What is Cell Cellular CDMA RS232 data modem

WHAT IS CDMA

  CELLULAR DIGITAL MODEMS

                  (Code Division Multiple Access) A method for transmitting real-time

                  signals over a shared portion of the spectrum. The foremost application of

                  CDMA is the digital cellular phone technology from QUALCOMM that

                  operates in the 800MHz band and 1.9GHz PCS band. CDMA phones are

                  noted for their excellent call quality and low current draw.

                  CDMA is less costly to implement, requiring fewer cell sites than the GSM

                  and TDMA digital cell phone systems and providing three to five times the

                  calling capacity. It provides more than 10 times the capacity of the analog

                  cell phone system (AMPS). CDMA has become widely used in North America

                  and is also expected to become the third-generation (3G) technology for

                  GSM.

                  Unlike GSM and TDMA, which divides the spectrum into different time slots,

                  CDMA uses a spread spectrum technique to assign a code to each conversation.

                  After the speech codec converts voice to digital, CDMA spreads

                  the voice stream over the full 1.25MHz bandwidth of the CDMA channel,

                  coding each stream separately so it can be decoded at the receiving end. The

                  rate of the spreading signal is known as the "chip rate," as each bit in the

                  spreading signal is called a "chip" (no relation to an integrated circuit). All

                  voice conversations use the full bandwidth at the same time. One bit from

                  each conversation is multiplied into 128 coded bits by the spreading

                  techniques, giving the receiving side an enormous amount of data it can

                  average just to determine the value of one bit.

                  CDMA transmission has been used by the military for secure phone calls.

                  Unlike FDMA and TDMA methods, CDMA's wide spreading signal makes it

                  difficult to detect and jam. For more information, contact the CDMA

                  Development Group (CDG) at www.cdg.org. See wireless generations, IS-95,

                  CDMA2000, W-CDMA, GSM, FDMA, TDMA, CDPD, CDG and spread

                  spectrum.

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