Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-07-27
2001-02-20
Trost, William G. (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S446000, C455S424000
Reexamination Certificate
active
06192244
ABSTRACT:
This invention relates to the analysis of neighbouring cells in cellular telecommunications systems.
The introduction of the cellular concept is one of the major breakthroughs in solving the problem of spectral congestion and user capacity experienced by early mobile radio systems. In cellular networks, the whole area covered is divided into small cells and the coverage is assured by lower powered transmitters. The whole available spectrum is also divided into small portions and assigned to groups of adjacent cells to form a cluster. Afterwards, this cluster is regularly repeated over the whole area to be covered. Typical values of the cluster size are 4, 7 and 12, but different cluster sizes might be necessary to achieve the desired capacity. The reciprocal of the cluster size is instead called the frequency re-use factor.
The design process of selecting and allocating frequencies to all cells within a network is called frequency planning. This task, which might look easy, is very difficult indeed since representations of cells using hexagons are only a high level abstraction. In reality, cell shapes are very irregular so that the application of the cluster concept is very difficult. The difficulty of the frequency planning task significantly increases with the increase of the frequency re-use factor.
Increasing the re-use factor or equally reducing the cluster size increases system capacity since the whole spectrum, partitioned into smaller groups, is assigned to smaller areas and therefore it can be reused more often. But interference limits the increase of the re-use factor. In fact, the smallest achievable value of the cluster size is related to the interference level that both mobiles and base stations can tolerate whilst maintaining the desirable quality of communications. Therefore, cells with the same frequency must be far away from each other to ensure that the interference caused by this re-use, i.e. co-channel interference, is kept below acceptable levels.
Clearly, two opposite requirements affect the re-use factor. Capacity pushes it up and interference pushes it down so that finding the right compromise is not easy at all. Furthermore, macro/micro cell architectures increase the complexity of the frequency planning due to the layered nature of the problem.
Patent document WO-A-97/06648 describes a method of neighbourhood cell list creation and verification for use with a cellular telecommunications system comprising a plurality of active mobile stations and a static network, the static network having a first cell and a plurality of cells neighbouring the first cell, each of the cells having a base station, and each mobile station in said first cell reporting messages to the static network indicating strengths of signals detected by that mobile station from base stations in neighbouring cells. The method of WO-A-97/06648 comprises the steps of: extracting from the static network such reporting messages for said first cell; producing a list including, for each of the neighbouring base stations, the average of the received signal strengths; ordering the list by average signal strength, and using the ordered list to create or update a neighbouring cell list.
The method of WO-A-97/06648 does not take into account various anomalies which arise in such systems, especially GSM and GSM-like systems.
A first aspect of the present invention relates to a method of analysing lists of neighbouring cells in a cellular telecommunications system comprising a plurality of active mobile stations and a static network, the static network having a first cell and a plurality of cells neighbouring the first cell, some of the neighbouring cells being determined by an operator of the system as planned neighbouring cells, each of the cells having a base station.
The first aspect of the invention makes use of the features that, in such a system, each base station transmits, on a control channel, a signal including a base station identifier of that base station; each mobile station in the first cell is provided with an ordered control channel list of control channel frequencies to be detected by that mobile station; and each mobile station in said first cell reports messages to the static network indicating the base station identifiers of control channels detected by that mobile station and the position in the control channel list of the respective control channel. These may be existing features of the system, such as a GSM or GSM-like system.
In accordance with the first aspect of the present invention, the method of analysing neighbouring cells comprises the steps of: extracting from the static network such reporting messages for said first cell and producing a reporting list including, for each position in the control channel list, the number of times that any of the base station identifiers has been reported for that position; obtaining a planned neighbour list of the control channels and respective base station identifiers of the planned neighbouring cells; correlating the reporting list and the planned neighbour list with respect to the control channels; and analysing the correlated lists to determine whether any of the control channels is affected by bad frequency planning.
The first aspect of the invention therefore can take account of the fact that two or more neighbouring cells, whether planned neighbouring cells or not, may be using the same control channel.
The analysing step may include the steps of: determining whether, for any of the control channels, there is more than one base station identifier in the planned neighbour list; and if so, classifing that control channel in a first class (which will sometimes be hereinafter called “red”). This indicates that there are two or more planned neighbouring cells using the same control channel and that immediate attention may be required.
Additionally or alternatively, the analysing step may include the steps of: determining whether, for any of the control channels, there is only one base station identifier in the reporting list which does not correspond to the base station identifier in the planned neighbour list; and if so, classifying that control channel in a second class (which may be the same as the first class (red)). This indicates that there is a neighbouring cell using the base channel of a planned neighbouring cell, but which is not a planned neighbouring cell, and that immediate attention may be required.
Additionally or alternatively, the analysing step may include the steps of: determining whether, for any of the control channels, there is more than base station identifier in the reporting list; if so, determining whether that one of the base station identifiers in the reporting list having the larger/largest number of reports does not correspond to the base station identifier in the planned neighbour list; and if so, classifying that control channel in a third class (which may be the same as the first and/or second class (red)). This indicates that there are a planned neighbouring cell and a non-planned neighbouring cell using the same base channel, with the non-planned neighbouring cell being more significant, and that immediate attention may be required.
Additionally or alternatively, the analysing step may include the steps of: determining whether, for any of the control channels, there is more than one base station identifier in the reporting list; if so, determining whether that one of the base station identifiers in the reporting list having the larger/largest number of reports corresponds to the base station identifier in the planned neighbour list but is not predominant; and if so, classifying that control channel in a fourth class (which will sometimes be hereinafter called “yellow”). This indicates that there are a planned neighbouring cell and a non-planned neighbouring cell using the same base channel, with the planned neighbouring cell being more significant but not predominant, and that further analysis may be required. Various measures of predominance may be employed. In one example, a base station ident
Hewlett -Packard Company
Trost William G.
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