Pass band implementation of Amplitude shift keying, Frequency Shift Keying, Binary Phase Shift Keying: Generation and Detection
Digital modulation schemes are techniques used to encode information into a carrier signal by varying its properties according to discrete signal levels or symbols. Here’s an overview of three common digital modulation schemes: Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK). Amplitude Shift Keying (ASK) is the simplest digital modulation technique. In this modulation method, there is only one carrier, which is switched ON/OFF depending upon the input binary sequence to transmit symbols 0 and 1. The binary ASK system was one of the earliest forms of digital modulation used in wireless telegraphy. For Frequency Shift Keying (FSK), two binary values are represented by two different frequencies. For example, we choose two carrier frequencies, f1 and f2, where f1 > f2. Then we modulate binary bit "1" with f1 and binary bit "0" with frequency f2, which is lower than f1. In Phase Shift Keying (PSK), the carrier signal phase is modulated according to the input signal; binary "1" is represented by a change in phase relative to the last bit, and binary "0" is sent with the same phase as the preceding one. For example, whenever we need to transmit binary "1", we change the signal's phase by 180 degrees, but the phase remains the same when we transmit binary "0". Each modulation scheme has its advantages and is chosen based on the specific requirements of the communication system, such as bandwidth, power efficiency, and noise resilience.