Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-08-11
2003-12-16
Maung, Nay (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000
Reexamination Certificate
active
06665538
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to cellular communications systems, in particular to cellular data communications systems, and the determination of cell borders in such systems.
DESCRIPTION OF RELATED ART
Cellular communications systems such as GSM (Global System for Mobile Communications), AMPS (Advance Mobile Phone System) or D-AMPS (Digital Advance Mobile Phone System) are now well known. A characteristic of such cellular communications systems is that in the course of established communication sessions with mobile stations, for example mobile telephones, the mobile stations may move from one cell of the system to another cell so that the mobile station concerned communicates via different base stations, serving the different cells. Procedures and means for such “handover” of a communication from one cell or base station to another are known in the context of these cellular communications systems.
An important factor for the successful operation of cellular communications systems is the design of the cells of hence the determination of the borders between adjacent cells. Cell design, and the determination of cell borders, are in general based upon measurements made in the field, “by hand”, of actual communications conditions in the cells of the system. The measurements may be, for example C/I (carrier/interference) measurements. These measurements, and any consequent adjustments to cell design, represent a significant overhead and cost factor for the operator of a mobile communications system. This is particularly so because measurements of actual communications conditions have to be repeated, because the characteristics of the communications system and the cells within the system change with time. For instance, new cells may be added to the system or changes in environmental factors may affect the characteristics of cells.
Cellular communications systems, originally primarily concerned with voice communications, are now being developed to more efficiently carry data communications. One development, conceived for supplementing GSM communications systems, is the GPRS (General Packet Radio System) cellular data communications system, which is a packet based data communications system. GPRS, and other cellular data communications systems, also face the need to hand over an on-going communication from a mobile station—in this case a mobile data terminal, such as a notebook computer or a multifunctional voice/data communications device—from one cell or base station to another. GPRS, and other cellular data communications systems, also require careful cell design setting of cell borders. These aspects of the communications system may be more vital for data communications in order for data to be transmitted at necessary higher rates in comparison with rates used for voice communications, to establish a satisfactory level of data throughput in the system.
A feature which cellular communications systems may offer, and which is provided by the GPRS data communications system, is the availability of different coding schemes for data transmitted in the system and the ability to dynamically change from one coding scheme to another. This is known as dynamic link adaptation. Thus, for example, the GPRS system offers four different coding schemes (for instance for downlink, i.e. base station to mobile station, communications), giving different levels of error protection to transferred data and/or different levels of redundancy in transmitted data signals. In the GPRS system, for example, the coding scheme used, and hence the effective data transfer rate, can be dynamically adapted for an established communications link using link adaptation functionality provided in the system. This link adaptation functionality may use, for example, reports transmitted from mobile stations to the system in response to an order from the system. Such a report may for instance contain information relating to the last transmitted series of radio blocks from the system to the mobile station. Information included may be carrier strength (C), interference (I), signal variance (Sign_VAR), block error rate and bit error rate. Depending on this information, link adaptation functionality can select the coding scheme, of those available, for a next sequence of radio blocks. Hence, the effective date transfer rate can be changed depending for example on the current communications (e.g. radio) situation.
PROBLEMS ADDRESSED BY THE PRESENT INVENTION
In a cellular communications system, in particular for data communications, the establishment of an efficient cell plan is a vitally important aspect of the system. The cell plan, i.e. the layout of cells, is a vital aspect of the system, especially for data communications. However, the effort and cost involved in establishing a cell plan, and adapting the cell plan as necessary to meet changed conditions, is a significant technical and economic burden on the system operator. If the cell plan is inappropriate to communication conditions generally applying to the areas covered by cells this can lead to acute inefficiencies in the system, so that the cost of monitoring the effectiveness of the cell plan, and adapting that plan, cannot be avoided.
In cellular communications systems, in particular for data communications, the provision of a satisfactory overall level of data throughput is also a matter of concern. Moreover, when a communications link has been established, if there is a change of data transfer rate in the link—for example at cell handover—the effects of this change of rate cannot always be predicted and may cause disruption of the data transfer.
SUMMARY (OF THE PRESENT INVENTION)
According to one aspect of the present invention there is provided a method of determining a cell border between first and second cells in a cellular communications system in which communications with mobile stations can be effected at different effective transfer rates in dependence upon communication conditions with the mobile stations, and in which on-going communications with the mobile stations can be handed over from the first cell to the second cell, the method comprising
storing information relating to the transfer rates of communications with mobile stations prior to cell handover of those communications from the first cell to the second cell,
storing information relating to transfer rates of the communications with mobile stations subsequent to the cell handover of the respective communications concerned from the first cell to the second cell,
analyzing and processing the stored information, and in dependence thereupon determining the cell border between the first and the second cell such that, at communication handover, transfer rates before and after handover are more likely or most likely to be the same.
According to another aspect of the present invention there is provided apparatus for determining a cell border between first and second cells in a cellular communications system in which communications with mobile stations can be effected at different effective transfer rates in dependence upon communication conditions with the mobile stations, and in which on-going communications with the mobile stations can be handed over from the first cell to the second cell, the apparatus comprising
means for storing information relating to the transfer rates of communications with mobile stations prior to cell handover of those communications from the first cell (A) to the second cell (B),
means for storing information relating to transfer rates of the communications with mobile stations subsequent to the cell handover of the respective communications concerned from the first cell to the second cell,
means for analyzing and processing the stored information, and in dependence thereupon providing for determination of the cell border between the first and the second cell such that, at communication handover, transfer rates before and after handover are more likely or most likely to be the same.
Method and apparatus in accordance with the present invention c
Gantt Alan T.
Maung Nay
Telefonaktiebolaget LM Ericsson (publ)
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