JP2009232256A - Base station, radio communication method, and communication program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for performing scheduling to select radio terminals satisfying required communication quality as many as possible in a beam forming system in a multi-user environment. <P>SOLUTION: The base station includes: a first beam forming means to form m beams using a plurality of antennas; a pilot signal transmitting means to transmit a pilot signal by each of m beams; a reception state value receiving means to receive the reception state values of m beams from the radio terminals; a communication quality acquisition means to acquire information on the required communication quality of each radio terminal; a scheduling means to determine n (1≤n≤m) beams to be used, and n radio terminals to which n beams are allocated so that n radio terminals satisfy the respective predetermined communication quality; a second beam forming means to form the beam with respect to each of n radio terminals; and a data transmitting means to transmit data by the beam formed with respect to each radio terminal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a base station that performs wireless communication using a plurality of antennas, a wireless communication method, and a communication program, for example, a base station that performs scheduling.

  As a transmission method for accelerating existing wireless communication, a transmission method called MIMO (Multiple Input Multiple Output) that performs communication using a plurality of transmission antennas and a plurality of reception antennas has been proposed. In the MIMO transmission method, streams independent from a plurality of transmission antennas are multiplexed and transmitted at the same frequency, and the interference stream is separated by spatial filtering or maximum likelihood determination in the receiving apparatus. One of the MIMO transmission methods is a beam forming method.

  In the beamforming method, by forming a beam and communicating, spatial multiplexing (SDMA, Spatial Division Multiple Access) can be performed, and communication with a plurality of user terminals can be performed simultaneously. In addition to a method called ZF (Zero-Forcing) or DPC (Dirty Paper Cording), which forms a beam based on the propagation path response between the transmitting and receiving device antennas fed back from each user terminal in the beamforming method in the transmission device, In order to reduce the amount of feedback, a random beam forming technique is also known in which communication is performed using a beam formed in advance by a base station at random. In the random beam forming method, communication is performed using a beam randomly formed by the base station without using a channel response between the transceiver antennas.

  In the random beam forming method in a multi-user environment, the base station determines the beam to be used and the beam to be used based on feedback information from the user terminal (information on the reception state of a known signal transmitted by the beam formed by the base station). Select the user terminal to be assigned. This is called scheduling, and scheduling is generally performed by selecting to maximize the channel capacity.

In the optimal scheduling method, which is one of the scheduling methods, the channel capacity is calculated for a combination of user terminals to which each beam is allocated for every combination of beams. Then, the combination of the beam and the user terminal when the channel capacity is maximized is selected. However, in the optimal scheduling method, the amount of calculation is enormous because the entire search is performed, and the amount of calculation increases exponentially as the number of users and beams increases. Since the time required for scheduling is proportional to the amount of calculation, a large amount of calculation causes a decrease in the overall throughput. Therefore, a scheduling method with a reduced amount of calculation has been proposed, and one of them, the Greedy method, first selects one user with the best propagation path state, and then sequentially selects the already selected users. The combination of users is determined by combining them. As a result, the calculation load is reduced while maximizing the channel capacity (for example, Non-Patent Document 1).
Vicario, JL Bosisio, R. Spagnolini, U. Carles Anton-Haro, “Adaptive Beam Selection Techniques for Opportunistic Beamforming,” in Proc. PIMRC, Sep. 2004.

  In the scheduling for the purpose of maximizing the channel capacity as described above, the characteristics of a small number of user terminals having particularly good propagation path conditions are dominant in the entire system, so that the number of selected user terminals is reduced. In addition, inequality occurs in communication opportunities between user terminals.

  For example, in the above-mentioned Greedy method, the user terminal selected first is selected without considering interference from the user terminal selected later, so it is not necessarily selected due to the interference generated by adding a new user terminal. The total channel capacity does not always increase as the number of user terminals increases. In this case, since only a small number of previously selected user terminals are selected, the number of selected user terminals is reduced, and inequalities in communication opportunities between the user terminals become significant.

  Scheduling for the purpose of maximizing the channel capacity is effective when selecting a user terminal that can transmit at a high transmission rate so as to transmit a large size of data. However, it is not suitable for selecting a large number of user terminals that perform communication at the same time.

  Furthermore, the user terminals selected by the scheduling for the purpose of maximizing the channel capacity may include user terminals that do not satisfy the required communication quality, and data communication was performed with such user terminals. However, the efficiency of communication deteriorates, for example, reception fails and retransmission becomes necessary.

  The present invention provides a wireless communication device, a communication program, and a wireless communication method for performing scheduling that enable selection of as many wireless terminals (user terminals) that satisfy required communication quality as possible with a small amount of calculation. .

The base station as one aspect of the present invention is:
A base station that communicates with a plurality of wireless terminals using a plurality of antennas,
First beam forming means for forming m (m is an integer of 1 or more) beams using the plurality of antennas;
Pilot signal transmitting means for transmitting a pilot signal in each of the m beams;
Receiving state value receiving means for receiving the receiving state values of the m beams from each of the wireless terminals;
Communication quality acquisition means for acquiring required communication quality information required by each wireless terminal;
Based on the reception state value for the m beams of each of the radio terminals, n (1 ≦ n ≦) used among the m beams so that the n radio terminals satisfy the required communication quality. m) scheduling means for determining n beams and n radio terminals to which the n beams are allocated;
Second beam forming means for forming the n beams respectively corresponding to the n radio terminals determined by the scheduling means;
Data transmitting means for transmitting data to each wireless terminal by a beam formed for each wireless terminal;
It is provided with.

A communication program as one aspect of the present invention is:
A communication program executed in a computer that communicates with a plurality of wireless terminals using a plurality of antennas,
A first beam forming step of forming m (m is an integer of 1 or more) beams using the plurality of antennas;
A pilot signal transmission step of transmitting a pilot signal in each of the m beams;
A reception state value receiving step of receiving reception state values of the m beams from each of the wireless terminals;
A communication quality acquisition step of acquiring information on required communication quality required by each of the wireless terminals;
Based on the reception state value for the m beams of each of the radio terminals, n (1 ≦ n ≦) used among the m beams so that the n radio terminals satisfy the required communication quality. m) a scheduling step for determining n beams and n radio terminals to which the n beams are allocated;
A second beam forming step of forming the corresponding n beams for each of the n wireless terminals determined by the scheduling step;
A data transmission step of transmitting data to each wireless terminal by a beam formed for each wireless terminal;
It is provided with.

A communication method as one aspect of the present invention includes:
A communication method executed in a computer that communicates with a plurality of wireless terminals using a plurality of antennas,
A first beam forming step of forming m (m is an integer of 1 or more) beams using the plurality of antennas;
A pilot signal transmission step of transmitting a pilot signal in each of the m beams;
A reception state value receiving step of receiving reception state values of the m beams from each of the wireless terminals;
A communication quality acquisition step of acquiring information on required communication quality required by each of the wireless terminals;
Based on the reception state value for the m beams of each of the radio terminals, n (1 ≦ n ≦) used among the m beams so that the n radio terminals satisfy the required communication quality. m) a scheduling step for determining n beams and n radio terminals to which the n beams are allocated;
A second beam forming step of forming the corresponding n beams for each of the n wireless terminals determined by the scheduling step;
A data transmission step of transmitting data to each wireless terminal by a beam formed for each wireless terminal;
It is provided with.

  According to the present invention, it is possible to realize scheduling that enables selection of as many user terminals as possible that satisfy the required communication quality with a small amount of calculation.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a configuration diagram of a random beamforming MIMO system according to the first embodiment of the present invention.

  This MIMO system includes a base station 10 and a plurality of user terminals 20.

The base station 10 includes a digital signal processing unit 110, N _t pieces of the analog circuit portion 120, the higher the information signal processing unit 130, N _t antennas 140. A detailed configuration of the digital signal processing unit 110 is shown in FIG. The digital signal processing unit 110 includes a data signal transmission processing unit 111, a feedback signal reception processing unit 112, a scheduling unit 113, and a required communication quality information acquisition unit 114.

Each user terminal 20 includes a digital signal processing unit 210, _Nr analog circuit units 220, an upper information signal processing unit 230, and _Nr antennas 240. The number of antennas may be different for each user terminal 20. A detailed configuration of the digital signal processing unit 210 in the user terminal 20 is shown in FIG. The digital signal processing unit 210 includes a data signal reception processing unit 211 and a feedback signal transmission processing unit 212.

  FIG. 3 is a flowchart showing a processing flow until the base station 10 transmits data to each user terminal 20 in the random beamforming MIMO system. Hereinafter, the operation of each element in the base station 10 and the operation of each element in each user terminal 20 will be described based on the flowchart of FIG. The processing of this flowchart is largely made up of a propagation path information acquisition process A1, a scheduling process A2, and a user data transmission process A3.

であり、sはN_t次元パイロット信号ベクトル、Vはsに乗算されるN_t×N_tの送信ウェイト行列である。全ユーザ端末の総数（ユーザ総数）はKであるとする。 (Propagation path information acquisition process A1)
The data signal transmission processing unit 111 of the base station 10 transmits a known information signal (pilot signal) by N _t beams formed using N _t antennas before transmitting user data (S11). . FIG. 2 shows an example in which pilot signals are transmitted by randomly forming two beams. The data signal transmission processing unit 111 includes a first beam forming unit that forms a plurality of beams using a plurality of antennas, and a pilot signal transmission unit that transmits pilot signals using a plurality of beams. Assuming that the N _t- dimensional signal vector transmitted from the base station 10 is x, x is expressed by the following equation (1).

S is an N _t -dimensional pilot signal vector, and V is an N _t × N _t transmission weight matrix multiplied by s. Assume that the total number of all user terminals (total number of users) is K.

であり、H^(k)は基地局10とk番目のユーザ端末20との送受信機アンテナ間の伝搬路応答を要素とするN_r×N_t次元伝搬路行列、W^(k)はユーザ端末で受信信号に乗算されるN_r×N_rの受信ウェイト行列である。n^(k)は、各要素がユーザ端末20に含まれるアナログ回路220の雑音を表すN_r次元雑音ベクトルである。前記受信ウェイト行列W^(k)は、例えば、ユーザ端末で推定される実効伝搬路行列

に対し

として一般逆行列を乗じるZF法や、最小二乗誤差を最小にするMMSE（Minimum Mean Square Error）法といった空間フィルタリングを行う方法の他に、次式のように伝搬路行列を特異値分解して得られる左特異行列を用いる最大比合成法もある。

Each user terminal 20 receives the pilot signal transmitted from the base station 10 (S12). At this time, if the N _r -dimensional signal vector received at the k-th (1 ≦ k ≦ K) user terminal 20 is y ^(k) , y ^(k) is expressed by the following equation (2).

H ^(k) is an N _r × N _t- dimensional channel matrix whose element is a channel response between the transceiver antennas of the base station 10 and the k-th user terminal 20, and W ^(k) is a user terminal. It is a reception weight matrix of N _r × N _r multiplied by the reception signal. n ^(k) is an _Nr- dimensional noise vector in which each element represents the noise of the analog circuit 220 included in the user terminal 20. The reception weight matrix W ^(k) is, for example, an effective channel matrix estimated at the user terminal

Against

In addition to spatial filtering methods such as the ZF method that multiplies the general inverse matrix and the MMSE (Minimum Mean Square Error) method that minimizes the least square error, the channel matrix is obtained by singular value decomposition as There is also a maximum ratio synthesis method using a left singular matrix.

  Any method other than these methods may be used to generate the reception weight matrix.

The user terminal 20 processes the reception signal y ^(k) received by the N _r antennas 240 by the analog circuit 220 and notifies the digital signal processing unit 210 of the digital signal. The analog circuit 220 at the time of reception has a general configuration including a low noise amplifier, a frequency converter, an analog / digital (A / D) converter, and a filter, and thus detailed description thereof is omitted.

ここで、g^(k) _bはk番目のユーザ端末のb番目のビームに対する受信電力を表す。尚、

は、基地局のb番目のアンテナと、k番目のユーザ端末のi番目のアンテナとの間の実効伝搬路応答ベクトルを表す。受信状態値としては、通信路の一状態を表すものであれば、式（4）で計算される受信電力に限定されず、他のいかなる指標を算出しても良い。 The data signal reception processing unit 211 in the digital signal processing unit 210 demodulates and decodes the digital signal notified from the analog circuit 220. Then, the reception state vector (feedback information) is generated by estimating the reception state value for each beam using the pilot signal s (known signal) in Equation (2) (S13). That is, the reception state value for each beam of the k-th user terminal is expressed by the following equation (4) as an N _t -dimensional vector g ^(k) .

Here, g ^(k) _b represents received power for the b-th beam of the k-th user terminal. still,

Represents an effective channel response vector between the b-th antenna of the base station and the i-th antenna of the k-th user terminal. The reception state value is not limited to the reception power calculated by Expression (4) as long as it represents one state of the communication path, and any other index may be calculated.

When the data signal reception processing unit 211 of the user terminal calculates the reception state vector g ^(k) as feedback information in this way, it notifies the feedback signal transmission processing unit 212 of this. However, the feedback information does not have to be the reception state vector g ^(k) calculated by the equation (4), and even if the reception state vector g ^(k) is not subjected to the square process in the equation (4), the feedback information is effective. An N _t- dimensional vector having a propagation path response as an element may be used.

The feedback signal transmission processing unit 212 generates a feedback signal by performing encoding and modulation using the reception state vector g ^(k) notified from the data signal processing unit 211 as an information signal, and the generated feedback signal, It transmits to the base station 10 via the antenna 240 (S14). Therefore, the feedback signal from the user terminal includes reception state information for each beam of the user terminal.

  However, when a certain user terminal has a poor reception state for any beam, the certain user terminal does not need to feed back the reception state information for the beam, and for any beam, If the reception state is poor, the user terminal may not perform feedback itself. As a coding method and a modulation method applied to the feedback signal, any method may be used as long as decoding and demodulation are possible on the base station side.

  The base station 10 receives the feedback signal from the user terminal 20, processes this by the analog circuit 120 to generate a digital signal, and notifies the generated digital signal to the feedback signal reception processing unit 112 in the digital signal processing unit 110 (S15). The analog circuit 120 at the time of reception has a general configuration including a low noise amplifier, a frequency converter, an analog / digital (A / D) converter, and a filter, and thus detailed description thereof is omitted.

The feedback signal reception processing unit 112 demodulates and decodes the digital signal notified from the analog circuit 120, and obtains information on the reception state vector g ^(k) of each user terminal. The feedback signal reception processing unit 112 includes reception state value receiving means for receiving a reception state value from each user terminal. Note that the demodulation and decoding methods do not affect the essence of the present invention, and thus detailed description thereof is omitted. The feedback signal reception processing unit 112 notifies the scheduling unit 113 of the reception state vector g ^(k) of each user terminal.

(Scheduling process A2)
The scheduling unit 113 includes a reception state vector g ^(k) (1 ≦ k ≦ K) for each beam of each user terminal notified from the feedback signal reception processing unit 112, and a required communication quality information acquisition unit (communication quality acquisition unit). Based on the required communication quality information of each user terminal provided from 114, the used beam and the user terminal to be allocated to each used beam are determined (scheduled) (S16). K represents the total number of user terminals (total number of users) as described above. The scheduling in this embodiment does not maximize the channel capacity as in the prior art, but selects as many user terminals as possible that satisfy the required signal quality. Details of the scheduling will be described later.

  Here, the required communication quality information acquisition unit 114 sets the required communication quality as the required communication quality information for each user terminal according to the type of user data (for example, Internet data, VoIP data, etc.) held by the upper information signal processing unit 130. This is determined and notified to the scheduling unit 113. The required communication quality may be a quality of a propagation path state that is minimum required for transmitting user data, or may be a quality of a propagation path state that is necessary for achieving a desired communication speed for transmitting the user data. The required communication quality is a quality estimated in advance because the base station 10 transmits user data and the user terminal 20 successfully receives the data. The required communication quality may be any index as long as it is a physical quantity that can be compared with reception quality (or channel capacity) described later. The reception quality or channel capacity corresponds to, for example, communication quality.

  As a result of scheduling, the scheduling unit 113 acquires scheduling information including used beams, user terminals assigned to each used beam, and reception quality (or channel capacity) for the used beams of the user terminals to be assigned. The scheduling unit 113 notifies the data signal transmission processing unit 111 of the acquired scheduling information.

(User data transmission process A3)
The data signal transmission processing unit 111 is based on the scheduling information notified from the scheduling unit 113 (used beams, user terminals allocated to each used beam, and reception quality (or channel capacity) of the user terminals allocated to the used beams). Then, the user data of each user terminal held by the upper information signal processing unit 130 is assigned to each beam stream and transmitted (S17). Based on the scheduling information, the data signal transmission processing unit 111 includes second beam forming means for forming each beam used for each user terminal, and data addressed to each user terminal using a beam formed for each user terminal. Data transmitting means for transmitting.

  Specifically, the data signal transmission processing unit 111 encodes data to each user terminal selected by the scheduling with a coding rate and a modulation scheme corresponding to the reception quality (or channel capacity) of the user terminal. Modulate and multiply by a weight to form a beam to each user terminal. As the encoding method / modulation method in the present invention, any method may be used as long as the user terminal 20 can decode and demodulate. The data signal transmission processing unit 111 generates a digital signal for each antenna 140 using the modulation signal generated for each user terminal and the weight. The data signal transmission processing unit 111 sends the digital signal generated for each antenna 140 to the analog circuit 120.

  The analog circuit 120 converts the digital signal received from the data signal transmission processing unit 111 into an analog signal, and transmits the analog signal to each user terminal via each antenna 140. The analog circuit 120 at the time of transmission has a general configuration including a low noise amplifier, a frequency converter, an analog / digital (A / D) converter, and a filter, and thus detailed description thereof is omitted.

  Hereinafter, a scheduling method performed by the scheduling unit 113 will be specifically described. In this scheduling, the number of used beams is started from the maximum number, and if there is a user terminal that satisfies the required communication quality in each beam, a set of used beams and user terminals at this time (a plurality of such sets exist). One of them is adopted as the scheduling result. If there is no user terminal that satisfies the required communication quality in any of the considered beams, the same processing is repeated by reducing the number of used beams.

FIG. 6 is a flowchart of the scheduling procedure in the present embodiment. The number of antennas in the base station 10 to the N _t, the number of beams assigned to one user terminal and up to 1 beam. It is assumed that the scheduling unit 113 acquires feedback information from each user terminal (reception status information for each beam) and required communication quality of each user terminal.

(1-1) All beams are used beam candidates (m = N _t ).

(1-2) Based on feedback information from each user terminal, the reception quality (or channel capacity) for each beam candidate used by each user terminal is calculated. The scheduling unit 113 includes reception quality calculation means for calculating reception quality for each beam of each user terminal. The scheduling unit 113 includes channel capacity calculation means for calculating the channel capacity for each beam of each user terminal.

は、フィードバック情報から得られた受信状態ベクトルg^(k)の要素を用いて次式（5）で表される。

である。
ここで、σ²は雑音電力、P_tは総送信電力を表す。式（５）では各ユーザ端末への電力割当は均一としているが、総計がP_tとなればいかなる分配としても良く、電力分配方法としては各ユーザ端末の通信品質の逆数に応じて電力を配分することで最大のチャネル容量が得られる注水定理がよく知られている。 Here, the reception quality for the b-th beam of the k-th user terminal

Is expressed by the following equation (5) using elements of the reception state vector g ^(k) obtained from the feedback information.

It is.
Here, σ ² represents noise power, and P _t represents total transmission power. Power allocation to the formula (5) in each user terminal has been uniform, total well as any distributed if the P _t, allocate power as a power distribution method according to the inverse of the communication quality of each user terminal The water injection theorem is known so that the maximum channel capacity can be obtained.

  B represents a set of used beams. For example, B = {1, 4} indicates that the first beam and the fourth beam are used.

  The reception quality is not limited to the SINR shown in Equation (5), but may be SIR (Signal to Interference Ratio), and if it represents the quality of the propagation path, use other calculation formulas and norms. Also good.

を用いてk番目のユーザ端末がb番目のビームに対して得られるチャネル容量R^(k) _bは、次式（6）により求められる。

Also receive quality

The channel capacity R ^(k) _b obtained by the k-th user terminal for the b-th beam using is obtained by the following equation (6).

Next, the total channel capacity C _Q when using a plurality of beams is expressed by the following equation (7).

  As described above, Q indicates one combination of the used beam and the user terminal. For example, Q = {(1,3), (3,2)} is the first user terminal in the third beam. Is assigned, and the third user terminal is assigned to the second beam. The calculation method of the channel capacity and the total channel capacity is not limited to the formulas (6) and (7), and other calculation formulas and norms may be used as long as they represent the amount of information that can be communicated.

  After calculating the reception quality of each user terminal for each used beam candidate, the scheduling unit 113 checks whether there is a user terminal that satisfies the required communication quality for each beam. If there is a user terminal that satisfies the required communication quality in all the beams (YES), the process proceeds to step (1-3). If there is no user terminal satisfying the required communication quality in at least one of the used beam candidates (NO), the process proceeds to step (1-4).

(1-3) Each combination beam candidate (m) and one combination Q of user terminals that satisfy the required communication quality in each beam (one of them when there are multiple), and the combination Q A set of channel capacities (or a set of received qualities) D of each user terminal is used as a scheduling result.

  When there are a plurality of combinations of each used beam candidate (m) and user terminals that satisfy the required communication quality in each beam, the combination having the maximum total channel capacity is selected as Q. As another selection method, a combination including a user terminal having the maximum delay time from the generation of user data addressed to the user terminal to the present or the highest priority may be selected. Alternatively, a metric combining the delay time and the priority, or a combination including a user terminal having a maximum metric combining the total channel capacity, the delay time, and the priority may be selected. Alternatively, a combination that maximizes the sum of the former and latter metrics may be selected.

(1-4) A combination of m−1 use beam candidates is generated based on the current use beam candidates (m). And the reception quality with respect to each use beam candidate of each user terminal is calculated for every combination.

  If there is a user terminal satisfying the required communication quality for each beam in at least one combination (YES), the process proceeds to step (1-5), and if no such combination exists, the process proceeds to step (1-6). move on.

(1-5) Select one of the combinations of user terminals that satisfy the required communication quality in each beam (that is, remove one used beam candidate from the current used beam candidate), and perform step (1- Go to 3).

(1-6) It is determined whether m is greater than 1, and if it is greater than 1, the process proceeds to step (1-7). If it is less than 1, it is determined that there is no user terminal capable of communication ((1 -8)), scheduling is terminated.

(1-7) One usable beam candidate is excluded from the current usable beam candidates, and 1 is subtracted from m (m = m−1). And it returns to step (1-4). Use beam candidates to be excluded from the current use beam candidates are determined, for example, in the following [1], [2] or [3].
[1] When the current use beam candidate is used, the difference between the reception quality of each user terminal for each use beam candidate and the required communication quality of each user terminal is calculated, and the user terminal having the smallest difference is specified. To do. And the use beam candidate from which the largest difference is obtained when the difference of the specified user terminal is compared between each use beam candidate is made into the object to exclude.
[2] For each combination generated in step (1-4), the number of used beam candidates for which there is no user terminal satisfying the required communication quality is calculated, the combination having the smallest calculated number is specified, and the current use Among the beam candidates, use beam candidates that are not included in the specified combination are excluded.
[3] For each combination generated in step (1-4), a used beam candidate for which there is no user terminal satisfying the required communication quality is identified, and the reception quality of each user terminal for the identified used beam candidate, and each user terminal The minimum value of the difference with the required communication quality is obtained, and the obtained minimum value is totaled among each specified use beam candidate, and the combination when the total value (total value) is the minimum is selected (that is, the total value) Use beam candidates that are not used when is the minimum are excluded).

  The present inventors performed computer simulation to show the superiority of the scheduling method in the present embodiment, and compared the performance of the conventional scheduling method and the scheduling method in the present embodiment. As a conventional scheduling method, an optimum scheduling method for performing a full search for the purpose of maximizing the total channel capacity is adopted. Graphs created based on the simulation results are shown in FIGS.

FIG. 7 shows the number of antennas N _t = 3 of the base station (transmitting apparatus) 10, the number of antennas N _r = 1 of the user terminal (receiving apparatus) 20, the propagation path generation model is iid, and the SNR (signal to noise power ratio) = The total channel capacity with respect to the number of users K is 10 dB.

  As shown in the graph G1 of FIG. 7, it can be seen that the total channel capacity obtained by the above-described optimal scheduling method that does not use the required communication quality shows high characteristics. However, when the required communication quality is set to SINR = 9.4 dB, it can be seen that the characteristic obtained by subtracting the channel capacity of the user terminal that does not satisfy this is greatly deteriorated as shown in the graph G3. In contrast, the total channel capacity obtained by the scheduling method in the present embodiment when the required communication quality is SINR = 9.4 dB, as shown in the graph G2, shows that stable high characteristics are achieved. .

  FIG. 8 shows the result of comparing the number of selected users under the same conditions as in FIG. It is understood that the scheduling method according to the present embodiment has a larger user selection number characteristic than the above-described optimal scheduling method. For example, when the number of users is 100, in the scheduling method of this embodiment, the number of user selections is about 1.5 times that of the optimal scheduling method. Therefore, it can be understood that the scheduling method in this embodiment can select more user terminals than the above-described optimal scheduling method.

  As described above, according to this embodiment, in scheduling in a random beamforming MIMO system, it is possible to leave many beams having user terminals that satisfy the required communication quality, and users that satisfy the required communication quality in one scheduling. Many terminals can be selected. Moreover, according to this embodiment, since the user terminal whose propagation path state is particularly excellent is not necessarily selected, inequality among users can be reduced. Furthermore, when there is a user terminal that satisfies the required communication quality in all the used beam candidates, the scheduling is finished without considering the number of used beams less than the number of used beams at this time, so that the calculation load is reduced. You can also.

(Second Embodiment)
The configurations of the base station and the user terminal in the present embodiment are the same as those in FIGS. 1, 4 and 5, and the series of flow up to data transmission is also the same as the flow of the flowchart in FIG.

  This embodiment is different from the first embodiment in that one or more user terminals (priority terminals) to which beams are to be preferentially assigned are pre-selected at the time of scheduling execution. In scheduling, on the premise that a beam satisfying the required communication quality is allocated to a user terminal (priority terminal) selected in advance, a beam satisfying the required communication quality is allocated to as many other user terminals as possible. Here, one or more user terminals (priority terminals) selected in advance are, for example, the number of communication opportunities so far, the delay time from the generation of the user data addressed to the user terminal to the present, the priority of the user terminal, these It is determined according to any criterion other than.

  A specific scheduling method according to this embodiment will be described below.

  FIG. 9 is a flowchart showing a scheduling procedure in the present embodiment.

It is assumed that the number of antennas of the transmission apparatus 10 is N _t , the number of users selected in advance is M ₀ , and the number of beams allocated to one user terminal is up to one beam. The scheduling unit 113 is assumed to hold feedback information (reception status information for each beam) of each user terminal, required communication quality information, and information of a user terminal selected in advance.

(2-1) All beams are used as beam candidates (number of beam candidates m = Nt). That is, the examination starts from the maximum number of beams used.

(2-2) in advance the number of users M ₀ selected, if used below the beam candidate number m (YES), the flow advances to step (2-3), the user number M0 which is previously selected using the beam number of candidates m If it is greater than (NO), it is determined that the user terminals having the number of users M ₀ selected in advance cannot be selected at the same time ((2-8)), and the scheduling is terminated.

(2-3) When it is assumed that all m use beam candidates are used, the reception quality of each user terminal with the number of users M ₀ selected in advance is calculated. If there is a beam satisfying the required communication quality in each user terminal having the number of users M ₀ (YES), the process proceeds to step (2-4), and even one of the user terminals selected in advance satisfies the required communication quality. If no beam exists, the process proceeds to step (2-6).

(2-4) If each user terminal having the number of users M ₀ is assigned to any one of the used beam candidates (YES), step (2-5) Proceed to If there are no more beams (NO), go to step (2-7).

(2-5) A user terminal that calculates the reception quality of another user terminal different from the previously selected user terminal for the remaining beam candidates and satisfies the required communication quality for each of the remaining used beam candidates If there is any beam candidate for which there is no user terminal satisfying the required communication quality among the remaining used beam candidates, the process proceeds to step (2-6).

(2-6) One beam is excluded from the use beam candidates, m = m−1 is set, and the process returns to step (2-2).

  As the beam to be excluded at this time, for example, for each user terminal selected in advance, the difference between the reception quality of each used beam candidate obtained in step (2-3) and the required communication quality notified in advance is used. Based on this, one beam having the worst reception characteristics (the largest difference) may be targeted. Alternatively, for a user terminal selected in advance, a beam having the lowest reception quality of each used beam candidate may be targeted.

  Alternatively, in step (2-5), when searching for user terminals (non-priority terminals) to be assigned to the remaining use beam candidates, a beam for which no user terminal (non-priority terminal) satisfying the required communication quality exists is targeted. The user terminal (non-priority terminal) having the smallest difference between the required communication quality and the actual communication quality (reception quality) is detected, and the difference of the detected user terminal (non-priority terminal) is detected between the above beams. Compare and select the beam with this maximum difference.

  Alternatively, one beam may be selected according to another standard.

(2-7) Scheduling a combination Q of m use beam candidates and user terminals that satisfy the required communication quality with each use beam candidate, and a set (or set of reception quality) D of channel capacities of each user terminal As a result.

  When there are a plurality of combinations, the combination with the maximum total channel capacity is selected as Q, and the set D of channel capacities of each user terminal at this time is used as the scheduling result.

  As another selection method, the combination of the maximum delay time from the generation of user data addressed to the user terminal to the present, the combination including the user terminal having the highest priority, or the metric combining the delay time and the priority is the maximum. You may select the combination. Alternatively, a combination including a user terminal having a maximum metric including the total channel capacity, delay time, and priority may be selected. Alternatively, a combination that maximizes the sum of the former and latter metrics may be selected.

  As described above, according to the present embodiment, in addition to the effects of the first embodiment, a beam satisfying the required communication quality is allocated to a user terminal (priority terminal) selected in advance according to some norm, and yet another A beam that satisfies the required communication quality can also be assigned to the user terminal.

(Third embodiment)
The configurations of the base station (transmitting device) and user terminal (receiving device) in the present embodiment are basically the same as those in FIG. 1, FIG. 4, and FIG. This is the same as the flowchart in FIG.

  This embodiment is different from the first and second embodiments in that the pilot signal transmitted from the antenna of the base station is not random beam transmission but omnidirectional transmission, and the user terminal feeds back to the base station. The point is that the information is not a beam reception state but a propagation path matrix having a propagation path response between the transceiver antennas as an element.

  In the following description, the ZF method, which is one of the linear beam forming methods, will be described as an example of the beam forming method. However, the MMSE method that minimizes the error may be used instead of the ZF method. A nonlinear beam forming method such as a VP (Vector Perturbation) method may be used.

In the following description, for simplicity, the user terminal (receiving device) 20 has a single antenna (N _r = 1). However, a plurality of antennas may be used. The present embodiment can be applied by treating it as a set.

(Propagation path information acquisition process A1)
The base station 10 transmits a known information signal (pilot signal) to the user terminal 20 before transmitting user data (S11).

但し、sはN_t次元パイロット信号ベクトルであり、h^(k)は基地局10とk番目のユーザ端末20との送受信機アンテナ間の伝搬路応答を要素とするN_t次元伝搬路ベクトル、n^(k)は、各要素がユーザ端末20に含まれるアナログ回路220の雑音を表すN_r次元雑音ベクトルである。 Each user terminal 20 receives the pilot signal transmitted from the base station 10 (S12) If the received signal at the k-th (1 ≦ k ≦ K) user terminal 20 is y ^(k) , y ^(k) is It is expressed by equation (8).

Where s is an N _t -dimensional pilot signal vector, h ^(k) is an N _t -dimensional propagation path vector whose element is a propagation path response between the transceiver antennas of the base station 10 and the k-th user terminal 20, n ^(k) is an _Nr- dimensional noise vector in which each element represents the noise of the analog circuit 220 included in the user terminal 20.

In the user terminal 20, the reception signal y received through the antenna 240 of the N _r book ^(k) was treated by the analog circuit 220 generates a digital signal, and notifies the generated digital signal to the digital signal processor 210. The analog circuit 220 at the time of reception has a general configuration including a low noise amplifier, a frequency converter, an analog / digital (A / D) converter, and a filter, and thus detailed description thereof is omitted.

でも良い。 The data signal reception processing unit 211 in the user terminal 20 demodulates and decodes the digital signal notified from the analog circuit 220. At this time, since the pilot signal s in Equation (8) is known, each user terminal can estimate h ^(k) , and notifies this to the feedback signal transmission processing unit 212 as feedback information (S13, S14). ). At this time, the feedback information may be h ^(k) , and if the pilot signal s is multiplied by the N _t × N _t dimensional transmission weight matrix V in the base station 10, the N _t dimensional effective propagation path vector

But it ’s okay.

The feedback signal transmission processing unit 212 in the user terminal 20 encodes and modulates feedback information (propagation channel matrix h ^(k) ) notified from the data signal reception processing unit 211 as an information signal to generate a feedback signal. The received feedback signal is transmitted to the base station 10. As the encoding scheme / modulation scheme, any scheme may be used as long as decoding and demodulation are possible on the base station 10 side. The analog circuit 220 at the time of transmission has a general configuration including a filter, a digital analog (D / A) converter, a frequency modulator, and a power amplifier, and detailed description thereof is omitted.

  When the base station 10 receives the feedback signal from the user terminal 20 (S15), the received feedback signal is processed by the analog circuit 120 into a digital signal, and the digital signal is notified to the feedback signal reception processing unit 112. The analog circuit 120 at the time of reception has a general configuration including a low noise amplifier, a frequency converter, an analog / digital (A / D) converter, and a filter, and thus detailed description thereof is omitted.

The feedback signal reception processing unit 112 obtains information on the propagation path vector h ^(k) by demodulating and decoding the digital signal notified from the analog circuit 120. Since the demodulation / decoding method at this time does not affect the essence of the present invention, detailed description thereof is omitted. The feedback signal reception processing unit 112 notifies the scheduling unit 113 of the reception state vector h ^(k) from each user terminal.

(Scheduling process A2)
In the scheduling unit 113, the propagation path vector h ^(k) (1 ≦ k ≦ K) of each user terminal notified from the feedback signal reception processing unit 112 and each user terminal notified from the required communication quality information acquisition unit 114 Scheduling is performed based on the required communication quality information. Details of scheduling in this embodiment will be described later. Scheduling here means that the base station 10 selects a user terminal to communicate with, and the scheduling unit 113 determines the selected user terminal, the transmission weight at this time, and each user terminal as a result of scheduling. The reception quality (or channel capacity) is notified to the data signal transmission processing unit 111 as scheduling information.

(User data transmission process A3)
In the data signal transmission processing unit 111, based on the scheduling information notified from the scheduling unit 113 (the selected user terminal, the transmission weight at this time, and the reception quality (or channel capacity) of each user terminal), the upper information signal processing unit The user data held by 130 is assigned to the beam stream formed by the transmission weight of each user terminal and transmitted.

  Specifically, the user data to each selected user terminal is encoded and modulated at a coding rate and modulation scheme that matches the reception quality (or channel capacity) of each user terminal, and the modulated data is converted into each modulated data. On the other hand, the transmission weight of each user terminal is multiplied. As the encoding scheme / modulation scheme, any scheme may be used as long as it can be decoded and demodulated by the user terminal. The digital signal after transmission weight multiplication is sent to the analog circuit 120.

  The analog circuit 120 mainly performs processing of converting the digital signal notified from the data signal transmission processing unit 111 into an analog signal, and transmits the obtained analog signal via the antenna 140. The analog circuit 120 at the time of transmission has a general configuration including a filter, a digital analog (D / A) converter, a frequency modulator, and a power amplifier, and detailed description thereof is omitted.

  A specific scheduling method according to this embodiment will be described below.

  In the scheduling procedure in the present embodiment, if there is at least one combination that satisfies the required communication quality for each user terminal among all combinations of the transmission antenna and the user terminal, one of the combinations at this time is selected and scheduling is performed. Exit. If there is no combination that satisfies the required communication quality for each user terminal, the number of transmission antennas, that is, the number of selected users is decreased by 1, and the same process is repeated.

  FIG. 10 is a flowchart showing a scheduling procedure in the present embodiment.

Let N _t be the number of antennas of the base station 10. It is assumed that the scheduling unit 113 holds feedback information (transceiver channel matrix) of each user terminal and required communication quality information of each user terminal.

(3-1) The number m of used antennas is defined as the number of antennas Nt (maximum number) of the base station 10 (m = Nt). That is, the examination starts from the maximum number (= number of transmission antennas) of the number of used beams (number of users).

(3-2) The reception quality of each user terminal is calculated for all combinations of m used antennas and m user terminals among all user terminals. The reception quality can be calculated based on the following calculation method, for example.

_{M (1 ≦ M ≦ N t} ) channel matrix H _Q in combination Q of the user terminal at the time of multiplexing is that by combining in the order of transmit antennas assigned the channel vector of each user terminal expressed by the following equation Can do.

このとき、k(k∈Q)番目のユーザ端末の受信品質γ_kは、H_Qを用いて次式（10）で表される。

但し、P_kはk番目のユーザ端末に割り当てられた送信電力、P_tは総送信電力である。P_kは式（11）に示すように全ユーザ端末で均一にする必要はなく、総計がP_tとなればいかなる分配としても良い。電力分配方法としては各ユーザ端末の通信品質の逆数に応じて電力を配分することで最大のチャネル容量が得られる注水定理がよく知られている。 In the ZF method, interference between users is suppressed by using an inverse matrix of a channel matrix as a transmission weight. The transmission weight V is expressed by the following equation (9).

At this time, the reception quality gamma _k of k (K∈Q) th user terminal, using the H _Q represented by the following formula (10).

Here, P _k is the transmission power assigned to the kth user terminal, and P _t is the total transmission power. P _k does not need to be uniform for all user terminals as shown in equation (11), and any distribution may be used as long as the total is P _t . As a power distribution method, a water injection theorem that can obtain the maximum channel capacity by distributing power according to the reciprocal of the communication quality of each user terminal is well known.

Here, the channel capacity R ^(k) obtained by the k-th user terminal using the reception quality γ _k is expressed by the following equation (12).

The total channel capacity C _Q is expressed by the following equation (13).

Based on the above, when the reception quality of each user terminal is calculated for all combinations of m antennas used and m user terminals, it is checked whether there is a combination that satisfies the required communication quality of each m user terminal. If it exists (YES), the process proceeds to step (3-3). If not (NO), the process proceeds to step (S3-4). At this time, if M ₀ user terminals (priority terminals) are selected in advance as in the second embodiment according to some standard, a combination including the M ₀ user terminals is selected. To do.

(3-3) A set of user terminals in the above combination is Q, a transmission weight V obtained by Expression (9), and a set of channel capacities (or reception quality sets) D of each user terminal obtained by Expression (12). Is the scheduling result.

  When there are a plurality of the above combinations, for example, a set of user terminals in the combination having the maximum total channel capacity calculated by the equation (13) is selected as Q, and the corresponding transmission weight V and channel capacity of each user terminal are selected. A set (received quality set) D is a scheduling result.

  As another selection method, a combination in which the delay time from the generation of user data addressed to the user terminal to the present is the maximum, a combination including the user terminal having the highest priority, or a metric combining the delay time and the priority is the maximum You may select the combination. Alternatively, a combination including a user having a maximum metric including the total channel capacity, delay time, and priority may be selected. Alternatively, a combination that maximizes the sum of the former or latter metrics may be selected.

(3-4) Decrease the number of used antennas m by 1 (m = m−1), determine whether the number of used antennas m is 1 or more ((3-5)), and if 1 or more (YES), Return to step (3-2). If the number m of used antennas is less than 1 (NO), it is determined that there is no user terminal capable of communication ((3-6)), and the scheduling ends.

  As described above, according to the present embodiment, even if the information fed back from the user terminal is the beam forming method which is a propagation path matrix having the propagation path response between the transceiver antennas as an element, the first embodiment The same effect can be obtained.

(Fourth embodiment)
The configurations of the base station and user terminal in this embodiment are basically the same as those in FIGS. 1, 4 and 5, and the series of flow up to data transmission is also basically the same as the flow of the flowchart in FIG.

  The present embodiment differs from the first to third embodiments described so far in that the scheduling method of the present invention (first to third implementations) for selecting as many user terminals as possible that satisfy the required communication quality when executing scheduling. Any scheduling method) and a scheduling method based on (maximizing) channel capacity (for example, the Greedy method) are switched according to the situation. In the present embodiment, the scheduling unit 113 includes second scheduling means for executing a scheduling method based on channel capacity, and scheduling control means for switching the scheduling method.

  FIG. 11 is a flowchart showing a scheduling procedure in the present embodiment.

Let N _t be the number of antennas of the base station 10. It is assumed that the scheduling unit 113 holds feedback information from each user terminal (information on a reception state for each beam or a channel matrix between transmitter and receiver antennas) and information on required communication quality. If a user terminal (priority terminal) to which data is to be transmitted with priority is selected in advance, information on the user terminal is also held.

(4-1) In scheduling, it is determined whether scheduling according to the present invention or scheduling that maximizes channel capacity is necessary. That is, it is determined which one of the scheduling based on the number of users satisfying the required communication quality and the scheduling based on the channel capacity is necessary.

  At this time, if a user terminal (priority terminal) to which data is to be preferentially transmitted is selected in advance as a determination criterion, the determination may be made according to the type of user data addressed to the user terminal. You may judge with the required communication quality of a terminal (priority terminal). For example, if the type of user data is Internet data, it is determined that a scheduling method based on the channel capacity is necessary, and if it is VoIP data, it is determined that the scheduling method of the present invention is necessary.

  Alternatively, the determination may be made according to the ratio of all types of user data that the base station 10 should transmit or some types of user data having a high transmission priority (for example, a predetermined value or more). Or you may judge by the number of user terminals or the number of user terminals with which user data which should be transmitted exists.

  Alternatively, both scheduling methods may be switched periodically, or may be switched based on the time and the number of times of scheduling. The time can be obtained from the system clock, for example.

但し、式（14）中のZ_i,jは、i番目とj番目のユーザ端末の空間相関値を表す。 Alternatively, the determination may be made from the spatial correlation value E _Z of the entire user calculated from the feedback information by the following equation (14), for example.

However, Z _{i, j} in equation (14) represents the spatial correlation value of the i-th and j-th user terminals.

となる。 The feedback information from each user terminal is a reception state vector whose element is the reception state for each beam, and the reception state vectors fed back from the i-th and j-th user terminals are g ⁽ⁱ⁾ and g ^(j) , respectively. When represented

It becomes.

となる。 The feedback information from each user terminal is a propagation path vector whose element is a propagation path response between the transceivers, and the propagation path vectors fed back from the i-th and j-th user terminals are h ⁽ⁱ⁾ and h, respectively. ^When represented by ^(j)

It becomes.

  The calculation method of the spatial correlation value of the entire user and the spatial correlation value of the two users is not limited to the formula (14), the formula (15), and the formula (16), and an index of the spatial relationship of the user terminals to be combined is obtained. If it is, you may use another calculation method.

  The situation is judged based on the above criteria, and if scheduling of the present invention is necessary (YES), the process proceeds to step (4-2), and if scheduling based on the channel capacity is necessary (NO) ), Go to step (4-3).

(4-2) A scheduling method for maximizing the number of users satisfying the required communication quality is executed. Specifically, one of the scheduling methods in the first to third embodiments is executed.

(4-3) A scheduling method for maximizing the channel capacity is executed. As a specific example, for example, there is a Greedy method, but a different scheduling method may be used as long as it is a scheduling method that maximizes other channel capacity.

  As described above, according to the present embodiment, the scheduling method can be switched to an optimum one according to the situation, so that the quality of the entire service can be improved in a wireless communication system in which various applications are mixed. it can.

  In addition, the base station and user terminal in each embodiment described above can also be realized by using, for example, a general-purpose computer device as basic hardware. That is, the digital signal processing unit in the base station, the feedback signal reception processing unit, the scheduling unit, the data signal transmission processing unit, etc., and the digital signal processing unit, the data signal reception processing unit, the feedback signal transmission processing unit in the user terminal, This can be realized by causing a processor mounted on the computer apparatus to execute a program. At this time, the base station and the user terminal may be realized by installing the above program in a computer device in advance, or may be stored in a storage medium such as a CD-ROM, or may be stored via a network. You may implement | achieve by distributing and installing this program in a computer apparatus suitably.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram showing a configuration of a wireless communication system according to an embodiment of the present invention. The conceptual diagram of the MIMO transmission system which applied the random beam forming system. The flowchart which shows the flow of a process until data transmission is performed by a random beam forming system. The block diagram which shows the structure of the digital signal processing part in a base station (transmission apparatus). The block diagram which shows the structure of the digital signal processing part in a user terminal (reception apparatus). The flowchart explaining the scheduling method which concerns on 1st Embodiment. The figure which shows the total channel capacity obtained by the scheduling method which concerns on 1st Embodiment compared with the conventional scheduling method. The figure which shows the maximization effect of the user multiplexing number obtained by the scheduling method which concerns on 1st Embodiment compared with the conventional scheduling method. 9 is a flowchart for explaining a scheduling method according to the second embodiment. 10 is a flowchart for explaining a scheduling method according to the third embodiment. The flowchart explaining the scheduling method which concerns on 4th Embodiment.

Explanation of symbols

10 ... Base station
110 ・ ・ ・ Digital signal processor
111 ... Data signal transmission processing unit
112 ... Feedback signal reception processing unit
113 ・ ・ ・ Scheduling part
114 ・ ・ ・ Required communication quality information acquisition unit
120 ・ ・ ・ Analog circuit
130 ... Upper information signal processor
140 ... antenna
20 ... User terminal
210 ... Digital signal processor
211 ... Data signal reception processing section
212 ... Feedback signal transmission processing unit
220 ・ ・ ・ Analog circuit
230 ... Upper information signal processor
240 ... antenna

Claims (25)

A base station that communicates with a plurality of wireless terminals using a plurality of antennas,
First beam forming means for forming m (m is an integer of 1 or more) beams using the plurality of antennas;
Pilot signal transmitting means for transmitting a pilot signal in each of the m beams;
Receiving state value receiving means for receiving the receiving state values of the m beams from each of the wireless terminals;
Communication quality acquisition means for acquiring required communication quality information required by each wireless terminal;
Based on the reception state value for the m beams of each of the radio terminals, n (1 ≦ n ≦) used among the m beams so that the n radio terminals satisfy the required communication quality. m) scheduling means for determining n beams and n radio terminals to which the n beams are allocated;
Second beam forming means for forming the n beams respectively corresponding to the n radio terminals determined by the scheduling means;
Data transmitting means for transmitting data to each wireless terminal by a beam formed for each wireless terminal;
A base station characterized by comprising: The scheduling means determines m beams as the n beams to be used, determines m wireless terminals to which the m beams are allocated,
When no radio terminal is assigned to satisfy the required communication quality for the m beams, m−1 beams to be used among the m beams and the m−1 beams are used. The base station according to claim 1, wherein m−1 wireless terminals to be assigned are determined. The scheduling means targets the m beams when there is no radio terminal assignment that satisfies each required communication quality for any of the m-1 beam combinations in the m beams. Identifying a beam in which all of the plurality of wireless terminals do not satisfy the required communication quality,
For the identified beam, a radio terminal having a minimum difference between the required communication quality and the communication quality obtained from the reception state value for the m beams is detected, and the beam having the maximum difference of the detected radio terminal is detected. Detect
Using m−1 beams obtained by removing detected beams from the m beams, m−2 beams to be used among the m−1 beams and m−2 beams are used. The base station according to claim 2, wherein m−2 wireless terminals to be allocated are determined. The scheduling means, when there is no radio terminal allocation that satisfies the required communication quality for any of the m-1 beam combinations in the m beams,
For each combination of m-1 beams and m-1 radio terminals generated from the m beams and the plurality of radio terminals, each of the radio terminals has the required communication. Calculate the number of beams that do not meet quality,
Select the combination with the smallest calculated number,
Using m−1 beams included in the selected combination, m−2 beams to be used among the m−1 beams and m−2 beams to which the m−2 beams are allocated. The base station according to claim 2, wherein a base station is determined. The scheduling means, when there is no radio terminal allocation that satisfies the required communication quality for any of the m-1 beam combinations in the m beams,
For each combination of m-1 beams and m-1 radio terminals generated from the m beams and the plurality of radio terminals, each of the radio terminals has the required communication. Identify beams that do not meet quality,
For the identified beam, a wireless terminal having a minimum difference between the required communication quality and the communication quality obtained from the reception state value for each of the m−1 beams is detected;
Sum the differences of the detected wireless terminals for all of the identified beams;
Select the combination with the smallest total value,
Using m−1 beams included in the selected combination, m−2 beams to be used among the m−1 beams and m−2 beams to which the m−2 beams are allocated. The base station according to claim 2, wherein a base station is determined. Of the plurality of wireless terminals, further comprising a priority terminal specifying means for specifying a priority terminal to which data should be transmitted with priority,
The base station according to claim 1, wherein the scheduling means determines a radio terminal to which each beam is allocated so as to include the priority terminal. The scheduling means, when there is no terminal assignment to each beam to include the priority terminal,
Detecting the beam having the minimum communication quality obtained from the reception state value for the m beams for the priority terminal for the m beams,
Of the m beams, m−1 beams excluding detected beams are used, and m−2 beams to be used among the m−1 beams and the m−2 beams are used. The base station according to claim 6, wherein m−2 wireless terminals to be assigned are determined so as to include the priority terminal. The scheduling means includes
M beams are determined as the n beams to be used, the priority terminals are first assigned to the m beams, and then non-priority terminals different from the priority terminals are sequentially assigned to the remaining beams. allocation,
When the priority terminal assignment succeeds, but the non-priority terminal assignment fails,
The difference between the required communication quality and the communication quality obtained from the reception state value for the m beams is the minimum for the beam for which no non-priority terminal satisfying the required communication quality exists among the remaining beams. Non-priority terminals are detected, the beam having the largest difference between the detected non-priority terminals is detected
Using m−1 beams obtained by removing detected beams from the m beams, m−2 beams to be used among the m−1 beams and m−2 beams are used. The base station according to claim 6, wherein the m-2 radio terminals to be allocated are determined so as to include the priority terminals. The scheduling means includes
Determining m beams as the n beams to be used, and determining m wireless terminals to which the m beams are allocated so as to include the priority terminals;
When there is no terminal allocation to each of the beams including the priority terminal, m−1 beams to be used among the m beams and m−1 beams to which the m−1 beams are allocated. A wireless terminal to include the priority terminal,
When there is no assignment to include the priority terminal for any of the m-1 beam combinations in the m beams,
For each combination of m−1 beams generated from the m beams and the plurality of wireless terminals and m−1 wireless terminals including the priority terminal, each wireless terminal Calculate the number of beams that do not satisfy each of the required communication quality,
Select the combination with the smallest calculated number,
Using m−1 beams included in the selected combination, m−2 beams to be used among the m−1 beams and m−2 beams to which the m−2 beams are allocated. The base station according to claim 6, wherein a radio terminal is determined so as to include the priority terminal. The scheduling means includes
Determining m beams as the n beams to be used, and determining m wireless terminals to which the m beams are allocated so as to include the priority terminals;
When there is no terminal allocation to each of the beams including the priority terminal, m−1 beams to be used among the m beams and m−1 beams to which the m−1 beams are allocated. A wireless terminal to include the priority terminal,
When there is no assignment to include the priority terminal for any of the m-1 beam combinations in the m beams,
For each combination of m−1 beams generated from the m beams and the plurality of wireless terminals and m−1 wireless terminals including the priority terminal, each wireless terminal Identify each beam that does not meet the required communication quality,
For the identified beam, a wireless terminal having a minimum difference between the required communication quality and the communication quality obtained from the reception state value for each of the m−1 beams is detected;
Sum the differences of the detected wireless terminals for all of the identified beams;
Select the combination with the smallest total value,
Using m−1 beams included in the selected combination, m−2 beams to be used among the m−1 beams and m−2 beams to which the m−2 beams are allocated. The base station according to claim 6, wherein a radio terminal is determined so as to include the priority terminal. The scheduling means generates a plurality of combinations of the n beams and the n radio terminals so that each of the wireless terminals satisfies the required communication quality, and is calculated for each of the plurality of combinations. The base station according to any one of claims 1 to 10, wherein one of the plurality of combinations is selected based on a total channel capacity. The scheduling means generates a plurality of combinations of the n beams and the n radio terminals so that each of the radio terminals satisfies the required communication quality, and each of the radios included in the plurality of the combinations The base according to any one of claims 1 to 11, wherein one of the plurality of combinations is selected based on an elapsed time from generation of data to be transmitted to a terminal. Bureau. Priorities are set in advance for each of the plurality of wireless terminals,
The scheduling means generates a plurality of combinations of the n beams and the n radio terminals so that each of the radio terminals satisfies the required communication quality, and each of the radios included in the plurality of the combinations The base station according to any one of claims 1 to 12, wherein one of the plurality of combinations is selected based on a priority set for a terminal. A second scheduling means for performing scheduling based on the total channel capacity;
Scheduling control means for switching between the first scheduling means and the second scheduling means for performing scheduling;
The base station according to claim 1, further comprising: When there is a priority terminal to which data is to be transmitted with priority among the plurality of wireless terminals, the scheduling control means determines the type of data to be transmitted to the priority terminal or the required communication quality of the priority terminal. The base station according to claim 14, wherein the first and second scheduling means are switched accordingly. The base station according to claim 14, wherein the scheduling control means switches between the first scheduling means and the second scheduling means in accordance with a ratio of types of data to be transmitted to each of the plurality of wireless terminals. . A priority is set for each of the plurality of wireless terminals,
The scheduling control means performs switching between the first and second scheduling means according to a ratio of types of data to be transmitted to each of the wireless terminals having a priority level equal to or higher than a predetermined value. Item 15. The base station according to Item 14. 15. The scheduling control unit performs switching between the first and second scheduling units according to the number of the plurality of wireless terminals or a spatial correlation between the plurality of wireless terminals. The listed base station. A system clock,
The base station according to claim 14, wherein the scheduling control means switches between the first and second scheduling means according to the time of the system clock and the number of times of scheduling. A base station that communicates with a plurality of wireless terminals using m (m is an integer of 1 or more) antennas,
Pilot signal transmitting means for transmitting a pilot signal by each of the m antennas;
Propagation path response receiving means for receiving propagation path response information from each of the wireless terminals to the m antennas;
Communication quality acquisition means for acquiring required communication quality information required by each wireless terminal;
Based on the information on the channel response to the m antennas of each of the wireless terminals, n (1 ≦ n ≦ m) scheduling means for determining n antennas and n wireless terminals to which the n antennas are assigned;
Beam forming means for forming n beams for each of the n radio terminals according to the antenna assigned to each of the n radio terminals and the information of the propagation path response;
Data transmitting means for transmitting data to each wireless terminal by a beam formed for each wireless terminal;
A base station characterized by comprising: The scheduling means determines m antennas as the n antennas to be used, determines m wireless terminals to which the m antennas are allocated,
When there is no wireless terminal assignment that satisfies the required communication quality for the m antennas, m-1 antennas to be used among the m antennas and the m-1 antennas. 21. The base station according to claim 20, wherein m−1 wireless terminals to be assigned are determined. A second scheduling means for performing scheduling based on the total channel capacity;
Scheduling control means for switching between the first scheduling means and the second scheduling means for performing scheduling;
The base station according to claim 20, further comprising: A communication program executed in a computer that communicates with a plurality of wireless terminals using a plurality of antennas,
A first beam forming step of forming m (m is an integer of 1 or more) beams using the plurality of antennas;
A pilot signal transmission step of transmitting a pilot signal in each of the m beams;
A reception state value receiving step of receiving reception state values of the m beams from each of the wireless terminals;
A communication quality acquisition step of acquiring information on required communication quality required by each of the wireless terminals;
Based on the reception state value for the m beams of each of the radio terminals, n (1 ≦ n ≦) used among the m beams so that the n radio terminals satisfy the required communication quality. m) a scheduling step for determining n beams and n radio terminals to which the n beams are allocated;
A second beam forming step of forming the corresponding n beams for each of the n wireless terminals determined by the scheduling step;
A data transmission step of transmitting data to each wireless terminal by a beam formed for each wireless terminal;
A communication program comprising: A communication method executed in a computer that communicates with a plurality of wireless terminals using a plurality of antennas,
A first beam forming step of forming m (m is an integer of 1 or more) beams using the plurality of antennas;
A pilot signal transmission step of transmitting a pilot signal in each of the m beams;
A reception state value receiving step of receiving reception state values of the m beams from each of the wireless terminals;
A communication quality acquisition step of acquiring information on required communication quality required by each of the wireless terminals;
Based on the reception state value for the m beams of each of the radio terminals, n (1 ≦ n ≦) used among the m beams so that the n radio terminals satisfy the required communication quality. m) a scheduling step for determining n beams and n radio terminals to which the n beams are allocated;
A second beam forming step of forming the corresponding n beams for each of the n wireless terminals determined by the scheduling step;
A data transmission step of transmitting data to each wireless terminal by a beam formed for each wireless terminal;
A communication method comprising: A communication program executed in a computer that communicates with a plurality of wireless terminals using m (m is an integer of 1 or more) antennas,
A pilot signal transmission step of transmitting a pilot signal by each of the m antennas;
A channel response receiving step for receiving channel response information between each of the wireless terminals and the m antennas;
A communication quality acquisition step of acquiring information on required communication quality required by each of the wireless terminals;
Based on the information on the channel response to the m antennas of each of the wireless terminals, n (1 ≦ n ≦ m) scheduling steps for determining the antennas and n wireless terminals to which the n antennas are assigned;
A beam forming step of forming n beams for each of the n radio terminals in accordance with antennas respectively assigned to the n radio terminals and information of the propagation path responses;
A data transmission step of transmitting data to each of the wireless terminals by a beam formed for each of the wireless terminals;
A communication program comprising:

Images