WO2004013987A1

WO2004013987A1 - Method of power control for high speed data communication channels in case of soft handover

Info

Publication number: WO2004013987A1
Application number: PCT/GB2003/003416
Authority: WO
Inventors: Peter Chambers
Original assignee: Roke Manor Research Limited
Priority date: 2002-08-05
Filing date: 2003-08-04
Publication date: 2004-02-12
Also published as: GB0218119D0; AU2003249070A1

Abstract

A method for increasing pilot power for high speed dedicated physical control channel, in a cellular wireless communication system, comprising the steps of: storing a predetermined DPCCH/DPDCH power ratio (βc/βd) increment in a storage device in a portable terminal (12); in the portable terminal, detecting the presence of a soft handover condition; in the portable terminal, detecting that a high speed dedicated control channel (HS-DPCCH) (26) is active; in response to positive determinations of the presence of a soft handover condition and that the HS-DPCCH channel is active, retrieving the predetermined DPCCH/DPDCH power ratio (βc/βd) increment from the storage device; and applying the DPCCH/DPDCH power ratio (βc/βd) increment to the DPCCH/DPDCH power ratio (βc/βd), thereby increasing the DPCCH channel power. A corresponding method is provided for applying an increment to a target signal-to-interference ratio in a base station, also to increase the DPCCH channel power.

Description

METHOD OF POWER CONTROL FOR HIGH SPEED DATA COMMUNICATION CHANNELS IN CASE OF SOFT HANDOVER

[0001] The present invention relates to control signals transmitted between portable terminals, otherwise known as "User Equipment" or "UE" and network base stations, otherwise known as "Node B". In particular, the present invention relates to optimisation of power consumption in asymmetric third generation "3 GPP" mobile communications systems.

[0002] Fig. 1 schematically shows a network base station Node B 10 in communication with a number of portable terminals UE, 12. During asymmetric communication, a much greater quantity of data is transmitted to the UE 12 than is transmitted by the UE 12 to base station 10. For example, such asymmetric communication occurs when the UE 12 is used for functions such as gaming or web surfing. An example of such a system is known as the FDD HSDPA (High speed Downlink Packet Access) system. [0003] During a set-up phase in which the UE 12 is registered with the base station 10, a high speed data downlink channel HS-PDSCH (High-Speed Physical Downlink Subscriber CHannel) 14, which provides high speed downlink packet access, is established, providing data to the UE 12 at a relatively fast rate. This channel is the primary channel for communication from the base station 10 to the UE 12. A further channel DL-DPCH (Downlink Dedicated Physical CHannel) 16 is also provided to transfer data from the base station 10 to the UE 12. Finally, a low capacity uplink channel UL-DPCH (UpLink Dedicated Physical CHannel) is provided for transmitting the uplink channel. In an asymmetric communications scenario as shown, there will be relatively little data to transmit on the uplink. [0004] One of the main functions of the UL-DPCH 18 and DL-DPCH 16 is to establish and maintain the integrity of the HS-PDSCH 14.

[0005] The UL-DPCH 18 comprises a number of identifiable sub-channels as illustrated in Fig. 2. Each Uplink Dedicated Physical CHannel (UL-DPCH) 18 comprises a Dedicated Physical Control Channel (DPCCH) 22, a Dedicated Physical Data Channel (DPCDH) 24. [0006] Each of the sub-channels 22, 24, 26 has an assigned relative power. The relative power of the DPCCH 22 is represented as βc; the relative power of the DPDCH 24 is represented as βd; and the relative power of the HS-DPCCH 26 is represented as βhs. Typically, βhs is initially set equal to βc. The ratio of these relative powers, such as βd/βc, represents the corresponding channel power ratio, in this example, the ratio of the powers of the DPDCH channel to that of the DPCCH channel. In known systems, the values of βc, βd and βhs are set by higher-layer signalling.

[0007] Pilot bits P 28 are included withinDPCCH 22 to provide channel estimation for the channels HS-DPCCH, DPDCH and DPCCH. [0008] It is important that the HS-DPCCH channel is received at the base station 10 as clearly as possible, that is to say, with a relatively high SIR (signal to interference ratio), to provide a high probability of successful communication.

[0009] When a portable terminal UE 12 is within communication range of two or more base stations 10, a situation known as soft hand-over (SHO) occurs. A single UE 12 may communicate channels UL-DPCH 18 and DL-DPCH 16 with each of the two or more base stations 10 within range. This provides an advantage known as "SHO gain", whereby channels UL-DPCH 18 and DL-DPCH 16 operate with macro diversity benefit. This allows the transmitting power of the UL-DPDCH 24 and UL-DPCCH 22 to be reduced, while maintaining a certain effective SLR, as multiple paths are available. A control signal is sent to the user equipment UE 12 to instruct it to reduce the power levels βc and βd. However, the channel HS-DPCCH 26 can only be supplied by a single base station. When the transmitting power levels βc and βd are reduced, the power control in the user equipment UE 12 reduces the power level βhs to the HS-DPCCH 26, in order to maintain predetermined power ratios βhs/βc, βhs/βd. The pilot energy received at the high-speed serving cell will also drop. These effects can cause problems with the reception of HS- DPCCH 26 in the base station 10. As the available transmit power is reduced, without the compensating benefit of multiple paths, the SIR (signal-to-interference ratio) of the HS- DPCCH signal reduces, and errors in the reception of this sub-channel become more likely. This problem occurs in high speed cellular systems such as 3GPP, but was not an issue in earlier cellular communications systems, which did not have a High Speed Downlink Packet Access system providing the high data rate communication channel 14. [0010] Known proposed solutions to this problem all have drawbacks. For example, it has been proposed to provide a closed loop power control system specifically for the HS- DPCCH channel 26. Another suggested solution is to add dedicated pilot bits into the HS- DPCCH channel 26, reducing the number of available information bits. Another suggested solution is to increase the number of timeslots that the HS-DPCCH channel 26 occupies. However, each of these proposed solutions has a serious drawback, either in terms of data bits added to the channel protocol, or wasted data bits decreasing channel capacity, or increased power consumption at the UE 12.

[0011] The present invention accordingly aims to address the problem of reduced signal-to- interference ratio of the HS-DPCCH channel during soft handover, without wasting power or channel capacity, or increasing the complexity of the channel protocol.

[0012] In their paper 3GPP Tdoc Rl -02-0592, published at www.3gpp.org, Ericsson propose a system to overcome a problem which occurs during soft handover. The DPCH channels can be in a soft handover condition, in which their power is controlled by multiple Node Bs. However, the HS-DPCCH channel cannot operate in this soft handover condition since it must be received by the Node B which is serving the HS-PDSCH channel. In the soft handover condition, the DPCCH channel may not be strong enough to result in a sufficiently good channel estimate. Hence, the performance of the HS-DPCCH signalling could be limited by the received pilot energy rather than by the energy of the HS-DPCCH information fields. Ericsson propose to increase the power of the DPCCH, if necessary, for the purposes of channel estimation. To achieve this, Ericsson propose adjusting the DPCCH/DPDCH power ratio. By increasing this ratio, the outerpower control loop operated by the networkwill raise the target SIR (signal-to-interference ratio) value for DPCCH. The UE will respond by increasing the power of DPCCH, while the power of DPDCH remains essentially unchanged. The HS-DPCCH will benefit from increased pilot power for channel estimation in the high-speed serving cell.

[0013] The methods proposed by Ericsson do, however, have certain drawbacks. The control loop which operates to raise the target SIR (signal-to-interference ratio) value for DPCCH has a lengthy response time, and suffers from overshoot and lag effects. [0014] The present invention addresses these drawbacks and provides a procedure for execution in the UE and Node B for operation when HS-DPCCH is transmitted in the SHO condition.

[0015] Accordingly, the present invention provides a method for increasing pilot power for dedicated physical channel, in a cellular wireless communication system, comprising the steps of: storing a predetermined DPCCH/DPDCH power ratio increment in a storage device in a portable terminal; in the portable terminal, detecting the presence of a soft handover condition; in the portable terminal, detecting that a high speed dedicated control channel (HS-DPCCH) is active; in response to positive determinations of the presence of a soft handover condition and that the HS-DPCCH channel is active, retrieving the predetermined DPCCH/DPDCH power ratio increment from the storage device; and applying the DPCCH/DPDCH power ratio increment to the DPCCH/DPDCH power ratio, thereby increasing the DPCCH channel power.

[0016] The DPDCH transmitted power preferably remains substantially unchanged, thereby maintaining a link block error rate (BLER) unchanged.

[0017] The incremented DPCCH/DPDCH power ratio may be is maintained for the whole duration of the high speed downlink packet access (HSDPA) call.

[0018] The incremented DPCCH/DPDCH power ratio may be maintained for the duration of the slots of HS-DPCCH transmission only. [0019] The incremented DPCCH/DPDCH power ratio may be maintained for the duration of a number of slots encompassing HS-DPCCH transmission plus others, thereby providing a stabilisation period.

[0020] The incremented DPCCH/DPDCH power ratio may be maintained only until the

HS-DPCCH channel ends, or the portable terminal leaves the soft handoff condition. [0021] The predetermined increment may be a value to add to the existing

DPCCH/DPDCH power ratio.

[0022] The predetermined increment may be a scaling multiplier for the DPCCH/DPDCH power ratio.

[0023] The predetermined increment may be a standard value, established on installation or calibration of the portable terminal.

[0024] The predetermined increment may be transmitted to the portable terminal in an earlier transmission from a base station.

[0025] The present invention also provides a method for increasing pilot power for high speed dedicated physical control channel, in a cellular wireless communication system, comprising the steps of: storing a predetermined target signal-to-interference ratio value increment in a storage device in a base station; in the base station, detecting the presence of a soft handover condition; in the base station, detecting that a high speed dedicated control channel (HS-DPCCH) is active; in response to positive determinations of the presence of a soft handover condition and that the HS-DPCCH channel is active; retrieving the predetermined target SIR value increment from the storage device; and applying the target SIR value increment to the target SIR value, thereby increasing the

DPCCH channel power. [0026] The DPDCH transmitted power may remain substantially unchanged, thereby maintaining a link block error rate (BLER) unchanged.

[0027] The target SIR value may be maintained for the whole duration of the high speed downlink packet access (HSDPA) call. [0028] The incremented target SIR value may be maintained for the duration of the slots of

HS-DPCCH transmission only.

[0029] The incremented target SIR value may be maintained for the duration of a number of slots encompassing HS-DPCCH transmission plus others, thereby providing a stabilisation period. [0030] The incremented target SIR value may be maintained only until the HS-DPCCH channel ends, or the soft handoff condition ends.

[0031] The predetermined increment may be a value to add to the existing target SIR value.

[0032] The predetermined increment may be a scaling multiplier for the target SIR value.

[0033] The predetermined increment may be a standard value, established on installation or calibration of the base station.

[0034] The predetermined increment may be transmitted to the base station in an earlier transmission from an associated communications system.

[0035] The present invention also provides a method for increasing pilot power for high speed dedicated physical control channel, in a cellular wireless communication system, comprising a methods as defined in the preceding paragraphs. In such a method, the predetermined target signal-to-interference ratio (SLR) value increment may equal the

DPCCH/DPDCH power ratio increment. Any such method may further comprise the step of, in the base station, detecting whether the DPCCH power has increased; and, in response to a negative detection, removing the target SIR value increment from the target SIR value. [0036] The above, and further, objects, advantages and characteristics of the present invention will become clearer on consideration of the following description of certain embodiments thereof, in conjunction with the accompanying drawings, wherein:

[0037] Fig. 1 shows a known arrangement of channels used to communicate in a known cellular communications system; and [0038] Fig. 2 shows a typical arrangement of sub-channels in one of the channels of the system illustrated in Fig. 1.

[0039] The present invention provides an autonomous and implicit (that is to say, requiring no outside control commands) procedure for the control of UE and Node B in a cellular wireless communications network, which addresses the problem of low pilot power for HS- DPCCH in soft handover (SHO) for high speed cellular systems. In particular, according to the present invention, the procedure provides autonomous, implicit changing of the DPCCH power level and/or the target SLR value for DPCCH. [0040] While in the prior art, the relative power of HS-DPCCH, represented as βhs, was fixed as equal to βc, an aspect of the present invention allows the relative power of HS- DPCCH, βhs, to be varied, as controlled by the portable equipment UE. [0041] The procedure of the present invention is preferably operative when the HS- DPCCH channel is active, and when the UE is in a soft handover condition. When either or both of these conditions becomes untrue, the procedure of the present invention preferably ends.

[0042] According to the present invention, a predetermined DPCCH/DPDCH power ratio increment is stored in the UE. This increment may be a standard value, established on installation or calibration of the UE. Alternatively, the value may be transmitted to the UE in an earlier transmission from the Node B. For example, a value could be assigned during the UE's registration procedure at the Node B. During the soft handover (SHO condition), the UE reacts by firstly detecting the presence of the SHO condition, and the fact that the HS-DPCCH channel is active. The UE then retrieves the predetermined DPCCH/DPDCH power ratio (βc/βd) increment from its memory, or other storage device. This increment is then applied to the DPCCH/DPDCH power ratio (βc/βd), thereby increasing the DPCCH channel power. The DPDCH power transmitted would remain substantially the same in order to maintain link block error rate (BLER) unchanged.

[0043] The predetermined increment may be a value to add to the existing the DPCCH/DPDCH power ratio, or it may be a scaling multiplier for the DPCCH/DPDCH power ratio.

[0044] The UE could also reverse this effect, by removing the predetermined increment when either the HS-DPCCH channel ends, or the UE leaves the SHO condition. [0045] According to another aspect of the present invention, a predetermined target SIR value increment is stored in the Node B. This increment may be a standard value, established on installation or calibration of the Node B. Alternatively, the value may be transmitted by the UE in an earlier transmission to the Node B. For example, a value could be assigned during the UE's registration procedure at the Node B. Alternatively, the increment may be established by a different communication channel to the Node B. During a soft handover (SHO condition), the Node B reacts by firstly detecting the presence of the SHO condition, and the fact that the HS-DPCCH channel is active. The Node B then retrieves the predetermined target SIR value increment from its memory, or other storage device. This increment is then applied to the target SIR value, which has the effect of increasing the DPCCH channel power. The DPDCH power transmitted would remain substantially the same in order to maintain link block error rate (BLER) unchanged. [0046] The Node B could also reverse this effect, by removing the predetermined increment when either the HS-DPCCH channel ends, or the UE leaves the SHO condition. [0047] The predetermined increment may be a value to add to the existing target SIR value, or it may be a scaling multiplier for the target SIR value.

[0048] According to one aspect of present invention, an autonomous, implicit UE procedure is provided, that solves the problem of lack of pilot power for HS-DPCCH in soft handover (SHO) for high speed cellular systems, by locally changing DPCCH power. [0049] According to another aspect of present invention, an autonomous, implicit Node B procedure is provided, that solves the problem of lack of pilot power for HS-DPCCH in soft handover (SHO) for high speed cellular systems, by locally changing DPCCH power. [0050] Either or both of the aspects of the present invention may be employed without additional signalling at the time of use. This is important, in that any new procedures intended for use in cellular wireless communications systems should not place any additional burden upon the network in terms of uplink or downlink control signalling, in order to be acceptable to the service providers operating the network. [0051] In some embodiments of the present invention, both of the above-described aspects may be used at the same time. The predetermined increments may be the same in the UE and the Node B. Typically, such increments may be of ldB step size.

[0052] The boosted DPCCH would enable efficient operation to be achieved with a slightly reduced DPDCH power, enabling a welcome reduction in overall power consumption in ^■ the UE. [0053] In a further embodiment of the present invention, the methods of the present invention may be employed to boost the power of the DPCCH channel just before the uplink HS-DPCCH 26 becomes "active", that is to say, in those timeslots of the uplink HS- DPCCH channel in which transmission takes place. This is possible, since HS-DPCCH transmission times are known in advance. An advantage of this approach is that the DPCCH power is raised only when required for HS-DPCCH signalling. This reduces the power consumed at the UE, and also removes the boosted DPCCH channel, which acts only as a noise source if no HS-DPCCH transmission accompanies it.

[0054] The present invention provides methods for increasing the power of the DPCCH to ensure reliable high speed downlink packet access, without adding extra signalling requirements, by providing a predetermined increment for increasing the DPCCH/DPDCH power ratio in the UE; and/or by providing a predetermined increment for increasing the target SIR value in the Node B. These increments are activated upon detection in the UE and/or Node B, as appropriate, that the HS-DPCCH channel is about to become active. The increments may be removed when the HS-DPCCH ceases to be active.

[0055] Explanation of abbreviations used: HSDPA high speed downlink packet access

HS-PDSCH high speed physical downlink shared channel

UE user equipment

FDD frequency division duplex

SHO soft hand over DPCH dedicated physical channel

DPCCH dedicated physical control channel

DPDCH dedicated physical data channel

HS-DPCCH high speed dedicated physical control channel

BLER block error rate SIR signal to interference ratio

SHO soft handover

FDD HSDPA FDD High Speed Downlink Packet Access

Claims

CLAIMS:

1. A method for increasing pilot power for dedicated physical channel (26), in a cellular wireless communication system, comprising the steps of: - storing a predetermined DPCCH (22)/DPDCH (22) power ratio (βc/βd) increment in a storage device in a portable terminal (12); in the portable terminal, detecting the presence of a soft handover condition; in the portable terminal, detecting that a high speed dedicated control channel (HS- DPCCH) (26) is active; - in response to positive determinations of the presence of a soft handover condition and that the HS-DPCCH channel is active, retrieving the predetermined DPCCH/DPDCH power ratio (βc/βd) increment from the storage device; and applying the DPCCH/DPDCH power ratio (βc/βd) increment to the DPCCH/DPDCH power ratio (βc/βd), thereby increasing the DPCCH channel power.

2. The method according to claim 1 wherein the DPDCH transmitted power remains substantially unchanged, thereby maintaining a link block error rate (BLER) unchanged.

3. A method according to claim 1 or claim 2 wherein the incremented DPCCH/DPDCH power ratio (βc/βd) is maintained for the whole duration of the high speed downlink packet access (HSDPA) call.

4. A method according to claim 1 or claim 2 wherein the incremented

DPCCH/DPDCH power ratio (βc/βd) is maintained for the duration of the slots of HS- DPCCH transmission only.

5. A method according to claim 1 or claim 2 wherein the incremented DPCCH/DPDCH power ratio (βc/βd) is maintained for the duration of a number of slots encompassing HS-DPCCH transmission plus others, thereby providing a stabilisation period.

6. A method according to claim 1 or claim 2 wherein the incremented DPCCH/DPDCH power ratio (βc/βd) is maintained only until the HS-DPCCH channel ends, or the portable terminal leaves the soft handoff condition.

7. A method according to any preceding claim wherein the predetermined increment is a value to add to the existing DPCCH/DPDCH power ratio.

8. A method according to any preceding claim wherein the predetermined increment is a scaling multiplier for the DPCCH/DPDCH power ratio.

9 A method according to any preceding claim wherein the predetermined increment is a standard value, established on installation or calibration of the portable terminal.

10. A method according to any preceding claim wherein the predetermined increment is transmitted to the portable terminal in an earlier transmission from a base station.

11. A method for increasing pilot power for high speed dedicated physical control channel (26), in a cellular wireless communication system, comprising the steps of: storing a predetermined target signal-to-interference ratio (SIR) value increment in a storage device in a base station (10); in the base station, detecting the presence of a soft handover condition; in the base station, detecting that a high speed dedicated control channel (HS- DPCCH) (26) is active; in response to positive determinations of the presence of a soft handover condition and that the HS-DPCCH channel is active, retrieving the predetermined target SIR value increment from the storage device; and - applying the target SIR value increment to the target SIR value, thereby increasing the DPCCH channel power.

12. The method according to claim 11 wherein the DPDCH transmitted power remains substantially unchanged, thereby maintaining a link block error rate (BLER) unchanged.

13. A method according to claim 11 or claim 12 wherein the target SIR value is 5 maintained for the whole duration of the high speed downlink packet access (HSDPA) call.

14. A method according to claim 11 or claim 12 wherein the incremented target SIR value is maintained for the duration of the slots of HS-DPCCH transmission only.

10 15. A method according to claim 11 or claim 12 wherein the incremented target SLR value is maintained for the duration of a number of slots encompassing HS-DPCCH transmission plus others, thereby providing a stabilisation period.

16. A method according to claim 11 or claim 12 wherein the incremented target SLR 15 value is maintained only until the HS-DPCCH channel ends, or the soft handoff condition ends.

17. A method according to any of claims 11-16 wherein the predetermined increment is a value to add to the existing target SIR value. 0

18. A method according to any of claims 11-17 wherein the predetermined increment is a scaling multiplier for the target SIR value.

19. A method according to any preceding claim wherein the predetermined increment is 5 a standard value, established on installation or calibration of the base station.

20. A method according to any of claims 11-19 wherein the predetermined increment is transmitted to the base station in an earlier transmission from an associated communications system.

30

21. A method for increasing pilot power for high speed dedicated physical control channel, in a cellular wireless communication system, comprising a method according to any of claims 1-10 and a method according to any of claims 11-20.

22. A method according to claim 21 is which the predetermined target signal-to- interference ratio (SIR) value increment equals the DPCCH/DPDCH power ratio (βc/βd) increment.

23. A method according to claim 21 or claim 22, further comprising the step of, in the base station, detecting whether the DPCCH power has increased as a result of the method of any of claims 1-11; and, in response to a negative detection, removing the target SIR value increment from the target SIR value.

24. A method for increasing pilot power for high speed dedicated physical control channel, in a cellular wireless communication system substantially as described.