相移鍵控

Phase Shift Keying -- 相移鍵控

在某些調(diào)制解調(diào)器中用于數(shù)據(jù)傳輸?shù)恼{(diào)制系統(tǒng)，在最簡單的方式中，二進制調(diào)制信號產(chǎn)生0和1。載波相位來表示信號占和空或者二進制1和O。對于有線線路上較高的數(shù)據(jù)傳輸速率，可能發(fā)生4個或8個不同的相移，系統(tǒng)要求在接收機上有精確和穩(wěn)定的參考相位來分辨所使用的各種相位。利用不同的連續(xù)的相移鍵控，這個參考相位被按照相位改變而進行的編碼數(shù)據(jù)所取代，并且通過將相位與前面的位進行比較來檢測。
Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave).
Any digital modulation scheme uses a number of distinct signals to represent digital data. In the case of PSK, a finite number of phases are used. Each of these phases is assigned a unique pattern of binary bits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal — such a system is termed coherent.
Alternatively, instead of using the bit patterns to set the phase of the wave, it can instead be used to change it by a specified amount. The demodulator then determines the changes in the phase of the received signal rather than the phase itself. Since this scheme depends on the difference between successive phases, it is termed differential phase-shift keying (DPSK). DPSK can be significantly simpler to implement than ordinary PSK since there is no need for the demodulator to have a copy of the reference signal to determine the exact phase of the received signal (it is a non-coherent scheme). In exchange, it produces more erroneous demodulations. The exact requirements of the particular scenario under consideration determine which scheme is used.

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