WO2011142698A1

WO2011142698A1 - Method and apparatus for improving dl transmission power related to ues in state cell_fach

Info

Publication number: WO2011142698A1
Application number: PCT/SE2010/050514
Authority: WO
Inventors: Hans Hannu; Mårten ERICSON; Jinhua Liu; Rui Fan
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2010-05-11
Filing date: 2010-05-11
Publication date: 2011-11-17

Abstract

A method (400) in a controlling node (105) for scheduling UEs (115) in a CELL_FACH state (405) in a cell (110) in a WCDMA system (100). The method comprises receiving (410) RRC measurement reports from UEs, and further comprises: • assigning (415) a validity time period, TVALID, to RRC measurement reports from UE, • determining (420) an RRC measurement report's age t from when the RRC measurement report is received from the UE, • establishing (425) a priority order between the UEs using the age f of the UEs1 RRC measurement reports, • scheduling (426) the UEs for transmissions from the controlling node based on the priority order, with a UE being given a higher priority the newer that its RRC measurement report is, • excluding (435) a UE from said priority order if the validity time period of its RRC measurement report has expired, i.e. t ≥ TVALID-

Description

Method and apparatus for improving DL transmission power related to UEs in state CELL FACH

TECHNICAL FIELD

The present invention discloses a method and apparatus for a WCDMA system for downlink transmissions to UEs in the CELL_FACH state.

BACKGROUND

In a system for Wideband Coded Division Multiple Access, a WCDMA system, a User Equipment (UE), can be in a number of different states, one of which is the so called CELL_FACH state. Other states which are possible for a User Equipment in a WCDMA system include the following: Idle, CELL_DCH, URA_PCH and CELL_PCH. A User Equipment is shifted from one state to another depending on the need for throughput and power usage.

The CELL_FACH state is characterized by the following:

• No dedicated physical channel is allocated to the User Equipment,

• The User Equipment continuously monitors a FACH, Forward Access Channel, in the downlink,

· The User Equipment is assigned a default common or shared transport channel in the uplink, e.g. RACH, Random Access Channel, which it can use anytime according to the access procedure for that transport channel,

• The position of the User Equipment is known by the UTRAN, the UMTS Terrestrial Radio Access Network, on cell level according to the cell where the User Equipment last made a cell update,

The CELL_FACH state is beneficial to use in that it is a state in which a User Equipment does not use dedicated channels and thus has a lower resource usage than in, for example, the CELL_DCH state. However, a drawback of having a User Equipment in the CELL_FACH state is that the User Equipment's throughput in both uplink and downlink is generally lower than, for example, in the CELL_DCH state. Recently, the CELL_FACH state has been enhanced in that the HS-DSCH, High Speed Downlink Shared Channel, has been activated for DL, downlink, transmissions to User Equipments in the CELL_FACH state. At present, the DL transmission margins for HS-DSCH to User Equipments in CELL_FACH are sometimes large, which may in some cases lead to a waste of resources. The same problem can be anticipated for other channels which will be made available for DL transmissions to User Equipments in the CELL_FACH state.

SUMMARY

A purpose of the present invention is to obviate the problem of overly large transmission margins for DL transmissions to User Equipments in the CELL_FACH state in a Wideband Coded Division Multiple Access system. The solution should suitably be possible to apply to a number of Wideband Coded Division Multiple Access channels, such as, for example, the HS_DSCH.

This purpose is achieved by the invention in that it discloses a method in a controlling node for handling a scheduling process of user equipments which are in a CELL_FACH state in a cell. The controlling node is comprised in a Wideband Code Division Multiple Access communications system and serves the cell. The method comprises receiving Radio Resource Control, RRC, measurement reports from one or more User Equipments, and further comprises: assigning a validity time period, TVALID. to received RRC measurement reports from said one or more User Equipments,

determining an RRC measurement report's age r from the point in time when the RRC measurement report is received from the User

Equipment,

establishing a priority order between the User Equipments using the age f of the User Equipments' RRC measurement reports,

scheduling the User Equipments for transmissions from the controlling node based on the priority order, with a User Equipment being given a higher priority the newer that its RRC measurement report is, excluding a User Equipment from said priority order if the validity time period of its RRC measurement report has expired, i.e. t≥ TVALID-

Thus, by means of the invention, it is possible to use resources in a more efficient manner than previously, since User Equipments with newer RRC measurement reports can be prioritized, and the information comprised in the RRC reports of such User Equipments will be more "up to date" than those of other User Equipments. In one embodiment, the priority order of the invention is used together with the User Equipments' radio channel quality in the scheduling, with User Equipments being given higher priority the better that their radio channel quality is. Thus, in such an embodiment, the priority order of the invention is used to choose among a number of User Equipments who all have a "valid" RRC report, but have differing radio channel quality. The radio channel quality is here used as an additional criterion for scheduling a User Equipment for DL transmissions, since the controlling node may have a limitation such as, e.g. processing power, and the number of User Equipments which have a valid RRC report can be large. In one embodiment of the method of the invention, User Equipments whose radio channel quality is below a predetermined threshold are excluded from being scheduled for transmissions from the controlling node at a future point in time.

In one embodiment of the method of the invention, the margins for transmissions to User Equipments which are scheduled to receive transmissions are increased in inverse proportionality to the age t of a User Equipment's RRC measurement reports, so that larger margins are used for User Equipments with older RRC measurement reports.

In one embodiment of the method of the invention, the validity time period TVALID. for received RRC measurement reports from a User Equipment is chosen depending on the User Equipment's radio channel quality, and is chosen to be smaller than or equal to the system's RRC measurement report interval. In an alternative embodiment, T_VALID is a system parameter which is common within at least a cell of the system. In such an embodiment, TVALID is suitably set according to the average of the radio channel quality for the UEs in the cell, i.e. a high average value of the UEs' radio channel quality leads to a longer TVALID and a low average of the UEs' radio channel quality leads to a shorter TVALID. although TVALID is still chosen to be smaller than or equal to the system's RRC measurement report interval. In yet another embodiment in which TVALID is a system parameter, TVALID is chosen according to the radio channel quality of the User Equipment which has the poorest radio channel quality, but still chosen to be smaller than or equal to the system's RRC measurement report interval. The term "system parameter" as used here suitably refers to one or more cells within a WCDMA system. In one embodiment, the method of the invention is used for transmissions from the controlling node to the User Equipments on the WCDMA HS-DSCH channel. These and other embodiments will be described in more detail in the following description. The invention also discloses a controlling node, a NodeB, for a WCDMA system which is arranged to function according to the method of the system. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, with reference to the appended drawings, in which

Fig 1 shows an overview of a system in which the invention is applied, and Figs 2 and 3 illustrate principles of the invention, and

Fig 4 shows a schematic flow chart of a method of the invention, and

Fig 5 shows a schematic block diagram of a controlling node of the invention.

DETAILED DESCRIPTION

Fig 1 shows an overview of a system 100 in which the invention can be applied. The system 100 is a WCDMA communications system, .

As shown in fig 1 , the WCDMA system 100 comprises one or more cells 110. Each cell can accommodate one or more UEs 115, User Equipment, and for each cell there is a controlling node 105, a so called NodeB, through which all traffic to and from UEs in the cell is routed.

As mentioned previously, a UE in a WCDMA system can be in a number of different states. These states include the following: Idle, URA_PCH, CELL_FACH and CELL_DCH. Recently, the WCDMA standard has been enhanced in that the HS-DSCH, High Speed Downlink Shared Channel, has been activated for DL transmission to UEs in the CELL_FACH state. Although downlink transmission to UEs in the CELL_FACH state offers a number of improvements over DL CELL _FACH, one issue that needs to be resolved is the so called transmission margin used in downlink, DL, transmission, i.e. transmissions from the NodeB to a UE. This problem is addressed by the present invention by means of a solution which will be describe below with reference to the WCDMA channel known as HS-DSCH, High Speed Downlink Shared Channel. It should however be understood that this channel is merely used as an example in order to facilitate the reader's understanding of the invention, and should not be used to restrict the scope of protection sought for nor granted to the invention. The invention can in principle be applied to any channel used for DL transmissions to UEs in the CELL_FACH state.

In a WCDMA system the UEs supply the NodeB of their cell with so called Radio Resource Control, RRC, measurement reports in order to supply the NodeB with information on the channel conditions to the UE. The RRC measurement reports are supplied to the NodeB by the UEs in the following manner: the UEs transmit the RRC measurement reports to the NodeB which forwards them to the RNC, the Radio Network Controller, where the RRC measurement reports are interpreted and then sent to the NodeB.

The RRC measurement reports are supplied to the NodeB at time intervals or with a periodicity which are defined in the system. A principle of the invention is to assign a validity time period to each RRC report from a UE, the validity time period here being referred to as TVALIO- In addition, according to the invention, the "age", f, of a UE's last RRC report is taken into account when scheduling transmissions to the UE from the NodeB, so that UEs with newer RRC reports are given priority over UEs with older RRC reports. In this manner, the DL margin can be kept down, since a newer RRC report can be considered to comprise more reliable information than an older one, and accordingly, the DL margin for "degraded information" in the RRC report can be reduced. The principle of TVALID and the "age" of an RRC measurement report are also illustrated in figs 2 and 3: fig 2 shows three consecutive RRC measurement reports from a UE to its NodeB. Each RRC measurement report is assigned a validity time period TVALID. as shown in fig 2, which also shows a maximum time length, TMAX, during which a UE may be excluded from the scheduling.

If a UE's RRC measurement report is newer than TVALID, the UE is scheduled for a DL transmission on the HS-DSCH channel from the NodeB, and if not, the scheduling of DL HS-DSCH transmission to the UE will be delayed until the UE supplies the NodeB with an RRC measurement report which is newer than TVALID at the time of scheduling.

Suitably, the validity time period, TVALID. for received RRC measurement reports from a UE is chosen depending on the UE's radio channel quality, and is chosen to be smaller than or equal to the system's RRC measurement report interval. The term "radio channel quality" which is used here and throughout in this document should not be confused with the channels used in the WCDMA system, but refers to the quality of the radio connection between the UE and the eNodeB. In, for example, rural areas, the radio channel quality will typically vary little and slowly, while it may vary frequently in urban areas. In areas in which the radio channel quality varies little, a longer TVALIO should be chosen, while in areas in which the radio channel quality varies greatly, a shorter TVALID should be chosen. Fig 3 shows how the downlink, DL, margin and the scheduling priority of a UE vary over the "lifetime" of TVALID: A UE which has a completely new RRC measurement report can be given a low or near zero link margin, while the priority of the UE for being scheduled in HS-DSCH in CELL_FACH decreases as the "age" of the RRC measurement report increases and approaches TVALID, while the DL margin grows.

Thus, the "age", f, of a UE's RRC measurement report can be used by the NodeB of the cell in order to establish a priority order among the UEs, and to use this priority order when scheduling UEs for HS-DSCH in CELL_FACH transmissions at a future point in time.

It should be noted that in one aspect of the invention, the priority order established by means of the age of the UEs' RRC measurement reports is used together with the radio channel quality in order to schedule UEs for HS- DSCH in CELL_FACH transmissions at a future point in time, so that the priority order as such is used in order to determine which UEs that the NodeB should calculate a priority order for at all, and those UEs are then scheduled with an additional priority being given to UEs which have a good radio channel quality. This is due to the fact that the amount of UEs may be such that the NodeB's processing power is not sufficient for all UEs which have sufficiently new (i.e. newer than TVALID) RRC measurement reports.

According to the invention, TVALID is a configurable system parameter, and, as has emerged from the description above, a User Equipment is excluded from the priority order if the validity time period of its RRC measurement report has expired, i.e. t ≥ TVALID- However, in one embodiment of the invention, a UE is not excluded from the priority order for a longer time interval than an upper limit TMAX, which is suitably chosen to be shorter than the time which is necessary for the system to perform a chosen number of re-transmissions for an upper layer protocol's PDU, Protocol Data Unit. One such upper layer protocol is the RLC, Radio Link Control, protocol, which, for example, issues a removal of the received parts of an SDU, Service Data Unit, in case its peer entity is missing a corresponding PDU caused by the number of re-transmissions for the PDU having been done without reception of a corresponding acknowledgement at the sending entity. Hence, in this embodiment, when "the age" of a UE's TVALID exceeds TMAX, the UE will again be part of the priority order, in one embodiment with an extra high priority.

Fig 4 shows a schematic flow chart of a method 400 of the invention. Steps which are options or alternatives are indicated by means of dashed lines in fig 4. The method 400 is, as has been explained above, intended for use in a controlling node for handling a scheduling process of user equipments which are in a CELL_FACH state in a cell, as indicated in step 405. The controlling node is comprised in a Wideband Code Division Multiple Access communications system and serves the cell.

As indicated in step 410, the method comprises receiving RRC measurement reports from one or more UEs. The method further comprises:

• assigning, step 415, a validity time period, TVALID. to received RRC measurement reports from the one or more UEs, • determining, step 420, an RRC measurement report's age t from the point in time when the RRC measurement report is received from the UE,

• establishing, step 425, a priority order between the User Equipments using the age f of the User Equipments' RRC measurement reports,

• scheduling, step 426, the User Equipments for transmissions from the controlling node based on the priority order, with a User Equipment being given a higher priority the newer that its RRC measurement report is,

· excluding, step 435, a UE from said priority order if the validity time period of its RRC measurement report has expired, i.e. t≥ TVALID-

Suitably, the UEs who are scheduled are taken from a so called common priority queue in a scheduling unit in the NodeB, with the age t of the RRC measurement reports being used as described above as an instrument to create a priority order among those UEs.

In one embodiment of the method of the invention, as shown in step 430, the priority order is used together with the UEs' radio channel quality in the scheduling, with UEs being given higher priority the better their radio channel quality is. In one such embodiment of the method of the invention, UEs whose radio channel quality is below a predetermined threshold are excluded from being scheduled for transmissions from the controlling node at the future point in time.

In one embodiment of the method of the invention, the validity time period, T VALID, for received RRC measurement reports from a UE is chosen depending on the UE's radio channel quality, and is chosen to be smaller than or equal to the system's RRC measurement report interval. Thus, in this embodiment, TVALID is an individual parameter per UE, depending on the UE's radio channel quality. However, in an alternative embodiment, TVALIO is a system parameter which is common for the UEs within at least a cell of the system. In such an embodiment, TVALID is suitably chosen as an average of the radio channel quality for the UEs in the cell, but still smaller than or equal to the system's RRC measurement report interval. In yet another embodiment in which TVALID is a system parameter, TVALID is chosen according to the User Equipment in the system which has the poorest radio quality, but still chosen to be smaller than or equal to the system's RRC measurement report interval. The term "system parameter" as used here suitably refers to a system which comprises one or more cells within a WCDMA system.

In one embodiment of the method of the invention, the margins for transmissions to UEs who are scheduled are increased in inverse proportionality to the age f of the UEs' RRC measurement reports, so that larger margins are used for UEs with older RRC measurement reports. The term "margins" here refers to either the output power used in the DL HS- DSCH transmission or to the TFC, Transport Format Combination, i.e. code and modulation scheme and carried bits, or to a combination of the two, i.e. both the output power used in the HS-DSCH in CELL_FACH transmission and the TFC.

The TFC for a transmission to a UE is suitably determined by a special function or block for this in the NodeB, the scheduler.

According to the invention, the margin for a HS-DSCH in CELL_FACH transmission to a UE can be adjusted with respect to the "age" of the UE's RRC measurement report in at least two ways: By using the TFC which is determined by the NodeB's scheduler, and adjusting the output power used in the transmission.

By adjusting the TFC which is determined by the NodeB's scheduler, i.e. by "shrinking" the TFC in terms of, for example, the amount of data comprised in the TFC.

Fig 5 shows a schematic block diagram of components of a NodeB 500 of the invention, where the components shown in fig 5 are those components of the NodeB 500 which are mainly involved in carrying out the invention. As mentioned previously, the NodeB 500 of the invention is a controlling node for a cell in a WCDMA system, and is arranged to receive Radio Resource Control, RRC, measurement reports from one or more User Equipments in the cell which are in the CELL_FACH state. The reception of the RRC measurement reports is symbolically indicated by means of an arrow in fig 5.

As indicated in fig 5, the inventive NodeB 500 comprises the following units, which is to be seen as a non excusive list of components in the NodeB 500: an assigning unit 510 which is configured to assign a validity time period, T ALID_I to received RRC measurement reports from the one or more User Equipments,

a determining unit 515 which is configured to determine an RRC measurement report's age f from the point in time when the RRC measurement report is received from the User Equipment,

a priority handling unit 520 which is configured to establish a priority order between the User Equipments using the age t of the User Equipments' RRC measurement reports, • a scheduling unit 525 which is configured to schedule the User Equipments for transmissions from the controlling node based on the priority order, with a User Equipment being given a higher priority the newer that its RRC measurement report is.

In addition, the priority handling unit 520 is also configured to exclude a User Equipment from the priority order if the validity time period of its RRC measurement report has expired, i.e. t≥ TVALID- The invention can be designed as a "stand alone" unit in the NodeB 500 of the invention, i.e. the components shown in fig 5 can be designed as one or more separate units in the NodeB 500, but in a preferred embodiment the invention is realized as an extension of a scheduling unit and/or a control unit of the NodeB 500. It should be realized that this embodiment of the invention can be realized in a number of ways, i.e. with all of the features of the invention in either the scheduling unit or the control unit or in a combination of those two units.

Suitably, the UEs which are scheduled are taken from a so called common priority queue in a scheduling unit in the NodeB, with the age of the UEs' RRC measurement reports being used as described above as an instrument to create a priority order among those UEs.

In one embodiment, the NodeB 500 is arranged to use the User Equipments' radio channel quality in establishing the priority order, with User Equipments being given a higher priority the better their radio channel quality is. In one embodiment, the NodeB 500 is arranged to exclude UEs whose radio channel quality is below a predetermined threshold from being scheduled for transmissions from the controlling node at a future point in time. In one embodiment, the NodeB 500 is arranged to increase the margins for transmissions to UEs who are scheduled to receive transmissions in inverse proportionality to the age f of a UEs' RRC measurement reports, so that larger margins are used for UEs with older RRC measurement reports. In one embodiment, the NodeB 500 is arranged to set the validity time period, TVALID, for received RRC measurement reports from a UE depending on the UE's radio channel quality, and is set as smaller than or equal to the system's RRC measurement report interval. However, in an alternative embodiment, TVALID is a system parameter which is common within at least a cell of the system. In such an embodiment, TVALID is suitably set as an average of the radio channel quality for the UEs in the cell, but still smaller than or equal to the system's RRC measurement report interval. In yet another embodiment in which TVAUD is a system parameter, TVALID is set according to the User Equipment within the cell or cells which has the poorest radio quality, but still smaller than or equal to the system's RRC measurement report interval. The term "system parameter" as used here suitably refers to one or more cells within a WCDMA system.

In one embodiment of the NodeB 500, the transmissions to the UEs in the cell are on the HS-DSCH in CELL_FACH channel.

The invention is not limited to the examples of embodiments described above and shown in the drawings, but may be freely varied within the scope of the appended claims. ABBREVIATIONS

The following abbreviations and acronyms have been used in this document:

CELL_DCH: A UE state in a WCDMA system

CELL_FACH: A UE state in a WCDMA system

CELL_PCH: A UE state in a WCDMA system

DL: Downlink

FACH: Forward Access Channel

HS-DSCH: High Speed Downlink Shared Channel

NodeB: A controlling node for a cell in a WCDMA system

PDU: Protocol Data Unit

RACH: Random Access Channel

RRC: Radio Resource Control

RNC: Radio Network Controller

SDU: Service Data Unit

TFC: Transport Format Combination

UE: User Equipment

UMTS: Universal Mobile Telecommunications System

UTRAN: UMTS Terrestrial Radio Access Network

URA_PCH: A UE state in a WCDMA system

WCDMA: Wideband Code Division Multiple Access

Claims

1. A method (400) in a controlling node (105) for handling a scheduling process of user equipments (1 15) which are in a CELL_FACH state (405) in a cell (1 10), which controlling node (105) is comprised in a Wideband Code Division Multiple Access communications system (100), and which controlling node (105) serves the cell (110), the method comprising receiving (410) Radio Resource Control, RRC, measurement reports from one or more User Equipments, the method being characterized in that it further comprises:

• assigning (415) a validity time period, TVALID, to received RRC measurement reports from said one or more User Equipments,

• determining (420) an RRC measurement report's age t from the point in time when the RRC measurement report is received from the User Equipment,

• establishing (425) a priority order between the User Equipments using the age r of the User Equipments' RRC measurement reports,

• scheduling (426) the User Equipments for transmissions from the controlling node based on the priority order, with a User Equipment being given a higher priority the newer that its RRC measurement report is,

• excluding (435) a User Equipment from said priority order if the validity time period of its RRC measurement report has expired, i.e. r≥ TVALID-

2. The method (400) of claim 1 , according to which the User Equipments' radio channel quality is used when establishing the priority order, with User Equipments being given a higher priority the better their radio channel quality is.

3. The method (400, 430) of claim 2, according to which User Equipments whose radio channel quality is below a predetermined threshold are excluded from being scheduled for transmissions from the controlling node at a future point in time.

4. The method (400, 430) of any of claims 1-3, according to which the margins for transmissions to User Equipments which are scheduled to receive transmissions are increased in inverse proportionality to the age t of a User Equipment's RRC measurement reports, so that larger margins are used for User Equipments with older RRC measurement reports.

5. The method (400, 430) of any of claims 1-4, according to which the validity time period, TVALID. for received RRC measurement reports from a User Equipment is chosen depending on the User Equipment's radio channel quality, and is chosen to be smaller than or equal to the system's RRC measurement report interval.

6. The method (400) of any of claims 1-5, being used for transmission from the controlling node to the User Equipments on the WCDMA HS-DSCH channel.

7. A controlling node (500) for a cell (110) in a Wideband Code Division Multiple Access system (100), the controlling node being arranged (505, 515) to receive Radio Resource Control, RRC, measurement reports from one or more User Equipments (115) in the cell (110) which are in the CELL_FACH state, the controlling node being characterized in that it comprises: an assigning unit (510) configured to assign a validity time period, TVALID. to received RRC measurement reports from said one or more User Equipments,

a determining unit (515) configured to determine an RRC measurement report's age t from the point in time when the RRC measurement report is received from the User Equipment,

a priority handling unit (520) configured to establish a priority order between the User Equipments using the age f of the User Equipments' RRC measurement reports,

a scheduling unit (525) configured to schedule the User Equipments for transmissions from the controlling node based on the priority order, with a User Equipment being given a higher priority the newer that its RRC measurement report is, and

which priority handling unit (520) is further configured to exclude a User Equipment from said priority order if the validity time period of its RRC measurement report has expired, i.e. f≥ TVALID-

8. The controlling node (500) of claim 7, being arranged (520, 525) to use the User Equipments' radio channel quality in establishing the priority order, with User Equipments being given a higher priority the better their radio channel quality is.

9. The controlling node (500) of claim 8, being arranged (520, 525) to exclude User Equipments whose radio channel quality is below a predetermined threshold from being scheduled for transmissions from the controlling node at a future point in time.

10. The controlling node (500) of any of claims 7-9, being arranged (520, 525) to increase the margins for transmissions to User Equipments who are scheduled to receive transmissions in inverse proportionality to the age f of a User Equipment's RRC measurement reports, so that larger margins are used for User Equipments with older RRC measurement reports

11. The controlling node (500) of any of claims 7-10, being arranged (520, 525) to set the validity time period, TVALID, for received RRC measurement reports from a User Equipment is chosen depending on the User Equipment's radio channel quality, and is set to be smaller than or equal to the system's RRC measurement report interval.

12. The controlling node (500) of any of claims 7-11 , in which said transmissions to the User Equipments in the cell are on the WCDMA HS- DSCH.