5.
2.2.8 Controlling Phase Trajectories
In this section, we will discuss manipulating the phase trajectories, rather than having them determined
by the impulse response of the pulse-shaping filter and the modulation scheme chosen.
Specifically, we will briefly introduce what is commonly called Feher??™s PSK modulation schemes
(see [41??“43]).
What Dr. Feher realized is that linear modulation schemes require portable devices to operate
their transmit PA in its linear region. In this range, the PA is inefficient in terms of power consumption,
but is required in order to benefit from the spectral efficiency of linear modulation schemes.
Driving the PA into saturation will allow the PA to be more efficient; however, spectral regrowth
issues need to be addressed. Using constant envelope modulation schemes allows us to saturate the
PA; however, they are inherently spectrally inefficient. So a median ground must be found in order
to use the more efficient PAs. Dr. Feher??™s family of modulation schemes do this by controlling the
phase trajectories on the transmit signal constellation diagrams in a number of ways. We will walk
the reader through some of the approaches taken and then summarize by providing further reading
in the references [44??“49].
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