Digital Modulation Techniques in Mobile Communications_移动通信中的数字调....pdf

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Digital Modulation Techniques in Mobile Communications Fahredd'n Sadikoglu 1

Digital Modulation Technique Sender Destination Message Message Modulation Channel Demodulation Fahredd'n Sadikoglu 2

Modulation Techniques  Modulation is the process of encoding information from a message source in a manner suitable for transmition.  The ultimate goal of a modulation technique is to transport the message signal through a radio channel with the best possible quality while occupying the least amount of radio spectrum. Sender Modulation Channel Message D(t) C(t)=A COS (wt+Φ) Fahredd'n Sadikoglu 3

 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. C(t)=A COS (wt+Φ) ASK FSK PSK

Amplitude Shift Keying (ASK) - Pulse shaping can be employed to remove spectral spreading. - ASK demonstrates poor performance, as it is heavily affected by noise and interference.

Frequency Shift Keying (FSK) - Bandwidth occupancy of FSK is dependant on the spacing of the two symbols. A frequency spacing of 0.5 times the symbol period is typically used. - FSK can be expanded to a M-ary scheme, employing multiple frequencies as different states. -

Phase Shift Keying (PSK) - Binary Phase Shift Keying (BPSK) demonstrates better performance than ASK and FSK. - PSK can be expanded to a M-ary scheme, employing multiple phases and amplitudes as different states. - Filtering can be employed to avoid spectral spreading.

PSK & DPSK Fahredd'n Sadikoglu 8

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