Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-03-03
2002-08-13
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000
Reexamination Certificate
active
06434389
ABSTRACT:
FIELD OF INVENTION
The invention relates generally to cell selection by a mobile station in a cellular radio network where cells can be defined as subscriber-specific special cells.
BACKGROUND OF INVENTION
In cellular mobile communication systems a mobile station can move freely in the area of the mobile communication network and camp on the most suitable cell at each time. When the mobile station (MS) is switched on, it attempts to make contact with a public land mobile network (PLMN). A particular PLMN to be contacted can be selected either automatically or manually. The MS searches for a suitable cell of the selected PLMN and selects that cell to provide the available services and tunes onto the control channel (broadcasting channel) of the selected cell. The selection is referred to as camping on a cell. For the purpose of cell selection, the MS measures all radio channels of the PLMN or all radio channels according to a stored cell list. The MS typically calculates for each radio channel several averages of the measured received signal level used for cell selection. The MS can then also register its presence in the location area (LA) of the selected cell if necessary, by a location updating procedure or the like. When the MS has carried out the cell selection process and selected the cell, it starts to listen to the control channel of this cell to receive services. The cell that the MS is camped on in this way is called a serving cell. When the MS is camped on a cell but does not communicate with the cell (no call), it is in a mode called an idle mode. In the idle mode the MS measures not only the signal received from the serving cell, but at least the received signal levels of non-serving adjacent cells. An average is generally calculated from the measured signal levels of each cell, the average being used as a cell selection criterion as such, or by calculating specific cell selection parameters. The MS may also monitor the radio path loss between the mobile station and the serving base station and reject in the selection process the cells where the radio path loss is lower than a specific threshold value. Furthermore, cell selection criteria may include hysteresis and timings by which (in addition to averaging measurement results) unnecessary cell reselections and location updatings due to temporary variations in radio conditions are to be prevented. As examples of the camping facility and cell selection process and criteria of the mobile station, reference is made to GSM (Global System for Mobile Communications) and DCS (Digital Communication Systems) mobile communication systems, particularly to the GSM recommendation GSM 03.22 (version 5.0.0) and 05.08 (version 5.1.0).
One feature of cellular radio networks is that the network should know the location of the mobile station in the network to be able to page it and route calls to it. Logical location areas consisting one or more cells are typically defined in cellular networks. The information about the location of the mobile station is stored in the network at the accuracy of a location area. Cells broadcast information indicating the location area they belong to. When the mobile station upon selecting a new cell finds that the location area is changing, it makes a location updating to the network. In order to reduce location updating signalling it would be advantageous that the location areas were as large as possible. On the other hand, the mobile station is paged in all the cells of the location area, in which case it would be preferable for paging signalling that the size of the location area would be as small as possible. The size of the location area is typically a compromise between these two demands.
One known alternative is that instead of or in addition to fixed location areas, location areas specific for each subscriber are determined in the network, and cells are selected to the subscriber-specific location areas to the effect that the typical mobility area of a specific subscriber and other requirements are taken into account as well as possible.
One of the objectives in mobile communication systems has recently been to develop mobile station services to be more and more equal to the conventional services of the fixed network so that they could replace fixed-line services both in offices and at home. In other words, a subscriber or a company is provided with a service area to which specific cells are selected (known e.g. as special cells) where a local subscriber-specific service profile, for example, is defined. That is to say, services and tariffs dependent on the location of the subscriber are produced for the subscriber. This cluster of cells is referred to as a Localized Service Area LSA or an LGS area. The subscriber can be an ordinary home user, for example, whose LSA is part of the radio access network covering his/her home and its immediate surroundings. Within this LSA special tariffs can be offered only for the home subscriber. The subscriber can also be a company employee to whom the localized service area LSA forms a company-wide network that utilizes the radio access solutions in the premises, for example. In the LSA, special tariffs can be offered only for company employees. The LSA typically comprises a cell or a cluster of cells. The cells in the cluster of cells can also be dispersed.
It would be advantageous for the user to be able to use the special cells and the special tariffs and services provided by them as much as possible. As described above, in present cellular network systems the mobile station selects a cell with algorithms based on signal strength. In these algorithms all cells are treated democratically, that is, the selection can be directed to any suitable cell. When the subscriber of the LSA service is a home subscriber, the LSA is home, a flat or a house; a very compact area in any case. In that case the cell that is the dominating cell in this location area is selected as the subscriber's “home cell”. It can be assumed that mobile calls in this location area are served by the home cell, but this cannot be ensured because of the fading phenomenon associated with radio wave propagation, for example. This can lead to that the home subscriber is not always able to utilize a lower tariff or special services. Even if the mobile station was provided with a feature that would inform the subscriber if the subscriber is camped on a special cell or not, the use of the service would be uncertain and uncomfortable for the subscriber. Correspondingly, the LSA of a company subscriber could typically be an office or a factory area. The LGS service is provided by means of a base station placed in the company premises. The coverage area of the base station is planned so that the LSA cell covers the whole defined LSA, but it does not necessarily dominate the whole area. For example, at the boundaries of the LSA cell, such as near room windows, the downlink signal of some adjacent cell can be stronger, in which case under normal conditions the MS camps on this adjacent cell. If the office is small and office-specific cells are not installed there, the office cell is similar to the “home cell” concept described above.
DISCLOSURE OF INVENTION
The object of the invention is to improve cell selection in the cellular radio network to the effect that the mobile station prioritizes the special cell/cells whenever it is in its/their area.
This will be attained with the method of the invention for selecting a cell of a cellular radio network in a mobile station, which method comprises the steps of:
measuring signal levels of a serving cell and adjacent cells in a mobile station in the idle mode,
calculating a cell selection parameter for each measured cell by means of the measured signal levels, and
selecting the best cell to be the serving cell on the basis of the cell selection parameters.
The method is characterized in that the method further comprises the steps of:
comparing the cells to be measured with a special cell list stored in the memory of the mobile station,
checking if each cel
Jolma Petri
Meskanen Harri
Altera Law Group LLC
Cong Le Thanh
Nokia Networks Oy
Tran Tuan
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