U.S. patent application number 10/948606 was filed with the patent office on 2005-04-28 for systems and methods for mobility management in overlaid mobile communications systems.
Invention is credited to Dutta, Santanu.
Application Number | 20050090256 10/948606 |
Document ID | / |
Family ID | 34393027 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050090256 |
Kind Code |
A1 |
Dutta, Santanu |
April 28, 2005 |
Systems and methods for mobility management in overlaid mobile
communications systems
Abstract
Communications of a mobile station with a satellite mobile
communications system and a terrestrial mobile communications
system are coordinated. The mobile station is registered with the
terrestrial mobile communications system and, responsive to the
registration of the mobile station with the terrestrial mobile
communications system, the mobile station is concurrently
registered with the satellite mobile communications system. The
concurrent registration may include implicitly registering the
mobile station with the satellite mobile communications system,
e.g., by storing information identifying the mobile station may be
stored in a location register of the satellite mobile
communications system responsive to the registration of the mobile
station with the terrestrial mobile communications system, and
maintaining synchronization between the two registrations.
Authentication tokens may be pre-generated for quick
re-registration with a satellite mobile communications system.
Inventors: |
Dutta, Santanu; (Cary,
NC) |
Correspondence
Address: |
Robert M. Meeks
Myers Bigel Sibley & Sajovec, P.A.
P. O. Box 37428
Raleigh
NC
27627
US
|
Family ID: |
34393027 |
Appl. No.: |
10/948606 |
Filed: |
September 23, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60505526 |
Sep 23, 2003 |
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Current U.S.
Class: |
455/435.2 |
Current CPC
Class: |
H04W 8/12 20130101; H04B
7/18545 20130101; H04B 7/18563 20130101 |
Class at
Publication: |
455/435.2 |
International
Class: |
H04Q 007/20 |
Claims
What is claimed is:
1. A method of coordinating communications of a mobile station with
a satellite mobile communications system and a terrestrial mobile
communications system, the method comprising: registering the
mobile station at a home location register belonging to the
terrestrial mobile communications system, wherein such registration
includes location information about the mobile station; and
concurrently registering the mobile station at a home location
register belonging to the satellite mobile communications system,
responsive to the registration of the mobile station with the
terrestrial mobile communications system, wherein such registration
also includes location information about the mobile station; and
maintaining synchronization between location information about the
mobile station at the said location registers.
2. A method according to claim 1, further comprising synchronizing
the home location register of the terrestrial mobile communications
system and the home location register of the satellite mobile
communications system using a direct data interconnecting data
link.
3. A method according to claim 1, further comprising synchronizing
the home location register of the terrestrial mobile communications
system and the home location register of the satellite mobile
communications system by performing direct location updates from
the mobile station to the satellite mobile communications
system.
4. A method according to claim 3, wherein performing direct
location updates comprises performing a direct location from the
mobile station to the satellite mobile communications system
responsive to the mobile station detecting a change in a beam
identification parameter received from the satellite mobile
communications at the mobile station while the mobile station is
logged into the terrestrial mobile communications system.
5. A method according to claim 1, wherein concurrently registering
comprises implicitly registering the mobile station with the
satellite mobile communications system responsive to the
registration of the mobile station with the terrestrial mobile
communications system.
6. A method according to claim 5, wherein implicitly registering
the mobile station with the satellite mobile communications system
responsive to the registration of the mobile station with the
terrestrial mobile communications system comprises storing
information identifying the mobile station in a location register
of the satellite mobile communications system responsive to the
registration of the mobile station with the terrestrial mobile
communications system.
7. A method according to claim 6, wherein the information
identifying the mobile station comprises information identifying a
spot beam of the satellite mobile communications system.
8. A method according to claim 7, further comprising generating the
information identifying a spot beam of the satellite mobile
communications system responsive to a location update for the
mobile station in the terrestrial mobile communications system.
9. A method according to claim 6, wherein storing information
identifying the mobile station in a location register of the
satellite mobile communications system responsive to the
registration of the mobile station with the terrestrial mobile
communications system is preceded by transferring the information
identifying the mobile station from a location register of the
terrestrial mobile communications system to the location register
of the satellite mobile communications system.
10. A method according to claim 5, wherein implicitly registering
the mobile station with the satellite mobile communications system
responsive to the registration of the mobile station with the
terrestrial mobile communications system comprises concurrently
registering the mobile station with the satellite mobile
communications system without performing a location update for the
mobile station in the satellite mobile communications system.
11. A method according to claim 5, wherein implicitly registering
the mobile station with the satellite mobile communications system
responsive to the registration of the mobile station with the
terrestrial mobile communications system is followed by terminating
implicit registration of the mobile station with the satellite
mobile communications system responsive to passage of a
predetermined interval without a location update for the
terminal.
12. A method according to claim 1, wherein concurrently registering
the mobile station with the satellite mobile communications system
responsive to the registration of the mobile station with the
terrestrial mobile communications system comprises explicitly
registering the mobile station with the satellite mobile
communications system responsive to the registration of the mobile
station with the terrestrial mobile communications system.
13. A method according to claim 12, wherein explicitly registering
the mobile station with the satellite mobile communications system
responsive to the registration of the mobile station with the
terrestrial mobile communications system comprises initiating a
registration request from the mobile station to the satellite
mobile communications system responsive to the registration of the
mobile station with the terrestrial mobile communications system
without detecting a loss of communications between the mobile
station and the terrestrial mobile communications system.
14. A method according to claim 1, further comprising: generating
respective copies of a set of authentication tokens at respective
ones of the mobile station and the satellite mobile communications
system; and then performing successive registrations of the mobile
station with the satellite mobile communications system using
successive ones of the authentication tokens.
15. A method according to claim 14, wherein each of the successive
registrations of the mobile station with the satellite mobile
communications system comprises: communicating an authentication
token from the mobile station to the satellite mobile
communications system; and determining whether the communicated
authentication token matches an authentication token generated by
the satellite mobile communications system.
16. A method according to claim 14, wherein performing successive
registrations of the mobile station with the satellite mobile
communications system using successive ones of the authentication
tokens comprises: registering the mobile station with the satellite
mobile communications system using a first one of the
authentication tokens; establishing communications between the
mobile station and the terrestrial mobile communications system;
re-establishing communications between the mobile station and the
satellite mobile communications system; and re-registering the
mobile station with the satellite mobile communications system
using a second one of the authentication tokens.
17. A method according to claim 16, further comprising
communicating security data for the mobile station from the
terrestrial mobile communications system to the satellite mobile
communications system, and wherein generating respective copies of
a set of authentication tokens at respective ones of the mobile
station and the satellite mobile communications system comprises
generating the respective copies of the set of authentication
tokens at respective ones of the mobile station and the satellite
mobile communications system from the communicated security
data.
18. A method according to claim 17, wherein re-registering the
mobile station with the satellite mobile communications system
using a second one of authentication tokens comprises
re-registering the mobile station with the satellite mobile
communications system without retrieving additional security data
from the terrestrial mobile communications system.
19. A method according to claim 17, wherein the communicated
security data comprises a plurality of triplets, each including a
random number, an encrypted value generated from the random number
according to a key associated with a subscriber, and a cipher key,
and wherein generating respective copies of a set of authentication
tokens at respective ones of the mobile station and the satellite
mobile communications system from the communicated security data
comprises: communicating the random numbers from the satellite
mobile communications system to the mobile station; and generating
matching triplets at the mobile station from the communicated
random numbers.
20. A method according to claim 17, further comprising:
communicating new security data from the terrestrial mobile
communications system to the satellite mobile communications system
responsive to detecting that a predetermined number of the
previously generated authentication tokens have been used;
generating respective copies of a new authentication token at
respective ones of the mobile station and the satellite mobile
communications system from the communicated new security data
entity; and re-registering the mobile station with the satellite
mobile communications system using the new authentication
token.
21. A method of coordinating communications of a mobile station
with first and second overlaid mobile communications systems, the
method comprising: registering the mobile station with the first
mobile communications system; and concurrently registering the
mobile station with the second mobile communications system
responsive to the registration of the mobile station with the
terrestrial mobile communications system.
22. A method according to claim 21, wherein concurrently
registering comprises implicitly registering the mobile station
with the second mobile communications system responsive to the
registration of the mobile station with the first mobile
communications system.
23. A method according to claim 22, wherein implicitly registering
the mobile station with the second mobile communications system
responsive to the registration of the mobile station with the first
mobile communications system comprises concurrently registering the
mobile station with the satellite mobile communications system
without performing a location update for the mobile station in the
second mobile communications system.
24. A method according to claim 22, wherein implicitly registering
the mobile station with the second mobile communications system
responsive to the registration of the mobile station with the first
mobile communications system is followed by terminating implicit
registration of the mobile station with the second mobile
communications system responsive to passage of a predetermined
interval without a location update for the terminal.
25. A method of coordinating communications of a mobile station
with a satellite mobile communications system, the method
comprising: generating respective copies of a set of authentication
tokens at respective ones of the mobile station and the satellite
mobile communications system; and then performing successive
registrations of the mobile station with the satellite mobile
communications system using successive ones of the authentication
tokens.
26. A method according to claim 25, wherein each of the successive
registrations of the mobile station with the satellite mobile
communications system comprises: communicating an authentication
token from the mobile station to the satellite mobile
communications system; and determining whether the communicated
authentication token matches an authentication token generated by
the satellite mobile communications system.
27. A method according to claim 25, wherein performing successive
registrations of the mobile station with the satellite mobile
communications system using successive ones of the authentication
tokens comprises: registering the mobile station with the satellite
mobile communications system using a first one of the
authentication tokens; establishing communications between the
mobile station and a terrestrial mobile communications system;
re-establishing communications between the mobile station and the
satellite mobile communications system; and re-registering the
mobile station with the satellite mobile communications system
using a second one of the authentication tokens.
28. A method according to claim 27, further comprising
communicating security data for the mobile station from the
terrestrial mobile communications system to the satellite mobile
communications system, and wherein generating respective copies of
a set of authentication tokens at respective ones of the mobile
station and the satellite mobile communications system comprises
generating the respective copies of the set of authentication
tokens at respective ones of the mobile station and the satellite
mobile communications system from the communicated security
data.
29. A method according to claim 28, wherein re-registering the
mobile station with the satellite mobile communications system
using a second one of authentication tokens comprises
re-registering the mobile station with the satellite mobile
communications system without retrieving additional security data
from the terrestrial mobile communications system.
30. A method according to claim 28, wherein the communicated
security data comprises a plurality of triplets, each including a
random number, an encrypted value generated from the random number
according to a key associated with a subscriber, and a cipher key,
and wherein generating respective copies of a set of authentication
tokens at respective ones of the mobile station and the satellite
mobile communications system from the communicated security data
comprises: communicating the random numbers from the satellite
mobile communications system to the mobile station; and generating
matching triplets at the mobile station from the communicated
random numbers.
31. A method according to claim 28, further comprising:
communicating new security data from the terrestrial mobile
communications system to the satellite mobile communications system
responsive to detecting that a predetermined number of the
previously generated authentication tokens have been used; and
generating respective copies of a new authentication token at
respective ones of the mobile station and the satellite mobile
communications system from the communicated new security data.
32. A mobile communications system, comprising: a satellite mobile
communications system that supports registration of a mobile
station therewith concurrent with registration of the mobile
terminal with a terrestrial mobile communications system.
33. A system according to claim 32, wherein the satellite mobile
communication system is operative to implicitly register the mobile
station therewith responsive to registration of the mobile station
with the terrestrial mobile communications system.
34. A system according to claim 33, wherein the satellite mobile
communications system is operative to store information identifying
the mobile station in a location register thereof responsive to the
registration of the mobile station with the terrestrial mobile
communications system.
35. A system according to claim 34, wherein the information
identifying the mobile station comprises information identifying a
spot beam of the satellite mobile communications system.
36. A system according to claim 35, further comprising means for
generating the information identifying a spot beam of the satellite
mobile communications system responsive to a location update for
the mobile station in the terrestrial mobile communications
system.
37. A system according to claim 34, further comprising means for
transferring the information identifying the mobile station from a
location register of the terrestrial mobile communications system
to the location register of the satellite mobile communications
system.
38. A system according to claim 33, wherein the satellite mobile
communications system is operative to concurrently register the
mobile station therewith without performing a location update for
the mobile station in the satellite mobile communications
system.
39. A system according to claim 32, wherein the satellite mobile
communications system is operative to accept explicit registration
of the mobile station concurrent with maintenance of registration
of the mobile station with the terrestrial mobile communications
system.
40. A system according to claim 32, wherein the satellite mobile
communications system supports generation of respective copies of a
set of authentication tokens at respective ones of the mobile
station and the satellite mobile communications system, and is
further operative to subsequently accept successive registrations
of the mobile station with the satellite mobile communications
system using successive ones of the authentication tokens.
41. A system according to claim 40, wherein the satellite mobile
communications system is operative to receive security data for the
mobile station from the terrestrial mobile communications system
and to generate the copy of the set of authentication tokens from
the received security data.
42. A system according to claim 41, wherein the satellite mobile
communications system is further operative to transfer at least a
portion of the received security data to the mobile terminal to
support generation of the copy of the set of authentication tokens
at the mobile station.
43. A system according to claim 41, wherein the satellite mobile
communications system is operative to re-register the mobile
station therewith without retrieving additional security data from
the terrestrial mobile communications system.
44. A system according to claim 41, wherein the received security
data comprises a plurality of triplets, each including a random
number, an encrypted value generated from the random number
according to a key associated with a subscriber, and a cipher
key.
45. A system according to claim 41, wherein the satellite mobile
communications system is further operative to receive new security
data from the terrestrial mobile communications system responsive
to detecting that a predetermined number of the previously
generated authentication tokens have been used and to generating a
copy of a new authentication token from the received new security
data.
46. A system according to claim 45, wherein the satellite mobile
communications system is further operative to transfer at least a
portion of the received new security data to the mobile terminal to
support generation of a copy of the new authentication token at the
mobile station.
47. A mobile communications system, comprising: a satellite mobile
communications system that supports generation of respective copies
of a set of authentication tokens at respective ones of a mobile
station and the satellite mobile communications system and that is
further operative to subsequently accept successive registrations
of the mobile station with the satellite mobile communications
system using successive ones of the authentication tokens.
48. A system according to claim 47, wherein the satellite mobile
communications system is operative to receive security data for the
mobile station from a terrestrial mobile communications system and
to generate the copy of the set of authentication tokens from the
received security data.
49. A system according to claim 48, wherein the satellite mobile
communications system is further operative to transfer at least a
portion of the received security data to the mobile terminal to
support generation of the copy of the set of authentication tokens
at the mobile station.
50. A system according to claim 48, wherein the satellite mobile
communications system is operative to re-register the mobile
station therewith without retrieving additional security data from
the terrestrial mobile communications system.
51. A system according to claim 48, wherein the received security
data comprises a plurality of triplets, each including a random
number, an encrypted value generated from the random number
according to a key associated with a subscriber, and a cipher
key.
52. A system according to claim 48, wherein the satellite mobile
communications system is further operative to receive new security
data from the terrestrial mobile communications system responsive
to detecting that a predetermined number of the previously
generated authentication tokens have been used and to generate a
copy of a new authentication token from the received new security
data.
53. A system according to claim 52, wherein the satellite mobile
communications system is further operative to transfer at least a
portion of the received new security data to the mobile terminal to
support generation of a copy of the new authentication token at the
mobile station.
54. A system, comprising: a terrestrial mobile communications
system that supports registration of a mobile station therewith
concurrent with registration of the mobile terminal with a
satellite mobile communications system.
55. A system according to claim 54, wherein the terrestrial mobile
communication system supports implicit registration of the mobile
station with the satellite mobile communications system responsive
to registration of the mobile station with the terrestrial mobile
communications system.
56. A system according to claim 55, further comprising means for
transferring information identifying the mobile station from a
location register of the terrestrial mobile communications system
to a location register of the satellite mobile communications
system.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional
Application No. 60/505,526, filed Sep. 23, 2003, entitled Mobility
Management for Hybrid Terrestrial-Satellite Networks, the
disclosure of which is hereby incorporated herein by reference in
its entirety as if set forth fully herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to wireless communications
systems and methods, and more particularly, to mobility management
systems and methods for wireless communications.
[0003] An aim of hybrid terrestrial-satellite networks may be for
the satellite network to provide a ubiquitous coverage overlay for
the terrestrial network. However, this may give rise to a number of
mobility management challenges that may not be optimally handled by
the current state of the art.
[0004] FIG. 1 shows a satellite overlay for a terrestrial network.
Three types of regions are identified. A region A is the planned
coverage area of the cellular network; typically this will comprise
a multiplicity of cell sites and location areas (LAs), served by
multiple mobile switching centers (MSCs). "Location area" is a term
used in the cellular literature to indicate a collection of cell
sites over which paging is performed; an MSC may have several LA's
under its jurisdiction. A mobile station (MS) can move about (e.g.,
change broadcast control channel (BCCH)) within an LA without
re-registration, however it typically must re-register when it
crosses an LA boundary. This re-registration is called a Location
Area Update.
[0005] A region C is the planned coverage area of the satellite
network, comprising a multiplicity of spotbeams, served by one or
more gateways, which act as the satellite equivalent of the MSC. A
region B includes holes inside the cellular coverage region A that
are also covered by the satellite network. The holes exist mainly
in suburban areas and in corridors between urban areas where the
population density may not be sufficient for the cellular operator
to prioritize the deployment of more base station towers. In dense
urban areas, where a substantial amount of traffic is generated,
such holes are less common. Note that some holes may be covered by
neither network if the satellite view is under heavy blockage.
[0006] If the satellite and terrestrial networks are under
different administrations, they will typically view each other as
different Public Land Mobile Networks (PLMNs) offering "roamable
service". If the networks are under the same administration, then
the handover typically is performed as between different MSCs,
which is known in the present art. Roamable service means that the
services have commercial agreements and technical interfaces set up
to allow roaming from one network to another. The fact that these
networks involve different frequency bands generally is not a
technical impediment to roaming, as such roaming already takes
place, for example, in GSM between European 900 MHz and North
American 1900 MHz bands.
[0007] Essentially, once an MS, e.g., a handset, is unable to
locate a single forward control-channel carrier (e.g. BCCH carrier
in GSM) in the band that it last used, it will start scanning
carrier frequencies in alternate bands, like the satellite band.
Which bands the MS scans, and in what sequence, is typically
determined by a native login application in the MS. Once the MS
finds a suitable forward control-channel carrier, it will camp on
that carrier and control channel. Camping may include
synchronization to the carrier and control channel, and registering
to the network for service. Pages for incoming calls to the MS will
be sent on the camped-on forward control channel.
[0008] The roaming approach described above may be adequate when
the MS moves from the cellular coverage region A to the satellite
coverage regions C in the idle mode, as it is a quasi-permanent
change in the serving network for the MS and very rapid network
change may not be necessary. However, there may be at least two
cases when a very rapid change in the serving network, and/or a
change in network without explicit registration may be
desirable.
[0009] FIG. 1 shows a highway passing through a number of holes B
in the cellular coverage area A. A large number of MS's might be
passing through the holes B in idle mode and with no need for
satellite communications. However, as each of the MS's may be
programmed to roam to the satellite network if the terrestrial
service is unavailable, each MS, as it passes through the hole, may
attempt to perform an inter-PLMN roam, involving a Location Area
Update and Registration. This could create a huge and unnecessary
burden on the satellite resources of power and bandwidth, which may
be unnecessary, as most of the MS's may not need to use the
satellite network.
[0010] If an MS were moving from the cellular coverage region A to
a hole B or the satellite coverage region C (i.e., any region where
there is no cellular coverage) while it was engaged in a call, the
call, typically, would be dropped. Call dropping is generally
considered a very negative user experience in cellular services
and, if the user has been told that there is a satellite
coverage-overlay, he may expect the same seamless service as in
cellular. After being dropped, the MS (if it stayed sufficiently
long in the new region) would typically roam to the satellite
network and camp on to a satellite forward control channel. As the
mobile re-entered the cellular network it would typically roam back
again to the cellular network, which again could involve a
significant period of service unavailability for the user. This
means that when the MS is in the satellite network, it may
periodically search for cellular control-channel carriers and roam
to these, if available. This searching may be performed by a
variety of means described in the present art, including adjacent
cell monitoring as in GSM.
SUMMARY OF THE INVENTION
[0011] According to some embodiments of the present invention,
communications of a mobile station with a satellite mobile
communications system and a terrestrial mobile communications
system are coordinated. The mobile station is registered with the
terrestrial mobile communications system and, responsive to the
registration of the mobile station with the terrestrial mobile
communications system, the mobile station is concurrently
registered with the satellite mobile communications system. In some
embodiments, the concurrent registration includes implicitly
registering the mobile station with the satellite mobile
communications system. For example, information identifying the
mobile station may be stored in a location register of the
satellite mobile communications system responsive to the
registration of the mobile station with the terrestrial mobile
communications system, e.g., by transfer from a location register
of the terrestrial mobile communications system. Implicit
registration may be achieved without performing a location update
for the mobile station in the satellite mobile communications
system, and may be terminated responsive to passage of a
predetermined interval without a location update for the
terminal.
[0012] In further embodiments of the present invention, concurrent
registration of the mobile station with the satellite mobile
communications system may include explicitly registering the mobile
station with the satellite mobile communications system responsive
to the registration of the mobile station with the terrestrial
mobile communications system. For example, explicit registration of
the mobile station with the satellite mobile communications system
may include initiating a registration request from the mobile
station to the satellite mobile communications system responsive to
the registration of the mobile station with the terrestrial mobile
communications system without detecting a loss of communications
between the mobile station and the terrestrial mobile
communications system.
[0013] Some embodiments of the invention involve synchronizing the
registration and the location data of the MS in the terrestrial and
satellite networks through a link between the home location
registers of the two network. In other embodiments, this
synchronization may be performed by the MS unilaterally leaving the
terrestrial network when it detects that the beam identifier of a
forward control channel of the satellite network has changed and
performing a location update. It is noteworthy that the MS is
always aware of the beam identifier of the satellite network as it
always monitors the satellite control channels as an "adjacent
cell" of the terrestrial network.
[0014] According to further aspects of the present invention,
authentication tokens may be pre-generated for quick registration
with a satellite mobile communications system. Respective copies of
a set of authentication tokens are generated at respective ones of
the mobile station and the satellite mobile communications system.
Successive registrations of the mobile station with the satellite
mobile communications system are then performed using successive
ones of the authentication tokens. Re-registration of the mobile
station with the satellite mobile communications system may occur
without retrieving additional security data from the terrestrial
mobile communications system.
[0015] According to further embodiments of the present invention,
communications of a mobile station with first and second overlaid
mobile communications systems are coordinated. The mobile station
is registered with the first mobile communications system and,
responsive to the registration of the mobile station with the first
mobile communications system, the mobile station is concurrently
registered with the second mobile communications system. For
example, the mobile station may be implicitly registered with the
second mobile communications system responsive to the registration
of the mobile station with the first mobile communications
system.
[0016] In further embodiments of the present invention, a mobile
communications system includes a satellite mobile communications
system that supports registration of a mobile station therewith
concurrent with registration of the mobile terminal with a
terrestrial mobile communications system. The satellite mobile
communication system may be operative to implicitly register the
mobile station therewith responsive to registration of the mobile
station with the terrestrial mobile communications system. For
example, the satellite mobile communications system may be
operative to store information identifying the mobile station in a
location register thereof responsive to the registration of the
mobile station with the terrestrial mobile communications
system.
[0017] In still further embodiments of the present invention, a
mobile communications system includes a satellite mobile
communications system that supports generation of respective copies
of a set of authentication tokens at respective ones of a mobile
station and the satellite mobile communications system and that is
further operative to subsequently accept successive registrations
of the mobile station with the satellite mobile communications
system using successive ones of the authentication tokens. The
satellite mobile communications system may be operative to receive
security data for the mobile station from a terrestrial mobile
communications system and to generate the copy of the set of
authentication tokens from the received security data.
[0018] In additional embodiments of the present invention, a mobile
communications system includes a terrestrial mobile communications
system that supports registration of a mobile station therewith
concurrent with registration of the mobile terminal with a
satellite mobile communications system. The terrestrial mobile
communication system may support implicit registration of the
mobile station with the satellite mobile communications system
responsive to registration of the mobile station with the
terrestrial mobile communications system, and may include means for
transferring information identifying the mobile station from a
location register of the terrestrial mobile communications system
to a location register of the satellite mobile communications
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates exemplary relationships of a satellite
mobile communications system overlaid on a terrestrial mobile
communications system.
[0020] FIG. 2 illustrates apparatus and operations for location
database synchronization between a terrestrial mobile
communications system and a satellite mobile communications system
to support dual registration according to some embodiments of the
present invention.
[0021] FIGS. 3 and 4 illustrate apparatus and operations for
streamlined registration in a satellite communications system
according to further embodiments of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0022] Specific exemplary embodiments of the invention now will be
described with reference to the accompanying drawings. This
invention may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth
herein; rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art. In the
drawings, like numbers refer to like elements. It will be
understood that when an element is referred to as being "connected"
or "coupled" to another element, it can be directly connected or
coupled to the other element or intervening elements may be
present. Furthermore, "connected" or "coupled" as used herein may
include wirelessly connected or coupled. As used herein the term
"and/or" includes any and all combinations of one or more of the
associated listed items.
[0023] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless
expressly stated otherwise. It will be further understood that the
terms "includes," "comprises," "including" and/or "comprising,"
when used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0024] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0025] As discussed above, certain mobility management problems in
hybrid satellite-terrestrial networks may not be optimally
addressed by current state of the art. Two examples are: (a)
dual-mode (terrestrial-satellite) mobiles, passing through a
coverage hole in a cellular coverage area as a result, for example,
of the hole straddling a major highway, will likely want to
register to the satellite network, regardless of whether they will
use the satellite network--this can create a large and unnecessary
burden on the satellite network; and (b) if it is advertised that
the satellite network provides a ubiquitous coverage-overlay for
the cellular network, then the user may likely expect seamless,
in-call handover between the cellular and satellite network when
the user leaves the cellular network. If the cellular and satellite
networks are owned by different administrations, this may require
inter-PLMN handover. If the satellite and terrestrial home PLMN are
owned by the same administration, the handover may be performed as
an inter-MSC handover, whose procedure is known in the prior art.
However, if the user roams from the home terrestrial PLMN to a
visited terrestrial PLMN and then to the satellite network, then
inter-PLMN handover (between the visited terrestrial PLMN and the
satellite network) may still be required if the satellite coverage
overlay guarantee is to be offered to the user at all times. Some
embodiments of the invention described herein that may provide
solutions to such problems include: (a) dual registration in the
satellite and terrestrial home PLMN, using a single subscriber
identification module (SIM); (b) implicit registration in the
satellite network without loading the latter; (c) location updates
in the satellite network while the MS is in-coverage in the
terrestrial network and/or (d) rapid authentication using
temporary, "speedpass-type" authentication tokens of different
security levels.
[0026] A possible solution to the above-described problems
according to some embodiments of the present invention involves
implicit registration, whereby the satellite knows the MSs location
via, for example, home location register (HLR) synchronization with
the cellular network, without the need for explicit registration by
the MS. The MS is implicitly registered in the satellite network by
being explicitly registered in the cellular network. This means
that MS will be considered an implicit roamer to the satellite
network (i.e., that it has a virtual presence in the satellite
network), even though it may actually (physically) be in any
arbitrary cellular network (either the home PLMN or another PLMN
where it is roaming). In order to be considered a "roamer" to the
satellite network, the latter preferably knows in which spot beam
the MS is currently located. A database synchronizing link may be
established between the HLR of the cellular network and a combined
visited location register (VLR)/HLR of the satellite network.
[0027] An exemplary implementation of such synchronization
according to some embodiments of the present invention is
illustrated in FIG. 2. A terrestrial PLMN 210 includes a base
station subsystem (BSS) 216 that communicates with MS's under
control of an MSC 215 that is coupled to a public switched
telephone network (PSTN) 230. Associated with the MSC 215 are
various components that store information for access to and control
of the network 210. These include a home location register (HLR)
212 that serves as the main database of permanent subscriber
information for the network 210. Typically maintained by the
subscriber's home carrier (or the network operator where the user
initiated the call), the HLR 212 typically contains pertinent user
information, including address, account status, and preferences. A
visited location register (VLR) 214 maintains temporary user
information (such as current location) to manage requests from
subscribers who are out of the area covered by their home system.
Confidential keys for user authentication are stored in an
authentication center (AUC) 211, and serial numbers of valid mobile
equipment are stored in an equipment identify register (EIR)
213.
[0028] Similar components are present in an exemplary satellite
mobile communications network 220. The satellite mobile
communications network 220 includes a satellite spotbeam 225, which
functions much like a BSS of a terrestrial network, and an MSC 224,
which may be included in or operatively associated with a satellite
gateway that communicates with the satellite that supports the
spotbeam 225. A combined VLR/HLR 222 is associated with the MSC
224, along with an AUC 221 and an EIR 223. In the satellite mobile
communications network 220, the HLR and VLR functions may be
combined into one database when there is a single satellite
gateway, as all spotbeams, or satellite cells, may be visible from
the gateway. Otherwise, the architecture may be identical to the
case of the cellular infrastructure.
[0029] A synchronization link 240 links the HLR 212 of the PLMN 210
with the satellite network VLR/HLR 222. Using the above
synchronization link 240, the satellite mobile communications
network 220 can be aware of the approximate location of the MS
relative to spotbeam coverage patterns. If the latter goes into a
cellular coverage hole, and it can still receive a strong satellite
carrier (e.g., forward control channel), it can synchronize to that
carrier and control channel as a normal roaming operation, but
without performing the location area update that would normally be
performed in an inter-PLMN roaming operation. This can reduce
communications with the satellite mobile communications network
220, the motivation for which was explained above. The MS is now
ready to receive pages on the satellite mobile communications
network 220.
[0030] When there is an incoming call for the MS, the home cellular
MSC 215, which may think that the mobile is still in the coverage
area of a terrestrial MSC (the one that is supposed to cover the
hole), may try to page the MS in the expected LA. After the normal
number of tries, the MSC 215, according to typical conventional
techniques, may declare the MS unavailable. In some embodiments of
the present invention, the call can be handed over to the satellite
gateway MSC 224, which can page the mobile in the spotbeam 225 that
covers the last reported position of the MS (as per the last
Location Area Update, which is captured in the HLR of the native
cellular network and communicated to the satellite gateway via the
synchronization link). The MS can also make outgoing calls in the
usual way--for all practical purposes, the MS can be considered
registered in the satellite mobile communications network 220.
[0031] When the mobile senses a readable cellular carrier again, it
can roam back to the terrestrial cellular network 210 and perform a
location area update (i.e. reregister). This may be necessary,
because the cellular MSC 215 may have marked the MS as detached,
which it may do if the MS does not perform a location update at
periodic intervals. The satellite mobile communications network 220
does not need to be informed of the transfer.
[0032] After entering the implicit registration phase, the MS
starts a timer. If the MS does not sense a cellular carrier within
a predetermined time period, it means that it is either in a
satellite coverage area or it is quasi-static. In either case, an
explicit registration to the satellite network can be performed.
Indefinite implicit registration may not be desirable for the same
reason that periodic location area updates are performed in
existing cellular networks, i.e., if the MS abruptly goes into
blockage and moves, then there may be an LA change with no
knowledge of the network (e.g., this scenario may occur when the MS
enters a tunnel or is put inside a shielded briefcase and
moved).
[0033] Another potential problem with inter-PLMN handover is that
registration typically is required. For example, it typically is
required, for security and commercial reasons, for an MS entering a
new PLMN to register, but current registration processes often take
too long to be included as a part of the handover process.
Therefore, some embodiments of the invention include rapid
authentication during handover, which may be combined with the
above described multiple concurrent registration.
[0034] An exemplary process according to some embodiments of the
present invention is illustrated in FIG. 3. Upon first switching
on, an MS 320 registers to the locally available MSC 330 of a
terrestrial PLMN. This may be the home PLMN of the MS or another
PLMN that it has roamed to. The process of registration involves
authentication. In GSM, for example, this is based on the mobile
being sent a random number, which it digitally signs (encrypts)
with a secret, symmetric key carried in a subscriber identification
module (SIM). A copy of this key resides in the HLR and is tied to
the subscription, identified by the international mobile subscriber
identification (IMSI). The signed object SRES is returned by the MS
320 to the local MSC 330. The latter has already requested and
received a copy of the true signature from the home PLMN; the local
PLMN checks the two signatures and admits the MS 320 to the network
if they match.
[0035] After it is registered to the local terrestrial PLMN, the MS
320 unilaterally leaves the local terrestrial PLMN and roams to the
satellite network. Note that this may be driven by a native
application in the MS, e.g., an application that determines the
MS's logon process, and need not be constrained by any
communications protocol or standard. In some embodiments, the MS
320 may continually monitor the satellite carriers as one of the
adjacent cells. Hence, roaming to the satellite network can be a
relatively quick operation, as scanning of a frequency list need
not be involved. The MS 320 may be registered in the usual way.
[0036] The MS 320 may include an LA update upon initial
registration. Operation may be limited to this one initial LA
update if, for example, synchronization of location registers of
the satellite and terrestrial systems is provided. In some
embodiments, however, the MS 320 may periodically return to the
satellite network to provide LA updates, rather than relying on
synchronization of location information between the networks. For
example, the MS 320 may roam to the satellite network and provide a
location update each time the MS 320 detects a satellite beam
identification change. Such an approach may, for example, avoid
configuration changes and other potential problems that may be
associated with location register synchronization between
terrestrial and satellite network databases, without introducing an
undue amount of message overhead, as such cell changes in the
satellite network would likely occur at a lower rate than cell
changes in the terrestrial system. It may be noted that the MS 320
preferably will be aware of the overlaying satellite beam ID as it
operates in the terrestrial network, as the MS 320 may need to roam
to it if there is a hole in the terrestrial coverage. Therefore,
monitoring of satellite beam changes may not introduce a burden on
the MS 320.
[0037] In addition to these procedures, FIG. 3 illustrates some
additional steps that may be introduced to provide a streamlined
authentication procedure. When the MS roams to it, a satellite
gateway MSC 310 may request security data, e.g., a plurality, N
(N>1), of GSM "triplets," from the home MSC 340. These triplets
may include the following: (a) a random number RAND; (b) the true
value of the signed response SRES, using the same secret key that
is in the SIM of the MS 320 and the above RAND; and (c) the cipher
key, K.sub.c, that is to be used for the link encryption. Of the N
triplets, M (<N) are sent to the MS 320 by the satellite gateway
310. Note that this is a departure from normal GSM practice, in
which only one triplet is sent to an MS per registration session,
although it is acceptable for the visited MSC to request more than
one triplet from the home MSC. The MS 320 uses the first triplet
for registration in the conventional way. The MS 320 also
pre-calculates (M-1) signed response values SRES and stores them,
along with (M-1) key values K.sub.c, in a moderately secure part of
the MS 320 volatile memory in a push-down stack architecture. The
use of identical push-down stacks at the MS 320 and the satellite
MSC 310 ensures that the records in the two stacks are
synchronized. To further guarantee record synchronization, an index
field may be included in the record at both locations; that is, in
addition to SRES and the K.sub.c, a record index is also stored.
The security may be software controlled and need not be based on
tamper resistant hardware (as is the memory where the secret key is
stored in the SIM). Higher security can increase MS cost and may
not be warranted by the present security risk; however, neither are
such higher security measures precluded by the present scheme.
[0038] After registering in the satellite network, the MS 320, once
again moves unilaterally back to the local terrestrial network,
registering again to the local MSC 330, e.g., by performing a
location update. Thereafter, the MS 320 behaves as a normal MS,
except in embodiments lacking HLR synchronization, where it may
temporarily leave the terrestrial network to perform a location
update on the satellite network, as described above, and thereafter
return to the terrestrial network.
[0039] When a rapid transfer to the satellite network is required,
the MS fetches a signed response value SRES and a key value K.sub.c
from the top of the pushdown stack and uses them. The retrieved
K.sub.c is used for encryption and the pre-computed signed value
SRES is used as a "speed-pass" (authentication token) that is
passed to the satellite network to achieve rapid authentication. If
a record index is used, it is unencrypted, along with the TMSI, to
allow rapid location of the record at the satellite gateway
MSC.
[0040] An exemplary rapid authentication process according to
further embodiments of the present invention is illustrated in FIG.
4. A payload of an over the air request_for_handover message 425
from the MS 320 to the satellite network MSC 310, illustrated in
FIG. 3, may include an unencrypted field 425a that has the
Temporary Mobile Station identification (TMSI) given to the MS 320
during the last time it was at the satellite network. Optionally,
the unencrypted part of the message may also include an index field
(not shown in FIG. 4). If low security suffices, then this may be
all that is required to authenticate the MS 320, and the procedure
described above regarding creating and storing multiple SRES values
in the MS may be unnecessary. However, for greater security, the
TMSI may be followed, in an encrypted part 425b of the payload, by
the signed response SRES, which is checked by the satellite
network. The satellite network retains a copy 410 of the stack 420
of authentication tokens carried by the MS 320, and values may be
discarded after one use, such that there is no uncertainty about
which pair of signed response SRES and key K.sub.c values is in use
for a given access by the MS 320. Before the stack is exhausted, it
may be replenished by another set of signed response SRES, and key
K.sub.c values. Alternatively, the set may be recycled (i.e., the
stack values are not discarded but saved in a backup stack), but
this may reduce security. Note that the satellite gateway may carry
a stack of signed response SRES and key K.sub.c values for each MS
that has performed implicit registration with it.
[0041] An even higher security approach, according to further
embodiments of the invention, is to store not the pre-calculated
signed responsive SRES values, but the random number RAND values.
The signed response SRES values are calculated, fresh and on
demand, at the time of fast authentication. However, the time to
calculate SRES is then added to the authentication time and may be
a price for the added security. It is expected that the time to
calculate SRES by symmetric encryption is of the order of 100
ms.
[0042] In the drawings and specification, there have been disclosed
exemplary embodiments of the invention. Although specific terms are
employed, they are used in a generic and descriptive sense only and
not for purposes of limitation, the scope of the invention being
defined by the following claims.
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