Course Wireless Communication Technologies 16332559 (Advanced Topics in Communication Engin(学习资料).pdf

Course: Wireless Communication Technologies 16:332:559 (Advanced Topics in Communication Engineering) Lecture #9 and #10 Instructor: Dr. Narayan Mandayam Summary by Guofeng Lu (guofeng@ece.rutgers.edu) I QPSK: In digital phase modulation, signal space diagram for M-ary modulation when M=4 is shown in figure 9.1. The dotted line represents the possible phase transition. This 4-phase PSK is also called Quadrature Phase Shift Keying (QPSK). 01 When phase transition goes through the origin, abrupt phase reversal will happen in signal envelope. Any kind of hardlimiting or nonlinear amplification of the origin- crossings brings back the filtered sidelobes since the fidelity of the signal at small voltage levels is lost in 11 00 transmission. To prevent the regeneration of side-lobes and spectral 10 widening, it is imperative that QPSK signals be amplified only using linear amplifiers, which are less efficient. A Fig 9.1 Phase modified form of QPSK, called offset QPSK (OQPSK) is transition of QPSK less susceptible to these deleterious effects and supports more efficient amplification. II OQPSK In QPSK, bit transitions are allowed that odd and even streams occur simultaneously. While in OQPSK, the bit stream is first broken into even and odd bit streams. And even and odd bitstreams are offset in alignment by