KR20110026683A - Cooperative multi hop relay apparatus and method thereof - Google Patents

Abstract

PURPOSE: A cooperative multi hop relay apparatus and a method thereof are provided to optimize the number of feedback bits by using a code book in consideration of the number of repeaters in order to configure an optimal channel environment when transferring feedback information from a base station. CONSTITUTION: A mobile communication terminal(10) transfers a pilot signal, and a repeater receives and transmits the pilot signal. A base station(30) transfers a feedback signal by using the repeater in consideration of the performance of a bit error rate. The base station confirms the channel state between the repeater and the base station based on the pilot signal received from the repeater. The mobile communication terminal transfers data through the repeater which considers the best channel environment between the repeater and the base station.

Description

Multi-hop cooperative relay apparatus and method {COOPERATIVE MULTI HOP RELAY APPARATUS AND METHOD THEREOF}

The present invention relates to a multi-hop cooperative relay apparatus and method, and more particularly, to a multi-hop cooperative relay apparatus and method for selecting a repeater having a good performance among a plurality of repeaters as a repeater system using a closed-loop multi-antenna transmission and reception technology.

4G (4G) mobile users are demanding various quality services from low to high speed, real time and non-real time through mobile communication network, like wired broadband network, and are expected to increase further in the future.

In a ubiquitous environment where anyone can easily use a computer and network anytime, anywhere, current mobile communication technologies have limitations to meet the needs of these users.

In this situation, multi-antenna transmission and reception technology is widely known as one of the technologies capable of continuously maintaining high capacity, high quality, high efficiency, and high reliability communication even in a poor transmission environment. However, when the user is at the end of a cell, obscured by tall buildings or mountains, or in deep fading, it is difficult to guarantee its performance. Therefore, cooperative relay communication using a repeater has been proposed. Cooperative relay communication expands the cell area and improves the user's performance at the cell end.

As shown in FIG. 1, a candidate for LTE-Advanced technology, which is currently being researched as a 4G mobile communication technology, is listed.

Cooperative communication began to be studied in 1979 after the information theory of relay channels was announced. Such a cooperative communication can obtain diversity gain by performing cooperative communication with another terminal from a terminal having one antenna.

Cooperative relay diversity schemes using multi-antenna transmission / reception techniques have been studied. These studies have been developed to obtain cooperative relay diversity using space-time codes that can obtain a large diversity gain effect.

If considering a less mobile environment between the repeater and the base station using a repeater rather than a cooperative terminal, as shown in FIG. 2, the maximum non-transmission for feeding back the channel state information than the technique using the space-time code such as the Alamoti technique, or Closed loop multi-antenna transmit / receive techniques such as gain transmission can achieve greater diversity.

On the other hand, Multiple Input Multiple Output (MIMO) is a transmission method including multiple transmit antennas and multiple receive antennas that significantly increase the link capacity of wireless communication systems. Various transmission strategies require a transmit array with some information about the channel response between each transmit antenna element and each receive antenna element, which is often a "closed-loop" MIMO. It is referred to as. Techniques such as uplink sounding in time division duplexing (TDD) systems and channel feedback in TDD or frequency division duplexing (FDD) systems can be used to obtain full broadband channel information at the transmitter. Limited feedback methods, such as feeding back an antenna selection indicator or codebook-based beamforming weights selection, can reduce the amount of feedback unlike full channel feedback. These limited feedback methods can be improved if the power weights are fed back according to codebook weights.

However, conveying power weights to the transmitter can require significant channel resources. Accordingly, there is a need for an efficient feedback method for providing power weights to transmitters.

Therefore, the next-generation mobile communication system not only increases cell coverage, but also requires higher error performance at cell edges and shadow areas, and thus, it is possible to apply techniques that can obtain better performance according to the situation and to exhibit higher performance. Skill is required.

Disclosure of Invention The present invention has been made in view of the above problems, and an object thereof is to provide a multi-hop cooperative relay apparatus and a method for applying a closed-loop multi-antenna transmission and reception technique in consideration of small mobility between a repeater and a base station.

Another object of the present invention is to provide a multi-hop cooperative relay apparatus and method for improving the error performance of transmission and reception by applying a closed loop multi-antenna transmission and reception technique to a repeater system.

Another object of the present invention is a multi-hop cooperative relay apparatus and method for optimizing and transmitting the number of feedback bits using a codebook to a corresponding repeater in consideration of the number of repeaters so as to provide an optimal channel environment when transmitting feedback information from a base station to a repeater. In providing.

It is another object of the present invention to provide a feedback frame format for improving the performance of a communication environment.

Technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A multi-hop cooperative relay apparatus according to an aspect of the present invention for achieving the above object, the multi-hop cooperative relay apparatus using a codebook, the mobile communication terminal for transmitting a pilot signal; At least one repeater receiving the pilot signal and transmitting the pilot signal; And acquiring a weight vector from channel characteristic information obtained from pilot signals received from the mobile communication terminal and the repeater, and determining a codebook index corresponding to the weight vector and an approximation to determine a signal-to-noise ratio of the pilot signal of the mobile communication terminal. And a base station configured to transmit the feedback information considering the performance of the bit error rate by selecting the at least one repeater for transmitting a pilot signal superior to (SNR), wherein the at least one selected repeater includes data transmitted from the mobile communication terminal. Decodes and encodes and transmits the codebook selected based on the codebook index together with the channel characteristic information to the base station.

Here, the codebook is a maximum ratio transmission (MRT) codebook of WiMAX.

Here, the feedback information includes repeater ID information of the repeater having excellent signal-to-noise ratio and codebook index information, and the total number of bits is 7 bits or less.

According to another aspect of the present invention, there is provided a multi-hop cooperative relay method, comprising: a multi-hop cooperative relay method using a codebook, the base station receiving pilot signals from a mobile communication terminal and a repeater respectively; Obtaining a weight vector from channel characteristic information obtained from pilot signals received from the mobile communication terminal and the repeater, respectively; Feedback information considering bit error rate performance by selecting at least one repeater for determining a codebook index corresponding to the weight vector and an approximation and transmitting a pilot signal superior to a signal-to-noise ratio (SNR) of a pilot signal of a mobile communication terminal. Transmitting; And receiving, by the repeater receiving the feedback information, a signal for decoding and encoding data transmitted from the mobile communication terminal and mixing and transmitting the codebook selected based on the codebook index with the channel characteristic information.

Here, the feedback information, the total number of bits is 7 bits or less, when one of the total repeaters is selected is made up of feedback information including only the repeater ID information of the selected repeater, all repeaters of the total repeaters are selected If it is selected, it does not include the repeater ID information of the selected repeater and consists of feedback information including only the codebook index, and if selected except the repeater of one of the total repeaters, it includes the repeater ID information of the excluded repeater and the codebook index. Consists of the feedback information included.

According to the above-mentioned problem solving means, the present invention not only increases cell coverage but also exhibits higher error performance in cell edges and shadowed areas, thereby improving the communication environment.

In addition, according to the repeater system and the repeater selection method using the closed-loop multi-antenna transmission and reception technology, the error performance can be improved than the conventional communication method using the repeater.

In the multi-hop cooperative relay apparatus and method according to the embodiment of the present invention, since there is no movement between the repeater and the base station, such as a mobile communication terminal, the maximum ratio transmission, which is a closed-loop multi-antenna transmission and reception technique, may be advantageously applied to such a situation. Accordingly, the base station checks the channel characteristic information between the repeater and the base station in the pilot signal received from the repeater, obtains the weight vector from the channel characteristic information, compares the weight vector with the codebook, and feeds back the adjacent codebook index to the repeater.

Accordingly, the present invention proposes a method for optimizing the number of bits of feedback information to be fed back and a technical configuration of a frame structure of the feedback information.

In the following description, specific details of the multi-hop cooperative relay apparatus and method of the present invention are shown to provide a more general understanding of the present invention, and the present invention may be easily implemented without these specific details and also by modification thereof. It will be apparent to those of ordinary skill in the art.

In the description of Haga, the repeater and the base station have the same codebook.

On the other hand, the present invention will be described for the operation and operation according to the multi-hop cooperative relay method using the MRT technique to help understand, but not only MRT technique, but also gain gain (EGT: Equal Gain) which is one of the closed loop MIMO technique In the case of Transmission), since the form of feedback is the same, the same may be applied.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail, focusing on the parts necessary to understand the operation and action according to the present invention.

Figure 3 is an exemplary view illustrating a multi-hop cooperative relay method according to an embodiment of the present invention.

Referring to FIG. 3, in general, in the cooperative relaying method, a mobile communication terminal 10 of a source terminal transmits data to a repeater 20 and a base station 30, and the repeater 20 may receive data from the mobile communication terminal 10. The signal is transmitted to the base station 30. In this case, the repeater 20 processes the signal received from the mobile communication terminal 10 and transmits the signal to the base station 30.

First, the repeater 20 of the cooperative terminal only amplifies a signal transmitted from the mobile communication terminal 10 and then transmits the signal to the base station 30 of the target terminal (amplify and forward method) and the mobile communication terminal 10. The decoding and forwarding method of decoding the signal transmitted from the () and the coded cooperation method (coded cooperation method) to integrate the channel coding (coded cooperation method), each of which is shown in Figure 4 Is shown.

As can be seen from the cooperative relay method of each of these methods, it can be seen that the signal-to-noise ratio (SNR) is superior to that when the cooperative relay is not performed at 10 dB or more.

At this time, if the SNR is written in an excellent order, the order is Coded cooperation-> Decoded and forward-> Amplify and forward.

Among them, Coded cooperation has the most excellent SNR, and since it is newly coded by the repeater 20, the decoded and forward technique, which is a technique of simply decoding and transmitting a signal of the mobile communication terminal 10, is most used.

Accordingly, in the multi-hop cooperative relay apparatus according to the present invention, a plurality of repeaters 20 using a decode and forward technique exist in a cell.

6 is an exemplary diagram for describing a cooperative relaying method of a multi-hop cooperative relay apparatus according to an exemplary embodiment of the present invention.

Referring to FIG. 6, the mobile communication terminal 10 first transmits a pilot signal to the repeaters 20a to 20d using an additive white gaussian noise (AWGN) channel.

In this case, if the channel state of the first hop in which the signals of the repeaters 20a to 20d are transmitted in the mobile communication terminal 10 is not good, the second communication between the repeaters 20a to 20d and the base station 30 is performed. Since the performance at the hop is greatly reduced, the present invention assumes that the first hop is an AWGN channel having only additive white gaussian noise.

The repeaters 20a to 20d decode the received pilot signal using a decode and forward technique, and then recode the transmitted pilot signal to the base station 30.

Then, the base station 30 checks the channel state between the repeater 20 and the base station 30 in the pilot signal received from the repeater 20 and obtains a weight vector from the channel.

A method for obtaining a weight vector is described as follows.

의 특이값을 아래의 수학식 1을 통해 분해한다. 여기서,

First, the channel at 2 hops

The singular value of is decomposed by Equation 1 below. here,

Here, U ² means a precoding vector and V ^2H means a combining vector.

At this time, the signal received from the base station 30 is shown in Equation 2 below, the SNR of the received signal is shown in Equation 3 below.

는 전송 신호 에너지를 의미한다.Where No means noise spectral density,

Means transmission signal energy.

Accordingly, the base station 30 obtains an optimization weight vector U _OPT of the weight vector U that can maximize the SNR of Equation 3 to find the codebook index using Equation 4 below.

는 2-놈을 의미한다.here,

Means 2-norm.

Subsequently, a weightbook index obtained through the above-described process is compared with a codebook, and the closest codebook index is selected and fed back to the repeater 20. At this time, by transmitting the ID information of the repeater with the largest signal-to-noise ratio (SNR) value of the channel, the repeater having the best channel state is selected.

Since the repeater can know whether it is selected by the ID information, the selected repeater notifies the mobile communication terminal 10 that the selected repeater is selected.

Accordingly, the mobile communication terminal 10 transmits data through a repeater considering the best channel environment between the repeaters 20a to 20d and the base station 30.

Then, the repeater having the best channel environment multiplies the channel characteristic information by the codebook and data and transmits the same to the base station 30.

On the other hand, if there are four repeaters 20a to 20d, there are four cases in which all four repeaters are selected from the case of selecting one repeater. The number of bits of feedback information that the base station 30 needs to feed back to the repeaters 20a to 20d according to the number of repeaters 20a to 20d is shown in FIG. 7, and the codebook is the maximum ratio transmission codebook of WiMAX. The bits V (2, 1, 3) and V (3, 1, 3) were used, and the total maximum number of bits was limited to 7 bits. At this time, the index information consists of repeater ID information and codebook index information.

The following describes how the base station 30 selects a repeater.

In a line of sight environment, the mobile communication terminal 10 transmits a pilot signal to the repeaters 20a to 20d and directly transmits a pilot signal to the base station 30 without passing through the repeaters 20a to 20d. .

As a result, the base station 30 compares the magnitude of the SNR of the pilot signal received from the mobile communication terminal 10 and the SNR of the pilot signal received from the repeaters 20a to 20d and receives the received signal from the mobile communication terminal 10. When the SNR of the pilot signal received from the repeaters 20a to 20d larger than the SNR of the pilot signal exists, the corresponding repeater is selected.

However, if the SNR of the pilot signal received from the repeaters 20a to 20d larger than the SNR of the pilot signal received from the mobile communication terminal 10 does not exist, the base station 30 is the mobile communication terminal 10 and the base station 30. Since the communication channel environment is the best, it is recognized that the use of the repeaters 20a to 20d is unnecessary and the corresponding repeater is not selected.

The feedback information is transmitted to the repeater selected by the repeater selection method as described above. In case of four repeaters, the feedback information and the number of bits of the feedback information will be described as follows.

First, when only one repeater is selected, since no maximum transmission is possible between the repeater and the base station 30, the feedback is selected using feedback information including only the repeater ID information (2 bits) without feeding back the codebook index bits. Feedback to the repeater. In this case, the total bit is 2 bits.

When two repeaters are selected, four bits (one repeater requires two bits) as the repeater ID information are fed back, and the feedback information is fed back to the selected repeater using feedback information including three bits as codebook index information. . In this case, the total bit is 7 bits.

When three repeaters are selected, a total of 6 bits is required because one repeater requires 2 bits as the selected repeater ID information, but the number of feedback bits is reduced by transmitting 2 bits with unselected repeater ID information. The feedback information is fed back to the selected repeater using feedback information including 3 bits as codebook index information. In this case, the total bit is 5 bits.

When four repeaters are selected, all the repeaters are selected, and thus, the repeater ID information does not need to be transmitted, and only 3 bits, which are codebook index bits, are fed back.

Accordingly, the number of bits of the feedback information can be limited to 7 bits at maximum, and the frame structure of the feedback information includes 2 to 4 bits of repeater ID information and 3 bits of codebook index information as shown in FIG. 8.

The repeater receiving the feedback information first checks the total number of bits to recognize how many repeaters the base station 30 has selected, and then checks the repeater ID information to determine whether it is selected.

If it is determined that it is selected, the repeater determines the codebook based on the codebook index information, and the determined codebook multiplies the channel characteristic information and transmits the data to the base station together when transmitting the data of the mobile communication terminal.

9 is an exemplary diagram for explaining a cooperative relay control protocol according to an embodiment of the present invention. In this case, it is assumed that U1 is a mobile communication terminal, R1 to R4 are first to fourth repeaters, and E1 is a base station, one mobile communication terminal, four first to fourth repeaters, and one base station. .

Referring to FIG. 9, first, FIG. 9A illustrates a case where one first repeater R1 is selected by the base station E1, and a pilot signal is generated by the mobile communication terminal U1. It is transmitted to the fourth repeaters R1 to R4, and is transmitted from the first to fourth repeaters R1 to R4 to the base station E1.

Since the feedback information is transmitted from the base station E1 to all the repeaters R1 to R4, the feedback information is transmitted to the first to fourth repeaters R1 to R4, and the selected first repeater R1 to the mobile communication terminal U1. Is sent).

The data signal is transmitted from the mobile communication terminal U1 to the first repeater R1 and from the first repeater R1 to the base station E1.

As a result of the experiment, as shown in FIG. 10A, when the SNR is 10 dB or less, even if one repeater is selected, the performance does not have a significant effect because the channel state difference is not large. However, the SNR is above 10dB BER of 10 ^- it can be seen that the ³ when increasing the performance of 20dB.

FIG. 9B illustrates a case in which two second and third repeaters R2 and R3 are selected by the base station E1, and pilot signals are generated by the first to fourth terminals in the mobile communication terminal U1. It is transmitted to the repeaters R1 to R4, and is transmitted from the first to fourth repeaters R1 to R4 to the base station E1.

Since the feedback information is transmitted from the base station E1 to all the repeaters R1 to R4, the feedback signal is transmitted to the first to fourth repeaters R1 to R4, and the selected second and third repeaters R2 and R3 are selected. Is transmitted to the mobile communication terminal U1.

The data signal is transmitted from the mobile communication terminal U1 to the second and third repeaters R2 and R3 and from the second and third repeaters R2 and R3 to the base station E1.

As a result of the experiment, the waveform diagram shows that the performance is improved when the SNR is 5dB or more, and the performance of the BER is increased by about 3dB at 10 ⁻³ .

FIG. 9C illustrates a case in which three first, second, and fourth repeaters R1, R2, and R4 are selected by the base station E1, and a pilot signal is transmitted from the mobile communication terminal U1. The first to fourth repeaters R1 to R4 are transmitted, and the first to fourth repeaters R1 to R4 are transmitted to the base station E1.

Since the feedback information is transmitted from the base station E1 to all the repeaters R1 to R4, the feedback signal is transmitted to the first to fourth repeaters R1 to R4, and the selected first, second, and fourth repeaters R1, R2 and R4 are transmitted to the mobile communication terminal U1.

Data signal is transmitted from the mobile communication terminal U1 to the first, second, and fourth repeaters R1, R2, and R4, and from the first, second, and fourth repeaters R1, R2, and R4. Is transmitted to the base station E1.

As a result of the experiment, the waveform diagram shows a larger improvement than when one or two repeaters are selected, as shown in FIG. 10C, but the BER performance increases as the SNR increases.

FIG. 9D illustrates a case where all four first to fourth repeaters R1 to R4 are selected by the base station E1, and a pilot signal is generated by the mobile communication terminal U1. It is transmitted to the four repeaters R1 to R4, and is transmitted from the first to fourth repeaters R1 to R4 to the base station E1.

Since the feedback information is transmitted from the base station E1 to all the repeaters R1 to R4, the feedback information is transmitted to the first to fourth repeaters R1 to R4, and the selected first to fourth repeaters R1 to R4. Is transmitted to the mobile communication terminal U1.

The data signal is transmitted from the mobile communication terminal U1 to the first to fourth repeaters R1 to R4 and transmitted from the first to fourth repeaters R1, R2 and R4 to the base station E1.

As can be seen from this, since the pilot signal must be received at all repeaters and transmitted to the base station, in all cases, the same cooperative relay control protocol is used. In addition, the feedback information transmits feedback information to all repeaters in order to inform the repeater selected by the base station, but the repeaters only need to inform the mobile communication terminal of the selected repeater. Since data is transmitted to the base station only through the selected repeater, it can be seen that when the repeater selection method is applied, the performance is improved at 5 dB or more.

11 is a waveform diagram showing the performance of the MRT method applied to the repeater according to an embodiment of the present invention.

Referring to FIG. 11, it is a waveform diagram showing the performance when the maximum ratio transmission is applied to the repeater, and when the maximum ratio transmission is used in the second hop, the SNR increases more than 5 dB and the bit error rate (BER) performance increases. Can be.

12 is a flowchart illustrating a multi-hop cooperative relay method according to an embodiment of the present invention.

Referring to FIG. 12, first, the mobile communication terminal 10 transmits a pilot signal to the repeaters 20a to 20d and the base station 30 (S1201).

The repeaters 20a to 20d transmit the pilot signal received from the mobile communication terminal 10 to the base station 30 (S1203).

Subsequently, the base station 30 obtains channel characteristic information from the pilot signals received from the repeaters 20a to 20d and the mobile communication terminal 10 to derive a weight vector, and calculates an SNR using the derived weight vector ( S1205).

The base station 30 compares the SNR of the pilot signal received from the mobile communication terminal 10 and the SNR of the pilot signal received from the repeaters 20a to 20d to compare the SNR of the pilot signal received from the mobile communication terminal 10. The corresponding repeater of the pilot signal having a larger SNR is selected (S1207).

In addition, the base station 30 compares the codebook and the weight vector to determine the closest codebook index (S1209).

The base station 30 transmits feedback information including the codebook index information determined together with the base station ID information with the maximum number of feedback bits as feedback information to the repeater having the best SNR selected in step 1207 (S1207) (S1211). .

Then, the repeater having the best SNR receives the feedback information and recognizes that it has been selected by the feedback information, and informs the mobile communication terminal 10 of this (S1213).

Subsequently, the repeater having the best SNR receives the data to be transmitted by the mobile communication terminal 10 and multiplies the channel characteristic information by the codebook with the received data and transmits the data to the base station 30 having the best SNR (S1215).

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

1 is an exemplary view showing a technology of LTE-Advanced which is a general fourth generation mobile communication technology.

Figure 2 is a waveform diagram comparing the performance of a typical Alamoti technique and the maximum ratio transmission.

Figure 3 is an exemplary view illustrating a multi-hop cooperative relay method according to an embodiment of the present invention.

4 is an exemplary view for explaining a method for processing a signal received from a mobile communication terminal in a repeater and transmitting to a base station according to an embodiment of the present invention.

5 is a waveform diagram showing the characteristics of the signal-to-noise ratio according to each transmission method in FIG.

6 is an exemplary diagram for explaining a cooperative relaying method of a multi-hop cooperative relay apparatus according to an exemplary embodiment of the present invention.

7 and 8 are exemplary diagrams for describing feedback information according to an embodiment of the present invention.

9 is an exemplary view for explaining each signal transmission process according to the repeater selection in accordance with an embodiment of the present invention.

10A to 10C are waveform diagrams showing BER and SNR according to repeater selection according to an embodiment of the present invention.

11 is a waveform diagram showing the performance when applying the MRT method to the repeater according to an embodiment of the present invention.

12 is a flowchart illustrating a multi-hop cooperative relay method according to an embodiment of the present invention.

Claims (5)

In the multi-hop cooperative relay apparatus using a codebook, A mobile communication terminal transmitting a pilot signal; At least one repeater receiving the pilot signal and transmitting the pilot signal; And After acquiring the weight vector from the channel characteristic information obtained from the pilot signals received from the mobile communication terminal and the repeater, the codebook index corresponding to the weight vector and the approximation is determined to determine the signal-to-noise ratio of the pilot signal of the mobile communication terminal ( And a base station for transmitting the feedback information considering the performance of the bit error rate by selecting the at least one repeater for transmitting a pilot signal superior to SNR, And the at least one selected repeater decodes and encodes data transmitted from the mobile communication terminal and transmits the codebook selected based on the codebook index together with the channel characteristic information to the base station. The method of claim 1, wherein the codebook, A multi-hop cooperative relay device, which is a WiMAX Maximum Ratio Transmission (MRT) codebook. The method of claim 1, wherein the feedback information is A multi-hop cooperative relay apparatus comprising repeater ID information and codebook index information of a corresponding repeater having an excellent signal-to-noise ratio, wherein the total number of bits is 7 bits or less. In the multi-hop cooperative relay method using a codebook, The base station receiving pilot signals from the mobile communication terminal and the repeater, respectively; Obtaining a weight vector from channel characteristic information obtained from pilot signals received from the mobile communication terminal and the repeater, respectively; The codebook index corresponding to the weight vector and the approximation value is determined to select the at least one repeater which transmits a pilot signal superior to the signal-to-noise ratio (SNR) of the pilot signal of the mobile communication terminal to obtain feedback information considering the performance of the bit error rate. Transmitting; And And receiving, by the repeater receiving the feedback information, a signal for decoding and encoding data transmitted from the mobile communication terminal, and mixing the codebook selected based on the codebook index with the channel characteristic information and transmitting the received signal. Multi-hop cooperative relay method. The method of claim 1, wherein the feedback information is When the total number of bits is 7 bits or less, and one of the repeaters is selected, the feedback information includes only the repeater ID information of the selected repeater. When all the repeaters are selected among the total repeaters, it does not include the repeater ID information of the selected repeater and consists of feedback information including only the codebook index. The multi-hop cooperative relay method comprising the feedback information including the codebook index and the repeater ID information of the corresponding repeater, which is excluded when only one of the total repeaters is selected.

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