WO2020194428A1 - Lower level radio base station and method for controlling number of spatial multiplex streams - Google Patents

Lower level radio base station and method for controlling number of spatial multiplex streams Download PDF

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Publication number
WO2020194428A1
WO2020194428A1 PCT/JP2019/012390 JP2019012390W WO2020194428A1 WO 2020194428 A1 WO2020194428 A1 WO 2020194428A1 JP 2019012390 W JP2019012390 W JP 2019012390W WO 2020194428 A1 WO2020194428 A1 WO 2020194428A1
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base station
matrix
radio base
terminal
destination
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PCT/JP2019/012390
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French (fr)
Japanese (ja)
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西本　浩
明▲徳▼ 平
彰浩 岡崎
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三菱電機株式会社
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Priority to JP2021508405A priority Critical patent/JP7003324B2/en
Priority to PCT/JP2019/012390 priority patent/WO2020194428A1/en
Publication of WO2020194428A1 publication Critical patent/WO2020194428A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0452—Multi-user MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/24—Cell structures
    • H04W16/28—Cell structures using beam steering

Definitions

  • the present invention relates to a method for controlling a lower radio base station and the number of spatial multiplex streams in a wireless communication system to which the MIMO (Multiple-Input Multiple-Output) method is applied.
  • MIMO Multiple-Input Multiple-Output
  • a MIMO system in which multiple antennas are installed on both transmitters and receivers is connected to a space division multiple access (SDMA: Space Division Multiple Access).
  • SDMA Space Division Multiple Access
  • MU Multi-User
  • the MU-MIMO system is a system in which a base station having a plurality of antennas and a plurality of terminals having a plurality of antennas are provided, and the base station simultaneously transmits to a plurality of terminals in the same radio frequency band.
  • the 5th generation mobile communication in addition to the conventional mobile communication, that is, the same frequency band as before the 4th generation mobile communication, it is expected to utilize radio waves in a higher frequency band than before.
  • the higher the frequency the stronger the straightness of the radio wave, and the greater the attenuation with respect to the propagation distance.
  • High frequency radio waves are blocked when they hit a building such as a building, and the propagation distance of the base station is shortened. Therefore, when using a high frequency band, the communication area covered by one base station, that is, The cells will be smaller than before, and the number of base stations is expected to increase compared to before the 4th generation mobile communication.
  • Patent Document 1 discloses a radio base station system that is divided into a higher radio base station and a lower radio base station.
  • the upper radio base station selects terminals for data transmission in the upper scheduler unit, determines the data transmission speed or data transmission amount of each terminal, and notifies the lower radio base station of these.
  • the lower radio base station determines the number of signal streams of each terminal based on the data transmission speed of the terminal and the terminal determined by the upper scheduler, and performs MU-MIMO precoding for each terminal to perform MU-MIMO precoding to the destination terminal.
  • MU-MIMO transmission is performed. Since the wireless base station system described in Patent Document 1 is composed of an upper wireless base station and a lower wireless base station which is a base station capable of wirelessly connecting to a mobile terminal, the lower wireless base station can be realized with a simple configuration. Will be done.
  • the lower radio base station described in Patent Document 1 transmits a signal stream to a terminal determined by a higher scheduler, and this signal stream has a high spatial correlation between a plurality of antennas included in the terminal or between terminals. It may be a signal stream.
  • the throughput of the lower radio base station and the signal power to interference noise power ratio (SINR: Signal-to-Interference plus Noise power Ratio) can be obtained. There was a problem that the communication quality deteriorated.
  • the present invention has been made in view of the above, and an object of the present invention is to obtain a lower radio base station capable of suppressing deterioration of throughput and communication quality.
  • the lower radio base station sets a plurality of destination terminals to which signal streams are assigned and data transmission speeds of the plurality of destination terminals as higher radio base stations. Is notified from, and based on multiple destination terminals and data transmission speed, a matrix based on the state of the transmission line corresponding to multiple destination terminals is calculated, and the absolute value of the elements of the stream is a predetermined threshold value.
  • a rank control unit that determines the number of signal streams of the destination terminal so as not to use a transmission line that does not satisfy the above, and a signal processing unit that performs Multi User-Multiple Input Multiple Output precoding on the signal stream corresponding to the destination terminal. It is characterized by having.
  • the lower radio base station according to the present invention has the effect of suppressing deterioration of throughput and communication quality.
  • FIG. 1 is a diagram showing a configuration example of a radio base station system according to an embodiment.
  • the radio base station system 100 includes an upper base station 10 and lower base stations 20-1 to 20-M (M is an integer of 1 or more).
  • the higher-level base station 10 is a radio base station that performs higher-level scheduling described later.
  • the lower base stations 20-1 to 20-M are shown without distinction, they are appropriately referred to as lower base stations 20.
  • the lower base station 20 is a radio base station that performs lower scheduling, which will be described later.
  • the wireless base station system 100 connects to MBH (Mobile Back Haul) and transmits / receives data to / from MBH.
  • MBH is a network defined by 3GPP (Third Generation Partnership Project) or ITU-R (International Telecommunication Union Radiocommunication Sector), and higher-level network devices such as SGSN (Serving General-packet-radio-service Support Node) are installed. It is a network that connects between the sites and the base station.
  • SGSN is one of the nodes that make up the core network of mobile terminals defined by 3GPP, and controls information such as user authentication and IP (Internet Protocol) address during packet communication.
  • the cells each subordinate base station 20 forms a radio base station system 100 includes the mobile terminal 90-1-1 ⁇ 90-M-K M is present.
  • the cell formed by the lower base station 20-m (m is an integer of 1 ⁇ m ⁇ M)
  • j (j is an integer of 1 or more) of mobile terminals 90-m-1 to 90-m-j. are doing.
  • the downlink data of each terminal that is, the communication data in the direction from the base station to the terminal is input from the MBH to the radio base station system 100 and transmitted from the radio base station system 100 to each terminal.
  • the MU-MIMO system is applied to the radio base station system 100 of the present embodiment.
  • MU-MIMO downlink In the downlink in the MU-MIMO system (hereinafter referred to as MU-MIMO downlink), a signal is sent from the base station to each terminal at the same time.
  • the uplink is excluded from the scope of the MU-MIMO method in the present invention.
  • the communication performance of the MU-MIMO downlink largely depends on the state of the transmission line between the base station and the terminal. Therefore, the base station has a combination of terminals that transmit MU-MIMO downlink, the number of signal streams that transmit the downlink to each terminal, that is, the number of ranks (RI: Rank Indicator), and the stream of each signal. It is necessary to determine the modulation method and the MCS (Modulation and Coding Scheme), which is an error correction coding method. This is because RI and MCS need to be determined according to the transmission line condition.
  • a signal stream is a spatial multiplex signal sequence transmitted by a base station to each terminal.
  • RI indicates the number of signal streams used in standards such as IEEE802.11n and LTE (Long Term Evolution) -Advanced
  • MCS is an index indicating a combination of a primary modulation method and an error correction coding method.
  • the base station determines the data transmission rate by using the determined MCS modulation method and error correction coding method.
  • the process of determining the combination of terminals that transmit MU-MIMO downlink, the number of signal streams RI that transmit the downlink to each terminal, and the MCS of each signal stream is generally called scheduling, and is a process of performing scheduling.
  • the part is commonly called a scheduler.
  • the base station can acquire the CSI of each terminal by estimating the CSI using the uplink signal transmitted from the terminal to the base station.
  • the method in which the base station acquires the CSI of each terminal is not limited to this, and may be, for example, a method in which the CSI estimated value estimated on the terminal side is fed back from the terminal side to the base station.
  • the base station performs radio signal processing for MU-MIMO downlink, that is, MU-MIMO signal processing based on the information determined by the scheduler, and outputs MU-MIMO downlink signals from a plurality of antennas provided in the base station.
  • MU-MIMO signal processing include error-correction coding for data signals for each terminal and precoding for spatial multiplexing of all terminals for a plurality of signal streams generated by primary modulation.
  • the MU-MIMO signal processing is not limited to precoding, and may be any processing as long as it is a radio signal processing that realizes the MU-MIMO downlink.
  • FIG. 2 is a diagram showing a configuration example of the upper base station 10 according to the present embodiment.
  • the upper base station 10 has a resource control unit 11.
  • the resource control unit 11 has M upper scheduler units 12-1 to 12-M corresponding to each of the M lower base stations 20.
  • the upper scheduler units 12-1 to 12-M are shown without distinction, they are appropriately referred to as the upper scheduler unit 12.
  • the upper scheduler unit 12-m selects L m (L m is an integer of 1 or more and j or less) of mobile terminals that actually transmit data from j mobile terminals.
  • the selection method is the terminal capacity index or CSI for j units notified from the lower base station 20-m and the required value (or data transmission amount) of the data transmission speed or data transmission amount for j mobile terminals input from MBH. This method is selected in consideration of the amount of standby buffer for data transmission).
  • the upper scheduler unit 12-m determines the data transmission speed or the data transmission amount of each mobile terminal. This process is called upper scheduling.
  • the terminal capacity index of each mobile terminal is a real number scalar amount, and the details are described in Patent Document 1.
  • the upper scheduler unit 12-m notifies the lower base station 20-m of the selected destination terminal and the requested data transmission speed of each destination terminal.
  • the destination terminal is a mobile terminal in the Lm range selected by the upper scheduler unit 12-m.
  • the upper-level scheduler unit 12-m is L m in order from the mobile terminals having the required terminal capacity index or more among the j mobile terminals, in descending order of the data transmission request value.
  • the required data transmission speed of the selected destination terminal the maximum data transmission speed can be used among those that do not exceed the terminal capacity index of the destination terminal, but this is not the case.
  • FIG. 3 is a diagram showing a configuration example of the lower base station 20 according to the present embodiment.
  • the lower base station 20-m will be described as an example.
  • the lower base stations 20-1 to 20-M all have the same configuration.
  • the number of antennas provided in the lower base station 20-m is T m (T m is an integer of 1 or more), and the number of mobile terminals existing in the cell formed by the lower base station 20-m is j.
  • the lower base station 20-m includes a lower scheduler unit 21, a radio baseband signal processing unit 22, a radio RF (Radio Frequency) signal processing unit 23, and T m antennas 24-1 to 24-T m . Be prepared.
  • the lower scheduler unit 21 includes a rank control unit 211.
  • the wireless baseband signal processing unit 22 includes a CSI acquisition unit 221 and a MU-MIMO signal processing unit 222. Further, the CSI acquisition unit 221 is also simply referred to as an acquisition unit.
  • the MU-MIMO signal processing unit 222 is also simply referred to as a signal processing unit.
  • the radio RF signal processing unit 23 is also simply referred to as a radio signal processing unit.
  • the subordinate scheduler is also simply called the scheduler.
  • the CSI acquisition unit 221 acquires the CSI by estimating from the uplink signal from the mobile terminals 90-m-1 to 90-m-j to the lower base station 20-m, and transfers this CSI to the lower scheduler unit 21. input.
  • the estimation method is not particularly limited, and a general method may be used.
  • MU-MIMO signal processing unit 222 to generate a baseband signal for MU-MIMO downlink L m stand destination terminal that is selected by the upper scheduler section 12.
  • the radio RF signal processing unit 23 converts the MU-MIMO downlink baseband signal into a radio signal having a radio RF frequency.
  • Antennas 24-1 ⁇ 24-T m sends a wireless RF signal to each destination terminal.
  • the lower scheduler unit 21 abstracts the CSI of j terminals input from the CSI acquisition unit 221 as the transmission path capacity of the terminals so that the upper scheduler unit 12-m can easily handle it, that is, a single real number scalar. Convert to quantity.
  • the transmission line capacity indicates the amount of data that can be downlinked to the terminal.
  • the transmission line capacity can generally be calculated from the transmission line information. It is expected that the number of terminals and the number of antennas will increase in the future, which will increase the amount of information of the transmission line information itself, and there is a possibility that the line will be tight when the transmission line information itself is transmitted.
  • the lower scheduler unit 21 transmits a terminal capacity index, which is a CSI converted into a single real number scalar amount, to the upper scheduler unit 12.
  • MIMO transmission capacity is an example of a scalar quantity that can express the characteristics of CSI, that is, can be abstracted. MIMO transmission capacity is also referred to as channel capacity, channel capacity, or Shannon capacity.
  • the terminal capacity index C m, j (f) disclosed in Patent Document 1 is used. f is a radio RF frequency between the lower base station 20-m and the mobile terminal 90-m-j.
  • the resource control unit 11, the upper scheduler unit 12, the lower scheduler unit 21, the wireless baseband signal processing unit 22, the rank control unit 211, the CSI acquisition unit 221 and the MU-MIMO signal processing unit 222 are electronic circuits that perform each processing. It is realized by a certain processing circuit.
  • the radio RF signal processing unit 23 is a transmitter and a receiver.
  • This processing circuit may be dedicated hardware or a control circuit including a memory and a CPU (Central Processing Unit, central processing unit) that executes a program stored in the memory.
  • the memory corresponds to, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), or a flash memory, a magnetic disk, an optical disk, or the like.
  • FIG. 4 is a diagram showing a configuration example of the control circuit of the embodiment.
  • This control circuit is, for example, the control circuit 400 having the configuration shown in FIG.
  • the processing circuit is, for example, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.
  • the control circuit 400 includes a processor 400a which is a CPU and a memory 400b.
  • a processor 400a which is a CPU and a memory 400b.
  • the processor 400a reading and executing the program corresponding to each process stored in the memory 400b.
  • the memory 400b is also used as a temporary memory in each process performed by the processor 400a.
  • a plurality of destination terminals that perform MU-MIMO transmission and data transmission speeds of each destination terminal are instructed from the upper base station 10 to the lower base station 20.
  • the lower base station 20 performs lower scheduling based on the instruction from the upper base station 10.
  • MU-MIMO transmission the configuration of the entire MIMO transmission line matrix changes depending on the combination of destination terminals and the number of signal streams to each destination terminal, and the determination of these parameters affects the transmission characteristics. Therefore, it is considered better to have a standard for tentatively determining the number of streams transmitted by the lower base station 20.
  • the lower base station 20 may indicate at least one to all the destination terminals in the lower scheduling, in addition to instructing the data transmission speeds of the plurality of destination terminals and each destination terminal that perform MU-MIMO transmission from the upper base station 10.
  • One is to allocate a signal stream.
  • the lower base station 20 may preferentially allocate a signal stream to a destination terminal having a high data transmission speed required for the destination terminal.
  • the time that one stream is transmitted is determined in units of subframes or slots specified by 3GPP. In the case of LTE, the stream is transmitted every 1 ms. In the case of 5G (5th Generation), the stream is transmitted every 0.5 ms or 0.25 ms.
  • the rank control unit 211 determines the number of signal streams to be transmitted to each destination terminal based on the provisional precoding matrix operation so as to satisfy the above-mentioned lower scheduling criteria.
  • the provisional precoding matrix operation will be explained.
  • the provisional precoding matrix operation is an operation based on the inverse matrix for determining the number of signal streams. Further, the provisional precoding matrix operation is different from the precoding matrix operation for MU-MIMO precoding used by the MU-MIMO signal processing unit 222 described later for downlink transmission.
  • the four destination terminals be terminal a, terminal b, terminal c, and terminal d, respectively.
  • the transmission line matrices Aa, Ab, Ac, and Ad of 2 rows and 8 columns (number of rows: number of receiving antenna ports, number of columns: number of base station transmitting antenna ports Tm ) corresponding to each terminal are expressed by equations (1) and (1) and (A), respectively. It is defined as (2), equation (3), and equation (4).
  • the characters indicating the matrix are shown in bold in the mathematical formula, but are shown in normal characters in the text.
  • the entire transmission line matrix A of 8 rows and 8 columns, which is composed of the transmission line matrix of each terminal as a submatrix, is defined as in equation (5). It can be said that the entire transmission line matrix A is a matrix indicating the state of the transmission lines corresponding to a plurality of destination terminals.
  • the rank control unit 211 reflects the priority order so as to give priority to the destination terminal having the faster data transmission speed of the lower scheduling described above, and sets the submatrix of the entire transmission line matrix A as in the equation (6).
  • the matrix in which the submatrix of the entire transmission line matrix A is replaced as in Eq. (6) is defined as the total transmission line matrix A ⁇ .
  • the rank control unit 211 picks up one antenna corresponding to the receiving port from each terminal for four lines. Are arranged from the top in the order of priority of terminal d, terminal b, terminal a, and terminal c, and the remaining four lines are arranged in the same order of priority. This is referred to as the entire transmission line matrix A ⁇ ⁇ .
  • the entire transmission line matrix A ⁇ ⁇ is represented by the equation (7).
  • a T indicates the transpose of the vector and the matrix. Swapping rows in the above matrix is an operation that improves the convenience of calculation without changing the characteristics of the transmission line matrix.
  • the rank control unit 211 aims to orthogonalize the transmission line space by using the MP (Moore-Penrose) general inverse matrix of the entire transmission line matrix.
  • the provisional precoding matrix W is obtained by the MP general inverse matrix of the total transmission line matrix A ⁇ ⁇ shown in the equation (8).
  • the MP general inverse matrix is also called a matrix calculated based on the state of the transmission line corresponding to a plurality of destination terminals.
  • a + 1 is the MP general inverse matrix operator
  • a H is the Hermitian transpose of vectors and matrices.
  • the third elementary transformation is a transformation that adds a constant multiple of one row to another.
  • the Gauss-Jordan method is a classical inverse matrix solution method (simultaneous linear equation solution method) in linear algebra, and detailed explanation of the principle is omitted here.
  • An augmented matrix D of 8 rows and 16 columns, each of which is a submatrix of an eighth-order Hermitian matrix B to be calculated and an eighth-order square matrix C in which an identity matrix is set as an initial value, is defined as in equation (10).
  • the range of the submatrix B is finally calculated as the identity matrix, and the range of the submatrix C is calculated as the inverse matrix. ..
  • the reciprocal of the value of the n-row n-column element may be multiplied by the nth row.
  • the reciprocal becomes close to dividing by 0 and tends to diverge, and such a case must be avoided.
  • Each line corresponds to a receiving antenna port, and this event occurs when the spatial correlation between terminal antennas and between terminals is high due to the receiving antenna port. Therefore, if the receiving antenna port is included in MU-MIMO and precoding is applied, the transmission performance may deteriorate.
  • the threshold value ⁇ is introduced, and the rank control unit 211 checks the size of the diagonal element in the nth stage. If the threshold value ⁇ is a real scalar value greater than 0 and the absolute value of the diagonal element is smaller than the threshold value ⁇ , the nth row and nth column of the submatrix B and C are deleted, and the submatrix is deleted. The calculation proceeds by reducing the order of B and C by one. That is, the number of rows of the augmented matrix D is reduced by one, and the number of columns is reduced by two. The number of rows of the augmented matrix D remaining after all the calculation stages are completed is the calculated number of ranks of MU-MIMO.
  • Inverse matrix operations by the Gauss-Jordan method generally start from the top row. Therefore, at least the first row is not omitted and the inverse matrix operation is performed, and the inverse matrix operation is performed with the highest priority.
  • the second line of the equation (9) is orthogonalized to the first line
  • the third line is orthogonalized to the first and second lines. In this way, since the number of rows that are orthogonalized increases in the lower rows, the diagonal elements due to orthogonalization tend to be less than the threshold value in the lower rows, and the probability of being excluded increases in the lower rows.
  • the rank control unit 211 first compares the size
  • ⁇ ⁇ it is assumed that
  • the second stage calculation is performed according to the usual Gauss-Jordan method.
  • the augmented matrix D has the form of equation (12).
  • the augmented matrix D becomes the form of the equation (13) after the completion of the fifth stage. ..
  • the rank control unit 211 compares the sizes of the 6-row, 6-column elements in the range of the submatrix B
  • the augmented matrix D has the form of equation (14).
  • the operation of the rank control unit 211 calculates a matrix calculated based on the state of the transmission line corresponding to the plurality of destination terminals based on the plurality of destination terminals and the data transmission speed, and the absolute elements of the matrix are calculated. It can be said that this is an operation of determining the number of signal streams of the destination terminal so as not to use a transmission line whose value does not satisfy a predetermined threshold value.
  • the rank control unit 211 compares the size
  • the operation of the sixth stage is performed according to the usual Gauss-Jordan method.
  • the augmented matrix D has the form of equation (15).
  • the rank control unit 211 performs the operations of the 7th stage according to the normal Gaussian-Jordan method, and as a result of a series of operations, the augmented matrix D is finally obtained. Is in the form of equation (16).
  • the matrix A' ⁇ ⁇ is a matrix of 7 rows and 8 columns excluding the 6th row from the matrix A ⁇ ⁇ as represented by the equation (17).
  • Submatrix of the left half of the matrix of Equation (16) is calculated as the inverse matrix of A' ⁇ ⁇ A' ⁇ ⁇ H.
  • the provisional precoding matrix is calculated by the rank control unit 211 as in equation (18).
  • the terminal b was calculated as having one signal stream, and the other terminals a, c, and terminal d were calculated as having two signal streams. Therefore, the total number of MU-MIMO signal streams is 7.
  • An example is a specific method for determining MCS in the lower scheduler unit 21.
  • MCS since the number of signal streams of each destination terminal, that is, RI is determined, MCS according to RI so as to satisfy the requested data transmission speed in order from the terminal having the highest notified requested data transmission speed. To determine.
  • the MCS is determined using the determined RI and the SNR estimate using the vector of the provisional precoding matrix described above. In this way, the MCS is determined in order for each destination terminal.
  • two MCS determination methods have been illustrated, but the present invention is not limited to this, and other methods may be used.
  • the MU-MIMO signal processing unit 222 performs MU-MIMO precoding on the signal stream corresponding to the destination terminal, but there is no limitation on the precoding method, and even if linear precoding represented by block diagonalization is performed. Alternatively, non-linear precoding represented by THP (Tomlinson Harashima Precoding) may be performed.
  • the lower scheduler unit 21 also determines the order of L m stand destination terminal. As a criterion for determining, for example, the size of the terminal capacity index, the order of the SNR estimated value using the vector of the provisional precoding matrix described above, the order of the angle of the terminal as seen from the lower base station 20, between the terminals. The positional relationship of the terminals is geographically close or far, and the movement speed of the terminal is in order, but these are not limited to these.
  • the number of signal streams that can be transmitted is obtained by orthogonalizing the transmission path space. Therefore, the lower base station 20 suppresses deterioration of throughput and communication quality by not allocating a signal stream having a high spatial correlation between terminal antennas and terminals except for rows and columns in which matrix elements below the threshold value appear. can do.
  • the configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

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Abstract

A lower level base station (20) is characterized by comprising: a rank control unit (211), which is notified of a plurality of destination terminals to which signal streams are to be assigned and a data transmission rate of the plurality of destination terminals from a higher-level radio base station, calculates a matrix based on the states of channels corresponding to the plurality of destination terminals on the basis of the plurality of destination terminals and the data transmission rate, and determines the number of signal streams of the respective destination terminals so that a channel in which the absolute values of the elements of the matrix do not satisfy a predetermined threshold value is not used; and an MU-MIMO signal processing unit (222) which performs multi-user multiple-input multiple-output precoding on the signal streams corresponding to the respective destination terminals.

Description

下位無線基地局および空間多重ストリーム数の制御方法How to control the number of lower radio base stations and spatial multiplex streams
　本発明は、ＭＩＭＯ（Multiple-Input　Multiple-Output）方式が適用される無線通信システムにおける下位無線基地局および空間多重ストリーム数の制御方法に関する。 The present invention relates to a method for controlling a lower radio base station and the number of spatial multiplex streams in a wireless communication system to which the MIMO (Multiple-Input Multiple-Output) method is applied.
　近年、第５世代移動体通信システムを適用した技術の研究、および第５世代移動体通信システムの標準化に向けた活動が活発化している。移動体通信システムのトラフィック量は、２０２０年代には２０１０年の１０００倍以上になると想定されている。このため、広い周波数幅を確保することで、伝送量を増やすことができる第５世代移動体通信システムの実現に向けて、無線リソースの有効活用および伝送効率の向上への関心が高まっている。 In recent years, research on technologies applying the 5th generation mobile communication system and activities toward standardization of the 5th generation mobile communication system have become active. The traffic volume of mobile communication systems is expected to increase more than 1000 times that of 2010 in the 2020s. For this reason, there is increasing interest in effective utilization of wireless resources and improvement of transmission efficiency toward the realization of a fifth-generation mobile communication system capable of increasing the transmission amount by securing a wide frequency width.
　第５世代移動体通信システム以降の無線リソースの有効活用および伝送効率の向上の方法の一例として、送受信機双方に複数のアンテナを設置したＭＩＭＯシステムに、空間分割多元接続（ＳＤＭＡ：Space　Division　Multiple　Access）方式を適用したマルチユーザＭＩＭＯ（ＭＵ（Multi-User）－ＭＩＭＯ）システムが挙げられる。ＭＵ－ＭＩＭＯシステムは、複数のアンテナを備える基地局と、複数のアンテナを備える複数の端末とを備え、基地局が同一の無線周波数帯において複数の端末に対して同時伝送を行うシステムである。 As an example of effective utilization of wireless resources and improvement of transmission efficiency after the 5th generation mobile communication system, a MIMO system in which multiple antennas are installed on both transmitters and receivers is connected to a space division multiple access (SDMA: Space Division Multiple Access). ) Method is applied to a multi-user MIMO (MU (Multi-User) -MIMO) system. The MU-MIMO system is a system in which a base station having a plurality of antennas and a plurality of terminals having a plurality of antennas are provided, and the base station simultaneously transmits to a plurality of terminals in the same radio frequency band.
　第５世代移動体通信以降では、従来の移動体通信、すなわち第４世代移動体通信以前と同様の周波数帯に加えて、従来よりも高い周波数帯の電波の活用も見込まれている。周波数が高くなると電波は直進性が強くなり、伝搬距離に対する減衰が大きくなる。高い周波数の電波は、ビルなどの建物にぶつかると遮蔽されてしまうことと、基地局の伝搬距離が短くなることから、高い周波数帯を用いる場合は、１つの基地局がカバーする通信エリア、すなわちセルは従来よりも小さくなり、基地局の数は、第４世代移動体通信以前より増加すると見込まれる。このため、各セルを形成する基地局、すなわち移動端末と無線接続可能な基地局は簡素な構成で実現されることが望ましい。特許文献１は、上位無線基地局と下位無線基地局に分割されて構成された無線基地局システムを開示する。上位無線基地局は、上位スケジューラ部にてデータ伝送を行う端末の選定と、各端末のデータ伝送速度またはデータ伝送量を決定し、これらを下位無線基地局に通知する。下位無線基地局は、上位スケジューラにより決定された端末と端末のデータ伝送速度に基づいて、各端末の信号ストリーム数を決定し、各端末に対してＭＵ－ＭＩＭＯプリコーディングを行うことで送信先端末にＭＵ－ＭＩＭＯ伝送を行う。特許文献１に記載の無線基地局システムは、上位無線基地局と、移動端末と無線接続可能な基地局である下位無線基地局とで構成されるため、下位無線基地局は簡素な構成で実現される。 After the 5th generation mobile communication, in addition to the conventional mobile communication, that is, the same frequency band as before the 4th generation mobile communication, it is expected to utilize radio waves in a higher frequency band than before. The higher the frequency, the stronger the straightness of the radio wave, and the greater the attenuation with respect to the propagation distance. High frequency radio waves are blocked when they hit a building such as a building, and the propagation distance of the base station is shortened. Therefore, when using a high frequency band, the communication area covered by one base station, that is, The cells will be smaller than before, and the number of base stations is expected to increase compared to before the 4th generation mobile communication. Therefore, it is desirable that the base station forming each cell, that is, the base station that can be wirelessly connected to the mobile terminal is realized with a simple configuration. Patent Document 1 discloses a radio base station system that is divided into a higher radio base station and a lower radio base station. The upper radio base station selects terminals for data transmission in the upper scheduler unit, determines the data transmission speed or data transmission amount of each terminal, and notifies the lower radio base station of these. The lower radio base station determines the number of signal streams of each terminal based on the data transmission speed of the terminal and the terminal determined by the upper scheduler, and performs MU-MIMO precoding for each terminal to perform MU-MIMO precoding to the destination terminal. MU-MIMO transmission is performed. Since the wireless base station system described in Patent Document 1 is composed of an upper wireless base station and a lower wireless base station which is a base station capable of wirelessly connecting to a mobile terminal, the lower wireless base station can be realized with a simple configuration. Will be done.
国際公開第２０１９／００３２９８号International Publication No. 2019/003298
　しかしながら、特許文献１に記載の下位無線基地局は、上位スケジューラによって決定された端末へ信号ストリームを伝送するが、この信号ストリームは、端末が備える複数のアンテナ間、または端末間の空間相関が高い信号ストリームである場合がある。このような空間相関が高い信号ストリームをＭＵ－ＭＩＭＯに含めてプリコーディングを適用すると下位無線基地局のスループットおよび信号電力対干渉雑音電力比（ＳＩＮＲ：Signal-to-Interference　plus　Noise　power　Ratio）などの通信品質が劣化するという問題があった。 However, the lower radio base station described in Patent Document 1 transmits a signal stream to a terminal determined by a higher scheduler, and this signal stream has a high spatial correlation between a plurality of antennas included in the terminal or between terminals. It may be a signal stream. When such a signal stream with high spatial correlation is included in MU-MIMO and precoding is applied, the throughput of the lower radio base station and the signal power to interference noise power ratio (SINR: Signal-to-Interference plus Noise power Ratio) can be obtained. There was a problem that the communication quality deteriorated.
　本発明は、上記に鑑みてなされたものであって、スループットおよび通信品質の劣化を抑制することができる下位無線基地局を得ることを目的とする。 The present invention has been made in view of the above, and an object of the present invention is to obtain a lower radio base station capable of suppressing deterioration of throughput and communication quality.
　上述した課題を解決し、目的を達成するために、本発明に係る下位無線基地局は、信号ストリームを割り当てる複数の送信先端末と、複数の送信先端末のデータ伝送速度とを上位無線基地局から通知され、複数の送信先端末およびデータ伝送速度に基づいて、複数の送信先端末に対応する伝送路の状態に基づく行列を算出し、行列の要素の絶対値があらかじめ定められたしきい値を満たさない伝送路を用いないように送信先端末の信号ストリーム数を決定するランク制御部と、送信先端末に対応する信号ストリームにMulti　User－Multiple　Input　Multiple　Outputプリコーディングを行う信号処理部と、を備えることを特徴とする。 In order to solve the above-mentioned problems and achieve the object, the lower radio base station according to the present invention sets a plurality of destination terminals to which signal streams are assigned and data transmission speeds of the plurality of destination terminals as higher radio base stations. Is notified from, and based on multiple destination terminals and data transmission speed, a matrix based on the state of the transmission line corresponding to multiple destination terminals is calculated, and the absolute value of the elements of the stream is a predetermined threshold value. A rank control unit that determines the number of signal streams of the destination terminal so as not to use a transmission line that does not satisfy the above, and a signal processing unit that performs Multi User-Multiple Input Multiple Output precoding on the signal stream corresponding to the destination terminal. It is characterized by having.
　本発明にかかる下位無線基地局は、スループットおよび通信品質の劣化を抑制することができるという効果を奏する。 The lower radio base station according to the present invention has the effect of suppressing deterioration of throughput and communication quality.
実施の形態にかかる無線基地局システムの構成例を示す図The figure which shows the configuration example of the radio base station system which concerns on embodiment 実施の形態にかかる上位基地局の構成例を示す図The figure which shows the configuration example of the upper base station which concerns on embodiment 実施の形態にかかる下位基地局の構成例を示す図The figure which shows the configuration example of the lower base station which concerns on embodiment 実施の形態の制御回路の構成例を示す図The figure which shows the structural example of the control circuit of embodiment
　以下に、本発明の実施の形態にかかる下位無線基地局および空間多重ストリーム数の制御方法を図面に基づいて詳細に説明する。なお、この実施の形態によりこの発明が限定されるものではない。 Hereinafter, the method for controlling the number of lower radio base stations and the number of spatial multiplex streams according to the embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.
実施の形態．
　図１は、実施の形態にかかる無線基地局システムの構成例を示す図である。無線基地局システム１００は、上位基地局１０と、下位基地局２０－１～２０－Ｍ（Ｍは１以上の整数）と、を備える。上位基地局１０は、後述する上位スケジューリングを行う無線基地局である。下位基地局２０－１～２０－Ｍを区別せずに示すときは、適宜、下位基地局２０と称する。下位基地局２０は、後述する下位スケジューリングを行う無線基地局である。 Embodiment.
FIG. 1 is a diagram showing a configuration example of a radio base station system according to an embodiment. The radio base station system 100 includes an upper base station 10 and lower base stations 20-1 to 20-M (M is an integer of 1 or more). The higher-level base station 10 is a radio base station that performs higher-level scheduling described later. When the lower base stations 20-1 to 20-M are shown without distinction, they are appropriately referred to as lower base stations 20. The lower base station 20 is a radio base station that performs lower scheduling, which will be described later.
　無線基地局システム１００は、ＭＢＨ（Mobile　Back　Haul）と接続し、ＭＢＨとの間でデータの送受信を行う。ＭＢＨとは、３ＧＰＰ（Third　Generation　Partnership　Project）またはＩＴＵ－Ｒ（International　Telecommunication　Union　Radiocommunication　Sector）で規定されるネットワークであり、ＳＧＳＮ（Serving　General-packet-radio-service　Support　Node）などの上位ネットワーク装置が設置されたサイトの間と、基地局とを接続するネットワークである。ＳＧＳＮは、３ＧＰＰで規定されている移動端末のコアネットワークを構成するノードの１つで、パケット通信時のユーザの認証、ＩＰ（Internet　Protocol）アドレスなどの情報の制御を行う。 The wireless base station system 100 connects to MBH (Mobile Back Haul) and transmits / receives data to / from MBH. MBH is a network defined by 3GPP (Third Generation Partnership Project) or ITU-R (International Telecommunication Union Radiocommunication Sector), and higher-level network devices such as SGSN (Serving General-packet-radio-service Support Node) are installed. It is a network that connects between the sites and the base station. SGSN is one of the nodes that make up the core network of mobile terminals defined by 3GPP, and controls information such as user authentication and IP (Internet Protocol) address during packet communication.
　無線基地局システム１００が備える各下位基地局２０が形成するセルには、移動端末９０－１－１～９０－Ｍ－ＫＭが存在している。下位基地局２０－ｍ（ｍは１≦ｍ≦Ｍの整数）が形成するセルには、ｊ（ｊは１以上の整数）台の移動端末９０－ｍ－１～９０－ｍ－ｊが存在している。各端末のダウンリンクデータ、すなわち基地局から端末へ向かう方向の通信のデータは、ＭＢＨから無線基地局システム１００へ入力され、無線基地局システム１００から各端末へ送信される。本実施の形態の無線基地局システム１００は、ＭＵ－ＭＩＭＯ方式が適用されている。 The cells each subordinate base station 20 forms a radio base station system 100 includes the mobile terminal 90-1-1 ~ 90-M-K M is present. In the cell formed by the lower base station 20-m (m is an integer of 1 ≦ m ≦ M), there are j (j is an integer of 1 or more) of mobile terminals 90-m-1 to 90-m-j. are doing. The downlink data of each terminal, that is, the communication data in the direction from the base station to the terminal is input from the MBH to the radio base station system 100 and transmitted from the radio base station system 100 to each terminal. The MU-MIMO system is applied to the radio base station system 100 of the present embodiment.
　ここで、一般的なＭＵ－ＭＩＭＯシステムについて説明する。ＭＵ－ＭＩＭＯシステムにおけるダウンリンク（以下、ＭＵ－ＭＩＭＯダウンリンクという）では、基地局から各端末へ同時に信号を送る。なお、アップリンクは本発明ではＭＵ－ＭＩＭＯ方式の対象外とする。 Here, a general MU-MIMO system will be described. In the downlink in the MU-MIMO system (hereinafter referred to as MU-MIMO downlink), a signal is sent from the base station to each terminal at the same time. In addition, the uplink is excluded from the scope of the MU-MIMO method in the present invention.
　ＭＵ－ＭＩＭＯダウンリンクの通信性能は、基地局と端末との間の伝送路状態に大きく依存する。このため、基地局は、ＭＵ－ＭＩＭＯダウンリンクの伝送を行う端末の組み合わせと、各端末にダウンリンクを伝送する信号ストリーム数、すなわち、ランク数（ＲＩ：Rank　Indicator）と、各信号のストリームの変調方式と、誤り訂正符号化方式であるＭＣＳ（Modulation　and　Coding　Scheme）とを決定する必要がある。なぜならば、ＲＩとＭＣＳは伝送路状態に応じて決定される必要があるからである。信号ストリームとは、基地局が各端末に伝送する空間多重信号系列のことである。なお、ＲＩは、ＩＥＥＥ８０２．１１ｎ、ＬＴＥ（Long　Term　Evolution）－Ａｄｖａｎｃｅｄなどの規格で用いられる信号ストリーム数を示し、ＭＣＳは一次変調方式と誤り訂正符号化方式の組み合わせを示すインデックスである。 The communication performance of the MU-MIMO downlink largely depends on the state of the transmission line between the base station and the terminal. Therefore, the base station has a combination of terminals that transmit MU-MIMO downlink, the number of signal streams that transmit the downlink to each terminal, that is, the number of ranks (RI: Rank Indicator), and the stream of each signal. It is necessary to determine the modulation method and the MCS (Modulation and Coding Scheme), which is an error correction coding method. This is because RI and MCS need to be determined according to the transmission line condition. A signal stream is a spatial multiplex signal sequence transmitted by a base station to each terminal. RI indicates the number of signal streams used in standards such as IEEE802.11n and LTE (Long Term Evolution) -Advanced, and MCS is an index indicating a combination of a primary modulation method and an error correction coding method.
　基地局は、決定されたＭＣＳの変調方式と誤り訂正符号化方式とを用いて、データ伝送速度を決定する。ＭＵ－ＭＩＭＯダウンリンクの伝送を行う端末の組み合わせと、各端末にダウンリンクを伝送する信号ストリーム数ＲＩと、各信号ストリームのＭＣＳとを決定する処理は、一般にスケジューリングと呼ばれ、スケジューリングを行う処理部は一般にスケジューラと呼ばれる。 The base station determines the data transmission rate by using the determined MCS modulation method and error correction coding method. The process of determining the combination of terminals that transmit MU-MIMO downlink, the number of signal streams RI that transmit the downlink to each terminal, and the MCS of each signal stream is generally called scheduling, and is a process of performing scheduling. The part is commonly called a scheduler.
　また、基地局には、スケジューリングに必要な端末毎の伝送路状態を示す伝送路情報、すなわち、ＣＳＩ（Channel　State　Information）を取得するＣＳＩ取得部が備えられている。ここで、ＣＳＩとは、基地局アンテナポートと端末アンテナポートとの間のＭＩＭＯ伝送路行列を複素数で表現したものを指すが、これに限らず、例えば伝送路行列を実数表現したものであってもよく、アンテナポートではなくビーム空間に対応するポートであっても良い。 Further, the base station is provided with a CSI acquisition unit that acquires transmission line information indicating the transmission line state for each terminal required for scheduling, that is, CSI (Channel State Information). Here, the CSI refers to a MIMO transmission line matrix between the base station antenna port and the terminal antenna port expressed by a complex number, but is not limited to this, and is, for example, a real number representation of the transmission line matrix. It may be a port corresponding to the beam space instead of the antenna port.
　基地局は、端末から基地局へ送信されるアップリンクの信号を用いてＣＳＩを推定することによって、各端末のＣＳＩを取得可能である。基地局が各端末のＣＳＩを取得する方法は、これに限らず、例えば、端末側で推定したＣＳＩ推定値が、端末側から基地局へフィードバックされる方法であってもよい。 The base station can acquire the CSI of each terminal by estimating the CSI using the uplink signal transmitted from the terminal to the base station. The method in which the base station acquires the CSI of each terminal is not limited to this, and may be, for example, a method in which the CSI estimated value estimated on the terminal side is fed back from the terminal side to the base station.
　基地局では、スケジューラで決定した情報に基づき、ＭＵ－ＭＩＭＯダウンリンクのための無線信号処理、すなわち、ＭＵ－ＭＩＭＯ信号処理を行い、基地局が備える複数のアンテナからＭＵ－ＭＩＭＯダウンリンクの信号を送信する。ＭＵ－ＭＩＭＯ信号処理としては、各端末向けのデータ信号に対する誤り訂正符号化および一次変調により生成された複数の信号ストリームについて全端末分を空間多重化するプリコーディングが挙げられる。しかしプリコーディングに限らず、ＭＵ－ＭＩＭＯ信号処理は、ＭＵ－ＭＩＭＯダウンリンクを実現する無線信号処理であればいかなる処理であってもよい。 The base station performs radio signal processing for MU-MIMO downlink, that is, MU-MIMO signal processing based on the information determined by the scheduler, and outputs MU-MIMO downlink signals from a plurality of antennas provided in the base station. Send. Examples of the MU-MIMO signal processing include error-correction coding for data signals for each terminal and precoding for spatial multiplexing of all terminals for a plurality of signal streams generated by primary modulation. However, the MU-MIMO signal processing is not limited to precoding, and may be any processing as long as it is a radio signal processing that realizes the MU-MIMO downlink.
　これまでに説明した一般的なＭＵ－ＭＩＭＯシステムでは、基地局は、階層化されていないが、本実施の形態の無線基地局システム１００では、特許文献１にて開示されているように、一般的なＭＵ－ＭＩＭＯシステムの基地局のスケジューラの機能を、上位基地局１０と下位基地局２０とに振り分ける。すなわち、一般的なＭＵ－ＭＩＭＯシステムの基地局のスケジューラを、上位基地局１０の上位スケジューラ部と下位基地局２０の下位スケジューラ部とに分ける。一般的なＭＵ－ＭＩＭＯシステムの基地局に備えられているＣＳＩ取得部は、下位基地局２０に備えられる。ＭＵ－ＭＩＭＯ信号処理は下位基地局２０で行う。上位基地局１０と下位基地局２０とは一般的に有線接続され通信するが、これに限らず、無線で通信してもよい。 In the general MU-MIMO system described so far, the base stations are not layered, but in the radio base station system 100 of the present embodiment, as disclosed in Patent Document 1, general The function of the scheduler of the base station of the MU-MIMO system is divided into the upper base station 10 and the lower base station 20. That is, the scheduler of the base station of a general MU-MIMO system is divided into an upper scheduler unit of the upper base station 10 and a lower scheduler unit of the lower base station 20. The CSI acquisition unit provided in the base station of a general MU-MIMO system is provided in the lower base station 20. MU-MIMO signal processing is performed by the lower base station 20. The upper base station 10 and the lower base station 20 are generally connected by wire and communicate with each other, but the present invention is not limited to this, and wireless communication may be performed.
　図２は、本実施の形態にかかる上位基地局１０の構成例を示す図である。上位基地局１０はリソース制御部１１を有する。リソース制御部１１は、Ｍ台の下位基地局２０それぞれに対応するＭ個の上位スケジューラ部１２－１～１２－Ｍを有する。上位スケジューラ部１２－１～１２－Ｍを区別せずに示すときは、適宜、上位スケジューラ部１２と称する。 FIG. 2 is a diagram showing a configuration example of the upper base station 10 according to the present embodiment. The upper base station 10 has a resource control unit 11. The resource control unit 11 has M upper scheduler units 12-1 to 12-M corresponding to each of the M lower base stations 20. When the upper scheduler units 12-1 to 12-M are shown without distinction, they are appropriately referred to as the upper scheduler unit 12.
　上位スケジューラ部１２－ｍは、ｊ台の移動端末から実際にデータ伝送を行うＬｍ（Ｌｍは１以上ｊ以下の整数）台の移動端末を選定する。選定する方法は、下位基地局２０－ｍから通知されたｊ台分の端末容量指標またはＣＳＩと、ＭＢＨから入力されるｊ台分の移動端末に対するデータ伝送速度またはデータ伝送量の要求値（またはデータ伝送のための待機バッファ量）とを考慮し選定する方法である。また、上位スケジューラ部１２－ｍは、各移動端末のデータ伝送速度、またはデータ伝送量を決定する。この処理を上位スケジューリングと称する。なお、各移動端末の端末容量指標は実数スカラ量であり、詳細については特許文献１に記載されている。 The upper scheduler unit 12-m selects L m (L m is an integer of 1 or more and j or less) of mobile terminals that actually transmit data from j mobile terminals. The selection method is the terminal capacity index or CSI for j units notified from the lower base station 20-m and the required value (or data transmission amount) of the data transmission speed or data transmission amount for j mobile terminals input from MBH. This method is selected in consideration of the amount of standby buffer for data transmission). Further, the upper scheduler unit 12-m determines the data transmission speed or the data transmission amount of each mobile terminal. This process is called upper scheduling. The terminal capacity index of each mobile terminal is a real number scalar amount, and the details are described in Patent Document 1.
　上位スケジューラ部１２－ｍは、選定した送信先端末と、各送信先端末の要求データ伝送速度とを、下位基地局２０－ｍに通知する。なお送信先端末とは、上位スケジューラ部１２－ｍが選定したＬｍ台の移動端末である。上位スケジューリングの具体的なアルゴリズムとしては、例えば、上位スケジューラ部１２－ｍは、ｊ台の移動端末のうち所要の端末容量指標以上となる移動端末から、データ伝送要求値の大きいものから順にＬｍ台の送信先端末を選定する方法がある。選定された送信先端末の要求データ伝送速度は、当該送信先端末の端末容量指標を超えないもののうち最大となるデータ伝送速度を用いることができるが、この限りではない。 The upper scheduler unit 12-m notifies the lower base station 20-m of the selected destination terminal and the requested data transmission speed of each destination terminal. The destination terminal is a mobile terminal in the Lm range selected by the upper scheduler unit 12-m. As a specific algorithm for higher-level scheduling, for example, the upper-level scheduler unit 12-m is L m in order from the mobile terminals having the required terminal capacity index or more among the j mobile terminals, in descending order of the data transmission request value. There is a method of selecting a destination terminal. As the required data transmission speed of the selected destination terminal, the maximum data transmission speed can be used among those that do not exceed the terminal capacity index of the destination terminal, but this is not the case.
　図３は、本実施の形態にかかる下位基地局２０の構成例を示す図である。ここでは、Ｍ台の下位基地局２０のうち下位基地局２０－ｍを例に挙げて説明する。下位基地局２０－１～２０－Ｍは全て同じ構成である。下位基地局２０－ｍが備えるアンテナの数はＴｍ（Ｔｍは１以上の整数）、下位基地局２０－ｍが形成するセルに存在する移動端末数はｊとする。 FIG. 3 is a diagram showing a configuration example of the lower base station 20 according to the present embodiment. Here, among the M lower base stations 20, the lower base station 20-m will be described as an example. The lower base stations 20-1 to 20-M all have the same configuration. The number of antennas provided in the lower base station 20-m is T m (T m is an integer of 1 or more), and the number of mobile terminals existing in the cell formed by the lower base station 20-m is j.
　下位基地局２０－ｍは、下位スケジューラ部２１と、無線ベースバンド信号処理部２２と、無線ＲＦ（Radio　Frequency）信号処理部２３と、Ｔｍ本のアンテナ２４－１～２４－Ｔｍとを備える。下位スケジューラ部２１は、ランク制御部２１１を備える。無線ベースバンド信号処理部２２は、ＣＳＩ取得部２２１とＭＵ－ＭＩＭＯ信号処理部２２２とを備える。また、ＣＳＩ取得部２２１を単に取得部とも称する。ＭＵ－ＭＩＭＯ信号処理部２２２を単に信号処理部とも称する。無線ＲＦ信号処理部２３を単に無線信号処理部とも称する。下位スケジューラは、単にスケジューラとも呼ばれる。 The lower base station 20-m includes a lower scheduler unit 21, a radio baseband signal processing unit 22, a radio RF (Radio Frequency) signal processing unit 23, and T m antennas 24-1 to 24-T m . Be prepared. The lower scheduler unit 21 includes a rank control unit 211. The wireless baseband signal processing unit 22 includes a CSI acquisition unit 221 and a MU-MIMO signal processing unit 222. Further, the CSI acquisition unit 221 is also simply referred to as an acquisition unit. The MU-MIMO signal processing unit 222 is also simply referred to as a signal processing unit. The radio RF signal processing unit 23 is also simply referred to as a radio signal processing unit. The subordinate scheduler is also simply called the scheduler.
　ＣＳＩ取得部２２１は、移動端末９０－ｍ－１～９０－ｍ－ｊから下位基地局２０－ｍへのアップリンク信号から推定することにより、ＣＳＩを取得し、このＣＳＩを下位スケジューラ部２１に入力する。推定方法については特に限定されず、一般的な方法でよい。ＭＵ－ＭＩＭＯ信号処理部２２２は、上位スケジューラ部１２で選定されたＬｍ台の送信先端末のＭＵ－ＭＩＭＯダウンリンク用ベースバンド信号を生成する。無線ＲＦ信号処理部２３は、ＭＵ－ＭＩＭＯダウンリンク用ベースバンド信号を無線ＲＦ周波数の無線信号に変換する。アンテナ２４－１～２４－Ｔｍは無線ＲＦ信号を各送信先端末に送出する。 The CSI acquisition unit 221 acquires the CSI by estimating from the uplink signal from the mobile terminals 90-m-1 to 90-m-j to the lower base station 20-m, and transfers this CSI to the lower scheduler unit 21. input. The estimation method is not particularly limited, and a general method may be used. MU-MIMO signal processing unit 222 to generate a baseband signal for MU-MIMO downlink L m stand destination terminal that is selected by the upper scheduler section 12. The radio RF signal processing unit 23 converts the MU-MIMO downlink baseband signal into a radio signal having a radio RF frequency. Antennas 24-1 ~ 24-T m sends a wireless RF signal to each destination terminal.
　下位スケジューラ部２１は、ＣＳＩ取得部２２１から入力されるｊ台の端末のＣＳＩを、上位スケジューラ部１２－ｍが取扱い易いように端末の伝送路能力として値を抽象化、すなわち単一の実数スカラ量に変換する。伝送路能力とは、当該端末に対してダウンリンク伝送可能なデータ容量を示す。伝送路能力は、一般に伝送路情報から算出可能である。今後は端末数およびアンテナ数が増加することが予想され、これにより伝送路情報自体の情報量が増え、伝送路情報自体を送信すると回線が逼迫する可能性がある。伝送路情報自体の代わりに端末に対してダウンリンク伝送可能なデータ容量を示す単一の実数スカラ量を用いると回線の逼迫を抑制することができる。下位スケジューラ部２１は単一の実数スカラ量に変換されたＣＳＩである端末容量指標を上位スケジューラ部１２へ送信する。 The lower scheduler unit 21 abstracts the CSI of j terminals input from the CSI acquisition unit 221 as the transmission path capacity of the terminals so that the upper scheduler unit 12-m can easily handle it, that is, a single real number scalar. Convert to quantity. The transmission line capacity indicates the amount of data that can be downlinked to the terminal. The transmission line capacity can generally be calculated from the transmission line information. It is expected that the number of terminals and the number of antennas will increase in the future, which will increase the amount of information of the transmission line information itself, and there is a possibility that the line will be tight when the transmission line information itself is transmitted. By using a single real number scalar amount indicating the data capacity that can be downlinked to the terminal instead of the transmission line information itself, it is possible to suppress the tightness of the line. The lower scheduler unit 21 transmits a terminal capacity index, which is a CSI converted into a single real number scalar amount, to the upper scheduler unit 12.
　ＣＳＩの特徴を表現可能な、すなわち抽象化可能なスカラ量として、ＭＩＭＯ伝送容量が挙げられる。ＭＩＭＯ伝送容量は、通信容量、チャネル容量、またはShannon容量とも呼ばれる。本実施の形態では、特許文献１にて開示されている端末容量指標Ｃｍ,j(f)を用いるものとする。ｆは、下位基地局２０－ｍと、移動端末９０－ｍ－ｊとの間の無線ＲＦ周波数である。下位基地局２０がＣＳＩを上位基地局１０へ通知する場合、ＣＳＩを端末毎にＭＩＭＯ伝送路行列Ｈｍ,ｊ(f)の行列要素数分だけ上位基地局１０に通知する必要があったが、ＣＳＩを実数スカラ量であるＣｍ,j(f)に抽象化することにより、当該通知に係る情報伝送量を（Ｈｍ,ｊ(f)の行列要素数×２）分の１に削減することができる。例えば、移動端末９０－ｍ－ｊの受信アンテナポート数が４、下位基地局２０－ｍのアンテナポート数をＮｍ＝１６とすると、本抽象化（ＣＳＩを単一の実数スカラ量に変換すること）により、ＣＳＩ（複素数行列）がこのまま通知される場合に比べて情報伝送量を１／１２８に削減できる。 MIMO transmission capacity is an example of a scalar quantity that can express the characteristics of CSI, that is, can be abstracted. MIMO transmission capacity is also referred to as channel capacity, channel capacity, or Shannon capacity. In this embodiment, the terminal capacity index C m, j (f) disclosed in Patent Document 1 is used. f is a radio RF frequency between the lower base station 20-m and the mobile terminal 90-m-j. When the lower base station 20 notifies the upper base station 10 of the CSI, it is necessary to notify the upper base station 10 of the CSI by the number of matrix elements of the MIMO transmission line matrix H m, j (f) for each terminal. By abstracting CSI to C m, j (f) , which is a real scalar quantity, the amount of information transmission related to the notification is reduced to 1/2 (number of matrix elements of H m, j (f) x 2). can do. For example, assuming that the number of receiving antenna ports of the mobile terminal 90-mj is 4 and the number of antenna ports of the lower base station 20-m is N m = 16, this abstraction (converts CSI into a single real scalar quantity). Therefore, the amount of information transmission can be reduced to 1/128 as compared with the case where the CSI (complex number matrix) is notified as it is.
　下位スケジューラ部２１は、上位基地局１０の上位スケジューラ部１２－ｍから通知されるＬｍ台の送信先端末について、併せて通知された各送信先端末の要求データ伝送速度に基づき、各送信先端末のＲＩとＭＣＳを決定する。この処理手続きを下位スケジューリングと称する。また下位スケジューリングは、上位基地局１０により通知される１つ以上の移動端末のなかから選択された移動端末である送信先端末と送信先端末のデータ伝送速度とに基づいて、送信先端末の信号ストリーム数および変調符号化方式を決定するスケジューラであるともいえる。 Lower scheduler unit 21, for L m stand destination terminal notified from the host scheduler section 12-m of the upper base station 10, based on the requested data transmission rate of each destination terminal that is collectively notified, each destination Determine the RI and MCS of the terminal. This processing procedure is called sub-scheduling. Further, the lower scheduling is based on the data transmission speed of the destination terminal and the destination terminal, which are mobile terminals selected from one or more mobile terminals notified by the upper base station 10, and the signal of the destination terminal. It can be said that it is a scheduler that determines the number of streams and the modulation coding method.
　実施の形態にかかる無線基地局システム１００のハードウェア構成について説明する。リソース制御部１１、上位スケジューラ部１２、下位スケジューラ部２１、無線ベースバンド信号処理部２２、ランク制御部２１１、ＣＳＩ取得部２２１、およびＭＵ－ＭＩＭＯ信号処理部２２２は、各処理を行う電子回路である処理回路により実現される。無線ＲＦ信号処理部２３は、送信機および受信機である。 The hardware configuration of the wireless base station system 100 according to the embodiment will be described. The resource control unit 11, the upper scheduler unit 12, the lower scheduler unit 21, the wireless baseband signal processing unit 22, the rank control unit 211, the CSI acquisition unit 221 and the MU-MIMO signal processing unit 222 are electronic circuits that perform each processing. It is realized by a certain processing circuit. The radio RF signal processing unit 23 is a transmitter and a receiver.
　本処理回路は、専用のハードウェアであっても、メモリ及びメモリに格納されるプログラムを実行するＣＰＵ（Central　Processing　Unit、中央演算装置）を備える制御回路であってもよい。ここでメモリとは、例えば、ＲＡＭ（Random　Access　Memory）、ＲＯＭ（Read　Only　Memory）、フラッシュメモリなどの、不揮発性または揮発性の半導体メモリ、磁気ディスク、光ディスクなどが該当する。図４は、実施の形態の制御回路の構成例を示す図である。この制御回路は例えば、図４に示す構成の制御回路４００となる。処理回路が、専用のハードウェアである場合、処理回路は、例えば、ＡＳＩＣ（Application　Specific　Integrated　Circuit）、ＦＰＧＡ（Field　Programmable　Gate　Array）、またはこれらを組み合わせたものである。 This processing circuit may be dedicated hardware or a control circuit including a memory and a CPU (Central Processing Unit, central processing unit) that executes a program stored in the memory. Here, the memory corresponds to, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), or a flash memory, a magnetic disk, an optical disk, or the like. FIG. 4 is a diagram showing a configuration example of the control circuit of the embodiment. This control circuit is, for example, the control circuit 400 having the configuration shown in FIG. When the processing circuit is dedicated hardware, the processing circuit is, for example, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.
　図４に示すように、制御回路４００は、ＣＰＵであるプロセッサ４００ａと、メモリ４００ｂとを備える。図４に示す制御回路４００により実現される場合、プロセッサ４００ａがメモリ４００ｂに記憶された、各処理に対応するプログラムを読みだして実行することにより実現される。また、メモリ４００ｂは、プロセッサ４００ａが実施する各処理における一時メモリとしても使用される。 As shown in FIG. 4, the control circuit 400 includes a processor 400a which is a CPU and a memory 400b. When it is realized by the control circuit 400 shown in FIG. 4, it is realized by the processor 400a reading and executing the program corresponding to each process stored in the memory 400b. The memory 400b is also used as a temporary memory in each process performed by the processor 400a.
　無線基地局システム１００では、上位基地局１０から下位基地局２０へ、ＭＵ－ＭＩＭＯ伝送を行う複数の送信先端末と各送信先端末のデータ伝送速度が指示される。このとき下位基地局２０は、上位基地局１０からの指示に基づき下位スケジューリングを行う。ここで、ＭＵ－ＭＩＭＯ伝送では送信先端末の組み合わせおよび各送信先端末への信号ストリーム数によって全体のＭＩＭＯ伝送路行列の構成が変わり、これらのパラメータの決定が伝送特性に影響を及ぼす。このため、下位基地局２０が伝送するストリーム数を仮決めするための基準があるほうがよいと考えられる。例えば、下位基地局２０は、上位基地局１０からのＭＵ－ＭＩＭＯ伝送を行う複数の送信先端末と各送信先端末のデータ伝送速度の指示に加えて、下位スケジューリングにおいて全送信先端末に少なくとも１つ信号ストリームを割り当てることが挙げられる。また、例えば、下位基地局２０は、下位スケジューリングにおいて、送信先端末に要求されるデータ伝送速度が速い送信先端末に優先して信号ストリームを割り当てることが挙げられる。１つのストリームが伝送される時間は、３ＧＰＰで規定されるサブフレームまたはスロットの単位で決定される。ＬＴＥの場合、１ｍｓごとにストリームが伝送される。５Ｇ（5th　Generation）の場合、０．５ｍｓまたは０．２５ｍｓごとにストリームが伝送される。本発明にかかるランク制御部２１１は、上記の下位スケジューリング基準を満たすよう、暫定プリコーディング行列演算に基づき各送信先端末へ伝送する信号ストリーム数を決定する。 In the wireless base station system 100, a plurality of destination terminals that perform MU-MIMO transmission and data transmission speeds of each destination terminal are instructed from the upper base station 10 to the lower base station 20. At this time, the lower base station 20 performs lower scheduling based on the instruction from the upper base station 10. Here, in MU-MIMO transmission, the configuration of the entire MIMO transmission line matrix changes depending on the combination of destination terminals and the number of signal streams to each destination terminal, and the determination of these parameters affects the transmission characteristics. Therefore, it is considered better to have a standard for tentatively determining the number of streams transmitted by the lower base station 20. For example, the lower base station 20 may indicate at least one to all the destination terminals in the lower scheduling, in addition to instructing the data transmission speeds of the plurality of destination terminals and each destination terminal that perform MU-MIMO transmission from the upper base station 10. One is to allocate a signal stream. Further, for example, in the lower scheduling, the lower base station 20 may preferentially allocate a signal stream to a destination terminal having a high data transmission speed required for the destination terminal. The time that one stream is transmitted is determined in units of subframes or slots specified by 3GPP. In the case of LTE, the stream is transmitted every 1 ms. In the case of 5G (5th Generation), the stream is transmitted every 0.5 ms or 0.25 ms. The rank control unit 211 according to the present invention determines the number of signal streams to be transmitted to each destination terminal based on the provisional precoding matrix operation so as to satisfy the above-mentioned lower scheduling criteria.
　暫定プリコーディング行列演算について説明する。暫定プリコーディング行列演算は、信号ストリーム数を決定するための逆行列を規範とした演算である。また、暫定プリコーディング行列演算は、後述するＭＵ－ＭＩＭＯ信号処理部２２２がダウンリンク伝送に用いるＭＵ－ＭＩＭＯプリコーディングのためのプリコーディング行列演算とは異なるものである。 The provisional precoding matrix operation will be explained. The provisional precoding matrix operation is an operation based on the inverse matrix for determining the number of signal streams. Further, the provisional precoding matrix operation is different from the precoding matrix operation for MU-MIMO precoding used by the MU-MIMO signal processing unit 222 described later for downlink transmission.
　例として、無線基地局システム１００では、送信先端末台数Ｌｍ＝４、基地局送信アンテナポート数Ｔｍ＝８、各端末が２本の受信アンテナポートを備えるものとする。４台の送信先端末をそれぞれ端末ａ、端末ｂ、端末ｃ、端末ｄとする。各端末に対応する２行８列（行数：受信アンテナポート数、列数：基地局送信アンテナポート数Ｔｍ）の伝送路行列Ａａ、Ａｂ、Ａｃ、Ａｄを、それぞれ式（１）、式（２）、式（３）、および式（４）のように定義する。なお、本明細書では、数式においては行列を示す文字を太字で表すが、本文中では通常文字で示す。 As an example, in the wireless base station system 100, it is assumed that the number of destination terminals L m = 4, the number of base station transmission antenna ports T m = 8, and each terminal has two receiving antenna ports. Let the four destination terminals be terminal a, terminal b, terminal c, and terminal d, respectively. The transmission line matrices Aa, Ab, Ac, and Ad of 2 rows and 8 columns (number of rows: number of receiving antenna ports, number of columns: number of base station transmitting antenna ports Tm ) corresponding to each terminal are expressed by equations (1) and (1) and (A), respectively. It is defined as (2), equation (3), and equation (4). In this specification, the characters indicating the matrix are shown in bold in the mathematical formula, but are shown in normal characters in the text.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　各端末の伝送路行列を部分行列として構成した８行８列の全体伝送路行列Ａを式（５）のように定義する。全体伝送路行列Ａは複数の送信先端末に対応する伝送路の状態を示す行列であるともいえる。 The entire transmission line matrix A of 8 rows and 8 columns, which is composed of the transmission line matrix of each terminal as a submatrix, is defined as in equation (5). It can be said that the entire transmission line matrix A is a matrix indicating the state of the transmission lines corresponding to a plurality of destination terminals.
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　ここで、各端末に要求されるデータ伝送速度は端末ｄが最も速く、次に端末ｂ、端末ａ、端末ｃの順に速くなるものとする。これに基づき、ランク制御部２１１は、前述した下位スケジューリングのデータ伝送速度が速い送信先端末を優先するように優先順を反映し、全体伝送路行列Ａの部分行列を式（６）のように入れ替える。全体伝送路行列Ａの部分行列を式（６）のように入れ替えた行列を全体伝送路行列Ａ￣とする。式（６）で下位スケジューリングのデータ伝送速度が速い送信先端末を優先するように優先順を反映させる理由については後述する。 Here, it is assumed that the data transmission speed required for each terminal is the fastest in the terminal d, followed by the terminal b, the terminal a, and the terminal c in that order. Based on this, the rank control unit 211 reflects the priority order so as to give priority to the destination terminal having the faster data transmission speed of the lower scheduling described above, and sets the submatrix of the entire transmission line matrix A as in the equation (6). Replace. The matrix in which the submatrix of the entire transmission line matrix A is replaced as in Eq. (6) is defined as the total transmission line matrix A￣. The reason for reflecting the priority order in the equation (6) so as to give priority to the destination terminal having the faster data transmission speed of the lower scheduling will be described later.
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　更に、前述した下位スケジューリングの全送信先端末に少なくとも１ストリームの信号伝送を行うようにするために、ランク制御部２１１は、各端末から受信ポートに対応するアンテナを１つずつピックアップし４行分を端末ｄ、端末ｂ、端末ａ、端末ｃの優先順で上から並べ、次に残る４行を同様の優先順で並べる。これを全体伝送路行列Ａ￣￣とする。全体伝送路行列Ａ￣￣は、式（７）で表される。 Further, in order to transmit a signal of at least one stream to all the destination terminals of the lower scheduling described above, the rank control unit 211 picks up one antenna corresponding to the receiving port from each terminal for four lines. Are arranged from the top in the order of priority of terminal d, terminal b, terminal a, and terminal c, and the remaining four lines are arranged in the same order of priority. This is referred to as the entire transmission line matrix A￣￣. The entire transmission line matrix A￣￣ is represented by the equation (7).
Figure JPOXMLDOC01-appb-M000004
Figure JPOXMLDOC01-appb-M000004
　式（７）においてａｉ（ｉ＝１、２、…、７）は８次元ベクトルであり、ａＴはベクトル及び行列の転置を示す。以上の行列内の行の入替は伝送路行列の特性を変えずに演算の利便性を改善する操作である。 In equation (7), a i (i = 1, 2, ..., 7) is an 8-dimensional vector, and a T indicates the transpose of the vector and the matrix. Swapping rows in the above matrix is an operation that improves the convenience of calculation without changing the characteristics of the transmission line matrix.
　次に、全体伝送路行列Ａ￣￣の逆行列を考える。一般に全体伝送路行列は長方形行列（横長）であるため、ランク制御部２１１は、全体伝送路行列のＭＰ（Moore-Penrose）一般逆行列を用いて伝送路空間の直交化を図る。暫定プリコーディング行列Ｗは、式（８）に示される全体伝送路行列Ａ￣￣のＭＰ一般逆行列により求められる。ＭＰ一般逆行列は、複数の送信先端末に対応する伝送路の状態に基づいて算出される行列とも呼ばれる。 Next, consider the inverse matrix of the entire transmission line matrix A￣￣. Since the entire transmission line matrix is generally a rectangular matrix (horizontally long), the rank control unit 211 aims to orthogonalize the transmission line space by using the MP (Moore-Penrose) general inverse matrix of the entire transmission line matrix. The provisional precoding matrix W is obtained by the MP general inverse matrix of the total transmission line matrix A￣￣ shown in the equation (8). The MP general inverse matrix is also called a matrix calculated based on the state of the transmission line corresponding to a plurality of destination terminals.
Figure JPOXMLDOC01-appb-M000005
Figure JPOXMLDOC01-appb-M000005
　式（８）においてＡ＋１はＭＰ一般逆行列の演算子、ＡＨはベクトル及び行列のエルミート転置である。ここで、実質的な逆行列演算では正方行列部分（Ａ￣￣Ａ￣￣Ｈ）－１を用いるため、Ａ￣￣Ａ￣￣Ｈを行列Ｂとおく。行列Ｂは、式（９）で表される。 In equation (8), A + 1 is the MP general inverse matrix operator, and A H is the Hermitian transpose of vectors and matrices. Here, for using the square matrix portion (A¯¯A¯¯ H) -1 is a substantial inverse matrix calculation, put the matrix B the A¯¯A¯¯ H. The matrix B is represented by the equation (9).
Figure JPOXMLDOC01-appb-M000006
Figure JPOXMLDOC01-appb-M000006
　式（９）において、ｂｉ，ｊはｂｉ，ｊ＝ａＴ ｉ　ａ＊ｊの関係にある。また、行列Ｂはエルミート行列である。行列Ｂの逆行列演算としてガウス・ジョルダン法を適用する。ガウス・ジョルダン法は、ガウスの消去法、または掃き出し法とも呼ばれる。ガウス・ジョルダン法は３つの行基本変形を活用し対象の行列を対角化するとともに対象の行列の逆行列も算出できる手法である。１つ目の行基本変形は、２つの行を入れ替える変形である。２つ目の行基本変形は、ある行を０でない値で定数倍する変形である。３つ目の行基本変形は、ある行に他のある行の定数倍を加える変形である。ガウス・ジョルダン法は線形代数における古典的な逆行列解法（連立一次方程式解法）であり、ここでは詳細な原理の説明は省く。演算対象の８次エルミート行列Ｂと、初期値として単位行列を設定した８次正方行列Ｃをそれぞれ部分行列とした８行１６列の拡大行列Ｄを式（１０）のように定義する。 In the formula (9), b i, j is a relationship of b i, j = a T i a * j. Further, the matrix B is a Hermitian matrix. The Gauss-Jordan method is applied as the inverse matrix operation of the matrix B. The Gauss-Jordan method is also called Gaussian elimination or sweeping method. The Gauss-Jordan method is a method that can diagonalize the target matrix and calculate the inverse matrix of the target matrix by utilizing the three elementary transformations. The first row basic transformation is a transformation that swaps two rows. The second elementary transformation is a transformation in which a row is multiplied by a constant with a non-zero value. The third elementary transformation is a transformation that adds a constant multiple of one row to another. The Gauss-Jordan method is a classical inverse matrix solution method (simultaneous linear equation solution method) in linear algebra, and detailed explanation of the principle is omitted here. An augmented matrix D of 8 rows and 16 columns, each of which is a submatrix of an eighth-order Hermitian matrix B to be calculated and an eighth-order square matrix C in which an identity matrix is set as an initial value, is defined as in equation (10).
Figure JPOXMLDOC01-appb-M000007
Figure JPOXMLDOC01-appb-M000007
　拡大行列Ｄにガウス・ジョルダン法を用いることで逆行列は算出される。演算対象の部分行列Ｂの範囲がＮ次正方行列のとき、ガウス・ジョルダン法は計Ｎステージの演算ステージを要し、第ｎ（ｎ＝１、２、…、Ｎ）ステージの演算では、ランク制御部２１１は、部分行列Ｂの第ｎ列の要素のうち対角要素であるｎ行ｎ列要素が１、ｎ行ｎ列以外の要素が０となるよう行基本変形を適用する。拡大行列Ｄの行全体に適用されるため、第１ステージから第Ｎステージまで演算を実施すると、最終的に部分行列Ｂの範囲は単位行列となり、部分行列Ｃの範囲は逆行列として算出される。 The inverse matrix is calculated by using the Gauss-Jordan method for the augmented matrix D. When the range of the submatrix B to be calculated is an Nth-order square matrix, the Gauss-Jordan method requires a total of N stages of calculation stages, and in the calculation of the nth (n = 1, 2, ..., N) stage, the rank The control unit 211 applies the row basic transformation so that among the elements of the nth column of the submatrix B, the n rows and n columns elements, which are diagonal elements, are 1, and the elements other than the n rows and n columns are 0. Since it is applied to the entire row of the augmented matrix D, when the operations are performed from the first stage to the Nth stage, the range of the submatrix B is finally calculated as the identity matrix, and the range of the submatrix C is calculated as the inverse matrix. ..
　ここで、ｎ行ｎ列要素を１とするにはｎ行ｎ列要素の値の逆数を第ｎ行に乗ずれば良い。このとき、ｎ行ｎ列要素の大きさが極めて小さい場合、この逆数は０で割ることに近くなるため発散傾向となり、このようなケースを避ける必要がある。各行は受信アンテナポートに対応しており、この事象が生じるのは当該受信アンテナポートに起因して端末アンテナ間及び端末間の空間相関が高い場合である。このため、当該受信アンテナポートをＭＵ－ＭＩＭＯに含めてプリコーディングを適用すると伝送性能が劣化する可能性がある。本発明では、しきい値τを導入し、ランク制御部２１１が第ｎステージで対角要素の大きさをチェックする。しきい値τは０より大きい実数スカラ値であり、対角要素の絶対値がしきい値τより小さい場合には、部分行列Ｂ及びＣの第ｎ行及び第ｎ列を削除し、部分行列Ｂ及びＣの次数を１つ減らして演算を進める。すなわち、拡大行列Ｄの行数が１つ減り、列数が２つ減ることとなる。全演算ステージが終了した後に残る拡大行列Ｄの行数が、算出されるＭＵ－ＭＩＭＯのランク数である。式（６）で下位スケジューリングのデータ伝送速度が速い送信先端末を優先するように優先順を反映させた理由について説明する。ガウス・ジョルダン法による逆行列演算は、一般的に上の行から処理を行う。このため、少なくとも最初の行が省かれて逆行列演算されることはなく、最優先で逆行列演算される。例えば、式（９）の２行目は、１行目と直交化が行われ、３行目は、１行目および２行目との直交化が行われる。このように、下の行ほど直交化が行われる行が増えるため、下の行ほど直交化による対角要素がしきい値以下となりやすく、下の行ほど除かれる確率が高くなる。 Here, in order to set the n-row n-column element to 1, the reciprocal of the value of the n-row n-column element may be multiplied by the nth row. At this time, if the size of the n-by-n-column element is extremely small, the reciprocal becomes close to dividing by 0 and tends to diverge, and such a case must be avoided. Each line corresponds to a receiving antenna port, and this event occurs when the spatial correlation between terminal antennas and between terminals is high due to the receiving antenna port. Therefore, if the receiving antenna port is included in MU-MIMO and precoding is applied, the transmission performance may deteriorate. In the present invention, the threshold value τ is introduced, and the rank control unit 211 checks the size of the diagonal element in the nth stage. If the threshold value τ is a real scalar value greater than 0 and the absolute value of the diagonal element is smaller than the threshold value τ, the nth row and nth column of the submatrix B and C are deleted, and the submatrix is deleted. The calculation proceeds by reducing the order of B and C by one. That is, the number of rows of the augmented matrix D is reduced by one, and the number of columns is reduced by two. The number of rows of the augmented matrix D remaining after all the calculation stages are completed is the calculated number of ranks of MU-MIMO. The reason why the priority order is reflected so as to give priority to the destination terminal having the faster data transmission speed of the lower scheduling in the equation (6) will be described. Inverse matrix operations by the Gauss-Jordan method generally start from the top row. Therefore, at least the first row is not omitted and the inverse matrix operation is performed, and the inverse matrix operation is performed with the highest priority. For example, the second line of the equation (9) is orthogonalized to the first line, and the third line is orthogonalized to the first and second lines. In this way, since the number of rows that are orthogonalized increases in the lower rows, the diagonal elements due to orthogonalization tend to be less than the threshold value in the lower rows, and the probability of being excluded increases in the lower rows.
　適用例を説明する。第１ステージでは、ランク制御部２１１は、まず部分行列Ｂの１行１列要素ｂ７，７の大きさ｜ｂ７，７｜としきい値τを比較する。ここでは｜ｂ７，７｜≧τであるとする。この場合、通常のガウス・ジョルダン法に従って第１ステージの演算を行う。第１ステージ演算の結果、拡大行列Ｄは、式（１１）の形となる。 An application example will be described. In the first stage, the rank control unit 211 first compares the size | b 7,7 | of the 1-row, 1-column elements b7,7 of the submatrix B with the threshold value τ. Here, it is assumed that | b 7,7 | ≧ τ. In this case, the first stage calculation is performed according to the usual Gauss-Jordan method. As a result of the first stage operation, the augmented matrix D has the form of equation (11).
Figure JPOXMLDOC01-appb-M000008
Figure JPOXMLDOC01-appb-M000008
　第２ステージでは、ランク制御部２１１は、まず第１ステージ演算後の部分行列Ｂの範囲の２行２列要素の大きさ｜ｂ３，３ （１）｜としきい値τとを比較する。ここでは｜ｂ３，３ （１）｜≧τであるとする。この場合、通常のガウス・ジョルダン法に従って第２ステージの演算を行う。第２ステージ演算の結果、拡大行列Ｄは、式（１２）の形となる。 In the second stage, the rank control unit 211 first compares the size | b 3,3 (1) | of the two-row, two-column element within the range of the submatrix B after the first stage calculation with the threshold value τ. Here, it is assumed that | b 3,3 (1) | ≧ τ. In this case, the second stage calculation is performed according to the usual Gauss-Jordan method. As a result of the second stage operation, the augmented matrix D has the form of equation (12).
Figure JPOXMLDOC01-appb-M000009
Figure JPOXMLDOC01-appb-M000009
　このように、第３ステージから第５ステージまで対角要素の大きさがしきい値τ以上の大きさであるとすると、第５ステージ終了後は、拡大行列Ｄは、式（１３）の形となる。 As described above, assuming that the size of the diagonal elements from the third stage to the fifth stage is the size of the threshold value τ or more, the augmented matrix D becomes the form of the equation (13) after the completion of the fifth stage. ..
Figure JPOXMLDOC01-appb-M000010
Figure JPOXMLDOC01-appb-M000010
　第６ステージにおいて、ランク制御部２１１は、部分行列Ｂの範囲の６行６列要素の大きさ｜ｂ４，４ （５）｜としきい値τとを比較すると、｜ｂ４，４ （５）｜＜τであったとする。この場合、当該受信アンテナポートが悪条件であることから、ランク制御部２１１は、第６行と部分行列Ｂの範囲の第６列及び部分行列Ｃの範囲の第６列を除く。拡大行列Ｄは、式（１４）の形となる。このランク制御部２１１の動作は、複数の送信先端末およびデータ伝送速度に基づいて、複数の送信先端末に対応する伝送路の状態に基づいて算出される行列を算出し、行列の要素の絶対値があらかじめ定められたしきい値を満たさない伝送路を用いないように送信先端末の信号ストリーム数を決定する動作といえる。 In the sixth stage, the rank control unit 211 compares the sizes of the 6-row, 6-column elements in the range of the submatrix B | b 4,4 (5) | with the threshold value τ, and | b 4,4 (5). ) | <τ. In this case, since the receiving antenna port is in a bad condition, the rank control unit 211 excludes the sixth row, the sixth column of the range of the submatrix B, and the sixth column of the range of the submatrix C. The augmented matrix D has the form of equation (14). The operation of the rank control unit 211 calculates a matrix calculated based on the state of the transmission line corresponding to the plurality of destination terminals based on the plurality of destination terminals and the data transmission speed, and the absolute elements of the matrix are calculated. It can be said that this is an operation of determining the number of signal streams of the destination terminal so as not to use a transmission line whose value does not satisfy a predetermined threshold value.
Figure JPOXMLDOC01-appb-M000011
Figure JPOXMLDOC01-appb-M000011
　これにより、下位基地局２０は、端末ｂには信号ストリームを１つのみ伝送することとなり、端末ｂのＲＩは１となる。引き続き、ランク制御部２１１は、変形後の部分行列Ｂの範囲の６行６列要素の大きさ｜ｂ２，２ （５）｜としきい値τとを比較し、｜ｂ２，２ （５）｜≧τであるとする。この場合、通常のガウス・ジョルダン法に従って第６ステージの演算を行う。第６ステージ演算の結果、拡大行列Ｄは、式（１５）の形となる。 As a result, the lower base station 20 transmits only one signal stream to the terminal b, and the RI of the terminal b becomes 1. Subsequently, the rank control unit 211 compares the size | b 2,2 (5) | of the 6-by-6 element in the range of the submatrix B after transformation with the threshold value τ, and | b 2,2 (5). ) | ≧ τ. In this case, the operation of the sixth stage is performed according to the usual Gauss-Jordan method. As a result of the sixth stage operation, the augmented matrix D has the form of equation (15).
Figure JPOXMLDOC01-appb-M000012
Figure JPOXMLDOC01-appb-M000012
　第７ステージも対角要素がしきい値以上の大きさとすると、ランク制御部２１１は、通常のガウス・ジョルダン法に従って第７ステージの演算を行い、一連の演算の結果、最終的に拡大行列Ｄは、式（１６）の形となる。 Assuming that the diagonal elements of the 7th stage are larger than the threshold value, the rank control unit 211 performs the operations of the 7th stage according to the normal Gaussian-Jordan method, and as a result of a series of operations, the augmented matrix D is finally obtained. Is in the form of equation (16).
Figure JPOXMLDOC01-appb-M000013
Figure JPOXMLDOC01-appb-M000013
　ここで、行列Ａ’￣￣は、式（１７）に表されるとおり、行列Ａ￣￣から第６行を除いた７行８列の行列となる。 Here, the matrix A'￣￣ is a matrix of 7 rows and 8 columns excluding the 6th row from the matrix A￣￣ as represented by the equation (17).
Figure JPOXMLDOC01-appb-M000014
Figure JPOXMLDOC01-appb-M000014
　式（１６）の行列の左半分の部分行列はＡ’￣￣Ａ’￣￣Ｈの逆行列として算出される。これを用いて、暫定プリコーディング行列はランク制御部２１１によって、式（１８）のように計算される。 Submatrix of the left half of the matrix of Equation (16) is calculated as the inverse matrix of A'¯¯A'¯¯ H. Using this, the provisional precoding matrix is calculated by the rank control unit 211 as in equation (18).
Figure JPOXMLDOC01-appb-M000015
Figure JPOXMLDOC01-appb-M000015
　結果として、端末ｂは信号ストリームの数が１、その他の端末ａ、端末ｃ、端末ｄは信号ストリーム数が２として算出された。よって、ＭＵ－ＭＩＭＯトータルの信号ストリーム数は７となる。 As a result, the terminal b was calculated as having one signal stream, and the other terminals a, c, and terminal d were calculated as having two signal streams. Therefore, the total number of MU-MIMO signal streams is 7.
　以上のように、本発明のランク制御部２１１が行う暫定プリコーディング行列演算により、前述の下位スケジューリング基準に即したランク制御を実現できる。なお、暫定プリコーディング行列適用時の第ｎストリームのＳＮＲは、１アンテナ送信時のＳＮＲをγ０とすると、式（１９）のように第ｎストリームのプリコーディングベクトルにより推定することができる。 As described above, the provisional precoding matrix operation performed by the rank control unit 211 of the present invention can realize rank control in line with the above-mentioned lower scheduling criteria. The SNR of the nth stream when the provisional precoding matrix is applied can be estimated from the precoding vector of the nth stream as in Eq. (19), assuming that the SNR at the time of transmitting one antenna is γ 0 .
Figure JPOXMLDOC01-appb-M000016
Figure JPOXMLDOC01-appb-M000016
　下位スケジューラ部２１におけるＭＣＳ決定の具体的な方法を例示する。１つ目の例として、各送信先端末の信号ストリーム数、すなわちＲＩは決定しているため、通知された要求データ伝送速度の大きい端末から順に、要求データ伝送速度を満たすようＲＩに応じてＭＣＳを決定する。２つ目の例として、決定したＲＩとともに前述の暫定プリコーディング行列のベクトルを用いたＳＮＲ推定値を用いてＭＣＳを決定する。このように各送信先端末について順にＭＣＳを決定していく。ここでは２つのＭＣＳ決定方法を例示したが、この限りではなく、他の方法を用いても良い。 An example is a specific method for determining MCS in the lower scheduler unit 21. As a first example, since the number of signal streams of each destination terminal, that is, RI is determined, MCS according to RI so as to satisfy the requested data transmission speed in order from the terminal having the highest notified requested data transmission speed. To determine. As a second example, the MCS is determined using the determined RI and the SNR estimate using the vector of the provisional precoding matrix described above. In this way, the MCS is determined in order for each destination terminal. Here, two MCS determination methods have been illustrated, but the present invention is not limited to this, and other methods may be used.
　ＭＵ－ＭＩＭＯ信号処理部２２２では、送信先端末に対応する信号ストリームにＭＵ－ＭＩＭＯプリコーディングを行うが、プリコーディング方法に制限は無く、ブロック対角化に代表される線形プリコーディングを行っても良いし、ＴＨＰ（Tomlinson　Harashima　Precoding）に代表される非線形プリコーディングを行っても良い。非線形プリコーディングを適用する場合、下位スケジューラ部２１では、Ｌｍ台の送信先端末の順序も決定する。決定する規範として、例えば端末容量指標の大きさとする、前述した暫定プリコーディング行列のベクトルを用いたＳＮＲ推定値の順とする、下位基地局２０から見た端末の角度の順とする、端末間の位置関係が地理的に近い順、または遠い順とする、端末の移動速度の順とする、などが挙げられるが、これらの限りではない。 The MU-MIMO signal processing unit 222 performs MU-MIMO precoding on the signal stream corresponding to the destination terminal, but there is no limitation on the precoding method, and even if linear precoding represented by block diagonalization is performed. Alternatively, non-linear precoding represented by THP (Tomlinson Harashima Precoding) may be performed. When applying a non-linear precoding, the lower scheduler unit 21 also determines the order of L m stand destination terminal. As a criterion for determining, for example, the size of the terminal capacity index, the order of the SNR estimated value using the vector of the provisional precoding matrix described above, the order of the angle of the terminal as seen from the lower base station 20, between the terminals. The positional relationship of the terminals is geographically close or far, and the movement speed of the terminal is in order, but these are not limited to these.
　以上説明したように、本実施の形態では、第４世代移動体通信において１基の基地局が行っていた処理を、上位基地局１０と下位基地局２０とで分ける。詳細には、上位基地局１０が、ＭＵ－ＭＩＭＯダウンリンクの伝送を行う端末の組み合わせを決定する処理を行い、下位基地局２０が、各端末にダウンリンクを伝送する信号ストリーム数ＲＩと、各信号ストリームのＭＣＳとを決定する処理を行う。また、下位基地局２０は、ランク制御部２１１を備え、ランク制御部２１１は、上位基地局１０からの送信先端末への伝送の指示に従いながらＭＰ一般逆行列を用いることで送信先端末ごとに伝送路空間を直交化することで伝送可能な信号ストリーム数を求める。したがって、下位基地局２０は、しきい値以下の行列要素があらわれる行および列を除き、端末アンテナ間および端末間の空間相関が高い信号ストリームを割り当てないことで、スループットおよび通信品質の劣化を抑制することができる。 As described above, in the present embodiment, the processing performed by one base station in the 4th generation mobile communication is divided into the upper base station 10 and the lower base station 20. Specifically, the upper base station 10 performs a process of determining the combination of terminals that transmit the MU-MIMO downlink, and the lower base station 20 performs a process of determining the number of signal streams RI for transmitting the downlink to each terminal, and each of them. Performs a process of determining the MCS of the signal stream. Further, the lower base station 20 includes a rank control unit 211, and the rank control unit 211 uses the MP general inverse matrix for each destination terminal while following the instruction of transmission from the upper base station 10 to the destination terminal. The number of signal streams that can be transmitted is obtained by orthogonalizing the transmission path space. Therefore, the lower base station 20 suppresses deterioration of throughput and communication quality by not allocating a signal stream having a high spatial correlation between terminal antennas and terminals except for rows and columns in which matrix elements below the threshold value appear. can do.
　以上の実施の形態に示した構成は、本発明の内容の一例を示すものであり、別の公知の技術と組み合わせることも可能であるし、本発明の要旨を逸脱しない範囲で、構成の一部を省略、変更することも可能である。 The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations without departing from the gist of the present invention. It is also possible to omit or change the part.
　１０　上位基地局、１１　リソース制御部、１２－１～１２－Ｍ　上位スケジューラ部、２０，２０－１～２０－Ｍ　下位基地局、２１　下位スケジューラ部、２２　無線ベースバンド信号処理部、２３　無線ＲＦ信号処理部、２４－１～２４－Ｔｍ　アンテナ、９０－１－１～９０－Ｍ－ＫＭ　移動端末、１００　無線基地局システム、２１１　ランク制御部、２２１　ＣＳＩ取得部、２２２　ＭＵ－ＭＩＭＯ信号処理部、４００　制御回路、４００ａ　プロセッサ、４００ｂ　メモリ。 10 Upper base station, 11 Resource control unit, 12-1 to 12-M Upper scheduler unit, 20, 20-1 to 20-M Lower base station, 21 Lower scheduler unit, 22 Radio baseband signal processing unit, 23 Radio RF signal processing unit, 24-1 ~ 24-T m antennas, 90-1-1 ~ 90-M-K M mobile terminal, 100 a radio base station system, 211 rank controller, 221 CSI acquisition unit, 222 MU-MIMO signal Processing unit, 400 control circuit, 400a processor, 400b memory.

Claims (8)

  1. 　信号ストリームを割り当てる複数の送信先端末と、前記複数の送信先端末のデータ伝送速度とを上位無線基地局から通知され、前記複数の送信先端末および前記データ伝送速度に基づいて、前記複数の送信先端末に対応する伝送路の状態に基づく行列を算出し、前記行列の要素の絶対値があらかじめ定められたしきい値を満たさない伝送路を用いないように前記送信先端末の信号ストリーム数を決定するランク制御部と、
    　前記送信先端末に対応する前記信号ストリームにMulti　User－Multiple　Input　Multiple　Outputプリコーディングを行う信号処理部と、
    　を備えることを特徴とする下位無線基地局。     The upper radio base station notifies the plurality of destination terminals to which the signal stream is assigned and the data transmission speeds of the plurality of destination terminals, and the plurality of transmissions are performed based on the plurality of destination terminals and the data transmission speeds. A matrix based on the state of the transmission line corresponding to the destination terminal is calculated, and the number of signal streams of the destination terminal is set so as not to use a transmission line in which the absolute value of the elements of the matrix does not satisfy a predetermined threshold value. The rank control unit to decide and
    A signal processing unit that performs Multi User-Multiple Input Multiple Output precoding on the signal stream corresponding to the destination terminal, and
    A lower radio base station characterized by being equipped with.
  2. 　前記行列は、
    　Moore-Penrose一般逆行列であることを特徴とする請求項１に記載の下位無線基地局。     The matrix is
    The lower radio base station according to claim 1, wherein the Moore-Penrose general inverse matrix is used.
  3. 　前記ランク制御部は、
    　前記Moore-Penrose一般逆行列を算出する時にガウス・ジョルダン法を用いることを特徴とする請求項２に記載の下位無線基地局。     The rank control unit
    The lower radio base station according to claim 2, wherein the Gauss-Jordan method is used when calculating the Moore-Penrose general inverse matrix.
  4. 　前記ランク制御部は、
    　前記ガウス・ジョルダン法の演算の中で前記Moore-Penrose一般逆行列の中の要素の絶対値がしきい値より小さい場合、前記要素に対応する行および列を削除することを特徴とする請求項３に記載の下位無線基地局。     The rank control unit
    A claim characterized by deleting the row and column corresponding to the element when the absolute value of the element in the Moore-Penrose general inverse matrix is smaller than the threshold value in the operation of the Gaussian-Jordan method. The lower radio base station according to 3.
  5. 　上位無線基地局と、前記上位無線基地局と通信する複数の下位無線基地局とで構成される無線基地局システムの空間多重ストリーム数の制御方法であって、
    　下位無線基地局が、
    　信号ストリームを伝送する複数の送信先端末と、前記複数の送信先端末のデータ伝送速度とを上位無線基地局から通知され、前記複数の送信先端末および前記データ伝送速度に基づいて、前記複数の送信先端末に対応する伝送路の状態に基づく行列を算出し、前記行列の要素の絶対値があらかじめ定められたしきい値を満たさない伝送路を用いないように前記送信先端末の信号ストリーム数を決定する第１のステップと、
    　前記送信先端末に対応する前記信号ストリームにMulti　User－Multiple　Input　Multiple　Outputプリコーディングを行う第２のステップと、
    　を含むことを特徴とする空間多重ストリーム数の制御方法。     It is a method of controlling the number of spatial multiplex streams of a radio base station system composed of a higher radio base station and a plurality of lower radio base stations communicating with the higher radio base station.
    The lower radio base station
    The upper radio base station notifies the plurality of destination terminals for transmitting the signal stream and the data transmission speeds of the plurality of destination terminals, and the plurality of destination terminals and the plurality of data transmission speeds are notified based on the plurality of destination terminals and the data transmission speeds. The number of signal streams of the destination terminal is calculated based on the state of the transmission line corresponding to the destination terminal, and the number of signal streams of the destination terminal is not used so that the absolute value of the elements of the matrix does not satisfy a predetermined threshold value. The first step to determine and
    A second step of performing Multi User-Multiple Input Multiple Output precoding on the signal stream corresponding to the destination terminal, and
    A method of controlling the number of spatial multiplex streams, which comprises.
  6. 　前記行列は、
    　Moore-Penrose一般逆行列であることを特徴とする請求項５に記載の空間多重ストリーム数の制御方法。     The matrix is
    The method for controlling the number of spatial multiplex streams according to claim 5, wherein the Moore-Penrose general inverse matrix is used.
  7. 　前記第１のステップは、
    　前記Moore-Penrose一般逆行列を算出する時にガウス・ジョルダン法を用いることを特徴とする請求項６に記載の空間多重ストリーム数の制御方法。     The first step is
    The method for controlling the number of spatial multiplex streams according to claim 6, wherein the Gauss-Jordan method is used when calculating the Moore-Penrose general inverse matrix.
  8. 　前記第１のステップは、
    　前記ガウス・ジョルダン法の演算の中で前記Moore-Penrose一般逆行列の中の要素の絶対値がしきい値より小さい場合、前記要素に対応する行および列を削除することを特徴とする請求項７に記載の空間多重ストリーム数の制御方法。     The first step is
    A claim characterized by deleting the row and column corresponding to the element when the absolute value of the element in the Moore-Penrose general inverse matrix is smaller than the threshold value in the operation of the Gaussian-Jordan method. 7. The method for controlling the number of spatial multiplex streams according to 7.
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