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Unformatted text preview: Lecture Outline (Week 9, lecture 2) Quadrature Amplitude Modulation, Frequency Shift Keying Reading: Text1 sections 7.4 and 7.5 1. Quadrature Amplitude Modulation Recall from last lecture, we can have two signal rails for Binary PSK for the signal ) ( 2 sin 2 2 cos 2 ) ( t n ft T E ft T E t r + = The signal can also be seen as QPSK by rewriting ) ( ) 4 2 2 cos( 2 ) ( t n k ft T E t r + + + = for k = 0, 1, 2, 3. Signal constellation is given by: We can use more levels for each rail, e.g. 4 PAM. E.g. 16 QAM with 4 bits per symbol. ) ( 2 sin ) ( 2 cos ) ( ) ( t n ft t s ft t s t r Q I + + = ; ) ( ), ( t s t s Q I each can have one of 4 levels, i.e. ) ( t g A m where 3 , 1 , 1 , 3-- = m A . The pulse shape may be rectangular, e.g. T E t g g / ) ( = for T t Basis functions: 16 QAM Signal Constellation t f t g T t c 2 cos ) ( 2 ) ( 1 = t f t g T t c 2 sin ) ( 2 ) ( 2 = Optimal receiver: Find closest signal point to r . 1 2. Frequency Shift Keying (FSK) Recall for M PSK: ) 2 2 cos( ) ( ) ( M m t f t g t s c m + = , m = 0, 1, 2, , M-1 Information is carried by the phase at the beginning of the symbol....
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- Spring '09