JP6251118B2 - Spatial multiplexing scheduling method, base station apparatus, and program - Google Patents

Description

  The present invention relates to a spatial multiplexing scheduling method, a base station apparatus, and a program.

  Currently, with the explosive spread of smartphones, convenient frequency resources in the microwave band are depleted. As countermeasures, a shift from a third-generation mobile phone to a fourth-generation mobile phone and the allocation of a new frequency band are being carried out. However, since there are many businesses that want to provide services, the frequency resources allocated to each business are limited.

  In mobile phone services, studies are underway to improve frequency utilization efficiency with a multi-antenna system that uses multiple antenna elements. In the widely used wireless standard IEEE (Institute of Electrical and Electronics Engineers, Inc.) 802.11n, spatial multiplexing transmission is performed using a MIMO transmission technique using a plurality of antenna elements for both transmission and reception. . Thereby, in IEEE 802.11n, the transmission capacity is increased to improve the frequency utilization efficiency. The term MIMO is generally used on the assumption that both the transmitting station and the receiving station are provided with a plurality of antennas. When the receiving side is a single antenna, the term MISO (Multiple Input Single Output) is used instead of MIMO. However, in this specification, the term MIMO is used to encompass all of these.

  Moreover, as a recent communication technology, it is divided into a plurality of frequency components (subcarriers) on the frequency axis like OFDM (Orthogonal Frequency Division Multiplexing) modulation system and SC-FDE (Single Carrier Frequency Domain Equalization) system. In general, a signal processing method is used. In the following description, OFDM and SC-FDE are not particularly distinguished, and the description will be made using the term “subcarrier” on the premise of a general scheme common to them.

In the MIMO transmission technique, it is possible to perform more efficient transmission by knowing transmission path information between a transmitting station and a receiving station. In the simplest example, when N antenna elements are provided on the transmitting side and only one antenna element is provided on the receiving side, signals transmitted from the N antenna elements are combined in phase at the receiving antenna. Similarly, directivity control is performed on the transmission side. Thereby, the line gain can be increased. Specifically, when channel information between the j-th antenna of the transmitting station and the antenna of the receiving station in the k-th subcarrier is h _j ^(k) , the following mathematical formula (1) is given to the antenna element. Then, a transmission weight w _j ^(k) is calculated and a signal obtained by multiplying the transmission weight w _j ^(k) is transmitted from each antenna. Strictly speaking, the above-described channel information includes rotation of complex phases such as amplifiers and filters in transmission and reception RF (Radio Frequency) circuits and amplitude variation information.

A vector having channel information and transmission weight corresponding to each antenna as a component is referred to as channel information vector h ^(k) and transmission weight vector w ^{(k) in the} downlink. Strictly speaking, the channel information vector in the downlink → h ^(k) (the symbol “→” before “h ^(k) ” is a symbol given to h to represent the vector) is a row vector. , The transmission weight vector → w ^(k) should be expressed as a column vector. However, in this specification, for the sake of simplicity, the row vector and the column vector are not distinguished from each other. In the following description, the notation regarding the reception signal Rx, the transmission signal Tx, and the noise n should be clearly indicated by adding “→” to be a vector, but “→” because there is no other confusing notation. The description is omitted. The reception signal Rx is given by the following mathematical formula (2) with respect to the transmission signal Tx and the noise n.

When Expression (1) is substituted into Expression (2), a value obtained by adding the absolute values of the components of the channel information vector h ^(k) over all antenna components is obtained as the channel gain. In the case of N antennas, the amplitude of the received signal is expected to be N times that of transmission with one antenna. The received signal strength is improved to N ² times since it is proportional to the square of the amplitude. This value is a gain when a plurality of antenna elements are used as an array antenna.

  Generally, according to Shannon's theorem, it is known that the increase in transmission capacity is larger in the low SNR region and smaller in the high SNR region than the amount of improvement in SNR (Signal-Noise Ratio). Therefore, rather than aiming to improve the transmission capacity by improving the line gain, it is often aimed to improve the transmission capacity by providing a plurality of antennas on the receiving side and spatial multiplexing. The MIMO transmission technology aims to increase the transmission capacity by spatial multiplexing. When channel information between a plurality of transmission antennas and reception antennas is known, the channel matrix is decomposed by SVD (Singular Value Decomposition), and transmission in the eigenmode is performed to maximize the transmission capacity.

  Specifically, the channel matrix H is decomposed into a unitary matrix U and a unitary matrix V, and a diagonal matrix D having a singular value λ as a diagonal component as shown in the following equation (3).

  At this time, if the unitary matrix V is used as the transmission weight matrix, the reception signal vector Rx is given by the following equation (4) with respect to the transmission signal vector Tx and the noise vector n.

On the receiving side, the following formula (5) is obtained by multiplying the Hermite conjugate matrix U ^H of the unitary matrix U.

  In Equation (5), since the non-diagonal component of the diagonal matrix D is zero, the cross term of the transmission signal is already canceled and the signal is separated. The square value of the absolute value of each singular value λ corresponds to the line gain of an individual signal sequence. Each singular value λ is different for each signal system. The transmission capacity can be maximized by optimizing the transmission mode according to the singular value of the eigenmode. The transmission mode is a specific mode of signal transmission determined by a combination of the modulation multi-level number and the error correction coding rate.

  The above is a description of a single user MIMO transmission technique assuming one base station and one radio station. The same description can be extended to multi-user MIMO that performs communication on the same frequency axis at the same time between one base station and a plurality of radio stations. In multi-user MIMO, in general, each radio station performs communication using a smaller number of antenna elements than the total number of signal systems to be spatially multiplexed. Therefore, on the downlink, directivity control for suppressing inter-user interference is performed in advance on the transmission side. Although the specific expressions are slightly different, basically, as in the above eigenmode transmission, the transmission weight corresponding to the channel matrix is used after grasping the channel matrix.

  Further, in the above description, the description has been focused on the downlink. However, in the uplink as well, communication using the channel information can be performed after grasping the channel information in advance. For example, in the process as the array antenna described first, in-phase combining weight given by Equation (1) is used as a reception weight, and maximum ratio combining weight is given by Equation (6) below. It is also possible to use one.

The constant C in Equation (6) is a coefficient that is appropriately determined. Among the components of the vector, those having a large absolute value of h _j ^(k) are added with a large weight, and small signals are added with a small weight. As a result, a signal with a large SNR is emphasized, and adjustment is made so that noise of a signal with a small SNR does not excessively affect the signal.

  A large-scale antenna system has been proposed as a new spatial multiplexing transmission technology that is a further development of the above-described multi-user MIMO and array antenna technologies (for example, see Non-Patent Document 1 to Non-Patent Document 4).

  FIG. 13 is a diagram showing an outline of a large-scale antenna system. In FIG. 13, a base station 1, a radio station 2, a line-of-sight wave 3, a stable reflected wave 4 by a structure, multiple reflected waves 5 to 6 near the ground, and a structure 7 are shown. In the large-scale antenna system of FIG. 13, the base station 1 includes a large number (for example, 100 or more) of antenna elements, and is installed at a high place such as a rooftop of a building or a high steel tower. Similarly, the radio station 2 is installed at a high place such as on the roof of a building, on the roof of a house, on a telegraph pole or a steel tower. For this reason, the base station 1 and the radio station 2 are generally in a line-of-sight environment. Between the base station 1 and the radio station 2, in addition to the path of the line-of-sight wave 3, the stable reflected wave 4 of the large stable structure 7, etc., multiplexing by a moving object such as a car or a person near the ground Reflected waves 5 to 6 are mixed. Further, especially when a directional antenna is used, the reception levels of the multiple reflected waves 5 to 6 near the ground are lower than those of the line-of-sight wave 3 and the stable reflected wave 4.

  FIG. 14 is a diagram illustrating an impulse response in a line-of-sight environment and a non-line-of-sight environment. FIG. 14A shows an impulse response in a non-line-of-sight environment, and FIG. 14B shows an impulse response in a line-of-sight environment. 14A and 14B, the horizontal axis represents the delay time, and the vertical axis represents the reception level of each delayed wave. In the case of the non-line-of-sight environment shown in FIG. 14 (a), there are no direct wave components in the line-of-sight section, many multiple reflected waves of various paths exist as components, and each amplitude and complex phase becomes intense with time. fluctuate.

  On the other hand, when a line-of-sight environment such as the large-scale antenna system shown in FIG. 13 is assumed, the level of the stable path of the line-of-sight 3 and the stable reflected wave 4 by the structure 7 is high. When the delay amount is larger than that of the stable reflected wave 4 by the line-of-sight wave 3 and the structure 7, the multiple reflected wave of the variable path is relatively level as shown in FIG. Becomes smaller. When such channel information is acquired and averaged a plurality of times, the stable path component is stable each time in both amplitude and complex phase, so that the change from the averaged channel information is small. On the other hand, the components of the time-varying path are synthesized and averaged randomly in the complex space. Therefore, only stable components can be extracted effectively by averaging.

The base station 1 calculates the transmission / reception weight based on the channel information of the stable path without time fluctuation obtained in this way. The base station 1 performs directivity control for performing in-phase synthesis with a large number of antenna elements using the calculated transmission / reception weights. By using the transmission / reception weight described above, the base station 1 can increase the directivity gain to the radio station of the communication partner that is the target of directivity control in proportion to the square of the number N of antennas. In addition, since the directivity gain of interference to radio stations other than the target remains N times, a gap of N times is generated between the desired signal and the interference signal by simple calculation. As a result, the expected value of SIR (Signal to Interference Ratio) is ₁₀ Log ₁₀ (N) dB. This expected value is 20 dB when N is 100. Furthermore, when a radio station having a small correlation is selectively spatially multiplexed, further improvement in SIR characteristics is expected, and higher spatial multiplexing can be realized.

Non-Patent Document 3 and Non-Patent Document 4 introduce a technique for further suppressing interference that cannot be suppressed by the above transmission / reception weights and a technique for selecting a combination of radio stations that can obtain a lower channel correlation. Yes. In order to realize super-high-order spatial multiplexing, it is important to combine radio stations with small correlation of channel information. Channel information vector → h _j ^(k) having channel information on the k-th subcarrier between a number of antennas of the base station and the j-th radio station as a component, and channel information vector at another i-th radio station → h _i The channel correlation with ^(k) is given by Equation (7) below.

Assuming a virtual channel model composed only of line-of-sight waves, the above-described channel correlation is considered to exhibit a behavior that strongly depends on the azimuth difference angle θ between the azimuths from the base station to two different radio stations. FIG. 15 is a diagram illustrating two radio stations that exist with an azimuth difference angle θ from the base station. As shown in the figure, the channel information vector between one radio station and the base station is set to → h ₁ ^(k), and the channel information vector between the other radio station and the base station is set to → h ₂ ^{(k )} , The dependence of the channel correlation on the orientation difference angle θ can be calculated.

  FIG. 16 is a diagram illustrating the dependence of the channel correlation on the azimuth difference angle θ in the two radio stations. The simulation conditions here assume that the number of antennas of the base station is 128, and that 128 antennas are arranged in a circle at intervals of two wavelengths in the frequency band of 5.2 GHz. The distance between the base station and the radio station is fixed at 3 km, and the channel correlation is calculated while moving the coordinates of the radio station in a circle. When FIG. 16 is read, when the azimuth difference angle θ is, for example, about 5 degrees or less, the channel correlation may become a large value. However, when the predetermined threshold value α degree is exceeded, the correlation is approximately 0.2 or less. The scheduling method shown in Non-Patent Document 4 actively uses the low channel correlation when the misorientation angle is 5 degrees or more.

Atsushi Ota, Kaoru Kurosaki, Kazuki Maruta, Takuto Arai, Masataka Iizuka, “B-5-175 Proposal of Large-scale Antenna Wireless Entrance System”, Proceedings of the IEICE General Conference 2013 (Communication_1), 2013 March 5, p. 585 Takuto Arai, Atsushi Ota, Atsushi Kurosaki, Kazuki Maruta, Masataka Iizuka, “B-5-176 Calculation Method of Transmit / Receive Weights in Large Antenna Radio Entrance System”, IEICE General Conference Proceedings 2013 (Communication_1) March 5, 2013, p. 586 Kazuteru Maruta, Atsushi Ota, Atsushi Kurosaki, Takuto Arai, Masataka Iizuka, “B-5-177 Inter-User Interference Suppression Method in Large Antenna Wireless Entrance System”, IEICE General Conference Proceedings 2013 (Communication_1) ), March 5, 2013, p. 587 Satoshi Kurosaki, Atsushi Ota, Kazuki Maruta, Takuto Arai, Masataka Iizuka, “B-5-178 Low Correlation Scheduling Method in Large Antenna Radio Entrance System”, IEICE General Conference Proceedings 2013 (Communication_1) March 5, 2013, p. 588

  The scheduling method described in Non-Patent Document 4 is a result obtained by arranging the antennas on the base station side on a circular array, and such a relationship often does not hold in a general antenna configuration. For example, when an antenna arrangement in which antenna elements are arranged one-dimensionally to constitute an array antenna, or an antenna arrangement in which planar antennas exhibiting high directivity gain in the front direction are arranged on a vertical plane is used in a base station. Depending on the azimuth difference angle θ between the two radio stations, a correlation as shown in FIG. 16 cannot be obtained. In this case, it is general that the correlation is completely different from the correlation shown in FIG. In other words, in order to show different channel correlation characteristics depending on the antenna configuration on the base station side, a more general scheduling method is required.

  In view of the above circumstances, the present invention provides a spatial multiplexing scheduling method, a base station apparatus, and a program capable of reducing channel correlation in a combination of radio stations to be subjected to spatial multiplexing communication regardless of the antenna configuration of the base station apparatus. It is intended to provide.

One aspect of the present invention includes a base station apparatus including a plurality of antenna elements and a plurality of radio stations, and a plurality of the radio stations using a MIMO channel formed between the base station apparatus and the radio stations. In a wireless communication system capable of performing spatial multiplexing communication, a base station apparatus determines a combination of wireless stations that perform spatial multiplexing at the same time. Channel information acquisition step of acquiring channel information between each antenna element and each of the radio stations for each frequency component and storing the channel information in a channel information storage unit, and scheduling processing from the radio station waiting for allocation of a communication opportunity. One radio station is selected as a radio station to be determined, and each radio station to which a communication opportunity has already been assigned is determined. The first case and or already communication opportunities is less than the threshold value the evaluation value calculated based on the correlation value is predetermined for the acquired channel information for all or part of the frequency components assigned to the target wireless station The accumulated value of each evaluation value with respect to another wireless station is calculated for each wireless station between the wireless station and the determination target wireless station, and all the accumulated values are less than a predetermined second threshold value. In this case, the spatial multiplexing scheduling method includes: an assigned radio station determining step for allocating a communication opportunity to the determination target radio station.

Further, according to one aspect of the present invention, in the spatial multiplexing scheduling method described above, based on channel information stored in the channel information storage unit, all or part of each pair of radio stations in the plurality of radio stations An evaluation value calculating step of calculating a correlation value of channel information acquired by frequency components , calculating an evaluation value of each pair of wireless stations based on each calculated correlation value, and storing the evaluation value in a evaluation value table storage unit; In the assigned radio station determining step, the evaluation value of the pair of the radio stations is read from the evaluation value table storage unit, and whether or not a communication opportunity is assigned to the determination target radio station is determined based on the read evaluation value. It is characterized by performing.

  Further, according to one aspect of the present invention, in the spatial multiplexing scheduling method described above, after communication opportunities are once allocated to more radio stations than the number of radio stations that are actually spatially multiplexed in the allocated radio station determination step. For each radio station to which a communication opportunity is assigned, calculate a cumulative value of evaluation values with other radio stations to which a communication opportunity is assigned, and narrow down the radio stations to which a communication opportunity is actually assigned based on the calculated cumulative value A step of narrowing down assigned radio stations;

各数式におけるＫは２以上の整数であり、数式（Ｃ）におけるαは所定の正の実数であり、数式（Ｆ）におけるδは０＜δ＜１を満たす実数であることを特徴とする。 Further, according to an aspect of the present invention, in the spatial multiplexing scheduling method described above, the normalized correlation value in the channel information between the i-th radio station and the j-th radio station in the k-th frequency component is expressed as f [i, j, k ], The evaluation value of the pair of the i-th radio station and the j-th radio station is calculated by F [i, j] of any one of the following formulas (A) to (F),

K in each equation is an integer of 2 or more, α in equation (C) is a predetermined positive real number, and δ in equation (F) is a real number satisfying 0 <δ <1.

One embodiment of the present invention includes a base station apparatus including a plurality of antenna elements and a plurality of radio stations, and uses a MIMO channel formed between the base station apparatus and the radio stations to A base station apparatus in a wireless communication system capable of performing spatial multiplexing communication with a wireless station, wherein channel information between each of the plurality of antenna elements and each of the wireless stations is a frequency component before scheduling processing. A channel information acquisition unit that is acquired every time and stored in the channel information storage unit, and as a scheduling process, one radio station is selected as a determination target radio station from the radio stations waiting for allocation of communication opportunities, and a communication opportunity has already occurred. based on the correlation values of all or channel information acquired by the subset of frequency components of the assigned and the radio station each of which the determination target wireless station When the evaluation value to be issued is less than a predetermined first threshold and / or each of the other radio stations for each radio station in the radio station to which a communication opportunity has already been assigned and the radio station to be determined An allocated radio station determining unit that calculates a cumulative value of evaluation values and allocates a communication opportunity to the determination target radio station when all the cumulative values are less than a predetermined second threshold value. Base station apparatus.

  Another embodiment of the present invention is a program for causing a computer to execute the above spatial multiplexing scheduling method.

  According to the present invention, channel information between the base station device and each radio station is acquired before the scheduling process, and based on the evaluation value calculated from the correlation value of each frequency component between the acquired channel information, By determining the combination of radio stations to be multiplexed, channel correlation can be lowered without being affected by the antenna configuration of the base station apparatus. Thereby, the number of spatial multiplexing can be increased while improving the SIR characteristics.

It is a figure which shows the structure of the radio | wireless communications system in related technology. It is a block diagram which shows the structural example of the base station apparatus 100 in related technology. It is a 1st flowchart which shows the scheduling process which the base station apparatus 100 in related technology performs. It is a 2nd flowchart which shows the scheduling process which the base station apparatus 100 in related technology performs. It is a block diagram which shows the structure of the base station apparatus 200 in related technology. It is a figure which shows an example of the table contained in the table storage part. It is a figure which shows an example of the comparison result table which memorize | stores the determination result of process S5. It is a block diagram which shows the structure of the base station apparatus 300 in 1st Embodiment. It is a 1st flowchart which shows the scheduling process which the base station apparatus 300 in 1st Embodiment performs. It is a 2nd flowchart which shows the scheduling process which the base station apparatus 300 in 1st Embodiment performs. It is a flowchart which shows the scheduling process in 2nd Embodiment. It is a flowchart which shows the scheduling process in 3rd Embodiment. It is a figure which shows the outline | summary of a large-scale antenna system. It is a figure showing the impulse response in a line-of-sight environment and a non-line-of-sight environment. It is a figure which shows two radio stations which exist with the azimuth | direction difference angle (theta) from a base station. It is a figure which shows the azimuth | direction difference angle (theta) dependence of the channel correlation in two radio stations of azimuth | direction difference angle (theta).

[Related art of the present invention]
In a large-scale antenna system, the directivity gain and the SIR characteristic at the time of spatial multiplexing can be improved by synthesizing the transmitted and received signals with the same phase using a number of antennas. In contrast, in a conventional communication system using multi-user MIMO, a weight matrix used for transmission / reception (or corresponding to a weight vector if decomposed for each wireless station) is a combination of wireless stations that simultaneously perform spatial multiplexing. Depending on. Therefore, in order to accurately grasp the characteristics when spatial multiplexing is performed, it is necessary to calculate a weight matrix with a combination of spatially multiplexed radio stations. However, since the amount of calculation for calculating the weight matrix is enormous, it is difficult to evaluate the characteristics when actually applying transmission / reception weights to the combination patterns of many radio stations.

  The technique described in Non-Patent Document 4 is applicable when the line-of-sight wave is dominant and a circular array antenna is used on the base station apparatus side. Even if it cannot be ignored, sufficient effects cannot be obtained even if it is applied. In such a case, a simple scheduling technique that reflects actual SIR characteristics in the environment is required.

  Further, in the large-scale antenna system, the transmission / reception weight for realizing the in-phase synthesis uses Expression (1) or Expression (6), so the transmission / reception weight itself is obtained by multiplying the complex conjugate vector of the original channel vector by a constant. It is a vector. Therefore, the SIR characteristic before the application of the inter-user interference suppression method described in Non-Patent Document 3 is a physical quantity corresponding to the accumulated value (sum) of correlation values shown in Equation (7) for wireless stations that perform spatial multiplexing simultaneously. It depends mostly.

  The related art of the present invention will be described below with reference to the drawings. In the following description, the subscript k regarding the frequency component is described, which means an arbitrary frequency component. For example, in the case of a system that performs scheduling for each subcarrier individually as in the OFDMA (Orthogonal Frequency Division Multiplex Access) system, the related technique of the present invention can be used for scheduling with individual frequency components. Further, when the channel information has a certain degree of correlation between the frequency components in the band, it is possible to extract one frequency component and use the scheduling result of the extracted frequency component as the scheduling result for the entire band.

Furthermore, in the equation (7), two channel information vectors → h ₁ ^(k) and → h ₂ ^(k) are explicitly shown as arguments of the function f shown on the left side, but this will be simplified in the following description. F (→ h ₁ ^(k) , → h ₂ ^(k) ) is expressed as f [i, j, k]. Also, an identification number corresponding to a serial number is set in advance for a wireless station, and when scheduling is performed, the identification number of the wireless station whose assignment is determined j-th will be expressed as S (j). For convenience, it is assumed that j (= 0) is treated as S (0) = 0, f [i, 0, k] = f [0, i, k] = 0. In addition, although f [i, i, k], which represents the correlation between the same stations physically, should be 1, this scheduling process discusses the correlation between two different radio stations. For convenience, it is assumed that f [i, i, k] = 0.

  FIG. 1 is a diagram illustrating a configuration of a wireless communication system in the related art. As shown in FIG. 1, the wireless communication system includes one base station device 100 and a plurality of wireless stations 150. Base station apparatus 100 includes a plurality of antenna elements. The radio station 150 includes one antenna element. Base station apparatus 100 performs spatial multiplexing communication with a plurality of radio stations 150 using a MIMO channel formed with each radio station 150. The wireless communication system is used, for example, as a large-scale antenna system shown in FIG.

  When used as a large-scale antenna system, the plurality of antenna elements of the base station apparatus 100 are arranged at high places such as the rooftop of a building or a high steel tower like the antenna of the base station 1 in the large-scale antenna system shown in FIG. Installed. Similarly, the antenna elements of the radio stations 150 are also installed at high places. As a result, the reception level of the line-of-sight wave or the stable reflected wave or both of the reception signals of the base station apparatus 100 and each radio station 150 is increased.

  FIG. 2 is a block diagram illustrating a configuration example of the base station apparatus 100 in the related art. As illustrated in FIG. 2, the base station apparatus 100 includes a plurality of antenna elements 101, a radio communication unit 102, a channel information acquisition unit 103, a channel information storage unit 104, and a scheduling unit 110. The scheduling unit 110 includes a transmission opportunity queue 111, a determination target selection unit 112, a correlation value determination unit 113, a cumulative value determination unit 114, a buffer 115, and an assigned radio station determination unit 116.

  The wireless communication unit 102 communicates with a plurality of wireless stations 150 via the plurality of antenna elements 101. When communicating with a plurality of radio stations 150, the radio communication unit 102 was spatially multiplexed at the same time using a MIMO channel formed between the plurality of antenna elements 101 and the antenna elements of each radio station 150. Communicate. The combination of the radio stations 150 to be communicated with by the radio communication unit 102 is selected by the scheduling unit 110.

  The channel information acquisition unit 103 acquires channel information indicating a propagation environment with each wireless station 150 for each wireless station 150 based on a signal received by the wireless communication unit 102. The channel information for each radio station 150 acquired by the channel information acquisition unit 103 is channel information in each frequency component of the frequency band used in the radio communication system. The channel information acquisition unit 103 stores the channel information in each frequency component of each radio station 150 in association with the identification number for identifying the radio station 150 in the channel information storage unit 104. The channel information acquisition unit 103 acquires channel information of each radio station 150 in advance and stores the channel information in the channel information storage unit 104 before the scheduling unit 110 selects a combination of radio stations 150 to be communicated. The acquisition timing may be acquired sequentially while providing the communication service. Alternatively, in the large-scale antenna systems described in Non-Patent Documents 1 to 4, all channel information may be acquired and stored before the communication service is started. This channel information acquisition method is a technique independent of the scheduling process, and the scheduling process in this embodiment can be realized by any combination.

  The channel information storage unit 104 stores channel information of each frequency component for each radio station 150.

  When information to be transmitted to the radio station 150 is generated in the base station apparatus 100, the information (data) to be transmitted is input to the radio communication unit 102 and stored in a transmission buffer in the radio communication unit 102. In addition, in accordance with the input of information to be transmitted to the wireless communication unit 102, control information including destination information and information amount of the information is input to the transmission opportunity queue 111 of the scheduling unit 110. For the destination information, for example, the identification number of the wireless station 150 is used. The transmission opportunity queue 111 is a buffer that stores the identification numbers of the radio stations 150 in the order in which information to be transmitted to the radio station 150 is generated in the base station apparatus 100. When the identification number is stored in the transmission opportunity queue 111, there is a radio station 150 waiting for transmission opportunity assignment. Note that the transmission opportunity queue 111 may store information including the above-described information amount and the like together with the identification numbers of the wireless stations 150 stored in the order in which the information to be transmitted is generated.

  When the scheduling process is started, the determination target selection unit 112 reads one identification number stored in the transmission opportunity queue 111 from the top. The wireless station 150 with the identification number read by the determination target selection unit 112 is treated as a determination target wireless station 150 whether or not to give a transmission opportunity in the scheduling process. The determination target selection unit 112 outputs the read identification number to the correlation value determination unit 113, the cumulative value determination unit 114, and the assigned radio station determination unit 116.

  Correlation value determination section 113 includes channel information between radio station 150 and base station apparatus 100 selected as a determination target by determination target selection section 112, and each radio station 150 and base station to which a transmission opportunity has already been assigned. A correlation value with the channel information with the apparatus 100 is calculated for each frequency component. Correlation value determination section 113 receives notification of information on radio station 150 to which a transmission opportunity has already been allocated from allocated radio station determination section 116. Correlation value determination section 113 calculates a correlation value with each of these radio stations 150 based on the channel information stored in channel information storage section 104. Correlation value determination section 113 determines whether or not to assign a transmission opportunity to wireless station 150 to be determined based on the calculated correlation value of each frequency component. Correlation value determination section 113 outputs the determination result to assigned radio station determination section 116.

  Cumulative value determination section 114 receives notification of information of each radio station 150 to which a transmission opportunity has already been allocated from allocated radio station determination section 116. The cumulative value determination unit 114 calculates a correlation value based on the channel information stored in the channel information storage unit 104. Further, the cumulative value determination unit 114, for each wireless station 150 in the wireless stations 150 to be determined and the wireless stations 150 to which a transmission opportunity has already been assigned, is a cumulative value (sum total) of correlation values with other wireless stations 150. ) For each frequency component. The cumulative value determination unit 114 determines whether or not to assign a transmission opportunity to the determination target wireless station 150 based on the cumulative value calculated for each wireless station 150. Accumulated value determination section 114 outputs the determination result to assigned radio station determination section 116.

  The buffer 115 includes an allocated radio station buffer and a next allocation waiting buffer. In the assigned radio station buffer, an identification number of the radio station 150 to which a transmission opportunity is assigned in the scheduling process is stored. The correlation value determination unit 113 and the cumulative value determination unit 114 can acquire the radio station 150 to which a transmission opportunity has already been assigned by reading the identification number stored in the assigned radio station buffer. The next allocation waiting buffer stores the identification number of the radio station 150 to which no transmission opportunity is assigned as a result of determining whether or not to assign a transmission opportunity in the scheduling process.

  Whether the assigned radio station determination unit 116 assigns a transmission opportunity to the radio station 150 selected as a determination target by the determination target selection unit 112 based on the determination results output from the correlation value determination unit 113 and the cumulative value determination unit 114 Decide whether or not. When the assigned radio station determination unit 116 determines to assign a transmission opportunity to the determination target radio station 150, the assigned radio station determination unit 116 stores the identification number of the determination target radio station 150 in the assigned radio station buffer. When determining that the transmission opportunity is not allocated to the determination target radio station 150, the allocation radio station determination unit 116 stores the identification number of the determination target radio station 150 in the next allocation waiting buffer.

  Also, the assigned radio station determining unit 116 determines whether or not the number of identification numbers stored in the assigned radio station buffer has reached the upper limit number of spatial multiplexing. When the upper limit number is reached, the assigned radio station determination unit 116 reads the identification number stored in the assigned radio station buffer. The assigned wireless station determination unit 116 outputs the read identification number to the wireless communication unit 102 and causes the wireless communication unit 102 to communicate with the wireless station 150 of the identification number. If the upper limit number has been reached, the assigned radio station determination unit 116 reads the identification number stored in the next allocation waiting buffer and stores it in the head area of the transmission opportunity queue 111. The assigned radio station determination unit 116 includes a counter that counts the number of radio stations 150 to which transmission opportunities have been assigned in the scheduling process.

  Upon receiving notification of assignment determination including the identification number of each wireless station 150 to which a transmission opportunity is assigned from the assigned wireless station determination unit 116, the wireless communication unit 102 receives information (data) with the wireless station 150 having the identification number as a destination. ) Is read from the transmission buffer in the wireless communication unit 102. The wireless communication unit 102 transmits each read information (data) to each wireless station 150 to which a transmission opportunity is assigned after signal processing for predetermined wireless communication.

  FIG.3 and FIG.4 is a flowchart which shows the scheduling process which the base station apparatus 100 in related technology performs. In the scheduling process, a combination of wireless stations 150 to be subjected to spatially multiplexed communication at the same time is determined. When the scheduling process is started in the base station apparatus 100 (process S1), the assigned radio station determination unit 116 resets by assigning zero to a counter j for managing the number of assigned radio stations 150 (process). S2). When the resetting of the counter j is completed, the determination target selection unit 112 determines whether or not there is a radio station 150 waiting for allocation in the transmission opportunity queue 111 (processing S3).

  In the determination of the process S3, when there is a wireless station 150 waiting for transmission opportunity assignment (YES in the process S3), the determination target selection unit 112 selects the first wireless station 150 in the transmission opportunity queue 111 as a determination target wireless station. 150 is selected (processing S4). The correlation value determination unit 113 has a correlation value for each frequency component between the channel information of the determination target radio station 150 and the channel information of each of the j station radio stations 150 to which transmission opportunities have already been assigned, being equal to or less than a predetermined threshold β. It is determined whether or not there is a first step (step S5). Here, the correlation value is a value calculated by Equation (7). When the expression (7) is simplified and expressed using the above-described notation f [i, j, k], the determination condition in the process S5 is expressed as the following expression (8).

  In Equation (8), m is the identification number of the target radio station 150 that determines whether or not transmission opportunities can be assigned. S (i) (where 0 ≦ i ≦ j) is an identification number of the radio station 150 to which a transmission opportunity has already been assigned. That is, S (i) represents the identification number stored i-th in the assigned radio station buffer included in the buffer 115. The threshold value β is a predetermined real number where 0 <β <1. In the first process S5 in the scheduling process, that is, the process S5 when j = i = 0, f [S (i), m, k] on the left side of the equation (8) is zero because S (j) = 0. Equation (8) is always satisfied. In the scheduling process, the determination result of the first process S5 is a determination result that satisfies the condition.

  When the correlation value between each of the determination target radio station 150 and the assigned radio station 150 satisfies Expression (8) in the determination of the process S5 (YES in the process S5), the cumulative value determination unit 114 performs the second step. Is determined (step S6). As the determination of the second stage, the cumulative value determination unit 114 determines the determination target whose identification number is S (i) (0 ≦ i ≦ j) among the allocated wireless stations 150 and whose identification number is m. It is determined whether the following mathematical formula (9) and mathematical formula (10) are established for each frequency component. Γ (j) in Equation (9) and Equation (10) represents a predetermined threshold when the number of assigned radio stations 150 is j.

  When the formula (9) and the formula (10) are both satisfied for each assigned radio station 150 in the determination of the process S6 (YES in the process S6), the assigned radio station determination unit 116 determines the radio station 150 to be determined. The assignment is approved (process S7). The assigned wireless station determination unit 116 adds 1 to a counter j indicating the number of assigned wireless stations 150 (processing S9), and substitutes m for S (j) as the jth assigned wireless station 150. (Process S10). In other words, the assigned radio station determination unit 116 stores the identification number m of the determination target radio station 150 in the assigned radio station buffer as the identification number of the radio station 150 to which the transmission opportunity is assigned.

  The assigned radio station determination unit 116 determines whether or not the counter j has reached the upper limit J for the number of radio stations 150 to which a transmission opportunity is assigned (processing S11). If the counter j has not reached the upper limit value J (NO in process S11), the assigned radio station determining unit 116 returns the process to process S3 and repeats the allocation of transmission opportunities. When the counter j has reached the upper limit value J (YES in process S11), the assigned radio station determining unit 116 advances the process to process S12.

  If at least one of the correlation values between the determination target radio station 150 and the already assigned radio station 150 does not satisfy Expression (8) (NO in process S5) or has already been allocated in the determination of process S6 When there is a radio station 150 that does not satisfy the formula (9) among the radio stations 150 of the radio station 150 or when the radio station 150 with the identification number m does not satisfy the formula (10) (NO in step S6), the assigned radio station determination unit 116 The assignment to the determination target radio station 150 is not approved. In this case, the assigned wireless station determination unit 116 adds the identification number m of the wireless station 150 to be determined to the end of the next assignment waiting buffer (process S8), returns the process to S3, and repeats transmission opportunity assignment.

  When there is no wireless station 150 waiting for transmission opportunity assignment in the determination of the process S3 (NO in the process S3), or when the counter j has reached the upper limit value J in the determination of the process S11 (YES in the process S11). The assigned wireless station determination unit 116 sequentially moves the identification number of each wireless station 150 included in the next assignment waiting buffer to the top of the transmission opportunity queue 111 (process S12), and ends the scheduling process (process S13).

  The assigned radio station determination unit 116 reads all the identification numbers stored in the assigned radio station buffer after completing the scheduling process. The assigned wireless station determination unit 116 notifies the wireless communication unit 102 of the combination of the wireless stations 150 having the read identification numbers as the combination of the wireless stations 150 to be spatially multiplexed.

  Note that the value of the predetermined threshold value γ (j) included in Equation (9) and Equation (10) monotonically increases as j increases or is a single value, and γ (j) ≦ γ (j + 1) Any function may be used as long as it is a threshold value γ (j) that satisfies the above relationship. The simplest example is a case in which all indicate the same predetermined threshold value. Alternatively, γ (j) as expressed by the following formula (11) may be used.

  In Equation (11), β is a threshold in Equation (8), and β ′ is a predetermined constant such that 0 <β ′ <β. For an arbitrary Γ (j) satisfying 1> Γ (j) ≧ Γ (j + 1)> 0 for an integer j of Γ (1) = 1, 2 ≦ j, the following equation (12) is given. The threshold value γ (j) to be used may be used.

  In the scheduling process shown in FIG. 3 and FIG. 4, the determination at the first stage in the process S <b> 5 is that the correlation value between the two radio stations of the determination target radio station 150 and the already assigned radio station 150 is predetermined. It is confirmed that it is smaller than the threshold value β. The determination at the second stage in the process S6 confirms that the accumulated correlation value is smaller than a predetermined threshold value γ (j). When the determination at the first stage and the determination at the second stage are satisfied, the scheduling process is performed in a procedure in which it is approved to allocate a transmission opportunity to the wireless station 150 to be determined. Note that the values of the threshold value β and the threshold value γ (j) may be determined based on channel information, a transmission rate obtained in spatial multiplexing, or the like obtained from simulation results or measured values. Similarly, the upper limit value J may also be determined based on a simulation result or an actual measurement value.

  It should be noted that processing S8 and processing S12 in the scheduling processing are remedies for preferential determination in the next allocation for the radio station 150 to which no transmission opportunity has been allocated as a result of the determination. It corresponds to.

  The scheduling process here may be, for example, allocation of time slots in a TDMA (Time Division Multiple Access) frame in which time slots are divided, or may be allocation process for each transmission opportunity. In addition, since the information to be transmitted for each wireless station 150 is generally different, there remains data to be transmitted to the wireless station 150 to which transmission opportunities are assigned by the scheduling process illustrated in FIGS. 3 and 4. In addition, in the next allocation, the radio station 150 may be continuously allocated. In this case, if the number of radio stations 150 to be continuously allocated in the processing of FIGS. 3 and 4 is j, these radio stations 150 are assigned a new S (i) using a serial number i where j ≧ i. It is possible to reconfigure and manage as described above, and to resume the assignment in the form of interrupting the process S3 from the middle.

  Further, if j stations to be continuously allocated are arranged at the head of the transmission opportunity queue 111 in the original order and the scheduling process shown in FIGS. 3 and 4 is performed again from the beginning, the process S5 and the process for the j station are performed. Since all the determinations in S6 are satisfied and the process S7 is performed, continuous allocation can be realized. Conversely, all of these radio stations 150 may be regarded as having been assigned once and may be rearranged in order at the end of the transmission opportunity queue 111.

  Further, in general broadband systems, there are OFDM and OFDMA schemes in addition to single carrier transmission. In the OFDMA scheme, in order to perform individual allocation processing for each subcarrier, FIG. And you may perform the scheduling process shown in FIG. 4 for every frequency component. Here, as described above, with respect to the radio station 150 that has been assigned with a certain frequency component, the assignment may be performed continuously in the scheduling process for the next frequency component, and once the assignment is completed. May be rearranged in order at the end of the transmission opportunity queue 111. Although the handling of the radio station 150 for each scheduling opportunity differs depending on these transmission methods, the above-described scheduling process is characterized by the processes S5 and S6 shown in FIG. The wireless station 150 that satisfies the condition is approved as a wireless station 150 that simultaneously performs spatial multiplexing.

  Further, when the base station apparatus 100 centrally manages both uplink and downlink transmission opportunities, the base station apparatus 100 performs scheduling processing separately for the uplink and the downlink. As a method for requesting a transmission opportunity for each wireless station 150 to transmit information on the uplink, for example, a bandwidth request and an amount of information to be transmitted on the control line may be notified. Regardless, it may be assigned periodically to each radio station 150 by the round robin method, and the above-described scheduling process can be applied regardless of how the assignment request is managed.

  In addition, here, it is assumed that the channel information used for calculating the correlation value has been acquired before starting the scheduling process, but the channel information does not have to be time-variable. If it is allowed to update the channel information frequently when the channel information varies with time, the radio station 150 is not necessarily fixedly installed at a high place. Therefore, the scheduling process can be performed even if the radio station 150 is a mobile terminal. The channel information used here is acquired by feeding back channel information between the base station apparatus 100 and the radio station 150. In other words, some channel feedback processing is required, but the scheduling processing shown in FIGS. 3 and 4 does not depend at all on how to implement the feedback method, and any feedback method may be used. .

  Here, in the scheduling process shown in FIG. 3 and FIG. 4, it is determined whether or not the inequalities of Expression (8), Expression (9), and Expression (10) are satisfied when the determinations in Steps S5 and S6 are performed. There was a need to do. When the time variation of channel information is almost negligible as in a large-scale antenna system, the correlation value corresponding to Equation (7) is calculated in advance based on the channel information acquired in advance, and the calculated correlation value is Processing can be simplified by creating a table. In the following, a base station apparatus that simplifies the processing as described above will be described.

  FIG. 5 is a block diagram showing a configuration of base station apparatus 200 in the related art. As illustrated in FIG. 5, the base station apparatus 200 includes a plurality of antenna elements 101, a wireless communication unit 102, a channel information acquisition unit 103, a channel information storage unit 104, a correlation value calculation unit 201, a table storage unit 202, and a scheduling unit 110. It has. The difference between the base station apparatus 200 and the base station apparatus 100 is that the base station apparatus 200 includes a correlation value calculation unit 201 and a table storage unit 202. Among the functional units included in the base station device 200, the same functional units as the functional units included in the base station device 100 are denoted by the same reference numerals, and description of the functional units is omitted.

  The correlation value calculation unit 201 calculates the correlation value of the channel information in the two radio stations 150 based on the channel information for each radio station 150 stored in the channel information storage unit 104. Correlation value calculation section 201 associates the calculated correlation value with a set of two radio stations 150 corresponding to the correlation value and stores them in a table included in table storage section 202. The correlation value calculation unit 201 calculates correlation values for all pairs in the wireless station 150 included in the wireless communication system and stores them in the table. In addition, the correlation value calculation unit 201 calculates each set of correlation values for each frequency component k in the wireless communication system and stores them in the table.

  The table storage unit 202 includes a table for each frequency component k. In each table, a correlation value calculated by the correlation value calculation unit 201 is associated with a set of wireless stations 150 corresponding to the correlation value.

  The base station apparatus 200 performs the scheduling process illustrated in FIGS. 3 and 4 in the same manner as the base station apparatus 100. However, in the base station apparatus 200, when the correlation value determination unit 113 performs the determination in the process S5, the correlation value determination unit 113 displays the correlation value corresponding to the set of wireless stations 150 to be determined in the table of the table storage unit 202. Will be read from. Further, when the cumulative value determination unit 114 performs the determination in the process S <b> 6, the cumulative value determination unit 114 reads the correlation value corresponding to the set of wireless stations 150 that perform the determination from the table of the table storage unit 202.

  FIG. 6 is a diagram illustrating an example of a table included in the table storage unit 202. The numbers in the top row and the leftmost column of the table are the identification numbers of the radio stations 150. As shown in FIG. 6, the correlation value calculation unit 201 stores a table storing correlation values T (i, j) between the i-th radio station 150 and the j-th radio station 150 in the frequency component k. Each k is created before the scheduling process is performed. Thereby, the correlation value determination unit 113 and the cumulative value determination unit 114 can acquire the correlation value f [i, j, k] by referring to the table. The correlation value T (i, j) stored in each frequency component table takes a value between 0 and 1. In the following description of the table, the notation regarding the frequency component k is omitted for simplicity.

  For example, in the table shown in FIG. 6, T (1,2) = T (2,1) = 0.12, T (1,3) = T (3,1) = 0.34, T (1,4 ) = T (4,1) = 0.08, the correlation value is associated with the combination of the radio stations 150. By using such a table, the base station apparatus 200 does not need to calculate a correlation value in the determination of the processing S5 and the processing S6 in the scheduling processing shown in FIGS. The correlation value determination unit 113 and the cumulative value determination unit 114 can easily perform processing by reading the correlation value from the table corresponding to the frequency component k to be determined. The diagonal component T (i, i) is treated as zero for convenience.

  Further, since the determination in step S5 of FIG. 3 is a determination of comparing the table value against the predetermined threshold β, the comparison is made in advance without comparing the correlation value with the threshold β every time the determination is performed. A comparison result table that stores the results of performing the above may be provided separately. Thereby, the process can be further simplified. FIG. 7 is a diagram illustrating an example of a comparison result table that stores the determination result of the process S5. FIG. 7 shows a comparison result corresponding to the correlation value in the table of FIG. 6 when the threshold value β = 0.30. In the comparison result table shown in FIG. 7, since the combination of the radio stations 150 has symmetry, the lower left side of the diagonal component is blank. Such a comparison result table may be created in the table storage unit 202 when the correlation value calculation unit 201 calculates a correlation value, for example.

  When the table shown in FIG. 6 is used, the determination in step S5 in FIG. 3 is performed by using the identification number of the wireless station 150 to be determined as m for all i satisfying 1 ≦ i ≦ j with respect to m. This corresponds to the determination of whether i) and m) are equal to or greater than the threshold value β. In FIG. 7, the determination results are indicated by “◯” (maru) and “×” (X), but “1” is assigned to “○” and “0” is assigned to “×”. By assigning, the determination result may be digitized and stored in the comparison result table. When the determination result is represented by “1” and “0”, if the identification number of the wireless station 150 to be determined is m, the determination using the equation (8) in the process S5 is performed by the following equation (13). It can be treated as a determination of whether or not it is established.

  Here, since the calculation of Expression (13) is established when the determination results are all “1”, the hardware can be realized by a simple circuit using a logical product AND.

  In the related art, the correlation value stored in the table of the table storage unit 202 provided in the base station apparatus 200 may be updated to reflect the change in the propagation environment. At this time, the channel information necessary for updating the correlation value may also be updated in a manner that reflects the change in the propagation environment. Further, when the base station apparatus 200 accommodates a new radio station 150 without updating the acquired channel information, the channel information related to the new radio station 150 is acquired, and the new radio station 150 in the table is acquired. Updates may be made to add corresponding rows and columns. Further, when the radio station 150 once accommodated in the base station apparatus 200 stops operating or when the radio station 150 moves out of the communication range of the base station apparatus 200, the correlation value calculation unit 201 reads the correlation value from the table. The data of the radio station 150 may be deleted.

[Outline of the present invention]
In the scheduling process shown in FIGS. 3 and 4, if a broadband wireless communication system is assumed, attention is paid to a specific frequency component, and transmission opportunities are assigned based on the correlation value of channel information of the focused frequency component. Done. This is because the correlation between the channel information in the frequency direction is strong and the correlation value of the channel information obtained with a certain frequency component and the correlation value of the channel information with another frequency component in the band are approximately approximate, Even in a broadband wireless communication system, it is possible to perform scheduling processing by paying attention to one frequency component.

  However, in general, channel information correlation often shows different behavior for each frequency component under the influence of multipath. As described in the related art, for example, in a wireless communication system employing the OFDMA method, different scheduling processing is performed for each frequency component, so there is no problem even if different correlations are shown for each frequency component. However, some actual wireless communication systems are OFDM systems or single carrier systems, and perform band allocation management in units of sub-channels that divide the entire band or into several bands. Scheduling processing considering characteristics is required.

  For example, even if the correlation value is lower than a predetermined threshold value in a predetermined frequency component, other frequency components may show values higher than the threshold value. That is, generally, the threshold table has different contents for each frequency component. For this reason, it becomes complicated when handling a plurality of frequency components at the same time with the related technology, and some simplification is required.

  Therefore, in the embodiment shown below, the correlation is comprehensively evaluated using the tables as shown in FIGS. 6 and 7 and provided for each frequency component, and the correlation in the assumed frequency band is reduced. A scheduling process is performed by consolidating the data into one table and referring to the table. Here, an evaluation function F [i, j] between the i-th radio station 150 and the j-th radio station 150 using the correlation value of Formula (7) for each frequency component as an argument is expressed by the following formula ( 14), and the evaluation function value obtained by the evaluation function is managed as a table as shown in FIG. Or you may perform a scheduling process using the table like FIG. 7 which memorize | stored the determination result whether the evaluation function value exceeds the predetermined threshold value.

  In Equation (14), K is the total number of frequency components that are targets for evaluating the correlation. When the correlation value is managed for each subcarrier in the OFDM scheme, K corresponds to the number of subcarriers. Even in the OFDM scheme, when the correlation of channel information is strong between subcarriers, all subcarriers are not subject to evaluation, and a certain number of subcarriers are thinned out to obtain a formula for K that is smaller than the total number of subcarriers. (14) may be defined. For example, if it is a predetermined subcarrier interval (for example, 10 subcarriers) with respect to the entire subcarrier, or if the frequency correlation shows the same value over, for example, about 1 MHz, the subcarrier interval to be evaluated May be set to have an interval of about 1 MHz, and the correlation of some subcarriers in the entire band may be used as an argument. It should be noted that the function form of Equation (14) may be any form as long as it is a function form that monotonously increases for each of the K components.

[First Embodiment]
The wireless communication system in the first embodiment has the same configuration as the wireless communication system in the related technology shown in FIG. Note that the wireless communication system in the first embodiment includes a base station apparatus 300 described below instead of the base station apparatus 100. FIG. 8 is a block diagram illustrating a configuration of the base station apparatus 300 according to the first embodiment. As shown in FIG. 8, the base station apparatus 300 includes a plurality of antenna elements 101, a radio communication unit 102, a channel information acquisition unit 103, a channel information storage unit 104, an evaluation value calculation unit 301, an evaluation value table storage unit 302, and a scheduling. Part 310 is provided. The scheduling unit 310 includes a transmission opportunity queue 111, a determination target selection unit 112, an evaluation value determination unit 313, a cumulative value determination unit 314, a buffer 115, and an assigned radio station determination unit 116.

  The difference between the base station apparatus 300 and the base station apparatus 200 is that the base station apparatus 300 replaces the correlation value calculation unit 201, the table storage unit 202, and the scheduling unit 110 with the evaluation value calculation unit 301, the evaluation value table storage unit 302, and the scheduling. The point is that the portion 310 is provided. The difference between the scheduling unit 310 and the scheduling unit 110 is that the scheduling unit 310 includes an evaluation value determination unit 313 and a cumulative value determination unit 314 instead of the correlation value determination unit 113 and the cumulative value determination unit 114. Among the functional units included in the base station device 300, the same functional units as the functional units included in the base station device 100 or the base station device 200 are denoted by the same reference numerals, and description of the functional units is omitted.

  The evaluation value calculation unit 301 calculates evaluation values for all combinations of two wireless stations 150 in the plurality of wireless stations 150. The evaluation value calculation unit 301 stores the calculated evaluation value and the combination of the two radio stations 150 corresponding to the evaluation value in the evaluation value table storage unit 302 in association with each other. Here, the evaluation value is a value calculated based on the correlation value of the channel information of each frequency component of the two wireless stations 150. In this embodiment, instead of the correlation value f [i, j, k] (equation (8)) for each frequency component, the evaluation value F [i, j] (equation ( 14)). In this way, by using Equation (14) instead of Equation (8), it is possible to easily determine whether or not assignment is possible in the collective assignment of wideband frequency components using the OFDM modulation method, SC-FDE method, or the like. Can do.

  The evaluation value table storage unit 302 stores the evaluation value F [i, j] calculated by the evaluation value calculation unit 301 for each combination of two wireless stations 150 in the plurality of wireless stations 150.

  The evaluation value determination unit 313 reads, from the evaluation value table storage unit 302, evaluation values of the radio station 150 selected as the determination target by the determination target selection unit 112 and each of the radio stations 150 to which transmission opportunities have already been assigned. . The evaluation value determination unit 313 determines whether or not to allocate a transmission opportunity to the determination target radio station 150 based on the read evaluation value. Evaluation value determination section 313 outputs the determination result to assigned radio station determination section 116.

  The accumulated value determination unit 314 calculates, for each wireless station 150, the accumulated value of the evaluation values with the other wireless stations 150 in the wireless station 150 to be determined and each wireless station 150 to which a transmission opportunity has already been assigned. The accumulated value determination unit 314 determines whether to assign a transmission opportunity to the determination target radio station 150 based on the accumulated value calculated for each radio station 150. Accumulated value determination section 314 outputs the determination result to assigned radio station determination section 116.

  9 and 10 are flowcharts illustrating scheduling processing performed by the base station apparatus 300 according to the first embodiment. In the scheduling process, a combination of wireless stations 150 to be subjected to spatially multiplexed communication at the same time is determined. The difference between the scheduling process shown in FIGS. 9 and 10 and the scheduling process in the related technology shown in FIGS. 3 and 4 is that the scheduling process in this embodiment is different from the process S5 and the process S6 in the process S31 and the process S32. It is a point. In the scheduling process in the present embodiment, the formulas used for the determination in the process S31 and the process S32 are different, but the other processes are the same as the scheduling process in the related technology, and thus the description thereof is omitted.

  In the process S5 of the scheduling process in the related technology, the formula (8) is used as a determination condition, whereas in the scheduling process S31 in the present embodiment, the evaluation value represented by the formula (14) is used. (15) is used.

  M, S (i), j, and β in Equation (15) are the same parameters as m, S (i), j, and β in Equation (5). m is the identification number of the target radio station 150 that determines whether or not transmission opportunities can be assigned. S (i) (0 ≦ i ≦ j) is an identification number of the radio station 150 to which a transmission opportunity has already been assigned. j is the number of radio stations 150 to which transmission opportunities have already been assigned. The threshold value β is a predetermined real number where 0 <β <1.

  In the process S6 of the scheduling process in the related art, the expressions (9) and (10) are used as the determination conditions, whereas in the scheduling process S32 in the present embodiment, the following expressions (16) and (17) ) Is used. In the equations (16) and (17), the function f [i, j, k] in the equations (9) and (10) is replaced with the function F [i, j].

  In the scheduling process according to the present embodiment, the correlation values are obtained by aggregating the correlation values in the frequency direction without determining whether to assign a transmission opportunity to the determination target radio station 150 based on the correlation value for each frequency component. The obtained evaluation value F [i, j] is used. As a result, the base station apparatus 300 reduces the load in the scheduling process and simplifies the process while lowering the channel correlation in the combination of radio stations to be subjected to spatial multiplexing communication, regardless of the antenna configuration of the base station apparatus 300. And higher SIR characteristics can be realized.

  Here, as the function F [i, j] described in Expression (14), for example, any one of the following function forms from Expression (18) to Expression (23) is used.

  The function F [i, j] in the equation (18) is a function that calculates an average value of correlation values of each frequency component as an evaluation value. A function F [i, j] in Expression (19) is a function that calculates a mean square value of correlation values of each frequency component as an evaluation value. The function F [i, j] in the equation (20) is a function that calculates, as an evaluation value, an average value of the power of the base of the natural logarithm (Napier number) e with α times the correlation value of each frequency component as an exponent. . Α is a predetermined positive real number. A function F [i, j] in Expression (21) is a function for calculating an average value of logarithmic values of correlation values of frequency components as an evaluation value. The function F [i, j] in the equation (22) is a function F [i, j] that calculates the maximum correlation value of each frequency component as an evaluation value.

  The function Step (x) in Equation (23) is a step type function that takes 1 when the value of x is positive, 0 when it is negative, or 0. δ is a constant that satisfies 0 <δ <1. The intention of Equation (23) is that the function F [i, j] obtains the number of frequency components whose correlation value exceeds a predetermined constant δ. That is, the function F [i, j] in the equation (23) is a function for acquiring the number of correlation values exceeding the threshold δ among the correlation values of the respective frequency components. This equation (23) can also be regarded as a function for counting the number of subcarriers that may not satisfy the desired quality. In this sense, it is evaluated whether bit errors can be compensated by error correction or the like. It can be used as a function of.

  In Equation (19), the correlation value is squared to calculate the average value, but it may be a positive real power other than the square. In addition, in Equations (18) to (21), (1 / K) is multiplied by the sum to calculate the average value, but the evaluation value does not necessarily have to be an average value. The multiplication of K) may be omitted, or a coefficient different from (1 / K) may be multiplied. The function F [i, j] shown here is merely an example, and the evaluation value may be calculated using any function such as a function obtained by linearly combining these functions or a similar function. .

  As described above, the evaluation value is calculated in advance using the function F [i, j] having the correlation value for each frequency component as an argument, so that even in a wireless communication system having different correlation characteristics for each frequency component. It is possible to assign transmission opportunities in the scheduling process using one evaluation value table.

[Second Embodiment]
In the scheduling process shown in FIGS. 9 and 10 in the first embodiment, transmission opportunities are allocated on condition that both the determinations in the process S31 and the process S32 are satisfied. However, it is not always necessary to make the determinations of both the processing S31 and the processing S32, and transmission opportunities may be assigned based on one of the determinations.

  FIG. 11 is a flowchart showing a scheduling process in the second embodiment. The difference between the scheduling process shown in FIG. 11 and the scheduling process shown in FIGS. 9 and 10 is that the process S32 is omitted in the scheduling process of the present embodiment. In the scheduling process of the present embodiment, when the condition is satisfied in the determination of process S31 (YES in process S31), process S7 is performed. Based on the determination result by the evaluation value determination unit 313, the allocated radio station determination unit 116 determines whether or not to allocate a transmission opportunity to the radio station 150 selected as a determination target by the determination target selection unit 112.

[Third Embodiment]
In the scheduling process of the second embodiment, the configuration in which the process S32 in the scheduling process of the first embodiment is omitted has been described. In the third embodiment, a case in which the process S31 in the scheduling process of the first embodiment is omitted will be described.

  FIG. 12 is a flowchart showing the scheduling process in the third embodiment. In the scheduling process of this embodiment, the process S31 is omitted as described above. Process S32 is executed after process S4. In the scheduling process of the present embodiment, β and β ′ in Equation (11) are not necessarily different values, and γ (j) may be given by β × j, as in the first embodiment. Γ (j) may be given by Equation (12), or may be given as a fixed value without depending on j.

  In the scheduling process of this embodiment, the assigned radio station determination unit 116 determines whether to assign a transmission opportunity to the radio station 150 selected as the determination target by the determination target selection unit 112 based on the determination result by the cumulative value determination unit 314. To decide.

[Supplementary items for each embodiment]
Hereinafter, supplementary items according to each embodiment will be described. In the description of each embodiment, the configuration and processing corresponding to the difference are described based on the items described as the related art. The comparison result table of FIG. 7 described in the related art may be applied to the base station apparatus 300 of each embodiment and used to determine whether or not to allocate a transmission opportunity.

  Further, it is not always necessary to use the fixed value of the table T (i, j) in the evaluation value table storage unit 302. For example, in the related art, the correlation value stored in the table of the table storage unit 202 is changed in the propagation environment. It may be updated in the same manner as updating to reflect the above. At this time, the channel information stored in the channel information storage unit 104 is also updated to reflect the change in the propagation environment, and the evaluation value is updated in accordance with the change in the channel information. It can also be used in a mobile environment. In this case, if a certain amount of time is available for calculation processing, the table is updated sequentially based on the channel information that is sequentially updated, and the above processing is performed using the updated latest table. Good. As described above, the items described in the related art can be applied to the base station apparatus 300 of each embodiment.

  Further, in the scheduling process in each embodiment, a configuration has been described in which transmission opportunities are allocated to the radio stations 150 until the upper limit number J of spatial multiplexing is reached, and a combination of the radio stations 150 that are targets of spatial multiplexing is searched. However, after the upper limit number J of the assigned radio stations 150 in the scheduling process is set to a value larger than the upper limit number J ′ in the actual spatial multiplexing, the series of processes in the schedule process shown in FIG. Before executing step S12, the selected radio station 150 of the J station may be narrowed down to the radio stations 150 of the actual upper limit number J ′. When selecting the radio station 150 of the J ′ station from the radio station 150 of the selected J station, the evaluation is performed with the function expressed by the formula (14) (specifically, the formula (18) to the formula (23), etc.). By calculating the value and performing the processing S31 and / or the processing S32, the radio stations 150 are narrowed down. As a result, it is possible to select a radio station 150 that is a target of spatial multiplexing communication.

  When a transmission opportunity is assigned to the radio stations 150 having the upper limit number J ′ having a value larger than the actual spatial multiplexing upper limit number J ′, the radio stations 150 having the upper limit number J ′ are selected. Later, a cumulative value of evaluation values with the other wireless stations 150 selected for each wireless station 150 of the J station may be calculated, and the J ′ stations may be selected in order from the wireless station 150 having the smallest calculated cumulative value. Alternatively, after selecting the radio station 150 of the J station, the accumulated value of the evaluation values with the other selected radio stations 150 is calculated for each selected radio station 150, and the calculated accumulated value becomes the maximum value. It is also possible to exclude one station from the J station radio station 150 and narrow down to the J ′ station radio station 150 by repeating the process of excluding.

  Further, in the description of each embodiment, the description has been given assuming that there is one antenna element on the radio station 150 side. However, in the case where the wireless station 150 includes a plurality of antenna elements, if the spatial multiplexing transmission (multiple number of 2 or more) is not performed with respect to one wireless station 150 in actual communication, the predetermined number of antenna elements By using the transmission weight and the reception weight, it is possible to form one virtual antenna with directivity corresponding to the weight. Assuming this virtual antenna, channel information recognized by the base station apparatus is represented in the same manner as a vector format corresponding to one antenna element. If handled in this way, the number of antenna elements provided on the radio station 150 side is not necessarily one. Here, if individual antenna elements are defined as physical antennas, and antennas formed by transmission / reception weights are defined as virtual antennas, there is virtually no difference in handling between physical antennas and virtual antennas.

  Further, when the entire frequency band used by the radio communication system in each embodiment is divided into a predetermined number of subchannels, and scheduling processing is performed for each radio channel 150 in units of the subchannels, Alternatively, an evaluation value may be calculated according to Expression (14) using all or part of the subcarriers included in each subchannel as an argument, and scheduling may be performed according to the above embodiment based on the evaluation value. In many radio systems in particular, in order to enhance the error correction effect, subcarriers included in each subchannel are often distributed in the entire band. For example, when the whole is divided into a small number of subchannels, Considering the feature that the correlation values are approximately the same between the carriers, it can be expected that the individual subchannels exhibit substantially the same correlation characteristics as a whole. In this case, even if the subchannels are different, a common evaluation value table can be shared and the entire system can be operated with one evaluation value table.

  You may make it implement | achieve the base station apparatus in embodiment mentioned above with a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, a “computer-readable recording medium” dynamically holds a program for a short time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case may be included and a program that holds a program for a certain period of time. Further, the program may be for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. It may be realized using hardware such as PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array).

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes a design that does not depart from the gist of the present invention. Needless to say, the above-described embodiment and a plurality of modifications can be combined within a range in which the contents do not conflict with each other. Further, in the above-described embodiment and modification, the structure of each part has been specifically described. However, the structure and the like can be variously changed within a range that satisfies the present invention.

  The present invention can also be applied to a case where scheduling processing is required in spatial multiplexing communication between one base station apparatus and a plurality of radio stations.

DESCRIPTION OF SYMBOLS 1 ... Base station 2 ... Wireless station 3 ... Line-of-sight wave 4 ... Stable reflected wave 5, 6 ... Multiple reflected wave 7 ... Structure 100,200,300 ... Base station apparatus 101 ... Antenna element 102 ... Wireless communication part 103 ... Channel information Acquiring unit 104 ... Channel information storage unit 110, 310 ... Scheduling unit 111 ... Transmission opportunity queue 112 ... Determination target selection unit 113 ... Correlation value determination unit 114 ... Cumulative value determination unit 115 ... Buffer 116 ... Allocated radio station determination unit 201 ... Correlation value calculation unit 202 ... Table storage unit 301 ... Evaluation value calculation unit 302 ... Evaluation value table storage unit 313 ... Evaluation value determination unit 314 ... Cumulative value determination unit 150 ... Wireless station

Claims (6)

A base station apparatus including a plurality of antenna elements and a plurality of radio stations, and using a MIMO channel formed between the base station apparatus and the radio station, spatial multiplexing communication is performed for the plurality of radio stations. In a wireless communication system that can be performed, the base station apparatus is a spatial multiplexing scheduling method for determining a combination of wireless stations that simultaneously perform spatial multiplexing,
Before scheduling processing, channel information acquisition step of acquiring channel information between the plurality of antenna elements and each of the radio stations for each frequency component and storing it in a channel information storage unit,
As a scheduling process, one radio station is selected as a determination target radio station from the radio stations waiting for allocation of communication opportunities, and each of the radio stations to which communication opportunities have already been allocated and all of the determination target radio stations Or when the evaluation value calculated based on the correlation value of the channel information acquired with some frequency components is less than a predetermined first threshold and / or with the radio station already assigned a communication opportunity When the cumulative value of each evaluation value with each other wireless station is calculated for each wireless station and all cumulative values are less than a predetermined second threshold, the determination target wireless station A spatial multiplexing scheduling method comprising: an assigned radio station determining step for allocating a communication opportunity to a radio station. The spatial multiplexing scheduling method according to claim 1, wherein
Based on the channel information stored in the channel information storage unit, the correlation value of the channel information acquired with all or a part of the frequency components for each pair of radio stations in the plurality of radio stations is calculated and calculated. An evaluation value calculating step for calculating an evaluation value for each pair of wireless stations based on each correlation value and storing the evaluation value in a evaluation value table storage unit;
In the assigned radio station determining step,
The space is characterized in that the evaluation value of the wireless station pair is read from the evaluation value table storage unit and, based on the read evaluation value, whether or not to allocate a communication opportunity to the determination target wireless station is determined. Multiple scheduling method. In the spatial multiplexing scheduling method according to claim 1 or 2,
In the assigning radio station determining step, communication opportunities are assigned to each radio station to which a communication opportunity is assigned after a communication opportunity is once assigned to a number of the radio stations that are actually spatially multiplexed. A spatial multiplexing scheduling method comprising: an assigned wireless station narrowing step for calculating a cumulative value of evaluation values with other wireless stations and narrowing down wireless stations to which communication opportunities are actually allocated based on the calculated cumulative value . In the spatial multiplexing scheduling method according to any one of claims 1 to 3,
When the normalized correlation value in the channel information between the i-th radio station and the j-th radio station in the k-th frequency component is expressed by f [i, j, k], the i-th radio station and the j-th radio station The evaluation value is calculated by F [i, j] of any one of the following formulas (A) to (F),

K in each equation is an integer equal to or greater than 2, α in equation (C) is a predetermined positive real number, and δ in equation (F) is a real number satisfying 0 <δ <1. Multiple scheduling method. A base station apparatus including a plurality of antenna elements and a plurality of radio stations, and using a MIMO channel formed between the base station apparatus and the radio station, spatial multiplexing communication is performed for the plurality of radio stations. A base station apparatus in a wireless communication system capable of performing
Before scheduling processing, a channel information acquisition unit that acquires channel information between the plurality of antenna elements and each of the radio stations for each frequency component and stores it in a channel information storage unit,
As a scheduling process, one radio station is selected as a determination target radio station from the radio stations waiting for allocation of communication opportunities, and each of the radio stations to which communication opportunities have already been allocated and all of the determination target radio stations Or when the evaluation value calculated based on the correlation value of the channel information acquired with some frequency components is less than a predetermined first threshold and / or with the radio station already assigned a communication opportunity When the cumulative value of each evaluation value with each other wireless station is calculated for each wireless station and all cumulative values are less than a predetermined second threshold, the determination target wireless station A base station apparatus comprising: an assigned radio station determination unit that allocates a communication opportunity to a radio station.   A program for causing a computer to execute the spatial multiplexing scheduling method according to any one of claims 1 to 4.

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