Brief Working of CDMA
CDMA takes an entirely different approach from TDMA. CDMA, after digitizing
data, spreads it out over the entire available bandwidth. Multiple calls are overlaid on
each other on the channel, with each assigned a unique sequence code. CDMA is a form
of spread spectrum, which simply means that data is sent in small pieces over a number
of the discrete frequencies available for use at any time in the specified range.
In CDMA, each phone's data has a unique code.
All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is
spread over the entire bandwidth by a unique spreading code. At the receiver, that same
unique code is used to recover the signal. Because CDMA systems need to put an
accurate time-stamp on each piece of a signal, it references the GPS system for this
information. Between eight and 10 separate calls can be carried in the same channel
space as one analog AMPS call.
CDMA takes an entirely different approach from TDMA. CDMA, after digitizing
data, spreads it out over the entire available bandwidth. Multiple calls are overlaid on
each other on the channel, with each assigned a unique sequence code. CDMA is a form
of spread spectrum, which simply means that data is sent in small pieces over a number
of the discrete frequencies available for use at any time in the specified range.
In CDMA, each phone's data has a unique code.
All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is
spread over the entire bandwidth by a unique spreading code. At the receiver, that same
unique code is used to recover the signal. Because CDMA systems need to put an
accurate time-stamp on each piece of a signal, it references the GPS system for this
information. Between eight and 10 separate calls can be carried in the same channel
space as one analog AMPS call.
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