Patent Application
20060009237
1. Field of the Invention
The present invention generally relates to a network planning method used in a mobile communication network, and more particularly, relates to a partitioning method for a mobile communication network with overlapping location areas.
2. Description of the Prior Art
In a multi-cell mobile communication network such as GSM network, each cell represents the radio range of a base station therein. Mobile units move among the cells. One or more cells are grouped into a location area. Each cell within a location area is assigned a location area code (LAC). The network provides a register for each mobile unit to record the LAC of the location area where the mobile unit is currently located. When moving from a previous location area to a new one, a mobile unit performs a location update to change its LAC to that of the new location area. Also, when a call is initiated to a specific mobile unit, the network pages all mobile units in a specific location area according to the last location update performed by that specific mobile unit. Through applying this location area scheme, the network needn't track and page all mobile units when a call is initiated. The load of the network can be greatly reduced. However, in some situations, the location update load of the network may be increased to damage the network performance. For example, if a mobile unit moves back and forth between two location areas, a lot of redundant location updates will occur. This phenomenon is called a ping-pong effect, which will greatly increase the location update load.
The overlapping location area scheme, in which one cell may belong to two or more location areas, is developed to reduce the location update load of the network. In the overlapping location area scheme, each cell has a corresponding LAC list, as shown in
When adding an OLAC into the LAC list of a cell, the distribution for mobile units with each respective LAC within the cell (called LAC distribution in this specification) can be changed. Also, the location update load for the cell is changed since not all mobile units moving into the cell will trigger a location update.
By applying overlapping location area scheme, the location update load for the network may be reduced. However, paging load can be increased too. In this condition, the overall load of the network may not be decreased.
It is therefore an objective of the present invention to provide a partitioning method for a mobile communication network with overlapping location areas, thereby providing an optimal partitioning to upgrade the network performance.
Another objective of the present invention is to provide a method for determining a location area code (LAC) list of a cell in a mobile communication network, thereby minimizing location update load and keeping the network under paging load limit.
Another objective of the present invention is to provide a method for predicting a LAC distribution for a cell in a mobile communication network with overlapping location areas, thereby providing a systematic and accurate way to predict the LAC distribution for the cell.
According to one embodiment of the present invention, the method for determining a LAC list of a cell in a mobile communication network includes the following steps: finding at least a potential LAC labeling operation for the cell; determining a respective gain for each potential LAC labeling operation; selecting one of the potential LAC labeling operations according to the respective gains; and adjusting the LAC list according to the selected operation.
According to another embodiment of the present invention, the partitioning method for a mobile communication network with overlapping location areas applies the method for determining the LAC list mentioned above to each cell in the network.
According to another embodiment of the present invention, the method for predicting a LAC distribution of a cell in a mobile communication network with overlapping location areas includes the following steps: (a) determining a respective contribution to each LAC of the cell provided by a neighboring cell of the cell according to signal movements from the neighboring cell to the cell and an initial LAC distribution of the neighboring cell; (b) repeating step (a) for other neighboring cells of the cell; and (c) predicting the LAC distribution of the cell according to the contributions provided by the neighboring cells.
It should be noted that the term of location area is used specifically for the GSM network. However, it is also known as Paging Area, Routing Area, or Registration Area used for different mobile communication networks. For example, “Location Area” is typically used in GSM network and “Routing Area” is typically used in GPRS network. Also, “Registration Area” and “Paging Area” are generally used in many communication systems. Although their names are different, people skilled in the art know that their meanings are substantially the same, i.e., updating messages are required when moving across the boundary of location area (or routing area, or registration area) and mobile units are paged in their current location area (or routing area, or registration area). Similarly, the term of location area code (LAC) is also used specifically for the GSM network, and people skilled in the art know that its meaning is substantially the same to the like terms used in other kinds of mobile networks. The GSM network is used as an example in this specification, while the present invention is not limited to the GSM network.
In step 21, the potential LAC labeling operation is an Add operation, Replace operation, Swap operation, or Remove operation. These operations are used to adjust the LAC list of a cell, and illustrated in Table 1 below. The Add operation adds an OLAC into the LAC list, while the Remove operation removes an OLAC from the LAC list. The Replace operation replaces the RAC of the LAC list with the RAC of any neighboring cell. The Swap operation replaces the RAC of the LAC list with the RAC of any neighboring cell, and puts the old RAC as an OLAC into the LAC list. The Replace and Swap operations are mainly applied to modify RAC of the LAC list for a cell.
According to the current LAC lists of cell i and all its neighboring cells, the “potential” LAC labeling operations for cell i can be found. Each LAC (including RAC and OLAC) in the LAC list of any neighboring cell and not in that of cell i can be a candidate to be added into the list of cell i. Each OLAC in the LAC list of cell i can be removed. The RAC of any neighboring cell, if different from that of cell i, can be a candidate for swapping and replacing. In this manner, all the potential LAC labeling operations for cell i can be found in step 21.
In another embodiment, in step 21, a potential LAC labeling operation can be found according to any possible configuration of the LAC list of cell i. That is, for each possible configuration, there is a corresponding LAC labeling operation for adjusting the current LAC list to the possible configuration. The LACs (including RAC and OLAC) in any possible configuration are selected from the current LAC lists of cell i and all its neighboring cells.
After finding all the potential operations for cell i, step 22 is executed to determine a respective gain for each potential operation. The gain represents the benefit of applying the corresponding potential operation to cell i. Different operations may lead to different gain values. In the embodiment of
The location update load of the first portion is determined by accumulating respective location update load for each cell therein. The location update load for a cell is calculated based on the signal movements between the cell and its neighboring cells, as well as the current LAC distributions of the cell and its neighboring cells. The signal movement from a cell to a neighboring means that a mobile unit moves from the cell to the neighboring cell, or the medium via which the mobile unit connects with the network is changed from the cell to the neighboring cell.
As mentioned above, the LAC distribution of a cell is changed after applying a LAC labeling operation to the cell. The LAC distributions of the neighboring cells will also be changed correspondingly. The method for predicting the new LAC distribution of the cell will be disclosed later.
Then, the corresponding gain for the LAC labeling operation in
After the respective gain for each potential operation for cell i is determined in step 22, step 23 selects a potential operation with the maximum gain and step 24 applies the selected operation to adjust the LAC list of cell i. In another embodiment, step 23 selects the potential operation with a gain larger than a predetermined threshold. This means the operation with a lower gain (e.g. negative gain) will not be selected.
However, the adjustment of the LAC list should not result in a paging overload in the network. Thus, step 25 checks if some portion (denoted by second portion) of the entire network is paging-overloaded. In one embodiment, the second portion corresponds to the first portion mentioned earlier. In another embodiment, step 25 checks if the entire network is paging-overloaded. If any cell or location area, which is assigned a paging load limit, within the second portion (or entire network) is paging-overloaded, then the second portion (or entire network) is determined as paging-overloaded. Further, if the second portion (or entire network) is paging-overloaded, which means the adjustment made by step 24 is not proper, then step 26 restores the LAC list of cell i to a previous state before step 24 is performed (i.e. the pre-adjustment state). On the other hand, if the second portion (or entire network) is not overloaded, then the flow of
It is notable that the paging contribution made by a cell, which means the number of paging generated due to the mobile units in the cell during a period of time, can be divided into several LAC paging contributions according to the LAC distribution of the cell.
In another preferred embodiment of the partitioning method, a network partitioning algorithm is applied to the GSM network prior to step 21. The network partitioning algorithm can generate a plurality of non-overlapping location areas. In this preferred embodiment, the RAC of each non-overlapping location area is first determined by the network partitioning algorithm, and then the OLAC is added (or removed) to generate the optimized overlapping location area by the flow of
The applicable network partitioning algorithms include, but are not limited to, K-L (Kernighan-Lin) algorithm, greedy algorithm, F-M (Fiduccia-Mattheyses) algorithm, genetic algorithm, and simulated annealing algorithm. For information on K-L algorithm, please refer to “An Efficient Heuristic Procedure for Partitioning Graphs” (The Bell system technical journal, 49(1):291-307, 1970). For information on greedy algorithm, please refer to “Introduction to Algorithms: A Creative Approach, chapter 7” (pp.210.about.pp.211, Addison-Wesley Publishing Company, 1989). For information on F-M algorithm, please refer to “A Linear-Time Heuristic for Improving Network Partitions” (Proc. of DAC, 1982). For information on genetic algorithm, please refer to “A Genetic Algorithm For Optimizing Multiple Part Placement To Reduce Build Time” (Proceedings of the Fifth International Conference on Rapid Prototyping, Dayton, Ohio, June 1994). For information on simulated annealing algorithm, please refer to “Location Area Planning in Cellular Networks Using Simulated Annealing” (Proceedings of IEEE Infocom, The Conference on Computer Communications 2001, Anchorage, Ak., Apr. 22-26, 2001). The above-mentioned publications are incorporated herein by reference.
As mentioned above, after applying a potential LAC labeling operation to a cell, the LAC distribution of the cell should be re-determined in order to compute the new location update load for the cell. A preferred embodiment of the method for predicting the LAC distribution of the cell is shown in
In step 51, if a LAC of the neighboring cell is also labeled to cell i, then the respective contribution to the LAC of cell i provided by the neighboring cell is computed as the product of the signal movements from the neighboring cell to cell i and a distributed value of the LAC in the initial LAC distribution of the neighboring cell. On the other hand, if the LAC is not is labeled to cell i, then when a mobile unit carrying the LAC moves from the neighboring cell to cell i, the LAC in the mobile unit is replaced by a default LAC, i.e. RAC, of cell i. Thus, the respective contribution to the RAC of cell i provided by the neighboring cell will contain the product of the signal movements from the neighboring cell to cell i and a distributed value of the LAC in the initial LAC distribution of the neighboring cell.
In step 53, the distributed value of each LAC (RAC or OLAC) in the new LAC distribution of cell i is determined by accumulating the contributions to the LAC provided by all neighboring cells of cell i, and the new LAC distribution of cell i is then generated.
However, the new LAC distribution of cell i will change the LAC distributions of its neighboring cells. Thus, steps 54 to 56 are repeated until all the predicted LAC distributions of cell i and its neighboring cells approach to a stable state. Here the stable state means the difference between the previous and following LAC distributions is smaller than a threshold, which can be determined according to the realistic conditions of network operation.
While the present invention has been shown and described with reference to the preferred embodiments thereof and in terms of the illustrative drawings, it should not be considered as limited thereby. Various possible modifications and alterations could be conceived of by one skilled in the art to the form and the content of any particular embodiment, without departing from the scope and the spirit of the present invention.
The present application claims the benefit of U.S. Provisional Application No. 60/582,544, filed on Jun. 25, 2004, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60582544 | Jun 2004 | US |
