Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-05-28
2003-07-22
Maung, Nay (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S443000, C455S444000, C455S437000, C455S438000, C455S449000
Reexamination Certificate
active
06597911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to cellular telecommunications networks and, in particular, to a system, method, and apparatus for a cell search within a telecommunications network.
2. Description of Related Art
Reference is now made to
FIG. 1
wherein there is illustrated an exemplary cellular telephone network
100
. An arbitrary geographic region (hereinafter “the service area”)
105
is divided into a plurality of contiguous cells
110
schematically represented by hexagons. The cells
110
are then grouped into clusters
115
(outlined in bold to ease recognition). For example, in the frequency plan of
FIG. 1
, each cluster
115
includes seven cells
110
(
1
)-
110
(
7
). It will, of course, be understood that each cluster
115
may have more or fewer cells
110
as required by the selected frequency plan. Each cell
110
(
1
)-
110
(
7
) is associated with a base station
120
which provides telephone service to mobile stations
125
using traffic channels. Each cell
110
is also associated with a control channel.
As a subscriber having a mobile station
125
operating within the cellular telephone network
100
moves about the service area
105
, the subscriber is likely to leave the coverage area of one cell and enter the coverage area of another cell. If the mobile station
125
is turned on but not at that time engaged in a call, registration of the mobile station's
125
presence within a new cell
110
is made, as is understood in the art.
When the subscriber is engaged in a call, however, the transfer to the new cell
110
is a more complicated process than a mere registration. In this instance, not only must the mobile station's
125
presence within the coverage area of the new cell
110
be detected, confirmed and registered, but also the communications link with the mobile station
125
carrying the telephone call must be switched from one base
120
station in the prior cell
110
to another base station
120
in the new cell
110
as the mobile station
125
moves and responsibility for the link is transferred to that new cell
110
. The process for performing this action is commonly referred to as “handover” or “hand-off”. In order to preserve the mobility advantage provided by cellular telephone networks, it is vitally important that the handover of calls in a cellular telephone network occur timely, efficiently, accurately and transparently.
Under the Global System for Mobile Communications (GSM) standard, mobile stations
125
make signal strength measurements within the current cell
110
, as well as with respect to neighboring cells
110
. The channels measured by the mobile station
125
are identified in a list provided to the mobile station
125
by the cellular network
100
. The listed channels include handover measurement channels (usually the control channel) for cells
110
which are potential targets for a handover. The measurements are reported back to the serving base station
120
. At the same time, the serving base station
120
measures signal strength of received mobile station
125
transmissions. These mobile
125
and base station
120
measurements are processed by a base station controller (BSC)
130
to determine whether a handover is needed, and also to identify to which cell such handover should be made. Where a handover is needed, the base station controller
130
sends a handover command to the mobile station
125
including information on the channel to be used in the new cell
110
to carry the call. The mobile station
125
then tunes to the channel and continues the conversation. The previously used channel is then released and the BSC
130
transfers the call to the new base station
120
in the new cell
110
.
It is axiomatic that technological innovation creates for more advanced telecommunication networks and equipment which deliver more and better services to mobile subscribers than preexisting cellular networks, such as the cellular telephone network
100
shown in FIG.
1
. The more advanced networks are often referred to as next generation networks. For example, analog American Mobile Phone Service (AMPS) networks are often referred to as first generation networks, while digital networks, such as Digital-AMPS (D-AMPS) or Global System for Mobile Communications (GSM) are referred to as second generation networks. The emerging Personal Communications Systems (PCS) with Code Division Multiple Access (CDMA), for example, are referred to as third generation networks.
Transition from a preexisting cellular network
100
to a next generation network is often performed in an overlay fashion. In an overlay, the next generation network is gradually deployed alongside the preexisting cellular network. Although the infrastructure of the preexisting cellular network can be replaced wholly by the next generation network, there are, of course, a number of disadvantages associated with this more abrupt approach. For example, mobile stations designed to operate with the preexisting cellular network could be rendered useless, resulting in customer dissatisfaction, and possibly inducing customers to switch to a network maintained by a different operator.
Accordingly, overlaying a next generation network over a preexisting cellular network permits the network operator to gradually phase out the preexisting cellular network. It is noted, however, that next generation networks initially include a limited number of cells in a smaller service area. To promote acceptance of the next generation network, network operators often market dual-mode mobile stations
125
, illustrated in FIG.
2
. Dual-mode mobile stations
125
allow the subscriber to utilize both the preexisting cellular network as well as the next generation network. The dual-mode mobile station
125
selects a cell in the next generation network when the mobile station
125
is within an area served by the next generation network. However, when the mobile station
125
is in an area that is not served by the next generation network, the dual-mode mobile station registers with the preexisting cellular network
100
.
As a subscriber having a mobile station moves from outside the service area of the next generation service area to within the service area, it is desirable for the mobile station
125
to deregister with the preexisting cellular network
100
and register with the next generation network, notwithstanding the fact that the dual-mode mobile station
125
is also within the service area
105
of the preexisting cellular network
100
. If the dual-mode mobile station
125
is not engaged in a call at the time, the mobile station
125
deregisters with the preexisting cellular network and registers with the next generation network. However, when the subscriber is engaged in a call, a handover operation must be performed with a cell of the next generation network. Present networks, however, do not provide for inclusion of handover measurement channels for cells in different generation networks. Therefore, a handover from a preexisting cellular network
100
to a next generation network or vice versa is slow, resulting in undesirably long speech interruptions.
Accordingly, it would be advantageous if control channels from different generation networks could be provided to the mobile station.
SUMMARY OF THE INVENTION
The present invention is directed to a system, method and apparatus for performing a handover for a mobile station in a mobile telecommunications system including a preexisting cellular network and a next generation cellular network. A cell neighbor list, which includes cells within the preexisting cellular network as well as the next generation network, is transmitted from the serving base station to the mobile station. Responsive thereto, the mobile station measures the signal strength of handover measurement channels associated with the cells in the cell neighbor list, including cells from the next generation network.
REFERENCES:
patent: 5268933 (1993-12-01), Averbuch
patent: 551767
Ericsson Inc.
Jenkens & Gilchrist P.C.
Maung Nay
Orgad Edan
LandOfFree
System, method, and apparatus for cell searching in a next... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System, method, and apparatus for cell searching in a next..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System, method, and apparatus for cell searching in a next... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3087685