Electrical Communications Systems ECE.09.331 Spring 2008 Lecture 11b April 9, 2008 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring08/ecomms/

Plan Pulse Amplitude Modulation Digital Bandpass Communications Sampling Quantization TDM Standards T1 (DS-1) Line North American TDMA Hierarchy Line Encoding Digital Bandpass Communications Why digital modulation? Digital Modulation: Introduction (ASK, FSK, PSK) Binary Phase Shift Keying (BPSK)

ECOMMS: Topics

Digital Communications Transceiver Anti- aliasing Filter Data Encryption Encoder Error Control Encoder Sampling Channel/ Line Encoder Quantization Source Encoder MUX Modulator ADC Analog i/p CODEC MODEM Multiple access channel Analog o/p Data Encryption Decoder Error Control Decoder Audio Amp Reconstruction/ DAC Source Decoder Equalization / Decision Circuits DEMUX Demod-ulator

Pulse Code Modulation (PCM) Standard for all digital communications Analog Signal Sample & Hold Digital Bitstream Quantize Encode PAM PCM

Pulse Amplitude Modulation: Flat-top Sampling -0.5 0.5 1 1.5 2 2.5 3 3.5 4 -6 -4 -2 6 8 time Analog PAM Matlab Demo: pam.m

Quantization Uniform Non-Uniform m-Law A-Law Mid-rise Mid-tread Matlab Demos: quantization.m pcm.m Mid-rise Mid-tread Mid-rise Mid-tread Matlab Demos: companding.m pcm_mucompand.m pcm_mucompand2.m pcm_acompand.m pcm_acompand2.m

Digital Communications Transceiver Anti- aliasing Filter Data Encryption Encoder Error Control Encoder Sampling Channel/ Line Encoder Quantization Source Encoder Modulator MUX ADC Analog i/p CODEC MODEM Multiple access channel Analog o/p Data Encryption Decoder Error Control Decoder Audio Amp Reconstruction/ DAC Source Decoder Equalization / Decision Circuits DEMUX Demod-ulator

Time Division Multiplexing Message 1 Quantize & Encode Message 2 Channel Message N Message 1 LPF Decode Message 2 LPF Message N LPF

T1-Line TDM Format 1 Frame = (24 Channels + F) = 125 ms Channel 1 1 8 7 6 5 4 3 2 Channel 2 1 8 7 6 5 4 3 2 Channel 24 1 8 7 6 5 4 3 2 F 193 bits Frame Sync Bit Even Frames: 0 0 1 1 1 0 Odd Frames: 1 0 1 0 1 0 Every Sixth Frame LSB (8th bit) is a Signaling bit Bipolar R-Z Line Encoding

North American TDMA Hierarchy 64 kbs 1 VF DS-0 1 1 7 DS-2 6.312 Mbs 96 VF 3rd M U X 1 6 DS-3 44.736 Mbs 672 VF 4th M U X 1 2 DS-4 274.176 Mbs 4032 VF 5th M U X 1 4 DS-1 1.44 Mbs 24 VF 2nd M U X 1st M U X 24 DS-5 560.160 Mbs 8064 VF Figure 3-40, p. 207 in Couch Table 3-8, p. 208 in Couch Table 3-9, p. 209 in Couch

Digital Communications Transceiver Anti- aliasing Filter Data Encryption Encoder Error Control Encoder Sampling Channel/ Line Encoder Quantization Source Encoder MUX Modulator ADC Analog i/p CODEC MODEM Multiple access channel Analog o/p Data Encryption Decoder Error Control Decoder Audio Amp Reconstruction/ DAC Source Decoder Equalization / Decision Circuits DEMUX Demod-ulator

Line Encoding Couch, p. 162 Couch, p. 157

ECOMMS: Topics

Digital Communications Transceiver Anti- aliasing Filter Data Encryption Encoder Error Control Encoder Sampling Channel/ Line Encoder Quantization Source Encoder MUX Modulator ADC Analog i/p CODEC MODEM Multiple access channel Analog o/p Data Encryption Decoder Error Control Decoder Audio Amp Reconstruction/ DAC Source Decoder Equalization / Decision Circuits DEMUX Demod-ulator

Digital Bandpass Communications Why digital modulation? Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

Industry Trends Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

Applications Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

Digital Modulation Carrier signal: Ac cos (2pfct + f) Modulation: m(t) Modulated signal: Ac (t) cos (2pfc(t) t + f(t))  m(t); discrete Vary Vary Vary amplitude frequency phase Variations are discrete!!!!!

Recall: Dig Comm Principle Digital message 1 1 1 0 1 0……… 0 0 Digital code Analog message modulate 1 0 1 0 AM Sinusoidal carrier FM PM AM & PM

Signal Vector Representation s(t) = Ac(t) cos (2pfct + f(t)) fixed!!! Q S Magnitude Phase 0 degrees I I-Q Plane

Signal Changes: Representation in the IQ Plane Phase Change S1 S2 I Q Magnitude Change I-Q Diagrams or Constellations S1 S2 I Q Magnitude & Phase Change Frequency Change ???

Binary Phase Shift Keying (BPSK) s(t) = Ac cos(2pfct + f(t)) IQ Diagram Q p radians f(t) 1 0 radians t I

Summary