Communication Mediums for Signal, ITS, and Freeway Surveillance Systems Final Report (1996) / Chapter Skim
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A.1.1 Wire Mediums and Terminals
A.1.1 Wire Mediums and Terminals
Pages 10-62
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A.~.~.1 TWP Cable Plants Twisted Wire Pair CTWP) cable plants have been deployed by He telephone industry for more than 100 years and Heir chata~enstics have been extensively studied for voice, data via analog wavelike modems, and T!
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In high count TWP cables, crosstalk is often the major determinant of throughput capacity. Gauge Changes The public telephone network typically changes to higher gauge and lower pair count cable on runs from Central Office (CO)
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Table A.~.~.~2 Line Conditioning Specifications .
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Standard for Telecommunications Cable, Aircore, Polyolefin Insulated, Copper Conductor Technical Requirements.
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References rid Communications Handboolfor Traffic Control Systems, FlIWA Report No. FE1WA-SA93-052, April 1993.
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technology was created to permit the transmission of digital data over the analog voice telephone network. A typical voice telephone connection provides a communication channel within the audio frequency band between approximately 200 Hz and 3700 Hz (3500 Hz bandwidths.
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Additionally, Frequency Shift Key (FSK) modulation typically requires more bandwidth for a given symbol rate than phase modulation formats such as Phase Shift Key (PSK)
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Me required Sew to support an acceptable BER is most heavily influenced by the symbol rate and Be modulation format which collectively defines Be bit rate. A higher SNR is required to support higher symbol rates and greater bits per symbol.
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techniques over a single TWP are employed for symbol rates above approximately 600 symbols/second. In EC, sophisticated signal processing filtering algorithms are employed to generate and subtract the approximately known outbound local signal from the received signal leaving a sufficiently dominant remote signal to be demodulated.
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\ ~ I Lo CY i I | ~ ~ \ I O O O f ~ 1 3 ~ .= ~ in Q)
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to adapt to an initial inverting approximation. Adaption usually continues during data transmission, even after initial gaining, to account for changing circuits.
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Lo ~ llJ / \ LO c)
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A link budget establishes that the transmitter launch power, minus the circuit losses, is greater Man He modem receiver sensitivity. The losses in a TWP communication circuit include: 1.
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400 Modem ITU V.29 (Bell Standard 202) 9600 bps, DAM modulation 1200 bps FSK modulation , Launch power (dBm)
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This bandwidth is somewhat greater Han He bandwidth Hat a 1200 bps FSK modem requires, and the actual loss in dB/mile will be somewhat greater. For detailed design, the actual modulation frequency band that a modem requires should be obtained from He modem manufacturer and the estimated dimple loss for this frequency band should be obtained from the TWP cable manufacturer, especialRy for long circuits win tight link budgets.
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to He specific circuit of operation. The preferred filil duplex method for private networks is 4-wire which avoids He need for echo canceling and training time.
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Thus, multidrop modem design involves two analyses: link budget and throughput vs. number of supported drops per TWP.
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Table A.~.2.3~1 Example Mullidrop Analysis Parameter/Calculation Mode'400 Modem ITU V.29 (Bell Standard 202) 9600 bps, CAM modulation 1200 bps, FSK modulation Bit Rate: Rb in bits/second 1200 bps 9600 bps ._ Modem Tumaround Time: To 10 ms (millisecond 10~)
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From page 31... ...
Full duplex could only be achieved by 4-uire or split band over 2-wire. The highest speed fills duplex, spilt band modem was the 2400 bps, ITU V.22bis with a symbol rate of 600 symbols/second.
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l 0 cO ce o ~ o - - ii i ce o · o c~ o Q In S 0 In _ O O ~ _ CO In j Cat Cot HI _ ~ ~ O V ~2 ~ ~ In ~_ _ .
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o · ~°ra :com ..
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3. Bit rates of 4800, 7200, 9600 bps (note: this is 2x,- 3x, and 4x Me 2400 symbols/second)
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Thus, increasing bit rates require higher quality circuits for data transmission at acceptable BER. Trellis coding is a sophisticated error control aigori~n Hat is integrated with modulation to achieve substantially improved BER over lower quality circuits.
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These are achieved with the vanable symbol rates listed below and win bits/symbol ranging from 3 to 10 bitsIsymbol win one bit allocated for trellis encoding. Additionally, V.34 permits asymmetrical bit rates (not supported in Me V.32 standards)
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1 1 '1 1 1 ' Em m LLJ Cad ·_ en a)
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(V.32 employs 1800 Hertz only.) The selected camer frequency is a function of symbol rate and one of two frequencies according to channel characteristics.
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V.32/V.34 modems have not been extensively employed in traditional signal systems due to the extensive employment of multidrop circuits Mat are better accomplished with the older FSK, FLU V.29, and rru V.33 modems Mat support faster turnarounds; however, ITS is evolving to ATIS systems where the Raveling public will remotely dial into infonnation services. The V.32/V.34 Moslems will be significant enabling technologies for these applications.
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Typical PSTN impairments are presented in Table A.~.~.2.6-~. Table A.~.~.2.6~1 Public Service Telephone Network (PSTN)
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Most PSTN cans involve analog on 2-wire pairs only from the customer premises to the central office. Severe impairments of analog circuits do not exist on digital circuits and include frequency offset, forms of phase jitter, and related impairments.
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These~nclude: · Employing a Rewire private network adds very modest incremental costs and has significant benefits. FuR duplex operation is possible without echo canceling at higher bit rates than is possible with Unwire split band modems.
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m z 3: Q l l o ~1 1 C~ L-I o o O Z <( o z LLI J O Z O o oo o o Z \` O ~ z o CD ~ ~ ~ ~: o z Ct a' · _ 11 C)
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, could support higher bit rates by increasing He symbol rate and using more bits/symbol on He higher quality circuit. Interested manufacturers would need to be identified and motivated.
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The telephone industry and supporting equipment vendors have developed many products and services to provide higher bit rates over TWP-only circuits. These include: Repeatered T!
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; Cable plants must often be redesigned and conditioned; and Repeaters must be installed about every 6,000 feet. The high bit rate digital subscriber line (HDSL)
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BELLCORE Technical Reference TR-iNS-000342, February 1 991 . Available from BELLCORE Customer Service.
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References American National Standard for Telecommunications. Integrated Services Digital Network (ISDN9: Basic Access Interface for Use on Metallic Loops for application on the Network Side of the NT (Layer 1 Specification)
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As a solution, early implementations of the digital hierarchy were conceived that digitized up to 24 analog voice signals into 24 digital voice signals at ~ bits~sample and 8,000 samples/sec to create a DS-O digital signal at 64,000 bps. The analog voice signal is filtered to limit He bandwidth to less than 3100-3500 Hz.
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Test There are several altemative channel bank options that can be selected depending on He application. The multiplexed digital signal consists of 24 DS-0 digital signals at 64 kbps and one frame bit for a total of 1.544 Mbps.
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Except for PBX requirements, a switching capability or CO is usually not required for ITS and over private network infrastructure requirements; however, He transmission, multiplexing, and cross-connect equipment provides excellent capabilities. Of significance to ITS applications is He availability of high volume cost- effective, equipment for ITS communications infrastructure development.
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1 cn c: cn LLJ o z cy z c: o by is ~ 1 ' .
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Of particular importance to ITS are the ELA-232 bit rates that are multiplexed in a DS-O frame. The bit rates supported are: 2.4 kbps 4.8 kbps 9.6 kbps 19.2 kbps 28.8 kbps · 38.4 kbps Commercial services are available from telephone companies Mat support these DS-O subrates, typically under the name of digital data service (DDS)
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~At, ~m > 0 ~ D D D D ~ of =~0= · <4 ~ ~ a' ~ D D D CD 00 In (D Cot ~ _ l 1 \ C)
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Integrated Digital Loop Carrier System Generic Requirements, Objectives, and] Interface Belicore Technical Reference TR-TSY-000303, Sept.
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D3 and D4 Subrate Dataport Channel Unit Technical Reference and Compatibility Specification. AT&T Compatibility Bulletin No.
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