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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 + ± ± = π π • The signal can also be seen as QPSK by rewriting ) ( ) 4 2 2 cos( 2 ) ( t n k ft T E t r + + + ± = π π π 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 + + = π π ; ) ( ), ( 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 π ψ 2 cos ) ( 2 ) ( 1 = t f t g T t c π ψ 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 π π + = , m = 0, 1, 2, …, M-1 • Information is carried by the phase at the beginning of the symbol....
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- Spring '09
- Frequency, Phase-shift keying, error rate, bit error rate