N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 9 - Wireless Systems and Technologies                                                                                 Slide 14 of 80                                                                                                    ________________

Modulation Techniques

                                    Amplitude Shift Keying (ASF)

                                    Frequency Shift Keying (FSK)

                                    Phase Shift Keying (PSK)

                                    Quadrature Amplitude Modulation (QAM)

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Modulation is the process whereby a carrier wave of a perticular frequency is modulated by the message signal, so that the modulated carrier wave can be used to carry the message over a distance. There are three basic types of modulation techniques: ASF, FSK and PSK.

Amplitude Shift Modulation - The amplitude of the carrier wave is modulated in step with the message signal.

Frequency Shift Keying - The frequency of the carrier wave is modulated in step with the message signal.

Phase Shift Keying - The phase of the carrier wave is modulated in step with the message signal.

Quadrature Amplitude Modulation - Uses ASK and PSK at the same time on a carrier wave. The receiver is designed to detect amplitude and phase shifts and retrieve the digital message.
For example:    16-QAM carries 4 bits (0000,0001 etc) per carrier symbol (baud)
                     64-QAM carries 6 bits (000000, 000001, 000010 etc.) per baud