Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-07-01
2001-07-24
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S422100, C455S436000, C455S452200
Reexamination Certificate
active
06266531
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for cell load sharing within a wireless telecommunications system, and specifically to adapting the threshold for cell load sharing based upon current traffic situations.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to
FIG. 1
of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as wireless network
10
, which in turn is composed of a plurality of areas
12
, each with a Mobile Services Center (MSC)
14
and an integrated Visitor Location Register (VLR)
16
therein. The MSC/VLR areas
12
, in turn, include a plurality of Location Areas (LA)
18
, which are defined as that part of a given MSC/VLR area
12
in which a mobile station (MS)
20
may move freely without having to send update location information to the MSC/VLR area
12
that controls the LA
18
. Each Location Area
12
is divided into a number of cells
22
. Mobile Station (MS)
20
is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the wireless network
10
, each other, and users outside the subscribed network, both wireline and wireless.
The MSC
14
is in communication with at least one Base Station Controller (BSC)
23
, which, in turn, is in contact with at least one Base Transceiver Station (BTS)
24
. The BTS
24
is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell
22
for which it is responsible. It should be understood that the BSC
23
may be connected to several BTSs
24
and
28
, and may be implemented as a stand-alone node or integrated with the MSC
14
. In either event, the BSC
23
and BTS
24
and
28
components, as a whole, are generally referred to as a Base Station System (BSS)
25
. The radio interface between the BTS
24
and the MS
20
utilizes Time Division Multiple Access (TDMA) to transmit information between the BTS
24
and the MS
20
, with one TDMA frame per carrier frequency. Each frame consists of eight timeslots or physical channels. Depending upon the kind of information sent, different types of logical channels can be mapped onto the physical channels. For example, speech is sent on the logical channel, “Traffic Channel” (TCH), and signaling information is sent on the logical channel, “Control Channel” (CCH).
With further reference to
FIG. 1
, the PLMN Service Area or wireless network
10
includes a Home Location Register (HLR)
26
, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR
26
may be co-located with a given MSC
14
, integrated with the MSC
14
, or alternatively can service multiple MSCs
14
, the latter of which is illustrated in FIG.
1
.
The VLR
16
is a database containing information about all of the Mobile Stations
20
currently located within the MSC/VLR area
12
. If an MS
20
roams into a new MSC/VLR area
12
, the VLR
16
connected to that MSC
14
will request data about that MS
20
from its home HLR database
26
(simultaneously informing the HLR
26
about the current location of the MS
20
). Accordingly, if the user of the MS
20
then wants to make a call, the local VLR
16
will have the requisite identification information without having to reinterrogate the home HLR
26
. In the aforedescribed manner, the VLR and HLR databases
16
and
26
, respectively, contain various subscriber information associated with a given MS
20
.
Many wireless service providers have a feature called Cell Load Sharing (CLS), which is an efficient way to distribute the traffic evenly in the wireless system. Consequently, the radio resources are utilized in an efficient manner, resulting in an increased average capacity (handling ability). The traffic load, e.g., the percentage of available traffic channels in use, in a cell
22
varies over time. In addition, as the traffic load increases in one cell
22
, a neighboring cell
27
may have a low traffic load. The CLS feature allows service providers to share the traffic load between the neighboring cells
22
and
27
. For simplicity, only one neighboring cell
27
is shown in FIG.
1
. However, it should be understood that the number of neighboring cells
27
depends upon the type of cell cluster arrangement within the cellular network
10
.
In the current CLS functionality, one threshold defines at what load the traffic load shall be distributed to neighboring cells
27
(BTS's
28
) and another threshold determines at what load the traffic from neighboring cells
27
can be accepted. However, these thresholds are fixed, and thus, cannot take into account the dynamic nature of variations on the traffic load in a cellular network
10
. Consequently, the CLS feature does not work when an unexpected variation in the traffic load occurs in a cell
22
, such as when a high level of traffic occurs due to an automobile accident. For example, as the traffic in one cell
22
due to an unexpected variation increases beyond the threshold for sharing the load with neighboring cells
27
, the BSC
23
serving the cell
22
and neighboring cells
27
attempts to perform handovers to neighboring BTS's
28
for those MS's
20
near the border between the cells
22
and
27
. However, when the traffic load in the neighboring cells
27
rises above the threshold for accepting load, no handovers can be performed, resulting in a high traffic load in the problem cell
22
with no means of cell load sharing. If, however, the threshold for accepting load in the neighboring cell
27
can be lowered, the load on the problem cell
22
could be reduced. In addition, by raising the threshold for sharing load in the problem cell
22
, fewer handovers need to be performed, which results in a more efficient utilization of channel resources.
It is, therefore, an object of the present invention to provide for adaptive thresholds based upon the traffic load to determine cell load sharing between neighboring cells.
SUMMARY OF THE INVENTION
The present invention is directed to telecommunications systems and methods for providing adaptive thresholds for cell load sharing (CLS) based upon the current traffic situations. This can be accomplished by the BSC monitoring the traffic load in a cell during a predetermined time period, e.g., 30 minutes. If the traffic load is high for the entire time period, the CLS thresholds can be changed to maximize efficient channel resource utilization. In one embodiment, a look-up table can be used to set the thresholds for each cell based upon the traffic level, e.g., the percentage of idle channels, during the time period. Alternatively, the traffic load in both the serving cell and neighboring cells (preferably neighbors that are frequent handover candidates, e.g., three neighboring cells) can be monitored for the same time period. If the BSC determines that the traffic load is higher than usual in the serving cell, the CLS thresholds can be changed in the serving cell as follows: a) increase the threshold for accepting load; and b) decrease the threshold for sharing load. At the same time, if the traffic load in one of the neighboring cells is normal or lower than usual, the CLS threshold for that neighboring cell can also be changed as follows: a) decrease the threshold for accepting load; and b) increase the threshold for sharing lo
Bhatia Ranjit
Zadeh Bagher R.
Ericsson Inc.
Jenkens & Gilchrist P.C.
Maung Nay
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