Some basic doubts in Minimum Shift Keying from Simon Haykins book.

[SherlockBenedict]

I can understand MSK but there is something that I couldn't understand in the one given in Simon Haykin's book. Actually what is given in that book is they have kind of used a constellation for MSK similar to that of QPSK.

Consider

θ(t)= θ(0) ± (Π/2Tb)t where -Tb ≦ t ≦ -Tb

Now if you wish to send bit '1' then the symbol that you should send depends on phase θ(0) or θ(Tb) where depending on whether the data bit is phase or quadrature respectively. The only problem that I have is how to find out θ(0) or θ(Tb) after t> Tb so that I can find out what symbol from the constellation that I should transmit. I am attaching one image from his book where he has given one example-



Here I can't understand how he gets the angle (that he written above the signal in Fig (b) and (c) ) especially in t>Tb. If you can see Fig (b)
we have angles 0,Π,Π,0. I can understand how he gets 0 as angle initially but after that I am lost. Hope you would help.

thanks a lot

 

[zorro]

Hi Sherlock,

The transmission of a bit "1" corresponds to a phase increase of pi/2 in the carrier between consecutive bit slices.
The transmission of a bit "0" corresponds to a phase lag of pi/2.
Look at the sequence of phases shown (alternatively) in figures (b) and (c). The sequence is:

0, π/2, π, π/2, π, π/2, 0, -π/2

I.e., it is: 1,1,0,1,0,0,0

The same sequence with the corresponding phase trellis is shown in figure 6.28 of the same book.
Regards

Z