Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
1998-04-16
2001-08-07
Cumming, William (Department: 2749)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S013200, C455S428000, C455S435100, C455S433000, C455S453000, C342S357490, C342S357490, C370S203000, C370S209000, C370S316000
Reexamination Certificate
active
06272315
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to mobile satellite and terrestrial wireless communication systems call and, more particularly, to interworking techniques for enabling a dual-mode mobile satellite/terrestrial wireless phone to transparently switch between satellite and terrestrial wireless service providers.
BACKGROUND OF THE INVENTION
Mobile satellite systems (or “MSSs”) are satellite systems which support mobile voice and/or data services. MSSs have a number of advantages over more common terrestrial wireless communication systems such as cellular or personal communication systems (or “PCS”). One such advantage is that MSS systems typically provide larger coverage areas. MSS systems may also be more cost effective in undeveloped and lightly developed rural areas where a terrestrial mobile communication system may be both difficult and costly to install and maintain. For these reasons, MSS systems are often seen as the key to achieving global coverage for mobile communication systems.
MSS systems are not without their shortcomings, however. MSS systems may fail to deliver services when line-of-sight requirements are violated, for example, when service is attempted in urbanized areas populated with numerous high-rise buildings. Service from MSS systems is typically much more costly than service from terrestrial systems. MSS service also lacks many of the user features which have made cellular and PCS systems popular. Thus, from this perspective, cellular or PCS systems are often preferred over MSS systems when both are available.
While MSS and terrestrial wireless systems are often interconnected by way of the public switched telephone network (or “PSTN”), such interconnections have shortcomings. For example, in
FIG. 1
, an MSS system
10
, representatively illustrated by a MSS satellite and a terrestrial wireless system, representatively illustrated by a mobile switching center
12
bi-directionally coupled to a base station
14
, provide service coverage throughout geographic areas
16
and
18
, respectively. The MSS system
10
is coupled to PSTN
26
by a gateway
28
(a satellite dish physically coupled to the PSTN
26
and in two-way radio communication with the MSS system
10
) while the terrestrial wireless system
12
is coupled to the PSTN
26
by a local exchange carrier (or “LEC”)
30
bi-directionally coupled to the MSC
12
. Also shown in
FIG. 1
are first, second and third mobile terminals
20
,
22
and
24
, all of which are located within the coverage area
16
of the MSS system
10
but only two of which (the mobile terminals
20
and
22
) are located within the coverage area
18
of the terrestrial wireless system
12
. If one assumes that the first mobile terminal
20
is configured for operation as an MSS system terminal while the second and third mobile terminals
22
and
24
are configured for operation as terrestrial wireless system terminals, a call originated by the first mobile terminal
20
and having the second mobile terminal
22
as its destination is directed from the first mobile terminal
20
to the MSS system
10
, the gateway
28
, the PSTN
26
, the LEC
30
, the MSC
12
and the base station
14
before arriving at the second mobile terminal
22
. Thus, even though the first and second mobile terminals are in close physical proximity to each other, not only must a call between the two be directed along a circuitous route, but along a route subject to substantial toll charges. Furthermore, as the third mobile terminal
24
is outside the coverage area
18
of the terrestrial wireless system, a call from the first mobile terminal
20
to the third mobile terminal
24
cannot be completed even though the third mobile terminal
24
is within the coverage area
16
for the MSS system
10
. Thusly, the existing interconnection between the MSS system
10
and the terrestrial wireless system
12
typically provides limited service at relatively high cost.
In order to ensure the broadest possible geographical coverage and to avoid unnecessarily expensive calls, a wireless subscriber must currently carry both terrestrial wireless and MSS phones. As such a solution is both cumbersome (because of the need to carry two phones and two phone numbers) and expensive (because of the need to contract with two service providers), a dual mode phone capable of operating within both MSS and terrestrial wireless systems with manual mode switching between the two systems has been proposed. However, such a phone lacks the ability to automatically change operating mode when a switch between systems would be advantageous to the user. Manual switching systems also require considerable user knowledge as to when a switch between satellite and terrestrial systems would be advantageous and lack the “seamless” switching preferred by many consumers for multi-mode terminals.
For example, for a mobile terminal to first switch from operation in a terrestrial wireless mode to operation in a MSS mode and to then register with a MSS system, the mobile terminal must overcome certain obstacles. More specifically, before the mobile terminal can initiate the registration process, the mobile terminal must first locate a MSS system, determine its access type and determine synchronization information such as differential and propagation delay factors. Similar obstacles make it difficult for a mobile terminal to switch from the MSS mode into the terrestrial wireless mode and then register with a terrestrial wireless system. While the mobile terminal can search for and acquire all of the information needed to initiate the registration process, the process can be quite time consuming. For example, much of the needed information can be obtained from the control channel for the MSS or terrestrial wireless systems broadcast. However, each system (or cell within a system) broadcasts at a different frequency within an operating band. Thus, to locate a control channel, the mobile terminal must scan the entire operating band. While the mobile terminal is searching for and acquiring information needed to register with a system operating in a different mode, it may be forced to suspend all other operations. Thus, the mobile terminal may lose calls and miss incoming pages, thereby reducing terminal availability and call delivery success rates.
SUMMARY OF THE INVENTION
For a dual mode mobile terminal capable of operating a first mode in which calls are routed through a MSS system and a second mode in which calls are routed through a terrestrial wireless system such as a cellular or PCS system, the present invention is directed to interwork techniques for the dual mode mobile terminal which increase availability of the mobile terminal to receive calls by reducing the time required for the mobile terminal to switch between the first and second modes. Switch-over time is reduced by having the systems which operate in a first mode provide mobile terminals registered thereto with information which will assist the mobile terminals if they attempt to register with a system which operates in a second mode. By doing so, the mobile terminal can more quickly locate and register with a system operating in a different mode and will spend considerably less time unavailable while searching for a new system to register therewith.
The interwork techniques subject of the present invention also encourages the most economical use of such a dual-mode mobile terminal in that, as terrestrial wireless service provides such as cellular or PCS service providers are typically less expensive then calls routed through a MSS service provider, when registered to a MSS system service provider, the mobile terminal will continuously seek out a less expensive terrestrial wireless system service provider.
The interwork technique subject of the present invention also encourage broader continual geographical coverage for a mobile terminal by automatically seeking a suitable MSS service provider whenever the mobile terminal detects that it is leaving the coverage area for a terrestrial wireless system to which it is
Chang Jue
Kim Won S.
Lo Wing F.
Cumming William
Haynes and Boone LLP
Northern Telecom Limited
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