KR20130109796A

KR20130109796A - Method of channel state information feedback in carrier aggregation environment

Info

Publication number: KR20130109796A
Application number: KR1020120031831A
Authority: KR
Inventors: 정희상; 김일규
Original assignee: 한국전자통신연구원
Priority date: 2012-03-28
Filing date: 2012-03-28
Publication date: 2013-10-08

Abstract

Disclosed is a periodic CSI feedback method for a plurality of downlink component carriers in a carrier aggregation environment. The CSI feedback method according to the present invention comprises the steps of measuring CSI for each of a plurality of downlink component carriers, encoding the measured CSI and each of the CSIs encoded for the plurality of downlink component carriers, the first slot. Transmits using an uplink control channel radio resource allocated in a frequency division multiplexing (FDM) scheme, and transmits each CSI to the allocated uplink control channel radio resource in a second slot that is a next slot of the first slot. And frequency hopping and transmitting to a symmetrical position on the frequency axis.

Description

Periodic channel status information feedback method in carrier aggregation environment {METHOD OF CHANNEL STATE INFORMATION FEEDBACK IN CARRIER AGGREGATION ENVIRONMENT}

The present invention relates to feedback of channel state information (CSI), and more particularly, to channel state for a plurality of downlink component carriers (CCs) in a carrier aggregation (CA) environment. Information feedback method.

The 3GPP LTE-Advanced system can simultaneously use up to five 20MHz frequency bands compatible with the LTE system. This technique is called Carrier Aggregation (CA). In this case, each frequency band is defined as a component carrier (CC). Therefore, LTE-Advanced system can use up to five CC at the same time.

Meanwhile, mobile communication terminals operating in the LTE-Advanced system are configured to measure and calculate channel state information (CSI) using a reference signal received from a base station. Typically, the CSI is channel state information including detailed information such as a rank indicator (RI), a channel quality indicator (CQI), a precoding matrix indicator (PMI), and a precoding type indicator (PTI).

Since the CSI needs to be measured and reported separately for each frequency band, if 5 CCs are used in the LTE-Advanced system, a situation may occur in which up to 5 CSIs are fed back at the same time point (subframe). .

In the LTE-Advanced mobile communication system, the CSI measured by the UE through the uplink is reported to the base station, and the CSI report can be divided into a periodic report and an aperiodic report. The aperiodic report is transmitted with data in a piggyback manner on a physical uplink shared channel (PUSCH). On the other hand, the periodic report is transmitted through the PUSCH if there is a PUSCH transmission at the time to be reported, but is transmitted through the physical uplink control channel (PUCCH), which is an uplink control channel.

If the PUSCH and the PUCCH are simultaneously transmitted, uplink control information (UCI) consisting of only periodic CSI is transmitted through the PUCCH. Therefore, in any case, if CSI is transmitted through the PUSCH, it is not a problem because a sufficient number of bits can be sent. However, if CSI is transmitted through the PUCCH, there is a limitation of the number of bits according to a limited resource.

PUCCH formats for CSI reports include format 2, format 2a, and format 2b. Each PUCCH format is converted into 20-bit digital data through an encoding process and output to an antenna through a modulation process. Since the periodic CSI needs to send up to 11 bits of information in one subframe for one CC, the limitation of the number of bits is not a problem in transferring the CSI in the conventional manner when only a single CC exists.

However, in a carrier aggregation environment, two or more CCs can be activated and used, and control information generated in each CC must be transmitted using only one CC called a primary CC (PCC). Therefore, if you want to send CSI for two or more CCs in one subframe, a restriction on the number of bits may occur. For example, in a system including two CCs, if the CSI for each CC needs to be reported at the same time, priority is given to sending CSI for one CC and dropping the CSI for the other CC.

As a conventional method for solving this problem, there is a method of operating so as to reduce the probability of overlap by varying the period of the report for each CC. This method can be called TDM (Time-Domain Multiplexing) and alleviates the problem without adding or modifying a separate transmission format.

However, the TDM method is limited because up to five CCs can be increased. Even if five CCs are reported in the TDM method, a CSI report may be generated in the same subframe, thereby generating a CC having a CSI drop. Therefore, since the CSI report is delayed in time according to the CC, the downlink resource allocation does not reflect the correct channel state, resulting in performance degradation. In addition, a PUCCH overload occurs, in which the PUCCH is transmitted almost every subframe.

An object of the present invention is to provide a channel state feedback method in which performance degradation does not occur for a plurality of downlink component carriers (CCs) in a carrier aggregation (CA) environment.

CSI feedback method of the terminal according to an aspect of the present invention for achieving the above object of the present invention, as a periodic CSI feedback method for a plurality of downlink component carriers in a carrier aggregation environment, each of the plurality of downlink component carriers An uplink control channel allocated to a frequency division multiplexing (FDM) scheme in a first slot for measuring CSI, encoding the measured CSI, and encoding each of the CSIs encoded for the plurality of downlink component carriers In the second slot, which is the next slot of the first slot, the CSIs are frequency hoped to a position symmetrical on the frequency axis with respect to the allocated uplink control channel radio resource. It can be configured to include the step of transmitting.

According to the present invention, two or more PUCCH RBs are allocated in one subframe according to the selection of a base station, and the PUCCH RB allocation can be flexibly allocated according to the number of events of CSI reports simultaneously occurring from a plurality of downlink component carriers in a carrier aggregation environment. We proposed a way to.

By using the CSI feedback method according to the present invention as described above, an efficient periodic CSI report is possible for a plurality of downlink component carriers, it is possible to obtain the effect of minimizing the constraint of PUCCH resources.

1 is a conceptual diagram illustrating an embodiment of PUCCH resource allocation.
2 is a conceptual diagram illustrating another embodiment of PUCCH resource allocation.
3 is a flowchart illustrating a CSI feedback method according to the present invention.
4 is a conceptual diagram illustrating an embodiment of a CSI multiplexing method in a CSI feedback method according to the present invention when two downlink component carriers are activated.
5 is a conceptual diagram illustrating an embodiment of a CSI multiplexing method in the CSI feedback method according to the present invention when three downlink component carriers are activated.
6 is a conceptual diagram illustrating an embodiment of a CSI multiplexing method in the CSI feedback method according to the present invention when four downlink component carriers are activated.
7 is a conceptual diagram illustrating an embodiment of a CSI multiplexing method in the CSI feedback method according to the present invention when five downlink component carriers are activated.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

A "terminal" used in the present application includes a mobile station (MS), a user equipment (UE), a user terminal (UT), a wireless terminal, an access terminal (AT), a terminal, a subscriber unit, A subscriber station (SS), a wireless device, a wireless communication device, a wireless transmit / receive unit (WTRU), a mobile node, a mobile, or other terminology. Various embodiments of the terminal may be used in various applications such as cellular telephones, smart phones with wireless communication capabilities, personal digital assistants (PDAs) with wireless communication capabilities, wireless modems, portable computers with wireless communication capabilities, Devices, gaming devices with wireless communication capabilities, music storage and playback appliances with wireless communication capabilities, Internet appliances capable of wireless Internet access and browsing, as well as portable units or terminals incorporating combinations of such functions However, the present invention is not limited thereto.

A 'base station' used in the present application generally refers to a fixed or mobile point communicating with a terminal and includes a base station, a Node-B, an eNode-B, a BTS a base transceiver system, an access point, a relay, and a femto-cell.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the present invention, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

PUCCH is transmitted using one resource block (RB). For example, in the case of PUCCH format 2, encoded 20-bit information may be delivered. PUCCH format 3, which was newly introduced in Release 10, also uses one RB and transmits up to 21 bits in the case of time-domain duplex (TDD). PUCCH format 3 is different from format 2 because it uses transmission diversity using two uplink transmission antennas.

1 is a conceptual diagram illustrating an embodiment of PUCCH resource allocation.

In Fig. 1, the vertical axis indicates frequency and one compartment divided occupies a band of 180 kHz. In addition, the horizontal axis represents 1 ms, which is one subframe transmission time, and is composed of two slots of 0.5 ms units.

When a specific UE is allocated one PUCCH RB in slot n, it is configured to be frequency hopping to a symmetrical position on the frequency axis in slot n + 1. That is, the PUCCH RB is composed of a pair of RBs allocated in slot n and RBs at positions symmetrical on the frequency axis in slot n + 1.

If the system consists of only one CC (CC-A), the periodic CSI report is performed using one PUCCH RB.

2 is a conceptual diagram illustrating another embodiment of PUCCH resource allocation.

FIG. 2 illustrates a case where two downlink component carriers are activated, and each CC may be defined as CC-A and CC-B.

At this time, the CSI report for the CC-A may be made through one allocated PUCCH RB, or the report may be made for the CC-B.

In this case, a method of determining the priority for determining the CC to which the CSI report is dropped and the CC to which the CSI report is to be performed is as follows.

Priority Groups are prioritized according to the report mode and type.

For example, type 3, type 5, type 6 including RI (Rank Information) and type 2a including wideband Precoding Matrix Indicator (PMI) have the highest priority. Next, types 2, 2b, 2c, and 4, which include wideband channel quality indicator (CQI) and PMI information, have high priority. Finally, types 1 and 1a including subband CQI and PMI information belong to the same priority group.

If it belongs to the same priority group, a lower serving cell index is higher. According to this priority, the higher priority CSI becomes a report, but the CSI for other CCs can be configured to drop.

3 is a flowchart illustrating an embodiment of a CSI feedback method according to the present invention.

Referring to FIG. 3, the CSI feedback method according to the present invention is a periodic CSI feedback method for a plurality of downlink component carriers in a carrier aggregation environment, and measuring CSI for each of the plurality of downlink component carriers (S310). Encoding the measured CSI (S320) and uplink control channel radio resources allocated to the respective CSIs encoded for the plurality of downlink component carriers in a frequency division multiplexing (FDM) scheme in a first slot And frequency hopping the second CSI to a position symmetrical on a frequency axis with respect to the allocated uplink control channel radio resource in a second slot, which is a next slot after the first slot. It may be configured to include (S330).

First, in step S310, the channel state of the downlink component carrier is measured to generate a CSI value. At this time, the downlink component carrier to be measured includes not only a primary CC (PCC) but also one or more secondary CCs (SCCs).

Next, in step S320, the CSI value measured and generated in the previous step is encoded according to a predetermined rule. CSI encoding may be performed in the manner defined in the current 3GPP TS36.211 and TS36.212, or in a manner to be defined in the future.

Finally, in step S330, CSIs for a plurality of downlink component carriers are multiplexed in one subframe and transmitted.

That is, step S330 transmits each of the CSIs encoded for the plurality of downlink component carriers by using an uplink control channel radio resource allocated in a frequency division multiplexing (FDM) scheme in a first slot. In the second slot, which is the next slot of the first slot, the respective CSIs are configured to be frequency hoped and transmitted to the symmetrical position on the frequency axis of the allocated uplink control channel radio resource.

In this case, the CSI multiplexed transmission method in step S330 described above may be configured according to various embodiments described below with reference to FIGS. 4 to 7.

On the other hand, if five PUCCH RBs allocated to each of five CCs are allocated, the performance will be the best in terms of CSI simultaneous transmission, but the number of uplink control channels is very limited considering the case where the frequency band used is not sufficient. As a result, the system as a whole is less efficient.

Accordingly, in the following embodiments, even if the number of CCs is three or more, by assigning two PUCCH RB resources and using a TDM scheme in some cases, not only can the CSI report be efficiently but also the PUCCH resource constraints can be minimized. . That is, efficient periodic CSI report is possible for a plurality of CCs, and there is an effect of minimizing PUCCH resource constraints. However, the following embodiments are only preferable examples of trade-off in terms of resource efficiency of PUCCH and performance in order to minimize CSI drop, and the PUCCH RB in one subframe is the maximum number of activated CCs. It may be configured to be assigned as many.

FIG. 4 illustrates a case where two CCs are activated, FIG. 5 illustrates three CCs activated, FIG. 6 illustrates four CCs activated, and FIG. 7 illustrates a CSI multiplexing method when five CCs are activated. Conceptual diagram.

4 is a conceptual diagram illustrating an embodiment of a CSI multiplexing method in a CSI feedback method according to the present invention when two downlink component carriers are activated.

In FIG. 4, two downlink component carriers (CC-A, CC-B) are activated and two uplink control channel radio resource RBs are allocated.

In this case, the two RBs allocate resources in the frequency domain used when frequency hopping occurs according to slots. Whether two RBs are allocated may be selected by the base station and may be configured to inform the UE through signaling (eg, RRC signaling) in a higher layer of the physical layer or more.

Since there are two CCs and two PUCCH RBs, the CSI for each CC can be simultaneously reported in one subframe, so that the CSI for each CC does not need to be adjusted by the TDM scheme.

At this time, which CCC of which CC is to be allocated to which PUCCH RB may be in accordance with a predetermined rule. For example, a primary CC may be assigned to a low frequency and a secondary CC may be assigned to a high frequency or vice versa.

However, even if two CCs and two PUCCH RBs can be used, when only one CSI is reported in one subframe, only one PUCCH RB can be used, and it is not always necessary to occupy two PUCCH RBs.

5 is a conceptual diagram illustrating an embodiment of a CSI multiplexing method in the CSI feedback method according to the present invention when three downlink component carriers are activated.

In FIG. 5, three downlink component carriers CC-A, CC-B, and CC-C are activated, and two uplink control channel radio resource RBs are allocated.

In this case, the CC (CC-A) corresponding to the primary serving cell occupies one PUCCH RB, and the other two CCs (CC-B, CC-C) may be configured to share one PUCCH RB in a TDM manner. have.

In this case, the CSI of the CC-A can be fed back without colliding with the CSI of other CCs, but the remaining CCs (CC-B, CC-C) reports the CSI by the conventional TDM method, the intermittent collision of the CSI feedback This can happen. Therefore, in this case, when scheduling at the base station, in consideration of such a situation, it is necessary to allocate high priority data to the primary CC (CC-A) to obtain performance improvement through collision-free CSI feedback.

Meanwhile, even when all three CCs are activated, a situation in which CSIs for three CCs are simultaneously reported in one subframe may not always occur. That is, CSI reporting may be needed only in one CC or two CCs in one subframe. In this case, when a CSI report event occurs in only one CC, only one PUCCH RB is used, and when a CSI report event occurs in two CCs, a PUCCH RB may be allocated as illustrated in FIG. 4.

When the CSI report event occurs in the CC of the serving cell other than the CC of the primary serving cell, the RB allocation rule can be easily created. For example, the carrier indicator number assigned to each CC and the rules for allocating the RB frequency in ascending order or the rules for allocating in descending order.

6 is a conceptual diagram illustrating an embodiment of a CSI multiplexing method in the CSI feedback method according to the present invention when four downlink component carriers are activated.

In FIG. 6, four downlink component carriers CC-A, CC-B, CC-C, and CC-D are activated, and two uplink control channel radio resources RBs are allocated.

In this case, the CSI for the two CCs for each PUCCH RB may be configured to share and send in a TDM manner. That is, two pairs of two CCs (for example, a pair composed of CC-A and CC-B and a pair composed of CC-C and CC-D) exist. Within each pair, the same degree of collision will occur as in the case of resource allocation illustrated in FIG.

In this method, you can make a simple rule to map which CC's CSI to which PUCCH RB. As described above, a priority may be given to the CC of the primary serving cell and the remaining CCs may be prioritized according to the number of carrier indicators. Even if four CCs are activated, if only one CSI report event occurs in the same subframe, only one PUCCH RB is allocated. If two CSI reports are needed, two PUCCH RBs are allocated. If three CSI reports are needed, resource allocation as illustrated in FIG. 5 may be used.

Finally, FIG. 7 is a conceptual diagram illustrating an embodiment of the CSI multiplexing method in the CSI feedback method according to the present invention when five downlink component carriers are activated.

In FIG. 7, five downlink component carriers (CC-A, CC-B, CC-C, CC-D, and CC-E) are activated, and two uplink control channel radio resource RBs are allocated. have.

At this time, two CCs (CC-A, CC-B) are allocated to one RB in a TDM manner and the other three CCs (CC-C, CC-D, CC-E) are allocated to another RB.

When three CCs are allocated to one RB in a TDM manner, performance degradation will be relatively high, but a situation where CSIs occur simultaneously from five CCs may be very low.

Meanwhile, even if five CCs are active, if only two CSIs are generated at the same time, the allocation may be performed as illustrated in FIG. 4. If three CSI reports are needed at the same time, the allocation may be performed as illustrated in FIG. 5. If four CSI reports are needed at the same time, they can be allocated as illustrated in FIG.

Since the base station knows when the event for the periodic report occurs, it is not a problem to receive.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims

A periodic CSI feedback method for a plurality of downlink component carriers in a carrier aggregation environment,
Measuring CSI for each of a plurality of downlink component carriers;
Encoding the measured CSI; And
Each of the CSIs encoded for the plurality of downlink component carriers is transmitted using an uplink control channel radio resource allocated in a frequency division multiplexing (FDM) scheme in a first slot, and is a next slot of the first slot. And in the second slot, frequency hopping and transmitting each CSI to a position symmetrical on a frequency axis with respect to the allocated uplink control channel radio resource.