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namely φ
＝
0, π. The BPSK modulation signals can be generated by using the conventional analog
modulation method (using the NRZ signal double-sideband DSB amplitude modulation) or by using
the keying method. In modern communication devices, they are generally generated by using I/Q
modulators.
Attached Figure 2 BPSK Diagram
Quadrature phase shift keying QPSK
The most common digital modulation is quadrature phase shift keying (QPSK). Quadrature
phase shift modulation uses four different phase differences of the carriers to characterize the input
digital information. The four carrier phases are 45°, 135°, 225° and 275° respectively.
The data input by the modulator is a binary digital sequence. To match the quaternary carrier
phases, the binary data needs to be converted into quaternary data, that is to say, every two bits in
the binary digital sequence need to be grouped together and there are four combinations 00, 01, 10
and 11, each of which is called a double-bit symbol. Each double-bit symbol consists of two binary
information bits, which represent one of the four quaternary symbols respectively.
Each modulation in QPSK can transmit 2 information bits, which are transmitted through the four
phases of the carrier. The demodulator determines the information bits transmitted by the
transmitting end according to the constellation and the phases of the received carrier signals.
Attached Fig.2 QPSK Diagram
8 phase shift keying 8PSK
What are commonly used in wireless communications is BPSK and QPSK and can also be
extended to 8PSK or even 16PSK. However, 16PSK is rarely used since the utilization of its I/Q
plane is very low and the phase difference at the symbol points is small. From the conversion
process of the 8PSK vector diagram, it can be seen that a 180-degree symbol phase change causes
the signal trace to cross the original point during the modulation and its high peak-to-average ratio is
not conducive to transmission. Moreover, 8PSK is an absolute phase modulation and there is a phase
ambiguity problem, so it is less directly applied.
