Method and system for optimizing cell-neighbor lists

US 7 050 803 B2

Assignee
Telefonaktiebolaget LM Ericsson (publ)
Inventors
Julio Velo, Dwight Inman, Rafael Celedon, Ali Shah
Filing date
January 3 2003
Publication date
May 23 2006
Table of contents
Classifications
IPC: H04Q7/20
USPC: 455436, 455437, 455438

A count is made of the number of mobile assisted handoff (MAHO) attempts between a service cell and a targeted cell. A count is also made of the number of times the targeted cell is considered a Best Candidate (BestCand) for handoff from the service cell. If the targeted cell is not included in the service cell's neighbor list, a potential neighbor cell (PNC), hysteresis is added to the targeted cell to prevent handoffs to the targeted cell. The MAHO and BestCand counts are determined and if the counts meet or exceed predetermined threshold values the targeted cell is added to the list. If the targeted cell is on the neighbor list, no hysteresis is added. If the count data does not meet or exceed the threshold values, the target is removed from the list

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Claims

1. A method for adding a cell to a neighbor list comprising the steps of:
a) selecting a potential neighbor-cell (PNC):
b) adding a sufficiently high hysteresis value to said PNC to prevent any mobile station from handing off to said PNC:
c) adding said PNC having said sufficiently high hystersis value to said neighbor list: and
d) retrieving count data that establishes the number of times that said PNC having said sufficiently high hysteresis value receives a request for access and is considered a best candidate for adding to said neighbor list.

Show 3 dependent claims

5. A base station in a wireless telecommunications system, comprising:
an operating support system (OSS) associated with said base station;
a database associated with said OSS for storing count data associated with a potential neighbor-cell (PNC) wherein a sufficiently high hysteresis value to prevent mobile station handoffs is added to the PNC, wherein the PNC having the sufficiently high hysteresis value [and the PNC] is added to the neighbor list and count data comprises mobile assisted handoff (MHO) attempts and best candidate counts at said PNC having the sufficiently high hysteresis value;
a receiver for receiving said count data from the mobile station (MS);
a first counter for determining the number of times one of said cells in said telecommunications system is a best candidate for handoff between a service cell and said PNC having the sufficiently high hysteresis;
a second counter for determining the number of mobile assisted handoff attempts between said service cell and said PNC having the sufficiently high hysteresis; and
instructions within said OSS for one of removing said PNC having the sufficiently high hysteresis from the neighbor list if said count data does not correlate with a predetermined threshold and adding said potential neighbor-cell (PNC) to said neighbor list without the sufficiently high hysteresis value if said count data meets or exceeds said predetermined threshold value.

Show 5 dependent claims

11. A method for modifying a neighbor list in a cellular telecommunications network, comprising the steps of:
measuring data received from a mobile station;
storing and processing said data; and
adding potential neighbor-cells and removing neighbor-cells from said neighbor list wherein removing a neighbor-cell from said neighbor list comprises the steps of:
a) selecting a neighbor-cell to pair with a service cell;
b) counting the number of times that said neighbor-cell is a best candidate for handoff between said service cell and said neighbor-cell;
c) counting the number of mobile assisted handoff (MAHO) attempts between said service cell and said neighbor-cell;
d) analyzing the count data of said best candidate count and said MAHO attempts; and
e) removing said neighbor-cell from said neighbor list if said count data does not meet or exceed a predetermined threshold value; and
wherein adding a potential neighbor-cell (PNC) to said neighbor list comprises the steps of:
a1) selecting a potential neighbor-cell (PNC) to said neighbor list;
b1) applying a sufficiently high hysteresis value to said PNC to prevent the possibility of a mobile station handoff to said PNC;
c1) adding said PNC having said sufficiently high hysteresis value to said neighbor list;
d1) counting the number of mobile assisted handoff attempts on said PNC having said sufficiently high hysteresis value;
e1) counting the number of times that said PNC having said sufficiently high hysteresis value is a best candidate for handoff;
f1) analyzing the count data of said best candidate count and said mobile assisted handoff attempts; and
g1) adjusting said sufficiently high hysteresis value to a level that will allow mobile station handoff to said PNC having said sufficiently high hysteresis value if said best candidate count data and said mobile assisted handoff attempts meet or exceed a predetermined set of threshold values.

Show 7 dependent claims

Description

CLAIM OF PRIORITY UNDER 35 USC 119

Priority is hereby claimed under 35 USC 119(e) to Provisional Application Ser. No. 60/370,476 filed on Apr. 5, 2002.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to digital wireless communication systems. More particularly, the present invention relates to neighboring cells within a digital wireless communication system. Even more particularly, the present invention relates to managing neighbor-cell lists within the digital wireless communication system.

2. Description of Related Art

In cellular mobile communication systems, a mobile handset communicates with base transceiver stations (BTS's) positioned throughout a geographic area. Each BTS broadcasts on a discrete radio channel within a specified coverage area. A multiplicity of BTS sites may produce an array of cells that allows the system to provide radio coverage over a wide geographic area.

During a call, the user of a mobile handset will often move between neighboring cells within the system. As the mobile handset moves from one cell to a neighboring cell, the base station controller (BSC) of the serving cell typically transfers the call session to the BTS of the neighboring cell. This transfer of the call is termed handoff.

In digital cellular communication systems, such as those utilizing TDMA or CDMA signal transmission protocols, communications between multiple BTS sites and mobile handsets are carried out on radio frequency channels that can carry simultaneous communications. Using these digital protocols, communication sessions are typically performed using digitized voice or data signals that are transmitted as coded bursts or bursts within specified time slots. The coded bursts or time slots corresponding to multiple communication sessions are multiplexed onto the radio channels of the respective cells, and each mobile handset reads and communicates on an assigned decoded channels or assigned time slots on sending and receiving channels. Handoff in digital systems is typically performed using measurements from the mobile handset itself. Known as mobile-assisted handoff (MAHO), the method utilizes the mobile handset to periodically monitor and measure radio signals of neighboring BTS sites.

In Global System for Mobile communications (GSM), the mobile station monitors a neighbor cell's Absolute Radio Frequency Channel number (ARFCN) and does calculations for the neighbor cell and the serving cell. The ARFCN's are stored in a Broadcast Control Channel Allocation (BA) list that is broadcast to the mobile station in the idle and dedicated modes. The list of neighbors that the mobile handset measures on a periodic basis is typically contained in a neighbor-cell list (hereinafter neighbor list) of the wireless cell that is serving (service cell) the handset. The list may be kept on a database maintained at the site of the serving BTS, retained at a radio network controller (RNC) site controlling a plurality of BTS's, or at a centralized mobile switching center (MSC). In order to compare measured signals from the neighbor-cells on the neighbor list with the measured signal from the serving cell, the mobile station transmits the results of its measurements to the serving BTS. The serving BTS will in turn forward the measurements to either the applicable RNC's or to the MSC. If the received signal strength of the current channel in the serving cell falls below a threshold or is otherwise lower than the signal strength of a measured channel of a neighboring cell, the MSC or RNC may initiate handoff of the mobile handset's call session to a neighboring cell. Each cell includes an associated neighbor list that includes information on which BSC controls the neighboring cell.

Large neighbor lists in a cellular network result in a large number of handoff candidates. These lists can lead to excessive handoff problems, since the handoff candidates are in the neighbor list, such as dropped calls and loss in overall quality of the cellular network. Excessively large neighbor lists pose a frequency-planning problem as it becomes more difficult to identify available frequencies for neighboring cells without violating frequency-planning constraints.

As a part of preparing the network for an optimum use of cells and frequencies, neighbor lists need to be optimized, i.e., identify and remove unnecessary neighbor-cells. On the other hand, necessary handoff neighbors need to be determined and kept or added to the neighbor list. A current method, well known to those skilled in the art, utilizes peg counters to compute the number of times a handoff occurs between a cell-neighbor-cell (CELL-NCELL) pair. Network planners use this information to determine changes or additions to the system. In many systems facilities for such peg counters do not exist due to the fact that they are memory intensive. For example, in a system with 500 cells, 4000 CELL-NCELL neighbor-cell relationships may exist and a peg counter for each relationship implies 4000 peg counters with memory for each counter. Another drawback to the peg counter method is that the peg counter method cannot be used to identify new neighbor possibilities.

Therefore, It would be advantageous to have a method of optimizing neighbor lists by automatically removing and adding cells to overcome the disadvantages of the existing solutions. The present invention provides such a system and method.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a method and system for optimizing the number of cells in a neighbor list.

It is a further object of the present invention to provide a method and system for adding a cell to a neighbor list.

A neighbor list in a cellular telecommunications network may be modified by selecting a cell-neighbor-cell pair for consideration. Mobile assisted handoff count data and best candidate count data are analyzed and compared against a predetermined threshold values. If the count data is less than the threshold, the neighbor-cell is removed from the neighbor list. The process is repeated until all the cells in the neighbor list have been screened. As new cells are added, the process is repeated.

A potential neighbor-cell may be added to a neighbor list by adding a hysteresis value to the potential neighbor-cell and then adding the potential neighbor-cell to the neighbor list of a service cell. The added hysteresis value is large enough to prevent handoff between the service cell and the potential neighbor-cell which will allow normal operation without a mobile station actually accessing the potential neighbor cell. Mobile assisted handoff count data (potential) and best candidate count data (potential) is then gathered and analyzed even though no handoffs take place between the service cell and the potential neighbor-cell. If the data exceeds a predetermined threshold value, the cell is added to the neighbor list. The process is repeated for each potential neighbor-cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its numerous objects and advantages will become more apparent to those skilled in the art by reference to the following drawings, in conjunction with the accompanying specification, in which:

FIG. 1 depicts a high level diagram of a network in which a neighbor-cell is considered for removal from a neighbor list, in accordance with a preferred embodiment of the present invention;

FIG. 2 depicts a method for identifying cells that are to be removed or restricted from a neighbor list, according to a preferred embodiment of the present invention

FIG. 3 is a high level diagram of a network in which a neighbor-cell is considered for addition to a neighbor list, according to a preferred embodiment of the present invention; and

FIG. 4 illustrates a method for identifying cells to be added to a neighbor list in a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from theses specific details. In other instances detailed descriptions of well-known devices, circuit, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

FIG. 1 depicts a high level diagram of a telecommunications network in which a preferred embodiment of the present invention may be implemented, wherein a neighbor-cell is to be considered for removal. Included in the network, though not shown, is an operational support system (OSS) that is a set of programs to provide, among other functions, control and analyzing functions. The OSS creates commands to act (remove or add) on target cells in a mobile service center (MSC). Network 100 includes Mobile Station (MS) 102 that is in communication with service cell 104. Network 100 includes Neighbor-cells (Ncell) N1, N2, and N3. As one skilled in the art might conclude, there are more than three neighbor-cells in a typical wireless network. FIG. 1 is limited to three Ncells to simplify explanation and illustration of the present invention. Table 112 comprises measurements that are collected in cellular systems. The present invention optimizes a neighbor list for a particular cell in a cellular telecommunications network by automatically removing unnecessary cells and adding necessary neighbor-cells to the cell's neighbor list when warranted. Generally, measurements are stored and available in an MSC to use in determining the necessity for removing or adding a particular cell in a neighbor list.

High-level block diagram 110 depicts gathering statistics related to handoff attempts (MAHO data) at individual cells, and the number of times a neighbor-cell is determined to be a best candidate (BestCand data). The variable x in diagram 110 represents MAHO data and the variable y represents BestCand data. Each neighbor-cell (Ncell(1), Ncell(2), . . . Ncell(n)) provides x and y values for the neighbor list of cell i (in this example, cell A equates to service cell 104).

FIG. 1 shows two Ncells; N(1) and N(2) in reasonably close proximity to service cell 104. Ncell N(3) is also included in service cell's 104 neighbor list. Due to measurement data, as depicted in table 106, Ncell N(3) is a candidate for removal from service cell's 104 neighbor list. Table 106 displays example data retrieved from a Best Candidate (BestCand) counter and a Handoff (Hoff) attempts counter connected with each Ncell. BestCand data identifies a cell with a Radio Signal Strength Indicator (RSSI) that is at or above a predetermined threshold. In other words, even though a cell is included in a neighbor list, the cell may not be considered a BestCand if the RSSI is below a certain level.

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Assignee
Telefonaktiebolaget LM Ericsson (publ)
Inventors
Julio Velo, Dwight Inman, Rafael Celedon, Ali Shah
Filing date
January 3 2003
Publication date
May 23 2006
Table of contents
Classifications
IPC: H04Q7/20
USPC: 455436, 455437, 455438