I am currently reading Pasupathy, Subbarayan. "Minimum shift keying: A spectrally efficient modulation." IEEE Communications Magazine 17.4 (1979): 14-22.
The paper explains MSK as a form of OQPSK with a half sinusoid instead of rectangular weighting with a figure below:
But in my opinion, this figures seems incorrect. Because figure 5(a) shows a bit stream +1, -1, -1 and +1 inside a waveform, but the actual waveform is drawn as if its corresponding bit stream is +1, +1, -1, -1.
Am I missing something?
Maybe I learned that the original problem is solved by taking a phase into account.
Another problem is, a waveform in the IEEE 802.15.4 standard differs from the original one.
It seems that a direction (upward/downward) of a waveform indicates a bit.
Are both acceptable? Is 802.15.4's O-QPSK a variant of the original one?