KR101308681B1 - Apparatus and method for allocating resource based on reliablity of feedback channel in broadband wireless communication system - Google Patents

Abstract

The present invention relates to an apparatus and method for allocating resources in a broadband wireless communication system. The terminal includes a channel estimator for estimating a channel using a received signal, a message checker for confirming resource allocation information, and the resource allocation information. A feedback information configurator configured to determine a feedback form of a channel estimator value of the channel estimator with reference to the controller, adjust feedback information according to reliability of a feedback channel, and perform adaptive scheduling at a base station By doing so, performance degradation due to incorrect scheduling can be prevented.

Resource allocation, channel information, feedback

Description

Apparatus and method for allocating resources according to reliability of feedback channel in broadband wireless communication system {APPARATUS AND METHOD FOR ALLOCATING RESOURCE BASED ON RELIABLITY OF FEEDBACK CHANNEL IN BROADBAND WIRELESS COMMUNICATION SYSTEM}

1 is a diagram illustrating an example of a channel measurement result of a terminal in a broadband wireless communication system;

2 is a diagram illustrating an example of primary resource scheduling in a broadband wireless communication system according to an embodiment of the present invention;

3 is a diagram illustrating an example of secondary resource scheduling in a broadband wireless communication system according to an embodiment of the present invention;

4 is a block diagram of a terminal in a broadband wireless communication system according to the present invention;

5 is a block diagram of a base station in a broadband wireless communication system according to the present invention;

FIG. 6 is a diagram illustrating a procedure for a user equipment to feed back channel information in a broadband wireless communication system according to an embodiment of the present invention; FIG.

7 is a diagram illustrating a procedure for resource scheduling by a base station in a broadband wireless communication system according to an embodiment of the present invention; and

8 is a diagram illustrating scheduling performance according to a feedback channel state in a broadband wireless communication system.

The present invention relates to scheduling in a broadband wireless communication system, and more particularly, to an apparatus and method for preventing performance degradation due to incorrect scheduling in a broadband wireless communication system.

In the 4th Generation (hereinafter referred to as 4G) communication system, which is the next generation communication system, active research is being conducted to provide users with services having various Quality of Service (QoS) with a transmission rate of about 100 Mbps. It's going on. Particularly, in 4G communication systems, studies are being actively conducted to support high-speed services in a form of guaranteeing mobility and QoS for broadband wireless access (BWA) communication systems such as wireless local area network systems and wireless urban area network systems. Is going on. In addition, the representative communication system is the Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.

The IEEE 802.16 communication system is orthogonal frequency division multiplexing (hereinafter, referred to as OFDM) / orthogonal frequency division multiplexing to support a broadband transmission network on a physical channel of the wireless communication system. A communication system employing an access method (Orthogonal Frequency Division Multiple Access, hereinafter called OFDMA).

Including a communication system using the OFDM scheme as in IEEE 802.16, a process for scheduling a resource for the terminals by the base station is required for efficient resource utilization in the communication system. For the scheduling, the terminals feed back their own channel information to the base station, and the base station allocates resources using the channel information fed back by the terminals. In other words, the terminals configure channel information according to a preset form and feed back to the base station. The base station allocates resources by applying a corresponding scheduling scheme based on the fed back channel information, and then notifies the terminals of the allocated resource information.

However, in the above-described feedback and scheduling scheme, a channel mismatch, a feedback delay, or the like may occur due to a different channel condition between the time point at which the terminal feeds back and the time point at which the base station schedules due to a sudden change in channel. In other words, when problems such as channel mismatch and feedback delay occur, there is a problem in that resources that should not be allocated are allocated by scheduling using the feedback channel information. In addition, problems such as an increase in calculation amount due to unnecessary scheduling of the base station and an increase in overhead due to unreliable channel information feedback of the UE occur.

Accordingly, an object of the present invention is to provide an apparatus and method for preventing incorrect scheduling when channel information fed back in a broadband wireless communication system is incorrect.

Another object of the present invention is to provide an apparatus and method for configuring channel information to be fed back by a terminal according to reliability of a feedback channel in a broadband wireless communication system.

Another object of the present invention is to provide an apparatus and method for a base station to select a scheduling scheme according to a feedback channel reliability of a terminal in a broadband wireless communication system.

According to a first aspect of the present invention for achieving the above object, in a broadband wireless communication system, a terminal apparatus includes a channel estimator for estimating a channel using a received signal, a message checker for confirming resource allocation information, and the resource allocation. And a feedback information configurator configured to determine a feedback form of a channel estimate value of the channel estimator with reference to the information and to configure channel information to be fed back.

According to a second aspect of the present invention for achieving the above object, a base station apparatus in a broadband wireless communication system, a grouping group to group the terminals using the channel information fed back from the terminals, and scheduling the terminals in groups And a resource mapper for mapping the transmission signal of the corresponding terminal to the resource according to the scheduling result.

According to a third aspect of the present invention for achieving the above object, a method for a user equipment to feed back channel information in a broadband wireless communication system, the process of estimating the channel using the received signal, the process of identifying the resource allocation information And determining a feedback form of a channel estimate value of the channel estimator with reference to the resource allocation information, and configuring channel information to be fed back.

According to a fourth aspect of the present invention for achieving the above object, a scheduling method of a base station in a broadband wireless communication system, the process of checking the channel information fed back from the terminals, and grouping the terminals according to the feedback channel information And scheduling the terminals in group units.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Hereinafter, the present invention describes a technique for preventing performance degradation due to incorrect scheduling by selecting a scheduling method according to the reliability of a feedback channel in a broadband wireless communication system. In the following description, the wireless communication system is described by taking an orthogonal frequency division multiplexing system as an example, and may be similarly applied to other wireless communication systems.

First, a basic idea for selecting a scheduling scheme according to the reliability of a feedback channel in a broadband wireless communication system will be described.

In the broadband wireless communication system, the UE estimates a downlink channel using a pilot signal received from a base station. The terminal obtains channel information by estimating the downlink channel and feeds back the channel information to the base station. The base station, which has received the channel information, schedules the resource by reflecting the channel information.

 In this case, the terminal determines the type of channel information fed back according to the reliability of the feedback channel in the process of feeding back the channel information. In this case, the reliability of the feedback channel is confirmed through the degree of correspondence between the previously fed back channel information (preferred resource information) and the actually allocated resource. Therefore, the base station receives feedback of the channel information of the type selected by the terminal. In other words, the base station receives feedback of various kinds of channel information.

The base station receives feedback of the various kinds of channel information and groups the terminals according to the type of the channel information. Since the terminals included in one group all fed back the same kind of channel information, the base station applies the same scheduling technique in units of groups.

For example, examples of the reliability criterion of the terminal, the type of feedback information, and an example of a scheduling scheme for each group of the base station are shown in Table 1 below.

feedback
channel
Reliability


Prize

medium

Ha Reliability Judgment
(Terminal) Preferred resources
Within the top 20%
Resource allocation Preferred resources
Within the top 20-50%
Resource allocation Preferred resources
Within 50%
Resource allocation Feedback
Channel Information Type
(Terminal) CQI by Default Resource Allocation Unit Preferred Order by Default Resource Allocation Unit
No feedback Scheduling technique
(Base station) Wong's Method
The way ACG way
Scheduling According to predetermined rules
Resource allocation

In Table 1, the CQI (Channel Quality Information) is information such as Signal to Noise Ratio (SNR) or Signal to Interference and Noise Ratio (SINR). In addition, the Wong's Method method is a scheduling method using accurate channel information, and the Amplitude Craving Greedy (AGC) method is a scheduling method using only a preferred order of basic resource allocation units. Details of the Wong's Method and the AGC scheduling scheme will be described in detail with reference to FIGS. 2 and 3.

That is, when resources are allocated within the top 20% of the preferred resources according to the channel information fed back by the terminal, it becomes a basis for determining that the feedback information is accurately reflected in the scheduling process. Thus, the terminal can feed back a complex and large amount of channel information. On the other hand, if resources are allocated within the lower 50% of the preferred resources as opposed to the channel information fed back by the terminal, the feedback information is not reflected in the scheduling process. Therefore, since the feedback of the channel information for the scheduling is a waste of resources, the terminal does not feed back the channel information. Accordingly, the terminal feeds back channel information of a corresponding type based on the degree of agreement between the preferred resource and the allocated resource.

For example, as shown in FIG. 1, when the terminal estimates a channel, channel information fed back by the terminal is as follows. In FIG. 1, the horizontal axis represents an index of a basic resource allocation unit, and the vertical axis represents a CQI, representing a signal-to-noise ratio.

First, in case of a terminal allocated with resources within the top 20%, the terminal feeds back a signal-to-noise ratio value for each resource index. That is, detailed channel information as shown in Table 2 is fed back.

resource
index
One
2
3
4
5
6
7
8
CQI
0.8
0.4
0.8
1.2
1.6
2.0
1.6
1.2

However, feeding back all of the correct signal-to-noise ratio values is a significant overhead. Therefore, as shown in Table 3 below, a method of feeding back a difference value around one resource index may be used.

One
0
0
Reference value
One
One
0
0

In Table 3, '1' represents a CQI increase and '0' represents a CQI decrease.

That is, in the case of feeding back the channel information as shown in Table 3, it is not absolute information about the channel, but may feed back good or bad for each allocation unit in the entire channel.

Next, in the case of a terminal allocated to the resources within the upper 20-50%, the terminal feeds back the upper N resource indexes excellent in the signal-to-noise ratio. For example, when N is 3, the resource indexes [6, 5, 7] are fed back.

Also, for example, the scheduling scheme applied according to the group is as shown in FIGS. 2 and 3. The Wong's Method method is a method of sequentially applying both the methods shown in FIGS. 2 and 3, and the ACG method is a method of applying the method shown in FIG. 2.

First, referring to FIG. 2, it is assumed that the base station receives feedback of channel information from the terminal A 210, the terminal B 220, and the terminal C 230. In this case, the channel information is a preferred order according to the resource index as shown in (a) of FIG. Since the channel information fed back from the terminals included in the reliability 'above' is an accurate CQI for each basic resource allocation unit, the preference order can be inferred, and the feedback information of the terminals included in the reliability 'middle' can be used as it is. .

In this case, the base station allocates resources in the order most preferred by each terminal in a predetermined order. That is, first, the highest priority preference resource 201 of the terminal A 210 is allocated to the terminal A 210, and the highest priority of the terminal B 220 among the resources not allocated to the terminal B 220. Allocates preferred resource 203. Thereafter, the highest priority preferred resource 205 of the terminal C 230 is allocated to the terminal C 230 among the remaining resources in the same manner. Subsequently, the procedure is repeated in the same order and the highest priority resource of each terminal is allocated among the resources not allocated to each terminal. As a result, resources are allocated as shown in FIG.

After performing the scheduling of the ACG scheme as shown in FIG. 2, the UE performs scheduling using the correct CQI value as shown in FIG.

Referring to FIG. 3, the resources 301 and 303 of the lowest CQI values of the terminal A 310 and the terminal B 320 are allocated from the resources allocated primarily through the scheduling as shown in FIG. 2. Exchange with each other. That is, the base station exchanges the allocated resources between the respective terminals and schedules the sum of the CQI values of the allocated resources for each terminal to increase. The same process is performed between the terminal A 310 and the terminal C 330 and the terminal B 320 and the terminal C 330 to allocate an optimal resource.

In the following description, an embodiment of an apparatus and method for feeding back channel information and performing scheduling according to the above-described scheme will be described with reference to the accompanying drawings.

4 is a block diagram of a terminal in a broadband wireless communication system according to the present invention.

As shown in FIG. 4, the terminal includes a radio frequency (RF) receiver 401, an analog to digital converter (ADC) 403, an OFDM demodulator 405, and a resource demapper. 407, channel estimator 409, demodulator and decoder 411, message confirmer 413, and feedback information constructor 415.

The RF receiver 401 converts a signal of the RF band received through the antenna into a baseband signal. The ADC 403 converts an analog signal provided from the RF receiver 401 into a digital signal.

The OFDM demodulator 405 converts an OFDM symbol provided from the ADC 403, that is, a time domain signal, into a frequency domain signal by performing a fast fourier transform (FFT) operation. The resource demapper 407 demaps signals located on a frequency provided from the OFDM demodulator 405 in a corresponding order, and classifies an information signal and a pilot signal. That is, the information signal is output to the demodulator and decoder 411, and the pilot signal is output to the channel estimator 409.

The channel estimator 409 receives a pilot signal from the resource demapper 407 to estimate a channel. In other words, the channel estimator 409 obtains the CQI for each resource allocation unit by using the pilot signal. For example, the CQI may consider signal-to-noise ratio, signal-to-interference and noise ratio, carrier-band interference, and noise ratio.

The demodulator and decoder 411 demodulates and decodes the information signal provided from the resource large mapper 407 in a corresponding manner.

The message checker 413 identifies the allocated resources through a resource allocation message (MAP) message among the information provided from the demodulator and decoder 411.

The feedback information configurator 415 compares the channel information by comparing the allocated resource information provided from the message checker 413 with the preferred channel information, and configures channel information to be fed back later. In other words, as shown in Table 1, the type of channel information to be fed back is determined according to the degree of agreement between the preferred resource and the allocated resource, and the corresponding channel information is configured.

5 is a block diagram of a base station in a broadband wireless communication system according to the present invention.

As shown in FIG. 5, the base station includes a grouping unit 501, a scheduler 503, a message generator 505, an encoding and modulator 507, a resource mapper 409, an OFDM modulator 511, and a digital analogue. A digital to analog converter (hereinafter referred to as a DAC) 513 and an RF transmitter 515.

The grouping unit 501 groups the terminals according to the type of channel information fed back from the terminals. That is, when the channel information of the type shown in Table 1 is fed back, the grouping device 501 groups the terminals fed back the same type of channel information so that the scheduler 503 performs group-specific scheduling.

The scheduler 503 receives information of the grouped terminals from the grouping device 501 and schedules the information by applying a method corresponding to each group. That is, as shown in Table 1, the first group of UEs are scheduled by the Wong's Method method, the second group of UEs are scheduled by the ACG method, and the third group of UEs are allocated resources according to a predetermined rule.

The message generator 505 receives a resource allocation result from the scheduler 503 and generates a map message for notifying the allocated resource to the terminal.

The encoder and modulator 507 encodes and modulates a map message provided from the message generator 505 and user data provided from an upper end in a corresponding manner.

The resource mapper 509 refers to resource allocation information provided from the scheduler 503 and maps signals provided from the encoder and modulator 507 to corresponding frequency resources.

The OFDM modulator 511 performs an Invers Fast Fourier Transform (IFFT) operation on the frequency signal provided from the resource mapper 509 and converts the frequency signal into a time-domain OFDM symbol.

The DAC 513 converts the digital signal provided from the OFDM modulator 511 into an analog signal. The RF transmitter 515 converts the baseband signal provided from the DAC 513 into an RF band signal and transmits it through an antenna.

6 is a flowchart illustrating a procedure for feeding back channel information by a terminal in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 6, the terminal first checks whether resource allocation information is received in step 601. Here, the resource allocation information is included in the map message.

When the resource allocation information is received, the terminal proceeds to step 603 to compare the preferred resource and the allocated resource.

After comparing the preferred resource with the allocated resource, the terminal proceeds to step 605 and checks whether a resource included within the top 20% of the preferred resource is allocated.

If resources included within the top 20% are allocated, the terminal proceeds to step 607 and feeds back accurate channel information for each resource allocation unit as shown in Table 1 above.

On the other hand, if the resources included in the top 20% is not allocated, the terminal proceeds to step 609 and determines whether the resources included in the top 50% of the preferred resources are allocated.

If resources included within the top 50% are allocated, the terminal proceeds to step 611 to feed back only the preferred order for each resource allocation unit as shown in Table 1 above.

On the other hand, if resources included within the top 50% are not allocated, the terminal does not feed back channel information and terminates this procedure.

7 is a flowchart illustrating a resource scheduling procedure of a base station in a broadband wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 7, the base station first checks whether channel information of UEs is fed back in step 701.

If the channel information of the terminals is fed back, the base station proceeds to step 703 to group the terminals according to the type of the fed back channel information. Here, the type of channel information fed back is as shown in Table 1 above.

After grouping the terminals, the base station proceeds to step 705 to schedule resources of the first group of terminals by the Wong's Method.

After scheduling the resources of the first group terminals, the base station proceeds to step 707 to schedule the resources of the second group terminals in the ACG scheme.

After scheduling the resources of the second group terminals, the base station proceeds to step 709 to allocate resources to the third group terminals according to a preset rule.

8 illustrates scheduling performance according to a feedback channel state in a broadband wireless communication system. 8 is a graph showing simulation results assuming an environment as shown in Table 4 below.

Frequency band
10 MHz
Subcarriers
512
Frame time
2.5 ms
Guard interval time
138.4 us
Symbol time
57.6 us
Subcarrier Frequency Interval
19.53 125 kHz
Symbols per Frame
41
Uplink-Downlink Ratio
12:29 or 16:25
Subcarriers used
384 = 24 * 16: 16 * 24: 8 * 48
Number of terminals
8
Modulation and Coding Scheme
16-QAM / Convolution (1/3)

The graph shown in FIG. 8 shows bits versus signal-to-noise ratios in the case of applying Wong's Method and ACG scheduling to three situations in which the moving speed of the terminal is 10 km / h, 30 km / h, and 50 km / h, respectively. Error rate is shown. In the graph, the horizontal axis represents the signal-to-noise ratio, and the vertical axis represents the bit error rate.

Referring to FIG. 8, when the moving speeds of the terminal are 10 km / h and 30 km / h, it can be seen that the use of the Wong's Method method is lower than the case of using the AGC method. On the other hand, when the movement speed of the terminal is 50 km / h, it can be seen that the case of using the AGC method is lower than the case of using the Wong's Method method. In other words, as the movement speed increases, the channel change is severe, and when the reliability of the feedback channel is lowered, the scheduling of the Wong's Method method, which requires complicated and accurate calculations, causes performance degradation. Therefore, when the reliability of the feedback channel is low, better performance can be achieved by using a low complexity scheduling such as the AGC scheme.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, by adjusting the information to be fed back according to the reliability of the feedback channel in the broadband wireless communication system and performing adaptive scheduling, performance degradation due to incorrect scheduling can be prevented.

Claims (22)

A terminal device in a broadband wireless communication system, A message verifier for confirming resource allocation information received from the base station; And a feedback information configurator configured to determine a feedback form of channel information based on the resource allocation information and a preferred resource indicated by previously fed back channel information, and to generate and transmit channel information according to the determined feedback form. . The method of claim 1, And the feedback information configurator determines the feedback form according to the degree of agreement between the resource allocation information and the preferred resource. The method of claim 1, The feedback information configurator, And determining the feedback form as one of a first form indicating a channel state for each resource allocation unit, a second form indicating a preference rank for each resource allocation unit, and a third form including no channel information. The method of claim 3, The feedback information configurator, If the allocated resources are included in the top 20% of the preferred resources, configure the channel information to be fed back in the first form, If the allocated resources are included in the top 20% to 50% of the preferred resources, configure the channel information to be fed back in the second form, And if the allocated resource is included in the lower 50% of the preferred resources, configure the channel information to be fed back in the third form. The method of claim 3, The channel state is Signal to Noise Ratio (SNR), Signal to Interference and Noise Ratio (SINR) or Carrier to Interference and Noise Ratio (CINR). A base station apparatus in a broadband wireless communication system, A grouping grouping the terminals based on a feedback form of channel information fed back from the terminals, and the feedback form is determined based on resource allocation information received by each of the terminals and a preferred resource indicated by previously fed back channel information. , A scheduler for scheduling the terminals on a group basis; And a resource mapper for mapping the transmission signal of the corresponding terminal to the resource according to the scheduling result. The method according to claim 6, The grouping group, A first group if the channel information to be fed back is in a channel state for each resource allocation unit, A second group if it is a preference rank for each resource allocation unit, And if the channel information is not fed back, classify it into a third group. 8. The method of claim 7, The scheduler comprising: After allocating resources to the terminals included in the first group according to the preference order, the apparatus for scheduling the transmission rate is increased by exchanging the resources with the lowest preference among the terminals. 8. The method of claim 7, The scheduler comprising: Device for allocating resources according to a preference order to the terminals included in the second group. 8. The method of claim 7, The scheduler comprising: And allocating resources to terminals included in the third group according to a preset rule. 8. The method of claim 7, The channel state is Signal to Noise Ratio (SNR), Signal to Interference and Noise Ratio (SINR) or Carrier to Interference and Noise Ratio (CINR). A method for a user equipment to feed back channel information in a broadband wireless communication system, Estimating a channel using the received signal; Checking the resource allocation information, Determining a feedback form of channel information based on the resource allocation information and the preferred resource indicated by the previously fed back channel information; Generating and transmitting channel information according to the determined feedback type. 13. The method of claim 12, The process of determining the feedback form, Checking a degree of agreement between the resource allocation information and the preferred resource; And determining the feedback form according to the degree of correspondence. 13. The method of claim 12, The feedback form is, A first form indicating a channel state for each resource allocation unit, A second form representing a preference rank for each resource allocation unit, And one of the third forms that does not include channel information. 15. The method of claim 14, The process of determining the feedback form, Determining the feedback form as the first form when the allocated resource is included in the top 20% of the preferred resources; Determining the feedback form in the second form when the allocated resource is included in the top 20% to 50% of the preferred resource; And if the allocated resource is included in the lower 50% of the preferred resources, determining the feedback form in the third form. 15. The method of claim 14, The channel state is Signal to Noise Ratio (SNR), Signal to Interference and Noise Ratio (SINR) or Carrier to Interference and Noise Ratio (CINR). In the scheduling method of a base station in a broadband wireless communication system, Checking channel information fed back from the terminals; Grouping the terminals based on the feedback form of the fed back channel information, and the feedback form is determined based on resource allocation information received by each of the terminals and preference resources indicated by previously fed back channel information, Scheduling the terminals on a group basis. 18. The method of claim 17, The grouping process, Classifying the fed back channel information into a first group if a channel state of each resource allocation unit is provided; Classifying the resource into a second group if the resource allocation unit is a preferred order; And if the channel information is not fed back, classifying it into a third group. 19. The method of claim 18, The scheduling process, Allocating resources to terminals included in the first group according to a preference order; And exchanging resources among the lowest preferred ranks of respective terminals included in the first group. 19. The method of claim 18, The scheduling process, And allocating resources to the terminals included in the second group according to a preference order. 19. The method of claim 18, The scheduling process, And allocating resources to terminals included in the third group according to a predetermined rule. 19. The method of claim 18, Signal to Noise Ratio (SNR), Signal to Interference and Noise Ratio (SINR) or Carrier to Interference and Noise Ratio (CINR).

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