Amplitude, Phase, and Frequency Shift Keying (ASK, PSK, FSK) - Amplitude, Phase, and Frequency Shift Keying (ASK, PSK, FSK)
- These methods are among the simplest to implement, as they only involve variations in one signal quality: amplitude for ASK, phase for PSK, and frequency for FSK. Although these are easier to implement in terms of circuit design compared to other digital modulation methods, they can be limited in terms of bit rate.
Quadrature Methods - Quadrature Methods
- ASK, PSK, and FSK all have a variant that involves demodulating the received signal in quadrature. In quadrature modulation schemes, two portions of a digital bit stream are transmitted in parallel in a communications channel. The two bit streams are transmitted with a half-wave phase shift between them so that only one portion of the carrier wave is active at any time. The two bit streams are then combined with an adder and transmitted. At the receiver, the two signals are demodulated to recover the two modulating waveforms that correspond to the dual input bit streams.
Combined Shift Keying Methods - Combined Shift Keying Methods
- Shift keying methods can be combined in tandem, similar to QAM. One method used in satellite communication and tactical wireless communication as an alternative to QAM is amplitude phase shift keying (APSK). In this method, the transmitted signal is shifted between multiple phase levels and multiple amplitude levels, rather than having two different ASK signals that are out-of-phase.
- Pulse Modulation
- Pulse code modulation methods use a stream of pulses rather than a sinusoidal carrier signal to transmit data. In these modulation schemes, the pulse stream is modulated by varying the pulse duration (pulse duration modulation, or PDM), phase between pulses (pulse phase modulation, or PPM), frequency (pulse frequency modulation, or PFM), or amplitude (pulse amplitude modulation, or PAM). Digital PAM is the method used today to transmit high data rates in Gbps channels over copper and fiber, and it may be the key to getting to 224 Gbps and higher data rates.
| | | - Amplitude shift keying (ASK) and quadrature amplitude modulation (QAM)
| | - Amplitude phase shift keying (APSK)
| - Amplitude-modulated phase modulation (or vice versa)
| - Frequency shift keying (FSK) and quadrature frequency modulation (QFM)
| | - Phase shift keying (PSK) and quadrature phase shift keying (QPSK)
| | - Pulse methods (discrete duration, phase, amplitude, etc.)
| - Pulse methods (continuous duration, phase, amplitude, etc.)
| THE END
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