EP2880796A1

EP2880796A1 - Configurable size of "csi request" for aperiodical csi feedback triggering

Info

Publication number: EP2880796A1
Application number: EP12882377.0A
Authority: EP
Inventors: Xiaoyi Wang
Original assignee: Nokia Solutions and Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2012-08-01
Filing date: 2012-08-01
Publication date: 2015-06-10
Also published as: WO2014019169A1; EP2880796A4

Abstract

It is provided an apparatus, comprising determining means adapted to determine a size of a request field; deciding means adapted to decide, for each set of channel state indicators configured in a terminal, if the channel state indicators of the respective configured set are to be requested, wherein either all or none of the channel state indicators of the respective configured set are to be requested, and wherein the deciding means is adapted to decide for not more than a maximum number of configured sets that they are to be requested, wherein the maximum number corresponds to the determined size; providing means adapted to provide, to the terminal, the request field with the determined size indicating all configured sets for which the deciding means decided to request the respective channel state indicators.

Description

CONFIGURABLE SIZE OF "CSI REQUEST" FOR APSRIODZCAL CSI FEEDBACK

TRIGGERING Field of the invention

The present invention relates to an apparatus, a method, a system, anda computerprogramproduct related to channel state indicators . More particularly, the present invention relates to an apparatus, a method, a system, and a computer program product for aperiodic CSI feedback triggering.

Background of the invention Abbreviations

3GPP 3rd generation partnership project

LTE Long term evolution

ID Identity, Identifier

Rel Release

SA Service Architecture (group)

TR Technical report

TS Technical Specification

UE User equipment

eNB evolved NodeB

CSI Channel State Information

CSI-RS Channel State Information Reference Signal

CSI-RS resource A combination of CSI-RS parameters

RSRP Reference Signal Received Power

RSRQ Reference Signal Received Quality

DCI Downlink control information.

CC Component Carrier

CCE Control channel element

eCCE enhanced CCE

CoMP Coordinated Multi-Point (transmission and/or reception)

SS Search Space

CSS Common Search Space

CA Carrier Aggregation

FFS For further study RRC Radio Resource Control

PDCCH Physical Downlink Control Chanel

RAT Radio Access Technology

PDA Personal Digital Assistant

RE Resource Element

Different CoMP techniques have been identified, where the more powerful ones transmit simultaneouslyprecodeddata fromdifferent eNBs to several UEs on the same time frequency resource . Coherent precoding promises significant performance gains as they allow for optimum interference cancellation and have inherent diversity gains. From theory, large gains in the order of several 100% have been predicted. Thus, CoMP allows overcoming interference as well as provides diversity gains.

CoMP typically requires significant overhead with respect to reference signals for channel estimation in a multi cellular environment and generates significant overhead for feedback of channel state information (CSI) information. Inadditionthe signal processing complexity is quite high. This effort is typically only worth if rewarded by significant gains in terms of spectral efficiency or cell edge performance.

According to the CarrierAggregation (CA) concept, one base station may use component carriers of another base station to transmit data to a UE that may receive data from both base stations. Thus, the bandwidth for data transmission to these UEs may be increased. CA is available in LTE Rel. 10. In RANI meeting #69, it has been agreed that CoMP CSI aperiodical feedback shall follow the mechanism designed for Rel.10 CA. It means that the CSI request field defined in DCI-0 and DCI-4 (i.e. DCI formats 0 and 4) shall be reused to trigger CSI feedback for CoMP. The agreement is as follows (taken from the meeting report) :

• In the case of a single CC configuration where multiple CSIs are configured for COMP, 2-bit CSI request field will be used in DCI format 0 (if in UE SS) and DCI format 4 for triggering of aperiodic CoMP feedback

The candidate CSI reports are configured by RRC

1-bit CSI request remains in format 0 in the case of CSS · PFS the payload content of the report

Multiple CSI feedbacks couldbe multiplexedwithinone report instance

• FFS how to configure these multiple feedbacks into one report instance

- FFS the semi-static and dynamic signaling details

FFS if CSI request field is extended to other than 2 bits, by adding new bits or using existing codepoints

Note that aUE should searchtwo search spaces in PDCCH: aUE specific search space and a common search space (CSS) . CSS is typically used for broadcasted information. The size is quite fixed, therefore it ie difficult to add any bits for the DCI transmitted in CSS. In LTE uplink DCI (DCI format 0 and 4) , a CSI request field has been introduced to trigger the aperiodical feedback along with the PUSCH. In Rel. 8, CSI request field has only 1 bit to indicate whether or not this DCI will trigger CSI feedback. In Rel. 10, if UE is configured with multiple CC (component carriers) , then the CSI request field become 2 bits, where some status is used to indicate for which cell (or which sub-set of cells) the CSI should be reported. In Rel.11 CoMP work, it has been agreed that CA framework will be reused to trigger the aperiodical CSI feedback. That means CSI request field will be reused for CoMP. However, a combination of CA+ CoMP makes the situation extremely complicated, because the UE might be aggregated with multiple CC and multiple CSI-RS resources simultaneously. How to efficiently reuse the request field is a big problem to be solved.

Conventionally, whenever UE is configured with more than one CC, CSI request field has 2 bits, otherwise it has only 1 bit. CSIs may be grouped into sets of CSIs. eNB may use RRC signaling to configure sets of CSI processes (i.e. processes comprising measuring CSI and providing the measurement result; in this document, CSI and CSI process are used synonymously, if not otherwise clear from the context) . Conventionally, eNB has full freedom to configure any CSI processes in any set. No specified mapping rules apply. For example, using higher layer signaling, e.g. RRC signaling, eNB may configure 3 sets of CSI processes. Each set could include 1 or more CSI processes. E.g. one set could include CSI process 1, 3, 4, 5. Another set could include 3 and 4, and a 3rd set might only include CSI process 1.

Summary of the invention It is an object of the present invention to improve the prior art.

According to a first aspect of the invention, there is provided an apparatus, comprising determining means adapted to determine a size of a request field; deciding means adapted to decide, for each set of channel state indicators configured in a terminal, if the channel state indicators of the respective configured set are to be requested, wherein either all or none of the channel state indicators of the respective configured set are to be requested, and wherein the deciding means is adapted to decide for not more than a maximum number of configured sets that they are to be requested, wherein the maximum number corresponds to the determined size; providing means adapted to provide, to the terminal, the request field with the determined size indicating all configured sets for which the deciding means decided to request the respective channel state indicators.

The apparatus may further comprise signaling means adapted to signal, to the terminal, the size of the request field. In the apparatus, the size of the request field may depend on a number of the configured channel state indicators. According to a second aspect of the invention, there is provided an apparatus, comprising determining processor adapted to determine a size of a request field; deciding processor adapted to decide, for each set of channel state indicators configured in a terminal, if the channel state indicators of the respective configured set are to be requested, wherein either all or none of the channel state indicators of the respective configured set are to be requested, and wherein the deciding processor is adapted to decide for not more than a maximum number of configured sets that they are to be requested, wherein the maximum number corresponds to the determined size; providing processor adapted to provide, to the terminal, the request field with the determined size indicating all configured sets for which the deciding processor decided to request the respective channel state indicators .

The apparatus may further comprise signaling processor adapted to signal, to the terminal, the size of the request field. In the apparatus, the size of the request field may depend on a number of the configured channel state indicators.

According to a third aspect of the invention, there is provided a base station comprising an apparatus according to any of the first and second aspects.

According to a fourth aspect of the invention, there is provided an apparatus, comprising determining means adapted to determine a size of a received request field, extracting means adapted to extract the received request field from a received signal taking into account the determined size; evaluating means adapted to evaluate the extracted request field in order to obtain requested sets, wherein the request field indicates the requested Bets of one ormore configuredsets intowhichoneormore configuredchannel state indicators are grouped; measuring means adapted to measure all channel state indicators of the requested sets. In the apparatus, the determiningmeans maybe adapted to determine the size of the request field by determining a number of the configured channel state indicators and to determine the size of the request field corresponding to the number of the configured channel state indicators. In the apparatus, the determining means may be adapted to determine the size of the request fieldbased on a received indication signal . According to a fifth aspect of the invention, there is provided an apparatus, comprising determining processor adapted to determine a size of a received request field, extractingprocessor adapted to extract the receivedrequest fieldfromareceived signal taking into account the determined size; evaluating processor adapted to evaluate the extracted request field in order to obtain requested sets, wherein the request field indicates the requested sets of one ormore configuredsets into whichone ormore configured channel state indicators are grouped; measuring processor adapted to measure all channel state indicators of the requested sets. In the apparatus, the determining processor may be adapted to determine the size of the request field by determining a number of the configured channel state indicators and to determine the size of the request field corresponding to the number of the configured channel state indicators. In the apparatus, the determining processor may be adapted to determine the size of the request field based on a received indication signal.

According to a sixth aspect of the invention, there is provided a terminal, comprising an apparatus according to any of the fourth and fifth aspects. According to a seventh aspect of the invention, there is provided amethod, comprisingdetermininga size of a request field; deciding, for each set of channel state indicators configured in a terminal , if the channel state indicators of the respective configured set are to be requested, wherein either all or none of the channel state indicators of the respective configured set are to be requested, and wherein it is decided for not more than a maximum number of configured sets that they are to be requested, wherein the maximum number corresponds to the determined size; providing, to the terminal, the request field with the determined size indicating all configured sets for which it is decided to request the respective channel state indicators. The method may be a method of CSX feedback triggering.

The method may further comprise signaling, to the terminal, the size of the request field. In the method, the size of the request field may depend on a number of the configured channel state indicators.

According to an eighth aspect of the invention, there is provided amethod, comprisingdetermininga size of a receivedrequest field, extracting the receivedrequest field fromareceived signal taking into account the determined size; evaluating the extractedrequest field in order to obtain requested sets, wherein the request field indicates the requested sets of one or more configured sets into which one or more configured channel state indicators are grouped; measuring all channel state indicators of the requested sets.

The method may be a method of CSI feedback triggering. In the method, the determining may comprise determining the size of the request field by determining a number of the configured channel state indicators and determining the size of the request field corresponding to the number of the configured channel state indicators . In the method, the determining may comprise determining the size of the request field based on a received indication signal. According to a ninth aspect of the invention, there is provided a computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any one of the seventh and eighth aspects.

The computer program product maybe embodiedas a computer readable medium. According to embodiments of the invention, at least the following advantages are achieved:

Through a configurable CSI request length, the average CSI request length is reduced. Hence, the payload on PDCCH is reduced. A lower coding rate may be converted to lower aggregation level, which means less eCCE are used. Though this coding gain may be quite small (in some cases, only 1 bit is saved) , it is not negligible in general. Due to less payload on the DCI, a larger coverage may be achieved. In detail, the coverage of the control channel is depends on the maximum number of REs used for one control message and the payload of one control signaling. If the number of payload bits is reduced, the coverage may be enhanced.

More in detail, control signaling in LTE - like signaling of UL grants DCI 0 and 4 - is transmitted on PDCCH and the system has to ensure a very safe detection of PDCCHs by all UEs in the cell area. The size of the PDCCH directed to a certain UE depends on the payload size of the control information (DCI) and the effective coding rate . The coding rate on PDCCH is adapted by selecting the aggregation level on PDCCH such that it is suitable to the channel conditions, where the aggregation level determines the number of CCEs or eCCEs on PDCCH. But selection of aggregation levels allows only for a very coarse adjustment of the coding rate which may lead to rather inefficient usage of available PDCCH resources. Allowing for a configurable CSI request field is an additional means forcontrollingthe code rateonPDCCHbyadjusting thepayload conveyed on PDCCH. Longer CSI request fields may in particular be useful in systems using CA and CoMP for triggering a variety of specific CSI reports which may be used for improving scheduling decisions and for improving the arrangement of cooperative areas . But longer CSI request fields lead to higher coding rates which affects the usage of resources on PDCCH negatively. Cell sizes may be one aspect for determining the length of the CSI request field in a system. A longer CSI request field may be advantageous inareaswithsmall cells andahighnumberof availablebase stations or access points when a variety of specific CSI reports allows to obtain comprehensive information about the channel conditions while the small cell sizes ensure a low aggregation level and an efficient usage of PDCCH resources. On the other hand in the case of large cells with only few available base stations or access points there may be no need for configuring a variety of specific CSI reports and the system may more benefit from short CSI request fields and the more robust coding rate for minimizing the aggregation levels of PDCCHs and an efficient usage of PDCCH resources . It is to be understood that any of the above modifications can be applied singly or in combination to the respective aspects to which they refer, unless they are explicitly stated as excluding alternatives .

Brief description of the drawings Further details, features, objects, and advantages are apparent from the following detailed description of the preferred embodiments of the present invention which is to be taken in conjunction with the appended drawings, wherein Fig. 1 shows an apparatus according to an embodiment of the invention;

Fig.2 shows a method according to an embodiment of the invention; Fig.3 shows anapparatus according toanembodimentof the invention,· and Fig.4 shows a method according to an embodiment of the invention. Detailed description of certain embodiments

Herein below, certain embodiments of the present invention are described in detail with reference to the accompanying drawings, wherein the features of the embodiments can be freely combined with each other unless otherwise described. However, it is to be expressly understood that the description of certain embodiments is given forby way of example only, and that it is byno way intended tobe understoodas limiting the inventionto the discloseddetails .

Moreover, it is to be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method are described. In a case, where CoMP and CA are combined, the number of bits for CSI request field might be larger than 2. Then a way to indicate the size of the CSI request field to the UE is needed. Accordingto embodiments of the invention, it is provideda flexible way to decide the size of CSI request field. This is most relevant for a combined CA + CoMP case but may be applied to other configurations, too. There are two methods: Method 1 (explicit way) : a RRC signalling is created to indicate the size of CSI request field. WhenUE has multiple CSI to feedback, eNB can configure the size of CSI request field using UE specific RRC signalling, e.g. whether it is 1, 2 or 3 bits or even more bits in the CSI request field. In some embodiments, the maximum size of the CSI request field may be e.g. 3 bits. The size may depend on e.g. the number of configured CSIs, or on the number of CSIs that could be grouped together for feedback. Method 2 (implicit way) : the size of CSI request field is decided by the number of configured CSI (across all configured CC) or configured sets of CSIs. In some embodiments, a number of bits in the CSI request field may be the same as the number of configured CSIs or the number of configured sets.

The number of configured CSIs is the same as the number of sets into which the configured CSIs are grouped if each set comprises exactly one configured CSI and each configured CSI is comprised in exactly one set. Inother embodiments, thenumberof configuredsetsmaybe different . If the number of configured sets is higher than the number of bits in the CSI request field, only some of the sets may be triggered by the CSI request field. For example, if 7 sets are defined and the CSI request field has 2 bits, only two sets (e.g. the first two sets or the last two sets) may be triggered by the CSI request field, the other five sets not. Thus, the number of triggerable sets (sets whose CSIs may be triggered by the CSI request field) is independent from the number of configured sets. However, in these embodiments, the UE must be informed about the size of the CSI request field. This may be done by the explicit way (Method 1) , or, according to some embodiments, in the following way:

The maximum number of sets that may be triggered by the CSI request field (i.e. the size of the CSI request field) may depend on the number of configured CSI processes. An example is given in table 1, wherein it is exemplarily assumed that a maximum of 15 CSIs may be configured:

Size of CSI request field (bits) =

maximum number of triggerable sets Number of configured CSIs 1 bit 1 to 2

2 bits 3 to 5

3 bits 6 to 15 Table 1: Example of correlation of size of CSI request field and number of configured CSIs

This method has the advantage that no additional signalling of the size of the CSI request field is required. On the other hand, the UE has to calculate the size of the CSI request field.

Fig.1 shows anapparatus accordingto anembodiment of the inventio . The apparatus may be a base station such as a NodeB or an eNodeB . Fig.2 shows a method according to an embodiment of the invention. The apparatus according to Fig. 1 may perform the method of Fig. 2 but is not limited to this method. The method of Fig. 2 may be performed by the apparatus of Fig. 1 but is not limited to being performed by this apparatus.

The apparatus comprises determining means 10, deciding means 20, and providing means 30.

The determiningmeans 10 determines a size of a request field (S10) . In some embodiments, the size of the request field may depend on the number of configured channel state indicators.

The deciding means 20 decides, for each set of channel state indicators configured in a terminal, if the channel state indicators of the respective configured set are to be requested (S20) . Therein, it considers that either all or none of the channel state indicators of the respective configured set are to be requested. The deciding means 20 decides for a number of sets that they are to be requested, wherein this number does not exceed a maximum number. The maximum number corresponds to the size of the request field determined by the determining means 10.

The providingmeans 30 provides, to the terminal, the request field indicating all configured sets forwhich the decidingmeans decided to request the respective channel state indicators (S30) . The request field has the size determined by the determining means 10. Fig.3 showsanapparatus accordingto anembodiment of the invention. The apparatus may be a terminal such as a user equipment. Fig. 4 shows a method according to an embodiment of the invention. The apparatus according to Fig. 3 may perform the method of Fig. 4 but is not limited to this method. The method of Fig. 4 may be performed by the apparatus of Fig. 3 but is not limited to being performed by this apparatus.

The apparatus comprises determining means 110, extracting means 120, evaluating means 130, and measuring means 140.

The determining means 110 determines a size of a received request field (S110) . For example, the size may be determined based on a received indication or based on the number of configured CSIs.

The extracting means 120 extracts the received request field from a received signal taking into account the size of the request field as determined by the determining means 110 (S120) . The evaluating means 130 evaluates the extracted request field in order to obtain requested sets (S130) . In detail, the request field indicates the requested sets of one or more configured sets into which one or more configured channel state indicators are grouped.

The measuring means 140 measures all channel state indicators of the requested sets (S140) .

Embodiments of the invention are described with respect to an LTE-a system. However, other embodimentsmaybe implemented inLTE. HSxPA, WiFi, WiMax etc . , and mixed systems thereof , if a channel state indication may be requested from a terminal by a base station.

Achannel state indication gives feedback about a state of a certain channel, in particular a downlink channel. Such a channel state information is specified inLTE. However, according to embodiments of the invention, instead of or in addition to the specified information other information relevant for estimating a state of a channel may be comprised in the channel state information. In some embodiments, channel state information may comprise a subset of the specified information only. A terminal may comprise any kind of terminal that may be connected to a base station of the respective RAT such as user equipment, mobile phone, PDA, laptop, smartphone etc.

A base station may comprise any kind of base stations of the respective RAT such as NodeB, eNodeB, pico cell, femto cell, wireless access point etc. If not otherwise stated or otherwise made clear from the context, the statement that two entities are different means that they are differently addressed in the core network. It does not necessarily mean that they are based on different hardware. That is, each of the entities described in the present description may be based on a different hardware, or some or all of the entities may be based on the same hardware.

According to the above description, it should thus be apparent that exemplary embodiments of the present invention provide, for example a terminal suchas auser equipment, or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product (s) . Furthermore, it shouldthus be apparent that exemplaryembodiments of thepresent invention provide, for example a base station such as a NodeB or an eNodeB, or a component thereof, anapparatus embodying the same, a method for controlling and/or operating the same, and computer program (s) controlling and/oroperating the same as well as mediums carrying such computer program(s) and forming computer program product (s) . Implementations of anyof the above describedblocks, apparatuses, systems, techniques or methods include, as non limiting examples, implementations as hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. It is to be understood that what is described above is what is presently considered the preferred embodiments of the present invention. However, it should be noted that the description of the preferred embodiments is given by way of example only and that various modifications maybe made without departing from the scope of the invention as defined by the appended claims.

Claims

What is claimed is:

1. Apparatus, comprising

determining means adapted to determine a size of a request field;

deciding means adapted to decide, for each set of channel state indicators configured in a terminal, if the channel state indicators of the respective configured set are to be requested, wherein either all or none of the channel state indicators of the respective configured set are to be requested, and wherein the deciding means is adapted to decide for not more than a maximum number of configured sets that they are to be requested, wherein the maximum number corresponds to the determined size;

providing means adapted to provide, to the terminal, the request field with the determined size indicating all configured sets forwhich the deciding means decided to request the respective channel state indicators.

2. The apparatus according to claim 1, further comprising signaling means adapted to signal, to the terminal, the size of the request field.

3. The apparatus according to any of claims 1 and 2, wherein the size of the request field depends on a number of the configured channel state indicators.

4. Base station comprising an apparatus according to any of claims 1 to 3.

5. Apparatus, comprising

determiningmeans adapted to determine a size of a received request field,

extracting means adapted to extract the received request field from a received signal taking into account the determined size; evaluating means adapted to evaluate the extracted request field in order to obtain requested sets, wherein the request field indicates the requested sets of one or more configured sets into which one or more configured channel state indicators are grouped; measuring means adapted to measure all channel state indicators of the requested sets.

6. The apparatus according to claim 5, wherein

the determining means is adapted to determine the size of the request fieldby determining a number of the configured channel state indicators and to determine the size of the request field corresponding to the number of the configured channel state indicators .

7. The apparatus according to claim 5 , wherein

thedeterminingmeans is adaptedtodetermine the size of the request field based on a received indication signal.

8. Terminal, comprising an apparatus according to any of claims 5 to 7.

9. Method, comprising

determining a size of a request field;

deciding, for each set of channel state indicators configured in a terminal, if the channel state indicators of the respective configured set are to be requested, wherein either all or none of the channel state indicators of the respective configured set are to be requested, and wherein it is decided for not more than a maximum number of configured sets that they are to be requested, wherein the maximum number corresponds to the determined size; providing, to the terminal, the request field with the determined size indicating all configured sets for which it is decided to request the respective channel state indicators.

10. The method according to claim 9, further comprising signaling, to the terminal, the size of the request field.

11. The method according to any of claims 9 and 10, wherein the size of the request field depends on a number of the configured channel state indicators.

12. Method, comprising determining a size of a received request field,

extracting the receivedrequest field froma received signal taking into account the determined size;

evaluating the extractedrequest field in order to obtainrequested sets, wherein the request field indicates the requested sets of oneormore configured sets intowhichoneormore configuredchannel state indicators are grouped;

measuring all channel state indicators of the requested sets.

13. The method according to claim 12, wherein

the determining comprises determining the size of the request field by determining a number of the configured channel state indicators and determining the size of the request field corresponding to the number of the configured channel state indicators .

14. The method according to claim 12 , wherein

the determining comprises determining the size of the request field based on a received indication signal.

15. A computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any one of claims 9 to 14.

16. The computer program product according to claim 15, embodied as a computer readable medium.