WO2008096326A2

WO2008096326A2 - A method for signalling of power control command combining window

Info

Publication number: WO2008096326A2
Application number: PCT/IB2008/050448
Authority: WO
Inventors: Matthew P.J. Baker; Timothy J. Moulsley
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-02-07
Filing date: 2008-02-07
Publication date: 2008-08-14
Also published as: WO2008096326A3

Abstract

The present invention relates to a method for controlling power of a channel from a secondary station to a primary station, said method comprising the steps of a) at the primary station indicating a plurality of TPC commands to be applied by the secondary station, and b) signaling a combination parameter from UTRAN to indicate to the secondary station which TPC commands are to be combined. Wherin the combination parameter is a window size and/or an offset from a time reference. The method is provided for the cases of soft handover (SHO), non-SHO and softer handover.

Description

A METHOD FOR SIGNALLING OF POWER CONTROL COMMAND

COMBINING WINDOW

FIELD OF THE INVENTION

The present invention relates to method for signalling power control command from a primary station to secondary station.

This invention is, for example, relevant for telecommunication networks, and especially for mobile communication networks like UMTS networks comprising a plurality of primary stations or Base Stations or Node B's and a plurality of secondary stations or Mobile Stations or User Equipments. More specifically, this invention applies for communication systems employing closed loop power control, such as UMTS or cdma 2000.

BACKGROUND OF THE INVENTION

In a mobile telecommunication system enabling a closed loop power control, a primary station sends power indications to a secondary station which adjusts its transmission power in accordance with these power indications. More specifically, these indications are an indication of the sign of a power change to be applied to the transmission power, i.e. increase/decrease the transmission power. As will be explained further, some problems of synchronization and offset of the Downlink (from the primary station to the secondary station) and of the Uplink (from the secondary station to the primary station) has to be solved.

These problems of offset are more present when the secondary station is currently carrying out an handover, i.e. the secondary station is currently switching from a first cell to another. During the handover, the secondary station is linked to a plurality of cells, which can be controlled by different primary stations, having transmitting their power indications at different times. Because of that, and as will be explained hereafter, the secondary station receives some power indications too late to be processed in the current time slot, leading to a not accurate power closed loop. SUMMARY OF THE INVENTION

It is an object of the invention to propose a method enabling to solve the above mentioned problems.

Another object of this invention is to provide a method which allows to improve the power closed loop in particular in case of handover.

To this end, in accordance with the invention it is proposed a method for controlling power of a channel from a secondary station to at least one primary station, said method comprising the steps of a) at the primary station indicating a plurality of power indications to be applied by the secondary station, and b) signaling a combination parameter to indicate to the secondary station which power indications are to be combined.

As a consequence, the secondary station knows which power indications are to be combined, and the secondary station is not in an ambiguous situation to work out which power indications are to be combined.

The present invention also relates to a primary station comprising means for carrying out the method of the invention.

Another aspect if the invention relates to a secondary station comprising means for carrying out the method of the invention.

These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, wherein:

Fig.l is a time chart representing the uplink and downlink signals in accordance with a conventional method;

Fig.2 is a time chart representing the uplink and downlink signals in accordance with a conventional method;

Fig.3 is a time chart representing the uplink and downlink signals in accordance with a conventional method;

Fig.4 is a time chart representing the uplink and downlink signals in accordance with a conventional method; Fig.5 is a time chart representing the uplink and downlink signals in accordance with a conventional method;

Fig.6 is a time chart representing the uplink and downlink signals in accordance with a conventional method;

Fig.7 is a time chart representing the uplink and downlink signals in accordance with an embodiment of the invention; and

Fig.8 is a time chart representing the uplink and downlink signals in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for signalling power commands in a closed loop power control for stations communicating in a network.

The present invention is more especially dedicated to telecommunication systems as mobile telecommunication networks as UMTS, or GSM.

In 3GPP a modification to the UMTS, FDD F-DPCH (Fractional Data Packet Channel) is under discussion. So far it has been proposed to relax the timing restrictions for F-DPCH so that up to 10 users can be accommodated on each SF256 code in the downlink, thus maximising the code-saving ability of the F-DPCH. Different slot formats are introduced for F-DPCH, enabling the Transmit Power Commands (TPC) symbol to be positioned at any point in the slot, and the power control timing is modified accordingly.

In Rel-6, the uplink TPC commands are received approx 512 chips before the start of the pilot field where the uplink transmit power change takes place. This is shown in Fig.l (simplified to show only the UL power control).

With the enhanced F-DPCH, some or all of the TPC commands will often arrive too late for the uplink transmit power to be changed at this point, so it is proposed to delay the power change until the start of the first pilot field at least 512 chips after the last TPC command is received, as shown in Figure 2. This proposal is reasonable for the case without soft handover.

Soft-Handover (SHO) case

The specified method for combining TPC commands in SHO includes that the UL transmit power shall be reduced if a reliable "down" command is received from any of the radio link sets (RLSs). A RLS comprises all the communications from primary station to a secondary station (UE). In case of Soft Handover, the secondary station is currently switching from a cell to another and receives from a plurality of RLS. If all the cells involved in an handover are from a single primary station, the handover process is called Softer Handover, and will be discussed hereafter. This means that if any of the radio link sets has an Enhanced F-DPCH slot format with the TPC command in either of the first two positions of the slot, the UE does not need to take into account any of the later TPC commands when determining the power change if a reliable "down" command is already received. As the response to "down" commands is the most important for controlling RoT, it is better in such a situation to avoid delaying the transmit power reduction for another slot. This situation is illustrated in Fig.3.

Note that with a purely random allocation of time offsets for the RLSs in a UE's active set, at least one radio link's (RL's) TPC command would be received in the first two positions 53% of the time when three radio links are in the active set. In practice the proportion would be likely to be significantly higher, as it would benefit the network to preferentially allocate early positions whenever possible. Fig.3 shows a Soft Handover case with at least one F-DPCH with TPC command in one of the first two positions.

We also observe that there is likely to be some variation in the loop delay for the UL TPC for different RLSs: Due to the different timing offsets for the TPC commands, some TPC commands in a slot may be derived from different uplink pilot fields, as illustrated in Fig.4. This is clearly within the freedom of the network implementation. Note that the propagation delay shown in corresponds to a cell radius of 2km, whereas Figs.l to 3 illustrate a "worst case" of 20km. Fig.4 shows the derivation of uplink TPC commands for different TPC command timing offsets.

In view of the above observations, it no longer seems appropriate necessarily to combine the TPC commands received in SHO on the basis of the downlink slot in which they were sent. For the enhanced F-DPCH, the downlink slot boundaries are effectively in arbitrary positions.

It has therefore been suggested that the combining of TPC commands in SHO should instead be done according to the time window in which they are received and able to be applied to the uplink. This would mean that early-arriving TPC commands in one slot would be combined and processed quickly, while late-arriving TPC commands in the same slot would be combined and acted on at the later slot boundary. Specifically, it has been suggested that the combining window should include all TPC commands received with the last 8 offsets in slot n-\ and the first 2 offsets in slot n (where the notation "«" is used here purely for convenience) (where one offset is 256 chips, being one tenth of a timeslot). This is illustrated in Fig.5 which represents a proposed time window for combining of TPC commands in SHO with Enhanced F- DPCH. Note that in practice the different F-DPCHs will each be received at the UE with slightly different timing offsets due to the propagation delays, but for the sake of simplicity this is ignored in Fig.5 and the TPC commands are illustrated diagrammatically as arriving on the same physical channel.

Softer Handover

A special case would occur if the UE was in softer handover. In this case, all the uplink TPC commands received on one RLS in the same DL slot are known to be the same since they are coming from a single primary station as explained above. Typically, The UE could therefore soft-combine the TPC commands from one RLS within one DL slot, and then combine the result with any TPC commands received from other RLSs in one of the TPC command combining windows indicated in Fig.5. An example of combining TPC commands in softer handover in this way is shown in Fig.6. Fig.6 shows the combining of TPC commands in soft- and softer-handover. While the approach shown in Figure 6 allows an unambiguous specification of combining of power control commands, it has some drawbacks:

(1) The "TPC commands which are known to be same" (i.e. from one Node B), must lie within a single slot. This may not always be convenient, or possible, depending, for example, on the timing of the pilot field which is used to make the power measurement, and the processing time needed by the Node B (as shown in Fig.4).

(2) Processing of some TPC commands at the UE (e.g. those received at the start of the slot), may be unnecessarily delayed until the end of the slot, whereas they could in principle have been used to adjust power at the start of the previous Uplink pilot field.

According to the invention, signalling is provided from a primary station to a secondary station to indicate which TPC commands should be combined when deriving a power change to be made at a particular time instant. This can be in the form of a window of a particular size, offset from a time reference such as a slot boundary.

This flexibility largely solves both the problems mentioned above. The window may be defined to be of duration 1 slot, but could be shorter.

Either or both of the window duration and offset may be signalled.

More than one set of window and offset may be defined simultaneously, preferably non-overlapping. The window and offset may be specified independently for each Radio Link Set.

The indication may correspond to setting the window to cover TPC commands derived (or assumed to be derived) from a particular uplink pilot field.

In a first embodiment, shown on Fig.7, the combining of TPC commands in soft- and softer-handover, is configured with a window shifted to allow all the TPC commands to be derived from the same UL pilot field.

In a second embodiment, shown on Fig.8, the combining of TPC commands in soft- and softer-handover is configured with two windows, which allows received TPC commands to be used as soon as possible.

The signalling may also be implicit: For example, a rule may be predetermined that TPC commands from a RLS from which the first TPC command in a slot is received after offset X shall be acted upon at slot boundary Y, while TPC commands from other RLSs shall be acted upon at slot boundary Y-I. The offset X may be signalled or predetermined.

It is to be noted that the present invention is not limited to the examples described above and can be adapted. For instance, it is to be understood that in some adaptations, the role of the primary station may be a mobile station and the secondary station may be a base station. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

1. A method for controlling power of a channel from a secondary station to a primary station, said method comprising the steps of a) at the primary station indicating a plurality of power indications to be applied by the secondary station, and b) signaling a combination parameter to indicate to the secondary station which power indications are to be combined.

2. The method of claim 1, wherein the combination parameter comprises a window size.

3. The method of claim 1 or 2, wherein the combination parameter comprises an offset from a time reference.

4. The method of claim 3, wherein the power indications are sent within a timeslot, and wherein the time reference is a boundary of the timeslot.

5. The method of any of the preceding claims, wherein the primary station communicates to the secondary station over a plurality of cells, and wherein step a) comprises signaling a power indication for each cell.

6. The method of any of the preceding claims, wherein the secondary station communicates with at least one further primary station, and wherein each primary station transmits a combination parameter.

7. A primary station comprising means for controlling power of a channel from a secondary station to the primary station, said primary station further comprising means for indicating a plurality of power indications to be applied by the secondary station, and means for signaling a combination parameter to indicate to the secondary station which power indications are to be combined.

8. A secondary station comprising means for controlling power of a channel from the secondary station to a primary station, said secondary station further comprising means for receiving a plurality of power indications to be applied by the secondary station, means for receiving a combination parameter to indicate to the secondary station which power indications are to be combined, and means for combining the received power indications in accordance with the combination parameter.