About CDMA mobile phone

 About CDMA mobile phone

   

   CDMA (Code-Division Multiple Access) is a channel access method used by various radio communication technologies. It is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

CDMA Mobile phone

   CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes, which enhances privacy and makes cloning difficult.

The original CDMA standard, also known as CDMA One and still common in cellular telephones in the U.S offers a transmission speed of only up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and Wideband CDMA deliver data many times faster.

 CDMA, or Code Division Multiple Access, is a competing cell phone service technology to GSM, which is the world’s most widely used cell phone standard.

CDMA uses a “spread-spectrum” technique whereby electromagnetic energy is spread to allow for a signal with a wider bandwidth. This allows multiple people on multiple cell phones to be “multiplexed” over the same channel to share a bandwidth of frequencies.

With CDMA technology, data and voice packets are separated using codes and then transmitted using a wide frequency range. Since more space is often allocated for data with CDMA, this standard became attractive for 3G high-speed mobile Internet use

The CDMA standard was originally designed by Qualcomm in the U.S.

nd is primarily used in the U.S. and portions of Asia by other carriers. Sprint, Virgin Mobile and Verizon Wireless use CDMA while T-Mobile and AT&T use GSM.

While CDMA and GSM compete head on in terms of higher bandwidth speed (i.e. for surfing the mobile Web), GSM has more complete global coverage due to roaming and international roaming contracts.

GSM technology tends to cover rural areas in the U.S. more completely than CDMA. Over time, CDMA won out over less advanced TDMA technology, which was incorporated into more advanced GSM.

Advantages of CDMA mobile phone

1.  Efficient practical utilization of fixed frequency spectrum.
2.  Flexible allocation of resources.
3.  Many users of CDMA use the same frequency, TDD or FDD may be used
4.  Multipath fading may be substantially reduced because of large signal bandwidth
5. No absolute limit on the number of users, Easy addition of more users.
6.  Impossible for hackers to decipher the code sent
7.  Better signal quality
8. No sense of handoff when changing cells
9. The CDMA channel is nominally 1.23 MHz wide.
10. CDMA networks use a scheme called soft handoff, which minimizes signal breakup as a handset passes from one cell to another.
11. CDMA is compatible with other cellular technologies; this allows for nationwide roaming.
12. The combination of digital and spread-spectrum modes supports several times as many signals per unit bandwidth as analog modes.
13.  As the number of users increases, the overall quality of service decreases
14.  Self-jamming
15. Near- Far- problem arises
16. and many mores.