NASA NTRS · 19880016336
Codes for QPSK modulation with invariance under 90 degrees rotation
Abstract
The new rate 1/2 nonlinear convolutional codes for quadrature phase shift keying (QPSK) modulation allow the achievement of full 90 degree rotational invariance of coded QPSK signal sequences at no significant loss in real coding gains when compared to linear codes. For mobile communication systems operating in a fading environment with frequent periods of low signal-to-noise ratio and the possibility of losses of carrier phase synchronization in the receiver, the invariance to 90 degree ambiguous demodulation should be a significant advantage.
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Ungerboeck, Gottfried, Pietrobon, Steven S.. 1988-05-01. Codes for QPSK modulation with invariance under 90 degrees rotation. https://ntrs.nasa.gov/citations/19880016336
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