ASMS-TF Technical Group
S-UMTS Operational Models for
Point-to-Point Services
ASMS-TF Meeting
Toulouse April 24th - 26th 2001
[email protected]
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Background
 Viable operational models for point-to-point SUMTS shall be well conceived and assessed
before proposing solutions to UMTS operators
 Operational models cover issues such as:
 degree of satellite system connectivity (GW-to-beam)
 landing-GW flexibility
 ways of sharing satellite capacity among GWs
 ways to fit S-UMTS within the overall UMTS
 The above issues yield a remarkable impact on
S-UMTS design and on attainable efficiency
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Examples of Existing Systems
 IRIDIUM:
 full GW-to-beam connectivity, free landing GW selection
 system capacity is a common pool for all GWs
 Inmarsat:
 full GW-to-beam connectivity just limited by absence of ISLs
 satellite capacity is a common pool among visible GWs
 Globalstar:
 despite the LEO constellation with no ISLs, a certain GW-tobeam connectivity is in principle available
 but landing-GW is anyway fixed due to operators agreements
 capacity is shared among GWs on pre-assigned basis
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Ability To Select The Landing-GW
 Landing-GW should be selected on a call-by-call basis.
High GW-to-beam connectivity is required
 With MEO / GEO constellations, landing-GW selection is
more appealing, especially if the number of deployed GWs
is significant:
 terrestrial tails cost reduction (more important for circuit-based
services), though bulk rates are often offered to operators
 better GW traffic-load balancing
 Other advantages (w.r.t. transparent LEO non-ISL system):
 allows using satellites with highest elevation angle
 higher number of satellites available for diversity
 lower average number of satellite handoffs during a call (lower
dropped calls rate)
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Guidelines
 An S-UMTS system should ideally:
 be designed for maximum GW-to-beam connectivity and
capacity pooling
 but also be operated such that the built-in flexibility is
actually exploited
 Achieving high GW-to-beam connectivity may be
a challenge under typical S-UMTS scenarios:
 number of beams is great (e.g. > 100)
 access allowed to quite a great number of GWs:
 to maximize advantages deriving from landing-GW selection
 to allow more operators joining the system
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S-UMTS System Design Issues
 W-CDMA
offers
moderate
resources
assignment
granularity (5-MHz modules). With many GWs and beams,
GW-to-beam connectivity is constrained :
 risks of reduced
problem):
bandwidth
efficiency
(BIG
potential
 CDMA modules fill-factor may become low if a module is fully assigned
to a GW, but
 sharing CDMA modules among multiple GWs may hardly be feasible
 on-board processing (OBP) would help. Protocol adaptations likely
required
 risks of reduced power efficiency:
 control channels yield a significant overhead in terms of power
 sharing control channels among multiple GWs hardly possible
 again OBP could help
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Impact of Integration Strategy
 Other constraints arise from integration strategy
 Two alternatives are considered (VIRTUOUS):
 embedded system: S-UMTS implements a set of USRANs,
each attached to the core network of a service provider :
 satellite system mostly relies on T-UMTS mobility functions
 MT is bound to land at the GW owned by his service provider
 satellite resources are typically pre-assigned to GWs
 self-standing system: S-UMTS having its own core network
 MT is allowed to land at each GW, unless when unfeasible
 satellite resources flexibly shared among GWs, even on a callby-call basis
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Embedded System Model
RNC
GW
Satellites
cloud
S.P. #1 Capacity share
S.P. #2 Capacity share
S.P. #3 Capacity share
Node B
Node B
Node B
Node B
MSC
USRAN
SGSN
RNC
GGSN
Core
Network
RNC
UTRAN
Service Provider #1
PSTN
ISDN
USRAN
UTRAN
UTRAN
Core
S. P. #2
Packet
Data
Networks
USRAN
UTRAN
Core
S. P. #3
= Service Provider #n access point
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Self-Standing System Model
MSC
RNC
SGSN
GW
GGSN
PSTN
ISDN
Operator #1
Satellites
cloud
MSC
Pre-assigned or
shared resources
RNC
SGSN
GW
GGSN
Operator #2
MSC
RNC
SGSN
GW
GGSN
Packet
Data
Networks
Operator #3
USRAN
Core
Network
= local access point
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System Design Example
 Reference is here made to an hypothetical gap-filler SUMTS system:
 based on GSO satellites
 generating beams-clusters on earth regions not adequately
covered by T-UMTS (e.g. developing countries)
 a beams-cluster will eventually be moved to another earth
region when T-UMTS is starting to take place in the previous
one
 GSO satellites permit to largely bypass terrestrial networks.
Landing-GW flexibility should then be pursued as much
possible
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Approach With Transparent Satellites
 With a self-standing system:
 despite the GSO satellites wide-area coverage, each beamscluster will only be served by just a few GWs (not to impair
system efficiency)
 in developing countries most telephone calls may be local; the
GW should then be located not too far away
 for packet- services (e.g. Internet) the GW should be connected
to a backbone, possibly only available at great distances
 With an embedded system:
 further flexibility decrease if, as expected, MT will only be
allowed to connect the GW owned by his service provider
 sharing a GW among multiple operators should be encouraged
(adaptations required, e.g. BCCH), though capacity sharing will
still be on pre-assigment basis
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Approach With OBP Satellites
 On-board regeneration and switching can solve a
great deal of problems:
 full GW-to-beam connectivity becomes viable
 resources can be flexibly shared among GWs
 deviation from standard protocols probably unavoidable
 but OBP advantages may not fully be exploited is system is
embedded
 Regenerative return-link (harder to implement
than forward-link) may not be required:
 with a global-coverage down-link, GWs can exhaustively
demodulate all codes and only take those of their concern
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Conclusions
 Tight liason with UMTS operators will be needed:
 for better chances of being endorsed, S-UMTS shall have
those features and behave the way UMTS operators like, but
 the overall S-UMTS + T-UMTS operational model that UMTS
operators have in mind may not result in optimally
exploiting the satellite system resources and/or flexibility
 An in-depth appreciation of S-UMTS is crucial for:
 trading-off conflicting requirements within S-UMTS
 understanding all technical and economic implications of
the solutions that UMTS operators may propose
 at this regard, some studies are already being carried out
(e.g. the ESA funded “S-UMTS Bridging Phase)
 but more detail activities are required, specifically focused
on the S-UMTS operational models
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