06-09-2017, 12:29 PM
CDMA (Code Division Multiple Access) refers to any of several protocols used in second generation (2G) and third generation (3G) wireless communications. As the term implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of the available bandwidth. The technology is used in ultra-high-frequency (UHF) cell phone systems in the 800 MHz and 1.9 GHz bands.
CDMA uses analog-to-digital (ADC) conversion in combination with extended spectrum technology. The audio input is first digitized into binary elements. The frequency of the transmitted signal is then varied according to a defined pattern (code), so that it can only be intercepted by a receiver whose frequency response is programmed with the same code, so that it is followed exactly together with the frequency of the transmitter. There are trillions of possible frequency sequencing codes, which improves privacy and makes cloning difficult.
The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft transfer, which minimizes signal breakage when a handset passes from one cell to another. The combination of digital and spread spectrum modes supports several times as many bandwidth signals as analogue modes. CDMA is compatible with other cellular technologies; this allows for national roaming. The original CDMA standard, also known as CDMA One, offers a transmission rate of only 14.4 Kbps in its single-channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and CDMA broadband deliver data many times faster.
The CDMA2000 family of standards includes 1xRTT, EV-DO Rev 0, EV-DO Rev A and EV-DO Rev B (renamed Ultra Mobile Broadband - UMB). People often confuse CDMA2000 (a family of standards compatible with Verizon and Sprint) with CDMA (the physical layer multiplexing scheme).
CDMA uses analog-to-digital (ADC) conversion in combination with extended spectrum technology. The audio input is first digitized into binary elements. The frequency of the transmitted signal is then varied according to a defined pattern (code), so that it can only be intercepted by a receiver whose frequency response is programmed with the same code, so that it is followed exactly together with the frequency of the transmitter. There are trillions of possible frequency sequencing codes, which improves privacy and makes cloning difficult.
The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft transfer, which minimizes signal breakage when a handset passes from one cell to another. The combination of digital and spread spectrum modes supports several times as many bandwidth signals as analogue modes. CDMA is compatible with other cellular technologies; this allows for national roaming. The original CDMA standard, also known as CDMA One, offers a transmission rate of only 14.4 Kbps in its single-channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and CDMA broadband deliver data many times faster.
The CDMA2000 family of standards includes 1xRTT, EV-DO Rev 0, EV-DO Rev A and EV-DO Rev B (renamed Ultra Mobile Broadband - UMB). People often confuse CDMA2000 (a family of standards compatible with Verizon and Sprint) with CDMA (the physical layer multiplexing scheme).