What are the differences among PSK, 2PSK, DPSK and QPSK, and their respective applications in communication systems? Which is the most important and has the most development advantages? What is common

What are the differences among PSK, 2PSK, DPSK and QPSK, and their respective applications in communication systems? Which is the most important and has the most development advantages? What is commonly used now? QPSK is the most widely used in CDMA. Four-phase phase shift modulation is a kind of four-phase phase shift keying, which uses four different phase differences of the carrier to represent the input digital information. When M=4, QPSK is a phase modulation technique. It specifies four carrier phases, namely 45, 135, 225 and 3 15. The data input by the modulator is a sequence of binary digits. In order to match the quaternary carrier phase, it is necessary to convert binary data into quaternary data, that is to say, it is necessary to convert binary data into quaternary data. Each binary symbol consists of two bits of binary information, which respectively represent one of the four symbols in the quaternary. In QPSK, each modulation can transmit two information bits, which are transmitted through four phases of the carrier. The demodulator judges the information bits sent by the sender according to the constellation and phase of the received carrier signal. Digital modulation is described by "constellation diagram", in which two basic parameters of a modulation technique are defined: (1) signal distribution; (2) Mapping relationship with modulated digital bits. The corresponding relationship between constellation points and transmission bits is specified in the constellation diagram, which is called "mapping". The characteristics of modulation technology can be completely defined by signal distribution and mapping, that is, by constellation diagram. Firstly, the input serial binary information sequence is converted into m=log2M parallel data streams by serial-parallel conversion, and the data rate of each channel is R/m, where r is the data rate of serial input code. The I/Q signal generator converts each M-bit byte into a pair of (pn, qn) numbers and divides them into two sequences at half the rate. The level generator generates bipolar two-level signals I(t) and Q(t) respectively, then modulates coswct and sinwct, and adds them to obtain QPSK signals. QPSK is a digital modulation method with high spectrum utilization and strong anti-interference ability. It is widely used in various communication systems and is suitable for satellite broadcasting. For example, in digital satellite tv DVB-S2 standard, the threshold of channel noise is as low as 4. 5 dB, the transmission rate reaches 45M b? QPSK modulation is adopted, which ensures the efficiency of signal transmission and the performance of error code.