Forums

Mapping MSK ? How to regain the information from I and Q ?

Started by Florian Toulouse March 13, 2006
Hello ,

I despair on how to regain the initial information from the seperate I
and Q bits after MSK modulation/demodulation.

If

d(t) is the data, a sum of delta pulses

g(t) is the frequency response (MSK: REC) and

c(t)=g(t)*d(t)    (* convolution !)

then

phi(t) is the phase , which is calculated by  cumsum(c(t))
  (MSK:"linear ramps up and down according to the bit")


and thus  exp(j *phi(t)) represents  the equivalent complex baseband
signal s(t).

This works very well. A plot of   Real(s(t))  and Imag(s(t))   gives
the typical sin and cosine forms of the I and Q channel.

My question: After Demodulation , e.g. with matched filtering, I get
two bit streams I and Q but how do I demultiplex them to recuperate the
d(i) ? 

Thanks a lot

Florian Toulouse 
Berlin / Germany