NASA Technical Reports Server (NTRS) 19940018355: A practical system for regional mobile satellite services

6 Pages·0.45 MB·English

by  NASA Technical Reports Server (NTRS)

N94-22828
A Practical System for Regional Mobile Satellite Services
Randall Glein, Denis Leverson, and Dean Olmstead
Hughes Aircraft Company
Bldg. $64, MS B433
P.O. Box 80002
Los Angeles, CA 90009, USA
Telephone: [phone]
Fax: [phone]
ABSTRACT This network architecture consists of two
MSAT satellites (Figure 1, Table 1), satellite
The Regional Mobile Satellite (MSAT) control facilities, various earth stations, and the
concept proposes a worldwide, interconnected end users' mobile and fixed terminals. These
mobile satellite service (MSS) network in which components are common to any Regional
MSAT-type satellites provide the space segment MSAT system.
services to separate regions (i.e., one or a few The North American system's coverage
countries). Using this concept, mobile commu- spans the entire United States, Canada, Mexico,
nications users across entire continents can now Puerto Rico, the Virgin Islands, and the
be served by a handful of regionally controlled Caribbean (Figure 2). A user anywhere within
satellites in geostationary earth orbit (GEO). this range can place a call from his or her
All requirements, including handheld telephone
capabilities, can be cost-effectively provided 111
using proven technologies. While other con-
cepts of regional or global mobile communica- L-BAND RECEIVE
tions continue to be explored, the Hughes REFLECTOR
Regional MSAT system demonstrates the near-
term viability of the GEO approach. L-BAND TRANSMIT
REFLECTOR\
REGIONAL MSAT--A NORTH
AMERICAN EXAMPLE
Since the advent of mobile communica-
tions, users have enjoyed steadily increasing
freedom from the constraints imposed by hard
wire. Unfortunately, mobile communication has
ND
been limited by the height and range of radio
ANTENNA
towers. But now, high-power regional mobile
satellites eliminate these restrictions.
HS 601 BUS
North America, with its highly developed /
\
cellular infrastructure, has become a natural first
candidate for a regional mobile satellite system.
When its MSAT system is launched in 1994, the / SOLAR ARRAY
team of American Mobile Satellite Corp.
(AMSC) and Telesat Mobile, Inc. (TMI) will J
show how entire continents can be served by the
high-power spot beams of GEO satellite systems. Figure 1. Regional MSAT Satellite
PItKC;ED_r_G PAGE" BLANK NOT FR.MED 543
Table 1. Regional MSAT Space Segment compression technology, allowing reduced chan-
Summary nel spacing, can be incorporated as they occur
with minimal impact.
Spacecraftbus HS 601
Dryweight 2500 Ib This is how the technology is being put to
EOLpower 288O W use in the North American mobile communica-
L-bandantennas Two 6 x 5 m deployable tions market. But the advantages of this system
mesh reflectors
can be applied in regional markets anywhere in
Ku-bandantenna 1 m shaped reflector
the world.
L-bandfrequencies 1530 to 1559 MHz,
t631.5 to 1660.5 MHz
L-bandAEIRP 56.6 dBW at 18 dB NPR ADVANTAGES OF A GEOSTATIONARY
L-bandG/T 2.7 dB/K (CONUS) MSAT ARCHITECTURE
Eclipsecapability 85%
Servicelife 12 yrs Mobile satellite communications is not
just a novel technology application; it is a busi-
ness opportunity with significant potential for
profit. The financial practicality of a Regional
MSAT system is one of its most attractive
attributes. Though a GEO satellite may cost
more per satellite than a medium earth orbit
(MEO) or low earth orbit (LEO) satellite, only a
single GEO satellite is required to provide com-
plete regional coverage. This translates into
system costs dramatically lower than other
, architectural alternatives [3].
The Regional MSAT offers inherent flexi-
Figure 2. Approximate North American bility and modularity. Using high-power spot
Coverage Pattern beams, it can be tailored to meet the needs of any
specific region. This allows the GEO system to
mobile terminal. A dual-mode handset allows be planned and implemented independently of
users who are within range of a cellular system global developments. A Regional MSAT applied
to have their calls routed through the land-based in Asia, for example, will have entirely different
cellular network while calls from users outside requirements than a system developed for South
of their home cell site are automatically routed America. Yet the two systems can use compati-
through the satellite system. ble ground hardware and be interconnected using
Once the call enters the satellite system, existing facilities.
one of two Network Control Centers (NCCs) The payload design of the Regional MSAT
determines where and how to route the call. satellite also provides a high degree of flexibili-
The NCC monitors the entire ground network ty. The design of the hybrid matrix amp!!fica-
[1], choosing the appropriate private or public tion system enables power to be dynamically
gateway, assigning communications channels, shared among the various beams. This allows
and routing the call to achieve the most cost- any variation in traffic patterns to be accommo-
effective communications link. The NCC can dated through real-time allocation of total power
optimize resources and maintain service quality among the beams. This approach provides the
at the same time [2]. most efficient use of capacity based on user
The system uses proven technology to geography and population density over the life
accommodate a wide variety of mobile termi- of the system. Additionally, the Regional
nals. Its architecture, however, allows new tech- MSAT provides the ability to tailor coverage by
nologies to be easily incorporated as they shaping the spot beams to serve only the areas
become available. New services can be imple- that have the greatest demand. No power is
mented with no impact to the quality of the exist- wasted directing coverage beams over unpopu-
lated or unwanted areas.
ing service. For example, advances in speech
544
The system also efficiently uses the frequen- tions in two distinct ways: the dual-mode hand-
cy spectrum. It employs frequency reuse between set and the pocket phone.
nonadjacent beams with sufficient isolation. In The handset used in the MS.AT system is
addition, with power-limited capacity expected to capable of automatically operating in two modes:
be roughly 2,000 simultaneous 4.8 kbps voice As a regular cellular phone linked to the region's
channels, the total bandwidth requirements allow cellular infrastructure or as a direct link to the
multiple GEO systems to coexist within the allo- satellite. This dual-mode handset increases ver-
cated L-band MSS spectrum. satility and ease of user operations. When users
are within a cell site, the mobile earth terminal
APPLICATIONS IN A REGIONAL MSAT (MET) directs the call to the cellular system.
SYSTEM When outside of a cell, the call is routed through
the L-band transceiver in the MET. This func-
A Regional MSAT system can meet a tion is autonomous and transparent to the user.
myriad of service demands, from personal com- One model of the dual-mode phone will
munications to industry-specific applications to also have the capability of being a handheld
infrastructure development (Figure 3). It aug- portable cellular phone (Figure 4). When inside
ments existing cellular networks by providing a cell site, the handset for this model can be
service when users roam outside of their cover- detached and used as a normal portable cellular
age areas and expands them by serving uncov- telephone.
ered areas. Thus, the Regional MSAT is Now imagine that a handset can be discon-
inherently appealing to both the cellular roamer nected from the MET and operated when the
and the unserved rural mobile user, two of the user is beyond the reach of a terrestrial cell site.
largest segments of the satellite mobile commu- This is the Regional MSAT pocket phone con-
nications market. The system meets these cept. With the pocket phone, satellite transmis-
users' need for personal, handheld communica- sion and reception is conducted via a cordless
•-"AN IEARS TAOT.,
_N _ FEEAERDTEHR-SLITNAKTION ]J
IPUB(GLIACTESWWAIYTSC)HED I
ITELEPHONE
COMMUNICATIONS ICELLULARBACKBONE
NETWORK [
CONTROLLER INETWOROKR
OPERATIONS
CENTER
Figure 3. Regional MSAT System
545
EXTERNAL
HANDHELD PORTABLE
CELLULAR PHONE
HANDHELD PORTABLE
'_1_" REMOVABLE LEAD
TO EXTERNAL
CRADLE
ANTENNA
Figure 4. Multimode Phone
connection between the handset and the MET. truly private network can operate their own
Users need only stay within range of their MET gateway and ground station infrastructure
"base station" to complete their links to the satel- including a dedicated link to the satellite. Both
lite, a position they are most likely to be in if types of services are very attractive to private
they are beyond the reach of cellular communi- sector organizations that have large numbers of
cations. These capabilities give a Regional users, as well as government and public sector
MSAT system the ability to meet the variety of organizations such as the police, public utilities,
personal communications needs seen in the mar- and agencies responsible for developing a coun-
ket today, and in the foreseeable future. try's natural resources.
In areas where the traditional land-based
Regional MSAT applications reach well
communications infrastructure is still in devel-
beyond personal voice communications. One of
the largest applications in the North American opment, a Regional MSAT system provides
excellent access into rural area_s that even fixed
system is for the trucking industry. The MSAT
system allows each vehicle to be in constant con- satellite services (FSS) cannot economically
tact with a home base, customer, or destination. serve. When the cost of building an infrastruc-
This is especially useful for just-in-time deliver- ture is prohibitive, FSS-provided thin route ser-
ies, in-route itinerary changes, and roadside emer- vices can be cost-effective, except when service
gencies. Mobile terminals can be equipped with demands are extremely low. In this case, MSS
Global Positioning Service (GPS) or RS-232 provides a cost advantage over even FSS-deliv-
ports to allow voice, digital data, and positioning ered telephone service.
services to be provided. Similar applications
exist for the airline and rail industries, where reli- REGIONAL MOBILE SATELLITE SYS'
TEM ECONOMICS
able logistical communications are essential
while in route and many passenger telecommuni-
cations services are being increasingly demanded. To assess the business viability for a
The system's architecture also accommo- regional MSS system, we must understand the
dates private networks. Users can implement a economics from the perspective of both pur-
virtual private network if they need that level of chasing and providing service. In its initial
autonomy in their service. Users demanding a form, the MSAT system in North America will
546
providemobileterminalsforunder$2,000each wheretheaveragesubscribeirsassumedtospend
andoffervoiceserviceratesthatarecompeti- $100permonthonmobileservicesw, hichcould
tivewith existingcellularroamingcharges. includevoice,data,oracombination.This
Overtime,asthesubscriberbaseexpands,these amountisassumedtoincludeusageandmonthly
costsarelikely todecreaseandbecomeafford- accessteesthatmaybecharged.
abletomorecustomerst,husincreasingdemand Thenumberofsubscribersisassumedto
formobilesatellitecapacity.Theintroduction increaselinearlytoamaximumlevelof400,000
of RegionalMSATsystemsaroundtheworld users,basedontheassumptionsof 10,000min-
will expandthemarketforspacesegmentt,er- utesperchannelpermonth,apower-limitedsys-
restrialnetwork,andsubscriberhardware, temcapacityof2,000simultaneouschannels,
whichwill translateintofurthercostreductions andaverageusageof50minutespersubscriber
totheultimateconsumersoftheservices. permonth.Thismaximumlevelofsubscribers
Fortheserviceprovider,theeconomics isachievedinthefifth yearofoperationsafter
revolvearoundthestart-upcapitalexpensest,he launch.Theanalysisalsoincludesa2%sub-
revenuesderivedfromsubscribersa,ndtoa scriberchurnratepermonth,whichisthe
lesserextent,theannualoperatingexpenses monthlyturnoverofsubscriberswhodropthe
requiredtorunthebusiness.Fromanorganiza- service.Thisimpactsbothrevenuesandmar-
tionalstandpoint,theMSATarchitectureallows ketingexpenses.
variousdegreesofverticalintegration.For Finally,it isalsoassumedthatthesystem
example,independensterviceproviderscan providercapturesonly80%of thetotalrev-
providetheinterfacebetweenthespaceseg- enues.Theremainingrevenue,inadditionto
mentproviderandthemobileusers.Thespace thenewsubscribermarketingexpenses
segmentprovidermaybeawholesalerofsatel- describedabove,isdistributedamongother
litecapacity,ormaydirectlyserveendusers, independensterviceprovidersfortheirrolein
largeorsmall. signingupnewsubscribersandadministering
Thefollowingeconomicanalysistakesthe billing services.
perspectiveofaspacesegmentproviderwho Theresult,onapre-taxbasis,isaninter-
providesretailservicesdirectlytomobilecom- nalrateofreturntothesystemproviderof
municators. approximately20%. Assumingacapitalcostof
Capitalexpensesof$400Mareassumed, 15%,thisscenarioresultsinanetpresentvalue
whichincludesonehigh-powersatellite,a (NPV)of roughly$135M. Financingisnot
launchvehicle,launchinsurancea, ndsupport- included,thusthereturnsmaybeunderstated
inggroundinfrastructuresuchasatelemetry becausepotentialleverageeffectsresulting
andcommandfacility andmobilecommunica- fromdebtfinancingarenotaccountedfor.
tionsnetworkcontrolfunctions.Theseexpens- Additionally,thisscenarioresultsinapayback
esareall incurredduringathree-year periodonthecapitalinvestmentinjustover
constructionperiodbeforesatellitelaunch. 5yearsafterlaunch.Notealsothatthisanalysis
Theannualoperationael xpenseasrebro- assumeslaunchofonlyonespacecraftw, hich
kendownintotwocategories.Firstisavariable eliminatesopportunityforgrowthafterachiev-
expenseformarketingthatisbasedon$300for ingsystemcapacity,thuslimiting financial
eachsubscribearddedtothesystemplusafixed returnswhichcouldbeexperiencedbyaccom-
percentag(e10%)ofrevenuesthatisdesignated modatingmoreusers.
forgeneralpromotionandmarketingofthevari- Thebusinessriskof thissystemislow,
ousmobileservices.Thesecondcategoryisa basedonthepopulationthatcanbecovered
fixedexpenseequalto20%oftheoriginalcapi- fromasingleGEOsatellite.Withacapacityof
talexpensesperyeartoaccountforotheroperat- 400,000users,thistypeofsystemneedbe
ing,general,andadministrativeexpenses.These adoptedonlybyasmallpercentageofthepopu-
assumptionasrebasedon,butnotidenticalto, lation.Forinstancei,naregionofonebillion
thecellularbusinessmodelofreference[5]. people,apenetrationrateofonly0.04%will fill
Revenueasregeneratedonanindividual thesystem,whereasaregionwith250million
subscribebrasisoverthetwelve-yeasratellitelife, peoplewill needtobeadoptedby0.16%ofthe
547
population.Thesefiguresseemmorethanplau- REFERENCES
sibleevenwhenthepredictedavailabilityofcel-
lularcapacityisusedtolimit theaddressable [1] J. Lunsford, R. Throne, D. Gokhale, W.
marketsize. Garner, and G. Davies, "The AMSC/TMI
Thiseconomicanalysisisnotintendedto Mobile Satellite Services (MSS) System
representtheonlywaytoimplementaregional Ground Segment Architecture," A Collection of
mobilesatellitebusinessb,uttodemonstrate Technical Papers, Part 1; The 14th
thataRegionalMSATsystemingeostationary International Communication Satellite Systems
orbitoffersthepotentialfor lucrativereturnsto Conference and Exhibit, March 22-24, 1992,
investors.Inaddition,therevenueof $100per Washington, DC, pp. 405-426.
subscriberpermonthcanbeinterpretedas$50 [2] L. White, A. Agarwal, B. Skerry, B. Tisdale,
inaccessfeesandanaverageofonly$1.00per "North American Mobile Satellite System
minuteofusage,whichissignificantlybelow Signaling Architecture," A_Collection of
thoseratesexpectedwith alternativesystem Technical Papers, Par/1; _The 14t h .:_
architectures. International Communication Satellite Systems
Conference and Exhibit, March 22-24, 1992,
CONCLUSIONS Washington, DC, pp_ 427-439, .....
[3] B. Elbert, E Louie, ";Fhe Ec0nomicsof
The mobile communications market is one Mobile Service by Satellite," Proceedings of the
of the fastest growing segments of the global Second International Mobile Satellite
economy. Technology that exists today is fully Conference, IMSC "90, Ottawa, Ontario,
capable of supporting mobile communications Canada, June 17-20, 1990, pp 1875-1885.
for entire geographic areas. Through a GEO [4] D. Whalen, G. Churan, "The American
satellite system, MSAT developers can tailor an Mobile Satellite Corporation Space Segment,"
open systems architecture to meet the unique A Collection ofTechnicaIPapers, Part 1; The
14th International Communication Satellite
needs of a specific region's mobile communica-
tions users. In time, as new technologies Systems Conference and Exhibit, March 22-24,
become economically viable, a Regional MSAT 1992, Washington, DC, pp. 394-404.
system can evolve, eventually providing direct- [5] E. Kwerel, J. Williams, "CHANGING
to-handheld global communications coverage. CHANNELS: Voluntary Reallocation of UHF
With virtually unlimited applications available Television Spectrum," OPP Working Paper No.
today at a cost-effective rate, the Regional 27, Office of PIans and Policy, Federal
MSAT provides a practical--and affordable-- Communications Commission, November 1992.
choice for introducing mobile voice and data
services to regional mobile satellite service
markets around the world.
548