ECE8708_2010_ch5

ECE8708_2010_ch5 - ECE 8708 Wireless Communications :...

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ECE 8708 Wireless Communications : Modulation Techniques Wireless Communications ECE8708 ECE8708 - 2010 Spring 2010 Spring Chapter Chapter 5 Modulation Modulation Techniques Techniques Yimin Zhang, PhD Center for Advanced Communications Villanova University http://www.yiminzhang.com Yimin Zhang, Villanova University 1 p// y g ECE 8708 Wireless Communications : Modulation Techniques Outlines Concept of Modulation Power and Spectral Efficiency Nyquist Criterion & Pulse Shaping Digital Modulations g Linear – BPSK, QPSK, DPSK, OQPSK, /4 QPSK, 8PSK – QAM Nonlinear – FSK, MSK, GMSK Yimin Zhang, Villanova University 2 ECE 8708 Wireless Communications : Modulation Techniques Concept of Modulation and Demodulation 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 ompared to the baseband frequency. compared to the baseband frequency. The bandpass signal is called modulated signal and the baseband signal is called modulating 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. Yimin Zhang, Villanova University 3 ECE 8708 Wireless Communications : Modulation Techniques Modulation Techniques odulation Modulation Analog Modulation Digital Modulation (First Generation Mobile Radio) (Present & Future Systems) Amplitude modulation Angle modulation Amplitude shift keying (ASK) Frequency shift keying (FSK) - Frequency modulation - Phase modulation Phase shift keying (PSK) Quadrature amplitude modulation (QAM) Yimin Zhang, Villanova University 4
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ECE 8708 Wireless Communications : Modulation Techniques AM and FM Modulations M and FM signals AM and FM signals produced by a single tone. Carrier wave ( a ) Carrier wave. ( b ) Sinusoidal modulating ignal. signal. ( c ) Amplitude-modulated signal. ( d ) Frequency-modulated signal. Yimin Zhang, Villanova University 5 ECE 8708 Wireless Communications : Modulation Techniques Frequency Modulation vs. Amplitude Modulation AM signals have all their information in the amplitude of the carrier FM signals have all their information in phase or frequency of e carrier the carrier M signals are able to occupy less bandwidth as compared to AM signals are able to occupy less bandwidth as compared to FM signals FM signals usually occupy larger bandwidth and have better noise immunity when compared to AM Yimin Zhang, Villanova University 6 ECE 8708 Wireless Communications : Modulation Techniques Amplitude Modulation AM signal can be represented as ) 2 cos( )] ( 1 [ ) ( t f t m A t s c c AM or sinusoidal modulating ignal For a sinusoidal modulating signal e modulation index is given by ) 2 cos( ) / ( ) ( fmt A A t m c m the modulation index is given by c m A A k The spectrum of an AM signal can be show to be Yimin Zhang, Villanova University 7 )] ( ) ( ) ( ) ( [ 2 1 ) ( c c c c c AM f f M f f f f M f f A f S
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ECE8708_2010_ch5 - ECE 8708 Wireless Communications :...

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