Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-05-21
2003-07-15
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S438000, C370S331000
Reexamination Certificate
active
06594492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to inter-exchange handoff and, in particular, to network operations supporting anchor mobile switching center retrieval of information from a serving mobile switching center following completion of such an inter-exchange handoff.
2. Description of Related Art
Reference is now made to
FIG. 1
wherein there is shown a cell diagram illustrating an exemplary cell site configuration for a cellular communications network
100
in which the present invention may be implemented. The cellular communications network
100
operates in accordance with one of a number of known air interface types including, for example, a digital time division multiple access (TDMA) protocol. In a digital TDMA cellular telephone network, for example, each cell site (comprising either an omnidirectional cell, as shown for ease of illustration, or a sector cell) operates with an assigned set of transmission frequencies selected from one or more of the available cellular communications authorized hyperbands (e.g., 800 MHZ, 1900 MHZ, and the like) and frequency bands (A, B, and the like) therein. The set of frequencies assigned to each cell
112
includes frequencies supporting both at least one control channel and a plurality of traffic channels, with the control and traffic channels operable in either or both an analog and/or a digital mode. Sets of assigned frequencies are different for adjacent cells
112
, and such sets are not repeated for use by other cells except for those cells that are far enough away from each other to minimize the likelihood of adjacent or co-channel interference.
In the network
100
, a base station
114
is provided for each of the cells
112
. The base stations
114
engage in simultaneous communications with plural mobile stations
116
operating roughly within the area of the associated cell
112
. The control channel assigned to each cell
112
is used to carry system control signals between the base station
114
and proximately located mobile stations
116
, and also to assist in the network with mobile station cell reselection. Such control signals include call originations, page signals, page response signals, location registration signals, traffic channel assignments, maintenance instructions, and cell selection or reselection instructions. The traffic channels provided in each cell
112
are used to carry subscriber voice or data communications between the base station
114
and proximately located mobile stations
116
and also to assist in the handoff operation.
The base stations
114
are illustrated as being positioned at or near the center of each of the cells
112
. However, depending on geography and other known factors, the base stations
114
may instead be located at or near the periphery of, or otherwise away from the centers of, each of the cells. Each one of the base stations
114
includes a transmitter, a receiver, and a base station controller (none shown) connected to one or more directive antennae (also not shown) in a manner and with a configuration well known in the art.
The base stations
114
further communicate via signaling links and voice trunks
122
with a central control station, commonly referred to as a mobile switching center
118
, which functions to control operation of the network
100
. A boundary
134
is shown in bold in
FIG. 1
to differentiate between those cells
112
(collected in area
132
(
1
)) serviced by a first mobile switching center
118
(
1
), and those cells (collected in area
132
(
2
)) serviced by a second mobile switching center
118
(
2
). The mobile switching centers
118
are interconnected with each other and to the public switched telephone network (PSTN)
120
by signaling links and voice trunks
124
. The mobile switching centers
118
operate to selectively connect subscriber voice and data communications to the mobile stations
116
through its base stations
114
. Thus, the mobile switching center
118
controls system operation through and in response to the transmission of signals over the control channels to set-up on the traffic channels calls that are either originated by or terminated at the mobile stations
116
.
As the mobile stations
116
move within the service area of the network
100
, instances arise where a mobile station passes between two cells
112
within a single area
132
, or from one cell in a first area
132
(
1
) to another cell in a second area
132
(
2
). In moving between the cells
112
, the mobile stations
116
, in conjunction with base station
114
collected information and also orders exchanged with and between the mobile switching centers
118
, have an opportunity through hand-off to change the base station through which cellular radio communications are being effectuated. For example, a mobile station
116
(
1
) is shown moving in the direction of arrow
126
(
1
) between two cells
112
from area
132
(
1
) into area
132
(
2
). Here, an inter-exchange hand-off must occur in order to continue providing call service to the mobile station
116
(
1
). The mobile switching center
118
controls, through and in response to traffic channel signals, the hand-off of a subscriber communication from a traffic channel of one cell
112
to a traffic channel of another cell as the subscriber mobile station
116
roams throughout the cellular service area during an ongoing communication.
Reference is now additionally made to
FIGS. 2A-2B
wherein there is shown a signal flow and network operation diagram illustrating network operation in connection with a scenario wherein an inter-exchange hand-off is made from a cell
112
(
1
) within a first area
132
(
1
) generally towards cell
112
(
2
) within a second area
132
(
2
). The mobile station
116
(
1
), operating if capable in accordance with known mobile assisted hand-off (MAHO) principles, periodically makes downlink signal strength measurements
202
on the traffic channel (of cell
112
(
1
)) that is currently being used, and also periodically makes downlink signal strength measurements
204
on the control (i.e., measurement) channels of network identified cells
112
, including cells
112
(
2
) and
112
(
3
), which neighbor the cell
112
(
1
). These signal strength measurements are reported
206
to the base station
114
(
1
) for the currently serving cell
112
(
1
). The base station
114
(
1
) concurrently makes uplink signal strength measurements
208
on the traffic channel that is currently being used by the mobile station
116
(
1
).
The base station
114
(
1
) processes the mobile station
116
(
1
) reported
206
downlink signal strength measurements (
202
and
204
), if available, and the base station made uplink signal strength measurements (
208
) to determine first whether a hand-off is necessary (action
210
) and second, if yes, to which candidate cells the hand-off could and/or should preferably occur (action
212
). In this example, it is assumed that the base station
114
(
1
) determines
210
from deteriorating measured uplink and/or downlink signal strengths that a hand-off is necessary. It is further assumed that an identification
212
is made of a plurality of candidate cells
112
for hand-off. These candidate cells
112
may include cells in the same first area
132
(
1
) as the current cell
112
(
1
) such as cell
112
(
3
), as well as cells in other areas
132
, such as cell
112
(
2
) in second area
132
(
2
). It will, of course, be understood that the decision to hand-off may instead be made by the mobile station
116
(
1
) itself. A request
214
for hand-off including information comprising an identification of the currently serving cell
112
(
1
), the traffic channel being used for communication with mobile station
116
(
1
) in cell
112
(
1
), the time slot (for a digital traffic channel) carrying the cellular communication, the digital voice color code (DVCC), and the list of potential candidate cells
112
for hand-off, is then sent by the base station
114
(
1
) to the serving mobile sw
Choi Felix
Houde Michel
Surdila Sorin
Beauchesne Sandra
Jenkens & Gilchrist
Telefonaktiebolaget L M Ericsson (publ)
Tran Congvan
Trost William
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