How is the differentially encoded MSK modulation implemented in the Communications Toolbox 3.0 (R14)?

In the "diff" mode, the current and preceding bits should be XORed and then a positive or negative frequency offset should be applied depending on the bits being '1' or '0'. However, these are not the results I receive when using the function MSKMOD.

Answer 1

[MathWorks Support Team]

This enhancement has been incorporated in Release 2007b (R2007b). For previous product releases, read below for any possible workarounds:

Documentation on the MSKMOD function is missing from the Communications Toolbox manual. Here is additional information on the differential mode of the MSKMOD function:

In the following implementation of the DIFF mode of the function MSKMOD,

y=mskmod(x,'diff');

the input signal, x, represents a bitstream that has already been XORed to generate the sequence x.

The differentially encoded MSK output, y, of MSKMOD exhibits a phase shift within one bit period of +pi/2 when the input data x is 1, and –pi/2 when x is 0.