Half Sine Filter (Digital Demod)
The filter is used for measurements. The pulse shaping filter changes the vector diagram of an OQPSK Offset Quadrature Phase Shift Keying: A type of QPSK modulation that offsets the bit streams on the I and Q channels by a half bit. This reduces amplitude fluctuations and helps improve spectral efficiency. signal from a square to a circle. This eliminates any amplitude variations and turns the OQPSK signal into a constant envelope modulation. The OQPSK now resembles MSK Minimum Shift Keying.
The equation for the filter follows. (Tc is equal to the delay between the I and Q portions of the signal. The symbol period is 2Tc.)
The filter is a standard reference filter in Option AYA.
When this filter is selected for OQPSK, the reference constellation points fall on a circle with a magnitude of sqrt(2)/2, but the EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. is still expressed as a percentage of the magnitude of a QPSK Quadrature phase shift keying symbol point (magnitude = 1). See EVM for more information.
See Also
