WO2011162707A1

WO2011162707A1 - Method and apparatus for avoiding serving grant being set to zero

Info

Publication number: WO2011162707A1
Application number: PCT/SE2011/050819
Authority: WO
Inventors: Janne Peisa; Jose Luis Pradas; Waikwok Kwong
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2010-06-23
Filing date: 2011-06-22
Publication date: 2011-12-29

Abstract

To reduce the impact of a lack of grant to send data and the delay introduced until a new grant is received, when a non-serving relative grant is received in a UE from the network of a cellular radio system that sets the serving grant to zero the UE sets the serving grant to a grant specified by the network and/or transmits a Scheduling Information to the network. Hereby it can be avoided that an unwanted delay is introduced because either the grant will not be zero or the network will be informed that the grant is zero and can take appropriate action. One of the actions does not rule out the other so that the UE can both avoid setting the serving grant to zero in response to a non-serving relative grant trying to set the serving grant to zero and inform the network of the situation.

Description

METHOD AND APPARATUS FOR AVOIDING SERVING

GRANT BEING SET TO ZERO

FIELD OF THE INVENTION

The present invention relates to a method and arrangement in a telecommunication system, in particular to a method and arrangement for reducing delays for data transmission.

BACKGROUND

In some cellular radio systems, such as a High Speed Packet Access (HSPA) system, a User Equipment (UE) keeps a serving grant (SG) per activated uplink (UL) frequency which indicates th amount of scheduled data that the User

Equipment (UE) can send in the corresponding uplink (UL) in a Transmission Time Interval (TTI). The UE needs to update the SG associated to the UL frequency according to the absolute grant send on the corresponding downlink (DL) channel Enhanced Dedicated Channel (E-DCH) Absolute Grant Channel (E-AGCH) associated with the UL frequency and the relative grants sent on the DL channel E~ DCH ReSative Grant Channel (E-RGCH) associated to the UL frequency. There are two types of relative grants: serving relative grant, non-serving relative grant. The former can be only transmitted by the serving E-DCH Radio Link Set (RLS) while the latter can be only sent by the non-serving E-DCH RLS.

The possible commands which can be transmitted on the serving relative grant are "UP", "DOWN", and "HOLD". On the other hand, the commands which can be transmitted on the non-serving relative grant are only "DOWN" and "HOLD".

There are some variables which the UE uses to calculate the serving grant: These are termed "referenceJETPR" and "reference_ETPR2". "referenceJETPR" holds the E-DCH Dedicated Physical Data Channel (E-DPDCH) to Dedicated Physical Control Channel (DPCCH) power ratio used as reference for relative grant commands. The state variable reference_ETPR2 holds the E-DPDCH to DPCCH power ratio used as reference for non serving relative grant commands. This variable is set to the previously stored reference_ETPR on this Hybrid Automatic Repeat Request (HARQ) process when the reference__ETPR is updated with a new value.

According the current Medium Access Control (MAC) specifications (3GPP TS 25.321 v9.1 .0.), if no scheduled transmission took piace on a Hybrid Automatic Repeat Request (HARQ) process in the previous Transmission Time Interval (TTI), the reference_ETPR shall be set to inimum_Grant for that HARQ process.

The value Mi imum_Grant corresponds to the minimum E-DCH Dedicated Physical Data Channef (E-DPDCH) to Dedicated Physical Control Channel (DPCCH) power ratio that the UE considers. This value has the index 0 in the configured scheduling grant table. The configured scheduling grant table is configured by higher layers. Current specifications (3GPP TS 25.321 v9.1 ,G.), capture the scheduling grant tables in sub clause 9.2.5.2.1

When a UE receives a non-serving relative grant with command "DOWN¹', the UE calculates the new SG as follows:

- set reference_ETPR2 to referenceJETPR as defined above (sub clause 3.1.2);

- set reference__ETPR to the E-DPDCH to DPCCH power ratio as defined above (sub clause 3.1 .2 );

- if any Non-Serving Relative Grants indicate "DOWN" for this TTI and

Serving__Grant <> "Zero_ Grant": ~ Serving__Grant = IN(Serving_„Grant, Maximurrs_Serving J3rant, Serving__Grant determined as shown below (1) (see sub clause 9.2.5.2.1 );

- Maximum J3erving__Grant - Serving J3rant.

- if Non_Serving__RG_Tirner is not active it shall be started, otherwise it sha!l be restarted;

Non_Serving_RG__Timer is set to one HARQ RTT (40ms in the case of 10ms TTi, 16ms in the case of 2ms TTI). During the time non__Serving_RG_Timer is running, the variable Maximum_ServingJ3rant indicates the maximum E-DPDCH to DPCCH power ratio that the UE is allowed to use for scheduled data.

(1 ) The serving grant is caicuiated as follows:

- Determine the lowest power ratio in the configured Serving Grant (SG)-table thai is equal t or higher than the referenceJETPR, and determine the corresponding index in the SG-tabie: SGLUPR;

- Determine the lowest power ratio in the configured SG-table that is equal or higher to the maximum of reference_„ETPR2 of ail active HARQ processes, and determine the corresponding index in the SG-tabie: SGLUPR¾

- If the UE received a non-serving Relative Grant "DOWN", determine the SG:

SG_1 = SG[MAX(SGujPR2-1 , 0)]

SG - IN(Serving_ Grant, aximum_Serving_Grant, SG_1), and set yaximum_mServing_Grant - SG. In certain cases, the UE does riot have any scheduled data to transmit. In such cases, the UE may not have transmitted anything in any of the HARQ processes in the previous Transmission Time Interval (ΤΠ). When this situation happens, the reference_ETPR for all HARQ processes will be set to the Winimu JSrant. If the UE receives a non-serving relative grant with a "DOWN" command, then

"reference_ETPR2" wi!l be updated and will take the value update in the variable "refe-rence_ETPR", i.e. it will take the same value as inimum__Grani

The UE will determine that the lowest power ratio in the configured SG-table that is e ual or higher to the maximum of reference_ETPR2 of all active HARQ processes is the lnimum_„Gfant inimum__Gfant is in index 0 of the configured scheduiing grant tabie described in sub clause 9.2.5.2.1 [MAG].

Following ^'the formulas stated above to calculate the grant:

SGJ - SGpAX(SGt,upR2~1 , 0)}, in this case SGOJPRS is 0 as the -Minimum J3rant is ze o. Therefore,

SGJ = 0

SG - M!N-(Servir>g_Grant, Maximum JServing Brant, SGJ), SG = 0 and set Maximum Serving S rant - SG ^» 0.

Serving__ rant = MIN(Serving_ Grant, MaximumJServing__Grant, ServtngjSrant

(SG) determined above) - 0 In other words, the UE's serving grant is set to the MinimumjSrant. The value of the Minimum_Grant, however, specifies a very low power that is not sufficient for the UE to send any data. In addition, the non_mServing_RG_Timer will be (restarted. This implies that Maximum_Serving_Grant cannot be changed while this timer is running.

There is a constant desire to improve performance in ceiluiar radio systems Hence, there is a need for improved methods and devices to improve the performance in data transmission of a cellular radio system.

SUMMARY

It Is an object of the present invention to overcome or at least reduce some of the problems described above.

This object is obtained by the methods and device as set out in the appended claims.

As has been realized by the inventors, if data arrives to the UE buffer during that time, the UE is allowed to send control information via the Scheduling Information (SI). The Si includes the Total E-DCH Buffer Size (TEBS) which indicates the amount of data waiting to be transmitted. The network may decide then to schedule a grant for this specific UE. The time to schedule a grant varies depending on the network ioad; therefore, if may take several TTIs before a grant can be scheduled. Moreover, this SI can sometimes be lost due to network congestion or poor radio environment. Depending on network configuration, the UE may not be allowed to repeat sending this SI for quite a long time. The lack of grant to send data and the delay introduced until a new grant is received can have a serious impact on prioritized services. To reduce the impact, when a non-serving relative grant is received in a UE from the network of a ce!iu!ar radio system that sets the serving grant to zero the UE sets the serving grant to a grant specified by the network and/or transmits a Scheduling information to the network, Hereby it can be avoided that an unwanted delay is introduced because either the grant will not be zero or the network will be informed that the grant is zero and can take appropriate action. Of course one of the actions does not ru!e out the other so that the UE can both avoid setting the serving grant to zero in response to a non-serving relative grant trying to set the serving grant to zero and inform the network of the situation,

!n accordance with one embodiment an early indication is sent to the network that the UE serving grant was set to zero due to a reception of a non-serving relative grant and triggering for such purpose the Scheduling information. in accordance with one embodiment, when no scheduled transmission took pface in none of the HARQ process in the previous TTl , and a "DOWN" command is received, the UE does not set its grant to index zero, but to a value configured by the network.

Thus, in accordance with some embodiments a method in a user equipment, UE, adapted to connect to a network of a cellular radio system is provided. The method comprises receiving from the network a non-serving relative grant, The method further comprising determining if the received non-serving relative grant would set the serving grant to zero, and if it is determined that the received non-serving relative grant wouid set the serving grant to zero setting the serving grant to a specified grant specified by the network and/or transmitting a Scheduling

information, SI, to the network. In accordance with one embodiment, when more than one Uplink, UL, frequency is configured, and a relative grant is received with command "DOWN" in any downlink, DL. frequency the UE send Scheduling Information to the network on all activated UL frequencies. in accordance with one embodiment when more than one Uplink, UL, frequency is configured, and a relative grant is received with command "DOWN" in any downlink, DL, frequency, the UE sends the Scheduling information to the network on the UL frequency associated with the downlink frequency in which the relative grant was received.

In accordance with one embodiment the UE is adapted to use a specific code word in one of the field in the Scheduling Information to indicate that no scheduled transmissions took place on none of the HARQ processes in the previous TTI and a relative grant is received with command "DOWN". in accordance with one embodiment the specified grant is specified by the network via higher layer signaling.

Using the methods described herein will provide several benefits. First, an early indication is enabled to be sent to the network about the fact that the UE grant has been reduced to zero due to the reception of a "DOWN" command in the relative grant channel. This early indication will assist the network to decide to send a new grant to the UE reducing any possible delays which may be critical for prioritized services. Second it can be avoided that the UE grant is reduced to zero due to the reception of a "DOWN" command on the relative grant channel. Guaranteed and prioritized services will then be abie to be transmitted over scheduled flows without any additional delay because the grant cannot be set to zero but rather to a minimum value configured via the network. The invention also extends to a User Equipment provided with a controiler/oontroller circuitry for performing the above methods. The contro!ler(s) can be implemented using suitable hardware and or software. The hardware can comprise one or many processors that can be arranged to execute software stored in a readable storage media. The processor(s) can be implemented by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared or distributed. Moreover, a processor or may include, without limitation, digital -signal processor (DSP) hardware; ASIC hardware, read only memory (ROM), random access memory (RAM), and/or other storage media.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawing, in which;

- Fig, 1 is a view of a cellular radio system,

- Fig. 2 is a flow chart illustrating some steps performed in a UE when receiving a non-serving relative grant,

- Fig. 3 illustrates steps performed in accordance with a first illustrating

embodiment, and

- Fig. 4 illustrates steps performed in accordance with a second illustrating embodiment.

DETAL1ED DESCRIPTION

In Fig, 1 , a general view of a cellular radio system 100 is depicted. The system 00 depicted in Fig 1 is a UTRAN system, However it is also envisaged that the system can be a GERAN system, an LTE or another similar systems. The system 100 comprises a number of radio base stations 101 , whereof only one is shown for reasons of simplicity. The radio base station 101 can be connected to by user equipments in the figure represented by the UE 103 located in the area served by the radio base station 101. The UE access the network via an air interface between the UE and the radio base station. The radio base station and the user equipment further comprise controllers/controller circuitry 105 and 107 for providing functionality associated with the respective entities. The controllers 105 and 107 can for example comprise suitable hardware and or software. The hardware can comprise one or many processors that can be arranged to execute software stored in a readable storage media. The processor(s) can be implemented by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which ma be shared or distributed. Moreover, a processor may include, without limitation, digital signal processor (DSP) hardware, ASIC hardware, read only memory (ROM), random access memory (RAM}, and/or other storage media. The radio base station Is further connected to a central control node such as a Radio Network Controller provided to controi a number of radio base stations. in Fig. 2 a method in a user equipment (UE) adapted to connect to a network of a cellular radio system is depicted. First in a step 201 a non-serving relative grant is received from the network. Then In a step 203 the UE determines if the received non-serving relative grant would result in the setting the serving grant of the UE to zero in a step 203. If the UE determines that the received non-serving relative grant would result in the setting the serving grant of the UE to zero, the UE sets the serving grant to a specified grant specified by the network and/or transmits a

Scheduling Information to the network in a step 205.

Below some more detailed exemplifying scenarios are described to further illustrate the method described in conjunction with Fig. 2. in a first scenario no scheduled transmission took place on any of the HARQ process in the previous TTI and a relative grant is received with a command

"DOWN". in this first scenario if the UE has not transmitted data during that period, in practice, it means that the UE does not have any data in its buffer. In other words, the Total E-DCH Buffer Status (TEBS) is equal to zero. Current specifications do not allow the UE to send the S! as stand-alone message unless the UE has data in the buffer i.e. TEBS is larger than zero. However, in this scenario TEBS is equal to zero.

I n one embodiment, if no scheduied transmissions took place on any of the HARQ processes in the previous TTI and a relative grant is received with command "DOWN", the UE is adapted to trigger the Scheduling information and send the Scheduling Information to the network. fn another embodiment, when more than one Uplink (UL) frequency is configured, if no scheduied transmissions took place on any of the HARQ processes in the previous TTI in ail activated UL frequencies and a relative grant is received with command "DOWN" in any of the DL frequencies, the UE is adapted to trigger the Scheduling information and send Scheduling Information to the network on all activated UL frequencies. in yet another embodiment, when more than one UL frequency is configured, if no scheduled transmissions took place on none of the HARQ processes in the previous TTI in all activated UL frequencies and a relative grant is received with command "DOWN" in any DL frequency, the UE is adapted to trigger the

Scheduling information and send the Scheduling Information to the network on the UL frequency associated with the DL frequency in which the relative grant was received.

In another embodiment, the UE is adapted to use a specific codeword in one of the field in the Scheduling information to indicate that no scheduled transmissions took place on none of the HARG processes in the previous TTi and a relative grant is received with command "DOWN". A code word can for example be provided by setting one or more fields in the Scheduling Information to specific va!ues. in Fig. 3 some steps that can be performed in accordance with the first scenario are depicted, it is to be noted that triggering and reporting the Scheduling Information does not prevent the UE to perform other actions. First in a step 301 it is checked if the referenceJETPR is equai to the Mjnimum_Grani for all HARQ processes, if the reference JETPR is equai to the Minimum jGrani for ali HARQ processes ft is checked in a ste 303 if a "DOWN" command is received on the E~RGGH from a non-serving ceil, if a "DOWN" command is received on the E-RGCH from a non- serving cell a SI is triggered and reported to the network in a step 305.

In a second scenario no scheduled transmission took piace on none of the HARQ process in the previous TT , in this situation and according the current MAG specifications (3GPP TS 25.321 v9.1 ,0),and as explained above, the

referenceJETPR for ail HARQ processes are set to the Minimum_Grant. When a relative grant is received with command "DOWN", the "reference_ETPR2" will be updated and will take the value update in the variable "referenceJETPR", i.e. it will take the same value as inimum__Grant. The UE will determine the lowest power ratio in the configured SG-tab!e that is equal to or higher than the maximum of reference_ETPR2 of aii active HARQ processes is the Winimum Brant

Minimum J3rant is in index 0 of the configured scheduling grant table. The scheduling grant table is provided by higher layers and configured by the network. As explained in the previous section, in this case, the SG will be set to zero. Sn accordance with one embodiment it is avoided to set the serving grant to zero in this situation by replacing Minimum_Grant in this situation by another parameter specifying a minimum grant, here termed: minimum__RG_downjndex. The minimum grant parameter is provided by higher layers and configured by the network. In accordance with one embodiment if th network does not include a specified minimum grant parameter in the configuration, the UE is adapted to set the minimum_RG__downjndex value to the inimum_Grant value as a default value, in accordance with one embodiment the reference JETPR definition is modified such that: reference_ ETPR: The state variable referenceJ TPR holds the E-DPDCH to DPCCH power ratio used as reference for relative grant commands. This variable is set to the E-DPDCH to DPCCH power ratio used for the E-TFC selected for the previous ΤΤΊ on this HARQ process, calculated using the amplitude ratios prior to the quantization according to sub clause 5.1.2.58,2.3 or 5.1 2.5Θ.2.4 of 3GPP TS 25.321 v9.i .O, excluding non-schedu!ed transmissions, excluding any scaling applied according to sub clause 5.1.2,6 of 3GPP TS 25.321 v9,1.0, and is obtained from the physical layer. In case no scheduled transmission took place on a HARQ process in the previous TTl, reference_ETPR is be set to

minimum J¾G__downj dex for this HARQ process.

Sn accordance with another embodiment the reference_ETPR2 is set to the specified grant minimum_RG_„down Jndex. This parameter is used only in setting the reference_ETPR2 when no data is being transmitted. The value of the parameter for the specified grant is in some embodiments provided by higher layers and configured by the network. As a result non-serving relative grants will not be able to decrease the serving grant below the minimum_„reference_„ETPR2. Oniy serving relative grants and absolute grants can reduce the serving grant below the mi nim u m _jef e rence_ETPR2.

The above methods can be also applied in case there are more than one activated UL frequencies. Since the procedures are performed per Activated Uplink

Frequency; minimum J¾G_downJndex can be a specified grant set independently per UL frequencies or common to a Si UL frequencies. jn Fig. 4 some steps that can be performed in accordance with the second scenario are depicted. First in a step 401 it is checked if any scheduled transmission took place on a HARQ processes in the previous TTL If no scheduled transmission took place on a HARQ processes in the previous ΓΪΊ; the referenceJETPR is set to minimum J G__down jncSex for that HARQ process in a step 403.

Claims

1. A method in a user equipment, UE, adapted to connect to a network of a cellular radio system, the method comprising receiving (201) from the network a non- serving relative grant, the method being characterized by the steps of:

- determining (203) if the received non-serving relative grant would set the serving grant to zero, and

if H is determined that the received non-serving relative grant would set the serving grant to zero;

- setting (205) the serving grant to a specified grant specified by the network and/or

- transmitting (205) a Scheduling Information, Si, to the network.

2. The method according to ciaim 1 , when more than one Upiink, UL, frequency is configured, and a relative grant is received with command "DOWN" in any downlink, DL, frequency, the UE sends Scheduling Information to the network on all activated UL frequencies.

3. The method according to claim 1 , when more than one Uplink, UL, frequency is configured, and a relative grant is received with command "DOWN" in any downlink, DL, frequency, the UE sends Scheduling Information to the network on the UL frequency associated with the DL frequency in which the relative grant was received.

4. The method according to any of claims 1 - 3, wherein the UE uses a specific code word in one of the field in the Scheduling Information to indicate that no scheduled transmissions took place on none of the Hybrid Automatic Repeat Request, HARQ, processes in a previous Transmission Time interval, TTI, and a relative grant is received with command "DOWN",

5. The method according to any of claims 1 - 4, wherein the specified grant is specified by the network via higher layer signaling.

8. A user equipment, UE, (103) adapted to connect to a network of a cellular radio system (100), the UE being adapted to receive from the network a non-serving relative grant, the UE comprising:

controller circuitry (107) adapted to determine if the received non-serving relative grant would set the serving grant to zero, and

controller circuitry (107) adapted to:

- set the serving grant to a specified grant specified by the network and/or

- transmit a Scheduling information, SI, to the network,

upon determination that the received non-serving relative grant would set the serving grant to zero,

7. The user equipment method according to claim 6, wherein the UE is adapted to send Scheduling Information to the network on all activated UL frequencies when more than one Uplink, UL, frequency is configured, and a relative grant is received with command "DOWN" in any downlink, DL, frequency.

8. The user equipment according to claim 6, wherein the UE is adapted to send Scheduling Information to the network on the UL frequency associated with the DL frequency in which the relative grant was received when more than one Uplink, UL, frequency is configured, and a relative grant is received with command "DOWN" in any downlink, DL, frequency.

9. The user equipment according to any of claims 6 - 8, wherein the UE is adapted to use a specific code word in one of the field in the Scheduling Information to indicate that no scheduled transmissions took place on none of the Hybrid Automatic Repeat Request, HARQ, processes in a previous Transmission Time Interval, TTS and a relative grant is received with command "DOWN",

10. The user equipment according to any of claims 6 - 9, wherein UE is adapted to receive the specified grant from the network via higher layer signaling.