO, or IS-856, which provides the higher packet data transmission rates required by IMT-2000 and desired by wireless network operators.

The QUALCOMM CDMA system includes highly accurate time signals (usually referenced to a GPS receiver in the cell base station), so cell phone CDMA-based clocks are an increasingly popular type of radio clock for use in computer networks. The main advantage of using CDMA cell phone signals for reference clock purposes is that they work better inside buildings, thus often eliminating the need to mount a GPS antenna on the outside of a building.

This CDMA system is frequently confused with a similar but incompatible technology called Wideband Code Division Multiple Access (W-CDMA) which forms the basis of the W-CDMA air interface. The W-CDMA air interface is used in the global 3G standard UMTS and the Japanese 3G standard FOMA, by NTT DoCoMo and Vodafone; however, the CDMA family of US national standards (including cdmaOne and CDMA2000) are not compatible with the W-CDMA family of International Telecommunication Union (ITU) standards.

Another important application of CDMA — predating and entirely distinct from CDMA cellular — is the Global Positioning System or GPS.

[edit] Coverage and Applications

The size of a given cell depends on the power of the signal transmitted by the handset, the terrain, and the radio frequency being used. Various algorithms can reduce the noise introduced by variations in terrain, but require extra information be sent to validate the transfer. Hence, the radio frequency and power of the handset effectively determine the cell size. Long wavelengths need less energy to travel a given distance vs. short wavelengths, so lower frequencies generally result in greater coverage while higher frequencies result in shorter coverage. These characteristics are used by mobile network planners in determining the size and placement of the cells in the network. In cities, many small cells are needed; the use of high frequencies allows sites to be placed more-closely together, with more subscribers provided service. In rural areas with a lower density of subscribers, use of lower frequencies allows each site to provide broader coverage. (See also the Market situation section of GSM.)

Various companies use different variants of CDMA to provide fixed-line networks using Wireless local loop (WLL) technology. Since they can plan with a specific number of subscribers per cell in mind, and these are all stationary, this application of CDMA can be found in most parts of the world.

CDMA is suited for data transfer with bursty behaviour and where delays can be accepted. It is therefore used in Wireless LAN applications; the cell size here is 500 feet because of the high frequency (2.4 GHz) and low power. The suitability for data transfer is the reason for why W-CDMA seems to be "winning technology" for the data portion of third-generation (3G) mobile cellular networks.

Answer 2

Short for Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM, that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.

CDMA is a military technology first used during World War II by English allies to foil German attempts at jamming transmissions. The allies decided to transmit over several frequencies, instead of one, making it difficult for the Germans to pick up the complete signal. Because Qualcomm created communications chips for CDMA technology, it was privy to the classified information. Once the information became public, Qualcomm claimed patents on the technology and became the first to commercialize it.

Answer 3

CDMA, or Code Division Multiple Access is the technolgy that Verizon and Sprint use in nationwide networks. TDMA phones assign up to six calls in a single frequency, with each call getting only 1/6 or each second's airtime to transmit the voice.

CDMA uses a 16 bit encryption code that allows many callers to use the same frequency at the same time. (Estimates suggest that up to 50 callers can use the bandwidth at the same instant.)

CDMA is a true digital technology, which is why Sprint still uses a "pin drop" logo to emphasize the clarity of their calls. The encryption also gives greater protection against 'hacker' attacks. Calls pretty much cannot be intercepted.

The next step will be "Wimax" which will incorporate VoIP technology. Nokia, Samsung, and other vendors are already committed to building a 4th generation cell phone.

Answer 4

Code division multiple access (CDMA) is a form of multiplexing (not a modulation scheme) and a method of multiple access that does not divide up the channel by time (as in time division multiple access), or frequency (as in frequency-division multiple access), but instead encodes data with a special code associated with each channel and uses the constructive interference properties of the special codes to perform the multiplexing. CDMA also refers to digital cellular telephony systems that make use of this multiple access scheme, such as those pioneered by Qualcomm, and W-CDMA by the International Telecommunication Union or ITU.

CDMA has since been used in many communications systems, including the Global Positioning System and in the OmniTRACS satellite system for transportation logistics.

Answer 5

What Is Cdma Technology

Answer 6

An older connection technology but used very successfully by Verizon. CDMA (Code Division Multiple Access) is simply a method for transmitting simultaneous signals over a shared portion of the spectrum.

I prefer Cingular (ATT) for their GSM network because that is an International standard and my phone works in foreign countries.

Answer 7

CDMA= Code Divisional Multiple Access.
This is the system for cellular service provider. In India, Reliance and Tata works on this system. It does not work on band width but on particular codes. It does not have loong heighted towers like GSM but it has tiny dishes fitted at smaller distance. CDMA is limited to a particular range and is not available for international roaming as other CDMA providers cannot access any else's service. It's signal strength is strong as compare to GSM but it is limited to an area/region and so it is not widely accepted as compared to GSM providers.

Answer 8

It stands for Code Division Multiple Access and is used by Verizon Wireless as a way to process multiple users on a single tower. Each call is assigned a unique code. Other companies (such as ATT/Cingular) use TDMA, or Time Division Multiple Access.

Answer 9

cdma is code division multiple access, what that means is that phones communicate with one another similar to networked computers. they send code such as ###7**77# and decipher the code allowing infinite communication, hence code, division, multiple, access.

Answer 10

All I know is they went from TDMA to CDMA, other then that I have no clue