1. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems 0909.331.01 Spring 2005 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring05/ecomms/ Lecture 8b March 30, 2005

2. S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPlan Finishing up FM Spectra Digital Communications Introduction Digital Communications Transceiver (CODEC/MODEM) Digital Baseband Communications Source Encoding Huffman Coding

3. S. Mandayam/ ECOMMS/ECE Dept./Rowan University FM Signal & Spectrum Single-tone FM Signal Single-tone FM Spectrum 0 f c -3f m f c -2f m f c -f m f c f c +f m f c +2f m f c +3f m |S(f)| / (A c /2) f J0()J0() J1()J1() J2()J2() J3()J3()

4. S. Mandayam/ ECOMMS/ECE Dept./Rowan University ECOMMS: Topics

5. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Communications Some Milestones Claude Shannon, 1948 X.25 (Telephony) IEEE 802.3 (Ethernet) ARPANET, 1969 IEEE 802.5 (FDDI) ISO-OSI 7-layer Network Reference Model CDMA GSM VOIP SIP protocols.com

6. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Communications: Rationale Information Theory: What is the fundamental limit on the compression and refinement of information generated by the source? What is the fundamental limit on the transmission rate of information over a noisy channel? How do we approach these limits?

7. S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPrinciple 1 0 1 0……… 1 0 Analog message Digital code Digital message Sinusoidal carrier modulate AM FM PM AM & PM 1 0

8. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Communication Paradigms Multiplexer Message 2 Message 3 Message 1 1 2 3 S 1 2 2 3 S Demultiplexer Message 2 Message 3 Message 1 Packetizing Message 2 Message 3 Message 1 1H H 2 3 H H 2 1H 3 H H 2 1H 3 H Message 2 Message 3 Message 1 Depacket -izing Circuit Switching Packet Switching Sync bits Header bits

9. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Digital Communications Transceiver Anti- aliasing Filter SamplingQuantization Data Encryption Encoder Source Encoder Error Control Encoder Channel/ Line Encoder Modulator MUX Audio Amp Source Decoder Data Encryption Decoder Error Control Decoder Equalization / Decision Circuits Demod- ulator DEMUX Reconstruction/ DAC ADC CODEC MODEM Analog o/p Multiple access channel Analog i/p

10. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Source Encoding Why are we doing this? Analog Message A/D Converter Digital Source Encoder Source Symbols (0/1) Source Entropy Encoded Symbols (0/1) Source-Coded Symbol Entropy

11. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Source Encoding Requirements Decrease L av Unique decoding Instantaneous decoding

12. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Huffman Coding 2-Step Process Reduction List symbols in descending order of probability Reduce the two least probable symbols into one symbol equal to their combined probability Reorder in descending order of probability at each stage Repeat until only two symbols remain Splitting Assign 0 and 1 to the final two symbols remaining and work backwards Expand code at each split by appending a 0 or 1 to each code word Example m(j)ABCDEFGH P(j)0.10.180.40.050.060.10.070.04

13. S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversitySummary