JP2008236677A - Base station and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method for securely receiving communication start requests from user terminals exceeding a maximum space multiplex number by a present hardware constitution of an SDMA system. <P>SOLUTION: The control method includes: a reception control step of allocating a new space multiplex channel of only an uplink side to a new user terminal when a communication start request is received from the new user terminal when the maximum space multiplex number reaches the predetermined maximum space multiplex number, and controlling to perform reception processing using the allocated space multiplex channel; and a transmission control step of reallocating a space multiplex channel of a downlink side already allocated to another user terminal to the relevant other user terminal and the new user terminal in a predetermined order when transmitting data of the downlink side to the new user terminal, and controlling to perform transmission processing on the basis of the relevant reallocation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a base station and a control method thereof, and in particular, can accept a communication start request exceeding a maximum spatial multiplexing number by a new user terminal without changing a hardware design of a processor, and can immediately start communication. The present invention relates to a base station and a control method thereof.

  In a general wireless communication system, even when a communicable channel is filled, a user terminal side that desires to start communication with a base station cannot know the situation. Therefore, for example, in a wireless communication system to which SDMA (Spatial Multiplex Multiple Access) is applied, when a user terminal transmits a communication start request signal using a random access channel (RACH) of a certain carrier frequency, the carrier frequency is already set. The communication start request signal is discarded when the maximum number of spatial multiplexing has been reached (3 in the current commercial system iBurst (registered trademark)). Then, the user terminal whose communication start request signal is discarded and the connection is rejected tries to start communication by performing the same operation at another carrier frequency. However, it is necessary for the user terminal to repeat the retry until the connection acceptance permission at the vacant carrier frequency is obtained. Therefore, there is a problem that communication cannot be easily started in a situation where many user terminals are accessing and the communication channel is crowded.

In addition, a wide signal band necessary for voice or the like must be allocated to the call channel, but such a wide signal band is not necessary for a connection control signal used in connection control communication in the connection control phase. Therefore, a communication channel used in a wireless communication system of a multicarrier TDMA (time division multiple access) method, a communication channel for performing call communication, a connection control channel used for communication for line connection control between call communication partners, A technique has been proposed in which a link establishment control channel used to establish this connection control channel is provided independently (see Patent Document 1).
Japanese Patent Laid-Open No. 11-284587 (paragraph 0022-0024, FIG. 1)

  However, the proposed technique described above has a new problem that the control and processing become complicated due to an increase in the types of channels.

  Also, in the SDMA scheme, it is theoretically possible to increase the number of user terminals that can be accommodated in one carrier frequency if the number of spatial multiplexing is increased. For example, in a base station apparatus using the SDMA system, reception processing and transmission processing are performed by a DSP (digital signal processor), and a part of the function of “transmission processing” that requires simple arithmetic processing than the reception processing is performed by an FPGA (field programmable). Gate array) and other processors. However, although the FPGA is inexpensive, it cannot perform complicated arithmetic processing. Therefore, the number of spatial multiplexing is limited to the computing capacity of the FPGA (the number of multiplexing is 3 in the current system) and the same hardware configuration (DSP) And the set of FPGAs) it was difficult to increase the number of spatial multiplexing. In addition, it has been difficult from the viewpoint of cost to change the hardware design in order to improve the computing capability of a processor such as an FPGA. Further, if only the spatial multiplexing number on the reception side is increased, a new problem that the imbalance between the spatial multiplexing number on the reception side and that on the transmission side also occurs.

  Therefore, an object of the present invention is to accept a communication start request exceeding the maximum spatial multiplexing number by a new user terminal in the current hardware configuration of the SDMA system, that is, without changing the hardware design of the processor, and immediately It is another object of the present invention to provide a base station capable of starting communication and appropriately performing reassignment when there is an imbalance between the spatial multiplexing number on the reception side and that on the transmission side, and a control method therefor.

In order to solve the above-described problems, a control method for a base station according to the first invention is as follows:
A control method of a base station that performs radio communication simultaneously with a plurality of user terminals assigned with a plurality of spatial multiplexing channels spatially multiplexed in the same frequency band,
A transmission processing step for performing transmission processing for the plurality of user terminals;
A reception processing step of performing reception processing from the plurality of user terminals;
When a communication start request is received from a new user terminal when the predetermined maximum spatial multiplexing number has been reached, a new spatial multiplexing channel is allocated to the new user terminal only on the uplink side, and the allocated A reception control step for controlling to perform reception processing using the spatial multiplexing channel,
When transmitting data on the downlink side to the new user terminal, the downlink spatial multiplexing channel already assigned to the other user terminal is transferred to the other user terminal and the new user terminal. On the other hand, a transmission control step for performing reallocation in a predetermined order and controlling to perform transmission processing based on the reallocation,
It is characterized by including.

The base station control method according to the second aspect of the invention comprises:
The predetermined order in the transmission control step is determined by a round robin method.

The base station control method according to the third invention is
As the predetermined order in the transmission control step increases based on the data amounts to be transmitted to the new user terminal and the other user terminals, the allocation frequency increases as the data amount to be transmitted at each user terminal increases. Is determined to be high,
It is characterized by that.

A base station control method according to the fourth invention is:
The predetermined order in the transmission control step is assigned as the communication priority of each user terminal is higher based on the communication priority (for example, QoS, charging rank) in the new user terminal and the other user terminal. Determined to be more frequent,
It is characterized by that.

  As described above, the solution of the present invention has been described as a method. However, the present invention can be realized as a device, a program, and a storage medium storing the program substantially corresponding to these, and the scope of the present invention. It should be understood that these are also included.

For example, a base station according to a fifth aspect of the present invention that realizes the present invention as a base station (apparatus) is:
A base station that performs radio communication simultaneously with a plurality of user terminals assigned a plurality of spatial multiplexing channels spatially multiplexed in the same frequency band,
A transmission processing unit (such as a circuit) that performs transmission processing on the plurality of user terminals;
A reception processing unit (such as a circuit) that performs reception processing from the plurality of user terminals;
When a communication start request is received from a new user terminal when the predetermined maximum spatial multiplexing number has been reached, a new spatial multiplexing channel is allocated to the new user terminal only on the uplink side, and the allocated A control unit (a circuit, a processor such as a CPU and a DSP) that controls to perform reception processing using a spatial multiplexing channel.
The control unit is
When transmitting data on the downlink side to the new user terminal, the downlink spatial multiplexing channel already assigned to the other user terminal is transferred to the other user terminal and the new user terminal. In contrast, reallocation is performed in a predetermined order, and control is performed to perform transmission processing based on the reallocation.
It is characterized by that.

  According to the present invention, it is possible to reliably accept a communication start request from a user terminal while using the current hardware configuration of the SDMA method, and to immediately start communication without forcing the user to resend the start request. It becomes like this. Specifically, the number of users that can be connected simultaneously is changed by changing the control unit (circuit or program) so that only the receiving side improves the number of multiplexed users while maintaining the current hardware configuration such as the processor. It is possible to improve the performance before the change. Also, by increasing the number of spatial multiplexing on the receiving side, the number of spatial multiplexing on the receiving side and that on the transmitting side become imbalanced. Setting (reassignment) eliminates imbalance and assigns the transmission side (downlink) channel appropriately to new user terminals while assigning the transmission side channel to other existing users Will be able to.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a base station apparatus according to an embodiment of the present invention. As illustrated, the base station apparatus 100 includes a control unit (scheduler) 110, a DSP 120, an FPGA processing unit 130, a radio communication unit RF, and an adaptive array antenna AAA. Base station apparatus 100 further includes a storage unit (not shown) that stores a predetermined maximum spatial multiplexing number, a channel allocation table in which each user terminal is associated with a spatial multiplexing channel number allocated thereto. The control unit 110 performs assignment, release, time slot assignment, and the like of spatial multiplexing channels to each user terminal. The DSP 120 performs transmission signal processing of each user terminal using the spatial multiplexing channels SP1-SP3 assigned to the user terminals, and similarly performs reception signal processing using the spatial multiplexing channels SP1-SP3. A reception processing unit 120RC is included. The FPGA processing unit 130 includes three separation units DV1, DV2, DV3 corresponding to the number of spatially multiplexed channels 3 for transmission. These separators DV1 to DV3 separate the signals into 12 signals corresponding to the 12 antennas included in the adaptive array antenna AAA. The FPGA processing unit 130 further includes a coupling unit CM composed of 12 sections corresponding to 12 antennas. Similarly, the radio communication unit RF is composed of 12 sections. For convenience of explanation and drawing, only the coupling unit CM1 for the antenna ANT1 and the wireless communication unit RF1 will be described, but the processing of the other 11 units is the same. The coupling unit CM1 synthesizes the signal for the antenna ANT1 received from the separation unit DV1-DV3, converts it to one signal, and gives it to the radio communication unit RF1 for the antenna ANT1. The radio communication unit RF1 performs necessary signal processing on the signal received from the coupling unit CM1 and transmits the signal from the antenna ANT1. Thus, in this base station apparatus 100, the maximum spatial multiplexing number and the maximum spatial multiplexing channel number are three. Therefore, in normal allocation control, since there are three channels, three user terminals are allocated simultaneously to one carrier frequency.

  On the other hand, on the receiving side, the received signal received from the antenna ANT1 of the adaptive array antenna AAA performs necessary signal processing in the radio communication unit RF1, and each multi-space channel (that is, each of the multiple spatial channels (ie, each User terminal) signal. Conventionally, when the maximum spatial multiplexing number (maximum spatial multiplexing channel number) 3 is reached, a communication start request from a new user terminal has been rejected. In the base station apparatus 100 according to the present invention, when the fourth user terminal exceeding the maximum spatial multiplexing number of 3 transmits a communication start request signal on the random access channel RACH, this is accepted and the reception processing unit 120RC uploads it. A fourth spatial multiplexing channel SP4 is newly assigned only to the link side (details will be described later).

  In this case, when the arithmetic processing / signal processing of the reception processing unit 120RC is overloaded, the code such as the corresponding software module is assembled (the code coded directly in the assembler, not the code coded and compiled in the high-level language). The processing time is shortened to enable execution of processing for four user terminals every frame. In this manner, the reception side can perform reception processing in order to allocate a new spatial multiplexing channel to a new user terminal. On the other hand, although it is necessary to send a response signal of the communication start request signal to a new user terminal, there is no spatial multiplexing channel that can be allocated to a new user terminal on the transmission side due to the restriction of the FPGA processing unit 130. For this reason, the existing 3 user terminals using other spatial multiplexing channels are time-shared with the downlink side on the spatial multiplexing channels (that is, multiplexing numbers). The scheduling is performed by the control unit (scheduler) 110. Unlike normal traffic, a response to a communication start request is completed in one frame or several frames. Therefore, even if scheduling is performed, only a few frames of the spatial multiplexing channel of the transmission system are added to the new user terminal (SP4). You can lend to. Thus, in the case of multi-carrier, it is possible to assign a channel of only uplink to a certain user as a communication channel, and the downlink side can use other multiplexed channels in time sharing with other users. Therefore, it is possible to increase the communication channel and improve the capacity for accommodating users by utilizing the current hardware configuration.

  Before specifically describing the configuration of the present invention, FIG. 19 shows a conventional network configuration diagram, and the shortcomings of the prior art will be described again. As shown in the figure, the base station apparatus BS has already assigned sessions to the existing user terminals MS1-MS3 by assigning spatial multiplexing channels SP1-SP3. The new user terminal MS4 cannot start communication unless it tries again and again until a carrier frequency having a vacant space that has not reached the maximum spatial multiplexing number is found. On the other hand, FIG. 2 shows a network configuration diagram according to an embodiment of the present invention. As shown in the figure, the base station apparatus BS has already assigned a session to the existing user terminals MS1-MS3 by assigning spatial multiplexing channels SP1-SP3. In this configuration, even after reaching the maximum spatial multiplexing number 3, the base station apparatus BS waits for the RACH signal including the communication start request, and the new user terminal MS4 is immediately uplinked. The spatial multiplexing channel SP4 on the side is assigned, and communication can be started immediately after a predetermined process. Therefore, the user terminal does not have to retry many times by shifting the carrier frequency.

  In the case of a multicarrier base station, it is also possible to perform 4 multiplexing for a certain carrier and share only 3 transmissions by scheduling processing. In this way, even with the current hardware configuration, it is possible to realize a radio communication system control method with improved frequency utilization efficiency, and shorten the waiting time even when the terminal side transmits a communication start request. Becomes possible, and the frequency can be used more efficiently.

  The present invention is used as a means for receiving a RACH signal that could not be received in the past when the spatial multiplexing of three users that could communicate in the conventional method is used. In this case, for example, the base station apparatus BS that has received the RACH signal stops transmission processing of the signal with the lowest priority among SP1 to SP3 and performs transmission processing for the spatial multiplexing channel SP4. This priority order is comprehensively determined by looking at QoS and retransmission status. For example, if there is a user who has a low QoS and has not repeated retransmission, transmission is stopped and a signal for a new user terminal (SP4) is transmitted. Thus, frequency allocation is performed quickly, and even in an environment where only three multiplexed signals can be transmitted, the RACH signal can be received, so that unnecessary retransmission of the RACH signal is not required. The spatial multiplexing channel with the lowest priority is given a certain frame to the RACH. However, if the normal operation is resumed immediately after the transmission is completed, there is not much influence.

  FIG. 3 is a flowchart of user terminal acceptance processing when the maximum spatial multiplexing number is exceeded according to an embodiment of the present invention. Here, the maximum spatial multiplexing number is set to 3. As shown in the figure, it is determined whether or not the number of spatially multiplexed (SP) users is 3 in step S10, and the conventional operation is performed before the maximum (step S11). When the number of spatial multiplexing (SP) users is 3 (the maximum number of spatial multiplexing has been reached), the start request for the fourth user is started waiting on the random access channel (communication allocation request channel) RACH (step S12). ). In step S13, the RACH signal of the fourth user is received, and the spatial multiplexing channel SP4 is assigned to the terminal of the fourth user only on the uplink side. Next, in step S14, one spatial multiplexing channel to be used for the response of the RACH signal or the like is selected based on the priorities of the user terminals using the spatial multiplexing channels SP1 to SP3, and the fourth user is selected. Temporarily assign to the terminal for downlink. In step S15, the weight of the spatial multiplexing channel SP4 and the SP4 signal are transmitted using the temporarily assigned downlink spatial multiplexing channel SP. After the transmission of the RACH signal in step S15 is finished and the predetermined post-processing for the terminal of the fourth user (shift to another carrier, etc. will be described in detail later) is completed in step S16. The transmission of the SP3 multiplexed signal is started.

  FIG. 4 is a flowchart showing post-processing for a user terminal that has accepted beyond the maximum spatial multiplexing. As shown in the figure, in step S20, a new carrier frequency in which the spatial multiplexing channel SP1-3 is to be given to this new user terminal to the user terminal assigned the spatial multiplexing channel SP4 only on the uplink side. And assigns a free channel to the new user and informs the new user terminal of this (step S21). Next, proceeding to step S22, the base station starts communication with the new user terminal using the notified "new carrier frequency and spatial multiplexing channel". Accordingly, at the original carrier frequency, the spatial multiplexing channel SP4 on the uplink side is released, and the RACH signal waiting for the fourth user is resumed (step S23).

  Next, as Example 1, a detailed configuration and principle when the present invention is applied to a more specific wireless communication system will be described. As an example of a wireless communication system to which the present invention is applied, consider a system as shown in FIG. The base station 200 has an antenna array composed of six antenna elements, and establishes a digital radio path with the radio terminal 300. As a channel model, it is assumed that a large number of scatterers are distributed between the base station 200 and the radio terminal 300 and a frequency non-selective multiple propagation path is formed. Since the wireless terminal 300 can move by carrying, the multiple propagation paths between the wireless terminal 300 and the base station 200 have different Doppler frequencies.

  FIG. 6 is a block diagram illustrating a radio unit configuration of the base station 200 according to the first embodiment. As shown in the figure, the base station 200 includes a timing processor (scheduler) 210, an RF array 220RF, a control unit CON, a spatial multiplexing operation unit for SP1 (SP1_TX-FPGA) 220SP1, and a spatial multiplexing operation unit for SP2 (SP2_TX-FPGA). 220SP2, RXANTENNA-DSP interface bus B1, DSP-TXFPGA interface bus B2, and adaptive array antenna AA. The RF array 220RF includes an RF unit RF1-6 for each antenna, an analog / digital converter ADC1-6, and a digital / analog converter DAC1-6. The control unit CON includes a DSP 230 and an upper layer UL. The upper layer UL has an ARQ (Automatic Repeat reQuest) processing unit AR.

  The timing processor 210 generates the frame timing shown in the TDMA-TDD frame configuration example, the transmission timing shown in the downlink signal format, and the uplink reception timing. All of the six antennas ANT1-6 constituting the adaptive array antenna AA are used for both transmission and reception. Of course, since the TDMA-TDD method is used, transmission and reception are not performed simultaneously. At the timing of uplink reception, the base station detects and modulates the reception signal at the antenna end by the RF array 220RF and amplifies it as a reception IF (intermediate frequency) signal. The amplified IF signal is sampled by the AD converter ADC 1-6 and converted into a digital signal. Received signals from the six antennas are passed to the DSP 230 (digital signal processor) in the control unit CON via the RF array 220RF.

  Base station 200 calculates antenna weights (weights) for each wireless terminal from six systems of IF signals obtained by uplink reception, and uses them as antenna weights for the next transmission. The antenna weight is calculated by the DSP 230, and in the above case, each antenna of the spatial multiplexing operation unit for SP1 (SP1-TX-FPGA) 220SP1 and the spatial multiplexing operation unit for SP2 (SP2-TX-FPGA) 220SP2 which are two-space multiplexed. Is set in the wait register WR. The SP1 spatial multiplexing arithmetic unit 220SP1 and the SP2 spatial multiplexing arithmetic unit 220SP2 derive transmission IF signals for each of the six antennas from the antenna weight for each wireless terminal and the transmission signal for each wireless terminal. The IF signal for each antenna is amplified by the RF array 220RF and emitted from the antenna end.

  The SP1 spatial multiplexing operation unit 220SP1 includes a TX signal generator SG and a wait register WR. The TX signal generator SG and the wait register WR receive the SP1 transmission signal and the calculated / determined weight from the DSP 230 via the DSP-TXFPGA interface bus B2. The SP1 spatial multiplexing operation section 220SP1 includes antenna weight control sections (SP1_Ant1-6) W1-6 for the respective SP1 antennas, and each of the antenna weight control sections W1-6 is a weight stored in the weight register WR. Based on the above, the antenna weight for each antenna is calculated. Then, the transmission data generated based on the signal for transmission by the TX signal generator SG is multiplied by the antenna weight for each antenna calculated by the antenna weight control unit W1-6 using a multiplier, and Create transmission data. The transmission data for each antenna created by the two SP1,2-TX-FPGAs are added by an adder and combined with the transmission data for each antenna. The transmission data for each antenna created in this way is AD-converted, then modulated by the RF unit RF1-6, and passed to each mixer (not shown).

  Next, the configuration of the DSP 230 will be described in detail. Prior to the description of the DSP according to the present invention, a DSP having a conventional configuration will be described in order to help understanding of the present invention. FIG. 7 is a block diagram showing the internal configuration of a DSP according to the prior art. As shown in the figure, the DSP 230 is connected to the RF array 220RF, the SP1 spatial multiplexing unit 220SP1, and the SP2 spatial multiplexing unit 220SP2 via the DSP-TXFPGA interface bus B2 and the RXANTENNA-DSP interface bus B1. . When receiving a traffic channel, a desired wave and an interference wave are superimposed and received on each antenna element. The superimposed signal is passed from the RF array 220RF to the DSP 230 as a reception IF signal from the six antennas.

  The DSP 230 applies the received IF signal to the matched filter MF1-6 and passes it to the Rzz diagonal term calculation processing unit RZ. The Rzz diagonal term calculation processing unit RZ prepares for calculating the correlation with the known training by calculating the covariance matrix for each of the six received signals. The users 1 and 2 training sequence generators TS1 and TS2 generate the same signal as the signal that the wireless terminal gives as an uplink training sequence. This is prepared for each of the multiple radio terminals. The user 1 and 2 weight calculation units WC1 and WC2 derive the optimum antenna weight by examining the correlation between the Rzz diagonal term and the known training sequence signal. The received antenna weight and the six received IF signals are separated as received IF signals for each traffic channel of each wireless terminal. The reception IF signal for each traffic channel of each wireless terminal is processed by the users 1 and 2 reception baseband processing units RxB1 and RxB2, and transferred to the upper layer UL as user data. The upper layer UL includes a user 1 upper layer UP1 and a user 2 upper layer UP2. At the time of transmission of the traffic channel, the optimum antenna weight derived at the time of reception is set in the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2 (SP1 and SP2-TX FPGA) and each wireless terminal from the upper layer UL User data for each traffic channel is converted into IF signals by the users 1 and 2 transmission baseband processing units TxB1 and TxB2, and transferred to the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2. In the conventional configuration shown in this figure, both the reception multiplex number and the transmission multiplex number are 2, which coincides with the transmission multiplex number supported by the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2.

  FIG. 8 is a block diagram showing the internal configuration of the DSP 230 according to the first embodiment of the present invention. As shown in the figure, in the DSP configuration according to the present invention, the reception multiplexing number is larger than the transmission multiplexing number supported by the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2 (SP1,2-TX FPGA). Accordingly, the number of processes necessary for demultiplexing at the time of reception by the base station 200 has increased from two to three. Regarding transmission from the base station 200, the number of baseband processing units is increased to three for both reception and transmission. That is, the DSP 230 further includes a user 3 reception baseband processing unit RxB3 and a user 3 transmission baseband processing unit TxB3. The antenna weight for transmission is not directly set in the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2, but is passed to the scheduler 240, and from the scheduler 240 to the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2. The configuration will be changed.

  When receiving a traffic channel (signal), a desired wave and an interference wave are superimposed on each antenna element and received. The number of traffic channels that can be supported is 2 to 3, and uplink signals from three different wireless terminals are superimposed. The superimposed signal is passed from the RF array 220RF to the DSP 230 as a reception IF signal from the six antennas. The DSP 230 applies the received IF signal to the matched filter MF1-6 and passes it to the Rzz diagonal term calculation processing unit RZ. The Rzz diagonal term calculation processing unit RZ prepares for calculating the correlation with the known training by calculating the covariance matrix for each of the six received signals. The users 1 to 3 training sequence generators TS1 to TS3 generate the same signals as the signals given by the wireless terminals as uplink training sequences. This is prepared for each of the multiple radio terminals. The user 1 to 3 weight calculators WC1 to WC3 derive the optimum antenna weight by examining the correlation between the Rzz diagonal term and the known training sequence signal. The received antenna weight and the six received IF signals are separated as received IF signals for each traffic channel of each wireless terminal. The reception IF signal for each traffic channel of each wireless terminal is processed by the users 1 to 3 reception baseband processing units RxB1-3 and transferred as user data to the users 1 to 3 in the upper layer UL to the upper layers UP1-UP3. As described above, the difference between the configuration of the present invention and the conventional configuration in the process at the time of reception in the base station 200 is merely an increase in the number of multiplexing.

  At the time of transmission of the traffic channel (signal), the optimum antenna weight derived at the time of reception is once passed to the scheduler 240. There are also three transmission data from the upper layer UL, which are converted from the user 1 to 3 transmission baseband processing units TxB1-3 into transmission IF signals for each traffic channel of each wireless terminal, and once passed to the scheduler 240. The scheduler 240 associates two SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2 (SP1,2-TX FPGA) with traffic channels of two of the three wireless terminals. The data of the remaining one traffic channel is discarded. The scheduler 240 performs processing for determining traffic channels associated with the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2 so that the downlink throughput of the three traffic channels is flattened. In this way, the scheduler 240 sets the optimum antenna weights derived at the time of reception of the traffic channels corresponding to the two traffic channels at the time of transmission to the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2, and the upper layer UL. The IF signal for each traffic channel of each wireless terminal is transferred to the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2. In the example of this figure, the reception multiplexing number is 3, whereas the transmission multiplexing number is 2. However, an allocation method for dealing with the spatial multiplexing number imbalance between transmission and reception will be described.

<Fair distribution with simple round robin>
FIG. 9 is a transition diagram for each TDMA-TDD frame showing a fair allocation method by round robin. The scheduler 240 associates the SP1 and SP2 spatial multiplexing arithmetic units 220SP1 and SP2 (SP1-TX FPGA and SP2-TX FPGA) with the traffic channel according to the number of traffic channels currently established by the base station 200. Switch methods.

  FIG. 9A is a transition diagram for each TDMA-TDD frame in the case of one traffic channel. As shown in the figure, when there is only one traffic channel established by the base station 200 (traffic channel 1) and communication is performed with one wireless terminal, the traffic channel 1 is Allocate to SP1-TX FPGA.

  FIG. 9B is a transition diagram for each TDMA-TDD frame in the case of two traffic channels. As shown in the figure, when there are two traffic channels (traffic channel 1 and traffic channel 2) established by the base station 200 and communication is performed with two wireless terminals, wireless communication is performed. The traffic channel 1 of the terminal 1 is allocated to the SP1-TX-FPGA, and the traffic channel 2 of the wireless terminal 2 is allocated to the SP2-TX-FPGA.

  FIG. 9C is a transition diagram for each TDMA-TDD frame in the case of three traffic channels. As shown in the figure, there are three traffic channels established by the base station 200 (traffic channel 1, traffic channel 2, and traffic channel 3), and communication is performed with three wireless terminals. In this case, a traffic channel that cannot be assigned to the TX-FPGA is generated in each TDMA-TDD frame. Therefore, the traffic channel is regarded as a rest time and is not assigned to the TX-FPGA. For example, traffic channel 1 of wireless terminal 1 is allocated to SP1-TX-FPGA, and traffic channel 2 of wireless terminal 2 is allocated to SP2-TX-FPGA. All traffic channels are allocated to SP1-TX-FPGA and SP2-TX-FPGA and between rest periods (break time) so that the rest time (break time) for each traffic channel is not biased in each TDMA-TDD frame. Circulate with the Robin method.

  As shown in FIG. 9C, when there are three traffic channels in the base station 200, the throughput in the uplink direction can secure the original traffic channel throughput. The throughput in the downlink direction becomes 2/3 because it experiences a rest time once every three TDMA-TDD frames. Instead, the base station 200 can support three traffic channels even though the TX-FPGA does not support downlink transmission of two traffic channels.

  In this way, when the number of traffic channels is less than the number of downlink transmissions supported by TX-FPGA, the throughput is the same as before, and the number of traffic channels exceeds the number of downlink transmissions supported by TX-FPGA. It can be accommodated. That is, it is possible to increase the number of wireless terminals that can be simultaneously connected to the base station without making a new investment in the hardware of the base station. This makes it possible to reduce the number of base station installations. In addition, since the number of base stations supported exceeds the number of accommodations supported by the base station, it is possible to reduce the busy state experienced by the wireless terminal (a state in which wireless connection with the base station cannot be performed).

  However, when this configuration is applied, if attention is paid to an arbitrary traffic channel, downlink transmission at regular intervals on the TDMA-TDD frame is not performed. That is, when viewed from the wireless terminal 300, downlink signals cannot be detected at regular intervals. This may affect the automatic retransmission control by ARQ. Assume that SR (Select Request) type ARQ is performed in data transmission from the base station 200 to the radio terminal 300. The base station 200 performs transmission by assigning a sequence number j to transmission data in Frame n. It is assumed that the wireless terminal 300 completes decoding and recognizes downlink reception data in Frame n with Frame n + 1. The radio terminal 300 transmits ACK (acknowledgment) of the uplink signal to which the latest sequence number received without missing at the time of Frame n + 2 is added in Frame n + 2.

  The base station 200 should recognize the uplink signal in Frame n + 2 as Frame n + 3 and retransmit the data in Frame n depending on whether or not the sequence number for the data transmitted in Frame n is included in the ACK. It is determined whether or not. If the sequence number assigned to the data transmitted in Frame n is newer than the sequence number included in the ACK, the data transmitted in Frame n is retransmitted in Frame n + 3. Alternatively, when the sequence number assigned to the data transmitted in Frame n matches the sequence number included in the ACK, new data is transmitted.

  In the above-described ARQ, the time from when data is transmitted until retransmission is determined and transmitted is determined by the round trip time, and the base station 200 transmits data and the frame recognized by the radio terminal 300 is 2 The frame that the base station recognizes when the wireless terminal 300 transmits ACK is set to 1. Therefore, the round trip time is 3 frames and the retransmission cycle is 3. In this example, since a rest time is experienced once every three frames, the retransmission cycle and the rest time cycle coincide with each other, which causes a problem that retransmission failure of a specific packet continues.

  FIG. 10 shows an example of a sequence when a problem occurs. As shown in the figure, in this sequence, the data of sequence number 2 transmitted by the base station 200 with Frame = n + 2 matches the rest time, and therefore the data of sequence number 2 is not transmitted to the radio terminal 300. Therefore, the base station 200 receives NAK (negative acknowledgment) including the sequence number 1 with Frame = n + 5. The base station 200 retransmits the data of sequence number 2 with Frame = n + 5, but Frame = n + 5 is also the rest time and is not transmitted to the radio terminal 300. After all, the wireless terminal 300 cannot receive the data of sequence number 2. Therefore, in this sequence, the reception of sequence number 2 fails even if it is retried, and eventually fails. The radio terminal 300 often performs reordering of the received sequence number, but cannot receive the missing sequence number 2 and therefore cannot transfer the received data to the upper layer.

  This problem can be avoided by changing the retransmission control method. FIG. 11 shows a sequence diagram of a retransmission control technique executed in the base station according to Embodiment 1 of the present invention. As shown in the figure, in this sequence, the base station 200 tries to transmit data of sequence number 2 with Frame = n + 2 to the wireless terminal, but cannot transmit because of the rest time. However, since the base station 200 knows from the scheduler (shown in FIG. 12) that Frame = n + 2 is the rest time, it retransmits at the next Frame, Frame = n + 3. Base station 200 recognizes NAK (negative acknowledgment) including sequence number 1 with Frame = n + 5, but the data of sequence number 2 to be retransmitted is retransmitted with Frame = n + 3, and three frames have passed. Since Frame = n + 5, it tries to transmit data of new sequence number 4. Of course, since Frame = n + 5 is a rest time, the data of sequence number 4 is retransmitted with Frame = n + 6 by the same processing. The base station receives ACK of sequence number 2 retransmitted with Frame = n + 6 and Frame = n + 3. The above-described retransmission control solves the problem in SR-type ARQ (retransmission control).

  FIG. 12 shows a block diagram of the DSP 230 that executes retransmission control. In this figure, it is determined whether or not a frame to be transmitted to the scheduler 240 is a rest period before each user 1 to 3 of the upper layer UL determines data to be transmitted when performing downlink transmission. Are transmitted through the signal lines L1-L3 connecting the users 1 to 3 to the upper layer UP1-3 and the scheduler 240. When it is a rest time, it can be realized by performing control so that data scheduled to be transmitted in the frame is transmitted in the next frame. In this embodiment, the case of the reception spatial multiplexing number 3 and the transmission spatial multiplexing number 2 is described, but as described above, the reception spatial multiplexing number 4 and the transmission spatial multiplexing number 3 device, etc. It can be carried out in the same way.

<Method of changing allocation frequency according to traffic volume>
FIG. 13 shows a block diagram when the frequency of downlink channel allocation is changed according to the traffic volume of each wireless terminal. FIG. 9 illustrates a method for fairly distributing each TX-FPGA (ie, downlink channel) to each traffic channel by simple round robin. However, round robin reassignment has the advantage of being simple and easy to implement, but does not necessarily maximize the throughput of the entire system. It is rare that the amount of downlink data is uniform in all traffic channels, and when attention is paid to a certain time unit, there are cases where a large amount of downlink data traffic occurs or almost zero. To do. For example, in the case of a client / server communication model, a request is sent from a wireless terminal as a client to a base station as a server, and the base station transmits a large amount of data to the wireless terminal in a downlink in response to the request. . After that, the user of the wireless terminal may view a large amount of received data or perform some processing. In such a situation, the wireless terminal does not transmit a request to the base station, and thus the downlink transmission. Is almost zero. In the base station according to the embodiment of the present invention, as shown in Table 1, it is possible to allocate more downlink time (that is, increase channel allocation frequency) to a traffic channel having a downlink with a large amount of traffic. is there. The upper layer in the base station usually has a transmission queue for transmission, and the size of data can be determined by referring to the size of data stored in the transmission queue. Based on the determined data size, it is possible to determine the priority order of allocation by referring to a table such as Table 1 that defines classification according to the degree of transmission amount.

In FIG. 13, the base station includes a transmission priority order determination unit 250, users 1 to 3 upper layers UP 1 to 3.
Each user 1-3 transmission queue determination unit QJ1-3 for determining the size of the downlink data queued in each user 1-3 transmission queue Q1-3 is further provided. In the transmission queue Q1-3, when the transmission queue is full, it can be determined that the downlink traffic is very large, and conversely, if the transmission queue Q1-3 is free, it can be determined that the downlink traffic is small, and the queue is If it is completely empty, it can be determined that the downlink traffic is zero. The size determination results as described above by the users 1 to 3 transmission queue determination units QJ1-3 are collected in the transmission priority determination unit 250, and the respective size determination results are compared. Allocate a lot of downlink time (that is, the number of times) to the traffic channel where data is accumulated, and allocate a small downlink time by increasing the rest time (break time) to the traffic channel where data is not accumulated Is possible. By assigning such downlink times (channels / slots), the assignment becomes very efficient and the throughput of the entire system can be improved.

  By assigning the downlink time again at a predetermined cycle, the throughput of the entire system can be further improved. A traffic channel with a low priority may not have a downlink channel for a long period of time. In such a case, ARQ control in L2 (layer 2) may be hindered. In order to cope with the case where ACK cannot be received over a long period of time, a continuous rest time counter (not shown) for counting the number of consecutive rest periods is provided. By using this counter, when the occurrence of continuous rest more than a certain number of times is detected, control is performed so that the downlink channel is preferentially allocated to the traffic channel (user) where the continuous rest has occurred. A trouble of ARQ control can be avoided.

  FIG. 14 is a flowchart illustrating an example of an allocation process for avoiding trouble of ARQ control. As shown in the figure, in step S30, it is determined whether or not there are three traffic channels. If it exists, it is determined in step S31 whether or not there is a traffic channel for which the continuous rest time counter is 5 times or more. If there is a traffic channel that has become five or more times, the process proceeds to step S32, and the continuous rest time counter of the traffic channel is cleared. Thereafter, in step S33, the traffic channel is assigned to SP1_TX-FPGA, which is one of the two spatial multiplexing units (SP1_TX-FPGA, SP2_TX-FPGA). Next, in step S34, the data retention amounts in the transmission queues of the remaining two traffic channels out of the three traffic channels are compared. Proceeding to step S35, the traffic channel with the larger amount of data in the transmission queue, that is, the one with less vacancy is assigned to the SP2-TX-FPGA, and the remaining one traffic channel is set to the rest time. Next, in step S36, the continuous rest time counter of the traffic channel set as the rest time in step S35 is incremented by one.

  When the determination condition of step S30 is not satisfied (when the traffic channel is 2 or less), the process proceeds to step S37, and normal allocation is performed. That is, one TX-FPGA is assigned to each traffic channel. After executing step S37, the process proceeds to step S36, where the counter is incremented and the process ends. When the determination condition of step S31 is not satisfied (when there is a counter of 5 times or more), the process proceeds to step S38, and the transmission queues of the three traffic channels are compared. Thereafter, in step S39, the traffic channel with the smallest available transmission queue is assigned to the SP1-TX-FPGA. Next, in step S40, the traffic channel with the second smallest available transmission queue is allocated to the SP2-TX-FPGA. The rest of the traffic channels are set as rest time (step S41). After executing step S41, the process proceeds to step S36, where the counter is incremented and the process ends.

<Method of changing allocation frequency according to transmission type>
In the foregoing, several allocation techniques that optimize system throughput have been described. Some of the above-described methods merely determine control from the viewpoint of maximizing performance as a data transmission path. However, the present invention can also be configured to determine the allocation time allocation of the downlink of each traffic according to the use for each traffic (user / channel / slot). For example, a lot of downlink time is allocated to a traffic channel that requires a high QoS such as VoIP (Voice Over IP) or a high QoS value is set. Control is performed to allocate a small downlink time to a traffic channel in which a certain or low QoS value is set.

  The usage of the downlink of the traffic channel in the base station can be confirmed by examining the type / type of the packet flowing in the upper layer. Many communication technologies for transmitting data from the transmitter side to the receiver side have been proposed, but recently, IP (Internet Protocol: RFC_791_IETF) has been proposed for reasons such as packet orientation and freedom of destination. A method based is preferred. When the purpose of transmission is the purpose of transmitting media packets such as voice and moving images, UDP (User Datagram protocol: RFC_768_IETF) is preferably used with IP packets as lower layers. RTP carries voice codec data stored in the payload, and examples of the voice codec include G729A. The header information of each protocol can be referred to in the middle of the route, and the usage of the traffic channel can be determined / estimated by looking at the header information of the packet flowing in the downlink. For example, by providing a transmission type inspection unit for each traffic channel (that is, for each user) in the base station, it is possible to determine / estimate the usage of the traffic channel.

  FIG. 15 shows a block diagram when the frequency of downlink channel allocation is changed according to the transmission type. As shown in the figure, the users 1 to 3 transmission type inspection units TC1-3 monitor the header of the packet flowing in the downlink direction, and calculate the frequency (ratio) of the G729A / RTP / UDP / IP packet. The traffic channel determination unit 260 receives the frequency information of various packets acquired by the users 1 to 3 transmission type inspection units TC1-3, and based on the frequency information for each user (traffic channel), the downlink time of each traffic channel (Number of times) Allocation priority is determined. As an example of a priority determination method, the higher the frequency (ratio) of G729A / RTP / UDP / IP packets, the higher the priority of the traffic, and conversely the frequency (ratio) of G729A / RTP / UDP / IP packets. There is a method of lowering the priority as there are fewer. For example, based on the frequency (ratio) of G729A / RTP / UDP / IP packets, the priority order is determined with reference to a table such as Table 2.

  A traffic channel set with a low priority may not be assigned a downlink channel for a long time. In such a case, although ARQ control in L2 (layer 2) may be hindered, a continuous rest time counter (not shown) is provided as described above. By using this counter and controlling to preferentially allocate a downlink channel when occurrence of continuous rest more than a certain number of times is detected, the above-described trouble of ARQ control can be avoided.

  FIG. 16 is a flowchart illustrating an example of an allocation process that avoids the trouble of ARQ control in the allocation process based on the transmission type. As shown in the figure, in step S50, it is determined whether or not there are three traffic channels. If it exists, in step S51, it is determined whether or not there is a traffic channel whose continuous rest time counter is 5 or more. If there is a traffic channel that has become five or more times, the process proceeds to step S52, and the continuous rest time counter of the traffic channel is cleared. Thereafter, in step S53, the traffic channel is allocated to SP1_TX-FPGA, which is one of the two spatial multiplexing units (SP1_TX-FPGA, SP2_TX-FPGA). Next, in step S54, the frequency (ratio) of G729A / RTP / UDP / IP packets of the remaining two traffic channels out of the three traffic channels is compared. Proceeding to step S55, the traffic channel with the higher G729A packet frequency, that is, the higher QoS (communication priority) to be set is assigned to the SP2-TX-FPGA, and the remaining one traffic channel is set as the rest time. Set. Next, in step S56, the continuous rest time counter of the traffic channel set as the rest time in step S55 is incremented by one.

  When the determination condition of step S50 is not satisfied (when the traffic channel is 2 or less), the process proceeds to step S57, and normal allocation is performed. That is, one TX-FPGA is assigned to each traffic channel. After executing step S57, the process is terminated. When the determination condition of step S51 is not satisfied (when there is a counter of 5 times or more), the process proceeds to step S58, and the frequencies (ratio) of G729A / RTP / UDP / IP packets of the three traffic channels are compared. Thereafter, in step S59, the traffic channel with the highest frequency of G729A packets is assigned to the SP1-TX-FPGA. Next, in step S60, the traffic channel with the second highest frequency of G729A packets is assigned to the SP2-TX-FPGA. The remaining traffic channels are set as rest periods (step S51). After executing step S51, the process proceeds to step S56, where the counter is incremented and the process ends.

<Method of changing the allocation frequency according to QoS>
A traffic channel with a high downlink (time / slot) allocation frequency will have a higher value than a traffic channel with a low downlink allocation frequency (ie, a long rest period). For this reason, the downlink allocation frequency is increased for users set with a high charge (rank), and conversely, the downlink allocation frequency is decreased for users set with a low charge (ie, rest time). It is also possible to perform such control as to make the The user registration information (rank information / billing information) is stored in, for example, an external RADIUS (Remote Authentication Dial In User Service), and the QoS registration information of RADIUS is acquired when PPP is established. The priority of each traffic channel (each user) is determined according to the registration information. For example, the priority order is determined with reference to a table such as Table 3 based on the QoS registration information.

  FIG. 17 shows a block diagram when the frequency of downlink channel allocation is changed according to the user registration information. As shown in the figure, the traffic channel determination unit 260 receives registration information from each user upper layer (RADIUS client) UP1-R, UP2-R, UP3-R storing registration information of each user, and receives these users. (Traffic channel) registration information is compared, and the priority of downlink time allocation is determined based on the comparison result. The priority determined by the traffic channel determination unit 260 is passed to the scheduler 240, and the scheduler 240 allocates a downlink time to each traffic channel according to the priority.

  A traffic channel set with a low priority may not be assigned a downlink channel for a long time. In such a case, although ARQ control in L2 (layer 2) may be hindered, as described above, a continuous rest time counter (not shown) is provided. By using this counter and controlling to preferentially allocate a downlink channel when occurrence of continuous rest more than a certain number of times is detected, the above-described trouble of ARQ control can be avoided.

  FIG. 18 is a flowchart illustrating an example of an allocation process for avoiding the trouble of ARQ control in the allocation process based on QoS (communication priority). As shown in the figure, in step S70, it is determined whether or not there are three traffic channels. If it exists, it is determined in step S71 whether or not there is a traffic channel whose continuous rest time counter is 5 or more. If there is a traffic channel that has been 5 times or more, the process proceeds to step S72, and the continuous rest time counter of the traffic channel is cleared. Thereafter, in step S73, the traffic channel is assigned to SP1_TX-FPGA, which is one of the two spatial multiplexing units (SP1_TX-FPGA, SP2_TX-FPGA). Next, in step S74, QoS (Quality Of Service) registration information of the remaining two traffic channels out of the three traffic channels is compared. Proceeding to step S75, the traffic channel with the higher QoS registration information is assigned to the SP2-TX-FPGA, and the remaining one traffic channel is set to rest time. Next, in step S76, the continuous rest time counter of the traffic channel set as the rest time in step S75 is incremented by one.

  When the determination condition of step S70 is not satisfied (when the traffic channel is 2 or less), the process proceeds to step S77, and normal allocation is performed. That is, one TX-FPGA is assigned to each traffic channel. After executing step S77, the process is terminated. When the determination condition of step S71 is not satisfied (when there is a counter of 5 times or more), the process proceeds to step S78, and the QoS registration information of the three traffic channels is compared. Thereafter, in step S79, the traffic channel with the highest QoS registration information is assigned to the SP1-TX-FPGA. Next, in step S80, the traffic channel with the second highest QoS registration information is assigned to the SP2-TX-FPGA. The remaining traffic channels are set as rest time (step S81). After executing step S81, the process proceeds to step S76, and the counter is incremented to finish the process.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each unit, each means, each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, steps, etc. can be combined or divided into one. It is.

It is a block diagram of the base station apparatus by one embodiment of this invention. It is a network block diagram by one embodiment of this invention. It is a flowchart of a user terminal acceptance process when the maximum spatial multiplexing number is exceeded by the embodiment of this invention. It is a flowchart which shows the post-process with respect to the user terminal received exceeding the maximum spatial multiplexing. It is a network block diagram which shows an example of the radio | wireless communications system to which this invention is applied. FIG. 3 is a block diagram illustrating a configuration of a radio unit of a base station 200 according to the first embodiment. It is a block diagram which shows the internal structure of DSP by a prior art. It is a block diagram which shows the internal structure of DSP230 by Example 1 of this invention. It is a transition diagram for every TDMA-TDD frame which shows the fair allocation method by a round robin. It is a figure which shows an example of the sequence when a problem generate | occur | produces. It is a sequence diagram of the retransmission control method performed in the base station according to the first embodiment of the present invention. It is a block diagram of DSP230 which performs resending control. It is a block diagram in the case of changing the allocation frequency of a downlink channel according to the traffic amount of each radio | wireless terminal. It is a flowchart which shows an example of the allocation process which avoids the trouble of ARQ control. It is a block diagram in the case of changing the allocation frequency of a downlink channel according to a transmission classification. It is a flowchart which shows an example of the allocation process which avoids the trouble of ARQ control in the allocation process based on a transmission classification. The block diagram in the case of changing the allocation frequency of a downlink channel according to user registration information is shown. It is a flowchart which shows an example of the allocation process which avoids the trouble of ARQ control in the allocation process based on QoS. It is a conventional network block diagram.

Explanation of symbols

100 Base station apparatus 110 Control unit 120 DSP
120RC reception processing unit 120TR transmission processing unit PR reception preprocessing unit 130 FPGA processing unit 200 base station RF array 220RF
RF1-6 RF
210 Timing processor (scheduler)
CON control unit 220SP1 SP1 spatial multiplexing unit (SP1_TX-FPGA)
220SP2 SP2 spatial multiplexing unit (SP2_TX-FPGA)
230 DSP
B1 RXANTENNA-DSP interface bus B2 DSP-TXFPGA interface bus ADC1-6 Analog to digital converter DAC1-6 Digital to analog converter UL Upper layer UP1-3 User 1 to upper layer A ARQ processing unit AA, AAA Adaptive array antenna ANT1-6 Antenna CM, CM1 coupling unit DV1-DV3 separation unit BS base station apparatus MS1-MS4 user terminal RF, RF1 radio communication unit RxB1-3 user 1-3 reception baseband processing unit TxB1-3 user 1-3 transmission baseband processing unit RZ Rzz diagonal term calculation processing unit SG Signal generators TS1, TS2, TS3 Training sequence generation unit W1-6 Antenna weight control unit WC1-3 User 1 to 3 weight calculation unit WR Wait register 240 Scheduler BF1-3 User 1 3 reception buffer Q1-3 user 1-3 transmission queue QJ1-3 user 1-3 transmission queue determination unit TC1-3 user 1-3 transmission type inspection unit UP1-R, UP2-R, UP3-R user 1-3 Tier (RADIUS client)
250 Transmission priority order determination unit 260 Traffic channel determination unit 300 Wireless terminal

Claims (5)

A control method of a base station that performs radio communication simultaneously with a plurality of user terminals assigned with a plurality of spatial multiplexing channels spatially multiplexed in the same frequency band,
A transmission processing step for performing transmission processing for the plurality of user terminals;
A reception processing step of performing reception processing from the plurality of user terminals;
When a communication start request is received from a new user terminal when the predetermined maximum spatial multiplexing number has been reached, a new spatial multiplexing channel is allocated to the new user terminal only on the uplink side, and the allocated A reception control step for controlling to perform reception processing using the spatial multiplexing channel,
When transmitting data on the downlink side to the new user terminal, the downlink spatial multiplexing channel already assigned to the other user terminal is transferred to the other user terminal and the new user terminal. On the other hand, a transmission control step for performing reallocation in a predetermined order and controlling to perform transmission processing based on the reallocation,
A control method for a base station. The base station control method according to claim 1,
The predetermined order in the transmission control step is determined by a round robin method.
A control method for a base station. The base station control method according to claim 1,
As the predetermined order in the transmission control step increases based on the data amounts to be transmitted to the new user terminal and the other user terminals, the allocation frequency increases as the data amount to be transmitted at each user terminal increases. Is determined to be high,
A control method for a base station. The base station control method according to claim 1,
The predetermined order in the transmission control step is determined based on communication priorities in the new user terminal and the other user terminals such that the higher the communication priority of each user terminal is, the higher the allocation frequency is. ,
A control method for a base station. A base station that performs radio communication simultaneously with a plurality of user terminals assigned a plurality of spatial multiplexing channels spatially multiplexed in the same frequency band,
A transmission processing unit that performs transmission processing on the plurality of user terminals;
A reception processing unit that performs reception processing from the plurality of user terminals;
When a communication start request is received from a new user terminal when the predetermined maximum spatial multiplexing number has been reached, a new spatial multiplexing channel is allocated to the new user terminal only on the uplink side, and the allocated A control unit that controls to perform reception processing using a spatial multiplexing channel,
The control unit is
When transmitting data on the downlink side to the new user terminal, the downlink spatial multiplexing channel already assigned to the other user terminal is transferred to the other user terminal and the new user terminal. In contrast, reallocation is performed in a predetermined order, and control is performed to perform transmission processing based on the reallocation.
A base station characterized by that.

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