WO2012143973A1

WO2012143973A1 - Wireless communication system and wireless communication device

Info

Publication number: WO2012143973A1
Application number: PCT/JP2011/002306
Authority: WO
Inventors: 栄里子武田; 藤嶋　堅三郎; 矢野　隆; 齋藤　利行; 学川辺
Original assignee: 株式会社日立製作所
Priority date: 2011-04-20
Filing date: 2011-04-20
Publication date: 2012-10-26
Also published as: JP5736449B2; JPWO2012143973A1

Abstract

Provided is a method for efficiently transmitting pilot signals in a distributed antenna system. The present invention has: a base station, which is configured of a plurality of wireless units, which at least transmit and receive radio frequency signals, and a baseband unit; and a terminal that communicates with the base station. The base station transmits pilot signals from the wireless units, and changes the kinds of the wireless units on the basis of information fed back from the terminal, said wireless units transmitting the pilot signals using different wireless resources.

Description

Wireless communication system and wireless communication apparatus

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

The characteristics of the spatial propagation path formed between the base station and the terminal are estimated using known signals between the base station and the terminal. Hereinafter, in this specification, the known signal is referred to as a pilot signal. In a system using frequency division duplex (FDD), characteristics of a spatial propagation path when a signal is transmitted from a base station to a terminal are estimated on the terminal side by a pilot signal transmitted from the base station. When the terminal feeds back information on the spatial propagation path characteristics to the base station, the base station can obtain information on the characteristics of the spatial propagation path when a signal is transmitted to the terminal.

Also, the characteristics of the spatial propagation path when a signal is transmitted from the terminal to the base station are estimated by the base station receiving a pilot signal transmitted from the terminal.

Patent Document 1 discloses a transmission method of pilot signals and data signals in a distributed antenna system. Patent Document 1 discloses that communication data of another remote antenna is allocated to a resource used for transmitting a pilot signal of a remote antenna apparatus to which an antenna index is not allocated among a plurality of remote antenna apparatuses.

Further, Patent Document 2 discloses a multiple input multiple output (MIMO) technique using a plurality of antennas and a transmission station and a plurality of receptions in order to increase the speed and / or quality of wireless communication. A multi-user MIMO (MU-MIMO) technology that allows stations to connect simultaneously is disclosed.

JP 2010-68496 A JP 2007-214993 A

In order to improve the performance of MIMO or MU-MIMO, it is considered that information on the spatial channel formed between the base station and the terminal is necessary.

In order to reduce the variation in communication speed between the base station and the terminal in the communication area, the antennas of the base station are distributed and the antenna that forms a good spatial propagation path with the terminal It is effective to communicate with.

The above-described pilot signal is used for estimation of the spatial propagation path between each antenna and the terminal, but the base station can identify the pilot signal from one antenna and the pilot signal from the other antenna. Must be sent. For this reason, when the number of distributed antennas increases, more radio resources are used for transmission of pilot signals, and overhead increases. For this reason, Patent Document 1 discloses that a data signal is transmitted using a radio resource used for a pilot signal transmitted by an antenna with which one terminal does not communicate. However, when the technique disclosed in Patent Document 1 is used, when there are a plurality of users, communication is performed by dividing the frequency or time.

However, in the distributed antenna system, it is more probable that radio resources can be effectively used if the system is configured to communicate with a plurality of terminals simultaneously than with a single terminal.

Therefore, in the distributed antenna system, pilot signal radio resources transmitted from the distributed antenna are used for pilot signal transmission, and pilot signal transmission overhead is reduced, and communication with multiple terminals is also considered. Providing a pilot signal transmission method in a distributed antenna system is an issue.

As one aspect of the present invention for solving at least one of the above-described problems,
A radio communication system, comprising: a base station comprising a plurality of radio units that transmit and receive at least radio frequency signals; and a baseband unit that performs control for transmission signal creation and reception signal processing and base station operation; A base station that communicates with the base station, wherein the base station transmits pilot signals from the plurality of radio units, and arrangement of radio resources in which the pilot signals transmitted from the radio units are arranged, or It is assumed that at least one of the patterns of the pilot signal is changed based on information fed back from the terminal.

Another aspect is an aspect in which the arrangement of pilot signals transmitted from the base station is determined in accordance with the spatial propagation path between the radio transmission / reception units of the base stations arranged in a distributed manner and the terminals.

According to another aspect, the distributed radio units are divided into several groups, and the arrangement or pattern of pilot signals is changed in each group.

According to one aspect of the present invention, it is possible to effectively use radio resources used for transmission of pilot signals.

Configuration diagram of wireless communication system Flow chart of base station operation in embodiment 1 Flowchart of base station operation in embodiment 2 Table showing the relationship between terminal rank and pilot signal allocation number Pilot signal layout that can identify pilot signals of four radio units Arrangement diagram of pilot signals that can distinguish pilot signals of two radio units Flow chart of base station operation in Embodiment 3 Table showing the relationship between negative response frequency and pilot signal allocation number Operation sequence between base station and terminal in embodiment 3 Configuration diagram of a wireless communication system when there are a plurality of terminals in the fourth embodiment Flow chart of base station operation in embodiment 4 Table showing the relationship between changes in total throughput and pilot signal allocation numbers Configuration diagram of wireless communication system when there are a plurality of terminals in the fifth embodiment

Flowchart 1 of base station operation in the fifth embodiment Table showing the relationship between the change in the minimum value of the throughput of each terminal and the pilot signal arrangement number

Flowchart 2 of base station operation in the fifth embodiment Configuration diagram of radio communication system in which radio unit is divided into two groups Sequence when base station and terminal operating according to the present invention start communication Terminal configuration diagram Base station configuration diagram that can also be manually controlled by a management device Table showing the relationship between pilot signal allocation and pilot signal allocation number Base station configuration diagram of Embodiment 1 Base station configuration diagram of Embodiment 2 Base station configuration diagram of Embodiment 3 Base station configuration diagram of Embodiment 4

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

1 is an example of a configuration diagram of a wireless communication system according to Embodiment 1 of the present invention, FIG. 22 is an example of a configuration diagram of a base station according to Embodiment 1 of the present invention, and FIG. 2 is an operation of a base station according to Embodiment 1 of the present invention. It is an example of the flowchart of.
As shown in FIG. 1, in the base station, radio units 1 to 7 (121 to 127) including an antenna (111) and radio modulation / demodulation units 1 to 7 (1121 to 1127), and the seven radio units transmit A baseband unit (110) for controlling generation of a signal to be processed, processing of a received signal, and operation of a base station. Each of the radio units 1 to 7 has at least one antenna (111), and transmits and receives radio signals to and from the terminal 128.

In the first embodiment, a terminal (128) having four antennas (118) communicates with a base station. In the first embodiment, a case where a signal is transmitted from a base station to a terminal will be described.

FIG. 5 shows a conceptual diagram of resources to which signals are allocated. FIG. 5 shows the horizontal axis as the time direction and the vertical axis as the frequency direction. In the first embodiment, since the terminal can receive signals of up to four layers, the base station sets the initial value of the radio unit to be identified by the terminal as 4. Therefore, the pilot signals shown in FIGS. 5A to 5D are used so that the four pilot signals can be received separately. For example, in FIG. 5A, a pilot signal is transmitted using a resource (155) indicating hatching. In addition, the resource (159) from which the other radio unit outputs the pilot signal is configured not to output the signal. Data signals and control signals are transmitted using other resources (160). Similarly, a pilot signal is transmitted using the resources indicated as 156 in FIG. 5B, 157 in (c), and 158 in (d).

In the first embodiment, there are seven radio units, and the pilot signal transmitted by each radio unit is any one of the above (a) to (d). Therefore, there are three radio units that output pilot signals with the same resource. There are pairs. Therefore, it is desirable that the pilot signals transmitted from these radio units be arranged so that interference with each other is reduced. In the first embodiment, the wireless unit 1 (121) is arranged as shown in FIG. 5A, the wireless unit 2 (122) is arranged as shown in FIG. 5B, and the wireless unit 3 (123) is arranged as shown in FIG. The radio unit 4 (124) is arranged as shown in FIG. 5D, the radio unit 5 (125) is arranged as shown in FIG. 5A, the radio unit 6 (126) is arranged as shown in FIG. 5B, and the radio unit 7 (127). ) Is configured to transmit a pilot signal having the arrangement shown in FIG.

The configuration of the base station in the present embodiment will be described with reference to FIG. The base station (400) includes a radio unit (404) including an antenna and a radio modulation / demodulation unit (1404), and a baseband unit (403). Further, it is connected to the backhaul network (401) via the backhaul network interface (402), and exchanges data addressed to or from each terminal with the backhaul network. The wiring (120) for connecting the wireless unit and the baseband unit may be an optical fiber or a wiring using copper.

The antenna of the radio unit is associated with an antenna identifier that is an individual number for identifying the antenna. The antenna identifier is used to determine which antenna the terminal is connected to.

The baseband unit (403) includes a signal processing unit (407) that performs transmission signal generation and reception signal processing, and a control unit (405) that performs control for base station operation.

The signal processing unit 407 includes a demapping unit 421. A signal received from the terminal is input to the demapping unit 421 via each radio unit, CP removing unit 418, FFT unit 419, and reception processing unit 420. The signal input to the demapping unit is a signal mapped to the frequency / time resource shown in FIG. The demapping unit separates the input signal into a control signal including feedback information fed back from the terminal and a data signal, and outputs each of them.

The control unit (405) includes a pilot signal control unit (425) that controls a pilot signal transmitted from each radio unit of the base station.

Feedback information required for changing the pilot signal, for example, information regarding the rank of each terminal and information regarding negative acknowledgment are input to the pilot signal control unit (425).

The pilot signal control unit (425) includes a feedback information collection unit 801, a pilot signal change determination unit 802, and a pilot signal determination unit 803. The feedback information collection unit 801 collects information fed back from the terminal that has received the signal from the base station via at least one radio unit. The pilot signal change determination unit 802 monitors changes over time in collected information, checks whether there is a change from the conventional one, and determines a change in the pilot signal if there is a change from the conventional one. The pilot signal determination unit 803 receives the result of the pilot signal change determination unit (802) and determines whether or not the pilot signal is changed.

The mapping control unit (431) controls the mapping (411) of the transmission signal, and the data signal, the synchronization signal (415), the control signal (416), and the pilot signal (417) output from the modulation unit (410) Mapping to frequency / time resource elements as shown in FIG. The mapping control unit 431 notifies the mapping control information 490 to the mapping 411 and the demapping control information 495 to the demapping unit 421.

Other base station operations are the same as commonly used base station operations, so the operation of each part will be briefly described.

When the base station (400) receives data from the backhaul network (401) via the backhaul network interface (402), the base station 400 stores the received data in the transmission buffer (408). Next, the error control unit (409) encodes the data with an error detection code and an error correction code, and the modulation unit (410) modulates the encoded data. The mapping unit 411 outputs the data signal output from the modulation unit (410), the synchronization signal (415), the control signal (416), and the pilot signal (417) according to the mapping control information 490 from the mapping control unit (431). , Mapping to time frequency elements (radio resource elements with time and frequency as axes).

Thereafter, the transmission processing unit (412) performs interference control and transmission weight multiplication, the IFFT unit (413) converts the signal into a time domain signal, and the CP adding unit (414) adds a CP (cyclic prefix). Then, the transmission signal is input to the wireless modulation / demodulation unit (1404). The wireless modulation / demodulation unit 1404 converts the input digital signal into an analog signal, converts it into a radio frequency signal, and outputs the signal from the antenna.

Similarly, a signal transmitted from the terminal is received by the antenna, converted to a baseband frequency by the radio modem unit (1404), converted from an analog signal to a digital signal, and then input to the baseband unit (403). Is done. CP is removed by the CP removing unit (418), and converted into a frequency domain signal by the FFT unit (419). The reception processing unit (420) performs processing such as multiplication of reception weights on the converted frequency domain signal. The demapping unit (421) separates the input signal into a data signal and a control signal and outputs the data signal and the control signal. The control signal is input to the control unit (405), the data signal is input to the demodulation / decoding unit (422), and demodulated / decoded by the demodulation / decoding unit 422. The demodulated / decoded signal is subjected to error correction and error detection by an error control unit (423) and input to a reception buffer (424). The exchange between the signal processing unit (407) and the control unit (405) is performed via the bus (406).

In FIG. 22, the processing from the transmission buffer to the transmission processing is shown as a system example. However, in order to perform MIMO communication with a terminal using a part of distributed antennas, or to perform simultaneous MIMO communication with a plurality of terminals, It is good also as a structure which performs the signal processing of a system | strain in parallel. FIG. 22 shows an example of the configuration of the base station, and other configurations may be used as long as they can be realized without changing the gist of the present invention.

Next, with reference to FIG. 2, an operation flowchart showing the setting process of the pilot signal of the base station will be described. First, the base station transmits a signal from each radio section 404 based on the pilot signal determined as the initial value, and starts communication with the terminal (101). The base station collects the information fed back from the terminal that receives the signal from the base station in a timely manner (102) in the feedback information collection unit (801) of FIG. The change with time of the collected information is monitored, and the pilot signal change determination unit (802) of FIG. 22 compares it with feedback information collected in the past to check whether there is a change from the past (103).

If there has been a change from the prior art, the pilot signal change determination unit (802) of FIG. 22 determines the change of the pilot signal, and if it is determined that the system performance is improved by the change of the pilot signal (104), the pilot of FIG. The pilot signal is changed by the signal from the signal determination unit (803) (105), and the new pilot signal is notified to the terminal (107).

If the system performance is not improved even if the pilot signal is changed, the pilot signal is not changed (106).

As shown in the present embodiment, by performing control to dynamically change the pilot signal based on information fed back from the terminal, it is possible to effectively use radio resources and improve system performance.

The pilot signal can be identified not only from the arrangement of the pilot signal used in FIG. 5, but also from which radio section the pilot signal can be identified by changing the pattern of the pilot signal or by changing them in combination. Can do. For example, the pilot signal can be identified by using a Walsh code in the pattern of the pilot signal.

Therefore, in the embodiment of the present invention, as shown in FIG. 5, an example of changing the arrangement of pilot signals has been described. However, it is obvious that the same effect can be obtained by changing the pattern.

Therefore, in the embodiment shown in FIG. 22, the pilot signal determination unit (803) can output two types of information of pilot arrangement and pattern. Information on the pilot arrangement is transmitted to the mapping control unit 431. Information about the pattern is transmitted to the pilot signal (417) via the bus 406.

When the pilot signal arrangement is changed as shown in FIG. 5 and a predetermined value is used for the pattern, the signal output from the pilot signal determining unit (803) is configured to be information on the pilot arrangement. You may do it.

Hereinafter, this embodiment will be described in detail using other examples.

Embodiment 2 of the present invention will be described with reference to FIG. 23, FIG. 3, FIG. 4, and FIG. In the second embodiment, the base station collects information on the rank of the terminal as feedback information fed back from the terminal (132). The base station checks whether the number of ranks has decreased (133). If the number of ranks decreases, the base station changes the pilot signal arrangement (134) and notifies the terminal of the new pilot signal arrangement number (135). If there is no decrease in the number of ranks, the pilot signal arrangement is not changed (136). In the configuration of the second embodiment, differences from the first embodiment will be described. About the point which description is abbreviate | omitted in Example 2, it is the same as that of another Example.

FIG. 4 is a table (141) showing the relationship between the time (142), the rank number of terminals (143), and the pilot signal arrangement number (144). The table 141 is held in a memory (811) that collects rank number information. The pilot signal arrangement number 144 is associated with the number that is an identifier for specifying the arrangement pattern with respect to the arrangement of the pilot signal. That is, the table 141 stores the number of ranks fed back from the terminal and the arrangement of pilot signals in association with each other.

FIG. 21 is a table (701) showing the relationship between pilot signal arrangement and pilot signal arrangement number. In the table 701, at least one pilot signal arrangement number 702 is associated with one or more pilot signal arrangement patterns corresponding to the arrangement number. The pilot signal arrangement (703) associated with the pilot signal arrangement number 1 is associated with the pattern (A). As shown in FIG. 21, in the pattern (A), a pilot signal is arranged in the hatched resource (1701), and a signal other than the pilot signal, such as a data signal, is arranged in the other resource (1702). The

Pilot signal arrangements associated with pilot signal arrangement number 2 are pattern (B) and pattern (C). In pattern (B) and pattern (C), pilot signals are arranged in different resources. In the pattern (B), no signal is arranged in the resource (1703) in which the pilot signal is arranged in the pattern (C). Similarly, in pattern (C), no signal is allocated to the resource in which the pilot signal is allocated in pattern (B). With this signal arrangement, the terminal can identify the pilot signal.

Pilot signal arrangements associated with pilot signal arrangement number 3 are patterns (D), (E), and (F). Pilot signal arrangements associated with pilot signal arrangement number 4 are patterns (G), (H), (I), and (J). The arrangement method of pilot signals in these patterns is the same as the pattern associated with pilot signal arrangement number 2. Similarly to patterns (A), in patterns (B) to (J), signals other than pilot signals, such as data signals, are arranged in unhatched resources.

If information on the arrangement pattern as shown in FIG. 21 is shared in advance between the base station and the terminal, the pilot signal arrangement is notified by notifying the pilot signal arrangement itself, but the pilot signal arrangement number. The side can grasp. The base station may notify the pilot signal arrangement number corresponding to the pattern of the pilot signal arrangement used by each radio unit using the broadcast signal.

FIG. 23 shows the configuration of the base station according to the second embodiment.
In the second embodiment, information on the rank number of the terminal fed back from the terminal is held in the memory (811) included in the pilot signal control unit (425). The number of ranks used in this embodiment is the number of layers that can be transmitted simultaneously in MIMO communication.

The pilot signal arrangement change determining unit (427) compares the number of ranks included in the information fed back from the terminal with the number of ranks fed back in the past and already held in the memory 811, and whether or not the number of ranks has decreased. And the information is transmitted to the pilot signal arrangement determining unit (428). That is, the pilot signal arrangement change determination unit 427 monitors the time change of the rank number by referring to the table 141.

The pilot signal arrangement determining unit (428) decides to change the pilot signal arrangement if the information from the pilot signal arrangement change determining unit (427) is “there is a decrease in the number of ranks”, and “no decrease in the number of ranks”. If so, it is determined not to change the pilot signal arrangement. That is, according to the number of ranks, pilot signal arrangement determining section 428 determines whether or not the pilot signal arrangement needs to be changed. The pilot signal control unit 425 in the second embodiment holds a pilot signal arrangement number table in the memory (430) in advance, and the pilot signal arrangement number determination unit (428) performs mapping control on the determined pilot signal arrangement number. Part (431).

FIG. 3 shows the operation of the base station in the second embodiment. As described above, in the second embodiment, the base station collects the rank number of the terminal fed back from the terminal in the memory (811) for collecting the rank number information of FIG. 23 (132). The pilot signal arrangement change determination unit (427) of FIG. 23 refers to the information on the number of ranks held in the memory 811 and checks the change in the number of ranks (133). When the number of ranks decreases as a result of the check at 133, the base station changes the pilot signal arrangement in the pilot signal arrangement determining unit (428) of FIG. 23 (134), and assigns the changed pilot signal arrangement number to the terminal. Notification (135) is made. If there is no decrease in the number of ranks, the pilot signal arrangement determining unit does not change the pilot signal arrangement (136), and the base station returns to the process of checking the change in rank number.

In the case of the wireless communication system shown in FIG. 1, since the terminal (128) has four antennas, the terminal (128) can be configured to transmit and receive signals of up to four layers. However, communication is performed based on standardized specifications. In this case, the number of layers that can be transmitted from the base station to the terminal or from the terminal to the base station is determined by the specification.

In the second embodiment, as shown in FIG. 4, the pilot signal arrangement number (144) at time t (0) is set to 4, and feedback from the terminal is performed between time t (0) and t (m−1). Since the number of ranks (143) to be performed is 4, the pilot signal arrangement number (144) is communicated as 4, and it is known that the number of ranks is 2 by the information fed back when the time is t (m). Based on this, the pilot signal arrangement number is changed to the pilot signal arrangement of 2, and the subsequent communication is continued. By operating in this way, radio resources used for pilot signals can be reduced to ½, and radio resources that are no longer used for pilot signal transmission can be used as data signal resources. Can measure.

When there is one terminal communicating with the base station, the number of ranks indicated by the terminal is the number of paths that can be formed between the terminal and the base station (that is, when the base station does not perform transmission diversity, The number of antennas that can form a path with the terminal), so that communication with the antennas of the radio unit exceeding the rank number is not possible. The main reason for the decrease in rank means that the radio unit of the base station and the terminal, which have been able to communicate so far, can no longer communicate due to propagation path fluctuations. Since the base station can know which radio unit can communicate with the information fed back, the arrangement of the pilot signal may be changed so that the pilot signal from the radio unit can be identified.

Next, Example 3 will be described with reference to FIGS. 24, 6, 7, 8, and 9. In the third embodiment, the base station determines the change of the pilot signal arrangement based on the negative response included in the information fed back from the terminal.

FIG. 24 shows the configuration of the base station of the third embodiment. The difference from the other embodiments is that the memory (812) in the pilot signal control unit (425) stores information on negative acknowledgment. Other configurations are the same as those of the second embodiment shown in FIG.

FIG. 8 shows a table (191) showing the relationship between the information regarding the negative response fed back from the terminal stored in the memory (812) of the base station and the pilot signal arrangement number in the third embodiment. In the table (191), it is determined whether the frequency of negative responses is larger than a threshold value (193), and whether the frequency of negative responses after changing the modulation scheme / coding rate is larger than a threshold value (194), and the pilot at that time The signal arrangement number (195) is recorded with time (192).

In Example 3, there are mainly two reasons why the negative response from the terminal increases. The first is deterioration of the propagation environment between the radio unit and the terminal. For example, the terminal (128) shown in FIG. 1 is in a propagation environment where signals from the radio unit 1 (121) and the radio unit 4 (124) can be received, and the base station is connected to the radio unit 1 (121) from FIG. When communicating with the terminal using the pilot signal arrangement (161) shown in (a) and from the radio unit 4 (124) using the pilot signal arrangement (162) shown in FIG. 6 (b) This is a case where the propagation environment between the wireless unit 1 (121) and the terminal (128) deteriorates and an error occurs in the modulation scheme and coding rate used conventionally. In this case, the demodulation can be correctly demodulated by performing communication with the modulation multi-level number and / or the coding rate lower than in the prior art.

Second, in the past, a pilot signal did not reach the terminal, but a signal from another radio unit that transmits a pilot signal using the same radio resource may reach the terminal due to a change in the propagation environment. This is the case. For example, as described above, in FIG. 1, the terminal (128) that was initially able to receive only the signals of the wireless unit 1 (121) and the wireless unit 4 (124) may change, for example, due to a change in the propagation environment. This is a case where a signal from the wireless unit 5 (125) that transmits a pilot signal using the same wireless resource as (121) can be received due to a change in the propagation environment. At this time, the terminal (128) performs propagation path estimation using the pilot signal on which the pilot signal of the wireless unit 5 (125) is superimposed as a pilot signal received only from the wireless unit 1 (121), and the result is Give feedback to the station. Therefore, since the information fed back from the terminal is different from the actual propagation path, the terminal cannot correctly demodulate the signal transmitted from the base station. In this case, it is necessary to change the pilot signal arrangement so that the terminal can correctly receive the pilot signals from the radio unit 1, the radio unit 4, and the radio unit 5.

FIG. 9 is a sequence diagram of the terminal and the base station in the third embodiment. FIG. 9 is a sequence in the case where it is determined that the negative response rate is greater than the threshold value, and the negative response rate is higher than the threshold value even when the modulation multi-level number and the coding rate are lowered. The operation sequence of the base station and the terminal according to this embodiment will be described with reference to FIG. The base station (712) transmits a data signal (713) to the terminal (711). The terminal performs error correction / error detection (714) on the received signal, and feeds back (715) acknowledgment / negative acknowledgment information to the base station.

The base station determines that the negative response rate> threshold (716), and lowers the modulation multi-value number / coding rate from the modulation multi-value number / coding rate used in the communication so far (717). A signal is transmitted (718). The terminal performs error correction / error detection (719) on the received signal, and feeds back acknowledgment / negative acknowledgment information to the base station (720). The base station determines that the negative response ratio> threshold (721), determines that a pilot signal collision has occurred (722), and determines the pilot signal arrangement change (723). The base station notifies the terminal of the changed pilot signal allocation number (724), the terminal prepares for communication using the notified pilot signal allocation number (725), and feeds back an acknowledgment (726). The base station receives the signal and transmits a data signal (727).

Next, FIG. 7 is a flowchart for explaining the details of the base station operation related to the sequence described in FIG. The base station starts communication with a pilot signal arrangement corresponding to the initial value (181), and collects negative acknowledgment information from the terminal (182). The result is stored in a table in memory. The base station determines whether the negative response is larger than the threshold value using the threshold value held in advance (183), and if it is equal to or less than the threshold value, continues the communication without changing the pilot signal arrangement (189). On the other hand, if it is larger than the threshold value, the base station transmits the modulation multi-level number and the coding rate lower than the conventional one (184).

In the case of a wireless system that feeds back a CQI (channel quality indicator), if the rate of negative response is larger than the threshold even if the modulation multi-value number and coding rate judged appropriate from the CQI are used, the base station The station transmits the signal with a lower modulation multi-level number and a lower coding rate.

In this state, the base station performs transmission, and similarly collects negative acknowledgment information from the terminal (185). If the negative response is larger than the threshold even after lowering the modulation multi-level number and the coding rate (186), the base station changes to a pilot signal arrangement with the rank number increased by 1 (187), and a new pilot is sent to the terminal. The signal arrangement number is notified (188). If the negative response is less than or equal to the threshold, the base station does not change the pilot signal arrangement (189).

As shown in the third embodiment, when the ratio of negative response from the terminal exceeds the threshold, the cause is clarified, and the modulation scheme and coding rate are changed, or the pilot signal arrangement is changed. Thus, the negative response rate of the terminal can be reduced and the throughput can be improved. In the present embodiment, a method of avoiding a collision by rearranging pilot signals when it is determined that a pilot signal collision has occurred is shown. On the other hand, for example, if the system guarantees the throughput for the terminal and the guaranteed throughput can be satisfied even if the transmission from the radio unit with which the pilot collides is stopped, the arrangement of the pilot signal is changed. Without changing, it is also possible to stop transmission of a signal from a radio unit in which a pilot signal collision occurs. As a result, if the resources used by the radio unit for the terminal where the pilot signal has collided can be utilized for other terminals and the total throughput can be improved, the base station can perform signal transmission. The method may be controlled as described above.

In the above-described embodiment, the initial value of the pilot signal arrangement is a value considered to be an average rank number in the area where a plurality of radio units are installed and can communicate with those radio units, or the same number as the radio units. May be the initial value. When a standardized system is used, the maximum number of layers defined by the standard may be used.

When increasing the pilot signal arrangement number, it is difficult to quantitatively grasp the collision of the pilot signals, so it is preferable to increase by one. However, when changing the pilot signal arrangement in response to a decrease in the rank number Does not have to be lowered one by one. For example, when communication is started with an initial value of the pilot signal arrangement number set to 4, and information indicating that the rank number is 2 is fed back from all terminals due to changes in the spatial propagation path, it is suitable for the rank number 4 The pilot signal arrangement may be changed to a pilot signal arrangement suitable for rank number 2.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. In the fourth embodiment, as shown in FIG. 10, a base station configured with a plurality of radio units and a baseband unit (250) of radio units 1 (221) to m (229), and a plurality of terminals 1 to Terminal n (241-243) is communicating.

In the fourth embodiment, the base station monitors the number of ranks fed back from each terminal as in the second embodiment. However, in Example 4, since a plurality of terminals communicate with the base station, not only a change in a spatial propagation path between one terminal and the radio unit, but also a spatial propagation path between the plurality of terminals and the radio unit. Considering the above, the pilot signal arrangement is determined. The structure of the base station of Example 4 is shown in FIG. The configuration of the fourth embodiment is the same as that of the second embodiment, but the memory (813), the pilot signal arrangement change determining unit (427), and the pilot signal arrangement determining unit (428) in the pilot signal control unit (425). The operation is different.

In the fourth embodiment, the memory (813) stores information on the proportion of terminals with reduced ranks among terminals communicating with the base station, and the pilot signal arrangement change determination unit (814) stores the memory 813. , It is determined whether the pilot signal arrangement should be changed when the ratio exceeds a predetermined threshold. Hereinafter, an example in which the pilot signal arrangement change determination unit 427 determines whether to change the pilot signal arrangement on the basis of a change in total throughput will be described.

For example, when communication is started with the pilot signal arrangement number of the initial value being 3, and a terminal having a rank number reduced to 2 due to a variation in the spatial propagation path, for a terminal with a rank number of 2, it corresponds to the rank number 2. By adopting the pilot signal arrangement, the base station can use the resources used for transmitting the pilot signal of the radio unit that cannot communicate with the terminal for transmitting the data signal, thereby improving the throughput. On the other hand, for terminals that can communicate with rank 3, pilot signal collision occurs when the pilot signal arrangement corresponding to rank 2 is used, so throughput decreases for such terminals. In this way, when a plurality of terminals are communicating with the base station, it is necessary to change the pilot signal arrangement in consideration of the fluctuations of the plurality of terminals as well as the fluctuations of the individual terminals. Therefore, in the fourth embodiment, when the total throughput of a plurality of terminals is increased by changing the pilot signal arrangement as a reference for changing the pilot signal arrangement, the pilot signal arrangement determining unit (428) changes the arrangement of the pilot signal. And change the pilot signal arrangement.

FIG. 12 is a table (271) showing the relationship between the change in the total throughput held in the base station memory (813) and the pilot signal arrangement number. This table (271) also holds the determination result of the pilot signal arrangement change determination unit (427). The table 271 in FIG. 12 includes an entry 273 in which a change in the number of ranks according to time is recorded for each rank number of terminals, an entry of a relationship 274 between the ratio of terminals in which the number of ranks has decreased per time and a threshold, and pilots A change in total throughput 275 due to a change in signal arrangement and an arrangement number for each time of pilot signal arrangement number 276 are held.

The base station records the time change (272) of the number of ranks (273) for each terminal, and determines whether the ratio of the number of terminals whose rank number decreases is larger than the threshold with respect to the number of terminals accommodated by the base station. Judgment is made (274). At time t (k), it is determined that the ratio of rank-decreasing terminals is greater than the threshold value, so the change in total throughput due to the pilot signal allocation change is calculated. As a result, the total throughput decreases due to the pilot signal allocation change. Since it is determined, the pilot signal arrangement number (276) is assumed to be conventional. Further, at time t (m), it is determined that the total throughput increases due to the change of the pilot signal arrangement, so the pilot signal arrangement number (276) is changed.

FIG. 11 shows an operation flowchart of the base station in the fourth embodiment. In the fourth embodiment, as in the second embodiment, the number of ranks fed back from each terminal is monitored, and the operation is as follows.

The base station starts communication with a pilot signal arrangement corresponding to the initial value (261), and collects information on the number of ranks of each terminal fed back from the terminal (262). The base station determines whether the ratio of the number of terminals having a reduced number of ranks among a plurality of communicating terminals is larger than a preset threshold using the collected feedback information (263). If it is not greater than the threshold, the base station does not change the pilot signal arrangement (268). If it is larger than the threshold, the base station calculates the total throughput of the entire terminal before changing the pilot signal arrangement and after changing the pilot signal arrangement in accordance with the decrease in the number of ranks (264). As a result, it is determined whether or not the total throughput increases due to the change of the pilot signal arrangement (265). If the total throughput increases as a result of the determination, the base station changes the pilot signal arrangement (266) and notifies the terminal of the new pilot signal arrangement number (267). When the total throughput does not increase, the base station does not change the pilot signal arrangement (268).

In the fourth embodiment, whether or not to change the pilot signal arrangement is determined based on a change in total throughput, but the trigger for determining the change in the pilot signal arrangement is determined based on whether or not the ratio of terminals having a reduced number of ranks is greater than a threshold value. . An arbitrary value may be used as the threshold value. However, if the threshold value is set to a small value, the determination of the change of the pilot signal arrangement is frequently made. It is desirable to make a decision based on the ratio at the time of performing and the processing capability of the base station.

As a modification of the present embodiment, the pilot signal arrangement may be changed when the number of ranks of all terminals decreases. Further, the pilot signal arrangement may be changed when the maximum number of ranks fed back from the terminal decreases.

Next, Example 5 will be described with reference to FIG. 13, FIG. 14, FIG. 15, and FIG.

FIG. 13 shows a block diagram of a wireless communication system according to the fifth embodiment of the present invention. In the fifth embodiment, the terminal 2 (332) and the terminal 3 (333) each have two antennas (322, 323). If the terminal 2 and the terminal 3 can receive signals from the wireless unit 2 (312), the wireless unit 3 (313), the wireless unit 4 (314), and the wireless unit 5 (315), these 4 It is also possible for a certain radio unit to simultaneously transmit signals to two terminals, that is, to perform multi-user MIMO communication.

Example 5 is the same as the other examples described so far, but the criterion for changing the pilot signal arrangement is the change in the minimum value in the throughput of each terminal.

FIG. 15 is a table (361) showing the relationship between the change in the minimum value of the throughput of each terminal with the passage of time and the pilot signal arrangement number in this embodiment. The base station holds the table (361) shown in FIG. 15 in a memory in the pilot signal control unit. The table (361) includes the number of ranks for each terminal (363), the comparison result of the ratio of the number of rank-decreasing terminals and the threshold (364), and the minimum of the throughput of each terminal when the pilot signal arrangement is changed. It includes a change in value (365) and a pilot signal constellation number (366) at a certain time 362.

Based on the number of ranks of a plurality of collected terminals, the comparison result 364 of the ratio of rank-decreased terminals and the threshold indicates that the ratio of the number of terminals with the reduced number of ranks to the total number of terminals collected by the base station is , It indicates whether it is larger than the threshold stored in advance by the base station.

For example, at time t (k) or t (m−1), the ratio of terminals with a reduced number of ranks is greater than the threshold value. Even if the pilot signal arrangement is changed in accordance with the decrease in the number of ranks, Since the minimum value of the throughput does not change or decreases, the pilot signal arrangement is the same as at time t (0). However, at time t (m), the minimum value of the throughput of each terminal increases, so the pilot signal arrangement is changed.

FIG. 14 shows a flowchart of base station operation in the fifth embodiment. The difference between the fourth embodiment and the fifth embodiment is a difference in the reference for changing the pilot signal arrangement. In the fourth embodiment, the change was made in the total throughput of a plurality of terminals. In the fifth embodiment, a change in the minimum value among the throughputs of the respective terminals is used as a determination criterion. That is, in this embodiment, the base station determines whether or not the ratio of the number of terminals whose number of ranks has decreased is greater than a threshold (353). If the result of determination is not greater than the threshold value, the pilot signal arrangement is not changed (358). If it is larger than the threshold, the throughput of each terminal before and after changing the pilot signal arrangement is calculated (354), and if the minimum value of the throughput of each terminal is increased (355), the pilot signal arrangement is changed. (356), and notifies the terminal of the new pilot signal arrangement number (357). If the minimum value of the throughput of each terminal does not increase, the pilot signal arrangement is not changed (358).

The fifth embodiment is a preferable method when building a wireless system that prioritizes guaranteeing the minimum value of the throughput of the terminal rather than improving the total throughput of each terminal.

In the fifth embodiment described so far, when the minimum value of the throughput of each terminal does not increase, the pilot signal arrangement is not changed (358). However, as shown in FIG. Even if the value does not increase, if the total throughput increases (361), the pilot signal arrangement may be changed (362).

In addition, as another modification of the present embodiment, other determination criteria are used, such as determining the number of terminals that can obtain the guaranteed throughput for each user as a determination criterion for changing the pilot signal arrangement. May be.

Next, Example 6 will be described with reference to FIG. The radio base station according to the sixth embodiment includes a plurality of radio units (381, 382) and a baseband unit 385 as shown in FIG. The plurality of radio units are grouped into a plurality of groups. In FIG. 17, the radio unit 381 belongs to the group A and the radio unit 382 belongs to the group B. The baseband unit includes a group A baseband unit 386 and a group B baseband unit 387 corresponding to the groups A and B, respectively. The group A baseband unit 386 controls the pilot signal arrangement for the group A. The group B baseband unit 387 controls the pilot signal arrangement for the group B.

Multiple radio units are divided into two or more groups, and the pilot signal arrangement is controlled individually in each group, so that control more suitable for each group than when pilot signal arrangement is controlled as one group Therefore, the configuration shown in this embodiment is suitable when better wireless communication can be realized as a result.

For example, the probability that the pilot signal arrangement corresponding to the rank number 4 is changed to the initial value is higher than the case where communication is started using the pilot signal arrangement corresponding to the rank number 2 as the initial value. The radio unit having a low value is set as group A, while the pilot signal arrangement corresponding to rank number 2 is set as an initial value compared to the case where communication is started using the pilot signal arrangement corresponding to rank number 4 as an initial value. Then, a radio unit having a low probability of changing the pilot signal arrangement thereafter is defined as group B. By grouping in this way, group A can start communication with the pilot signal arrangement corresponding to rank number 4 as an initial value, while group B can start communication with the pilot signal arrangement corresponding to rank number 2 as an initial value. it can. As a result, both groups can start communication using a pilot signal arrangement suitable for each group.

In addition, for example, when one base station covers an area where many users gather like a downtown area and an area where a user does not exist as much as a downtown area such as a general residential area, the radio unit 2 It may be divided into two groups. In a downtown area, if the density of radio units is higher than that in residential areas, if the cell design is such that any radio unit transmits signals with the same power, the number of radio units that the terminal can receive pilot signals The average is different in the downtown area and the residential area, so the time average of the number of ranks fed back from the terminal is also different in the downtown area and the residential area. Thus, by grouping the radio units according to the communication environment, it is possible to control the pilot signal arrangement more finely.

As another embodiment, the radio units may be grouped according to the number of maximum ranks of terminals. Even when the maximum number of ranks is the same, the groups may be further divided by the frequency with which the pilot signal arrangement changes. For example, if the propagation environment of the communication area is almost stable and the change frequency of the pilot signal arrangement is low, and if the change of the propagation environment of the communication area is large and the pilot signal arrangement is changed frequently, wireless communication It is desirable to control as a separate group in the area where the system performance is improved. As a result, the pilot signal arrangement can be changed at a frequency suitable for each area, and there is an effect that the load on the system required to determine the change can be made to an appropriate amount.

As shown in FIG. 17, in the sixth embodiment, in the baseband unit (385) of the base station, a group A baseband unit (386) and a group B baseband unit (387) are individually provided, The pilot signal arrangement method is controlled. The pilot signal arrangement of each group may be controlled in the same manner as in the first to fifth embodiments described so far. Further, the determination criteria for changing the pilot signal arrangement may be the same for group A and group B, or may be different criteria. Further, in the sixth embodiment, although divided into two groups, it may be divided into more groups. The grouping may be performed so that the number of both wireless units is equal, or may be divided so that the number of wireless units is different.

Example 7 will be described with reference to FIG. FIG. 18 shows a sequence when the terminal (391) starts communication with the base station (392) operating based on the above-described embodiment.

The base station according to the seventh embodiment broadcasts control information (393) such as synchronization information required for communication with the terminal and pilot signal arrangement information at regular intervals. After the power is turned on (394), the terminal searches for a synchronization signal (395), and then obtains control information necessary for starting communication with the base station from the control information (396).

The terminal (391) broadcasts a communication start inquiry signal (397), receives a communication start permission from the base station, and receives a control signal related to the wireless unit that first received the communication start inquiry signal (398). The base station 392 uses this control signal to notify the pilot signal arrangement number used by the radio unit with which the terminal (391) starts communication. Based on the notified pilot signal arrangement number, the terminal prepares to detect the pilot signal and starts communication with the base station (399). Thereafter, as in the embodiment described so far, communication is continued while timely feedback of information such as the number of ranks and negative response to the base station.

Next, the configuration of the terminal according to this embodiment will be described with reference to FIG.

The configuration of the terminal 503 includes a signal processing unit 507, a control unit 505, an application 501, and an interface 502 between the application 501, the signal processing unit 507, and the control unit 505, which are connected by a bus. Further, the terminal includes a wireless modulation / demodulation unit and a wireless unit 504 having an antenna. The signal processing unit 507 includes a transmission buffer 508, an error control unit 509, a modulation unit 510, a mapping unit 511, a transmission processing unit 512, an IFFT unit 513, a CP addition unit 514, a reception buffer 524, an error control unit 523, and a demodulation / decoding unit. 522, a demapping unit 521, a reception processing unit 520, an FFT unit 519, and a CP removal unit.

Since the transmission / reception of the data signal is almost the same as the operation of the signal processing unit 407 of the base station described with reference to FIGS. 22 and 23, the difference from the base station will be described.

The base station shown in FIG. 25 dynamically changes the pilot signal arrangement and notifies the terminal of the arrangement as a pilot signal arrangement number.

The output from the reception processing unit 520 in the signal processing unit 507 is transmitted to the pilot signal arrangement number reading unit 526, and the pilot signal arrangement number reading unit 526 reads the pilot signal arrangement number from the output from the reception processing unit 520. . Based on the number read out by the pilot signal arrangement number reading unit (526), the pilot signal is read out using a table indicating the relationship between the pilot signal arrangement number and the pilot signal arrangement stored in the memory (530). The pilot signal transmitted by the wireless unit communicating with the terminal is read out by the unit (528).

Based on the read pilot signal information, the rank number determination unit (529) determines the rank number of the signal received by the terminal, and transmits the information to the control information generation unit (531). The generated control information (515) is mapped to a time-frequency element (a radio resource element around time and frequency) together with a pilot signal (517) of a terminal and a modulated data signal, and after transmission signal processing, Output from the antenna.

The configuration shown in FIG. 19 shows the configuration of a terminal used in a wireless communication system that determines a change in pilot signal arrangement based on information on the number of ranks, but the change in pilot signal arrangement is determined based on negative acknowledgment information. The same configuration may be applied to the terminal used in the system.

The series of operations related to the change of the pilot signal arrangement in the embodiments described so far may be automatically executed by a program stored in the baseband unit of the base station. Also, as shown in FIG. 20, manual control and automatic control may be switched as appropriate for operation. In FIG. 20, manual control and automatic control are mainly described. Therefore, in the embodiments described so far, for example, the IFFT unit, the FFT unit, the CP adding unit, the CP removing unit, and the radio unit described with reference to FIG. Although omitted from the drawing, the processing not described in the ninth embodiment is the same as in the other embodiments.

Details of the above control will be described with reference to FIG. The management device (601) includes a user interface (602), a memory (603), a processor (604), and a backhaul network interface (606) as components. A pilot signal arrangement control unit (605) is provided in the processor, and an administrator can manually control the arrangement of pilot signals.

In this embodiment, the mapping control information (612) is used when the mapping unit (411) maps the pilot signal in order to arrange the desired pilot signal. As the mapping control information, information (609) by automatic control created by the pilot signal arrangement automatic control unit (613) is used, or the pilot signal arrangement control unit (605) of the management apparatus (601) Which of manual control information (607) created manually can be switched by a switch (610) and a switch control signal (608). This switch control signal is also controlled by the management device (601). The switch 610 selects information 609 by automatic control or manual control information 607 according to the switch control signal 608 and transmits the selected information to the signal processing unit 407.

With such a configuration, either automatic control of pilot signal arrangement or manual control can be performed.

Further, the setting of the criterion for determining the pilot change for each group in the sixth embodiment may be notified from the management apparatus 601 to the base station. Further, the management apparatus 601 may determine whether to change the pilot arrangement of each group and notify the group baseband unit. Any one of the control units 405 in the baseband group for the base station may determine the pilot arrangement change for each of the plurality of groups.

Although the embodiments of the present invention have been described with reference to the drawings, the configurations and flowcharts shown in these drawings are merely examples, and the present invention is not limited to the scope of the present invention. It is clear that the effects of the present invention can be obtained even if the above is appropriately changed. For example, it is obvious that the determination reference may be changed by appropriately changing the arrangement of pilot signals or by appropriately combining the determination criteria for changing the arrangement of pilot signals described in each embodiment.

111: Antenna 121-127: Radio unit 128: Terminal 110: Baseband unit 211-219: Antenna 221-229: Radio unit
231-233: Antenna 241-243: Terminal 250: Baseband unit 383: Group A
384: Group B
385: Baseband unit 386: Group A baseband unit 387: Group B baseband unit 400: Base station 403: Baseband unit 404: Radio unit 405: Control unit 425: Pilot signal control unit 802: Pilot signal determination unit 803: Pilot signal determining unit 427: Pilot signal arrangement determining unit 428: Pilot signal arrangement determining unit 526: Pilot signal arrangement number reading unit 528: Pilot signal reading unit 529: Rank number determining unit 531: Control information generating unit 601: Management device 605: Pilot signal arrangement control unit 607: Manual control information 608: Switch control signal 610: Switch 612: Mapping control information 613: Pilot signal arrangement automatic control unit 801: Feedback information collection unit

Claims

A wireless communication system,
A terminal,
A plurality of radio units that transmit and receive radio signals to and from the terminal;
A base station having a baseband unit that determines a pilot signal to be transmitted to the terminal via the radio unit based on information fed back from the terminal. .
The wireless communication system according to claim 1,
The baseband unit determines an arrangement of radio resources to be allocated to the transmitted pilot signal.
The radio communication system according to claim 1, wherein the baseband unit determines a pattern of the transmitted pilot signal.
A wireless communication system according to claim 3,
The baseband unit uses a Walsh code in the pattern of the pilot signal.
The wireless communication system according to claim 1,
The baseband unit collects feedback information at a predetermined timing, and determines a pilot signal to be transmitted based on the feedback information collected at different timings.
The wireless communication system according to claim 5, wherein
The wireless communication system, wherein the information fed back from the terminal is information indicating the number of ranks that can be received by the terminal.
The wireless communication system according to claim 5,
The wireless communication system, wherein the information fed back from the terminal is a negative response.
The wireless communication system according to claim 6,
If the rank number is reduced, reducing the radio unit transmitting at least one pilot signal using different radio resources;
A wireless communication system.
The wireless communication system according to claim 6,
If the negative response is reduced by increasing the radio unit transmitting the pilot signal using different radio resources, increasing the radio unit transmitting the pilot signal using different radio resources;
A wireless communication system.
The wireless communication system according to claim 1,
The wireless communication system, wherein the baseband unit determines a pilot signal to be transmitted for each of the plurality of wireless units.
The wireless communication system according to claim 5, wherein
The baseband unit determines, for each radio unit, a pilot signal to be transmitted based on feedback information collected from a plurality of the terminals;
A wireless communication system.
A wireless communication system according to claim 11, wherein
The information fed back from the plurality of terminals is information indicating the number of ranks,
The baseband unit is configured to change the radio unit that causes the pilot signal to be transmitted using different radio resources when a ratio of terminals indicating a decrease in the number of ranks exceeds a threshold;
A wireless communication system.
A wireless communication system according to claim 11, wherein
Information fed back from the plurality of terminals is a negative response,
The baseband unit is configured to change the radio unit that causes the pilot signal to be transmitted using different radio resources when a ratio of terminals that feed back a negative response exceeds a threshold;
A wireless communication system.
The wireless communication system according to claim 5,
The baseband unit is configured to change the radio unit that transmits the pilot signal using different radio resources when total throughput for the plurality of terminals is improved.
A wireless communication system.
The wireless communication system according to claim 5,
The baseband unit is configured to change the radio unit for transmitting the pilot signal using different radio resources when the minimum throughput to the plurality of terminals increases.
A wireless communication system.
The wireless communication system according to claim 1, wherein the baseband unit notifies information regarding a pilot signal to be determined to at least one terminal, and transmits the pilot signal after the notification.
A wireless communication system.
The wireless communication system according to claim 1,
The base station performs multi-user MIMO communication for simultaneously transmitting data signals from the same plurality of radio units to the plurality of terminals;
A wireless communication system.
The wireless communication system according to claim 1,
Each of the plurality of radio units is associated with one of two or more groups,
Changing the radio unit for transmitting the pilot signal using a different radio resource for each group based on information fed back from a terminal communicating with the radio unit associated with the group;
A wireless communication system.
The wireless communication system according to claim 18, wherein
A radio communication system, wherein the radio units are grouped based on a rank number of the terminals communicating with the radio unit.
A method for arranging pilot signals transmitted to a terminal from a plurality of radio transmission / reception units provided in a base station,
Collecting feedback information from a plurality of the terminals to the base station at a predetermined timing;
Storing the collected feedback information and comparing the feedback information collected at different timings;
A pilot signal arrangement method, wherein pilot signals transmitted by a plurality of radio units are determined based on a comparison result.
A wireless terminal that performs wireless communication with a wireless base station,
A table in which pilot signal arrangements are associated with numbers;
When information is reported from the base station, the controller refers to the table, identifies the pilot signal arrangement, and receives a pilot signal from the base station based on the identified pilot signal arrangement;
A wireless terminal characterized by comprising: