Digital Modulation Review

Digital Modulation 1

CHAPTER 4 (DIGITAL MODULATION) - CHAPTER 4 (DIGITAL MODULATION) - REVIEWREVIEW

1.1. The analog signal is converted to a digital The analog signal is converted to a digital signal (pulses) by using ADC before signal (pulses) by using ADC before transmitted.transmitted.

2. 2. Types : Types : 1. 1. Pulses - PAM, PWM, PPMPulses - PAM, PWM, PPM 2. 2. Binary - ASK, FSK, PSK, BPSK, Binary - ASK, FSK, PSK, BPSK,

DBPSK,DBPSK, PCM, QAMPCM, QAM



3.3. The channel capacity : The channel capacity : I = 3.32BWlog(1 + SNR) in bpsI = 3.32BWlog(1 + SNR) in bps

4.4. Bit : Bit : The speed of data transmission before The speed of data transmission before

entering digital modulator, unit = bpsentering digital modulator, unit = bps

5.5. Baud : Baud : The speed of data transmission after The speed of data transmission after

undergone digital demodulatorundergone digital demodulator



6.6. Baud can be define as: Baud can be define as: Bit rate / number of bit at one signal, Bit rate / number of bit at one signal, Baud = fBaud = fb b / n/ n 7. 7. FSK :FSK : i) Space Frequency, fi) Space Frequency, fs s at logic ‘1’ (Low Freq)at logic ‘1’ (Low Freq) ii) Mark frequency, fii) Mark frequency, fm m at logic ‘0’ (High Freq)at logic ‘0’ (High Freq) iii) fiii) fa a (the highest fundametanl analog freq) = (the highest fundametanl analog freq) =

ffb b / 2/ 2 iv) Frequency deviation, iv) Frequency deviation, f = f = |f|fm m - f- fss|/2|/2



8.8. BPSK :BPSK : I) Logic ‘1’ at 0I) Logic ‘1’ at 0oo

II) Logic ‘0’ at 180II) Logic ‘0’ at 180oo

III) 2 possible ouputs [ 0 or 1]III) 2 possible ouputs [ 0 or 1] 9.9. QPSK :QPSK : I) 2 Channel, I = in-phase, Q = 90I) 2 Channel, I = in-phase, Q = 90o o out of phase out of phase II) Logic ‘0’ at 180 degreeII) Logic ‘0’ at 180 degree III) 4 possible output [00, 01, 10, 11]III) 4 possible output [00, 01, 10, 11] IV) Bandwidth, BW = fIV) Bandwidth, BW = fb b / 2/ 2 v) For 3-bit systems, BW = fv) For 3-bit systems, BW = fb b / 3/ 3



10.10. QAM QAM I) Combination of Amplitude & Phases Shift toI) Combination of Amplitude & Phases Shift to optimize the constellation diagramoptimize the constellation diagram II) 8-QAM => 8 output condition (2II) 8-QAM => 8 output condition (233) ) BW = Baud = fBW = Baud = fb b / 3/ 3 III) 16-QAM => 16 output conditiion (2III) 16-QAM => 16 output conditiion (244), ), BW = Baud = fBW = Baud = fb b / 4/ 4

* REFER TO TABLE 9-1 (Textbook, page 384)* REFER TO TABLE 9-1 (Textbook, page 384) 11.11. PCM :PCM : I) Assign binary to the Pulse signalI) Assign binary to the Pulse signal II) Produced by ADCII) Produced by ADC III) 2 type of sampling : III) 2 type of sampling : - Natural (did not involve Sample & Hold cct) - Natural (did not involve Sample & Hold cct) - Involve Sample & Hold cct- Involve Sample & Hold cct IV) Sampling rate, fIV) Sampling rate, fs s ≥ 2f≥ 2faa v) Dynamic range, DR = Vmax / Vmin = Vmax / resolution v) Dynamic range, DR = Vmax / Vmin = Vmax / resolution in Db = 20log Vmax/Vminin Db = 20log Vmax/Vmin



11.11. PCM Line SpeedPCM Line Speed VI) Line speed, Bit rate = samples/sec x bits/sampleVI) Line speed, Bit rate = samples/sec x bits/sample VII) Sampling time = 1 / fVII) Sampling time = 1 / fss 12.12. Multiplexing :Multiplexing : I) 3 typical types : TDM, FDM & CDMI) 3 typical types : TDM, FDM & CDM II) For multiple users => TDMA, FDMA & CDMAII) For multiple users => TDMA, FDMA & CDMA III) Frame => contains number of channel for number ofIII) Frame => contains number of channel for number of bit per samplebit per sample Framing bit => inserted for data protectionFraming bit => inserted for data protection IV) Example calculation:IV) Example calculation: If there are 24 channels per frame with a frame containsIf there are 24 channels per frame with a frame contains 8 bits per channel and the sampling frequency of 8 kHz,8 bits per channel and the sampling frequency of 8 kHz, The line speed :The line speed : ffb b = 24 channel/frame x 8 bits/channel x 8000 sample/sec= 24 channel/frame x 8 bits/channel x 8000 sample/sec = 1.536 Mbps= 1.536 Mbps if 1 framing bit inserted, thenif 1 framing bit inserted, then Line spped = [(24 channel/fram x 8 bits/channel) + 1] x Line spped = [(24 channel/fram x 8 bits/channel) + 1] x

80008000 sample/secsample/sec = 1.544 Mbps= 1.544 Mbps



13.13. Quantization LevelQuantization Level I) depend on number of bit, L or M = 2I) depend on number of bit, L or M = 2nn

II) The higher the quantization level, the II) The higher the quantization level, the higher the DR, SNR and the number of bit higher the DR, SNR and the number of bit per sampleper sample

14.14. Line Coding :Line Coding : I) Source CodingI) Source Coding II) Channel CodingII) Channel Coding III) Used for data protection & errors/noiseIII) Used for data protection & errors/noise Framing bit => inserted for data Framing bit => inserted for data

protectionprotection

Digital Modulation Review

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