JP2009212560A - Base station, communication program, and wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform scheduling for obtaining a large channel capacity while reducing a calculation amount by appropriately setting the number of using beams. <P>SOLUTION: The base station is provided with: a first beam formation means for forming M pieces, which is the number of beam candidates, of beams using a plurality of antennas; a pilot signal transmission means for transmitting pilot signals by each of M pieces of the beams; a beam number determination means for determining the number L (L is an integer ≥1 and ≤M) of the using beams on the basis of the number of a plurality of wireless terminals to be communication objects and the number M of the beam candidates; a notification means for notifying the plurality of wireless terminals of the number L of the using beams; a feedback reception means for receiving feedback information from the respective wireless terminals; and a scheduling means for determining the L pieces of the using beams and the wireless terminals to allocate the L pieces of the using beams. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a base station that performs communication using a plurality of antennas, a communication program, and a radio communication system, and more particularly to a base station that performs scheduling.

  As a transmission method capable of speeding up 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. The MIMO transmission method is a technique in which streams independent from a plurality of transmission antennas are multiplexed and transmitted at the same time and at the same frequency, and the received stream is separated by spatial filtering or maximum likelihood determination.

  One of the MIMO transmission systems is a transmission system called a transmission beamforming system. In the transmission beamforming method, a plurality of users can be spatially multiplexed by forming a beam and transmitting, and communication with a plurality of users can be performed at the same time and the same frequency. Such a MIMO communication system is generally called a multi-user MIMO system or a SDMA (Spatial Division Multiple Access) system. In a multi-user MIMO system, a beam is usually formed based on the channel response between the transceiver antennas fed back from each user. However, since the amount of information to be fed back is large, the feedback time or bandwidth increases, Throughput decreases.

One of the methods that can reduce the amount of information fed back by the user is a method called a random beamforming method (for example, Non-Patent Document 1). In the random beam forming method, transmission is not performed with a beam formed based on a propagation path response between transceiver antennas, but is performed with a beam randomly formed by a base station. In a multi-user MIMO system using a random beamforming method, the information fed back by the user is not the channel response between the transceiver antennas but the reception gain or desired beam number for the beam arbitrarily formed by the base station . Therefore, the feedback amount can be significantly reduced as compared with the case where the propagation path response is fed back, and high transmission characteristics can be obtained by performing scheduling for appropriately selecting the user to be allocated to the beam at the base station.
M. Sharif and B. Hassibi, “On the capacity of MIMO broadcast channel with partial side information,” IEEE Trans. Information Theory, Vol. 51, no. 2, pp. 506-522, Feb. 2005. Vicario, JL Bosisio, R. Spagnolini, U. Carles Anton-Haro, “Adaptive Beam Selection Techniques for Opportunistic Beamforming,” in Proc. PIMRC, Sep. 2006. Zhengang Pan, Lan Chen, “Complexity-reduced Adaptive Opportunistic Spatial Division Multiple Access for Downlink with Close-loop Control,” IWCMC, pp.159-164, 2006

  In a random beamforming method in a multi-user environment, the base station selects a beam to be used and a user to be assigned to the beam to be used based on feedback information from the user (for example, reception gain or desired beam number to be assigned). This is called scheduling, and scheduling requires selection to increase the channel capacity as much as possible. Scheduling when reception gain is fed back from each user includes a method called full search method or Greedy method (Non-patent Document 2). These methods select the beam to be used and the user assigned to the beam to be used so as to obtain the best channel capacity. At this time, there is a problem that the amount of calculation becomes enormous because the search is performed up to the number of used beams as parameters. When scheduling is performed with the number of used beams limited, the amount of calculation can be reduced, but a large (for example, the best) channel capacity cannot be obtained unless an appropriate number of used beams is set.

  Furthermore, the number of beams to be used is determined in advance, and for scheduling when the desired beam number is fed back from each user, users who can match the desired beam number are selected (Non-Patent Document 3). . In this case, there is a problem that a large channel capacity cannot be obtained depending on the number of beams used.

  For this reason, in a multi-user MIMO system using a random beamforming method, it is necessary to appropriately determine the number of beams to be set in advance in order to obtain a large channel capacity while reducing the amount of calculation by scheduling.

  The present invention provides a base station, a communication program, and a wireless communication system that enable scheduling to obtain a large channel capacity while reducing the amount of calculation by appropriately setting the number of used beams.

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 number of beam candidates using the plurality of antennas;
Pilot signal transmitting means for transmitting a pilot signal in each of the M beams;
Beam number determining means for determining the number of used beams L (L is an integer of 1 or more and M or less) based on the number of the plurality of wireless terminals to be communicated and the number of beam candidates M;
Notifying means for notifying the number of used beams L to the plurality of wireless terminals;
Feedback receiving means for receiving feedback information based on the pilot signal transmitted in each of the M beams and the number of used beams L from each of the wireless terminals;
Scheduling means for determining the L used beams and the radio terminals to which the L used beams are allocated by performing scheduling based on feedback information received from each of the wireless terminals;
Second beam forming means for forming the beam determined by the scheduling means for each wireless terminal determined by the scheduling means;
Data transmitting means for transmitting data to each of the determined wireless terminals by a beam formed for each of the determined wireless terminals;
Is provided.

A communication program as one aspect of the present invention is:
A communication program for causing a computer to communicate with a plurality of wireless terminals using a plurality of antennas,
A first beam forming step of forming M beams using the plurality of antennas;
A pilot signal transmission step of transmitting a pilot signal in each of the M beams;
A beam number determination step of determining a beam number L (L is an integer of 1 to M) based on the number of the plurality of wireless terminals to be communicated and the beam candidate number M;
A notification step of notifying the number of used beams L to the plurality of wireless terminals;
A feedback reception step of receiving feedback information based on the pilot signal transmitted in each of the M beams and the number of used beams L from each of the wireless terminals;
A scheduling step of determining the L used beams and the radio terminals to which the L used beams are allocated by performing scheduling based on feedback information received from each of the wireless terminals;
A second beam forming step of forming a beam determined by the scheduling step for each of the wireless terminals determined by the scheduling step;
A data transmission step of transmitting data to each determined wireless terminal by a beam formed for each determined wireless terminal;
Is provided.

A wireless communication system as one aspect of the present invention includes:
A wireless communication system comprising a plurality of wireless terminals and a base station that communicates with the plurality of wireless terminals using a plurality of antennas,
The base station
First beam forming means for forming M number of beam candidates using the plurality of antennas;
Pilot signal transmitting means for transmitting a pilot signal in each of the M beams;
Beam number determining means for determining the number of used beams L (L is an integer of 1 or more and M or less) based on the number of the plurality of wireless terminals to be communicated and the number of beam candidates M;
Notifying means for notifying the number of used beams L to the plurality of wireless terminals;
Feedback receiving means for receiving feedback information based on the pilot signal transmitted in each of the M beams and the number of used beams L from each of the wireless terminals;
Scheduling means for determining the L used beams and the radio terminals to which the L used beams are allocated by performing scheduling based on feedback information received from each of the wireless terminals;
Second beam forming means for forming the beam determined by the scheduling means for each wireless terminal determined by the scheduling means;
Data transmitting means for transmitting data to each of the determined wireless terminals by a beam formed for each of the determined wireless terminals;
With
Each of the wireless terminals
Pilot signal receiving means for receiving a pilot signal transmitted from each of the M beams from the base station;
Used beam number receiving means for receiving notification of the used beam number L from the base station;
Feedback information generating means for generating the feedback information based on each pilot signal received by the pilot signal receiving means and the number of used beams L;
Feedback information transmitting means for transmitting the feedback information to the base station;
Is provided.

  According to the present invention, by appropriately setting the number of used beams, it is possible to perform scheduling such that a large channel capacity can be obtained while reducing the amount of calculation.

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

(First embodiment)
FIG. 1 is a diagram illustrating a configuration example of a multi-user MIMO system using a random beamforming method.

  This multi-user MIMO system includes a transmission device (base station) 10 and a plurality of reception devices 20 (user terminals).

The base station 10 includes a digital signal processing unit 102, N _t radio units 101, and N _t antennas 103. A detailed configuration of the digital signal processing unit 102 is shown in FIG. The digital signal processing unit 102 includes a data signal transmission processing unit 1021, a scheduling unit 1022, and a feedback signal reception processing unit 1024.

  Each of the plurality of user terminals 20 includes a digital signal processing unit 202, a radio unit 201, and a single antenna 203. A detailed configuration of the digital signal processing unit 202 is shown in FIG. The digital signal processing unit 202 includes a data signal reception processing unit 2021 and a feedback signal transmission processing unit 2022.

  FIG. 5 is a flowchart showing a flow of a series of processes performed in the base station 10 and each user terminal 20 until the base station 10 transmits data to each user terminal 20 in the multi-user MIMO system using the random beamforming method. is there. FIG. 6 is an example of a slot structure used by the multiuser MIMO system of the present invention.

  As shown in FIG. 5, the processing flow performed in the multi-user MIMO system is performed in the order of propagation path information acquisition process A1, scheduling process A2, and user data transmission process A3. Further, the slot structure shown in FIG. 6 includes a propagation path information estimation time zone, a propagation path information feedback time zone, and a data transmission time zone corresponding to each process of FIG. These time zones can be set according to system requirements. Here, detailed description of the slot structure is omitted.

  Hereinafter, the processing flow of the flowchart of FIG. 5 will be described in detail. However, in this embodiment, the base station determines the number of used beams L (≦ M) in advance according to the number M of beam candidates and the total number of users (the number of user terminals to be subjected to data communication), It is assumed that the determined number L of used beams is notified to each user terminal in advance. This is one of the major features of this embodiment. The reason why the number L of used beams is determined according to the total number of users and a specific determination method will be described in detail later.

(Propagation path information acquisition process A1)
Before transmitting data signals, the base station 10 transmits pilot signals (known signals) to each user terminal 20 using M (M < N _t ) transmission beam candidates using N _t antennas (S11). . FIG. 2 shows an example in which pilot signals are transmitted by randomly forming two beams. The data signal transmission processing unit 1021 includes first beam forming means that forms M beam candidates using a plurality of antennas, and pilot signal transmission means that transmits pilot signals using M beams.

は次式（1）で表される。

但し、sはＭ次元の情報信号ベクトルである。Ｗは情報信号ベクトルsに乗算されるN_t×M次元の複素送信ウェイト行列であり、複素送信ウェイトベクトル

から構成される。なお、C^Nt×1はN_t行×１列の複素数の集合を示し、w_mはN_t行×１列の複素数の集合の１つである。ここで複素送信ウェイト行列Ｗは、任意の行列の特異値分解により得られる右特異行列を用いてもよいし、任意の行列に対してGram-Schmidt直交化を適用させた行列を用いてもよい。また、コードブック（Codebook）として予め用意されたウェイトを選択して用いてもよい。本発明における複素送信ウェイト行列Ｗの生成法は上記に制限されるものではない。また、複素送信ウェイト行列Ｗは、スロット毎に異なるものを用いても良いし、伝搬路時間変動などに応じて複数スロットに跨いで同一のものを用いてもよい。 N _t -dimensional complex transmission signal vector transmitted from the base station 10

Is represented by the following equation (1).

Here, s is an M-dimensional information signal vector. W is an N _t × M-dimensional complex transmission weight matrix multiplied by the information signal vector s, and the complex transmission weight vector

Consists of C ^{Nt × 1} represents a set of complex numbers of N _t rows × 1 column, and w _m is one of a set of complex numbers of N _t rows × 1 column. Here, as the complex transmission weight matrix W, a right singular matrix obtained by singular value decomposition of an arbitrary matrix may be used, or a matrix obtained by applying Gram-Schmidt orthogonalization to an arbitrary matrix may be used. . Also, a weight prepared in advance as a codebook (Codebook) may be selected and used. The method of generating the complex transmission weight matrix W in the present invention is not limited to the above. Also, the complex transmission weight matrix W may be different for each slot, or the same one may be used across a plurality of slots according to propagation path time fluctuation.

は次式（２）で表される。

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次元の伝搬路応答ベクトルであり、伝搬路応答ベクトル

のi番目の要素h_k,iは、基地局10の第i番目アンテナ103とユーザ端末20のアンテナ203間の伝搬路応答特性を示す。n_kは各要素がｋ番目のユーザ端末20に含まれる無線部201における雑音を表す。 Each user terminal 20 receives the pilot signal transmitted from the base station 10 (S12). Now, assuming that the total number of users is K, the _Nr- dimensional complex received signal vector received at the kth (1 < k < K) th user terminal 20 at this time.

Is represented by the following equation (2).

h _k is an N _t -dimensional channel response vector having a channel response between the transceiver antennas of the base station 10 and the k-th user terminal 20 as an element, and the channel response vector

I-th element h _{k, i} indicates a channel response characteristic between the i-th antenna 103 of the base station 10 and the antenna 203 of the user terminal 20. n _k represents noise in the radio unit 201 included in the k-th user terminal 20 with each element.

In the k-th user terminal 20, the reception signal y _k received via the antenna 203 is processed by the radio unit 201 to be converted into a digital signal and notified to the digital signal processing unit 202. The radio unit 201 for performing the reception process 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.

として次式（3）で表される。

ここで、g_k,mはｋ番目ユーザ端末のｍ番目ビームに対する受信電力を表す。本実施形態では各ビームの受信状態として受信電力を用いたが、受信電力に限定されるものではなく、各ビームの受信状態を把握できるものであれば他のいかなる規範を用いても良い。 The data signal reception processing unit 2021 demodulates and decodes the digital signal notified from the wireless unit 201. In the propagation path information acquisition process A1, since the information signal vector s in Equation (2) is known, the user terminal can measure the reception state for each beam. The reception state for each beam of the kth user terminal is an M-dimensional vector

Is expressed by the following equation (3).

Here, g _{k, m} represents received power for the m-th beam of the k-th user terminal. In this embodiment, the received power is used as the reception state of each beam. However, the present invention is not limited to the received power, and any other standard may be used as long as the reception state of each beam can be grasped.

The data signal reception processing unit 2021 calculates the reception state vector g _k by measuring the reception state for each beam as described above. When the reception state vector g _k is calculated at each user terminal, the beam combination that maximizes the SINR (Signal to Interference and Noise Ratio) according to the number of used beams L notified in advance from the base station 10 Is derived by the following steps. The data signal reception processing unit 2021 includes used beam number receiving means for receiving notification of the used beam number L from the base station 10.

（２）ユーザkにとって受信ゲインが最小となるL-1個のビームの番号の集合P_kを決定する

（３）前記ステップ（１）、（２）で決定したビーム番号に従いSINR_kを計算する

(1) The beam number d _k that maximizes the reception gain for the user _k is determined.

(2) Determine a set P _k of L-1 beam numbers that minimizes the reception gain for user k.

(3) SINR _k is calculated according to the beam number determined in steps (1) and (2).

The data signal reception processing unit 2021 generates d _k , P _k , and SINR _k as feedback information according to steps (1) to (3) (S13), and notifies the generated feedback information to the feedback signal transmission processing unit 2022. . d _k corresponds to the number of the beam that the user terminal k wants to assign to itself, and P _k corresponds to the number of the beam that the user terminal k wants to assign to another user terminal. Information of d _k and P _k corresponds to desired use information, and SINR _k corresponds to reception quality information. However, the reception quality information is not limited to SINR, and other standards (for example, SIR (Signal to Interference Ratio)) may be used as long as they indicate reception quality.

  The feedback signal transmission processing unit 2022 generates a feedback signal by encoding and modulating the feedback information notified from the data signal reception processing unit 2021 as an information signal, and transmits the generated feedback signal to the base station 10 (S14). As a coding method and a modulation method applied to the feedback signal, any method may be used as long as the base station 10 can decode and demodulate.

  The base station 10 receives the feedback signal from the user terminal 20, processes the received feedback signal into a digital signal by the radio unit 101, and notifies the digital signal to the feedback signal reception processing unit (feedback receiving unit) 1024. (S15). Since the wireless unit 101 has a general configuration including a low noise amplifier, a frequency converter, an analog / digital (A / D) converter, and a filter, detailed description thereof is omitted.

Feedback signal reception processing section 1024 demodulates and decodes the digital signal notified from radio section 101, and obtains d _k , P _k , and SINR _k information. 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 1024 notifies the scheduling unit 1022 of d _k , P _k , and SINR _k of each user terminal.

(Scheduling process A2)
The scheduling unit (scheduling unit) 1022 performs scheduling based on the feedback information (d _k , P _k , SINR _k ) notified from the feedback reception signal processing unit 1024 and the total number of users information 1023 notified from the upper layer (S16). ).

  Total user information (terminal number information) 1023 indicates the total number of users (the number of user terminals that are targets of data communication) existing in the cover area of the base station. The base station performs authentication with the user terminals existing in the cover area, whereby the base station grasps the total number of users. The total user information 1023 is given to the scheduling unit 1022 from the upper layer, for example. The base station may include storage means for storing the total user information 1023.

とが得られ、これらをスケジューリング情報として、データ信号送信処理部1021に通知する。この際、選択されたユーザ端末のSINRも、スケジューリング情報に含めて、データ信号送信処理部1021に通知してもよい。 Here, the scheduling means that the base station 10 determines the used beam and the user terminal assigned to each used beam. Details of the scheduling process will be described later. As a result of scheduling by the scheduling unit 1022, the used beam and user terminals allocated to each used beam

And these are notified to the data signal transmission processing unit 1021 as scheduling information. At this time, the SINR of the selected user terminal may be included in the scheduling information and notified to the data signal transmission processing unit 1021.

(Data transmission process A3)
In the data signal transmission processing unit 1021, information transmitted from an upper layer based on the scheduling information (used beam, user assigned to each used beam, and SINR of the user terminal assigned to the used beam) notified from the scheduling unit 1022 A process of transmitting a signal (user data) to be assigned to each beam stream is performed (S17). The data signal transmission processing unit 1021 sends second user beam forming means for forming a beam determined by scheduling to each user terminal determined by scheduling, and each user terminal by using the beam formed for each user terminal. Data transmitting means for transmitting the data.

  Specifically, the digital signal is generated by encoding and modulating the user information signal selected by scheduling in the data signal transmission processing unit 1021 and further multiplying by a weight for forming a transmission beam. To do. At this time, the data signal transmission processing unit 1021 may determine the coding rate and the modulation scheme based on the reception quality of each user terminal indicated in the scheduling information. As the encoding method / modulation method in the present invention, any method may be used as long as it can be decoded and demodulated by the user terminal. The radio unit 101 is notified of the digital signal after weight multiplication.

  Radio section 101 mainly performs a process of converting a digital signal notified from data signal transmission processing section 1021 into an analog signal, and transmits the analog signal via antenna 103. Since the wireless unit 101 has a general configuration including a filter, a digital-analog converter, and a power amplifier, detailed description thereof is omitted.

(Scheduling explanation)
The scheduling unit 1022 of the base station 10 determines a user terminal whose channel capacity is maximized based on feedback information from each user terminal.

When U _opt is a combination of users that maximizes channel capacity, U _opt is expressed by the following equation.

That is, among the user combinations that can match the beam number d _k that the user terminal k wants to be assigned to the beam number P _k that is desired to be assigned to another user terminal, the user combination that maximizes the channel capacity _Is selected as U _opt .

When the number M of beam candidates is large with respect to the total number of users, or when the total number K of users is small, the probability that there is a user combination that can be matched decreases. When there is no matching user combination, the scheduling unit 1022 of the base station 10 performs scheduling by reducing (or increasing) the number of used beams. However, in this case, since scheduling is performed based on feedback information (d _k , P _k , SINR _k ) calculated assuming the number of used beams L, scheduling for obtaining a large channel capacity is performed when the number of used beams is reduced. Difficult to implement.

  In order to minimize the execution of such imperfect scheduling, it is considered to increase the probability that there is a user combination that can be matched by adaptively controlling the number L of used beams. .

  For example, when the number of beam candidates M = 10, the probability that there is a matching user combination is higher when the number of used beams L = 2 than when the number of used beams L = 3, and incomplete scheduling Can reduce the possibility of executing.

  However, for example, when the total number of users is small, there is a low probability that there is a combination of a beam and a user terminal that originally reduces inter-user interference. Nevertheless, in scheduling, selection is performed so as to spatially multiplex user terminals that can be matched, so it is difficult to obtain a large channel capacity. On the other hand, when there are many user terminals, the probability that there exists a combination of a beam and a user terminal with which the interference between users becomes small increases. Nevertheless, if the number of beams used L is set small to increase the probability that there is a combination that can be matched, the effect of multi-user diversity gain cannot be obtained sufficiently, and it is difficult to obtain the best channel capacity .

  In this way, the base station determines the number of used beams L (≦ M) in advance, and the optimum setting of the number of used beams L in a system in which the number of used beams L is known also on the user terminal side affects system performance. This is an important issue.

Therefore, the present embodiment is characterized in that the number of used beams L is determined from the relationship between the number of beam candidates M (≦ N _t ) used in the base station and the total number of users K, and the determined number of used beams L is used. .

  FIG. 7 shows the total number of users K versus channel capacity characteristics when the number of used beams is L = 1, 2, 3 when the number of transmitting antennas of the base station is 3, the number of receiving antennas of the user terminal is 1, and the number of beam candidates is 3. . This characteristic graph is created based on the result of the simulation performed independently by the present inventors.

  As shown in FIG. 7, the number of used beams is 1 when the total number of users is 1 to 10, the number of used beams is 2 when the total number of users is 11 to 1500, and the number of used beams is 3 when the total number of users is 1501 or more. It turns out that there is a tendency.

  Therefore, in the system described in the present embodiment, it is understood that the possibility of executing imperfect scheduling is reduced and a large channel capacity can be obtained by determining the number L of used beams by the total number K of users. Is done.

  As described above, in order to determine the number of used beams from the number of beam candidates and the total number of users, the scheduling unit 1022 holds in advance, as table data, the relationship between the total number of users and the number of used beams for each number of beam candidates. The number of used beams L is determined by referring to the table data based on the number M and the total number of users K, and the determined number of used beams L is notified to each user terminal.

  Instead of the table data, a function for obtaining the number of used beams from the number of beam candidates and the total number of users may be held. In addition, as long as the correspondence information correlates the number of beam candidates, the total number of users, and the number of used beams, information different from table data and functions may be used. Corresponding information includes (1) the total number of users for each number of used beams vs. channel capacity characteristics acquired in advance for each number of beam candidates, and (2) the total number of users for each number of used beams vs. SINR (signal to interference noise power ratio) characteristics, (3) It is preferable to create based on the total number of users for each number of used beams versus SIR (signal to interference power ratio) characteristics.

  The scheduling unit includes a storage unit that stores correspondence information (for example, a table and a function), and a beam number determination unit that determines the number L of used beams by referring to the correspondence information based on the number of beam candidates and the total number of users information 1023. And notification means for notifying each user terminal of the determined number L of used beams.

When notifying the determined number of used beams L, a general frame configuration including a preamble part, a control signal part, and a data part shown in FIG. 8 can be used. The base station 10 notifies the user terminal of the number of used beams L determined by the total number K of users using the control signal portion of the frame. As a result, the data signal reception processing unit 2021 in each user terminal can know the optimum number L of used beams. Each user terminal, based on the reported number of used beams L and the pilot signal received from the base station, assigns desired beam number d _k , beam number P _k desired to be assigned to other user terminals, SINR _k , Is calculated.

  As described above, according to the present embodiment, the number of beam candidates (the number of beams that form a pilot signal transmission, that is, the number of beams formed by the first beam forming unit) and the total number of users are used. By determining the number of beams L, the possibility of executing imperfect scheduling is reduced, and a large channel capacity can be obtained.

Above, it has been described how many antennas the user terminal as one in the present embodiment, in the case of N _r book of the present invention by treating as there are K × N _r base of the user terminal applies without problems Is possible. That is, the number of wireless terminals to be communicated may be handled as the total number of antennas of each wireless terminal. In addition, although the description has been made on the assumption of a single carrier system, this embodiment has also been described for each subcarrier in a multicarrier system such as OFDM (Orthogonal Frequency Division Multiplexing) or OFDMA (Orthogonal Frequency Division Multiple Access). It is possible to apply the method (second embodiment)
The configurations of the base station and the user terminal in this embodiment are the same as those in FIG. 1, FIG. 3, and FIG. 4, and the series of flow from the propagation path information acquisition process A1 to the user data transmission process A3 is also the same as in FIG. The slot structure is also the same as in FIG. The main difference between this embodiment and the first embodiment is that the number of used beams L is not determined in advance, and the information fed back from each user terminal is a vector g _k representing the reception state for all beam candidates. It is a point. Hereinafter, this embodiment will be described in detail.

は前述の式（２）で表される。 (Propagation path information acquisition process A1)
Before transmitting data signals, the data signal transmission processing unit 1021 of the base station 10 pilots each user terminal 20 with M (M < N _t ) transmission beam candidates formed using N _t antennas. A signal (known signal) is transmitted (S11). Each user terminal 20 receives the pilot signal transmitted from the base station 10 (S12). At this time, the N _r -dimensional complex received signal vector received at the k-th (1 < k < K) user terminal 20

Is represented by the above-mentioned formula (2).

として前述の式（3）で表される。 The data signal reception processing unit 2021 in the user terminal 20 calculates the reception state vector g _k as feedback information by measuring the reception state for each beam (S13). The reception state for each beam of the kth user is an M-dimensional vector.

Is expressed by the above-described formula (3).

The data signal reception processing unit 2021 notifies the calculated feedback information (reception state vector g _k ) to the feedback signal transmission processing unit 2022. At this time, the feedback information may not be the reception state vector g _k calculated by Expression (3), but may be an effective channel response.

The feedback signal transmission processing unit 2022 generates a feedback signal by encoding and modulating the feedback information (reception state vector g _k ) notified from the data signal reception processing unit 2021 as an information signal, and the generated feedback signal Transmit to the base station 10 (S14). That is, the feedback signal from the user terminal includes reception state information for each beam of the user terminal. However, when the reception state is bad for any beam, 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 the base station 10 can decode and demodulate.

  The base station 10 receives the feedback signal from the user terminal 20, processes the received feedback signal by the radio unit 101 to be a digital signal, and notifies the digital signal to the feedback signal reception processing unit 1024 (S15).

Feedback signal reception processing section 1024 demodulates and decodes the digital signal notified from radio section 101 to obtain information on reception state vector g _k . 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 1024 notifies the scheduling unit 1022 of the reception state vector g _k of each user terminal.

(Scheduling process A2)
The scheduling unit 1022 performs scheduling based on the reception state vector g _k (1 < k < K) for each beam of each user terminal notified from the feedback signal reception processing unit 1024 and the total number of users information 1023 notified from the upper layer. Perform (S16). At this time, it is not always necessary to schedule the M beams used in the channel information acquisition process A1 to be used in the user data transmission process A3. The selection of 1 ≦ L ≦ M) is also included in the scheduling. Details of the scheduling process A2 will be described later. As a result of scheduling by the scheduling unit 1022, information on the used beam, the user assigned to each used beam, and reception quality (for example, SINR) are obtained, and these are notified to the data signal transmission processing unit 1021 as scheduling information.

(Data transmission process A3)
The data signal transmission processing unit 1021 transmits from the upper layer based on the scheduling information notified from the scheduling unit 1022 (used beam, user assigned to each used beam, and reception quality of the user terminal assigned to the used beam). A process of transmitting an information signal (user data) so as to be assigned to each beam stream is performed (S17). Since the processing content is the same as that of the first embodiment, detailed description thereof is omitted.

である。ここで、N₀は雑音電力を表す。また、Bは使用するビームの集合を表し、例えばB={1,4}とは、1番目ビームを形成するウェイトw₁と4番目ビームを形成するウェイトw₄を使用することを示す。また、|B|は集合Bの要素総数であり、B={1,4}の場合、|B|=2である。前記受信品質SINR_k,mを用いてｋ番目ユーザがｍ番目ビームに対して得られるチャネル容量Ｒ_k,mは、次式（9）により表される。

(Scheduling explanation)
The reception quality SINR _{k, m} for the m-th beam of the k-th user terminal is expressed by the following equation (8) using the element g _{k, m} of the reception state vector g _k obtained from the feedback information.

It is. Here, N ₀ represents noise power. B represents a set of beams to be used. For example, B = {1, 4} indicates that the weight w ₁ for forming the _first beam and the weight w ₄ for forming the fourth beam are used. | B | is the total number of elements of set B. When B = {1,4}, | B | = 2. The channel capacity R _{k, m} obtained by the k-th user for the m-th beam using the reception quality SINR _{k, m} is expressed by the following equation (9).

ここでQとは、k番目のユーザ端末に割り当てるｍ番目ビームの組み合わせ（k,m）の集合を表し、例えば

とは、1番目のユーザ端末に3番目のビームを割り当て、3番目のユーザ端末に2番目のビームを割り当てる組み合わせの集合を示す。 The total channel capacity _CQ is expressed by the following equation (10).

Here, Q represents a set of m-th beam combinations (k, m) assigned to the k-th user terminal, for example,

Indicates a set of combinations in which the third beam is allocated to the first user terminal and the second beam is allocated to the third user terminal.

As a method of selecting a combination _Q that maximizes the total channel capacity CQ, a full search method or a Greedy method is generally known. In these scheduling methods, a search is performed using the number of used beams L as a parameter to determine a combination of a beam and a user terminal that can obtain a large channel capacity. Therefore, when the number M of beam candidates increases, there is a problem that the amount of calculation in the scheduling process becomes enormous. The search can be reduced by limiting the number of used beams, but if the limited number of used beams is not appropriate, the channel capacity is greatly reduced.

  Therefore, in the present embodiment, the number of used beams L to be searched is determined according to the number of beam candidates M and the total number of users K, and a large channel capacity is obtained with a small amount of calculation by performing a search with the determined number of used beams L. It is characterized by that. This will be described in detail below.

  When the total number K of users is relatively small with respect to the number M of transmission beam candidates, the probability that there is a combination of a beam and a user terminal that reduces the interference between users is low. As a result, when the number L of used beams is increased, a high channel capacity cannot be expected due to the influence of inter-user interference. On the other hand, when the total number of users K is relatively large with respect to the number M of transmission beam candidates, the probability that there exists a combination of a beam and a user terminal that reduces the inter-user interference increases. As a result, a high channel capacity can be expected even when the number L of used beams is increased. Therefore, if the number M of beam candidates to be used at the base station is determined, the best number L of used beams can be determined according to the total number K of users.

  FIG. 9 shows the total number of users when the number of used beams is limited to L = 1, 2, 3 when the number of transmitting antennas of the base station is 3, the number of receiving antennas of the user terminal is 1, and the number of used beam candidates is 3. An example of channel capacity characteristics is shown. This characteristic graph is created based on the result of the simulation performed independently by the present inventors.

  As shown in FIG. 9, the total channel capacity tends to be large when the total number of users 1 to 10 is 1, the number of used beams is 1, the total number of users is 11 to 1000, the number of used beams is 2, and the total number of users is 1001 or more. I know that there is.

  As described above, in order to determine the number of used beams from the number of beam candidates and the total number of users, the scheduling unit 1022 holds in advance, as table data, the relationship between the total number of users and the number of used beams for each number of beam candidates. The number of used beams L is determined by referring to the table data based on the number M and the total number K of users. By performing the search for the number of used beams L determined in this way, the calculation amount can be greatly reduced and the best channel capacity can be obtained.

  Instead of the table data, a function for obtaining the number of used beams from the number of beam candidates and the total number of users may be held. In addition, as long as the correspondence information correlates the number of beam candidates, the total number of users, and the number of used beams, information different from table data and functions may be used. Corresponding information includes (1) the total number of users for each number of used beams vs. channel capacity characteristics acquired in advance for each number of beam candidates, and (2) the total number of users for each number of used beams vs. SINR (signal to interference noise power ratio) characteristics, (3) It is preferable to create based on the total number of users for each number of used beams versus SIR (signal to interference power ratio) characteristics.

  Here, when it is not certain that either the number of used beams 1 or the number of used beams 2 can provide a larger channel capacity as in the case of the total number of users K = 10 given in the example of FIG. Scheduling with both Equation 1 and the number of beams used 2 may ensure a large channel capacity. Even in this case, since the scheduling is not performed in the case of the number of used beams 3 where a high channel capacity cannot be expected, the calculation amount can still be reduced.

  In addition, the present embodiment is not applicable only to the full search method or the Greedy method as a scheduling method, and other scheduling methods may be used. In any scheduling method, the best number of used beams with respect to the total number of users is checked in advance, so that only the best number of used beams is searched in the scheduling process, and the channel capacity is maximized while reducing the calculation amount. It is possible.

Above, it has been described how many antennas the user terminal as one in the present embodiment, in the case of N _r book of the present invention by treating as there are K × N _r base of the user terminal applies without problems Is possible. That is, the number of wireless terminals to be communicated may be handled as the total number of antennas of each wireless terminal. In addition, although the description has been made on the assumption of a single carrier system, this embodiment has also been described for each subcarrier in a multicarrier system such as OFDM (Orthogonal Frequency Division Multiplexing) or OFDMA (Orthogonal Frequency Division Multiple Access). It is possible to apply the method.

  As described above, according to the present embodiment, the base station determines the number of used beams on the basis of the number of beam candidates and the total number of users, thereby performing a search for the determined number of used beams when performing scheduling. As a result, the calculation amount can be greatly reduced and a large channel capacity can be obtained.

  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, a digital signal processing unit, a radio unit, a feedback signal reception processing unit, a scheduling unit, a data signal transmission processing unit, etc. in a base station, and a digital signal processing unit, a radio unit, a data signal reception processing unit, feedback in a user terminal The signal transmission processing unit can be realized by causing a processor mounted on the computer device 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 the above program 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.

The block block diagram of the radio | wireless communications system concerning embodiment of this invention. The conceptual diagram of the MIMO transmission system which applied the 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 which shows the flow of a process until the data transmission in a random beam forming system. The figure which shows an example of a slot structure. The figure of an example which shows the user total versus channel capacity | capacitance characteristic for every use beam number in 2nd Embodiment. The figure which shows an example of a frame format. The figure of an example which shows the user total versus channel capacity | capacitance characteristic for every use beam number in 1st Embodiment.

Explanation of symbols

10 ... Transmitting device (base station)
101 ... Radio unit in transmitter
102: Digital signal processing unit in transmission device
1021 ・ ・ ・ Data signal transmission processing unit
1022 ・ ・ ・ Scheduling part
1023 ・ ・ ・ User total number information
1024 ・ ・ ・ Feedback signal reception processor
20 ... Receiving device (user terminal)
201 ... Radio unit in receiver
202 ... Digital signal processing unit in the receiving apparatus
2021 ・ ・ ・ Data signal reception processing section
2022 ... Feedback signal transmission processing unit

Claims (23)

A base station that communicates with a plurality of wireless terminals using a plurality of antennas,
First beam forming means for forming M number of beam candidates using the plurality of antennas;
Pilot signal transmitting means for transmitting a pilot signal in each of the M beams;
Beam number determining means for determining the number of used beams L (L is an integer of 1 or more and M or less) based on the number of the plurality of wireless terminals to be communicated and the number of beam candidates M;
Notifying means for notifying the number of used beams L to the plurality of wireless terminals;
Feedback receiving means for receiving feedback information based on the pilot signal transmitted in each of the M beams and the number of used beams L from each of the wireless terminals;
Scheduling means for determining the L used beams and the radio terminals to which the L used beams are allocated by performing scheduling based on feedback information received from each of the wireless terminals;
Second beam forming means for forming the beam determined by the scheduling means for each wireless terminal determined by the scheduling means;
Data transmitting means for transmitting data to each of the determined wireless terminals by a beam formed for each of the determined wireless terminals;
Base station equipped with. A storage unit that stores correspondence information in which the number of beam candidates, the number of wireless terminals to be communicated, and the number of used beams are associated;
The beam number determining means determines the number L of used beams by referring to the correspondence information based on the number M of beam candidates and the number of the plurality of wireless terminals to be communicated. Item 4. The base station according to Item 1.   The base station according to claim 1 or 2, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus channel capacity characteristics acquired in advance for each number of beam candidates.   3. The base station according to claim 1, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus SINR (signal to interference noise power ratio) acquired in advance for each number of beam candidates.   The base station according to claim 1, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus SIR (signal to interference power ratio) acquired in advance for each number of beam candidates. The feedback information is
Indicates H (H is an integer greater than or equal to 1) first beams that the wireless terminal desires to use, and LH second beams that the wireless terminal desires to use by other wireless terminals. Desired usage information and
Reception quality information indicating reception quality of the wireless terminal obtained when the first beam is used by the wireless terminal and the LH second beams are used by the other wireless terminal;
The base station according to claim 1, further comprising:   The base station according to claim 6, wherein the scheduling section performs the scheduling so that the desired usage information of each of the wireless terminals to which the L number of used beams are allocated matches.   The scheduling means increases or decreases the number of used beams L by a predetermined number and performs the scheduling again when scheduling that matches the desired usage information of each wireless terminal to which the L used beams are allocated cannot be performed. The base station according to claim 7. The data transmission means includes
Based on the reception quality for the beam assigned to each wireless terminal, determined from the feedback information received from each of the determined wireless terminals, determine the coding rate and modulation scheme of data addressed to each wireless terminal;
The base station according to any one of claims 1 to 8, wherein data addressed to each wireless terminal is encoded and modulated according to each determined coding rate and modulation scheme. A base station that communicates with a plurality of wireless terminals using a plurality of antennas,
First beam forming means for forming M number of beam candidates using the plurality of antennas;
Pilot signal transmitting means for transmitting a pilot signal in each of the M beams;
Reception state value receiving means for receiving the reception state value of each beam from each wireless terminal;
Beam number determining means for determining the number of used beams L (L is an integer of 1 or more and M or less) based on the number of the plurality of wireless terminals to be communicated and the number of beam candidates M;
Scheduling means for determining the L used beams and the radio terminals to which the L used beams are allocated based on reception state values of the beams received from the radio terminals;
Second beam forming means for forming the beam determined by the scheduling means for each wireless terminal determined by the scheduling means;
Data transmitting means for transmitting data to each of the determined wireless terminals by a beam formed for each of the determined wireless terminals;
Base station equipped with. A storage unit that stores correspondence information in which the number of beam candidates, the number of wireless terminals to be communicated, and the number of used beams are associated;
The beam number determining means determines the number L of used beams by referring to the correspondence information based on the number M of beam candidates and the number of the plurality of wireless terminals to be communicated. Item 11. The base station according to Item 10.   12. The base station according to claim 11, wherein the correspondence information is based on the number of radio terminals for each number of used beams versus channel capacity characteristics obtained in advance for each number of beam candidates.   The base station according to claim 11, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus SINR (signal to interference noise power ratio) acquired in advance for each number of beam candidates.   The base station according to claim 11, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus SIR (signal to interference power ratio) acquired in advance for each number of beam candidates. The data transmission means includes
The coding rate and modulation of the data addressed to each wireless terminal based on the reception quality for the beam allocated to each wireless terminal, which is obtained from the determined reception state values of the plurality of beams received from each of the wireless terminals. Decide the method,
The base station according to any one of claims 10 to 14, wherein data addressed to each wireless terminal is encoded and modulated according to each determined coding rate and modulation scheme. A communication program for causing a computer to communicate with a plurality of wireless terminals using a plurality of antennas,
A first beam forming step of forming M beams using the plurality of antennas;
A pilot signal transmission step of transmitting a pilot signal in each of the M beams;
A beam number determination step of determining a beam number L (L is an integer of 1 to M) based on the number of the plurality of wireless terminals to be communicated and the beam candidate number M;
A notification step of notifying the number of used beams L to the plurality of wireless terminals;
A feedback reception step of receiving feedback information based on the pilot signal transmitted in each of the M beams and the number of used beams L from each of the wireless terminals;
A scheduling step of determining the L used beams and the radio terminals to which the L used beams are allocated by performing scheduling based on feedback information received from each of the wireless terminals;
A second beam forming step of forming a beam determined by the scheduling step for each of the wireless terminals determined by the scheduling step;
A data transmission step of transmitting data to each determined wireless terminal by a beam formed for each determined wireless terminal;
A communication program with A communication program for causing a computer to communicate with a plurality of wireless terminals using a plurality of antennas,
A first beam forming step of forming M number of beam candidates 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 a reception state value of each beam from each of the wireless terminals;
A beam number determining step for determining a beam number L to be used that is equal to or less than the number of beams that transmitted the pilot signal based on the number of the plurality of wireless terminals to be communicated and the beam candidate number M;
A scheduling step of determining the L used beams and the radio terminals to which the L used beams are allocated based on reception state values of the beams received from the radio terminals;
A second beam forming step of forming a beam determined by the scheduling step for each of the wireless terminals determined by the scheduling step;
A data transmission step of transmitting data to each of the determined wireless terminals by a beam formed for each of the determined wireless terminals;
A communication program with A wireless communication system comprising a plurality of wireless terminals and a base station that communicates with the plurality of wireless terminals using a plurality of antennas,
The base station
First beam forming means for forming M number of beam candidates using the plurality of antennas;
Pilot signal transmitting means for transmitting a pilot signal in each of the M beams;
Beam number determining means for determining the number of used beams L (L is an integer of 1 or more and M or less) based on the number of the plurality of wireless terminals to be communicated and the number of beam candidates M;
Notifying means for notifying the number of used beams L to the plurality of wireless terminals;
Feedback receiving means for receiving feedback information based on the pilot signal transmitted in each of the M beams and the number of used beams L from each of the wireless terminals;
Scheduling means for determining the L used beams and the radio terminals to which the L used beams are allocated by performing scheduling based on feedback information received from each of the wireless terminals;
Second beam forming means for forming the beam determined by the scheduling means for each wireless terminal determined by the scheduling means;
Data transmitting means for transmitting data to each of the determined wireless terminals by a beam formed for each of the determined wireless terminals;
With
Each of the wireless terminals
Pilot signal receiving means for receiving a pilot signal transmitted from each of the M beams from the base station;
Used beam number receiving means for receiving notification of the used beam number L from the base station;
Feedback information generating means for generating the feedback information based on each pilot signal received by the pilot signal receiving means and the number of used beams L;
Feedback information transmitting means for transmitting the feedback information to the base station;
A wireless communication system. The base station further comprises storage means for storing correspondence information that associates the number of beam candidates, the number of wireless terminals to be communicated, and the number of used beams,
The beam number determining means in the base station determines the beam number L to be used by referring to the correspondence information based on the beam candidate number M and the number of the plurality of wireless terminals to be communicated. The wireless communication system according to claim 18, characterized in that:   20. The wireless communication system according to claim 19, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus channel capacity characteristics acquired in advance for each number of beam candidates.   The wireless communication system according to claim 19, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus SINR (signal to interference noise power ratio) acquired in advance for each number of beam candidates.   The wireless communication system according to claim 19, wherein the correspondence information is based on the number of wireless terminals for each number of used beams versus SIR (signal to interference power ratio) acquired in advance for each number of beam candidates. The feedback information generating means in the wireless terminal, as the feedback information,
Indicates H (H is an integer greater than or equal to 1) first beams that the wireless terminal desires to use, and LH second beams that the wireless terminal desires to use by other wireless terminals. Desired usage information and
Reception quality information indicating reception quality of the wireless terminal obtained when the first beam is used by the wireless terminal and the LH second beams are used by the other wireless terminal;
23. The wireless communication system according to any one of claims 18 to 22, wherein the wireless communication system is generated.

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