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A.~.7 Commercial Communication Services
Commercial services have ITS applications and win be increasingly Important as Advanced
Traveler Formation Systems (ATIS) are deployed. Historically, implementation/operation of
Advanced Traffic Management Systems (ATMS) has not found commercial infrastructure to be
cost competitive wad private networks, as indicated in He survey conducted as a part of Phase
of this project. This section win address:
· Rates for Commercial Services
Satellite Communications
Broadcast SubcalTiers for ITS
Commercial Wireless Services, and
ISDN.
A.~.7.1 Rates for Commercial Services
Rates for commercial services vary widely by geographic area and service provider. This section
win briefly summarize rates that have some consistency nationwide. Table A.~.7.! presents
representative cellular rates.
Depending on preferences, users may select monthly access rates, peak/off-peak, and nightly
rates; including free minutes in the monthly access rate; and/or including a service contract.
Table A.~.7.~-2 presents wireless data service rates. Emerging CDPD services win influence
these rates in He future. Table A.~.7.~-3 presents ISDN rates.
L:\NCHRP\Phasc2.rpr\ NCHRP3-51 · Phase2F~nalReport A1-255
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Table A.~.7.1
Representative Cellular Rates
| Average Monthly Access | $30 - $189 per month
| Peak per/minute . | $.25 - $.60 per minute
| Off-peak per/minute | $.05 - $.030 per minute
Night $0 - $.30 per minute
Included free minutes ~ Peak 0 - t200 Night 0 - 200 Offpeak 30 - 100
Service contract (years) 1 - 3 years
. ~
Peak:
7:00 am - 8:00 pm, Monday - Fnday
Offpeak: 8:00 pm - ~ ~ :00 pm, Monday - Fnday
7:00 am - Il:OO pm, Weekends
Night: Il:00 pm - 7:00 am, 7 days
Table A.~.7.~-2
Wireless Data Service Rates
Monthly Rate
$ | kilobytes | ,
_
ARDIS $19.95 20 _
$50.00 150
$100.00 350
$190.00 750 _
RAM $25 100
$65 200
$88 275
_ $135 500
CDPD _
Amentech $20 100
$55 500
$99 1,000
AT&T $15 50
$50 500
$ each additional
kilobyte
$.54
$.35
$.33
$.31
$.27
$.20
$.11
$.10
$.11 to$.16
$.08
L:WCHRP\Phase2~pt\ NCHRP3-51 · Phase2FmalReport A1-256
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Table A.~.7.~3
tSDN Rates
Monthly Access Rate ~ Per Minute
Basic Rate Circuit (BRI) $19 - $90/month $.00 - $.15/minute
2B ~ D = 2 x 64 + 16 = 144 (Typically standard ~WP)
kbps
Primary Rate Circuit ~ $1,000/month Nl/A
23B ~ D = 1.544 Mbps (Requires 2 TWP)
ISDN circuits have various combinations of B (bearers channels and D (data) channels.
Normally, one D channel is provided for network control/monitoring/connection functions;
however, the B channels can be configured as individual voice channels or consolidated for
higher speed data access. Often these special configurations require telephone company
configuration support, and perhaps additional charges.
The traffic on T} and SONET/fiber circuits varies Widely. For this reason, we have not included
pricing data. Local service providers can provide pricing information. With passage of the 1996
Telecommunications Act, a competitive environment may soon emerge, drastically changing
services, provider options, and prices.
(This space intentionally left bland)
~wCHR~.rpt\ NCHRP 3-51 · Phase 2 Fmal Report A1-257
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A.~.7.2 Satellite Communications
by Comsat Laboratones CIarksburg, Maryland
A. 1.7.2. 1 Satellite Alternatives and ITS Applications
There are many areas in which satellite communications can be applied to ITS, often providing
the best solution to a problem. The applications can be categorized into several areas.
Table A.~.7.2.~-1 presents five broad applications of satellite communications, with specific
examples of each.
A.~.7.2.2 SafeIIife Performance Charaeferisfics
This section covers We venous aspects of a satellite system and Weir effects on We overall
performance character~shcs. Initially, the key features of sateHite-based communications are
presented. Then, a discussion is offered on We ~eory/concepts of satellites as a communication
medium. This is followed by short explanations of We various aspects of a satellite system such
.,
as orbits, satellite frequencies, channel bawds, typical digital bit-rates, and coverage
capabilities.
Key features of satellite-based communications
There are many unique advantages to using sateDite-based communications. The key features of
sateUite-based communications (as compared to terrestrial commurucabons mediums) are
presenter! In Table A.~.7.2.2.~-~.
L\NCHRP\Phase2.rpt\ NCHRP3-51 ~ Phase2FinalReport A1-258
OCR for page 267
Table A.~.7.2.~-1
Applications of Satellite Communications to ITS
1
2
Applications
Broadcast
Information
(Could be
transmitted to
specific regions or
broadcast
nationally.)
Data collection
(Sensors could be
rapidly deployed to
areas of concern or
interest without
reworking a ground
network.)
3 Transmission of
control information
(To specific sites or
groups of sites.)
Examples Comments
. _ .
Highway Advisory Including delivery of: Traffic flow
Radio data, road conditions, detour
information, other public service
information
Transmission of Including delivery of: Weather
weather-related data forecasts and current road
conditions (raintsnow storms, icy
roads, high winds, low visibility,
and other weather-related
phenomena which impedes traffic)
Traffic-related video Including delivery of: Detour maps'
information hazardous-area maps, traffic
congestion (video/maps), and
other visual information
_
Traffic flow-rate Report traffic flow information for
sensors critical sections of highways
(congested areas, construction
zones, etc.)
. _
Weather-related Indicate when roads are freezing,
sensors flooded' experiencing high-winds,
or low-visibility
Highway Issue regular reports on the status
superstructure stress of bridges, tunnels, overpasses,
monitoring sensors and other vulnerable structures
Smart signs Notify travelers of traffic congestion
and suggest alternate routes
Traffic flow control Include changing traffic light timing
devices or controlling various traffic
control-gates, based on traffic flow
data
National roadside Dropped off and set-up within
assistance phones minutes
Collision activated Transmit distress beacon to a
distress beacons national reaction center along with
precise location of vehicle
Highway officials and Broad range of transmission rates'
law enforcement from low (modem-type) data to
personnel voice transmissions, up to a full
T1-rate for backbone data services
4
Emergency/distress
· .
communlca. :lons
services
5
Two-way voice/data
· -
communications
L:\NCHRP\Phase2.rpt\ NC~P3-51 · Phase2FmalReport A1-259
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Theory/concepts of satellites as a communication medium
In general, a satellite may be considered to be a distant radio-freguency ~F) communications
repeater that receives upland transmissions and re-transm~ts them in its downlink beams.
Figure A.~.7.2.2.2-! illustrates the end-to-end communications required in establishing a
satellite link. The link is shown in its most generic form with transmit and receive capabilities at
both ends. Such facilities are characteristic of the two-way fixed and mobile services. Broadcast
and data collection applications transmit only at one end and receive only at Me over end of We
lick.
The overall problem can be divided into two parts. The first deals with the satellite RF link
which establishes communications between a transmitter and a receiver using the satellite as a
repeater. In describing the satellite radio link, we quantify its capability in terms of the overaU
available ca~Tier-to-noise ratio (C/N)A. This figure of merit, representing the ratio of the carrier
power (the desired signal) to the noise power measured in a bandwidth, is directly related to the
channel-carrying capability of Me satellite linlc. The value of (C/N)A depends on a variety of
factors, which in turn depend on the available power and bandwidth for the earner.
The second part of the problem concentrates on Me link between the earth terminal and Me user
environment which, in most small systems, is incorporated into the user equipment. In the user
environment customers are typically concerned with establishing voice, data, or video
communications with either one-way or two-way connections. The quality of these ~`baseband',
links is characterized by venous figures of merit such as transmission rates, error rate, signal-to-
noise ratio, and other performance measures. For example, a data communications link used to
transmit financial account balances must exhibit an extremely low rate of error to be effective.
The error-rate specification for such a data communications service is directly translated into a
required rate (C/N)Req per channel. The two parts of the problem can then be finked together
when Me available (CIN)A of Me satellite link is compared to the required (C/N)Req dictated by
the user application. The difference between the required (C/N)Req and the available (CIN)A is
called Me link margin. Usually a link is designed to achieve a certain link margin, which is used
as a buffer against occasional link degradations which are largely weaker related. The selection
of ail appropriate link margin is highly dependent upon Me link's operating environment and its
availability requirements. Availability is the percentage of Me time Mat Me link must operate
LO\ NC~P 3-S! . Phi 2 Fin Report
A1-261
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Representative terms from entire chapter:
satellite communications
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without a serv~ce-outage (typical availabilities range from 95% to better than 99.9% of the year).
Intelsat fixed service offers an availability of 99.96%, unless redundant sites are used.
The Satellite RF Link
Ihe performance of a satellite link is typically specified in teens of its channel capacity. For this
discussion, the following definitions are relevant.
A channel is a one-way link from a transmuting earth station through the satellite to Me
receiving earn station.
A circuit is compnsed of two channels used for bi-dimctional communications between two
earn stations.
The capacity of a link is specified by We types and numbers of channels and the performance
requirements of each channel. In practical terms, a voice service must provide circuits to its
customers. The term "channel," however, may also apply to television and data circuits as well.
For broadcast and data collection applications, one-way channels are typical.
The channel-caIIying capacity of a satellite RF link is directly related to the overall available
carner-to-noise ratio (C/N)A . Exclusive of interference, three basic elements are considered in
designing this RF lick. The first is the uplink, representing the channel from Me transmitting
earth station to Me satellite. The quality of this link is usually expressed in teens of Me uplink
carrier-to-noise ratio (CINJu . The (C/N)U depends on the power of the transmitting each
station, the gain of Me transmitting antenna, the gain of the receiving antenna, and Me satellite
system noise temperature. The power of the transmitter on the ground depends on the size of the
power amplifier employed. The gains of both the transmuting and receiving antennae are
directly related to Heir sizes and efficiencies. The system noise temperature is a measure of Me
degradation of the received signal caused by elements in Me receiver. This is composed of the
receiver's amplifier noise the noise due to losses between Me antenna and Me amplifier, and Me
antenna noise.
\NCH]WhaS~\ NCHRP3-51 · PhaSe2Fina1RePOrt
A1-263
The second element In Me RF link is the downlink. The corresponding figure of merit is caned
the downlink caIrier-to-noise ratio (CM)D . Similar to We uplink, (C/N)D depends on Me power
of the satellite transmitter, the gain of Me transmuting and receiving antennae, and Me earn
station's system noise temperature. The third element to be considered in Me RF link design is
Me satellite electronics system itself, which produces undesirable noise-like signals Mat are
normally expressed in a caner-to-noise ratio which we can cad (~/N)I . Sever impairments,
pnmarily intetmodulation effects caused by the non-linear operation of the satellite amplifiers,
can be included In the (CHILI component. Interference from over satellites and terrestrial
systems can also be coBec~vely characterized by a carner-to-~nterference ratio.
one makes certain typical assumptions about He nature of Me noise-~ce impairments, then the
three elements [(C/N)U (C/N)D and (CIN)I ~ can be easily combined to yield an overall camer-
to-noise redo, (C/N)A . Due to the way this overall available camer-to-noise ratio (C/N)A is
calculated, it can never be better Man Me worst of the three individual elements.
Two basic components are required to establish a satellite link. The first is the satellite repeater,
usually carded a transponder, and the second is a satellite earn station.
The Satellite Transponder
A satellite functions as a distant RF communications repeater which receives uplindc
transmissions and provides fiItenug, amplification, processing, and frequency translation to the
downlink band for retransmission. These sub-functions are briefly descnbed below.
The typical transponder is a quasi-linear repeater amplifier, a block diagram of which is shown
Figure A.~.7.2.2.2-2. The uplink and downlink bands are separated In frequency to permit
simultaneous transmission and reception without self-interference. Moreover, Me lower-
frequency band is normally used on the downJink to exploit the reduced atmospheric losses (at
these lower frequencies), thereby minimizing satellite power amplifier requirements. Typical
satellite transponder amplifiers must provide relatively large gains (amplifying Me signal power
from 100 million to 10 billion times) while maintaining relatively low-noise operation.
Channeliz~ng filters must be designed to minimize interference from adjacent channels, as well as
[.WC~.~.Q,lK NCHRP3-51 ~ Ph~2~RePOrt
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Use of Time Division Multiple Access (TDMA) digital modulation which permits multiple
~ .
users on one frequency pair.
· Use of Code Division Multiple Access (CDMA) which permits multiple users on one
frequency pair. CDMA is a form of spread spectrum digital modulation (see Section
A.1.3.4).
Competing standards have emerged in bow the cellular and PCS services. Both TDMA and
CDMA are digital modulation techniques and requure speech codecs that digitize and compress
the analog speech signal. The quality of the speech codec Algonquins is a significant determinant
of die user's perceived quality of service. These digital modulation techniques, when widely
deployed, can efficiency support data without a modem. None of these competing digital
standards have substantial current U.S. deployment in either cellular or PCS. AMPS is still
dominant; however, PCS win be deployed more as competitive pressures win undoubtedly force
an eventual transition to digital cellular for added capacity and additional features.
Table A.~.7.4-2 presents He primary cellular/PCS systems in Be U.S. and key operational
parameters. It should be noted that Global Systems for Mobile (GSM) is an adaption of Be
European system for emerging PCS services and has been selected by several PCS service
providers because equipment is available for rapid deployments. CDMA has been selected by
several of Be service providers because it debatably offers increased capacity. Unlike analog
cellular, digital cellular and PCS have multiple deployed standards. Time and the marketplace
will determine user acceptance.
Cellular Digital Packet Data (CDPD) is a service available from analog cellular providers, which
offers packet data capability in the cellular bands. CDPD Besets bursty packet data on idle
cellular analog channels. Because it fits data between voice conversations, CDPD has not yet
(early '96) verified that it will operate satisfactorily in overloaded metropolitan areas. S~m~lar
CDPD services will be offered via digital cellular/PCS bands and the already digital modulation
may provide more cost effective services and equipment.
The PCS bands are being auctioned and few are operational in '95/'96. The allocated frequency
bands are presented in Figure A.~.7.4-2. It should be noted Mat Be FCC has allocated bow
t.:`NC~Phasc:.rpr\ NCHRP3-51 · Phase2FinalReport
A1-326
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licensed and unlicensed bands. As previously noted, PCS will be digital on initial deployments.
It should also be noted that the FCC PCS frequency avocations constrain two unlicensed bands.
One is asychronous for packet data applications and one is isochronous (equal delay) for
potential voice/video applications; such as wireless PBXs.
Two wireless packet data services offer commercial capabilities using He Specialized Mobile
Radio (SMR) frequencies near 800/900 MHz, offering coverage to about 90% of urban business
areas. Advanced Radio Data Infotmabon Service (ARDIS) is available in more than 200
metropolitan areas. RAM Mobile Data (RAM or RMD) service is available In 216 metropolitan
areas. ARDIS and RAM have more Han 52,000 subscribers nationwide. Table A.~.7.4-3
provides an overnew of these services and, for comparison, equivalent information on CDPD.
Table A.~.7.4~3
Commercial Wireless Data Services
ARDIS ~ RAM ~ CDPD
Mobitex Architecture)
Data Rate | 4.8 kbps | kbps | 19.2 kbps
19.2 kbps
Frequency Band | SMR | MR | Cellular l
800/900 MHz 800/900 MHz 824 - 894 Mbps
Number of Channels 10 - 30 Cellular frequencies
each Metropolitan
area
Coverage ~410 MSA 210 MSA 50 MSA
(MSA- Metropolitan
Service Area)
Comment ~ Proprietary protocol ~ Proprietary protocol ~ Public protocol
Analog modems over c~rcuit-sw~tched celdular phones are frequently used for wireless data
transmissions. These are typically the V.32/V.34 wireline modems; however, He cellular
telephone network has different characteristics from He standard wired network and special
protocols are required for reliable commun~cabon. Two ceDular-specific error correction
protocol standards are employed:
1) Enhanced Throughput Cellular (ETC), developed by AT&T (now Lucent Technologies); and
L;`NCH~Phase2.~p~\ NCHRP3-51 · Phase2FinalReport A1-330
2) Microcom Network Protocol lO Enhanced Cellular (MNPlOEC), developed by Rockwell
International.
Both of these protocols are extensions of the ITU V.42 error control and correction protocol. It
should be noted that, even with special cellular protocols, He throughput (byte per second) can
be substantially less Can rated land line circuit performance.
In addidon to the proliferation of wireless communications services, the wireless explosion is
providing many standard "air interfaces" Mat could prove useful and adaptable to ITS
applications.
A.1.7.5 ISDN
Integrated Services Digital Network (ISDN) is a digital dialup telephone service that was
conceived to provide end-to-end digital telephone service. After years of hype and unrealized
potential, ISDN appears to have achieved some recent successes largely as a result of demand for
higher speed (compared to dialup modem) access to Internet services. It is also widely used by
the radio broadcast industry for higher quality voice transmission from remote sites (e.g., sports
arena, etc.) and win offer similar benefits to rRs.
For years, He commercial telephone network has employed digital switching, multiplexing (i.e.,
T! digital hierarchy), and transmission. However, the TWP connecting He Central Office (CO)
switch to subscriber telephones has been analog as depicted in the lower part of Figure
A.~.7.5-! ISDN essentially extends the digital DS-O (or B channel In ISDN terminology) to He
subscriber premise as depicted In He upper part of Figure A.~.7.5-~.
A D (or data) channel is also provided to serve the equivalent telephone signallcontro] fimctions
such as on/off hook, DTMF dial tones, busy signal, etc., tones Hat are provided "in-band" on He
standard analog telephone circuits. Additionally, this D channel may also serve as a packet data
channel for packet services, although most current services appear to use B channels.
L;mC~Phasc2~p~\ NCHRP3-51 · Phase2FmalReport
A1-331
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ISDN is basically a WAN service that is available In two forms:
Basic Rate Interface (BRI).
Primary Rate Interface (PRO.
BR] provides the following:
· 2 B Channels (DS-O, 64 kbps) for a total of 128 kbps.
· ~ D Channel at 16 kbps.
Deployment over existing telephone company TWP loop plant by providing ISDN terminals
at bow the customer premises and Be service CO (also in Figure A.~.7.5-~.
PRI provides:
Essentially DS-] service at 1.544 Mbps
Up to 23 DS-O channels available within the DS-l frame, (although over rates can be
supported).
~ D channel at Be DS-O rate of 64 kbps.
· This requires special 4-wire TWP circuits and repeaters for longer distances (the equivalent
of T1 DS-1 circuit requirements).
N
L:\NCHRP\Phase2.rptN NC~3-51 ~ P~2F~Re ~A1-333
Endnotes:
1. The infrastructure can be a regional traffic center, an incident center, a real-time map update facility, etc.
2. The Communications Act of 1934 (as amended) requires He FCC to judge all requests for radio spectrum by determining
if the need is "in the public interest, convenience or necessity."
3. SCA, or Subsidialy Communications Authorization was a FCC description that was deleted from the FCC Rules (47 CI;R
73) in a rule making proceeding in 1983. It was replaced by the description Subsidiary Communications Service, but the
initials SCS never caught on. In any case, these terms are very narrow and exclude F'M RDS and various TV aural
subchannels. In addition, neither SCA nor SCS are descriptive of the channels. Calling these channels "broadcast
subcamers" is both inclusive and technically descriptive.
4. Edwin H. Armstrong, "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation,"
Proc. of the I.R.E., Vol 24, No. 5, May 1936. Repunted; Jacob Klapper ed, Selected Papers on Frequency Modulation,
Dover, New York, 1970.
5. A minor exception to this is in the case of non-commercial FM stations that must, if they use any subcarriers for profit
making activities, make an additional one available for use by radio reading services for the blind.
6. Effective radiated power is the transmitter power output available at the antenna multiplied by the gain of the antenna
7. This is a holdover from ten years ago when there were FCC Rules governing subcarrier technical operations. Today there
are no such rules, but the practices continue from 'Force of habit."
8. There is a large distinction between "throughput" or the information rate and the signaling speed.
Depending on Me level of error correction, the signaling speed may be several times faster Wan the data
throughput. The later section "Data Rates" discusses this issue in more detail.
9. T. Beale and D. Kopitz, " RDS in Europe, REDS in Me USA ~ What are Me differences and how can
receivers cope win bow systems?," European Broadcasting Union (EBU) Renew - Technical, Spring 1993,
pages ~8.
10. "United States REDS Standard, Draft No. 2.0, NRSC Document, August 1, 1992" National Association of
Broadcasters and The Electronic Industry Association.
11. A. G. Lyner, '~xpenmental Radio Data System (RDS): A Survey of Reception Reliability in the UK," Report BBC RD
1987/17, British Broadcasting Corporation Research Department, Engineering Division, Nov 1987.
12. Ibid.
13. "IKE Colloquium on 'The RDS System - Its Implementation and Use' (Digest 128)"; IKE, London, UK; Dec 1988.
14. K. H. Schwaiger and J. Mielke, 'prowess With He RDS System and Experimental Results," European Broadcasting
Union (EBU) Review - Technical, No. 217, June 1986, pages 150~158.
15. F. Stollenwerk and N. Pfeiffer, 'first Operational Results of the Radio Data System (RDS)," lIG-Fachberichte, Vol
106, Pages 123-128, 1988 (In German).
L.\NCHRP\Phasc2.'ptY CHAP 3-51 · Phase 2 Fmal Report A1-334
16. J. H. Paffenbarger, "Optimized Implementation of SCA Subcarriers for Minimum Degradation of FM Stereo
Reception," Proceedings: 41st Annual Broadcast Engineenng Conference; 1987, National Association of Broadcasters,
Washington, DC. A contrary position is taken by Paffenbarger. However, the FM station discussed is a fine arts type of
station much closer to the traditional European norm than the U.S.
17. This may be a self seeing position for some non-commercial fine arts stations. Non-commercial FM stations are
obligated by the FCC to provide subcanier service to reading services for the blind if they make commercial use of any of
their subca~riers. Objecting to subca~Tiers on technical grounds offers an credible way to refuse being forced to "give away"
one of their subcarriers.
18. Ibe character of broadcasting, especially FM, is changing in Europe win He Mowing movement toward private
ownership of radio and television stations. These new stations are evolving very much in He style of U S. commercial
broadcasting.
19. D. J. Thyme, 'the transmission of Two Program~s From Band ITEM Transmitters: an assessment of 'Storecasdng',"
Report BBC RD 1976ll4, British Broadcasting Corporation Research Department, Engineenng Division, June 1976.
Reprinted in the European Broadcasting Union (EBU) Review - Technical, No 161, February 1977, pages 20-30.
20. In the presence of competing signals, as is the case in the FM band, the greater the average deviation (loudness), the
greater and more reliable will be the coverage of the radio station.
21. The visual portion of He TV signal is much more susceptible to interference from other visual signals, so it sets the
spacing requirements between stations. The aural carrier is significantly more resistant to interference than the visual, so
it gets a "Bee rice" in terms of interference Tom other aural signals on the same channel. In addition, because the TV sound
channel is adjacent in frequency to Be much wider band visual signal, interference from stations on adjacent channels is not
an issue. This contrasts wig FM stations, for which adjacent and co-channel interference is the major factor in limiting
coverage.
22. "OET Bulletin No. 60, Revision A"; Office of Engineering and Technology, Authorization and Evaluation Division;
February 1986; Federal Communications Commission.
23. The frequency response is 50 Hz to 101tHz, with a signal-to-noise ratio better Han 60 dB.
24. The FCC Rules - 47 CORK 73.682(c)~1-9) provide Hat a television station may use non program related subca~riers from
16 kHz to 120 1~z at a total deviation not to exceed 50 kHi.
25. Data WorId or ITS Boulder, div of NIST.
26. The Federal Communications Bar Association, 1150 Connecticut Avenue N.W., Swte 1050, Washington, DC 20036.
Telephone (202) 833-2684, fax (202) 833-1308.
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