CN114375002A

CN114375002A - Method, device and storage medium for determining coverage area of cell

Info

Publication number: CN114375002A
Application number: CN202111635975.8A
Authority: CN
Inventors: 袁灿光; 卢荣深
Original assignee: China Telecom Corp Ltd
Current assignee: China Telecom Corp Ltd
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-04-19

Abstract

The present application relates to the field of communications technologies, and in particular, to a method, an apparatus, and a storage medium for determining a coverage area of a cell. In the embodiment of the application, measurement report MR data of a cell is acquired, wherein the MR data comprises a timing advance TA and an antenna arrival angle AOA; and determining the coverage area of the cell based on the time advance TA and the antenna arrival angle AOA. Therefore, MR data needing to be acquired is reduced, and the cost for determining the cell coverage is effectively reduced; and the coverage area of the cell can be determined by analyzing and calculating the time advance TA and the antenna arrival angle AOA, and the efficiency of determining the coverage area of the cell is effectively improved.

Description

Method, device and storage medium for determining coverage area of cell

Technical Field

The present application relates to the field of communications technologies, and in particular, to a method, an apparatus, and a storage medium for determining a coverage area of a cell.

Background

In a mobile communication network, a large number of cells are usually included, each cell has its own signal coverage, and the signal coverage of the cell is one of the key factors determining the communication quality of the mobile communication network. Therefore, how to determine the coverage of each cell in a mobile communication network comprising a large number of cells is crucial for network optimization.

In some technical schemes, a measurer travels along a certain measurement path in a cell to be measured and a cell where a sampling point is located by walking, driving and the like, and measures a field intensity value of the cell on the measurement path point by using a field intensity tester in the traveling process to obtain a coverage area of the cell. Due to the limitation of ground, terrain, cost and other factors, the complete coverage of the cell cannot be obtained, and the determined coverage of the cell is inaccurate.

In other technical solutions, the coverage area of the cell is predicted by analyzing, fitting and counting a large amount of measured data of the cell. However, in this scheme, a large amount of data needs to be collected, so that more resources of the user terminal and the base station are consumed, and the calculation amount is large.

Therefore, how to provide an efficient and low-cost method for determining the cell coverage is an urgent technical problem to be solved.

Disclosure of Invention

The embodiment of the application provides a method, a device and a storage medium for determining a coverage area of a cell, which are used for determining the coverage area of the cell and reducing the cost for determining the coverage area of the cell.

In a first aspect, an embodiment of the present application provides a method for determining a coverage area of a cell, where the method includes: acquiring measurement report MR data of a cell, wherein the MR data comprises a time advance TA and an antenna arrival angle AOA; determining a coverage area of a cell based on the TA and the AOA.

In the embodiment of the present application, the coverage area of a cell is determined based on a timing advance TA and an antenna arrival angle AOA. The data required to be collected by the measuring equipment is less, so that the cost is effectively reduced; and the amount of calculation is small, so that the efficiency of determining the coverage area of the cell is high.

In one possible design, the determining a coverage area of a cell based on the TA and the AOA includes: determining a first distance between a user terminal served by the cell and a base station based on the TA; determining a first angle of the user terminal relative to the base station based on the AOA; determining first geographical location information of the user terminal according to the first distance, the first angle, the reference azimuth of the cell and the geographical location information of the base station; and taking the area corresponding to the first geographical position information as the coverage area of the cell.

In one possible design, the taking the area corresponding to the first geographical location information as the coverage area of the cell includes: acquiring Reference Signal Received Power (RSRP) of the cell; weighting the first geographical position information based on a preset coefficient corresponding to the RSRP to obtain a grid area corresponding to the first geographical position information; and determining the grid area as the coverage area of the cell.

In the design, the mobility and the instability of the user terminal are considered, the geographical position information of the user terminal is weighted by combining a preset coefficient corresponding to Reference Signal Received Power (RSRP) of a cell, and some weak signals can be effectively prevented from becoming interference items, so that the determined coverage area of the cell is more accurate.

In one possible design, the method further includes: determining a first azimuth angle and a first downtilt angle corresponding to a coverage area of the cell; matching the first azimuth based on a second azimuth preset by the cell, and judging whether the first azimuth has an error; and/or matching the first downward inclination angle based on a second downward inclination angle preset by the cell, and judging whether the first downward inclination angle has an error or not; and if the first azimuth angle and/or the first declination angle have errors, re-determining the coverage area of the cell.

In one possible design, acquiring MR data includes: and acquiring the MR data through a wireless operation maintenance center OMC-R system.

In the design, the MR data is acquired through a wireless operation maintenance center OMC-R system, so that the coverage area of a cell is determined to be independent of a terminal and a base station, and the pressure of the terminal and the base station is relieved.

In a second aspect, an embodiment of the present application provides an apparatus for determining a coverage area of a cell, where the apparatus includes means for implementing the method in the first aspect and any optional design of the first aspect.

Illustratively, the apparatus comprises:

an obtaining module, configured to obtain measurement report MR data of a cell, where the MR data includes a timing advance TA and an antenna arrival angle AOA;

a processing module configured to determine a coverage area of a cell based on the TA and the AOA.

In one possible design, the processing module, when configured to determine a coverage area of a cell based on the TA and the AOA, is specifically configured to:

determining a first distance between a user terminal served by the cell and a base station based on the TA;

determining a first angle of the user terminal relative to the base station based on the AOA;

determining first geographical location information of the user terminal according to the first distance, the first angle, the reference azimuth of the cell and the geographical location information of the base station;

and taking the area corresponding to the first geographical position information as the coverage area of the cell.

In a possible design, the processing module is configured to use an area corresponding to the first geographical location information as a coverage area of the cell, and specifically configured to:

acquiring Reference Signal Received Power (RSRP) of the cell;

weighting the first geographical position information based on a preset coefficient corresponding to the RSRP to obtain a grid area corresponding to the first geographical position information;

and determining the grid area as the coverage area of the cell.

In one possible design, the processing module is further to:

determining a first azimuth angle and a first downtilt angle corresponding to a coverage area of the cell;

matching the first azimuth based on a second azimuth preset by the cell, and judging whether the first azimuth has an error; and/or matching the first downward inclination angle based on a second downward inclination angle preset by the cell, and judging whether the first downward inclination angle has an error or not;

and if the first azimuth angle and/or the first declination angle have errors, re-determining the coverage area of the cell.

In a third aspect, an embodiment of the present application provides an apparatus for determining a coverage area of a cell, including at least one processor and at least one memory, where the memory stores a computer program, and when the program is executed by the processor, the processor is caused to perform the steps of the method for determining a coverage area of a cell in the embodiment of the present application.

In a fourth aspect, embodiments of the present application provide a storage medium storing computer instructions that, when executed on a computer, cause the computer to perform the steps of a method of determining a coverage area of a cell.

The embodiment of the application provides a method for determining a coverage area of a cell. In the embodiment of the application, measurement report MR data of a cell is acquired, wherein the MR data comprises a timing advance TA and an antenna arrival angle AOA; and determining the coverage area of the cell based on the time advance TA and the antenna arrival angle AOA. Therefore, MR data needing to be acquired is reduced, and the cost for determining the cell coverage is effectively reduced; and the coverage area of the cell can be determined by analyzing and calculating the time advance TA and the antenna arrival angle AOA, and the efficiency of determining the coverage area of the cell is effectively improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments will be briefly introduced, and it is obvious that the drawings in the following description are only some embodiments of the present invention.

FIG. 1 is a diagram of a system architecture according to an embodiment of the present application;

fig. 2 is a flowchart of a method for determining a coverage area of a cell according to an embodiment of the present disclosure;

fig. 3 is a schematic structural diagram of an apparatus for determining a coverage area of a cell according to an embodiment of the present disclosure.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments, but not all embodiments, of the technical solutions of the present invention. All other embodiments obtained by a person skilled in the art without any inventive work based on the embodiments described in the present application are within the scope of the protection of the technical solution of the present invention.

Technical terms referred to in the embodiments of the present application are described below.

1. Timing Advance (TA): and the time for the user terminal to adjust the uplink transmission time of the PUCCH/PUSCH/SRS of the main cell is adjusted. Generally, the method is used for uplink transmission of a user terminal, that is, in order to enable an uplink data packet of the user terminal to reach a base station at a preset time, a radio frequency transmission delay caused by a distance is estimated, and the uplink data packet is sent out at a corresponding time in advance. In the random access procedure, the base station determines TA by measuring the received pilot signal. For example, in a Radio Resource Control (RRC) connected state, the base station determines a TA adjustment value for each user terminal based on measuring uplink transmission of the corresponding user terminal. The TA value range is (0, 1, 2,. multidot.1282) × 16 Ts; specifically, if TA is 5, the reporting point is approximately between 312.48 meters and 390.6 meters away from the cell location.

2. Angle Of Arrival (AOA): an estimated angle of a user terminal with respect to a reference direction of the antenna normal. Illustratively, the measurement reference direction should be north and counterclockwise. The data represents raw measurements of the received angle of arrival of the serving cell antenna, with a north-up value of from 0 to 719, with 1 value between 0-0.5 degrees. Therefore, when A0A is 2, it is actually 1 degree or more and less than 1.5 degrees. If the 720 values are involved in the operation, the operation amount is multiplied; meanwhile, the lobe of the antenna, the reporting error and the like need to be considered. The AOAs can be equally divided into 72 equal parts, thus extending the precision to 5 degrees.

In order to improve the efficiency of determining the coverage of a cell and reduce the cost of determining the coverage of the cell, embodiments of the present application provide a method for determining the coverage of a cell. In the embodiment of the application, measurement report MR data of a cell is acquired, wherein the MR data comprises a timing advance TA and an antenna arrival angle AOA; and determining the coverage area of the cell based on the time advance TA and the antenna arrival angle AOA. Therefore, MR data required to be acquired by the measuring equipment is reduced, and the cost for determining the cell coverage is effectively reduced; and the coverage area of the cell can be determined by analyzing and calculating the time advance TA and the antenna arrival angle AOA, and the efficiency of determining the coverage area of the cell is effectively improved.

First, a system architecture to which the embodiments of the present application are applicable is described.

Referring to fig. 1, fig. 1 is a schematic diagram illustrating a system architecture applicable to the embodiment of the present application. The system includes a computing device and an Operation and Maintenance Center (OMC-R) system.

And the OMC-R system stores MR data of the cell to be tested. Thus, in one possible embodiment, a computing device may obtain measurement report MR data for a cell by an OMC-R system, the MR data comprising a timing advance TA and an antenna angle of arrival AOA; in turn, the computing device may determine a coverage area of the cell based on the timing advance, TA, and the antenna angle of arrival, AOA. Therefore, MR data needing to be acquired is reduced, and the cost for determining the cell coverage is effectively reduced; and the coverage area of the cell can be determined by analyzing and calculating the time advance TA and the antenna arrival angle AOA, and the efficiency of determining the coverage area of the cell is effectively improved.

Optionally, the system may further include a base station and a user terminal, and the OMC-R may receive MR data from the base station or the user terminal. The MR data includes, among other things, the physical layer, RLC layer of the user terminal and base station, and measurement reports generated during radio resource management. For example, the ue may report the RRC measurement report to the base station, and the base station may send the RRC measurement report to the OMC-R system.

It is understood that the number of the user terminals may be one or more, and the embodiment of the present application is not particularly limited.

It should be noted that the above-mentioned system architecture is only shown for the convenience of understanding the spirit and principle of the present application, and the embodiments of the present application are not limited in any way in this respect. Rather, the embodiments of the present application may be applied to any applicable scenario.

The method for determining the coverage area of a cell according to the embodiment of the present application is described below with reference to the system architecture shown in fig. 1.

As shown in fig. 2, an embodiment of the present application provides a method for determining a coverage area of a cell, where the method may be applied to the computing device in fig. 1, and the method includes:

step 201: measurement report MR data is acquired, the MR data comprising a timing advance TA and an antenna angle of arrival AOA.

As can be seen from the foregoing description, the TA is a time for the ue to adjust uplink transmission time of the primary cell PUCCH/PUSCH/SRS; AOA is the estimated angle of a user terminal with respect to the antenna normal reference direction.

In one possible embodiment, the MR data is acquired by an OMC-R system. Therefore, the coverage area of the cell is determined without depending on the terminal and the base station, and the pressure of the terminal and the base station is relieved.

It should be noted that the MR data may be data reported by the measurement device based on a measurement period, or may be data triggered based on a special event, or may be data obtained by performing statistical analysis on data reported based on a measurement period, and the embodiment of the present application is not limited specifically. The period may be 2 weeks, 1 week, etc., and the examples of the present application are not particularly limited.

In one possible embodiment, the measurement devices of the timing advance TA and the antenna angle of arrival AOA are base stations.

Step 202: based on the TA and the AOA, a coverage area of the cell is determined.

In one possible implementation, the process by which the computing device determines the coverage area of a cell based on TA and AOA may be: determining a first distance between a user terminal served by a cell and a base station based on TA; determining a first angle of the user terminal relative to the base station based on the AOA; determining first geographical position information of the user terminal according to the first distance, the first angle, the reference azimuth of the cell and the geographical position information of the base station; and taking the area corresponding to the first geographical position information as the coverage area of the cell.

It is understood that the number of the user terminals served by a cell may be one or more, and the embodiment of the present application is not particularly limited.

For example, suppose the earth is defined as a near sphere with radius of radius, O is the center of the earth, the ue and the bs are two points a and B on the sphere, the first distance is the arc length between the bs a point and the bs B point, AOA is an, longitude is la, and latitude is ph.

The method for determining the first distance between the user terminal and the base station according to the TA comprises the following steps:

step 1: the spherical coordinates of the base station point a and the user terminal point B are represented by (r, la, ph), the spatial coordinates are represented by (x, y, z), and accordingly, the following relationship exists between the spatial coordinates and the spherical coordinates:

x＝r*cos(ph)*cos(la)，y＝r*cos(ph)*sin(la)，z＝r*sin(ph)；

step 2: an included angle cos (an) between a vector OA formed by the point A of the base station and the point O of the sphere center and a vector OB formed by the point B of the user terminal and the point O of the sphere center is calculated, wherein the included angle is represented by X, and X is (the module of the OA vector OB vector module)/(the dot product of the OA and OB vectors) cos (ph A) cos (ph B) cos (la A-la B) + sin (ph A sin (ph B)), and because of an arccos (X), TA ran radius is substituted into the value of TA, the arc length between the point A of the base station and the point B of the user terminal, namely the first distance, can be obtained.

Wherein, the first included angle between the vector Na tangent to the base station point A and the vector AB formed by the base station point A and the user terminal point B is taken as an example, and the step of calculating the first included angle comprises the following steps:

x＝r*cos(ph)*cos(la)，y＝r*cos(ph)*sin(la)，z＝r*sin(ph)；

further, the spatial coordinates of the base station a point and the user terminal B point can be determined by referring to the coordinates of the sphere center.

Step 2: according to the space coordinates of the base station point A and the user terminal point B, determining the space coordinates of the vector Na and the vector AB:

na vector is (-cos (ph A) cos (la B), -cos (ph A) sin (la B),1/sin (ph A) -sin (ph a));

and AB vector-OA vector-B spatial coordinate-A spatial coordinate.

And step 3: and calculating an included angle Y between the vector Na and the vector AB according to the space coordinates of the vector Na and the vector AB:

cosY ═ (dot product of Na vector and OB vector)/(modulo vector Na and modulo vector OB) ═(sin (ph b) × sin (ph a))/sqrt (2-2 × cos (ph a));

where sqrt is the square root.

After obtaining the first distance and the first angle, the computing device may determine first geographical location information of the user terminal according to the first distance, the first angle, the reference azimuth of the cell, and the geographical location information of the base station; and taking the area corresponding to the first geographical position information as the coverage area of the cell. It should be understood that the reference azimuth of the cell may be a preset antenna azimuth, and the embodiment of the present application is not particularly limited.

For example, the user terminals take 4 as an example, the first distance includes 4 distances between the 4 user terminals and the base station, the first angle includes 4 angles between the 4 user terminals and the base station, the geographic location information of the base station includes latitude and longitude coordinates of the base station, and the reference azimuth of the cell is the north-south direction, then the latitude and longitude coordinates of the 4 user terminals can be determined according to the first distance, the first angle, the reference azimuth of the cell, and the geographic location information of the base station, and an area formed by the latitude and longitude coordinates of the 4 user terminals is used as a coverage area of the cell.

In another possible implementation, the step of using, by the computing device, an area corresponding to the first geographic location information as a coverage area of the cell includes: acquiring Reference Signal Received Power (RSRP) of the cell; weighting the first geographical position information based on a preset coefficient corresponding to the RSRP to obtain a grid area corresponding to the first geographical position information; and determining the grid area as the coverage area of the cell. In the design, the mobility and the instability of the user terminal are considered, the geographical position information of the user terminal is weighted by combining a preset coefficient corresponding to Reference Signal Received Power (RSRP) of a cell, and some weak signals can be effectively prevented from becoming interference items, so that the determined coverage area of the cell is more accurate.

Exemplarily, the value range of RSRP corresponds to a preset coefficient, and the computing device may perform weighted multiplication on the first geographical location information based on the preset coefficient to obtain a grid area corresponding to the first geographical location information; and determining the grid area as the coverage area of the cell.

TABLE 1

RSRP interval	Coefficient of performance
		RSRP>-44	10
-44<RSRP<＝-50	10
		-50<RSRP<＝-55	9
-55<RSRP<＝-60	8
		-60<RSRP<＝-65	7
-65<RSRP<＝-70	6
		-70<RSRP<＝-75	5
-75<RSRP<＝-80	4
		-80<RSRP<＝-85	3
-85<RSRP<＝-90	2
		-90<RSRP<＝-95	1
-95<RSRP<＝-100	1
		-100<RSRP<-110	0.8
RSRP<-110	0.5

In one possible implementation, the measurement device that acquires RSRP of a cell may be a terminal.

In one possible implementation, the computing device may also determine a first azimuth angle and a first downtilt angle corresponding to a coverage area of the cell; matching the first azimuth based on a second azimuth preset by the cell, and judging whether the first azimuth has an error; and/or matching the first downward inclination angle based on a second downward inclination angle preset by the cell, and judging whether the first downward inclination angle has an error or not; and if the first azimuth angle and/or the first declination angle have errors, re-determining the coverage area of the cell. It is understood that the preset second azimuth angle and the preset second downtilt angle of the cell are preset parameters of the cell. Therefore, the accuracy of the coverage area can be judged by verifying the antenna parameters corresponding to the determined cell coverage area based on the preset parameters.

In the embodiment shown in fig. 2, measurement report MR data of a cell is obtained, where the MR data includes a timing advance TA and an antenna angle of arrival AOA; and determining the coverage area of the cell based on the time advance TA and the antenna arrival angle AOA. Therefore, MR data needing to be acquired is reduced, and the cost for determining the cell coverage is effectively reduced; and the coverage area of the cell can be determined by analyzing and calculating the time advance TA and the antenna arrival angle AOA, and the efficiency of determining the coverage area of the cell is effectively improved.

Based on the same technical concept, an apparatus for determining a coverage area of a cell is provided in the embodiments of the present application, as shown in fig. 3, the apparatus includes:

an obtaining module 301, configured to obtain measurement report MR data of a cell, where the MR data includes a timing advance TA and an antenna arrival angle AOA;

a processing module 302 configured to determine a coverage area of a cell based on the TA and the AOA.

In one possible design, when the processing module 302 is configured to determine a coverage area of a cell based on the TA and the AOA, specifically, to: determining a first distance between a user terminal served by the cell and a base station based on the TA; determining a first angle of the user terminal relative to the base station based on the AOA; determining first geographical location information of the user terminal according to the first distance, the first angle, the reference azimuth of the cell and the geographical location information of the base station; and taking the area corresponding to the first geographical position information as the coverage area of the cell.

In a possible design, the processing module 302 is configured to use an area corresponding to the first geographic location information as a coverage area of the cell, and specifically configured to: acquiring Reference Signal Received Power (RSRP) of the cell; weighting the first geographical position information based on a preset coefficient corresponding to the RSRP to obtain a grid area corresponding to the first geographical position information; and determining the grid area as the coverage area of the cell.

In one possible design, the processing module 302 is further configured to: determining a first azimuth angle and a first downtilt angle corresponding to a coverage area of the cell; matching the first azimuth based on a second azimuth preset by the cell, and judging whether the first azimuth has an error; and/or matching the first downward inclination angle based on a second downward inclination angle preset by the cell, and judging whether the first downward inclination angle has an error or not; and if the first azimuth angle and/or the first declination angle have errors, re-determining the coverage area of the cell.

Based on the same technical concept, an apparatus for determining a coverage area of a cell is provided in an embodiment of the present application, and includes at least one processor and at least one memory, where the memory stores a computer program, and when the program is executed by the processor, the processor is caused to perform the steps of the method for determining a coverage area of a cell in the embodiment of the present application.

Based on the same technical concept, embodiments of the present application provide a storage medium storing computer instructions, which when executed on a computer, cause the computer to perform the steps of the method for determining a coverage area of a cell in the embodiments of the present application.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, and the like) having computer-usable program code embodied therein.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A method of determining a coverage area of a cell, comprising:

acquiring measurement report MR data of a cell, wherein the MR data comprises a time advance TA and an antenna arrival angle AOA;

determining a coverage area of a cell based on the TA and the AOA.

2. The method of claim 1, wherein the determining the coverage area of the cell based on the TA and the AOA comprises:

3. The method according to claim 2, wherein the using the area corresponding to the first geographical location information as the coverage area of the cell comprises:

acquiring Reference Signal Received Power (RSRP) of the cell;

and determining the grid area as the coverage area of the cell.

4. The method according to any one of claims 1-3, further comprising:

5. The method of any one of claims 1-3, wherein acquiring MR data comprises:

and acquiring the MR data through a wireless operation maintenance center OMC-R system.

6. An apparatus for determining a coverage area of a cell, comprising:

7. The apparatus of claim 6, wherein the processing module, when configured to determine the coverage area of the cell based on the TA and the AOA, is specifically configured to:

8. The apparatus of claim 7, wherein the processing module, when configured to determine the first geographical location information of the ue according to the first distance, the first angle, the reference azimuth of the cell, and the geographical location information of the base station, is specifically configured to:

acquiring Reference Signal Received Power (RSRP) of the cell;

adjusting the first distance based on an inverse relation between the RSRP and the first distance to obtain a second distance; wherein the second distance is different from the first distance;

and determining first geographical position information of the user terminal according to the second distance, the first angle, the reference azimuth of the cell and the geographical position information of the base station.

9. The apparatus of any of claims 6-8, wherein the processing module is further configured to:

10. A storage medium storing computer instructions which, when executed on a computer, cause the computer to perform the steps of the method according to any one of claims 1 to 5.