JP2012074888A - Base station and base station control method - Google Patents

Abstract

The format of a CQI report is changed according to the number of communication terminals under its control.
A base station 1 according to the present invention is a base station 1 compatible with an OFDM system, and includes a receiving unit 10 that receives channel quality information from a communication terminal under its own station, and each of the base stations 1 based on the channel quality information. A scheduler 21 that schedules transmission data and subbands to communication terminals, and a determination that detects the number of communication terminals under its own station based on the channel quality information and determines a channel quality information format according to the number of communication terminals Unit 22 and a transmission unit 30 for transmitting a change instruction to the channel quality information format to a communication terminal under its control.
[Selection] Figure 1

Description

  The present invention relates to a base station, and more particularly to a base station corresponding to an OFDM system.

  Standards based on OFDM (Orthogonal Frequency-Division Multiplexing) systems such as LTE (Long Term Evolution) and UMB (Ultra Mobile Broadband) are known as wireless communication systems between base stations and communication terminals. ing. In the OFDM system, the frequency band used for wireless communication is divided into a plurality of subbands. When transmitting data to communication terminals under its control, the base station performs scheduling of radio resources such as which subband data is allocated to which communication terminal. The base station uses a CQI (Channel Quality Indicator) report received from the communication terminal in order to appropriately perform scheduling. The CQI report is a report in which a communication terminal transmits downlink radio quality to a base station. The base station can improve downlink throughput by scheduling transmission data to a communication terminal in a frequency band with good radio quality based on the received CQI report (for example, Non-Patent Documents 1 and 2). reference).

  There are various formats for the CQI report transmitted from the communication terminal to the base station. For example, the CQI report includes average radio quality for all frequency bands, average radio quality for each subband, and the like. In addition, the data size of the CQI report varies depending on the format of the CQI report.

  For example, when the CQI report includes only the average radio quality of all frequency bands, the data size of the CQI report is reduced, and consumption of radio resources in the uplink direction can be suppressed. In addition, although the amount of information processed by the base station is small, in this case, the base station cannot acquire the radio quality for each subband only by the average radio quality of all frequency bands. For this reason, the base station may not be able to allocate communication terminals to subbands with good radio quality and may not be able to perform scheduling with high frequency utilization efficiency.

  Further, for example, when the CQI report includes the average radio quality for each subband in addition to the average radio quality of all frequency bands, the data size of the CQI report becomes large and the consumption of radio resources in the uplink direction increases. Moreover, although the amount of information processed by the base station increases, in this case, the base station can acquire the average radio quality for each subband for all the subbands. For this reason, the base station can perform scheduling with high frequency utilization efficiency by assigning communication terminals to subbands with good radio quality.

3GPP TS36.300 “11.5 CQI reporting for scheduling” 3GPP TS36.213 “7.2 UE procedure for reporting channel quality indication (CQI), precoding matrix indicator (PMI) and rank indication (RI)”

  As described above, the consumption of uplink radio resources and the scheduling load of the base station vary depending on the format of the CQI report. However, in the conventional technology, not all communication terminals under the base station use the same format CQI report, and a specific method for dynamically changing the format of the CQI report according to the surrounding situation is considered. Was not.

  For example, when the number of communication terminals under the base station is small, the base station does not necessarily have to perform strict scheduling because there is a sufficient communication band. However, in the conventional technique, if the CQI report is set to include fine information due to initial setting or the like, redundant information is transmitted from the communication terminal to the base station. There was a problem that the consumption of radio resources increased.

  Accordingly, an object of the present invention made in view of such points is to provide a base station that can change the format of a CQI report used by all communication terminals in accordance with the number of communication terminals under its control.

In order to solve the above-described problems, the invention of the base station according to the first aspect is as follows:
A base station compatible with the OFDM system,
A receiving unit for receiving channel quality information from a communication terminal under its own station;
A scheduler for scheduling transmission data and subbands to each communication terminal based on the channel quality information;
A determination unit that detects the number of communication terminals under its own station based on the channel quality information and determines a channel quality information format according to the number of communication terminals;
A transmission unit that transmits a change instruction to the channel quality information format to a communication terminal under its own station,
It is characterized by providing.

The invention according to the second aspect is a base station according to the first aspect,
The scheduler, when the channel quality information includes an average radio quality of all frequency bands and an average radio quality of at least one subband,
Scheduling is performed according to the difference between the average quality of the entire frequency band and the average radio quality of the at least one subband.

  As described above, the solution of the present invention has been described as an apparatus. However, the present invention can be realized as a method, a program, and a storage medium storing the program, which are substantially equivalent thereto, and the scope of the present invention. It should be understood that these are also included.

For example, the invention of the control method of the base station according to the third aspect that implements the present invention as a method is as follows:
A base station control method corresponding to an OFDM system,
Receiving channel quality information from a communication terminal under its control;
Scheduling transmission data and subbands to each communication terminal based on the channel quality information;
Detecting the number of communication terminals under its own station based on the channel quality information;
Determining a channel quality information format according to the number of communication terminals;
Transmitting a change instruction to the channel quality information format to a communication terminal under its own station;
It is characterized by including.

  According to the present invention, the format of the CQI report used by all communication terminals can be changed according to the number of communication terminals under its own station.

FIG. 1 is a diagram illustrating a schematic configuration of a base station according to an embodiment of the present invention. FIG. 2 is an operation flowchart of the base station shown in FIG. FIG. 3 is a flowchart showing details of the CQI report determination process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of a base station according to an embodiment of the present invention. The base station 1 receives a CQI report (channel quality information) from a communication terminal (not shown) under its control, a control unit 20 that controls the functions of the entire base station 1, and data to the communication terminal. The transmission part 30 which transmits. The control unit 20 includes a scheduler 21 that schedules transmission data and downlink subbands to each communication terminal based on the CQI report received from the communication terminal, and a CQI report format (channel quality) according to the number of communication terminals under its own station. CQI report determination unit 22 (determination unit) that determines (information format).

Here, in the present embodiment, the following four CQI report formats are used between the base station and the communication terminal.
Type 1: Average All Bands The “all band average” format CQI report includes only the average radio quality (all band averages) of all frequency bands used for downlink communication.
Type 2: Average of all bands + average of best subbands The CQI report in the form of "average of all bands + average of best subbands" shows the subband (best subband) with the best radio quality in addition to the average radio quality of all frequency bands. It includes an average radio quality (best subband average) and an identifier indicating the position of the best subband.
Type 3: Average of all bands + M subband average The CQI report in the form of "Average of all bands + M subband average" is the top M subbands (M subbands) with good radio quality in addition to the average radio quality of all frequency bands. The average radio quality (M subband average) and an identifier indicating the position of the M subbands are included.
Type 4: Average of all bands + average of all subbands The CQI report in the form of "average of all bands + average of all subbands" shows the average radio quality for all subbands in addition to the average radio quality of all frequency bands. Is included.

  FIG. 2 is an operation flowchart of the base station 1 shown in FIG. When receiving the CQI report from the communication terminal under its own station, the receiving unit 10 supplies the CQI report to the scheduler 21 (step S101).

  Based on the CQI report supplied from the receiving unit 10, the scheduler 21 performs scheduling of transmission data and downlink subbands to each communication terminal (step S102). The scheduling by the scheduler 21 differs depending on the CQI report format. Hereinafter, the scheduling operation of the scheduler 21 for each type 1 to type 4 CQI report format will be described in detail.

(Type 1: Average of all bands)
When the CQI report from each communication terminal is in the “all-band average” format, the scheduler 21 performs scheduling assuming that the radio quality of each subband is the radio quality indicated by “all-band average”. However, depending on the subband, the radio quality may be lower than “average of all bands”, so the scheduler 21 assumes that the radio quality of each subband is lower than “average of all bands”, and the margin It is also possible to perform scheduling in consideration of the above. The scheduler 21 assigns an arbitrary subband to the communication terminal according to the amount of data to each communication terminal. Here, actually, the radio quality of each subband is different. For this reason, the scheduler 21 can average the throughput to each communication terminal by rotating the subbands allocated to each communication terminal in the entire frequency band. By assigning subbands by rotation, the throughput to each communication terminal can be averaged without performing TPC (Transmission Power Control) control. The scheduler 21 can further stabilize the throughput to each communication terminal by performing TPC control.

(Type 2: Average of all bands + Best subband average)
When the CQI report from each communication terminal is in the “all band average + best subband average” format, the scheduler 21 performs scheduling to assign each communication terminal to the “best subband” of each communication terminal in principle. When the best subbands of a plurality of communication terminals overlap, the scheduler 21 performs scheduling for allocating the best subband to communication terminals having a larger difference between the average of all bands and the average of the best subbands. This is because when the difference between the average of the entire band and the average of the best subband is large, the amount of resources required differs greatly when the transmission data is allocated to the best subband and when allocated to other subbands. It is. For subbands with good radio quality, an efficient modulation class can be used, so that a large amount of data can be allocated to few radio resources. On the other hand, since efficient modulation classes cannot be used for subbands with poor radio quality, the number of required radio resources increases even with the same data amount. That is, the scheduler 21 can improve the user capacity by preferentially allocating the best subband to the communication terminal having a large difference between the average of all bands and the average of the best subband. The scheduler 21 assigns communication terminals that are not assigned to the best subband to other subbands. In this case, the scheduler 21 can average the throughput to each communication terminal by rotating the subbands assigned to each communication terminal in the entire frequency band. The scheduler 21 can further stabilize the throughput to each communication terminal by performing TPC control.

(Type 3: Average of all bands + M subband average)
When the CQI report from each communication terminal is in the “average of all bands + M subband average” format, the scheduler 21 basically transmits each communication to any subband included in the “M subband” of each communication terminal. Scheduling to allocate terminals. When M subbands of a plurality of communication terminals overlap, the scheduler 21 performs scheduling for preferentially assigning M subbands to communication terminals having a larger difference between the average of all bands and the average of M subbands. . The scheduler 21 can improve the user capacity by preferentially allocating subbands included in the M subband to communication terminals having a large difference between the average of all bands and the average of M subbands. The scheduler 21 assigns communication terminals that have not been assigned to the M subband to other subbands. In this case, the scheduler 21 can average the throughput to each communication terminal by rotating the subbands assigned to each communication terminal in the entire frequency band. The scheduler 21 can further stabilize the throughput to each communication terminal by performing TPC control.

(Type 4: Average of all bands + average of all subbands)
When the CQI report from each communication terminal is in the “all band average + all subband average” format, the scheduler 21 can obtain the average radio quality for each subband for all the communication terminals. The scheduler 21 performs scheduling for preferentially assigning a subband having the maximum difference to a communication terminal having a larger maximum value of the difference between the average of all bands and the average radio quality of each subband. In the case of this CQI report, the processing load on the scheduler 21 increases, but it is possible to assign an appropriate subband to each communication terminal.

  After the scheduling by the scheduler 21, the CQI report determination unit determines the CQI report format according to the number of communication terminals under its own station (step S103). FIG. 3 is a flowchart showing details of CQI report determination in step S103 of FIG. Note that the threshold 1 to 3 in FIG. 3 is assumed to be threshold 1 <threshold 2 <threshold 3. Here, the threshold 1 means a relatively small number of communication terminals. For example, communication when each communication terminal can secure a subband necessary for transmitting desired data without competing with other communication terminals. It shows the number of terminals. Moreover, the threshold value 2 means that the number of communication terminals has slightly increased. For example, the communication terminal in the case where the overlap between the best subband of each communication terminal and the best subband of another communication terminal starts to occur. Indicates a number. Further, the threshold value 3 means that the number of communication terminals has increased considerably. For example, the upper M subbands of each communication terminal and the upper M subbands of other communication terminals start to overlap. In this case, the number of communication terminals is shown. The thresholds 1 to 3 can be set when the base station is installed, or can be dynamically changed through operation of the base station.

  In the flowchart of FIG. 3, the CQI report determination unit 22 first detects the number of communication terminals under its own station based on the CQI report received from each communication terminal (step S201). Next, the CQI report determination unit 22 compares the number of communication terminals with the threshold value 1 (step S202). When the number of communication terminals is less than the threshold 1, the CQI report determination unit 22 sets the “all band average” format as the CQI report format (step S203). That is, when the number of communication terminals is relatively small, a CQI report in the “all band average” format is used.

  When the number of communication terminals is equal to or greater than the threshold value 1, the CQI report determination unit 22 compares the number of communication terminals with the threshold value 2 (step S204). When the number of communication terminals is less than the threshold value 2, the CQI report determination unit 22 sets the “all band average + best subband average” format as the CQI report format (step S205). That is, when the number of communication terminals is slightly increased, a CQI report of the “average of all bands + best subband” format is used.

  When the number of communication terminals is equal to or greater than the threshold value 2, the CQI report determination unit 22 compares the number of communication terminals with the threshold value 3 (step S206). When the number of communication terminals is less than the threshold 3, the CQI report determination unit 21 sets the “all band average + M subband average” format as the CQI report format (step S207). That is, until the number of communication terminals increases considerably, a CQI report of the “average of all bands + M subbands” format is used.

  When the number of communication terminals is equal to or greater than the threshold 3, the CQI report determination unit 22 sets the “average of all bands + average of all subbands” format as the CQI report format (step S208). That is, when the number of communication terminals has increased considerably, a CQI report in the form of “average of all bands + average of all subbands” is used.

  When the CQI report format determined in step S104 is different from the current CQI report format (Yes in step S104), the CQI report determination unit 22 instructs the transmission unit 30 to change to the CQI report format determined in step S104. Is transmitted to the communication terminal under its control (step S105). The communication terminal that has received the change command changes the CQI report format and transmits the radio quality information to the base station in the changed CQI report format.

  Thus, according to the present embodiment, the CQI report determination unit 22 detects the number of communication terminals under its own station based on the received CQI report, determines the CQI report format according to the number of communication terminals, and An instruction to change the CQI report is transmitted to the communication terminal. As a result, the base station 1 can change the format of the CQI report used by all the communication terminals according to the number of communication terminals under its control, which unnecessarily increases the consumption of uplink radio resources. There is no end. Also, the scheduling load of the base station can be adjusted according to the number of communication terminals under its control.

  Further, in the present embodiment, when the CQI report includes the average radio quality of all frequency bands and the average radio quality of at least one subband, the scheduler 21 has an average quality of all frequency bands and at least 1 Scheduling is performed according to the difference between the average radio quality of two subbands. As a result, transmission data can be efficiently allocated to a small number of radio resources, and the user accommodation rate can be improved.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each unit, each step, etc. can be rearranged so that there is no logical contradiction, and a plurality of components, steps, etc. can be combined or divided into one. .

DESCRIPTION OF SYMBOLS 1 Communication terminal 10 Reception part 20 Control part 21 Scheduler 22 CQI report determination part 30 Transmission part

Claims (3)

A base station compatible with the OFDM system,
A receiving unit for receiving channel quality information from a communication terminal under its own station;
A scheduler for scheduling transmission data and subbands to each communication terminal based on the channel quality information;
A determination unit that detects the number of communication terminals under its own station based on the channel quality information and determines a channel quality information format according to the number of communication terminals;
A transmission unit that transmits a change instruction to the channel quality information format to a communication terminal under its own station,
A base station comprising: The base station according to claim 1, wherein
The scheduler, when the channel quality information includes an average radio quality of all frequency bands and an average radio quality of at least one subband,
Scheduling according to a difference between an average quality of the entire frequency band and an average radio quality of the at least one subband;
A base station characterized by that. A base station control method corresponding to an OFDM system,
Receiving channel quality information from a communication terminal under its control;
Scheduling transmission data and subbands to each communication terminal based on the channel quality information;
Detecting the number of communication terminals under its own station based on the channel quality information;
Determining a channel quality information format according to the number of communication terminals;
Transmitting a change instruction to the channel quality information format to a communication terminal under its own station;
The control method characterized by including.

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