1. Amplitude Shift Keying (ASK): ASK is a technique in which the amplitude of a carrier signal is modulated according to the data signal. The data is represented as a series of binary digits (0s and 1s), which are then converted into corresponding variations in the amplitude of the carrier signal. When a 0 is sent, the amplitude is kept at a low level, while a 1 is represented by a higher amplitude.
2. Frequency Shift Keying (FSK): FSK is a technique in which the frequency of a carrier signal is modulated according to the data signal. Similar to ASK, the data bits are represented as binary digits, which are then converted into corresponding frequency changes in the carrier signal. When transmitting a 0, the frequency is kept at a lower value, while a 1 is represented by a higher frequency.
3. Phase Shift Keying (PSK): PSK is a technique in which the phase of a carrier signal is modulated according to the data signal. In this case, the binary data bits are represented by variations in the phase of the carrier signal. A 0 is represented by a phase shift of 0 degrees, while a 1 is represented by a specific phase shift. There are different types of PSK modulation schemes including BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), and 8PSK (8-Phase Shift Keying), each having different phase shifts for the different binary combinations.