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Tdma and fdma

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Mikebits

Well-Known Member
In TDMA the frequency remains constant, but all the channels are given a slice of time. FDMA the channels constantly change frequency so no one user occupies the same frequency at one time.
 

OlPhart

Member
Standard use of FDMA is to assign each path their own (or set of) frequencies, so none collide. While they can change, or "hop", in something like catv the assignments are fixed.
 

RCinFLA

Well-Known Member
GSM is a TDMA system providing 8 voice time slot channels every 4.7 msec in a 200 kHz channel spacing assignment. When you handover to another site it tries to give you the same slot and RF channel if it is available but it can direct you to change RF channel if your previous RF channel is already in full use.

CDMA and WCDMA uses code division mulitplex on the same RF channel. It too can change RF channel on you during a handover if your previous RF channel is booked up at the new cell site. Because there are more voice channels carried on a single RF channel the RF channel change is less frequent then GSM.

So in short, all cellular systems use some FDMA in addition to TDMA or CDMA. Old AMPS analog phone use FDMA exclusively.

4G LTE (Long Term Evolution) uses OFDM. It uses many small bandwidth subcarriers. The lines between time, and frequency really blur on LTE as data bits are spread across many RF subcarriers in various time slots.
 
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