Introduction to Communication Theory

Transcription

1 Introduction to Communication Theory Lijun Qian Department of Electrical Engineering PVAMU

2 Figure 1 Elements of a communication system.

3 Elements of a communication system Transmitter To convert the message signal produced by the source into a form suitable for transmission over the channel. Channel Received signal is a corrupted version of the transmitted signal due to Channel imperfection Added noise and interference Receiver Operate on the received signal to reconstruct a recognizable form of the original message signal.

4 Analog Communication vs. Digital Communication An analog communication system transfers information from an analog source (which produce messages that are defined on a continuum, for example, the output voltage describes the information in the sound from a microphone) to the sink/destination. A digital communication system transfers information from a digital source (which produce a finite set of possible messages, for example, messages from a typewriter) to the sink/destination.

5 Advantages and Disadvantages of Digital Communication Advantages Inexpensive digital circuits Privacy by data encryption Noise does not accumulate Use of error correction coding Disadvantages More bandwidth is required than that for analog systems Synchronization is required

6 Figure 9 Block diagram of digital communication system.

7 Function blocks in a digital communication system Source coding (source encoder/decoder) Data compaction, reduce the unnecessary redundancy in messages generated by the information source Channel coding (channel encoder/decoder) Introduce controlled redundancy to combat channel imperfection and noise/interference Modulation (modulator/demodulator) a.k.a. MODEM

8 Figure 10 Elements of a digital communication system. (a) Block diagram of transmitter. (b) Block diagram of channel. (c) Block diagram of receiver.

9 Communication networks Wireline vs. Wireless communication networks Wirelinenetworks Example: Ethernet, token ring, fiber optic networks, the Internet Wireless networks Example: 3G CDMA cellular and PCS networks, 2G TDMA cellular networks, WLAN (802.11b/a/g), Bluetooth, wireless sensor networks

10 Communication networks (contd.) Local area networks vs. Wide area networks Local area networks Examples: Ethernet, WLAN (802.11b/a/g), the computer network within PVAMU Wide area networks Examples: Trans-Atlantic fiber optic backbone networks, ATM backbone networks in the U.S., the backbone network connect all computer networks within Texas A&M University System

11 Figure 4 Communication network.

12 Figure 5 OSI model; the acronym DLC in the middle of the figure stands for data link control.

13 Figure 6 An interconnected network of subnets.

14 Figure 7 Illustrating the network architecture of the Internet.

15 Global Wireless Standards Evolution CDMA IS-95-A Voice 14.4 kbps CSD & PD 2G 2.5G IS-95-B Voice 64 kbps Packet RF Backward Comp. CDMA2000 1X High Capacity Voice 153 kbps Packet RF Backward Comp. 3GCDMA - IMT-2000 Compliant CDMA2000 1xEV-DO 2.4 Mbps Packet RF Backward Comp. CDMA2000 1xEV-DV Higher Cap Voice/ Data RF Backward Comp TDMA IS-136 Voice 9.6 kbps CSD EDGE (US) EDGE (Europe 384 kbps Packet GSM Voice 9.6 kbps CSD PDC PDC GSM GPRS 114 kbps Packet RF Backward Comp. W-CDMA (Japan) W-CDMA (Europe & US) Voice Voice 9.6 kbps 28.8 kbps RF Backward Comp part of this 2001 presentation is from High Capacity Voice 384+ kbps Packet New RF

16 Infrastructure backhaul PDSN Internet HLR ANSI-41 network PCN AAA BSC MSC PSTN wireless access BS BS cell