WO2015040659A1

WO2015040659A1 - Radio communication method, radio communication system, radio base station and radio terminal

Info

Publication number: WO2015040659A1
Application number: PCT/JP2013/005599
Authority: WO
Inventors: 耕太郎椎▲崎▼
Original assignee: 富士通株式会社
Priority date: 2013-09-20
Filing date: 2013-09-20
Publication date: 2015-03-26

Abstract

The objective of the technique disclosed herein is to enable the solution of problems occurring in CoMP predicated on an unideal backhaul. A radio communication method disclosed herein is a radio communication method for performing a coordinated transmission in which first and second radio base stations are coordinated to transmit a radio signal to a first one of one or more radio terminals. According to this radio communication method, the first radio base station transmits, to a second radio terminal that is one of the one or more radio terminals, downstream scheduling information that is to be used for performing the coordinated transmission, and the second radio terminal transmits the downstream scheduling information to the second radio base station.

Description

Wireless communication method, wireless communication system, wireless base station, and wireless terminal

The present invention relates to a radio communication method, a radio communication system, a radio base station, and a radio terminal.

In recent years, in a wireless communication system (cellular system) including a wireless base station such as a mobile phone system, discussions have been made on next-generation wireless communication technology in order to further increase the speed and capacity of the wireless communication. . For example, 3GPP (3rd Generation Partnership Project), a standardization organization, proposes a communication standard called LTE (Long Term Evolution) and a communication standard called LTE-A (LTE-Advanced) based on LTE wireless communication technology. Has been. Hereinafter, unless otherwise specified, “LTE” includes, in addition to LTE and LTE-A, other wireless communication systems in which these are expanded.

3GPP is studying various elemental technologies that make up LTE (LTE-A), and one of those technologies is CoMP (Coordinated Multiple Point). In short, CoMP is a general term for technologies that coordinate transmission / reception with respect to wireless terminals between different wireless base stations. As will be described later, there are several transmission methods (categories) in CoMP. By applying these, it is possible to enjoy the spatial diversity effect and suppress interference between radio base stations. Therefore, compared with the case where a radio base station does not cooperate, a communication characteristic can be improved by CoMP. Increasing the capacity of wireless communications has become an issue due to the widespread use of smartphones, and the importance of CoMP is expected to increase in the future.

On the other hand, the study on non-ideal backhaul has started in 3GPP in recent years. Here, the backhaul refers to a wired or wireless network that connects between wireless base stations or connects a wireless base station to a core network. The non-ideal backhaul refers to a non-ideal backhaul, and specifically means a backhaul with a relatively large delay. On the other hand, a backhaul with a relatively small delay is called an ideal backhaul. In various conventional 3GPP studies, an ideal backhaul was assumed, but it is assumed that high-speed backhaul laying using optical fibers is difficult. It is expected that the examination will be activated.

By the way, in the conventional CoMP study in 3GPP, it is assumed that control information for cooperation between radio base stations is transmitted and received via a backhaul. However, unlike the ideal backhaul assumed in the conventional study, it is inevitable that a delay occurs in the transmission / reception of such control information when a non-ideal backhaul is assumed. It is done. Therefore, there is a possibility that some inconvenience may occur in the LTE system due to the communication delay between the radio base stations due to such non-ideal backhaul. However, since CoMP based on a non-ideal backhaul has not been studied so far, there is a possibility that the inconveniences described above have not surfaced.

The disclosed technology has been made in view of the above, and provides a wireless communication method, a wireless communication system, a wireless base station, and a wireless terminal that can eliminate inconveniences that occur in CoMP based on non-ideal backhaul. Objective.

In order to solve the above-described problems and achieve the object, the disclosed wireless communication method is such that the first wireless base station and the second wireless base station cooperate with the first wireless terminal among the one or more wireless terminals. A radio communication method for performing coordinated transmission for transmitting radio signals, wherein the first radio base station transmits downlink scheduling information for performing the coordinated transmission to one of the one or more radio terminals. Transmitting to the radio terminal, the second radio terminal transmits the downlink scheduling information to the second radio base station.

According to one aspect of the wireless communication method, the wireless communication system, the wireless base station, and the wireless terminal disclosed in this case, there is an effect that it is possible to eliminate inconveniences that occur in CoMP based on a non-ideal backhaul.

1A to 1C are diagrams for explaining the concept of each CoMP method. FIG. 2 is a diagram for explaining DPS, which is one method of CoMP. FIG. 3 is a diagram for explaining the location of a problem in the present application. FIG. 4 is a diagram for explaining the location of a problem in the present application. FIG. 5 is a diagram showing an example of a processing sequence in the first embodiment of the present application. FIG. 6 is a diagram showing an example of a processing sequence in the first embodiment of the present application. FIG. 7 is a diagram illustrating an example of a processing sequence in the second embodiment of the present application. FIG. 8 is a diagram illustrating an example of a network configuration of the wireless communication system according to each embodiment. FIG. 9 is an example of a functional configuration diagram of a radio base station in the radio communication system of each embodiment. FIG. 10 is an example of a functional configuration diagram of a wireless terminal in the wireless communication system of each embodiment. FIG. 11 is an example of a hardware configuration diagram of a radio base station in the radio communication system of each embodiment. FIG. 12 is an example of a hardware configuration diagram of a wireless terminal in the wireless communication system of each embodiment.

Hereinafter, embodiments of the disclosed wireless communication method, wireless communication system, wireless base station, and wireless terminal will be described with reference to the drawings. In addition, although demonstrated as separate embodiment for convenience, it cannot be overemphasized that the effect of a combination can be acquired and usefulness can further be heightened by combining each embodiment.

[Location of problem]
First, before describing each embodiment, the location of problems in the prior art will be described. It should be noted that this problem has been newly found as a result of careful study of the prior art by the inventor and has not been known so far.

First, the outline of CoMP (multi-point coordination), which is a prerequisite technology of the present application, will be described. In CoMP, a transmitting station may be generally referred to as TP (Transmission Point). In downlink CoMP handled by the present application, TP is a concept that substantially corresponds to a radio base station. Therefore, in the present application, unless otherwise noted, the radio base station may be appropriately read as TP.

As mentioned above, several transmission methods (categories) are defined in CoMP. Here, joint transmission (JT), dynamic point selection (DPS), semi-static point selection (SSPS), coordinated scheduling (CS), coordinated beamforming (CB), etc. are known as downlink CoMP transmission methods. Yes.

The concept of CoMP transmission method will be described in order based on FIG. FIG. 1A is a diagram illustrating the concept of JT, which is one of CoMP. JT is a method in which a plurality of

radio base stations

10a and 10b simultaneously transmit (joint transmission) the same data addressed to a certain radio terminal 20, and improve the reception quality and throughput addressed to the radio terminal 20.

FIG. 1B is a diagram showing the concept of DPS and SSPS, which are one of CoMP. In DPS, the same data addressed to the radio terminal 20 is simultaneously present in a plurality of

radio base stations

10a and 10b. However, data transmission addressed to the radio terminal 20 is performed from a single radio base station 10a and other base stations 10b. Is blanking, i.e. not transmitting. This enables instantaneous dynamic cell (base station) selection that follows fading fluctuations rather than normal cell (base station) selection in an LTE system based on time-averaged channel conditions. SSPS is similar in concept to DPS, but cell switching is more gradual than PDS which switches cells every subframe.

FIG. 1C is a diagram showing the concept of CS and CB, which are one of CoMP. CS and CB are transmitted from a single

radio base station

10a or 10b to a

radio terminal

20a or 20b in a certain subframe, and other

radio base stations

10b or 10a reduce interference given to the transmission. It behaves like Here, in CS, other radio base stations perform muting to reduce interference with transmission by

radio base station

10a or 10b. In CB, other

radio base stations

10b or 10a perform beamforming. To reduce interference with transmission by the

radio base station

10a or 10b.

Next, an example of a general processing sequence of CoMP will be described based on FIG. FIG. 2 exemplifies a processing sequence in the case of executing DPS, which is one of the CoMP schemes, by the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c, which are three base stations. Yes. However, it should be noted that other CoMP schemes can be implemented by a similar processing sequence.

Here, in FIG. 2, it is assumed that the ideal backhaul described above is assumed.

First, it is assumed that downlink data (for example, download file) addressed to the wireless terminal 20 is generated in the serving base station 10a in S101 of FIG. At this time, the serving base station 10a needs to perform scheduling for transmitting downlink data to the radio terminal 20. In this scheduling, the presence / absence of application of DPS, the transmission base station in DPS, transmission parameters for performing DPS, and the like are determined.

In order to enable such scheduling, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c each transmit a downlink reference signal in S102a to S102c of FIG. The radio terminal 20 measures the quality of the downlink with each base station based on these reference signals. Thereafter, in S103, the radio terminal 20 feeds back a CQI (Channel Quality Indicator) indicating the downlink quality measured for each base station to the serving base station 10a.

In step S104, the serving base station 10a performs the above-described scheduling based on the received CQI. For example, the serving base station 10a can determine the base station with the best downlink radio quality indicated by CQI as the DPS transmission base station. Here, as an example, it is assumed that the serving base station 10a has decided to transmit downlink data by DPS using the first coordinated base station 10b as a transmission base station.

At this time, the serving base station 10a also uses the modulation coding scheme (MCS: Modulation and Coding Scheme) and the resource block (sub-scheme) used for transmission of downlink data from the first cooperative base station 10b to the radio terminal 20 based on CQI. Transmission parameters such as (carrier) can also be determined. The transmission base station determined in S104 and these transmission parameters are collectively referred to as downlink scheduling information here.

Next, in S105, the serving base station 10a transmits downlink data and downlink scheduling information to the first cooperative base station 10b via the backhaul based on the scheduling result in S104. In S106, the serving base station 10a transmits downlink scheduling information to the second coordinated base station 10c via the backhaul based on the scheduling result in S104. At this time, downlink data is transmitted to the first coordinated base station 10b which is a transmission base station, but is not transmitted to the second coordinated base station 10c which is not a transmission base station.

As mentioned above, Figure 2 assumes an ideal backhaul. Therefore, the delay in signal transmission / reception via the backhaul in S105 and S106 is minimal.

Finally, in steps S107a to S107c in FIG. 2, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c cooperate in downlink by DPS using the first cooperative base station 10b as a transmission base station. Data is transmitted to the wireless terminal 20. At this time, the first cooperative base station 10b, which is a transmission base station in S107b, transmits downlink data to the radio terminal 20 based on the downlink scheduling information received in S105. On the other hand, in S107a, the serving base station 10a performs blanking (no transmission) to the radio terminal 20 based on its scheduling result in S104. In 107c, the second coordinated base station 10c performs blanking for the radio terminal 20 based on the downlink scheduling information received in S106.

According to the processing sequence shown in FIG. 2, it is considered that DPS, which is one of the CoMP schemes, can be executed appropriately in response to downlink radio quality.

Next, the location of the problem in the present application will be described based on FIG. 3 and FIG.

Another example of the CoMP processing sequence will be described with reference to FIG. FIG. 3 illustrates a processing sequence in the case of applying DPS, which is one of the CoMP schemes, but other CoMP schemes can be implemented by a similar processing sequence.

Here, in FIG. 3 and FIG. 4 described later, it is assumed that a non-ideal backhaul is assumed, unlike FIG. 2 described above.

First, since S201 to S204 in FIG. 3 are the same as S101 to S104 in FIG. 2, description thereof is omitted here. In S204, based on the CQI of S203, the transmission base station is determined to be the first coordinated base station 10b, and downlink data transmission parameters (MCS, resource block, etc.) are determined.

Next, in S205 of FIG. 3, the serving base station 10a transmits downlink data and downlink scheduling information to the first cooperative base station 10b via the backhaul based on the scheduling result of S204. In S206, the serving base station 10a transmits downlink scheduling information to the second coordinated base station 10c via the backhaul based on the scheduling result in S204.

Here, as described above, FIG. 3 assumes a non-ideal backhaul. Therefore, the signal transmission / reception delay through the backhaul in S205 and S206 is relatively large. This delay is assumed to be several tens of milliseconds, for example. For this reason, as shown in FIG. 3, it is considered that the reception timing of the signals in S205 and S206 is considerably delayed from the transmission timing.

Incidentally, in the LTE system, downlink quality measurement and CQI transmission by the wireless terminal 20 as described above are periodically performed. This is because scheduling should be performed based on as new radio quality as possible. On the other hand, when scheduling is performed based on the old radio quality, it is considered that the possibility of the scheduling becoming inappropriate increases.

In the LTE system, the downlink quality measurement and CQI transmission period (referred to as CQI transmission period for convenience) by the radio terminal 20 is selectively selected from seven values of 2, 5, 10, 20, 40, 80, and 160. Can be set. Here, the unit is a subframe (one subframe is one millisecond).

Now, assume that the CQI transmission cycle in FIG. 3 is, for example, 20 subframes (20 milliseconds). It is assumed that the delay in transmitting and receiving the signal in S206 is 40 milliseconds.

At this time, while the transmission / reception of the signal in S206 is delayed (40 milliseconds), the CQI transmission cycle (20 milliseconds) elapses from the CQI transmission in S203. Therefore, as illustrated in FIG. 3, before the reception of the signal of S206 is completed, the CQI transmission is performed again in S208 after the downlink reference signal is measured again in S207a to S207c. The CQI transmission in S208 corresponds to the CQI transmission in the next cycle in S203. Thereby, at the timing of S209, scheduling can be performed based on the CQI of S208.

Here, it is assumed that the downlink quality of the second cooperative base station 10c exceeds that of the first cooperative base station 10b in the CQI of S208. If it is assumed that the downlink data of S201 (note that it has not been transmitted to the radio terminal 20 at this stage) is scheduled based on the CQI of S208 at the timing of S209, the DPS transmission base station performs the first coordination. It will be determined not the base station 10b but the second cooperative base station 10c. Here, for simplicity, it is assumed that the transmission base station is determined based only on the quality of the downlink radio link.

However, in practice, the downlink data is not scheduled in S201 at the timing of S209, and in S210a to S210c of FIG. 3, the downlink data is transmitted by DPS using the first coordinated base station 10b as the transmission base station. In the scheduling of S204, it is determined that the downlink data transmission base station is the first cooperative base station 10b, and DPS transmission based on the determination is executed regardless of the subsequent change in downlink quality. It is. Therefore, in the determination of the transmission base station for DPS transmission, a situation occurs in which the latest downlink quality at the time of DPS transmission is not reflected.

In the case shown in FIG. 3, the first cooperative base station 10b is actually transmitted although the second cooperative base station 10c is supposed to be the transmission base station from the viewpoint of communication efficiency. It becomes a base station. Such a situation should be avoided as much as possible because it leads to a decrease in the throughput of the entire wireless communication system. This point is a major problem in FIG. 3, and further study is considered necessary.

On the other hand, in the case of an ideal backhaul as shown in FIG. 2, scheduling of downlink data S105 and S106 is performed before the second CQI (not shown), and the above-described problem does not occur. .

In the above description, the description has focused on the fact that the latest downlink quality at the time of DPS transmission is not reflected in the determination of the transmission base station for DPS transmission. However, it should be noted that this problem is not limited to the determination of the transmission base station, but extends to the entire downlink scheduling in CoMP transmission. For example, the latest downlink quality at the time of DPS transmission is not reflected in the determination of downlink transmission parameters such as MCS used for DPS transmission and resource block allocation. This leads to a decrease in the throughput of the entire wireless communication system, as described with respect to the transmission base station.

In summary, in the case shown in FIG. 3, even if scheduling (timing of S204) is once performed for downlink data, rescheduling of downlink data (S209) according to the subsequent change in downlink quality. It is considered desirable to perform ( Thereby, it seems that the above-mentioned problem in FIG. 3 can be solved.

Fig. 4 shows the processing sequence for such rescheduling. FIG. 4 is largely the same as FIG. 3 except that information for notifying the result of rescheduling is transmitted after the scheduling of S209. Since this information notifies the scheduling result changed by rescheduling, it will be referred to as downlink scheduling change information. By notifying the downlink scheduling change information to the first coordinated base station 10b and the second coordinated base station 10c, these base stations can recognize the rescheduling result, and coordinated transmission such as DPS according to the change in downlink quality ( CoMP transmission) can be realized.

Here, similarly to S205 and S206, the downlink scheduling change information may be transmitted from the serving base station 10a to the first coordinated base station 10b or the second coordinated base station 10c via the backhaul. Seem. However, as described above, FIG. 4 assumes a non-ideal backhaul. Therefore, when downlink scheduling change information is transmitted via the backhaul, a relatively large delay is involved in the transmission / reception.

In such a case, as shown in FIG. 4, it is considered that the reception of the downlink scheduling change information is not in time for the execution of the DPS in S210a to S210c. As a result, also in FIG. 4, as in FIG. 3, DPS with the transmission base station as the first coordinated base station 10b is executed in S210a to S210c without reflecting subsequent changes in downlink quality. become. Therefore, the processing sequence of FIG. 4 cannot solve the above-described problem in the processing sequence of FIG.

As described above, when downlink CoMP transmission (for example, DPS) is performed on the premise of non-ideal backhaul, downlink scheduling information transmitted from the serving base station 10a to the cooperative base station via the backhaul There is a relatively large delay in reception. Therefore, when the serving base station 10a and the coordinated base station perform CoMP transmission based on downlink scheduling information, the latest downlink state is not reflected in the scheduling information, and thus the CoMP transmission is not appropriately performed. There is a problem that the situation can happen. Furthermore, even when trying to send downlink scheduling information reflecting the latest downlink state, the above problem cannot be solved because a relatively large delay is still involved via the backhaul. Such a problem is thought to be avoided as much as possible because it leads to a decrease in the throughput of the entire wireless communication system.

In the following, each embodiment for solving the above-described problem will be described.

[First Embodiment]
The first embodiment is an example of an embodiment that solves the above-described problem, and when the serving base station 10a changes the scheduling of cooperative transmission, the change is transmitted via the terminal 20 by the radio signal to the cooperative base station 20b. To send to.

More specifically, in the first embodiment, the first radio base station and the second radio base station cooperate with each other to transmit a radio signal to the first radio terminal 20 among the one or more radio terminals 20. A radio communication method for performing coordinated transmission, wherein the first radio base station transmits downlink scheduling information for performing coordinated transmission to a second radio terminal 20 that is one of the one or more radio terminals 20. The second radio terminal 20 is an embodiment related to a radio communication method for transmitting the downlink scheduling information to the second radio base station.

FIG. 5 is a diagram illustrating an example of a processing sequence according to the first embodiment.

The premise of the first embodiment will be described. As shown in FIG. 5, in the first embodiment, a radio terminal 20, and a serving base station 10a, a first coordinated base station 10b, and a second coordinated base station 10c, which are three radio base stations 10, appear. .

In the present embodiment and the following embodiments, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c may be collectively referred to simply as a radio base station 10. Further, the first cooperative base station 10b and the second cooperative base station 10c may be collectively referred to simply as the cooperative base stations 10b to 10c.

The wireless terminal 20 does not need to be communicating with the serving base station 10a, but is assumed to be under the management (under management) of the serving base station 10a. Further, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c, which are the three radio base stations 10, are in a cooperative relationship for performing cooperative transmission (CoMP transmission). In the LTE system, this cooperative relationship is defined by a set of radio base stations called a CoMP set. The CoMP set is notified in advance from the serving base station 10a to the radio terminal 20, so that the radio terminal 20 can communicate with the radio base stations 10 other than the serving base station 10a belonging to the CoMP set (the first coordinated base station 10b in FIG. 2 cooperative base stations 10c).

In the first embodiment, the above-described non-ideal backhaul is assumed. Therefore, it should be noted that a relatively large delay of, for example, several tens of milliseconds occurs in communication via the backhaul among the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c.

In the example shown in FIG. 5, there are two cooperative base stations 10b to 10c, but it goes without saying that this is only an example. The present invention is applicable when the number of coordinated base stations is one or more.

Also, FIG. 5 shows an example of applying DPS, which is one of the CoMP methods, but it should be noted that this is only an example. The present invention is applicable regardless of the CoMP method.

Hereinafter, each process shown in FIG. 5 will be described in order.

In step S301 in FIG. 5, downlink data is generated in the serving base station 10a. Downlink data is data addressed to the radio terminal 20, and includes high-layer control signals (RRC signals and the like) in addition to user data (application data).

For example, when the wireless terminal 20 downloads a file (including a web page or an e-mail) from a server on the Internet, downlink data (user data) is generated in the wireless base station 10 located between the server and the wireless terminal 20. To do. Further, when the radio base station 10 transmits an RRC control signal to the radio terminal 20, downlink data is generated in the base station. Thus, the downlink data generated in the radio base station 10 includes not only data generated from the radio base station 10 but also data generated by other devices and relayed by the radio base station 10. Please note.

In S302a, the serving base station 10a transmits a downlink reference signal. In the LTE system, some downlink reference signals are defined. In S302a, for example, a cell-specific reference signal (Cell-specific reference signal) or a channel state information reference signal (CSI (Channel State information) reference reference signal) A downlink reference signal for wireless quality measurement is transmitted.

In S302b, the first coordinated base station 10b also transmits a downlink reference signal, and in S302c, the second coordinated base station 10c also transmits a downlink reference signal. These can be performed similarly to S302a. Note that S302a to S302c may be transmitted in the same subframe or in different subframes.

In contrast, in S302a, the wireless terminal 20 receives a downlink reference signal from the serving base station 10a. In S302b, the radio terminal 20 also receives a downlink reference signal from the first coordinated base station 10b, and in S302c, the radio terminal 20 also receives a downlink reference signal from the second coordinated base station 10c.

At this time, the radio terminal 20 measures the radio quality (downlink radio quality) from each radio base station 10 to the radio terminal 20 based on each received downlink reference signal. As the radio quality here, for example, a signal-to-noise power ratio (SNR: “Signal-to-Noise-power” Ratio), a signal-to-noise interference power ratio (SINR: “Signal-to-Interference” plus “Noise-power” Ratio), and the like can be used. Then, the radio terminal 20 generates CQI (Channel Quality Indicator) based on the downlink radio quality. CQI is an index indicating downlink channel quality and is one of uplink control information defined in the LTE system. As the CQI is fed back to the radio base station 10, the radio base station 10 can grasp the downlink channel quality and can perform downlink scheduling and the like.

In S303, the radio terminal 20 transmits the CQI generated based on the downlink reference signals in S302a to S302c to the serving base station 10a. The CQI is transmitted through a physical uplink control channel (PUCCH: “Physical” Uplink “Control” CHannel) or a physical uplink shared channel (PUSCH: “Physical” Uplink “Shared” CHannel). The three CQIs generated in S302a to S302c may be transmitted in the same subframe or in different subframes.

Next, in S304, the serving base station 10a performs scheduling for transmitting the downlink data generated in S301 based on the CQI received in S303. In the scheduling in S304, the serving base station 10a makes various decisions for transmitting the downlink data generated in S301. In the following, these determinations will be described in order.

In S304, the serving base station 10a first determines the radio base station 10 (hereinafter referred to as a transmission base station for convenience) that transmits the downlink data generated in S301. In a normal LTE system, downlink data generated in the serving base station 10 a is transmitted to the radio terminal 20 by the serving base station 10 a. However, since CoMP is applied in the present application, downlink data generated in the serving base station 10a can be transmitted to the radio terminal 20 other than the serving base station 10a (of course, the serving base station 10a transmits the downlink data). Needless to say, you can do that.)

The transmission base station is selected from the radio base stations 10 included in the aforementioned CoMP set. In the present embodiment, since the CoMP set includes three serving base stations 10a, a first coordinated base station 10b, and a second coordinated base station 10c, the serving base station 10a determines a transmission base station from these. It should be noted that the determination of the transmission base station also has an aspect of determining the CoMP scheme. For example, when there are a plurality of transmission base stations, JT, which is one of the CoMP schemes, is inevitably applied.

In S304, the serving base station 10a can determine the transmission base station based on the CQI received in S303. As an example, based on the CQI received in S303, the serving base station 10a can determine the radio base station 10 with the best downlink quality with the radio terminal 20 as the transmission base station. In this case, DPS or SSPS, which is one of the CoMP methods, is performed. As another example, based on the CQI received in S303, the serving base station 10a transmits the radio base station 10 having the best downlink quality with the radio terminal 20 and the second radio base station 10 as transmission bases. Can be determined as a station. In this case, JT, which is one of the CoMP methods, is performed. As another example, the serving base station 10a determines that the serving base station 10a is a transmitting base station based on the CQI received in S303 and requests the coordinated base stations 10b to 10c to reduce interference. It can also be determined. In this case, CS or CB, which is one of the CoMP methods, is performed.

The serving base station 10a may determine the transmission base station in consideration of any element other than CQI. As an example, the serving base station 10a receives information on the load from the coordinated base stations 10b to 10c, and when there is only one radio base station 10 whose downlink quality is equal to or higher than a predetermined value and whose load is equal to or lower than a predetermined value. The radio base station 10 can be determined as a transmission base station (for example, DPS is performed). As described above, the serving base station 10a can determine the transmission base station based on the downlink radio quality of each radio base station 10 included in the CoMP set, and the load of each radio base station 10. Such determination of the transmission base station is generally performed by scheduling applicable to downlink CoMP transmission in the LTE system, and various conventional techniques are known. Omit. Examples of the load mentioned here include data rates handled by the radio base station 10, radio resource usage rates, operating rates of hardware such as processors of the radio base station 10, and members mounted on the radio base station 10. This corresponds to the amount of heat generated. In S304, the serving base station 10a next determines a parameter (hereinafter referred to as a downlink transmission parameter for convenience) for causing the previously determined transmission base station to transmit the downlink data generated in S301.

Here, the downlink transmission parameters include various parameters for transmitting or receiving downlink data. The downlink transmission parameters can include, for example, various parameters included in downlink control information (DCI: Downlink Control Information) defined by the LTE system. Several formats are defined in DCI. For example, DCI format 1 is control information accompanying downlink data, and includes various parameters necessary for transmitting and receiving the downlink data.

The downlink transmission parameters include, for example, MCS (Modulation and Coding Scheme) indicating a coding scheme and a modulation scheme applied to downlink data, and resource block allocation (Resource Block allocation) indicating a resource block (subcarrier) to which downlink data is mapped. ) Etc. are included. These correspond to the parameters included in the DCI format 1 described above.

The serving base station 10a can determine MCS and resource block allocation that are downlink transmission parameters based on the CQI received in S303. Further, these parameters may be determined in consideration of an arbitrary element other than CQI. Furthermore, these parameters can also be determined in consideration of the relationship with other radio terminals 20 under the serving base station 10a. The determination of these parameters is generally performed in downlink data scheduling in the LTE system, and various conventional techniques are known. Therefore, detailed description thereof is omitted here.

Next, we will explain the downlink transmission parameters. In addition to the above-described parameters, for example, the downlink transmission parameter can include information related to the timing at which the transmission base station transmits downlink data. Since the transmission unit on the time axis in the LTE system is a subframe (1 millisecond), this timing is specified by a subframe (downlink subframe). Hereinafter, this information will be referred to as downlink subframe information for convenience.

By the way, when determining the transmission timing of downlink data (downlink subframe information), it is necessary to consider the premise of non-ideal backhaul. As will be described later, in this embodiment, downlink subframe information (including downlink transmission parameters) is transmitted from the serving base station 10a to the coordinated base stations 10b to 10c via the non-ideal backhaul. Here, as described above, for example, a delay of several tens of milliseconds occurs in communication via the non-ideal backhaul. Due to this delay, there is a concern that if the transmission timing of the downlink subframe is too early, the notification of the transmission timing (reception of downlink subframe information by the cooperative base stations 10b to 10c) will not be in time for the transmission timing.

This will be explained with a specific example. Consider a case where a maximum delay of 40 milliseconds occurs in communication via a non-ideal backhaul. Now, suppose that the transmission timing of the downlink subframe is determined to be, for example, after 10 subframes (after 10 milliseconds). In this case, there is a possibility that the transmission timing may be passed 30 subframes (30 milliseconds before) of notification of transmission timing of the downlink subframe (reception of downlink subframe information by the cooperative base stations 10b to 10c).

Therefore, it is preferable to determine the transmission timing of the downlink subframe, for example, after 50 subframes (after 50 milliseconds) in consideration of the non-ideal backhaul delay. In this way, even if the notification of the transmission timing of the downlink subframe (reception of downlink subframe information by the cooperative base stations 10b to 10c) is delayed to the maximum, the transmission timing is 10 subframes later (10 milliseconds later). It becomes. As a result, the coordinated base stations 10b to 10c can meet the transmission timing of the downlink subframe with a margin.

Note that, in the above description, the transmission base station is first determined and then the downlink transmission parameters are determined, but it should be noted that the order of determination is not limited to this. In particular, the transmission base station and the downlink transmission parameters can be determined together. As an example, based on the CQI received in S303, the combination of the radio base station 10 and the resource block (subcarrier) with the best CQI is selected, and the radio base station 10 is determined as the transmission base station and A resource block assignment can be determined based on the resource block. The determination of the transmission base station and downlink transmission parameters is not limited to this example, and can be performed based on any method, rule, algorithm, or the like without departing from the spirit of the present application.

Return to description of S304. In S304, the serving base station 10a further transmits a parameter for transmitting the previously determined transmission base station and downlink transmission parameter change information to the cooperative base stations 10b to 10c via the uplink (hereinafter referred to as uplink for convenience. Called transmission parameters). In the present embodiment, the transmission base station and downlink transmission parameters are once determined in S304, but these may be changed according to the subsequent change in the downlink state. Here, in preparation for such a change, uplink transmission parameters for notifying the coordinated base stations 10b to 10c of the changed transmission base station and downlink transmission parameters are determined in advance.

The uplink transmission parameters include various parameters for transmitting or receiving change information. Although there is a small difference depending on whether the change information is transmitted using PUCCH or PUSCH, the uplink transmission parameters will be described below as an example when the change information is transmitted using PUSCH. Even when the change information is transmitted by PUCCH, it can be realized in the same manner, but details are omitted.

The uplink transmission parameters can include various parameters included in the DCI described above. As described above, several formats are defined for DCI. For example, DCI format 0 is control information that is notified prior to uplink data, and includes various parameters necessary for transmitting and receiving the uplink data. ing.

Uplink transmission parameters include, for example, MCS indicating a coding scheme and modulation scheme applied to uplink data, resource block allocation indicating a resource block (subcarrier) to which downlink data is mapped, and the like. These correspond to the parameters included in the DCI format 0 described above.

The serving base station 10a can determine MCS and resource block allocation that are uplink transmission parameters based on, for example, measurement results of uplink reference signals (not shown). Further, these parameters may be determined in consideration of arbitrary elements thereof. The determination of these parameters is generally performed in uplink data scheduling in the LTE system, and various conventional techniques are known. Therefore, detailed description thereof is omitted here.

Next, the uplink transmission parameters will be explained. In addition to the above-described parameters, for example, the uplink transmission parameter can include information related to the timing at which the transmission base station transmits the change information. In the LTE system, this timing is specified by a subframe (uplink subframe). Hereinafter, for convenience, this information will be referred to as uplink subframe information.

Note that it is necessary to consider the premise of non-ideal backhaul when determining the transmission timing (uplink subframe information) of change information. Since this point may be performed in the same manner as described above regarding the determination of the transmission timing of downlink data (downlink subframe information), detailed description thereof is omitted here.

Here, in an example of the processing in the present embodiment shown in FIG. 5, it is assumed that the serving base station 10a determines the first coordinated base station 10b as the transmission base station by scheduling in S304. Needless to say, this premise is merely an example for explaining a specific example of processing in the present embodiment. In the following, the description will proceed under this assumption.

In the following description, information indicating the transmission base station described above and downlink transmission parameters may be collectively referred to as downlink scheduling information. Further, the uplink transmission parameter described above may be referred to as uplink scheduling information.

Referring back to FIG. 5, in S305, the serving base station 10a transmits a signal including downlink data, downlink scheduling information, and uplink scheduling information to the first coordinated base station 10b via the backhaul. On the other hand, in S305, the first cooperative base station 10b receives a signal including downlink data, downlink scheduling information, and uplink scheduling information from the serving base station 10a via the backhaul. It should be noted that the transmission / reception in S305 is performed via a backhaul (non-ideal backhole), so that a relatively large delay occurs.

The signal of S305 can be realized by the X2 signal in the LTE system. In S305, downlink data, downlink scheduling information, and uplink scheduling information are transmitted and received as a single signal to the first coordinated base station 10b. However, these may be transmitted separately in a plurality of signals. .

In S306, the serving base station 10a transmits a signal including downlink data, downlink scheduling information, and uplink scheduling information to the second cooperative base station 10c via the backhaul. On the other hand, in S306, the second cooperative base station 10c receives a signal including downlink data, downlink scheduling information, and uplink scheduling information from the serving base station 10a via the backhaul. Since S306 may be performed in the same manner as S305, description thereof is omitted.

In S205 to S206 in FIG. 3, downlink data is transmitted only to the transmission base station, whereas in S305 to S306 in FIG. 5, downlink data is transmitted to all the coordinated base stations 10b to 10c. Be careful about what is done. In this embodiment, since the transmission base station may be changed later, the downlink data is transmitted in advance to all the coordinated base stations 10b to 10c that can become the transmission base station.

Next, in steps S307a to S307c in FIG. 5, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c transmit downlink reference signals to the radio terminal 20, respectively. In S308, the radio terminal 20 transmits CQI indicating the downlink quality measured based on the downlink reference signal in S307a to S307c to the serving base station 10a. In step S309, the serving base station 10a performs downlink data scheduling (rescheduling) in step S301 based on the CQI and the like in step S308.

As already described with reference to FIG. 3, in the LTE system, the CQI transmission cycle is selectively set from seven types of values of 2, 5, 10, 20, 40, 80, and 160 (the unit is subframe = millisecond). ). S307 (S307a to S307c) to S309 correspond to the scheduling process performed in the next CQI transmission cycle after S302 to S304. That is, S307 to S309 are performed after the CQI transmission cycle has elapsed from S302 to S304. Thereafter, the same scheduling process is periodically performed every time the CQI transmission period elapses.

Here, since S307a to S307c and S308 may be performed in the same manner as S302a to S302c and S303, description thereof is omitted here.

Since S309 is the same process as S304, a detailed description thereof will be omitted. However, in the example of processing in the present embodiment shown in FIG. 5, the initial scheduling of downlink data (generated in S301) is performed in S304, whereas the rescheduling of the downlink data is performed in S309. Note that this is done.

Here, in an example of processing in the present embodiment illustrated in FIG. 5, it is assumed that the serving base station 10 a determines the second coordinated base station 10 c as the transmission base station by scheduling in S <b> 309. That is, it is assumed that downlink data scheduling (for example, a transmission base station) is changed in S309 due to a change in downlink radio quality or the like from the time of scheduling in S304. Needless to say, this premise is merely an example for explaining a specific example of processing in the present embodiment. In the following, the description will proceed under this assumption.

Next, in S310, the serving base station 10a transmits downlink scheduling change information and uplink scheduling information to the radio terminal 20. On the other hand, the radio terminal 20 receives downlink scheduling change information and uplink scheduling information from the serving base station 10a.

Here, the downlink scheduling change information is information indicating the scheduling of the downlink data changed in S309. The information included in the downlink scheduling change information can include transmission base station information and downlink transmission parameters according to the information included in the downlink scheduling information. The downlink scheduling information may include only the contents changed from the downlink scheduling information, or may include all downlink scheduling information based on the latest scheduling.

Further, the uplink scheduling information transmitted / received in S310 is the same information that is transmitted from the serving base station 10a to the coordinated base stations 10b to 10c in S305 to S306. As a result, the uplink scheduling information is shared between the radio terminal 20 and each of the cooperative base stations 10b to 10c.

It should be noted that downlink scheduling change information and uplink scheduling information are transmitted from the serving base station 10a to the radio terminal 20 via a radio signal (downlink) in S310. It should be noted that although downlink scheduling information and uplink scheduling information are transmitted via the backhaul in S305 to S306, S310 is different from these. The technical significance of transmitting each piece of information via a radio signal in S310 will be described later.

Now, the downlink scheduling change information in S310 may be transmitted via PDCCH or may be transmitted via PDSCH. The downlink scheduling change information can be transmitted via the PDSCH by, for example, a downlink RRC signal. Also, the downlink scheduling change information can be transmitted via the PDCCH by the above-described DCI. It should be noted that in downlink transmission, it is not necessary to notify the radio terminal 20 of transmission parameters in advance as in uplink transmission, regardless of whether the transmission is through PDCCH or PDSCH.

Next, in S311 of FIG. 5, the radio terminal 20 transmits the downlink scheduling change information received in S310 to the first coordinated base station 10b based on the uplink scheduling information received in S310. On the other hand, the first cooperative base station 10b receives downlink scheduling change information from the radio terminal 20 based on the uplink scheduling information received in S305.

As described above, the uplink scheduling information includes uplink transmission parameters such as MCS for performing PUSCH transmission, resource block (subcarrier) allocation, timing (uplink subframe), and the like. In S311, the radio terminal 20 transmits downlink scheduling change information to the first coordinated base station 10b based on these uplink transmission parameters indicated by the uplink scheduling information received in S310. On the other hand, the first cooperative base station 10b receives downlink scheduling change information from the radio terminal 20 based on these uplink transmission parameters indicated by the uplink scheduling information received in S305.

The downlink scheduling information transmitted from the radio terminal 20 to the first cooperative base station 10b may be the one received in S311 as it is, or may be processed within a range that includes information necessary for the first cooperative base station 10b. You may use what you did.

The point to be noted here is that the downlink scheduling change information is transmitted from the radio terminal 20 to the first cooperative base station 10b via the radio signal (uplink) in S311. Note that the downlink scheduling information is transmitted via the backhaul in S305 to S306, but S311 is different from these.

It should be noted that if S310 and S312 are combined, the downlink scheduling change information from the serving base station 10a to the first cooperative base station 10b can also be interpreted as being relayed by the radio terminal 20. In other words, the downlink scheduling change information from the serving base station 10a to the first cooperative base station 10b is received by the radio terminal 20 on the downlink and transmitted on the uplink, thereby realizing relay transmission via the radio terminal 20 Will be.

Here, the technical significance of S310 and S311 will be described. Through S310 and S311, downlink scheduling change information is transmitted from the serving base station 10a to the first coordinated base station 10b via the radio terminal 20. Here, in both S310 and S311, the downlink scheduling change information is transmitted by a radio signal. Since the delay associated with the transmission / reception of the radio signal is minimal, the delay associated with the transmission of the downlink scheduling change information over S310 to S311 is considered to be about several subframes (several milliseconds).

Therefore, in FIG. 3 and FIG. 4, the problem caused based on the premise of the non-ideal backhaul is the first embodiment shown in FIG. 5, although the non-ideal backhaul is assumed. Does not occur. More specifically, in FIG. 5, the serving base station 10a transmits the result of rescheduling downlink data in S309 to the coordinated base stations 10b to 10c as downlink scheduling change information in S310 to S312. Here, since the latest downlink quality is considered in the rescheduling in S309, the downlink scheduling change information transmitted in S310 to S312 reflects the latest downlink quality. Therefore, if this downlink scheduling change information can be notified to the coordinated base stations 10b to 10c in time for the previously determined CoMP transmission timing, CoMP transmission reflecting the latest radio quality can be performed.

Here, as shown in FIG. 4, when the downlink scheduling change information is transmitted to the coordinated base stations 10b to 10c via the non-ideal backhaul, there is a problem that the delay is large and the timing of CoMP transmission is not in time. . However, in the present embodiment shown in FIG. 5, since the downlink scheduling change information is transmitted to the coordinated base stations 10b to 10c via the radio link, there is little delay and it is possible to make it in time for the CoMP transmission timing. . Therefore, according to the present embodiment, it is possible to perform CoMP transmission reflecting the latest radio quality.

Returning to the description of FIG. 5, in S312, the radio terminal 20 transmits the downlink scheduling change information received in S310 to the second cooperative base station 10c based on the uplink scheduling information received in S310. On the other hand, the second cooperative base station 10c receives downlink scheduling change information from the radio terminal 20 based on the uplink scheduling information received in S306. Since S312 may be performed in the same manner as S311, detailed description thereof is omitted here.

Finally, in S313a to S313c of FIG. 5, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c perform CoMP transmission (cooperative transmission) of the downlink data to the wireless terminal 20. Note that the CoMP transmission here reflects the latest downlink quality, as described above.

In the example of processing in the present embodiment shown in FIG. 5, the transmission base station is temporarily determined to be the first cooperative base station 10b in the scheduling of S304, but then the transmission base station is in the second cooperative state in the scheduling of S309. The base station 10c is changed. In addition, this change is notified from the serving base station 10a to the coordinated base stations 10b to 10c via the radio terminal 20 by downlink scheduling change information. Accordingly, in S313a to S313c, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c wirelessly transmit downlink data in cooperation with DPS using the second cooperative base station 10c as a transmission base station. It transmits to the terminal 20.

Specifically, the second cooperative base station 10c, which is a transmission base station in S313c, transmits downlink data to the radio terminal 20 based on the downlink scheduling change information received in S312. On the other hand, in S313a, the serving base station 10a performs blanking (no transmission) to the radio terminal 20 based on its own scheduling result in S309. In 313b, the first cooperative base station 10b performs blanking for the radio terminal 20 based on the downlink scheduling change information received in S311. And the radio | wireless terminal 20 receives downlink data from the 2nd cooperation base station 10c.

Note that the CoMP transmission (DPS) in S313a to S313c in FIG. 5 reflects the latest downlink quality as described above. Therefore, in the processing sequence shown in FIG. 5, it is considered that DPS, which is one of the CoMP schemes, can be appropriately executed in response to downlink radio quality.

Next, FIG. 6 shows another example of the processing sequence of the first embodiment.

In FIG. 5 described above, the scheduling of downlink data has been changed by rescheduling. That is, after the downlink data scheduling is performed once in the first scheduling (S304) in FIG. 5, the downlink data scheduling is changed in the second scheduling (S309) in accordance with a change in downlink quality or the like. It was. On the other hand, FIG. 6 is a diagram showing a processing sequence when downlink data scheduling is not changed by rescheduling.

6 are the same as S301 to S308 in FIG. 5, and therefore the details are omitted.

6 is also the same process as S309 in FIG. 5, and thus detailed description thereof is omitted. However, in FIG. 5, the serving base station 10 a determines the second coordinated base station 10 c as a transmission base station in the scheduling of S <b> 309. That is, the downlink data scheduling (for example, the transmission base station) is changed in S309 due to a change in downlink radio quality or the like from the time of scheduling in S304. On the other hand, in FIG. 6, it is assumed that the serving base station 10a determines the first coordinated base station 10c as a transmission base station in the scheduling of S409. That is, it is assumed that scheduling of downlink data (for example, a transmission base station) is not changed in S409 due to a small change in downlink radio quality from the time of scheduling in S404.

At this time, in FIG. 6, transmission / reception of the downlink scheduling change information as shown in S310 to S312 of FIG. 5 is not performed. This is because the scheduling of downlink data has not been changed in S409 of FIG. 6, and therefore the serving base station 10a does not need to notify the first cooperative base station 10b and the second cooperative base station 10c of the scheduling change in the first place.

In FIG. 6, in S410a to S410c, the serving base station 10a, the first coordinated base station 10b, and the second coordinated base station 10c cooperate with each other by DPS using the first coordinated base station 10c as a transmission base station. Then, the downlink data is transmitted to the wireless terminal 20. In the example of processing in the present embodiment shown in FIG. 6, the transmission base station is determined to be the first coordinated base station 10b by the scheduling of S404, and thereafter the transmission base station is not changed by the scheduling of S409. Therefore, in S410a to S410c, DPS using the first coordinated base station 10c as a transmission base station is performed according to the determination in the scheduling in S404.

Note that the CoMP transmission (DPS) in S410a to S410c in FIG. 6 reflects the latest downlink quality, similar to the CoMP transmission (DPS) in S313a to S313c in FIG. Therefore, in the processing sequence shown in FIG. 6 as well, as in FIG. 5, it is considered that DPS, which is one of the CoMP schemes, can be executed appropriately in response to downlink radio quality.

According to the first embodiment described above, it is possible to solve the above-described problem that occurs when a non-ideal backhaul is assumed. That is, according to the first embodiment, even when a non-ideal backhaul is assumed, the serving base station 10a and the coordinated base stations 10b to 10c perform CoMP transmission reflecting the latest downlink quality. Is possible. Therefore, 1st Embodiment has a remarkable effect which is not in the prior art that the fall of the throughput of the whole radio communications system is controlled.

[Second Embodiment]
The second embodiment is another example of the embodiment that solves the above-described problem. When the serving base station 10a notifies the scheduling of coordinated transmission, the notification is coordinated via the radio terminal 20 by a radio signal. The data is transmitted to the base stations 10b to 10c.

Since the second embodiment has many points in common with the first embodiment, the second embodiment will be described in detail below with a focus on differences from the first embodiment. It should be noted that in the second embodiment, descriptions overlapping with those in the first embodiment are omitted as appropriate.

FIG. 7 is a diagram illustrating an example of a processing sequence according to the second embodiment. Since the premise of the second embodiment is the same as that of the first embodiment, the description is omitted here. However, it should be noted that the second embodiment also assumes a non-ideal backhaul as in the first embodiment.

Since S501 in FIG. 7 may be performed in the same manner as S301 in FIG. 5 according to the first embodiment, a description thereof will be omitted.

The serving base station performs scheduling in S502 of FIG. In the scheduling in S502, an uplink transmission parameter is determined. In the scheduling in S502, unlike S304 in FIG. 5 according to the first embodiment, it is not necessary to determine a transmission base station, downlink transmission parameters, and downlink subframe information (downlink data transmission timing). Since the determination of the uplink transmission parameter in S502 may be performed in the same manner as the determination of the uplink transmission parameter in S304, a detailed description is omitted here.

In S503 of FIG. 7, the serving base station 10a transmits a signal including downlink data and uplink scheduling information to the first coordinated base station 10b via the backhaul. On the other hand, in S503, the first cooperative base station 10b receives a signal including downlink data and uplink scheduling information from the serving base station 10a via the backhaul.

In S503 of FIG. 7, unlike S305 of FIG. 5 according to the first embodiment, it is not necessary to transmit a transmission base station or downlink scheduling information (transmission base station, downlink transmission parameters, downlink subframe information, etc.). . The transmission of downlink data and uplink scheduling information in S503 may be performed in the same manner as the transmission in S305, and thus detailed description thereof is omitted here. It should be noted that the transmission / reception in S503 is performed via a backhaul (non-ideal backhole), so that a relatively large delay occurs.

In S504 of FIG. 7, the serving base station 10a transmits a signal including downlink data and uplink scheduling information to the second cooperative base station 10c via the backhaul. On the other hand, in S504, the second cooperative base station 10c receives a signal including downlink data and uplink scheduling information from the serving base station 10a via the backhaul. Since S504 may be performed in the same manner as S503, description thereof is omitted.

Next, in steps S505a to S505c in FIG. 7, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c transmit downlink reference signals to the wireless terminal 20, respectively. In S506a to S506c, the radio terminal 20 transmits CQI indicating the downlink quality measured based on the downlink reference signal in S505a to S505c to the serving base station 10a. In step S507, the serving base station 10a performs downlink data scheduling in step S501 based on the CQI and the like in step S506.

7 may be performed in the same manner as S302a to S302c, S303, and S304 of FIG. 5 according to the first embodiment, and thus description thereof is omitted here.

However, care should be taken with respect to the timing of performing S505a to S505c, S506, and S507 in FIG. The timing for performing these is the timing corresponding to the latest CQI transmission at the timing indicated by the uplink subframe information included in the uplink scheduling information transmitted and received in S503 to S504. As a result, the latest downlink quality is reflected in the scheduling of S507, and downlink scheduling information (described later) transmitted thereafter reflects the latest downlink quality.

Here, in an example of processing in the present embodiment shown in FIG. 7, it is assumed that the serving base station 10a determines the second coordinated base station 10c as the transmission base station in the scheduling of S509. Needless to say, this premise is merely an example for explaining a specific example of processing in the present embodiment. In the following, the description will proceed under this assumption.

Next, in S508 of FIG. 7, the serving base station 10a transmits downlink scheduling information and uplink scheduling information to the radio terminal 20 based on the determination in the scheduling of S507. On the other hand, the radio terminal 20 receives downlink scheduling information and uplink scheduling information from the serving base station 10a. In S509, the radio terminal 20 transmits the downlink scheduling information received in S508 to the first coordinated base station 10b based on the uplink scheduling information received in S508. On the other hand, the first cooperative base station 10b receives downlink scheduling information from the radio terminal 20 based on the uplink scheduling information received in S503. Further, in S510, the radio terminal 20 transmits the downlink scheduling information received in S508 to the second cooperative base station 10c based on the uplink scheduling information received in S508. On the other hand, the second cooperative base station 10c receives downlink scheduling information from the radio terminal 20 based on the uplink scheduling information received in S504.

Note that as described above, the latest downlink quality is reflected in the downlink scheduling information transmitted and received in S508 to S510.

7, downlink scheduling information is transmitted and received instead of downlink scheduling change information transmitted and received in S310 to S312 of FIG. 5 according to the first embodiment. This is because the downlink transmission scheduling information is transmitted via the back hose in S305 to S306 in FIG. 5 according to the first embodiment, but not transmitted in S503 to S504 in FIG.

Since transmission / reception of downlink scheduling information and uplink scheduling information in S508 may be performed in the same manner as transmission / reception of downlink scheduling change information and uplink scheduling information in S310, detailed description thereof is omitted here. Further, since transmission / reception of downlink scheduling information in S509 to S510 may be performed in the same manner as transmission / reception of downlink scheduling information in S311 to S312, detailed description thereof is omitted here.

Then, in S511a to S511c of FIG. 7, the serving base station 10a, the first cooperative base station 10b, and the second cooperative base station 10c are cooperatively downloaded by DPS using the second cooperative base station 10c as a transmission base station. Data is transmitted to the wireless terminal 20. In the example of processing in the present embodiment shown in FIG. 7, since the transmission base station is determined to be the second cooperative base station 10b by the scheduling of S507, the second cooperative base station 10c is set as the transmission base station in S511a to S511c. DPS is performed.

Note that the CoMP transmission (DPS) in S511a to S511c in FIG. 7 reflects the latest downlink quality, similar to the CoMP transmission (DPS) in S313a to S313c in FIG. This is because the latest downlink quality is reflected in the downlink scheduling information as described above. Therefore, also in the processing sequence shown in FIG. 7, it is considered that DPS, which is one of the CoMP schemes, can be appropriately executed in response to the downlink radio quality, as in FIG.

According to the second embodiment described above, it is possible to solve the above-described problem that occurs when a non-ideal backhaul is assumed. That is, according to the first embodiment, even when a non-ideal backhaul is assumed, the serving base station 10a and the coordinated base stations 10b to 10c perform CoMP transmission reflecting the latest downlink quality. Is possible. Therefore, 1st Embodiment has a remarkable effect which is not in the prior art that the fall of the throughput of the whole radio communications system is controlled.

[Other embodiments]
Here, embodiments and modifications other than the above-described embodiments will be described. These can be carried out alone or in appropriate combination with the above-described embodiments.

In each of the embodiments described above, the wireless terminal 20 that receives downlink data by CoMP transmission (cooperative transmission) and the wireless terminal 20 that relays downlink scheduling change information and the like via a wireless link are the same wireless terminal 20. is there. As an example, in FIG. 5, the wireless terminal 20 receives downlink data by CoMP transmission in S313a to S313c, but the same wireless terminal 20 relays downlink scheduling change information via a wireless link in S310 to S312. Sending. The same applies to FIG. 6 and FIG. However, in each of the embodiments described above, the wireless terminal 20 that receives downlink data by CoMP transmission and the wireless terminal 20 that relays downlink scheduling change information and the like via a wireless link are different wireless terminals 20. Note that it does not matter.

In each of the above-described embodiments, it is assumed that CoMP transmission (cooperative transmission) is performed, and the radio terminal 20 transmits downlink scheduling change information transmitted and received between the radio base stations 10 in order to perform CoMP transmission. Relay transmission via wireless link. However, the present invention is not based on the assumption that CoMP transmission (cooperative transmission) is performed, and the wireless terminal 20 can relay and transmit arbitrary information transmitted and received between the wireless base stations 10 via the wireless link. Is. As an example, when one radio base station 10 performs scheduling of radio communication performed by another radio base station 10, the radio terminal 20 can relay and transmit information including the scheduling result via a radio link. . According to the present invention, when a plurality of radio base stations 10 perform arbitrary processing in cooperation, the radio terminal 20 relays any information transmitted / received between the plurality of radio base stations 10 via a radio link. It is possible to send.

Further, in each of the above-described embodiments, the wireless terminal 20 relays and transmits information transmitted and received between the wireless base stations 10. However, the present invention may be such that a device other than the wireless terminal 20 performs relay transmission. As an example, a wireless relay station (wireless relay device) can relay and transmit information transmitted and received between the wireless base stations 10. As another example, the third radio base station 10 can relay and transmit information transmitted and received between the first radio base station 10 and the second radio base station 10. For example, the non-ideal backhaul is between the first radio base station 10 and the second radio base station 10, but between the first radio base station 10 and the third radio base station 10 and third When the wireless base station 10 and the second wireless base station 10 are ideal backhaul, the third wireless base station 10 performs relay transmission, so that the same effects as those of the above embodiments are obtained. It is possible to play.

In each of the above-described embodiments, description has been given of determining downlink scheduling information of downlink data in the serving base station 10a based on the CQI of the downlink reference signal from each radio base station 10 from the radio terminal 20. The present invention is not limited to this. Even if the radio terminal 20 calculates the CQI for the downlink reference signal from each radio base station 10, the radio terminal 20 similarly determines downlink scheduling information for downlink data based on this, and notifies each radio base station 10 of the same. Good. Further, each radio base station 10 notifies the radio terminal 20 of the load information, so that the radio terminal 20 can determine downlink scheduling data while considering the load of each radio base station 20.

In the above-described embodiments, the invention is applied to a non-ideal backhaul, but the present invention is not limited to this. It is also one of the embodiments that the present invention is implemented as a preparation for becoming a non-ideal backhaul in the future due to the secular change or the like of the current ideal backhaul. Needless to say.

[Network configuration of wireless communication system of each embodiment]
Next, based on FIG. 8, the network configuration of the radio communication system 1 of each embodiment will be described. As illustrated in FIG. 8, the wireless communication system 1 includes a wireless base station 10 and a wireless terminal 20. Here, in FIG. 8, three radio base stations 10a to 10c and seven radio terminals 20a to 20g are shown, but it goes without saying that this is only an example.

Each radio base station 10 forms a cell. Each wireless terminal 20 exists in a cell, in other words, is under the control (under management) of each wireless base station 10. As an example in FIG. 8, the radio terminals 20a to 20c are under the radio base station 10a, the radio terminals 20d to 20e are under the radio base station 10b, and the radio terminals 20f to 20g are under the radio base station 10c. is there.

The wireless base station 10 is connected to the network device 3 via a wired connection, and the network device 3 is connected to the network 2 via a wired connection. The radio base station 10 is provided so as to be able to transmit / receive data and control information to / from other radio base stations 10 via the network device 3 and the network 2.

As described in the above embodiments, in the present application, the backhaul, which is a network connecting wireless base stations, is assumed to be non-ideal. However, some of them may be ideal.

The radio base station 10 may separate the radio communication function with the radio terminal 20 and the digital signal processing and control function to be a separate device. In this case, a device having a wireless communication function is referred to as RRH (Remote Radio Head), and a device having a digital signal processing and control function is referred to as BBU (Base Band Unit). The RRH may be installed overhanging from the BBU, and may be wired with an optical fiber between them. Further, the radio base station 10 is a radio of various scales other than small radio base stations 10 (including a micro radio base station 10, a femto radio base station 10 and the like) such as a macro radio base station 10 and a pico radio base station 10. It may be the base station 10. When a relay station that relays wireless communication between the wireless base station 10 and the wireless terminal 20 is used, the relay station (transmission / reception with the wireless terminal 20 and its control) is also included in the wireless base station 10 of the present application. It is good.

Meanwhile, the wireless terminal 20 communicates with the wireless base station 10 by wireless communication.

The wireless terminal 20 may be a wireless terminal 20 such as a mobile phone, a smartphone, a PDA (Personal Digital Assistant), a personal computer (Personal Computer), various devices or devices (such as sensor devices) having a wireless communication function. Further, when a relay station that relays radio communication between the radio base station 10 and the radio terminal 20 is used, the relay station (transmission / reception with the radio base station 10 and its control) is also included in the radio terminal 20 of this paper. It is good.

The network device 3 includes, for example, a communication unit and a control unit, and these components are connected so that signals and data can be input and output in one direction or in both directions. The network device 3 is realized by a gateway, for example. As a hardware configuration of the network device 3, for example, the communication unit is realized by an interface circuit, and the control unit is realized by a processor and a memory.

In addition, the specific mode of distribution / integration of each component of the radio base station 10 and the radio terminal 20 is not limited to the mode of each embodiment, and all or a part thereof depends on various loads, usage conditions, and the like. Thus, it can be configured to be functionally or physically distributed and integrated in arbitrary units. For example, the memory may be connected as an external device of the radio base station 10 and the radio terminal 20 via a network or a cable.

[Functional Configuration of Each Device in Radio Communication System of Each Embodiment]
Next, the functional configuration of each device in the wireless communication system of each embodiment will be described with reference to FIGS.

FIG. 9 is a functional block diagram showing an example of the configuration of the radio base station 10. As illustrated in FIG. 9, the radio base station 10 includes, for example, a radio transmission unit 11, a radio reception unit 12, a control unit 13, a storage unit 14, and a communication unit 15. Each of these components is connected so that signals and data can be input and output in one direction or in both directions. The wireless transmission unit 11 and the wireless reception unit 12 are collectively referred to as a wireless communication unit 16.

The wireless transmission unit 11 transmits a data signal and a control signal by wireless communication via an antenna. The antenna may be common for transmission and reception. The radio transmission unit 11 transmits a radio signal (downlink radio signal) to the radio terminal 20. The radio signal transmitted by the radio transmission unit 11 can include arbitrary user data and control information for the radio terminal 20 (encoding and modulation are performed).

Specific examples of the radio signal transmitted by the radio transmission unit 11 include radio signals (arrows in the figure) transmitted from the radio base station 10 to the radio terminal 20 in FIGS. 5, 6, and 7. Is mentioned. The radio signal transmitted by the radio transmission unit 11 is not limited to these, and includes any radio signal transmitted from each radio base station 10 to the radio terminal 20 in each of the above embodiments and modifications.

The wireless receiving unit 12 receives a data signal and a control signal by wireless communication via an antenna. The radio reception unit 12 receives a radio signal (uplink radio signal) from the radio terminal 20. The radio signal received by the radio reception unit 12 can include arbitrary user data and control information (encoded or modulated) transmitted by the radio terminal 20.

Specific examples of the radio signal received by the radio receiving unit 12 include radio signals (arrows in the figure) received by the radio base station 10 from the radio terminal 20 in FIGS. 5, 6, and 7. It is done. The signals received by the wireless reception unit 12 are not limited to these, and include any wireless signal that each wireless base station 10 receives from the wireless terminal 20 in each of the above embodiments and modifications.

The control unit 13 outputs data and control information to be transmitted to the wireless terminal 20 to the wireless transmission unit 11. The control unit 13 inputs data and control information received from the wireless terminal 20 from the wireless reception unit 12. The control unit 13 inputs and outputs data, control information, programs, and the like with the storage unit 14 described later. The control unit 13 inputs / outputs data and control information transmitted / received to / from the other radio base station 10 and the like with the communication unit 15 described later. In addition to these, the control unit 13 performs various controls in the radio base station 10.

Specific examples of processing controlled by the control unit 13 include control on signals (arrows in the figure) transmitted and received by each radio base station 10 in FIGS. 5, 6, and 7, and each radio base station 10 The control for each process (rectangle in the figure) being performed is given. The process which the control part 13 controls is not restricted to these, but includes the control regarding all the processes which each radio base station 10 performs by said each embodiment and modification.

The storage unit 14 stores various information such as data, control information, and programs. The various information stored in the storage unit 14 includes all information that can be stored in each radio base station 10 in each of the above embodiments and modifications.

The communication unit 15 transmits / receives data and control information to / from another wireless base station 10 or the like via a wired signal or the like (which may be a wireless signal). Specific examples of the wired signal transmitted and received by the communication unit 15 include each wired signal transmitted and received by each wireless base station 10 with respect to the other wireless base station 10 in FIG. 5, FIG. 6, and FIG. Middle arrow). The wired signals transmitted and received by the communication unit 15 are not limited to these, and include all wired signals transmitted and received by each wireless base station 10 from other wireless base stations 10 and the like in the above-described embodiments and modifications.

The radio base station 10 may transmit and receive radio signals to / from radio communication devices other than the radio terminal 20 (for example, other radio base stations 10 and relay stations) via the radio transmission unit 11 and the radio reception unit 12. .

FIG. 10 is a functional block diagram showing an example of the configuration of the wireless terminal 20. As illustrated in FIG. 10, the wireless terminal 20 includes, for example, a wireless transmission unit 21, a wireless reception unit 22, a control unit 23, and a storage unit 24. Each of these components is connected so that signals and data can be input and output in one direction or in both directions. The wireless transmission unit 21 and the wireless reception unit 22 are collectively referred to as a wireless communication unit 25.

The wireless transmission unit 21 transmits a data signal and a control signal by wireless communication via an antenna. The antenna may be common for transmission and reception. The radio transmission unit 21 transmits a radio signal (uplink radio signal) to each radio base station 10. The radio signal transmitted by the radio transmission unit 21 can include arbitrary user data, control information, and the like (encoded and modulated) for each radio base station 10.

Specific examples of the radio signal transmitted by the radio transmission unit 21 include radio signals (arrows in the figure) transmitted from the radio terminal 20 to the radio base stations 10 in FIGS. 5, 6, and 7. Is mentioned. The radio signal transmitted by the radio transmission unit 21 is not limited to these, and includes any radio signal transmitted from the radio terminal 20 to each radio base station 10 in each of the above embodiments and modifications.

The wireless receiving unit 22 receives data signals and control signals by wireless communication via an antenna. The radio reception unit 22 receives a radio signal (downlink radio signal) from each radio base station 10. The radio signal received by the radio reception unit 22 can include arbitrary user data, control information, and the like (encoded or modulated) transmitted by each radio base station 10.

Specific examples of radio signals received by the radio receiver 22 include radio signals (arrows in the figure) received by the radio terminal 20 from the radio base station 10 in FIGS. 5, 6, and 7. . The signal received by the wireless reception unit 22 is not limited to these, and includes any wireless signal that the wireless terminal 20 receives from each wireless base station 10 in each of the above embodiments and modifications.

The control unit 23 outputs data and control information to be transmitted to each radio base station 10 to the radio transmission unit 21. The control unit 23 inputs data and control information received from each radio base station 10 from the radio reception unit 22. The control unit 23 inputs and outputs data, control information, programs, and the like with the storage unit 24 described later. In addition to these, the control unit 23 performs various controls in the wireless terminal 20.

Specific examples of processing controlled by the control unit 23 include control for each signal (arrow in the figure) transmitted and received by the wireless terminal 20 in FIGS. 5, 6, and 7, and the wireless terminal 20 performs. Control for each process (rectangle in the figure) is mentioned. The process which the control part 23 controls is not restricted to these, but includes the control regarding all the processes which the radio | wireless terminal 20 performs by said each embodiment and modification.

The storage unit 24 stores various information such as data, control information, and programs. The various information stored in the storage unit 24 includes all information that can be stored in the wireless terminal 20 in each of the above-described embodiments and modifications.

Note that the wireless terminal 20 may transmit and receive wireless signals to and from wireless communication devices other than the wireless base station 10 via the wireless transmission unit 21 and the wireless reception unit 22.

[Hardware Configuration of Each Device in Radio Communication System of Each Embodiment]
Based on FIGS. 11 to 12, the hardware configuration of each device in the wireless communication system of each embodiment and each modification will be described.

FIG. 11 is a diagram illustrating an example of a hardware configuration of the radio base station 10. As shown in FIG. 11, the radio base station 10 includes, as hardware components, an RF (Radio Frequency) circuit 112 including an antenna 111, a processor 113, a memory 114, and a network IF (Interface) 115, for example. Have. These components are connected so that various signals and data can be input and output via a bus.

The processor 113 is, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). In the present application, the processor 113 may be realized by a digital electronic circuit. Examples of digital electronic circuits include ASIC (Application Specific Integrated Circuit), FPGA (Field-Programming Gate Array), LSI (Large Scale Integration), and the like.

The memory 114 includes at least one of RAM (Random Access Memory) such as SDRAM (Synchronous Dynamic Random Access Memory), ROM (Read Only Memory), and flash memory, and stores programs, control information, and data. In addition, the radio base station may include an auxiliary storage device (such as a hard disk) not shown.

The correspondence between the functional configuration of the radio base station 10 shown in FIG. 9 and the hardware configuration of the radio base station 10 shown in FIG. 11 will be described. The wireless transmission unit 11 and the wireless reception unit 12 (or the wireless communication unit 16) are realized by the RF circuit 112, or the antenna 111 and the RF circuit 112, for example. The control unit 13 is realized by, for example, the processor 113, the memory 114, a digital electronic circuit (not shown), and the like. The storage unit 14 is realized by the memory 114, for example. The communication unit 15 is realized by the network IF 115, for example.

FIG. 12 is a diagram illustrating an example of a hardware configuration of the wireless terminal 20. As illustrated in FIG. 12, the wireless terminal 20 includes, as hardware components, an RF (Radio Frequency) circuit 122 including an antenna 121, a processor 123, and a memory 124, for example. These components are connected so that various signals and data can be input and output via a bus.

The processor 123 is, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). In the present application, the processor 123 may be realized by a digital electronic circuit. Examples of digital electronic circuits include ASIC (Application Specific Integrated Circuit), FPGA (Field-Programming Gate Array), LSI (Large Scale Integration), and the like.

The memory 124 includes at least one of RAM (Random Access Memory) such as SDRAM (Synchronous Dynamic Random Access Memory), ROM (Read Only Memory), and flash memory, and stores programs, control information, and data.

The correspondence between the functional configuration of the wireless terminal 20 shown in FIG. 10 and the hardware configuration of the wireless terminal 20 shown in FIG. 12 will be described. The wireless transmission unit 21 and the wireless reception unit 22 (or the wireless communication unit 25) are realized by the RF circuit 122, the antenna 121, and the RF circuit 122, for example. The control unit 23 is realized by, for example, the processor 123, the memory 124, a digital electronic circuit (not shown), and the like. The storage unit 24 is realized by the memory 124, for example.

1 wireless communication system 2 network 3 network device 10 wireless base station 20 wireless terminal

Claims

A wireless communication method for performing cooperative transmission in which a first wireless base station and a second wireless base station cooperate to transmit a wireless signal to a first wireless terminal among one or more wireless terminals,
The first radio base station transmits downlink scheduling information for performing the coordinated transmission to a second radio terminal that is one of the one or more radio terminals,
The radio communication method in which the second radio terminal transmits the downlink scheduling information to the second radio base station.
The first radio terminal has a first quality measured based on a downlink with the first radio base station, and a second quality measured based on a downlink with the second radio base station, To the first station,
The radio communication method according to claim 1, wherein the first radio base station generates the downlink scheduling information based on the first quality and the second quality.
The maximum delay in the case where the first radio base station transmits information to the second radio base station without going through the one or more radio terminals is based on a cycle in which the transmission of the first quality and the second quality is performed. The wireless communication method according to claim 2.
The first radio base station transmits uplink scheduling information for the second radio base station to receive the downlink scheduling information from the second radio terminal without passing through the one or more radio terminals. The wireless communication method according to claim 1, wherein the wireless communication method transmits to a station.
The radio communication method according to claim 1, wherein the downlink scheduling information includes information indicating a transmission radio base station in the coordinated transmission.
The radio communication according to any one of claims 1 to 5, wherein the downlink scheduling information includes at least one of information indicating an encoding scheme and a modulation scheme in the coordinated transmission, and information indicating a subcarrier used in the coordinated transmission. Method.
7. The radio communication method according to claim 1, wherein the downlink scheduling information includes information indicating a timing for performing the coordinated transmission.
Even if there is a possibility that the second radio base station does not transmit the downlink data transmitted by the coordinated transmission, the first radio base station does not pass through the one or more radio terminals. The radio communication method according to claim 1, wherein the radio communication method transmits to the second radio base station.
The radio communication method according to any one of claims 1 to 8, wherein the first radio terminal and the second radio terminal are the same radio terminal.
One or more wireless terminals;
A first radio base station and a second radio base station that perform coordinated transmission for transmitting radio signals in cooperation with the first radio terminal among the one or more radio terminals;
The first radio base station transmits downlink scheduling information for performing the coordinated transmission to a second radio terminal that is one of the one or more radio terminals,
The second radio terminal is a radio communication system that transmits the downlink scheduling information to the second radio base station.
The wireless terminal in a wireless communication system that performs cooperative transmission in which the first wireless base station and the second wireless base station cooperate to transmit a wireless signal to the wireless terminal,
A radio terminal comprising: a reception unit that receives downlink scheduling information for performing the coordinated transmission from the first radio base station; and a transmission unit that transmits the downlink scheduling information to the second radio base station.
The radio base station in a radio communication system that performs coordinated transmission in which a radio base station and another radio base station cooperate to transmit a radio signal to a first radio terminal of one or more radio terminals,
The downlink scheduling information for performing the coordinated transmission is transmitted to a second radio terminal that is one of the one or more radio terminals, and the other radio base station that has received the downlink scheduling information from the second radio terminal and A radio base station comprising a transmission unit that performs the coordinated transmission.