Binary Digital modulation

The basic ways of binary digital modulation are: binary amplitude keying (2ASK)- the amplitude change of the carrier signal; Binary frequency shift keying (2FSK)- the frequency change of the carrier signal; Binary phase shift keying (2PSK)- Phase change of the carrier signal. Because of the phase uncertainty in 2PSK system, differential phase-shift keying 2DPSK is developed.

The bandwidth required by 2ASK and 2PSK is twice the code rate. 2FSK requires a higher bandwidth than both 2ASK and 2PSK.
The bit error rate of various binary digital modulation systems depends on the signal to noise ratio (SNR) of the demodulator. In terms of anti-additive white Gaussian noise, coherent 2PSK has the best performance, followed by 2FSK, and 2ASK has the worst performance.

ASK is one of the earliest basic modulation methods. Its advantages are simple equipment and high frequency band utilization; The disadvantage is that the anti-noise performance is poor, and it is sensitive to the change of channel characteristics, and it is not easy to make the sample decision detector work in the best decision threshold state.

FSK is an indispensable modulation method in digital communication. Its advantage is that it has strong anti-interference ability and is not affected by channel parameter changes, so FSK is especially suitable for fading channels. The disadvantage is that the occupied frequency band is wide, especially MF-SK, and the frequency band utilization is low. At present, frequency modulation system is mainly used in medium and low speed data transmission.

PSK or DPSK is a modulation mode with high transmission efficiency, its anti-noise ability is stronger than ASK and FSK, and it is not easily affected by the change of channel characteristics, so it has been widely used in high and medium speed data transmission. Absolute phase shift (PSK) has the problem of carrier phase ambiguity in coherent demodulation, so it is rarely used in direct transmission in practice. MDPSK is more widely used.

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