Which is the digital modulation used today in telecomn?
(whatever his question meant the answer was CDMA)
2) Why is walse code used? then, noncoherent detection,
coherent detection, Pn code(y it is used?) etc
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Answer Posted / amisha
in GSM we use GMSK
Spreading Code are use for following reason:
The effectiveness of CDMA scheme relies on the mutual
orthogonality of spreading codes to minimize the cross
interference among physical code channels.Therefore
spreading code should be consistently defined and generated
at transmitters and receivers such that this orthogonality
can be achieved and maintained across the radio link.
Walsh Code:Walsh Code are set of perfectly orthogonal codes
typically used for channelization ,that is,separating
different physical channels transmitted by a node.
PN Code:PN codes are set of psuedo-random but
deterministically generated sequences .
Properties of Psuedo Code are:
1Sharp Autocorrelation ,so that any time shifted version of
a PN code has almost no correlation with the original sequence
2 Equal number of '1' andd '0' in any long segment of the
sequence ,so that the signal has no bias
3 Random and independent appearances of '1' and '0' so that
it is difficult to to reconstruct from any short segment
Basically PN codes act as Base station signature.
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