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.

Phase Shift Keying (PSK) Oscillator 180 o 90 o 180 o BPSK QPSK Bit 0 Bit

Phase Shift Keying (PSK) Oscillator 180 o 90 o 180 o QPSK Bit 0 Bit

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

Carrier Recovery f IF f IF X 2 2 f IF PD Loop Filter VCOX 2 PD LPF Data

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

Differential QPSK Phase Reference: Previous Carrier Phase

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

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

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