CN111031602A

CN111031602A - Bandwidth part updating method and terminal

Info

Publication number: CN111031602A
Application number: CN201811171938.4A
Authority: CN
Inventors: 王桂英
Original assignee: China Mobile Communications Group Co Ltd; China Mobile Communications Ltd Research Institute
Current assignee: China Mobile Communications Group Co Ltd; China Mobile Communications Ltd Research Institute
Priority date: 2018-10-09
Filing date: 2018-10-09
Publication date: 2020-04-17
Anticipated expiration: 2038-10-09
Also published as: CN111031602B

Abstract

The embodiment of the invention provides a bandwidth part updating method and a terminal, wherein the bandwidth part updating method comprises the following steps: acquiring real-time traffic of a terminal; and updating the bandwidth part BWP according to the real-time traffic. The scheme of the invention can effectively reduce the power consumption of the terminal, and meanwhile, the network can flexibly adapt to the terminal service, thereby achieving the high-efficiency utilization of resources.

Description

Bandwidth part updating method and terminal

Technical Field

The present invention relates to the field of communications technologies, and in particular, to a method and a terminal for updating a bandwidth portion.

Background

The three application scenarios of 5G are URLLC (Ultra Reliable and Low Latency Communication), eMBB (enhanced Mobile broadband Band), and mtc (massive Machine Type of Communication). In order to support different service scenarios, the 5G NR (New Radio Access Technology) supports configuring different BWPs (bandwidth parts) for a UE (user equipment). A subset of the entire bandwidth of the cell is defined as a BWP, which can be smaller than the system bandwidth of the cell and can be flexibly adjusted; the BWP may be shifted in position in the frequency domain and the subcarrier spacing may be different.

In a serving cell, a set of (at most 4) downlink BWPs is configured to the UE via higher layer parameters DL-BWP, and a set of (at most 4) uplink BWPs is configured to the UE via higher layer parameters UL-BWP.

For each downstream BWP or upstream BWP, the following parameters need to be configured: subcarrier spacing, CP (cyclic prefix) length, RB (resource block) offset value and a set of consecutive PRBs (physical resource blocks), index (index) of uplink and downlink BWPs, and scheduling timing.

In each downlink BWP, the UE receives PDCCH and PDSCH according to the subcarrier interval and CP length configured by the BWP; and in each uplink BWP, the UE transmits PUCCH and PUSCH according to the subcarrier interval and CP length configured by the BWP.

If a BWP indication field is configured in the DCI format 1_1, the value indicates activated downlink BWP for downlink reception;

if the BWP indication field is configured in the DCI format 0_1, the value indicates an activated uplink BWP for uplink transmission.

The higher layer parameter Default-DL-BWP may be used to indicate the Default downlink BWP in the configured set of downlink BWPs. If the UE is not configured with the default downlink BWP, the initial activation of the downlink BWP is the default downlink BWP. The current protocol does not take into account the specific update basis of BWP.

Disclosure of Invention

The invention provides a bandwidth part updating method and a terminal. The power consumption of the terminal can be effectively reduced, and meanwhile, the network can be flexibly adapted to the terminal service, so that the high-efficiency utilization of resources is achieved.

To solve the above technical problem, an embodiment of the present invention provides the following solutions:

a method for updating a bandwidth portion, comprising: acquiring real-time traffic of a terminal; and updating the bandwidth part BWP according to the real-time traffic.

The acquiring of the real-time traffic of the terminal includes: acquiring a Buffer Status Reporting (BSR) of a terminal; and acquiring the real-time traffic of the terminal from the BSR.

Wherein updating the bandwidth part BWP according to the real-time traffic comprises: and updating the BWP according to the real-time traffic.

Wherein, according to the real-time traffic, updating the upstream bandwidth part BWP includes:

and if the value of the real-time traffic is continuously greater than the upward updating threshold M1 for N1 times, switching to BWP with the bandwidth greater than a first preset value, wherein both N1 and M1 are positive integers.

The method for updating the bandwidth part further comprises the following steps: and if the real-time traffic is less than the threshold M1 before N1 times, controlling a first counter to be cleared.

The method for updating the bandwidth part further comprises the following steps: and after switching to the BWP with the bandwidth larger than the first preset value, continuously switching the value of the real-time traffic to the BWP with the bandwidth larger than the second preset value, wherein the value of the real-time traffic is still larger than the M1 for N1 times, and switching to the BWP with the bandwidth larger than the second preset value, wherein the second preset value is larger than the first preset value.

Wherein, according to the real-time traffic, updating the upstream bandwidth part BWP includes: and if the value of the real-time traffic is continuously smaller than the downward updating threshold M2 for N2 times, switching to BWP with the bandwidth smaller than a third preset value, wherein both N2 and M2 are positive integers.

The method for updating the bandwidth part further comprises the following steps: and if the real-time traffic is larger than the M2 before N2 times, controlling a second counter to be cleared.

The method for updating the bandwidth part further comprises the following steps: and after switching to the BWP with the bandwidth smaller than the third preset value, continuously performing N2 times on the value of the real-time traffic volume to be smaller than the M2, and switching to the BWP with the bandwidth smaller than a fourth preset value, wherein the fourth preset value is smaller than the third preset value.

The method for updating the bandwidth part further comprises the following steps: and in the process of updating the upstream bandwidth part BWP, if no real-time service transmission exists, switching to the default BWP.

The acquiring of the real-time traffic of the terminal includes: obtaining the cache content of a packet data convergence protocol PDCP of a terminal; and acquiring the real-time traffic of the terminal from the cache content of the PDCP.

Wherein updating the bandwidth part BWP according to the real-time traffic comprises: and updating the BWP of the downlink bandwidth part according to the real-time traffic.

Wherein, according to the real-time traffic, updating the BWP of the downlink bandwidth part includes: and if the value of the real-time traffic is continuously greater than the upward updating threshold M3 for N3 times, switching to BWP with the bandwidth greater than a fifth preset value, wherein both N3 and M3 are positive integers.

The method for updating the bandwidth part further comprises the following steps: and if the real-time traffic is less than the M3 before N3 times, controlling a third counter to be cleared.

The method for updating the bandwidth part further comprises the following steps: and after switching to the BWP with the bandwidth larger than a fifth preset value, continuously switching the value of the real-time traffic to the BWP with the bandwidth larger than a sixth preset value, wherein the value of the real-time traffic is still larger than the M3 for N3 times, and switching to the BWP with the bandwidth larger than the sixth preset value, and the sixth preset value is larger than the fifth preset value.

Wherein, according to the real-time traffic, updating the BWP of the downlink bandwidth part includes: and if the value of the real-time traffic is continuously smaller than the downward updating threshold M4 for N4 times, switching to BWP with the bandwidth smaller than a seventh preset value, wherein both N4 and M4 are positive integers.

The method for updating the bandwidth part further comprises the following steps: and if the real-time traffic is larger than the M4 before N4 times, controlling a fourth counter to be cleared.

The method for updating the bandwidth part further comprises the following steps: and after switching to the BWP with the bandwidth smaller than the seventh preset value, continuously performing N4 times on the value of the real-time traffic volume to be smaller than the M4, and switching to the BWP with the bandwidth smaller than an eighth preset value, wherein the eighth preset value is smaller than the seventh preset value.

The method for updating the bandwidth part further comprises the following steps: and in the process of updating the BWP of the downlink bandwidth part, if no real-time service transmission exists, switching to the default BWP.

An embodiment of the present invention further provides a terminal, including: the processor is used for acquiring the real-time traffic of the terminal; and updating the bandwidth part BWP according to the real-time traffic.

An embodiment of the present invention further provides a terminal, including: a processor, a memory storing a computer program which, when executed by the processor, performs the method as described above.

Embodiments of the present invention also provide a computer-readable storage medium including instructions that, when executed on a computer, cause the computer to perform the method as described above.

The scheme of the invention at least comprises the following beneficial effects:

according to the scheme, the real-time traffic of the terminal is acquired; and updating the bandwidth part BWP according to the real-time traffic. The power consumption of the terminal can be effectively reduced, and meanwhile, the network can be flexibly adapted to the terminal service, so that the high-efficiency utilization of resources is achieved.

Drawings

FIG. 1 is a flow chart of a bandwidth segment update method according to an embodiment of the present invention;

FIG. 2 is a flowchart illustrating an embodiment of a method for updating a bandwidth portion according to the present invention;

fig. 3 is a schematic diagram of the architecture of the terminal according to the present invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

As shown in fig. 1, an embodiment of the present invention provides a method for updating a bandwidth part, including:

step 11, acquiring real-time traffic of a terminal;

and step 12, updating the bandwidth part BWP according to the real-time traffic.

The embodiment can effectively reduce the power consumption of the terminal, and meanwhile, the network can flexibly adapt to the terminal service, thereby achieving the efficient utilization of resources.

In one implementation of this embodiment, the step 11 includes:

step 111, obtaining a Buffer Status Report (BSR) of the terminal;

and step 112, acquiring the real-time traffic of the terminal from the BSR.

Accordingly, the step 12 may include: and updating the BWP according to the real-time traffic.

Specifically, an initial BWP (initial BWP) is used by the UE for initial access, and a bandwidth up-update threshold M1 and a first counter T1, a bandwidth down-update threshold M2 and a second counter T2 are set in the MAC (media access control) entity, where M2 is smaller than M1, and M1 and M2 are both positive integers.

And if the value of the real-time traffic is continuously greater than the upward updating threshold M1 for N1 times, switching to BWP with the bandwidth greater than a first preset value, wherein N1 is a positive integer.

And if the real-time traffic is less than the threshold M1 before N1 times, controlling a first counter T1 to be cleared.

After switching to the BWP with the bandwidth larger than the first preset value, the value of the real-time traffic is still continuously larger than the M1 for N1 times, and switching to the BWP with the bandwidth larger than a second preset value, wherein the second preset value is larger than the first preset value; until the second preset value is the maximum bandwidth.

And if the value of the real-time traffic is continuously smaller than the downward updating threshold M2 for N2 times, switching to BWP with the bandwidth smaller than a third preset value, wherein N1 is a positive integer.

And if the real-time traffic is larger than the M2 before N2 times, controlling a second counter T2 to be cleared.

And after switching to the BWP with the bandwidth smaller than the third preset value, continuously switching the value of the real-time traffic to the BWP with the bandwidth smaller than the M2 for N2 times, and switching to the BWP with the bandwidth smaller than a fourth preset value, wherein the fourth preset value is smaller than the third preset value until the fourth preset value is the minimum bandwidth.

In the above embodiment, during the process of updating the BWP of the uplink bandwidth part (during the process of switching BWP), if there is no real-time service transmission, the BWP is switched to the default BWP.

In another implementation of this embodiment, the step 11 includes:

step 121, obtaining the cache content of a Packet Data Convergence Protocol (PDCP) of the terminal;

and step 122, acquiring the real-time traffic of the terminal from the cache content of the PDCP.

Accordingly, the step 12 may include: and updating the BWP of the downlink bandwidth part according to the real-time traffic.

Specifically, the UE initially accesses to the UE using initial BWP (initial BWP), and a bandwidth downward update threshold M3 and a third counter T3, a bandwidth downward update threshold M4 and a fourth counter T4 are set in the MAC (media access control) entity, where M4 is smaller than M3, and M3 and M4 are both positive integers.

And if the value of the real-time traffic is continuously greater than the upward updating threshold M3 for N3 times, switching to BWP with the bandwidth greater than a fifth preset value, wherein N3 is a positive integer.

And if the real-time traffic is less than the M3 before N3 times, controlling a third counter T3 to be cleared.

And after switching to the BWP with the bandwidth larger than a fifth preset value, continuously switching the value of the real-time traffic to the BWP with the bandwidth larger than a sixth preset value, wherein the value of the real-time traffic is still larger than the M3 for N3 times, and switching to the BWP with the bandwidth larger than the sixth preset value, and the sixth preset value is larger than the fifth preset value.

And if the value of the real-time traffic is continuously smaller than the downward updating threshold M4 for N4 times, switching to BWP with the bandwidth smaller than a seventh preset value, wherein N4 is a positive integer.

And if the real-time traffic is larger than the M4 before N4 times, controlling a fourth counter T4 to be cleared.

And after switching to the BWP with the bandwidth smaller than the seventh preset value, continuously performing N4 times on the value of the real-time traffic volume to be smaller than the M4, and switching to the BWP with the bandwidth smaller than an eighth preset value, wherein the eighth preset value is smaller than the seventh preset value.

In the above embodiment, during the process of updating the BWP of the downlink bandwidth part (during the process of switching the BWP), if there is no real-time service transmission, the BWP is switched to the default BWP.

The following describes the implementation of the above method with reference to specific applications:

as shown in fig. 2, UE (terminal) access uses initial BWP;

receiving a BSR, setting n1 to 0; n2 ═ 0;

if the BSR is greater than the upward update threshold M1; n1+ +;

until N1 is N1, switch to BWP of larger bandwidth;

if the switched BWP is the BWP with the maximum bandwidth, the UE returns to the default BWP to receive data while waiting for the inactivity timer to expire.

If the BSR is less than the downward update threshold M2; n2+ +;

until N2 is N2, switch to BWP with smaller bandwidth;

if the switched BWP is already the minimum bandwidth BWP, the UE returns to the default BWP to receive data while waiting for the inactivity timer to expire.

The update procedure of the downstream BWP is similar to the update procedure of the upstream BWP shown in fig. 2 and described above.

In the above embodiment of the present invention, in the uplink BWP update scheme, the UE uses initial BWP at initial access, and the MAC (media access control) entity sets a BWP bandwidth up-update threshold M1 and a counter T1, and a bandwidth down-update threshold M2 and a counter T2, where M2 is smaller than M1.

After each time the terminal reports the BSR, the MAC compares the value of the BSR with threshold values M1 and M2, when the BSR is continuously larger than a threshold M1 for N1 times, the terminal is switched to BWP with larger bandwidth through DCI (downlink control information) information, and if the BSR is smaller than the threshold M1 before N1 times, a counter T1 is cleared; when the BSR value on the new BWP is still continuously larger than the threshold M1N 1 times, switching to the BWP with larger bandwidth through the DCI information until the BWP with the largest bandwidth.

When the BSR is smaller than the threshold M2 for N2 times continuously, switching to BWP with smaller bandwidth through DCI information, and if the BSR is larger than the threshold M2 before N2 times, clearing the counter T2; when the BSR value on the new BWP is still N2 times less than the threshold M2, switching to the BWP with smaller bandwidth through the DCI information until the BWP with the smallest bandwidth. In the process of bandwidth switching, when the UE has no data transmission, the base station waits for the inactive timer to time out after finishing scheduling, and the UE returns to default BWP.

In the downlink BWP update scheme: the flow is basically the same as the uplink BWP updating scheme, and the MAC entity needs to set a bandwidth up-update threshold M3 and a counter T3, and a bandwidth down-update threshold M4 and a counter T4, where M4 is smaller than M3. The size of the PDCP buffer and the threshold value M3/M4 need to be compared.

The UE uses initial BWP when initially accessing, after the terminal reports PDCP each time, the MAC compares the value of PDCP with threshold values M3 and M4, when the BSR is continuously larger than the threshold M3 for N3 times, the BSR is switched to BWP with larger bandwidth through DCI information, if the BSR is smaller than the threshold M3 before N3 times, a counter T3 is cleared; when the PDCP value on the new BWP is still continuously greater than the threshold M3N 3 times, switching to the BWP with larger bandwidth through the DCI information until the BWP with the largest bandwidth.

When the PDCP is less than the threshold M4 for N4 times continuously, switching to BWP with smaller bandwidth through DCI information, and if the bandwidth is greater than the threshold M4 before N4 times, clearing the counter T4; when the PDCP value on the new BWP is still less than the threshold M4 for N4 times, switching to the BWP with smaller bandwidth through the DCI information until the BWP with the smallest bandwidth. In the process of bandwidth switching, when the UE has no data transmission, the base station waits for the inactive timer to be overtime after finishing scheduling, and the UE returns to default BWP.

The above embodiments of the present invention can improve the flexibility of BWP update and the adaptation of services, and reduce the power consumption of the terminal.

As shown in fig. 3, an embodiment of the present invention further provides a terminal 30, including: a processor 32, configured to obtain real-time traffic of the terminal; and updating the bandwidth part BWP according to the real-time traffic.

It should be noted that all the implementation manners in the above method embodiments are applicable to the embodiment of the terminal, and the same technical effect can be achieved. The terminal may further comprise a memory 33, a transceiver 31; the memory 33, the transceiver 31 and the processor 32, and the transceiver 31 and the memory 33 may be connected through a bus interface, the function of the transceiver 31 may be implemented by the processor 32, and the function of the processor 32 may also be implemented by the transceiver 31.

An embodiment of the present invention further provides a terminal, including: a processor, a memory storing a computer program which, when executed by the processor, performs all the steps of the method as described above and the embodied method.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.

In the embodiments provided in the present invention, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.

The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: various media capable of storing program codes, such as a U disk, a removable hard disk, a ROM, a RAM, a magnetic disk, or an optical disk.

Furthermore, it is to be noted that in the device and method of the invention, it is obvious that the individual components or steps can be decomposed and/or recombined. These decompositions and/or recombinations are to be regarded as equivalents of the present invention. Also, the steps of performing the series of processes described above may naturally be performed chronologically in the order described, but need not necessarily be performed chronologically, and some steps may be performed in parallel or independently of each other. It will be understood by those skilled in the art that all or any of the steps or elements of the method and apparatus of the present invention may be implemented in any computing device (including processors, storage media, etc.) or network of computing devices, in hardware, firmware, software, or any combination thereof, which can be implemented by those skilled in the art using their basic programming skills after reading the description of the present invention.

Thus, the objects of the invention may also be achieved by running a program or a set of programs on any computing device. The computing device may be a general purpose device as is well known. The object of the invention is thus also achieved solely by providing a program product comprising program code for implementing the method or the apparatus. That is, such a program product also constitutes the present invention, and a storage medium storing such a program product also constitutes the present invention. It is to be understood that the storage medium may be any known storage medium or any storage medium developed in the future. It is further noted that in the apparatus and method of the present invention, it is apparent that each component or step can be decomposed and/or recombined. These decompositions and/or recombinations are to be regarded as equivalents of the present invention. Also, the steps of executing the series of processes described above may naturally be executed chronologically in the order described, but need not necessarily be executed chronologically. Some steps may be performed in parallel or independently of each other.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for updating a portion of bandwidth, comprising:

acquiring real-time traffic of a terminal;

and updating the bandwidth part BWP according to the real-time traffic.

2. The method for updating the bandwidth portion according to claim 1, wherein acquiring the real-time traffic of the terminal comprises:

acquiring a Buffer Status Report (BSR) of a terminal;

and acquiring the real-time traffic of the terminal from the BSR.

3. The method for updating bandwidth segment BWP according to claim 2, wherein updating bandwidth segment BWP according to the real-time traffic comprises:

and updating the BWP according to the real-time traffic.

4. The method for updating bandwidth segment according to claim 3, wherein updating upstream bandwidth segment BWP according to the real-time traffic comprises:

5. The method for updating the bandwidth part according to claim 4, further comprising:

and if the real-time traffic is less than the threshold M1 before N1 times, controlling a first counter to be cleared.

6. The method for updating the bandwidth part according to claim 4, further comprising:

and after switching to the BWP with the bandwidth larger than the first preset value, continuously switching the value of the real-time traffic to the BWP with the bandwidth larger than the second preset value, wherein the value of the real-time traffic is still larger than the M1 for N1 times, and switching to the BWP with the bandwidth larger than the second preset value, wherein the second preset value is larger than the first preset value.

7. The method for updating bandwidth segment according to claim 3, wherein updating upstream bandwidth segment BWP according to the real-time traffic comprises:

and if the value of the real-time traffic is continuously smaller than the downward updating threshold M2 for N2 times, switching to BWP with the bandwidth smaller than a third preset value, wherein both N2 and M2 are positive integers.

8. The method for updating the bandwidth portion according to claim 7, further comprising:

and if the real-time traffic is larger than the M2 before N2 times, controlling a second counter to be cleared.

9. The method for updating the bandwidth portion according to claim 7, further comprising:

and after switching to the BWP with the bandwidth smaller than the third preset value, continuously performing N2 times on the value of the real-time traffic volume to be smaller than the M2, and switching to the BWP with the bandwidth smaller than a fourth preset value, wherein the fourth preset value is smaller than the third preset value.

10. The method for updating the bandwidth part according to claim 3, further comprising:

and in the process of updating the upstream bandwidth part BWP, if no real-time service transmission exists, switching to the default BWP.

11. The method for updating the bandwidth portion according to claim 1, wherein acquiring the real-time traffic of the terminal comprises:

obtaining the cache content of a packet data convergence protocol PDCP of a terminal;

and acquiring the real-time traffic of the terminal from the cache content of the PDCP.

12. The method for updating the bandwidth part BWP according to the real-time traffic of claim 11, wherein the updating the bandwidth part BWP comprises:

and updating the BWP of the downlink bandwidth part according to the real-time traffic.

13. The method for updating the bandwidth segment according to claim 12, wherein updating the downstream bandwidth segment BWP according to the real-time traffic comprises:

and if the value of the real-time traffic is continuously greater than the upward updating threshold M3 for N3 times, switching to BWP with the bandwidth greater than a fifth preset value, wherein both N3 and M3 are positive integers.

14. The method for updating the bandwidth portion according to claim 13, further comprising:

and if the real-time traffic is less than the M3 before N3 times, controlling a third counter to be cleared.

15. The method for updating the bandwidth portion according to claim 13, further comprising:

16. The method for updating the bandwidth segment according to claim 12, wherein updating the downstream bandwidth segment BWP according to the real-time traffic comprises:

and if the value of the real-time traffic is continuously smaller than the downward updating threshold M4 for N4 times, switching to BWP with the bandwidth smaller than a seventh preset value, wherein both N4 and M4 are positive integers.

17. The method for updating the bandwidth segment according to claim 16, further comprising:

and if the real-time traffic is larger than the M4 before N4 times, controlling a fourth counter to be cleared.

18. The method for updating the bandwidth segment according to claim 16, further comprising:

19. The method for updating the bandwidth portion according to claim 12, further comprising:

and in the process of updating the BWP of the downlink bandwidth part, if no real-time service transmission exists, switching to the default BWP.

20. A terminal, comprising:

the processor is used for acquiring the real-time traffic of the terminal; and updating the bandwidth part BWP according to the real-time traffic.

21. A terminal, comprising: a processor, a memory storing a computer program which, when executed by the processor, performs the method of any of claims 1 to 19.

22. A computer-readable storage medium comprising instructions which, when executed on a computer, cause the computer to perform the method of any one of claims 1 to 19.