Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-11-11
2001-12-04
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S453000, C455S436000
Reexamination Certificate
active
06327472
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to Application No. 9803855-7 filed in Sweden on Nov. 11, 1998; the entire content of which is hereby incorporated by reference.
The present invention relates a radio network handling arrangement handling radio communication in a number of cells and serving a number of mobile stations in a cellular communications network which comprises means for assignment of traffic channels. The invention al so relates to a cellular communication system including a number of radio network handling arrangements. Still further the invention relates to a method of assigning a traffic channel to a mobile station accessing a cell in a cellular communication system including a number of radio network handling arrangements.
BACKGROUND
At call set-up, a mobile station is assigned a traffic channel which means that a mobile station is actually moved from a control channel to a traffic channel. Generally a mobile station is always assigned a traffic channel in the same cell as the control channel except when a cell fulfilling some given network requirements (in a hierarchical cell structure) exists or when there is traffic channel congestion in the cell in which the mobile station is connected to a control channel. A hierarchical cell structure is often used to gain capacity in a mobile radio network in a hierarchical cell structure cells of different sizes will cover one and the same geographical area and the advantage thereof is that frequencies can be reused with a closer reuse pattern.
When a mobile station is in an idle mode, it performs measurements on all control channels ( in the PDC (Personal Digital Cellular) system the control channels are denoted perch channels) in the area in which it is located or within the relevant location area. The control channel having the highest signal strength is chosen and it belongs to the cell that the mobile station will use at call set-up, also called the access cell. The mobile station then listens to broadcasting information sent out in a broadcasting information message on the selected control channel. The broadcasting information message among other information contains information about the number of reporting zones at call set-up. This information is thus (together with other information) received by the mobile station. The mobile station will then send signal strength information and control channel number, using the idle state measurements, to the system at call set-up for as many neighbouring cells as the information relating to the number of reporting zones has specified. In for example one implementation of the PDC-system two neighbouring cells are specified but the PDC standard as such e.g. allows twenty neighbouring cells to be specified.
When there is a high traffic load in a cell so called cell load sharing may be implemented. This means that the cell borders are moved through changing the handover offset parameter that is defined for a cell-neighbouring cell relation. Then mobile stations which are connected to a traffic channel in the cell having a high traffic load are made to perform a handover to the neighbouring cell which has a lower traffic load.
U.S. Pat. No. 5,241,685 relates to the provision of load balancing through mechanically moving the borders between any two cells such that an overloaded cell becomes smaller whereas the neighbouring cell becomes larger. According to this document this is achieved through lowering the entering signal strength threshold for handover to the neighbouring cell and/or increasing the entering signal strengh threshold for handover from the neighbouring cells, wherein the thresholds are unique for any two cells.
Assignment to a neighbouring cell is only activated when congestion occurs in a cell. However, when there is a request for a resource (i.e. a traffic channel) for a new call in a cell which is congested, the requirements for assignment to a neighbouring cell, might not be fulfilled. These requirements are based on (handover) parameters determining whether a mobile station is within the handover area between cells or not. Thus, if these requirements are not fulfilled such calls will be disconnected. Thus, congestion situations easily arise leading to the disconnection of calls. This is a serious drawback. Consequently an assignment to an assignment candidate forming an alternative to the access cell is only performed if there are no more resources in the access cell, in other words, there is congestion. The probability that a mobile station requesting resources in a congested cell is located in the handover area between two cells is quite low which means that the probability that the call be dropped is high.
SUMMARY OF THE INVENTION
What is needed is therefore a radio network handling arrangement in a cellular communication system enabling an efficient way of assigning traffic channels and through which the risk of loosing calls due to congestion in a cell is reduced. An arrangement is also needed through which the traffic load throughout the cells can be evened out. Moreover an arrangement is needed through which more calls can be accepted before a congestion situation arises.
A cellular communication system including a number of radio network handling arrangements is also needed in which the above mentioned objects are achieved.
Still further a method of allocating a traffic channel to a mobile station in a cellular communication system is needed through which the traffic load can be evened out among the cells. Still further a method is needed through which the risk of loosing calls can be reduced and through which more calls can be accepted before a congestion situation arises.
Therefore a radio network handling arrangement handling radio communication in a number of cells in a cellular communication network is provided, which comprises a number of radio channels assigned as control channels and traffic channels, means for assignment of traffic channels and parameter storing means for storing cell parameter information. Information holding or collecting means are also provided for holding/collecting information about signal strength measurements. The arrangement further comprises load monitoring means for holding information about the traffic load in at least a number of cells and the traffic assignment means comprises means for using information about cell parameters and about signal strength measurements for a number of cells to establish whether there are any neighbouring cells available as cell candidates for a mobile station accessing an access cell. The traffic load in the access cell and said available cells respectively is used in such a way that assignment can be performed taking the load situation into account, here also called load dependent assignment, for a mobile station accessing an access cell. Particularly signal strength values and cell parameters are used to establish whether there are any neighbouring cells available as candidates for a mobile station accessing an access cell using cell load considerations and to establish which such neighbouring cells are. In a particular implementation the cell parameters are handover parameters which are added, and/or subtracted from the signal strength values which are received from the mobile station in an initial access message provided to the access cell, to establish whether the mobile station is in the handover area between the access cell and at least one neighbouring cell in which case said neighbouring cell or cells forms(form) one or more available cell candidates or alternatives to the access cell. The offset parameter (OFFSET) is one such handover parameter and it is used to move the cell border in a cell-neighbouring cell relationship. This is particularly done in such a way that the offset value (in dB) either is subtracted or added to the signal strength value as reported by a mobile station. The handover parameter HYST (also in dB) is used in order to avoid oscillating handovers between cells in a cell-neigbouring cell relationship. The HYST parameter is
Ekstam Hanna
Eneland Simon
Kopp Nina
Ostrup Peter
Westroos Anders
Burns Doane Swecker & Mathis L.L.P.
Telefonaktiebolaget LM Ericsson (publ)
Tran Congvan
Trost William
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