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To: _Jim
When points cost money, thet'll be something.

I think FH is a CD. MA in a cellular network practically requires a reservation protocol, as I see it.
58 posted on 10/07/2002 10:28:49 PM PDT by apochromat
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To: apochromat
I think FH is a CD

Nope, not quite.

The key is this: Look at the IF filter bandwidth.

A DSSS (direct sequence spread spectrum) system (which CDMA is) literally occupies a bandwwidth as wide as the 'chipping' code - as wide as 1.2 MHz or so for CDMA as used in cellular systems ...

Whereas a FH system has *only* has an IF BW as wide as the data or modulation rate expected ... and the LO is 'frequency hopped' to keep track of the transmitted 'hopped' data ...

There are other differences too, such as a FH system *still* requires a S/N ratio of some 10 to 15 dB or more whereas a CDMA system can have Eb/No (Energy per bit to noise ratio) of just over one ... equivalently a unity S/N ratio ...

All non-coherent 'codes' during recovery (mixing with the original chipping code again, a demodulation process if you will) still results in noise whereas the *desired* signal, when the recovered bit stream is low-pass filtered, will result in the original bit stream ...

61 posted on 10/07/2002 10:42:11 PM PDT by _Jim
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To: apochromat
MA in a cellular network practically requires a reservation protocol, as I see it.

How about a strict assignment to either a chipping code or a time slot?

Chipping codes (one of 64 orthogonal Walsh codes if I recall correectly) for a DSSS - CDMA system or a particular time slot for a time division system ...

Of course, each one also requires a frequency during a channel assignment and the TDMA system also sends a time alignment value to correct for distance from the cell site (otherwise your slot starts to overlap into adjacent slots) ...

65 posted on 10/07/2002 10:47:57 PM PDT by _Jim
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