Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-12-11
2001-12-04
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S450000, C455S527000
Reexamination Certificate
active
06327469
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to methods for synchronizing a cellular telephone mobile station (MS) with its serving cell base station and neighbor cell base stations to facilitate hand-over decisions in a cellular radiotelephone network.
BACKGROUND OF THE INVENTION
In a cellular radiotelephone system, the area served by the system is divided into geographically-defined cells. Each cell has a base station which serves MSs within its geographic area. An MS is linked to its serving cell base station, and it must also identify multiple neighbor cell base stations in order to facilitate reliable handover if the MS travels outside of the geographic range of its present serving cell.
FIG. 1
shows part of a cellular radiotelephone system that uses a seven-cell cell cluster. A different number of cells can be implemented in a cell cluster, and seven is merely chosen for explanation purposes. An MS
190
in cell
110
should be linked to the base station
180
in cell
110
, thus the cell
110
is the MS
190
serving cell, and the serving cell base station should include surrounding cells
120
,
130
,
140
,
150
,
160
,
170
in the serving cell's broadcast channel (BCH) allocation list. According to Global System for Mobile Communications (GSM) specifications, a BCH allocation list can include the BCH frequencies of up to thirty-two neighbor cells. The MS measures the power of each channel in the BCH allocation list and reports on up to six neighbor cells to the serving cell base station in a reporting table. Normally, these six channels in the reporting table are the six strongest channels from the BCH allocation list.
The GSM specifications for a digital radiotelephone system require that an MS decode the base station identification code (BSIC) of each channel in the reporting table at least once every ten seconds. An MS must complete two basic steps to decode a BSIC: (1) detect a frequency burst or frequency correction channel (FCH) on a cell's BCH to synchronize with the base station in the frequency domain (and pre-synchronize with the base station in the time domain); and (2) demodulate the synchronization burst or synchronization channel (SCH) of the cell's BCH to synchronize with the base station in the time domain. After the SCH has been demodulated, the mobile is fully synchronized to the base station and the BSIC is decoded.
FIG. 2
shows a BCH multiframe
200
according to GSM specifications. A BCH is broadcast by each base station and uses a repeating 51-frame structure with an FCH
210
occurring during frame numbers
0
,
10
,
20
,
30
, and
40
as shown. An SCH
220
occurs during frame numbers
1
,
11
,
21
,
31
, and
41
in a BCH multiframe
200
as shown in FIG.
2
.
FIG. 3
shows a traffic channel (TCH) multiframe
300
according to GSM specifications. An MS uses a TCH to transmit user data, such as speech or computer data, to its serving cell base station. A TCH uses a repeating 26-frame structure with one idle frame
310
as the last frame in each TCH multiframe
300
. The MS can detect an FCH, or demodulate an SCH, on a cell's BCH during the idle frame of a TCH multiframe
300
.
FIG. 4
shows whether an idle frame of a TCH multiframe will intersect with an FCH, or an SCH, of a cell's BCH multiframe. Starting from frame
0
of the BCH multiframe
200
shown in
FIG. 2
being aligned with frame
0
of the TCH multiframe
300
shown in
FIG. 3
, the idle frame
310
will first align with frame
25
of the BCH multiframe
200
. Next, frame
0
of the TCH multiframe
300
aligns with frame
26
of the BCH multiframe
200
, and the idle frame
310
will next align with the FCH
210
in frame
0
of the next BCH multiframe. This FCH is shown as FCH
410
in FIG.
4
. The next idle frame aligns with a frame
26
of the BCH multiframe, and the fourth idle frame aligns with SCH
220
in frame
1
of the third BCH multiframe
200
. This SCH is shown as SCH
420
in FIG.
4
. The next six idle frames do not encounter either on FCH or an SCH. The alignment of the idle frames continues as shown in FIG.
4
. As seen from
FIG. 4
, the worst case scenario for detecting an FCH burst on a cell's BCH can take up eleven idle frames. In other words, in the worst case scenario, ten idle frames are wasted. Thus, there is an opportunity to use unused frames in a more efficient manner to synchronize to a cell's base station.
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Chen Sylvia Y.
Gesesse Tilahun
Motorola Inc.
Soldner Michael C.
Trost William
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