JP6259354B2 - 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. 15 is a diagram showing an outline of a large-scale antenna system. In FIG. 15, 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. 15, 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. 16 is a diagram illustrating an impulse response in a line-of-sight environment and a non-line-of-sight environment. FIG. 16A shows an impulse response in a non-line-of-sight environment, and FIG. 16B shows an impulse response in a line-of-sight environment. 16A and 16B, 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. 16 (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. 15 is assumed, the level of the stable path of the line-of-sight wave 3 and the stable reflected wave 4 by the structure 7 is high. When the amount of delay is larger than that of the line-of-sight wave 3 and the stable reflected wave 4 by the structure 7, the multiple reflected wave of the fluctuation path is relatively leveled 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. 17 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. 18 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. 18 is read, if the azimuth difference angle θ is about 5 degrees or less, for example, 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. 18 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 and storing the channel information in a channel information storage unit, and one radio station from the radio station waiting for allocation of a communication opportunity as a scheduling process Select a radio station to be determined, and each of the radio stations to which a communication opportunity has already been assigned and the radio station to be determined When the correlation value of the channel information is less than a predetermined first threshold and / or between the radio station to which a communication opportunity has already been assigned and the radio station to be determined An allocation radio station determination step of calculating a cumulative value of correlation values of channel information and allocating a communication opportunity to the determination target radio station when all the cumulative values are less than a predetermined second threshold value. Is a spatial multiplexing scheduling method characterized by

  Further, according to one aspect of the present invention, in the spatial multiplexing scheduling method described above, each of a pair of radio stations in the plurality of radio stations is based on channel information stored in the channel information storage unit before the scheduling process. Generating a table for storing correlation values of channel information of the channel, and in the allocation radio station determining step, the correlation value of channel information in the pair of radio stations is read from the table, and based on the read correlation value And determining whether to assign a communication opportunity to the radio station to be determined.

  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. A wireless value for which a communication opportunity is actually allocated based on the calculated cumulative value of a correlation value of channel information with another wireless station to which a communication opportunity is assigned for each wireless station to which a communication opportunity is assigned It has the allocation radio station narrowing-down step which narrows down a station.

  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 radio communication system capable of performing spatial multiplexing communication with a radio station, wherein channel information between the plurality of antenna elements and each of the radio stations is acquired before a scheduling process. The channel information acquisition unit to be 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 communication opportunity assignment, and a communication opportunity has already been assigned. When the correlation value of channel information between each of the radio stations and the radio station to be determined is less than a predetermined first threshold and / or when there is already a communication opportunity A cumulative value of correlation values of channel information with other wireless stations is calculated for each wireless station between the assigned wireless station and the determination target wireless station, and all accumulated values are determined in advance. The base station apparatus comprising: an allocated radio station determination unit that allocates a communication opportunity to the determination target radio station when the threshold is less than the threshold.

  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 apparatus and each radio station is acquired before the scheduling process, and based on the correlation value between the acquired channel information, the radio station to be subjected to spatial multiplexing communication By determining the combination, the 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 1st Embodiment. It is a block diagram which shows the structural example of the base station apparatus 100 in 1st Embodiment. It is a 1st flowchart which shows the scheduling process which the base station apparatus 100 in 1st Embodiment performs. It is a 2nd flowchart which shows the scheduling process which the base station apparatus 100 in 1st Embodiment performs. It is a block diagram which shows the structure of the base station apparatus 200 in 2nd Embodiment. It is a figure which shows an example of the table contained in the table memory | storage part 202 in 2nd Embodiment. It is a figure which shows an example of the comparison result table which memorize | stores the determination result of process S5 in 2nd Embodiment. It is a flowchart which shows the scheduling process in 3rd Embodiment. It is a flowchart which shows the scheduling process in 4th Embodiment. It is a block diagram which shows the structure of the base station apparatus 500 in 5th Embodiment. It is a 1st flowchart which shows the scheduling process which the base station apparatus 500 in 5th Embodiment performs. It is a 2nd flowchart which shows the scheduling process which the base station apparatus 500 in 5th Embodiment performs. It is a flowchart which shows process S14 in 5th Embodiment. It is another flowchart which shows process S14 in 5th 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).

[Basic Principle 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.

  Embodiments 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, 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.

[First Embodiment]
FIG. 1 is a diagram illustrating a configuration of a wireless communication system according to the first embodiment. 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 radio communication system is used, for example, as a large-scale antenna system shown in FIG.

  When used as a large-scale antenna system, a 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 according to the first embodiment. 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.

  3 and 4 are flowcharts illustrating a scheduling process performed by the base station apparatus 100 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. 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.

  Further, the scheduling process in the present embodiment 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 feature of the scheduling processing in this embodiment is that the processing S5 and the processing S5 shown in FIG. It is confirmed that the condition of the process S6 is satisfied, and the radio station 150 that matches the condition is approved as a radio station 150 that performs spatial multiplexing simultaneously.

  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 periodically assigned to each radio station 150 by the round robin method, and the scheduling processing in this embodiment can be applied to any method of managing the assignment request.

  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 of this embodiment can be performed even if the radio station 150 in this embodiment 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. That is, some kind of channel feedback processing is required, but the scheduling processing in the present embodiment does not depend at all on how to implement the feedback method, and any feedback method may be used.

  According to the base station apparatus 100 in the first embodiment, channel information between the base station apparatus 100 and the radio station 150 is acquired before scheduling processing and stored in the channel information storage unit 104 to store the channel information. Based on the correlation value between the channel information stored in unit 104, the combination of radio stations 150 to be subjected to spatial multiplexing communication is determined. Thereby, it is possible to determine the combination of the radio stations 150 to be subjected to the spatial multiplexing communication while suppressing the channel correlation to be low without being affected by the arrangement or shape of the antenna element 101 provided in the base station apparatus 100. As a result, it is possible to increase the number of spatial multiplexing while improving the SIR characteristics in each radio station 150.

  In addition, the base station apparatus 100 according to the first embodiment uses the correlation value of channel information and the accumulated value of the correlation value without evaluating the characteristics when the weight matrix is applied. Since the combination of wireless stations 150 to be determined is determined, the calculation amount and processing load required for the combination of wireless stations 150 can be reduced.

[Second Embodiment]
In the scheduling process shown in FIG. 3 and FIG. 4 in the first embodiment, whether or not the inequalities of Expression (8), Expression (9), and Expression (10) are satisfied when performing the determination in Step S5 and Step S6. It was necessary to make a judgment. 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. The base station apparatus in the second embodiment has a configuration that simplifies the processing as described above.

  FIG. 5 is a block diagram illustrating a configuration of the base station apparatus 200 according to the second embodiment. The radio communication system according to the second embodiment includes a base station apparatus 200 instead of the base station apparatus 100 of the radio communication system according to the first embodiment. 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 in the second embodiment and the base station apparatus 100 in the first embodiment 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.

  In the present embodiment, when the correlation value determination unit 113 performs the determination in the process S5, the correlation value determination unit 113 reads the correlation value corresponding to the set of wireless stations 150 to be determined from the table in the table storage unit 202. become. 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 according to the second embodiment. 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 according to the second embodiment. 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 second embodiment, 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.

  The base station apparatus 200 in the second embodiment can reduce the calculation load required for calculating the correlation value even when performing the same scheduling process as the scheduling process performed by the base station apparatus 100 in the first embodiment. . Further, by using the table shown in FIG. 7, the determination in the process S5 can be performed by an operation of reading the comparison result from the comparison result table, so that the calculation load can be further reduced.

[Third Embodiment]
In the scheduling process shown in FIGS. 3 and 4 in the first embodiment, transmission opportunities are assigned on condition that both the determinations in the process S5 and the process S6 are satisfied. However, it is not always necessary to determine both the process S5 and the process S6, and the process can be operated as a one-step process.

  FIG. 8 is a flowchart showing the scheduling process in the third embodiment. The difference between the scheduling process shown in FIG. 8 and the scheduling process shown in FIGS. 3 and 4 is that the process S6 is omitted in the scheduling process of this embodiment. In the scheduling process of the present embodiment, when the condition is satisfied in the determination of process S5 (YES in process S5), process S7 is performed. 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 correlation value determination unit 113.

  Note that the base station apparatus 200 in the second embodiment may perform the scheduling process shown in FIG. That is, the condition determination formula in the process S5 is determined by the table shown in FIG. 6 or FIG. 7, and particularly in the case of the table shown in FIG. 7, “1” and “0” instead of “◯” and “×”. ”Can be used to make a determination using equation (13).

[Fourth Embodiment]
In the scheduling process of the third embodiment, the configuration in which the process S6 in the scheduling process of the first embodiment is omitted has been described. In the fourth embodiment, a case where the process S5 in the scheduling process of the first embodiment is omitted will be described.

  FIG. 9 is a flowchart showing the scheduling process in the fourth embodiment. In the scheduling process of this embodiment, the process S5 is omitted as described above. Process S6 is performed 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 assigns 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 114. To decide.

  Note that the base station apparatus 200 in the second embodiment may perform the scheduling process shown in FIG.

[Fifth Embodiment]
In each of the above embodiments, the determination is performed on the radio stations 150 until the number (j) of radio stations 150 to be allocated in the scheduling process reaches the upper limit number J of spatial multiplexing. However, after the upper limit number J of the assigned radio stations 150 in the scheduling process is set to be larger than the actual upper limit number J ′ of spatial multiplexing, the radio stations 150 are assigned based on the upper limit number J, and then assigned. The number of radio stations 150 may be narrowed down to the upper limit number J ′.

  FIG. 10 is a block diagram illustrating a configuration of a base station device 500 according to the fifth embodiment. The wireless communication system in the fifth embodiment includes a base station device 500 instead of the base station device 100 of the wireless communication system in the first embodiment. As shown in FIG. 10, the base station device 500 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 510. The scheduling unit 510 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, an assigned radio station determination unit 116, and an assigned radio station narrowing unit 517. Yes. Among the functional units included in the base station device 500, 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 assigned radio station narrowing unit 517 narrows down the number of assigned radio stations 150 to the upper limit number J ′ or less after the assigned radio station determining unit 116 assigns transmission opportunities to the radio stations 150. In the present embodiment, the assigned radio station determining unit 116 notifies the assigned radio station narrowing unit 517 of a narrowing start instruction from the J station to the radio station 150 of the J ′ station, and the assigned radio station narrowing unit 517. After narrowing down the radio stations 150 by the above, the process of outputting the identification number stored in the allocated radio station buffer to the radio communication unit 102, and waiting for the transmission opportunity the identification number stored in the next allocation waiting buffer Processing to be stored in the matrix 111 is performed.

  FIG.11 and FIG.12 is a flowchart which shows the scheduling process which the base station apparatus 500 in 5th Embodiment performs. The difference between the scheduling process shown in FIGS. 11 and 12 and the scheduling process shown in FIGS. 3 and 4 is the difference between the processes S3 and S11 and S12 in the scheduling process of this embodiment. Is a point provided. Further, although it is not a clear difference on the flowchart, the upper limit value J in the process S11 of FIG. 3 was set as the upper limit number for actually performing the spatial multiplexing, but in the process S11 of FIG. Strictly speaking, the point is set to a value larger than the upper limit number for performing.

  In the fifth embodiment, when there is no radio station 150 waiting for transmission opportunity allocation in the determination of process S3 (NO in process S3), the allocated radio station narrowing unit 517 instructs the allocated radio station determining unit 116 to Accordingly, the radio station 150 of the J ′ station or less having a relatively small accumulated correlation value is selected from the allocated radio stations 150 recorded in the allocated radio station buffer in the buffer 115 (processing S14). The assigned wireless station narrowing-down unit 517 adds the identification number of the wireless station 150 removed from the assignment in the process S14 to the next assignment waiting buffer (process S15), and advances the process to the process S12. If the counter j has reached the upper limit value J in the determination in step S11 (YES in step S11), the assigned radio station narrowing unit 517 performs steps S14 and S15.

  Here, the accumulated correlation value is a correlation value between the wireless station 150 with the identification number S (j) to which the transmission opportunity is assigned and the wireless station 150 with the other identification number S (i). 7 is a cumulative value of correlation values calculated in 7). The accumulated value F (j, k) of the j-th selected radio station 150 in the frequency component k is given by the following formula (14).

  The addition range of Σ in Expression (14) is the assigned radio station 150. For example, when the number of radio stations 150 to which p stations have been assigned is assigned, the assigned radio station narrowing unit 517 performs the addition process of Expression (14) for the radio stations 150 of the p stations. The larger the value calculated by Equation (14), the larger the amount of interference. Therefore, when selecting a radio station 150 below the J ′ station that should actually perform spatial multiplexing from the assigned radio stations 150, the assigned radio station narrowing unit 517, for example, calculates the value calculated by Expression (14). The radio stations 150 of the J ′ station are selected in order from the radio station 150 having the smallest.

  FIG. 13 is a flowchart showing the process S14 in the fifth embodiment. The assigned radio station narrowing unit 517 starts the process S14 in FIG. 12 (process S21), and sets the number of assigned radio stations 150 to p (process S22). The assigned radio station narrowing unit 517 determines whether or not the number p of radio stations 150 is larger than the upper limit value J ′ (process S23). If p is equal to or less than J ′ (NO in process S23), the assigned radio station narrower 517 Since all of the wireless stations 150 can be assigned, the process ends the process S14 without narrowing down the wireless stations 150, and the process proceeds to the process S15 (process S25).

  When p is larger than J ′ in the determination of the process S23 (YES in the process S23), the assigned radio station narrowing unit 517 extracts the radio station 150 of the J ′ station from the radio stations 150 of the p station. The value of Expression (14) is calculated for each of the wireless stations 150, and the wireless station 150 of the J ′ station is selected in order from the wireless station 150 with the smaller calculated value (processing S24). The radio station 150 selected by the assigned radio station narrowing unit 517 in the process S24 is a target for spatial multiplexing. The assigned wireless station narrowing-down unit 517 notifies the assigned wireless station 150 to the assigned wireless station determining unit 116 after completing the selection of the wireless station 150 of the J ′ station in the process S24, ends the process S14, and performs the process S15. (Processing S25).

  FIG. 14 is another flowchart showing the process S14 in the fifth embodiment. In the process S14 shown in FIG. 13, the narrowing from the p station to the J ′ station is performed in one process (process S24), whereas in the process S14 shown in FIG. 14, the narrowing from the p station to the J ′ station is performed. The process S22, the process S23, and the process S26 are repeated. As shown in FIG. 14, a process S26 is provided instead of the process S24. In the process S26, the assigned radio station narrowing unit 517 excludes the radio stations 150 having the maximum accumulated correlation value given by Expression (14) from the assignment targets one by one, and finally becomes the J 'station. The process S22, the process S23 and the process S26 are repeatedly performed. In this process S22, the value of p is decremented by 1 each time the loop of process S22, process S23, and process S26 is repeated. Therefore, the process S22 is equivalent to the process of subtracting 1 from p after process S26 and returning to process S23. It is.

  This excludes the wireless station 150 (for the sake of convenience, the identification number is n) having the maximum accumulated value among the accumulated values calculated by Equation (14) for each wireless station 150 of the first p station from the assignment. In this case, in the process of further narrowing down the radio station 150 from the remaining radio stations 150 of (p−1), the station with the identification number n has already been excluded from the assignment. The correlation of [n, S (j), k] terms need not be considered. However, in the processing S24 in FIG. 13, since the evaluation is performed including the terms that do not need to be considered in order to narrow down from the station p to the station J 'at a stretch, the optimization is not complete. . Therefore, in processing S26 in FIG. 14, the assigned wireless station narrowing-down unit 517 detects the wireless station 150 that maximizes the value of Expression (14), excludes the detected wireless station 150, and returns the processing to processing S22. Then, the exclusion of the radio station 150 is repeated until it becomes the J 'station. As a result, the radio station 150 can be narrowed down by executing Expression (14) without including the term of f [n, S (j), k] corresponding to the excluded radio station 150.

  Note that the number p of assigned radio stations 150 in the process S22 is reduced by one from p → (p−1) for each repetition because one radio station 150 is excluded in the process S26. Therefore, the process S22 performed after the process S26 includes a process corresponding to the subtraction of the value of p, and a magnitude relationship with the value of the upper limit value J ′ in the process S23 for each subtraction of the value of p. A determination is made each time. Finally, the assigned radio station narrowing unit 517 notifies the assigned radio station determining unit 116 of the narrowed down radio station 150 when the subtracted value of p reaches the upper limit value J ′ (NO in step S23). Then, the process S14 is terminated and the process proceeds to the process S15 (process S25).

  In step S15, the assigned radio station narrowing unit 517 moves the assigned radio station 150 to the next assignment waiting buffer so that the assignment waiting order in the initial transmission opportunity queue 111 is the same as the order of waiting for assignment. Alternatively, the identification number of the wireless station 150 may be moved to the next allocation waiting buffer in the next allocation waiting buffer. Alternatively, the next allocation waiting buffer may be moved so that the identification number of the wireless station 150 is arranged at the head or tail of the next allocation waiting buffer.

A feature of the scheduling process in the fifth embodiment is that, after a series of allocation processes, a combination of radio stations 150 that are likely to be characteristically preferentially used is assigned preferentially to the allocated radio stations 150. is there. For example, when selecting a combination that spatially multiplexes three radio stations 150 from eight radio stations 150, in order to select a truly optimal combination, accumulation of correlations for all patterns of ₈ C _three combinations It is desirable to evaluate the values and select the combination of radio stations that minimizes the cumulative value. However, in the scheduling process in the first to fourth embodiments, since the final allocation result strongly depends on the order of the radio stations 150 waiting for allocation in the transmission opportunity queue 111, an allocation result deviating from the optimal allocation is obtained. May be obtained. On the other hand, in the scheduling process in the fifth embodiment, after the radio stations 150 are narrowed down by the upper limit value J (that is, J> J ′) that is looser than the upper limit value J ′ in the actual spatial multiplexing, the best among them is selected. The combination of the radio stations 150 having the above characteristics is selected. By this process, the scheduling process of the present embodiment is a simple method that can weaken the influence of the order of waiting for allocation in the transmission opportunity queue 111 and obtain a more optimal allocation.

  Here, in the above description of the fifth embodiment, the value of J ′ is treated as a constant, but it is not always necessary to provide it as a constant. For example, after the case of NO in the processing S3 described in FIG. 11 and FIG. 12 or the case of YES in the processing S11, if the number of radio stations 150 that have been allocated so far is equal to or greater than a predetermined threshold, the allocation has been completed A value obtained by subtracting a predetermined number (for example, 1 or 2) from the number of the wireless stations 150 may be given as J ′. In this case, a process of setting the value of J ′ according to the above rule may be added before the process S14.

  Note that the base station device 500 according to the fifth embodiment may include the correlation value calculation unit 201 and the table storage unit 202 included in the base station device 200 according to the second embodiment. In this case, the assigned wireless station narrowing-down unit 517 receives channel information corresponding to a pair of wireless stations from the table included in the table storage unit 202, similarly to the correlation value determination unit 113 and the cumulative value determination unit 114 in the second embodiment. The correlation values are read out and the radio stations 150 are narrowed down.

  Also, the base station device 500 according to the fifth embodiment can be implemented in a form in which either the processing S5 or the processing S6 is omitted, as in the third or fourth embodiment.

[Supplementary items for each embodiment]
Hereinafter, supplementary items according to each embodiment will be described. In the description of each embodiment, the antenna element on the radio station 150 side is described as one. 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 for one wireless station 150 in actual communication, a 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.

  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 100,200,500 ... Base station apparatus 101 ... Antenna element 102 ... Wireless communication part 103 ... Channel information Acquiring unit 104 ... Channel information storage unit 110, 510 ... 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 517 ... assigned radio station narrowing unit 150 ... radio station

Claims (5)

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,
Channel information acquisition step of acquiring channel information between the plurality of antenna elements and each of the radio stations and storing the channel information in a channel information storage unit before the scheduling process;
As the scheduling process, selected from the radio station to wait for the allocation of the communication opportunity one radio station of the determination target to the radio station, in the said radio station already in communication opportunities are assigned the determination target wireless station If all of the accumulated value calculating a cumulative value of the correlation value of the channel information with other radio stations per radio station is lower than the predetermined threshold value, the assignment that assigns a communication opportunity to the radio station of the determination target A spatial multiplexing scheduling method comprising: performing a radio station determination step. The spatial multiplexing scheduling method according to claim 1, wherein
Before the scheduling process, performing the step of generating a table based on said channel information stored in the channel information storage unit, and stores the correlation values of the respective pair of channel information of the radio stations in the plurality of radio stations And
In the assigned radio station determining step,
Spatial multiplexing, wherein a correlation value of channel information in the pair of wireless stations is read from the table, and based on the read correlation value, it is determined whether or not to allocate a communication opportunity to the determination target wireless station. 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 cumulative value of correlation values of channel information with other radio stations is calculated, and an assigned radio station narrowing step for narrowing down radio stations to which communication opportunities are actually allocated is executed based on the calculated cumulative value. Spatial multiplexing 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. wherein a base station apparatus in a wireless communication system capable of performing,
A channel information acquisition unit that acquires channel information between the plurality of antenna elements and each of the wireless stations and stores the channel information in a channel information storage unit before the scheduling process;
As the scheduling process, selected from the radio station to wait for the allocation of the communication opportunity one radio station of the determination target to the radio station, in the said radio station already in communication opportunities are assigned the determination target wireless station If all of the accumulated value calculating a cumulative value of the correlation value of the channel information with other radio stations per radio station is lower than the predetermined threshold value, the assignment that assigns a communication opportunity to the radio station of the determination target A base station apparatus comprising: a radio station determination unit.   The program for making a computer perform the spatial multiplexing scheduling method as described in any one of Claims 1-3.

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