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Published bySidney Tindall Modified over 2 years ago

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Digital Modulation The discontinuity between analog and digital modulation is that in analog modulation, there are theoretically an infinite number of possible states for the carrier/channel; in digital modulation, there is a finite number of states (symbols) for the carrier/channel, and we can design the set of states to optimize decision accuracy at the receiver.

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Phase Shift Keying (PSK) Oscillator 180 o 90 o 180 o BPSK QPSK 0 0 1 1 01 Bit 0 Bit 1 00 01 11 10

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Phase Shift Keying (PSK) Oscillator 180 o 90 o 180 o QPSK 0 0 1 1 + + Bit 0 Bit 1 00 01 11 10

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Differential Binary Phase Shift Keying (DBPSK) e.g., A zero causes a 180 degree phase change, a one causes no phase change. 0 0 0 0 0 1 1 1 1 0 delay Data To Phase Modulator delay LPF Data Rx Mixer

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Carrier Recovery BPSK @ f IF BP @ f IF X 2 BPF @ 2 f IF PD Loop Filter VCOX 2 PD LPF Data

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Quiz A 3 kHz BW analog signal of 5v p-p is quantized a resolution of DQ = 0.020 volts. What is the transmitted bit rate (+/- 5%)?

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Differential QPSK 00 01 11 10 Phase Reference: Previous Carrier Phase

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Quadrature Demodulation Carrier Recovery (x4) 90 o LPF 00 01 11 10 I-bit Q-bit I-data Q-data QPSK

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Bit Clock Recovery T/2 Delay I or Q Data RZ Signal Narrowband PLL: f c = 1/T Recovered Bit Clock T

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Other Quadrature Modulations 8-PSK 8-QAM (4 Phase) 8-QAM (8 Phase)16-QAM

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©1997 BG Mobasseri110/27/2015 V.29, V.32, V.32 bis... THE INS AND OUTS OF MODEMS.

©1997 BG Mobasseri110/27/2015 V.29, V.32, V.32 bis... THE INS AND OUTS OF MODEMS.

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