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A.2 ITS Communication System Design Communication Systems for rrs are designed to cost-effectively transmit data, video, and/or voice from sources to destinations (sinks) to meet user and application requirements. No single combination of communication architecture, topology, or mediums is optimum for aU requirements. Thus, con~nun~cations system design involves considerations, evaluations, and trade-offs of: I. User and application requirements; 2. Data loads (or equivalently composite data rate) between sources and destinations; 3. Geographic area and commun~cabon infrastructure topology; 4. Multimedia requirements: voice, data, and video; 5. Communication media alternatives; 6. Link budget analysis; 7. Communication Architectural requirements: TOC backup, data sharing, etc.; 8. Standards; 9. Reliability, maintainability, and availability requirements; 10. Operational and maintenance support requirements; and ~ I. Costs and available budgets. Section A.3 win present representative suburban, urban, metropolitan, and rural system designs wad cost estimates. Section A.4 win address reliability, maintainability, and availability, as weD as estimating requirements. A.2.1 Analog versus Digital Communication System Table A.2.1-! summarizes generic analog and digital communication systems and Weir comparative charactenstics. The principle advantage of digital communication channels is the complete reconstruction of the signal at repeaters (not amplifiers) and He availability of modern error control techniques. Figure A.2.1-1 illustrates He comparison of analog and digital communication links. t;`NCHRPPhase~rpti N~3-51 IF A2-1

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Table A.2.~1 Characteristics of Digital and Analog Communication Systems Characteristic Analog Digital Channel Type Description Transmits replica of source Creates digital version of waveform and reconstructs source waveform or data at waveform at receiver. transmitter, transmits digital data, and reconstructs source waveform or data at receiver. Measures of Bandwidth Bit rate performance Signal-to-Noise (SNR) Bit-Error-Rate (BER) as a function of SNR Principle Impairments Channel Distortions Channel Distortions Noise* Noise* Non Linear amplifier Non Linear amplifier Disto rtions Distortions Non Linear Digitization D slovens Principle Advantages Requires less processing Complem y n~=cu~s Sony Graceful, but cumulative, at digital repeaters, thus signal degradation minimal degradation above Usually less Bandwidth SNR threshold. Requirements than Digital Digital Error Control is Equivalent available Low cost digital components Principle Limitation Noise and Distortions: Abrupt Signal Degradation Cumulative even at below SNR threshold. repeaters becoming so Bandwidth Requirements often severe that SNR degrades greater than Analog below threshold. Equivalent (improves with Higher cost analog compression) components Higher Cost and availability of A/D and D/A Components as source bandwidth Examples with Voice: 3 kHz (telephone) Voice: 64 kbps Analog: Bandwidth (Uncompressed) Digital: Bit rate 4-32 kbps (Compressed) Video: 6 MHz (NTSC) Video: 3 Mbps (Compressed) Data: digital modems Data: 300 bps to over 10 Gbps AM Radio: 10 kHz~ FM Radio: 200 kHz~ * Usually expressed as SNR compared to desired source ** Currently no digital equivalent / L;\NCHEtP\Phase2Jpt\ NCHRP3-51 Phase2FmalReport A2-2

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