Wireless Communications Principles and Practice, Second Edition

Chapter 6. Modulation Techniques for Mobile Radio

Modulation is the process of encoding information from a message source in a manner suitable for transmission. It generally involves translating a baseband message signal (called the source) to a bandpass signal at frequencies that are very high when compared to the baseband frequency. The bandpass signal is called the modulated signal and the baseband message signal is called the modulating signal. Modulation may be done by varying the amplitude, phase, or frequency of a high frequency carrier in accordance with the amplitude of the message signal. Demodulation is the process of extracting the baseband message from the carrier so that it may be processed and interpreted by the intended receiver ...