# QPSK constellation Zero Crossings

What causes zero crossings in a QPSK constellation to be a a problem for linearity or PAPR ( Peak to Average Power Ratio)?

• See this answer for a brief description of why $\pi/4$-QPSK generally is preferred over plain QPSK in satellite channels. – Dilip Sarwate Jan 15 at 21:17
• how is the constellation for $\pi/4$-QPSK different from plain QPSK? – robert bristow-johnson Jan 16 at 16:51
• 135 degrees phase shift for pi/4 QPSK vs 180 degrees for plain QPSK and 90 degrees for OQPSK – ali khalil Jan 19 at 12:50