GB2415331A - Scheduling E-DCH transmissions from a mobile terminal in soft handover - Google Patents

Abstract

A method of scheduling enhanced dedicated channel transmissions from a mobile terminal (1) in soft handover comprises determining a sub-set (2,3,5) of base stations within an active set (2 to 6) which comply with specified criteria. Base stations (4, 6) outside the sub-set are caused to cease sending scheduling information in downlink (8) to the mobile terminal.

Description

A MET1101) OT; SC1:1F,DULING A MOBILE TERMINAL IN SOFT FTANI)OVER This

invention relates to a method of scheduling a mobile terminal in soft handover, in particular lor 3"i generation mobile phone systems.

The 3r generation project partnership (3CiPP) universal mobile telecommunications system (UMTS) cellular- radio system includes a capability known as Enhanced IJplink Dedicated Channel (E-DCH, also known as HSUPA). This capability enables a mobile terminal or user equipment ([] E) to transmit data, potentially at high rates, to base stations or Node B(s) under Node B scheduling control.

The rate at which the UE can transmit using E-DCH is controlled by one or more Node I () Bs based on information describing the amount of data stored by the [JE, or the data : .... rate that the UE indicates that it requires. [ he Node B(s) indicate to the UEs the highest .

. data rates, or alternatively transmit power levels, that the [JEs are permitted to use for a .e- given period of time. .

In 3CrPP UMTS, a UE can operate in a state that is known as soft handover. In this case it communicates through more than one Node B. using dedicated channels, i.e. physical channels Flat are exclusively assigned to the UK. Where the tJE is operating in - .e . soft handover and the UE is also using E-DCH, the E-OCH can be received by some or all of the Node Bs, with the resultant data streams being combined in the radio network controller (RNC). This gives a lower data error rate for the aggregate data stream effectively enabling higher data rates to be used on E-DCH for a given UE transmit power, than would otherwise be the case when not in Sl 10. Some or all node B's in the active set may send scheduling commands to the UK. Thesc commands can consist of resource limits or "up/down" indicators. In general the UE is obliged to obey the node B off ring the lowest instantaneous data rate, or indicating "down". However, it is inefficient for every node B to schedule the 1;JE and in some cases such scheduling has a high power requirement, as well as possible erTors arising between the UE and some node E3s if there is high path loss between them.

In accordance with the present invention, a method of scheduling enhanced dedicated channel transmissions from a mobile terminal in soft handover comprises determining a sub-set of base stations within an active set which comply with specified criteria; and causing base stations outside the sub-set to cease sending scheduling information in clownlinl; to the mobile terminal.

The invention provides a method for the selection of a group of scheduling base stations from all those in the active set, which allows more error prone pairs to be discarded, so saving power requirement at those basestations and improving the chances of successful signalling between the mobile terminal and those basestations which are selected.

Preferably, the content of the sub-set is updated in response to changing radio conclitions.

Pret'erably, the speci fled criteria comprise one of being below a downlink path loss limit, or being one of a given number of base stations in the active set having the ë : .. lowest path loss. e.e

. Preferably, when the sub-set comprises a single base station, the method further comprises optirnising the mobile terminal schetlulirlg algorithms in the base station .

accordingly. .e

Measurements made by the mobile terminal may be used to determine which base stations are within the subset that is responsible for sending the scheduling information k' the terminal, and the mobile terminal indicates to each basestation, either that it has been selected for the sub-set or indicates to a non-selected basestation that it should not send scheduling information. However, in one embodiment, the measurements reported by the mobile terminal are sent directly to each base station, which then decides whether to schedule the mobile terminal.

Alternatively, determination of the sub-set of base stations is carried out in the IJMTS terrestrial radio access network basecl on measurements reported by the mobile terminal.

Preferably, signalling of the occupants of the sub-set is by means of Node B identifiers added to a MAC header of each F.-DCH transport block.

Preterably, signalling of the measurements to be used in evaluating whether to schedule the mobile terminal are added to a MAC header of each E-DCI-T transport () block sent to the node B. Alternatively, signalling of the measurements to be used in evaluating whether to schedule the mobile terminal are sent via raclio resotrce control (ARC) signalling7 to the U I RAN network.

An example of a method ol schectuling7 a mobile tenniTlal in soft handover according to the present invention will now be described with reference to the accompanying drawings in which: Figure l is a block diagram illustrating one embodiment of the method of the present invention; anal, Figures 2a and 2b illustrate how node Bus are notified of their inclusion in a I () subset of the active set using the method of the present invention. -

:.: Fig. I illustrates a first example of the present inver1tiorl. A mobile terminal I is ..

. engaged in soft handover (SHO). An active set of base stations 2, 3, 4, 5, 6 involved in the soft harldover are shown around the mobile terminal. Rather than accept scheduling commands frorm all of the base stations in the active set, the present invention allows ë the mobile terminal I to indicate one or more preferred base stations for scheduling. In UMTS the mobile terminal is a UE and the base stations are node Bs and this .. terminology will be used to describe this embodiment.

Whilst it is possible for the UP to receive scheduling commands from all of the Node B's in its active set and the UE can be required, for example, to obey the scheclrler offering the lowest instantaneous data rate, there is an advantage if only a subset of Node B's in the active set schedule the UK. The enhanced dedicated channel in UMTS lets the UE indicate its preferred Nocle B(s) for scheduling and so, the UE has to decide which ofthe Node Bs in the active set are to schedule its E-DCH transmissions. If the UF, I has a high path loss to certain Node Us 4, 6, then scheduling information may not be received, or the information may be received in error. In any case signalling requires a large amount of node B power, which is wasteful if another node B can signal more effectively with less power.

Furthermore7 there is an increased likelihood of a large uplink pathless, in which case the E-DCI:I contributes less to the overall performance and gives rise to less noise r ise than for the stronger links to the other node Bs 2, 3, 5. In these circumstances it may be better if the UE is not scheduled by the Node Bs 4, 6 with the weakest links.

slaving selected a desired subset of Node Bs, the UE continues to send uplink trasmissiors 7 to call of the Node Bs, but only the selected Node B's 2, 3, 5 allocate downlink capacity 8. The Node Bs 4, (I which have been excluded front the scheduling subset by the IJE I do not assign downlink capacity to the UK, and that capacity can be tsecl for other [JEs with which the node B communicate, where the pathless is not so significant.

The [JE'S transmissions tnetI represent a noise cost rather than a scheduled capacity cost and thus the overall system capacity can increase. As described above, the node Bs 4, 6 that do not participate in scheduling remain part ol' the active set and hence 1() receive F,-l)CH transmissions on the uplink channel 7 Prom the UE and participate in the SHO COnneCtiOrI. If, as a result of selection process, only one Node R schedules the .

:.: .' IJE, the scheduling aigoritilTns ITT the NodeB can be optimized based on the Node B .e . knowing that a UE will definitely follow its scheduling commands, rather than making an allocation of capacity without knowing if the capacity will be used, which tends to ë be more conservative. .

in the present invention the IJE I identifies which are its pret'erred scheduling Node El(s) 2, 3, 5 based OTT pathless measurements made by the UK. The pathless .. measurements that are made by the UE can be based OT1 the common pilot indication channel (CPICH) received signal code power (RSCP) measurement that is already defined in UMTS. This preference is then signalled to all Node Bs that are in the soft hanclover group via the uplink 7. The subset of scheduling Node Bs can be selected, t'or example, on the basis of having downlink path losses that fall within thresholds signalled to it by the network. Alternatively, they can be selected as the 'n' cells that have the lowest path loss or they can be selected on a basis of a combination of these two methods.

(he preferred subset of Nocle B's can be signalled frequently to all the Node Bs in the active set, allowing adaptation to changing radio conditions. One method of signalling the preferred Node Bs is to include their identifiers jTT the media access control (MAC) header that is included in each E-DCH transport block, i.e. the block of data that is transmitted in one E-DCH TTI, where transmission time interval (TTI) denotes the forward error correction (FEC) coding interleaving period. This is illustrated in Fig. 2. Fig. 2a illustrates MAC protocol data units (PDU) showing PDU, MAC-d header and MAC-e header including multiplexing, scheduling information and indication of schecJuliTl node B. Fig. 2b shows MAC PDU showing PDU, MAC-d header and MA('-e header including multiplexing, scheduling infonnation and an indication of dcwnlirlk (Dl,) pathless from each Bs. An alternative is to use physical layer signalling, although this is more costly for the [JE h1 teens of transmit power and more costly for tile network in teens of interference resource.

An alternative to the UE signalling to the node B that is to do scheduling is that the RSCP measurement is reported by the UF. directly to the node B. and the node B then determines whether it should schedule E-DCI I transmissions to the UK. For example, the Node B can decide whether it should schedule tor the UE for a period of time, based upon whettler the measurements indicate that the path loss exceeds a .

threshold value. .e.

.. Alternatively, the method of the present invention can be carried out by letting the IJMTS radio access network (IJTRAN) select the preferred scheduling cells based ë on measurements of CPICE I RSC:I' provided by the UK, rather than letting the UE or Node B make the ciecision directly. A UE can, by existing standards clescription, be : commanded to send CPICII RSCP measurement reports to the UTRAN which enable a . choice of preferred scheduling Node Us to be made within the UTRAN network.

However, these measurements are made to the serving RNC (SRNC), which terminates the UEs core network, lu, connection, rather than being made to the one or more controlling RNCs (CRNC) that control the Node Bs. The SYNC signals the preferred Node Bs to the CRNCs which indicates this to the Node Bs. This option is not able to respond as quickly to radio path changes as when the UJ: identifies which are its preferred scheduling Node Bs, based on measurements made by the UK.

Claims (9)

1. A method of scheduling enhanced dedicated channel (E-DCH) transmissions from a mobile terminal in soil handover-; the method comprising determining a sub-set of base stations within an active set which comply with speci tied criteria; and causing base stations outside the sub-set to cease sending schedtrling information in downlink to the mobile tenninal.

2. A method according to claim I, wherein the content of the sub-set is updated in 1() response to changing radio conditions. .

:.: ..

3. A method according to claim I or claim 2, wherein the specified criteria comprise one of being below a downlink path loss limit, or being one of a given number of base stations in the active set having the lowest path loss. ë .

4. A methotl according to any preceding claim, wherein when the sub-set comprises a single base station, the method f;trthtr comprises optimising the mobile .. terminal scheduling algorithms in the base station accordingly.

2()

5. A method according to any preceding claim wherein measurements made by the mobile terminal are used to determine which basestations are within the sub-set that is responsible for sending scheduling information to the terminal, and the mobile terminal indicates, by signalling to each basestation, either that it has been selected for the sub-set or indicates to a norl-selected basestation that it should not send scheduling inf'onnation.

6. A method according to any of clahns I to 4, wherein the measurements reported by the mobile terminal are sent directly to each base station, which then decides whether to schedule the mobile terminal.

7. method according to any ot'claims I to 4, wherein determination of the sub set ot'base stations is carried out in the universal mobile telecommunications system (UMTS) terrestrial radio access network (U IRAN) based on measurements reported by the mobile terminal.

8. A method according to any preceding, claim, wherein sigr,nalling of the occupants of the sub-set is by means of Nocie B identifiers acided to a media access control (MAC) treader ofeach E-DCtI transport block.

9. A method aceorcling, to any preceding claim, wherein signalling of the measurements to be used in evaluating whether to schedule the mobile terminal are I O added to a MAC' heacier of each F-l)(:H transport block sent to the node B. . I (). A method according, to any of claims I to 8, wherein sig,nalling, of the .e . measurements to be used in evaluating whether to schedule the mobile terminal are sent via radio resource control (ARC') sig,nalling to the UTRAN network. ë ë

I 1. A method of scheduling enhanced dedicated charinel transmissions from a mobile terminal in soft handover as hereinbefore described with reference to the . .. aeeompanymgdrawmg,s.