WO2011123976A1

WO2011123976A1 - Method and apparatus for switching between flat feedback mode and hierarchical feedback mode

Info

Publication number: WO2011123976A1
Application number: PCT/CN2010/000446
Authority: WO
Inventors: 吕荻; 杨红卫
Original assignee: 上海贝尔股份有限公司; 阿尔卡特朗讯
Priority date: 2010-04-06
Filing date: 2010-04-06
Publication date: 2011-10-13
Also published as: CN102726108B; CN102726108A

Abstract

The present invention provides a method for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system, which includes: feeding back the precoding matrix index from a user terminal to a base station in the flat feedback mode, after associating the user terminal with the base station; monitoring the measurement which indicates the channel change speed of the user terminal; judging whether the measurement which indicates the channel change speed of the user terminal exceeds a predetermined threshold; and if judging that the measurement which indicates the channel change speed of the user terminal exceeds the predetermined threshold, feeding back the precoding matrix index from the user terminal to the base station by switching from the flat feedback mode to the hierarchical feedback mode.

Description

In flat feedback mode and hierarchical feedback mode

Method and device for switching between

Technical field

The present invention relates to the field of mobile communications, and more particularly to a method and apparatus for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system, capable of adapting differently according to channel conditions of a user terminal (UE) The feedback mode, and can use the hierarchical feedback mode to improve the feedback accuracy when the channel changes slowly. Background technique

In the Long Term Evolution Version 8 (LTE Rel-8) specification, feedback strategies and codebooks are specifically optimized for SU-MIM0 (single-user multiple-input multiple-output). However, it is known that MU-MIM0 is more sensitive to feedback accuracy than SU-MIM0. Low feedback accuracy will result in poor MU-MIM0 performance, thus hindering the development of the theoretical potential of MU-MIM0. To address this issue, the recent LTE-A discussion focused on advanced feedback mechanisms that improve the performance of MU-MIM0. Hierarchical feedback is one of the candidates with strong prospects.

The idea of hierarchical feedback has been proposed to take advantage of the correlation of the UE (i) terminal in the time or frequency domain. Hierarchical feedback is very useful in scenarios where the UE channel is slowly changing. However, when the time or frequency dependence of the channel is low, hierarchical feedback may result in inefficient use of feedback overhead.

There is a need to provide an effective way to improve MU-MIM0 (multi-user multiple input multiple output) feedback accuracy. Summary of the invention

In order to overcome the above drawbacks of the prior art, the present invention has been made. Accordingly, it is an object of the present invention to provide a method and apparatus for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system, capable of adapting different feedback modes according to channel conditions of a user terminal (UE), And the hierarchical feedback mode can be utilized to improve the feedback accuracy when the channel is slowly changing.

In order to achieve the above object, according to the present invention, a mobile communication system is proposed. The method for switching between the flat feedback mode and the hierarchical feedback mode includes: after the user terminal associates with the base station, adopting a flat feedback mode to feed back the precoding matrix index from the user terminal to the base station; monitoring indicates that the channel speed of the user terminal changes. Metric; determining whether a metric indicating a channel change speed of the user terminal exceeds a predetermined threshold; and if determining that the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold, switching from the flat feedback mode to the hierarchical feedback mode from the user terminal The precoding matrix index is fed back to the base station.

Preferably, the metric indicating the channel change speed of the user terminal is the correlation of the channel of the user terminal in the time domain or the frequency domain.

Preferably, the method further includes: in the hierarchical feedback mode, if the metric indicating the channel change speed of the user terminal becomes lower than a predetermined threshold, switching from the hierarchical feedback mode to the flat feedback mode from the user terminal to the base station Feedback precoding matrix index.

Preferably, the precoding matrix index fed back from the user terminal to the base station in the hierarchical feedback mode includes a portion of the index of the index of the corresponding codeword in the codebook in the hierarchical feedback mode.

Preferably, the precoding matrix index fed back from the user terminal to the base station in the hierarchical feedback mode includes bits indicating a "up" or "down" hierarchical tree search.

Preferably, the mobile communication system is a multi-user multiple input multiple output communication system. In order to achieve the above object, according to the present invention, an apparatus for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system is further provided, comprising: monitoring means for monitoring a metric indicating a channel change speed of the user terminal; Determining means, determining whether a metric indicating a channel change speed of the user terminal exceeds a predetermined threshold; and indexing feedback means, after the user terminal associates with the base station, using a flat feedback mode to feed back a precoding matrix index from the user terminal to the base station; If the determining means determines that the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold, then switching from the flat feedback mode to the hierarchical feedback mode to feed back the precoding matrix index from the user terminal to the base station.

Accordingly, the present invention proposes a feedback signaling and framework structure suitable for the channel conditions of each user, which can best utilize hierarchical feedback and flat feedback. DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the Detailed Description of Description

1 shows an example of a codebook of a binary tree structure in a hierarchical feedback mode; FIG. 2 is a flowchart showing a method of switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system;

Fig. 3 is a block diagram showing an apparatus for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system. detailed description

Hereinafter, the present invention will be described based on the drawings. In the following description, some specific embodiments are for illustrative purposes only and should not be construed as limiting the invention. Conventional structures or configurations will be omitted when it may result in obscuring the understanding of the present invention.

The idea of hierarchical feedback stems from improved feedback accuracy and improved overall performance of wireless communication systems with limited feedback. The hierarchical feedback mechanism utilizes the correlation of the physical channel in the time or frequency domain. The codebooks in the hierarchical feedback are organized in a binary tree structure, and the codeword-coupled indices in the given sub-tree of the j-th order have the same (j-i) valid bits, as shown in FIG.

When the channel changes slowly, the codewords corresponding to adjacent time slots or frequencies are only slightly different, and the positions of the different bits are towards the end of the codeword index, ie, most of the most significant bits of the adjacent codeword index are the same. . In this way, continuous feedback can result in a more accurate description of the UE channel than conventional feedback that utilizes equal amount of feedback overhead.

It is assumed that Bmax represents the total rank of the trees in the codebook of the hierarchical feedback, and B_feedback is the number of bits used to indicate the PMI (Precoding Matrix Index) in the uplink feedback signaling. For the current LTE specification, B_feedback = 4, and here as an example, Bmax = 12 is used. When the channel changes slowly, the following cases can be used as an example:

At the beginning of the uplink feedback, ie, at time t-0, the UE selects the codeword from the deepest level of the codebook with hierarchical feedback of the 12-bit index, and the index is ldx_0 = [1 0 0 1 0 0 1 0 0 1 1 0]. Then, the UE feeds back the previous B_feedback bits of Idx-0, and the PMI of the feedback at t-0 is: PMI_0=[1 0 0 1]. At the second feedback moment, ie, at time t_1, the UE selects a new codeword from the codebook of the hierarchical feedback. Due to the slow change of the UE channel, it is only assumed that the last 6 bits of the index of the new codeword are different from Idx-0, and the index of the newly selected codeword is Idx-1 = [1 0 0 1 0 0001 1 1 0] . According to the hierarchical feedback algorithm, in this case, the UE feeds back the middle (B_feedback-1) bits of Idx-1, while the extra bits used in the PMI feedback indicate the "down" case (ie, in the hierarchical tree) Search down)). Therefore, the feedback PMI at t-1 is: PMI-1 = [1 0 0 0], and the first bit "1" corresponds to "down" negotiated at the UE and the eNB (base station).

In this way, upon receiving PMI_1 = [1 0 0 0], the eNB can reconstruct a portion of Idx-0 based on PMI_1, PMI_0, and hierarchical feedback algorithms. The index of the reconstructed codeword is PMI-1-re = [1001000], where the first four bits are from PMI-0 and the last three bits are from PMI_1. At the subsequent feedback moment, whenever the PMI selection indicates a "down" condition, it follows the same process as described above.

It can be clearly seen from this example that the hierarchical feedback and its corresponding codebook structure enable more accurate feedback of channel information when the channel is slowly changing and adjacent codewords share a large number of most significant bits, since hierarchical feedback is utilized The number of bits (eg, 7) of the index reconstructed at the eNB may be much larger than the number of index bits (eg, 4) reconstructed in the flat algorithm. However, when the channel changes rapidly, that is, when the correlation between adjacent channels in the time domain or the frequency domain is low, the hierarchical feedback frame structure may cause inefficient use of feedback overhead. Here, the foregoing case will still be used as an example.

At the second feedback moment, at time t_1, the UE selects a new codeword from the codebook of the hierarchical feedback. Since the UE channel is assumed to be changing rapidly, the selected codeword is different from ldx_0, and Idx-1 = [1 0 1 0 0 1 0 0 1 0 1 0] is assumed. That is, only the first two bits of Idx-1 are the same as the first two bits of Idx-0. According to the hierarchical feedback algorithm, the UE feeds back the front (B-feedback-1) bits of Idx-1, while the first bit is used to indicate the "upward" condition (i.e., up search in the hierarchical tree). Therefore, the feedback PMI at t-1 is: PMI_1 = [0 1 0 1], where the first bit "0" corresponds to the "up" negotiated at the UE and the eNB.

In this way, when PMI-1 = [0 1 0 1] is received, the eNB knows that this is an "up" condition and can be reconstructed based on PMI-1 and hierarchical feedback algorithms. Part of ldx_ 0. The index of the reconstructed codeword PMI _ l -re =. [1 0 1] , which is only the first three bits of Idx_ l. In contrast to the flat feedback in which the PMI of the UE is always represented by four bits, in this case, the hierarchical feedback causes an inefficient use of its feedback overhead. This occurs when the UE channel is at medium speed or high speed.

In the flat feedback of B_feedback = 4, the UE selects a codeword from a codebook of size 16 (2 ^Λ 4 = 16) each time a codeword selection is made. In other words, the UE feedback accuracy is the same every time. Even if the codewords selected by the two consecutive feedbacks are the same, the same flaws need to be transmitted in the two feedbacks. As a result, the feedback overhead cannot be fully utilized.

The idea of the present invention is to propose a MU-MIM0 feedback framework and associated signaling that enables semi-dynamic switching between a hierarchical feedback mode and a conventional flat feedback mode. The MAC layer control module determines the feedback mode of the UE based on a particular metric of the UE channel (e.g., time or frequency correlation). When the metric reaches the threshold, the control module will reconfigure the feedback mode of the UE through downlink signaling. In this manner, the UE can be semi-dynamically switched between the hierarchical feedback mode and the conventional flat feedback mode to take full advantage of its channel characteristics and feedback overhead bits.

As discussed in the previous section, hierarchical feedback works effectively in scenarios where the channel is highly correlated in the time or frequency domain, and inefficient when the channel changes rapidly. Therefore, as an example, time domain correlation can be selected as a metric, and Temp-corre = 0.5 is used as a threshold for triggering feedback mode switching.

After the UE is associated with the base station, the feedback mode can be set to a conventional non-hierarchical flat feedback mode. In the subsequent uplink feedback, the PMI will be calculated and fed back in accordance with the LTE Rel-8 compatible approach. At the same time, the time domain correlation of the channel will be periodically monitored and calculated by the MAC layer control module. When the threshold Temp_corre = 0. 5 is reached, the transition from the flat feedback mode to the hierarchical feedback mode is triggered. The MAC layer control module will signal the handover to the physical layer and provide an indication to the UE regarding the handover. After the mode switch occurs, the UE will operate in a hierarchical feedback mode, and the PMI calculations and updates will follow the process described above.

Thereafter, the monitoring of the metric Temp_corre will be performed periodically, and if the time domain correlation of the channel becomes lower than the threshold Temp_corre = 0.5, the UE will switch from the hierarchical feedback mode to the flat feedback mode to perform the calculation and feedback of the PMI. 2 is a flow chart showing a method of switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system.

As shown in FIG. 2, in step 201, after the user terminal associates with the base station, a flat feedback mode is used to feed back the precoding matrix index from the user terminal to the base station. In step 203, a metric indicating the channel change speed of the user terminal (e.g., the correlation of the channel in the time domain or the frequency domain) is monitored. At step 205, it is determined whether the metric indicating the channel change speed of the user terminal exceeds a predetermined alarm value. Then, in step 207, if it is determined that the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold, the flat feedback mode is switched to the hierarchical feedback mode to feed back the precoding matrix index from the user terminal to the base station.

Fig. 3 is a block diagram showing an apparatus for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system.

As shown in FIG. 3, the apparatus according to the present invention includes: a monitoring device 301, a determining device 303, and an index feedback device 305. The monitoring device 301 monitors a metric indicating the speed of channel change of the user terminal. The determining means 303 determines whether the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold. The index feedback device 305, after the user terminal associates with the base station, uses a flat feedback mode to feed back the precoding matrix index from the user terminal to the base station. If the determining means determines that the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold, the index feedback means 305 switches from the flat feedback mode to the hierarchical feedback mode to feed back the precoding matrix index from the user terminal to the base station.

The feedback mode is fixed in LTE Reb 8, that is, the flat feedback mode. This is inefficient when the UE channel is highly correlated in the time or frequency domain. The semi-dynamic switching between hierarchical feedback and flat feedback proposed by the present invention can adapt the feedback mode according to the channel condition of the UE, and provides higher feedback accuracy with the same feedback overhead as LTE Re-8. Therefore, the performance of the MU-MIM0 system employing the mode switching of the present invention will be superior to that in the LTE Reb 8.

The present invention combines the advantages of hierarchical feedback (which has been proposed for MU-MIM0 in the LTE standard) and the flat feedback mechanism in LTE Re-8. A more accurate physical channel description than LTE Re-8 can be implemented with the same feedback overhead.

In addition, when the UE channel is correlated in the time domain or the frequency domain, the solution of the present invention adopts Hierarchical feedback is used to provide more accurate feedback on the UE channel. An increase in accuracy will result in an increase in the performance of the MU-MIM0 system.

The above examples are for illustrative purposes only and are not intended to limit the invention. It will be understood by those skilled in the art that various modifications and substitutions may be made to the embodiments without departing from the scope and spirit of the invention. In the scope. .

Claims

Claim

A method for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system, comprising:

After the user terminal associates with the base station, the flat feedback mode is used to feed back the precoding matrix index from the user terminal to the base station;

Monitoring a metric indicating a channel change speed of the user terminal;

Determining whether the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold; and

If it is determined that the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold, the flat feedback mode is switched to the hierarchical feedback mode to feed back the precoding matrix index from the user terminal to the base station.

2. The method according to claim 1, wherein the metric indicating the channel change speed of the user terminal is the correlation of the channel of the user terminal in the time domain or the frequency domain.

3. The method of claim 1 further comprising:

In the hierarchical feedback mode, if the metric indicating the channel change speed of the user terminal becomes lower than the predetermined threshold, the hierarchical feedback mode is switched to the flat feedback mode to feed back the precoding matrix index from the user terminal to the base station.

4. The method of claim 1, wherein the precoding matrix index fed back from the user terminal to the base station in the hierarchical feedback mode comprises a portion of bits of an index of a corresponding codeword in a codebook in a hierarchical feedback mode.

5. The method of claim 1, wherein the precoding matrix index fed back from the user terminal to the base station in the hierarchical feedback mode comprises bits indicating a "up" or "down" hierarchical tree search.

6. The method of claim 1 wherein the mobile communication system is a multi-user multiple input multiple output communication system.

7. A device for switching between a flat feedback mode and a hierarchical feedback mode in a mobile communication system, comprising:

a monitoring device, monitoring a metric indicating a channel change speed of the user terminal;

Determining means, determining whether the metric indicating the channel change speed of the user terminal exceeds the pre-measure a threshold; and

An index feedback device, after the user terminal associates with the base station, adopts a flat feedback mode to feed back the precoding matrix index from the user terminal to the base station; and if the determining device determines that the metric indicating the channel change speed of the user terminal exceeds a predetermined threshold, The pre-coding matrix index is fed back from the user terminal to the base station by switching from the flat feedback mode to the hierarchical feedback mode.

8. The apparatus according to claim 7, wherein the metric indicating the channel change speed of the user terminal is the correlation of the channel of the user terminal in the time domain or the frequency domain.

9. The apparatus according to claim 7, wherein in the hierarchical feedback mode, if the determining means determines that the metric indicating the channel change speed of the user terminal becomes lower than a predetermined threshold, the index feedback means switches from the hierarchical feedback mode The flat feedback mode is fed to feed back the precoding matrix index from the user terminal to the base station.

10. The apparatus according to claim 7, wherein the precoding matrix index fed back from the user terminal to the base station in the hierarchical feedback mode comprises a part of bits of an index of a corresponding codeword in a codebook in the hierarchical feedback mode.

1 1. The apparatus according to claim 7, wherein the precoding matrix index fed back from the user terminal to the base station in the hierarchical feedback mode comprises a bit indicating "up" or "down," hierarchical tree search.

12. Apparatus according to claim 7 wherein said mobile communication system is a multi-user multiple input multiple output communication system.