In frequency modulation, the frequency of the carrier wave is varied in accordance with the information signal. The amplitude and phase of the carrier wave remain constant. As the frequency of the carrier wave changes, the instantaneous frequency of the modulated signal changes accordingly. This variation in frequency is then detected at the receiving end, and the original information signal is recovered. FM is commonly used for radio broadcasting and mobile communication systems. In phase modulation, the phase of the carrier wave is varied in response to the information signal, while the frequency and amplitude remain constant. The amount of phase shift is proportional to the amplitude of the modulating signal. The modulated signal can be demodulated by comparing the phase of the received signal with that of a reference signal. PM is commonly used in digital communication systems, such as satellite communication and digital cellular systems. Both FM and PM have their advantages and disadvantages, and their use depends on the specific application and requirements. For example, FM is known for its good noise immunity and high-quality audio transmission, while PM is better suited for digital data transmission due to its constant envelope nature.