KR101468701B1 - Resource sharing based feedback reduction scheme in multicast environment - Google Patents

Abstract

A feedback reduction system through resource sharing in a multicast environment is provided. Wherein the feedback reduction system comprises a class determination unit for determining an MCS class of a user terminal, a code generation unit for generating a code corresponding to the MCS class, a code generation unit for generating a code generated from the code generation unit using the feedback resource allocated by the group, And a base station transceiver unit for receiving the code and confirming the MCS level of the user terminal and performing a multicast service at a transmission rate corresponding to a specific MCS level among the MCS levels.

Description

[0001] The present invention relates to a resource sharing based feedback reduction scheme in a multicast environment,

The present invention relates to a feedback reduction system and method. More particularly, the present invention relates to a system and method for reducing feedback by transmitting an orthogonal code corresponding to an MCS level of a user terminal in a group receiving the same service to a base station via a common feedback resource, And more particularly, to a system and method for reducing feedback through resource sharing in a multicast environment.

The unicast transmission scheme is widely used for Internet broadcasting and the like because one sender transmits data to another receiver. However, since the unicast transmission scheme transmits the same data to each user when transmitting the same data to each user, the efficiency of the network is greatly reduced due to the redundant transmission. On the other hand, the multicast transmission technique is a technique that can simultaneously transmit the same data to a plurality of receivers without increasing the load on the sender or the network. The advantage of multicast transmission technology is that it can overcome the limit of number of receivers.

In multicast transmission technology, a plurality of users receiving the same service form a group. In order to improve the performance of the multicast system, an opportunistic scheduling method of assigning resources to a group having the most advantageous channel state among a plurality of groups Can be used. In order to perform opportunistic scheduling in the system, the base station must know the channel information of the user. In this case, the channel information feedback must be preceded. The user feedbacks the channel information to notify the base station of its own channel state. In this case, the amount of feedback required increases in proportion to the number of users.

An example of such a multicast transmission technique is shown in FIG. 1 is a diagram for explaining a feedback process of a user terminal in a multicast environment according to the related art.

개의 피드백 자원이 필요하다. 따라서, 복수의 사용자로 구성된 그룹이 여러 개 있는 멀티캐스트 환경에서 피드백은 큰 오버헤드로 작용할 수 있다는 문제점이 있다.Referring to FIG. 1, each of the user terminals 1 to 4 in the same group has a log ₂ L (L: divided according to a channel state between a base station and a user terminal) to transmit its MCS rank to a base station The number of true MCS classes requires a feedback amount of bits. In this case, if the number of users of a specific group g among the G multicast groups is K _g , different resources are allocated to each user to feedback the MCS class

Feedback resources are needed. Therefore, in a multicast environment in which there are a plurality of groups composed of a plurality of users, there is a problem that feedback can act as a large overhead.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a method and apparatus for allocating feedback resources to a specific group without assigning feedback resources corresponding to the number of user terminals belonging to a specific group, And to provide a system and method for feedback reduction through resource sharing in a multicast environment in which feedback resources can be reduced by generating an orthogonal code corresponding to the MCS level of the orthogonal code and feeding back the orthogonal code to the base station.

In order to achieve the above object, a feedback reduction system for sharing resources in a multicast environment according to an embodiment of the present invention includes a class determining unit for determining an MCS level of a user terminal, a code generating unit for generating a code corresponding to the MCS level, A terminal transmitter / receiver for feeding back the code generated from the code generator to the base station using the feedback resource allocated by the group, a class checking unit for receiving the code and confirming the MCS class of the user terminal, And a base station transceiver unit for performing a multicast service at a transmission rate corresponding to the rate.

Further, according to the feedback reduction system according to the embodiment of the present invention, the class checking unit multiplies the feedback information received from the user terminal by a Hadamard matrix to confirm the MCS level of the user terminal.

In addition, according to the feedback reduction system according to the embodiment of the present invention, the code generation unit generates an orthogonal code corresponding to the MCS level of the user terminal.

In addition, according to the feedback reduction system according to the embodiment of the present invention, the class determining unit determines the MCS level using the SNR measured by the SNR measuring unit that measures the SNR between the user terminal and the base station .

In addition, according to the feedback reduction system according to the embodiment of the present invention, the base station transceiver unit performs a multicast service with a transmission rate corresponding to the lowest MCS class among the received MCS classes.

In order to achieve the above object, a feedback method through resource sharing in a multicast environment according to an embodiment of the present invention determines an MCS class of a user terminal from a class determination unit, generates a code corresponding to an MCS class from a code generation unit , A code corresponding to the MCS class is fed back to the base station from the terminal transceiver unit, and the received MCS class is checked to perform the multicast service at the transmission rate corresponding to the specific MCS class.

As described above, according to the system and method for reducing feedback through resource sharing in the multicast environment according to the embodiment of the present invention, since the amount of resources required for feedback by one group is fixed to bits corresponding to the number of MCS classes, Regardless of the number of users, a constant amount of feedback is provided, and the effect of feedback reduction obtained as the number of users increases is obtained.

In addition, according to the feedback reduction system and method according to the embodiment of the present invention, even if the codes transmitted from a plurality of user terminals are overlapped and fed back to the base station, the presence or absence of transmission of the orthogonal code can be confirmed .

1 is a diagram for explaining a feedback process of a user terminal in a multicast environment according to the related art.
FIG. 2 is a diagram for explaining a feedback reduction process through resource sharing in a multicast environment according to an embodiment of the present invention. Referring to FIG.
3 is a block diagram illustrating a feedback reduction system in accordance with an embodiment of the present invention.
4A and 4B are diagrams for explaining an example of feeding back an MCS rank to an orthogonal code according to an embodiment of the present invention.
5 is a flowchart for explaining a feedback reduction method according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the accompanying drawings, but the present invention is not limited to the illustrated embodiments.

These and other objects and novel features of the present invention will become more apparent from the description of the present specification and the accompanying drawings.

The channel information of the present invention refers to an MCS class that is graded by a predetermined interval based on a signal to noise ratio (SNR) value between a user and a base station. To ensure that all users in a group receive service without being missed, the rate of multicast service should be determined for the worst-in-group channel condition. That is, a service having a different MCS level for each user in the group and a transmission rate corresponding to the lowest MCS rating in a different situation can receive service without receiving any error.

The base station can determine the transmission rate of the multicast service by knowing only the information of the worst channel, regardless of the channel state of each user or the user having the worst channel state. Considering this characteristic, it is not necessary to feedback the channel information of each user by allocating feedback resources to each user. Even if the base station is informed of the worst channel information in the group, the multicast service can be performed, so that the feedback can be reduced through this method.

In the feedback reduction technique according to the present invention, a group is allocated resources to be used for feedback, and all users in the group share the same feedback resources allocated to the groups to feedback to the base station. That is, the feedback resource is allocated to each user and the channel is not fed back, the group is allocated a resource that can be used for feedback, and all the users in the group simultaneously use the resource to feed back the channel information. If the feedback resource allocated to the group is not large compared to the amount of resources allocated to each user, the amount of feedback can be reduced.

In this case, since the base station feeds back the same feedback resource to the user, it may be difficult to obtain channel information by receiving feedback of the overlapping channel information of several users. However, even if the base station can not know the channel information of each user, if there is a method of knowing only the worst channel information, it is possible to determine a proper transmission rate and service. In the method of finding the worst channel information in the overlapped channel information feedback, when the user informs the channel information of the user, feedback is performed using the orthogonal code corresponding to the MCS grade of the user.

That is, there are as many orthogonal codes as the number of MCS classes, and a one-to-one correspondence relationship allows the user to feed back the orthogonal code corresponding to the MCS class without feedbacking the MCS class. Since the base station receives the overlapped orthogonal codes sent by several users, the orthogonal codes are orthogonal to each other and do not interfere with each other. Therefore, it is possible to restore what orthogonal codes were transmitted when decoding. Therefore, the base station can determine the transmission rate according to the lowest rank among the MCS classes indicated by the transmitted code.

Hereinafter, the configuration of the present invention will be described in detail with reference to the drawings with reference to Figs. 2 to 4. Fig. FIG. 3 is a block diagram illustrating a feedback reduction system according to an exemplary embodiment of the present invention. FIGS. 4A and 4B are diagrams for explaining a feedback reduction process through resource sharing in a multicast environment according to an embodiment of the present invention. FIG. 4B is a view for explaining an example of feeding back an MCS rank to an orthogonal code according to an embodiment of the present invention.

Referring to Figures 2 and 3, a feedback reduction system according to an embodiment of the present invention includes a user terminal (MS) and a base station (BS). The base station (BS) provides a multicast service to a plurality of user terminals (MS) constituting each of a plurality of groups, and allocates a feedback resource to check the channel status of the user terminal (MS). The user terminal (MS) transmits its channel status to a base station (BS) using feedback resources provided from a base station (BS).

The user terminal MS includes an SNR measurer 11 for measuring a SNR with a base station BS and a class determiner 13 for determining an MCS class measured by the SNR measurer 11, Respectively. In this case, the MCS class may be divided into L according to the channel state between the base station (BS) and the user terminal (MS). If the MCS class is determined, the code generator 15 of the user terminal MS generates an orthogonal code corresponding to the MCS class. The orthogonal code is the same as the number of MCS classes and is fed back from the user terminal (MS) to the base station (BS).

Considering the amount of feedback from one user terminal (MS), log ₂ L bits were needed to feed back the MCS rating, but orthogonal codes seem to use more resources because L bits are needed. However, in the case of the orthogonal code, even if several different orthogonal codes are mixed and fed back to the base station (BS), the base station (BS) has an advantage of knowing whether or not orthogonal codes are transmitted. This is because they appear to overlap each other due to the characteristics of the orthogonal code, but other orthogonal codes do not influence each other when the base station (BS) discriminates.

Therefore, even if one group allocates an L-bit feedback resource without allocating a feedback amount by L bits for each user and all the users in the group share the feedback, the base station BS uses orthogonal codes corresponding to certain MCS classes Is transmitted. The base station determines the transmission rate according to the lowest MCS level among the MCS levels of the determined user.

The orthogonal codes used in the present invention use rows of a Hadamard matrix having 1 and -1 and having mutually orthogonal characteristics. The Hadamard matrix is a square matrix. In the case of the L * L matrix, L codes orthogonal to each other and having length L can be obtained. Therefore, one row can be used as an orthogonal code corresponding to one MCS class. The Hadamard matrix is obtained by Hadamard ordering of the Walsh function as shown in Equation (1) below.

[Equation 1]

, K=1, 2, …, n, n=log₂L, H(0)=1

, K = 1, 2, ... , n, n = log ₂ L, H (0) = 1

Examples related to this are shown in Figs. 4A and 4B.

4A and 4B, when the number of MCS classes used is 4, the number of orthogonal codes used is also 4, so that the Hadamard matrix is obtained as shown in the following equation (2).

&Quot; (2) "

In the above Equation (2), if MCS 1 to MCS 4 are sequentially arranged from the first to fourth rows, four orthogonal codes orthogonal to each other are generated.

The user terminal MS generates an orthogonal code corresponding to its MCS class. That is, if the MCS level of the four user terminals MS in one group is MCS 2, MCS 3, MCS 2, and MCS 4 in order, the user terminal MS in the following equation (2) -1, -1, -1, -1 and -1, -1, -1, -1 and -1, -1, -1, -1, 1).

Referring back to FIG. 2 and FIG. 3, the user terminal MS feeds an orthogonal code corresponding to the MCS class to the base station BS using the terminal transceiver 17. The BS receives an orthogonal code orthogonal to the other rows using the class checking unit 19 to check the MCS level of the MS. The rank checking unit 19 checks the MCS level of the user terminal by multiplying the feedback information received from the user terminal MS by the Hadamard matrix and transmits the multicast service with the lowest MCS rating from the base station transmitting / . For example, as shown in FIGS. 4A and 4B, the BS may receive orthogonal codes corresponding to MCS 2, MCS 3, and MCS 4, and adjust the transmission rate according to MCS 2.

Next, a method of reducing feedback through resource sharing in a multicast environment according to an embodiment of the present invention will be described with reference to FIG. 3 and FIG. 5 is a flowchart for explaining a feedback reduction method according to an embodiment of the present invention.

3 and 5, the feedback reduction method according to the embodiment of the present invention first determines the MCS level of the user terminal (MS) by measuring the SNR with the base station (BS) (S51) (S52). In step S51, if there are G multicast groups and L MCS classes, the BS allocates resources of G x L bits for feedback of MCS ratings from users of each group for multicast service, Allocate L bits of resources to the group again. In addition, the base station informs the users of each group about the allocated resources.

After step S52, the MS generates an orthogonal code corresponding to its MCS level (S53), and feeds back the generated orthogonal code to the base station BS (S54). The BS multiplies the feedback information received from the MS by a Hadamard matrix to check the MCS level of the feedback information in step S55 and transmits the multicast service with the transmission rate corresponding to the lowest MCS rating (S56). In step S55, even though the orthogonal codes transmitted from the plurality of user equipments (MS) overlap each other, the base station BS can confirm the MCS level of each of the MSs due to the orthogonal property. Therefore, the present invention can be applied to various communication systems such as 3GPP LTE, WiBro, WiFi, satellite communication, and IPTV for performing multicast service.

Although the present invention has been described in detail with reference to the above embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

11: SNR measuring unit 13:
15: code generation unit 17: terminal transmission /
19: Class checking section 21: Base station transmitting /
MS: user terminal BS: base station

Claims (10)

A classifying unit for determining an MCS class of the user terminal,
A code generator for generating a code corresponding to the MCS class,
A terminal transceiver for feeding back the code generated from the code generator to the base station using the feedback resource allocated by the group,
A class checking unit for receiving the code and checking the MCS level of the user terminal;
And a base station transceiver unit for performing a multicast service at a transmission rate corresponding to a specific MCS class among the MCS classes,
The class checking unit checks the MCS level of the user terminal by multiplying the feedback information received from the user terminal by a Hadamard matrix,
Wherein the code generation unit generates an orthogonal code corresponding to the MCS class of the user terminal. delete delete The method according to claim 1,
Wherein the class determiner determines an MCS class using a signal-to-noise ratio measured by an SNR measuring unit that measures a signal-to-noise ratio between a user terminal and a base station. The method according to claim 1,
Wherein the base station transceiver unit performs a multicast service with a transmission rate corresponding to the lowest MCS class among the received MCS classes. (a) determining an MCS rank of a user terminal from a rank determining unit,
(b) generating a code corresponding to the MCS class from the code generation unit,
(c) feeding back a code corresponding to the MCS rating from the terminal transceiver to the base station; and
(d) checking the MCS class received from the user terminal in the base station's class checking unit and performing a multicast service at a transmission rate corresponding to a specific MCS level in the base station transmitting / receiving unit,
The class checking unit checks the MCS level of the user terminal by multiplying the feedback information received from the user terminal by a Hadamard matrix,
Wherein the code generator generates an orthogonal code corresponding to the MCS class of the user terminal. delete delete The method according to claim 6,
Wherein the class determining unit determines an MCS level of the user terminal based on a signal-to-noise ratio with the base station measured from the SNR measuring unit. The method according to claim 6,
Wherein the base station transceiver unit performs a multicast service with a transmission rate corresponding to the lowest MCS class among the received MCS classes.

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