JP5958592B2 - Mobile station and base station - Google Patents

Description

  The present invention relates to a mobile station and a base station.

  Currently, 3GPP (Third Generation Partnership Project) is standardizing a 4G wireless communication system. In 4G, technologies such as relay, carrier aggregation, CoMP (Coordinated Multiple Point transmission and reception), and MU-MIMO (Multi User Multi Input Multi Output) are attracting attention.

  Relays are considered an important technique for improving cell edge throughput. Carrier aggregation is a technique that can handle a bandwidth of 20 MHz × 5 = 100 MHz by handling, for example, five frequency bands having a bandwidth of 20 MHz. This carrier aggregation is expected to improve the maximum throughput.

  CoMP is a technique in which a plurality of base stations cooperate to transmit and receive data in order to improve high data rate coverage. Furthermore, MU-MIMO is a technique for improving system throughput by using a plurality of users using spatially multiplexed resource blocks of the same frequency and the same time. As described above, in 4G (LTE-Advanced), it is discussed to further improve the performance with various technologies.

  Here, MU-MIMO will be described in more detail. In 3.9G (LTE), MU-MIMO and SU-MIMO (Single User MIMO) exist. SU-MIMO is a technique in which, as described in Patent Document 1, for example, UEs (User Equipment) do not spatially multiplex, but one UE uses a plurality of channels by spatial multiplexing.

  On the other hand, MU-MIMO is a technique in which each UE uses resource blocks of the same frequency and the same time in a spatially multiplexed manner (UEs are spatially multiplexed). However, in MU-MIMO realized by 3.9G, each UE can handle only one channel. On the other hand, 4G intends to realize MU-MIMO that allows each UE to handle a plurality of channels.

  In order to realize such MU-MIMO with 4G, it is considered that the base station uses two types of transmission weights (V1 and V2). V1 is a transmission weight for realizing directivity, and V2 is a non-directional transmission weight whose main purpose is to adjust the phase. These V1 and V2 can be determined in the UE, for example. More specifically, the UE receives the reference signal transmitted from the base station, acquires the channel matrix H from the reception result of the reference signal, and determines the optimum V1 and V2 for the channel matrix H.

JP 2005-184730 A

  As described above, in a system in which MU-MIMO and SU-MIMO are mixed, it is desired to realize switching between MU-MIMO and SU-MIMO.

  In order to solve the above-described problem, according to an aspect of the present invention, in a communication mode of either MU-MIMO (Multi User-Multiple Input Multiple Output) mode or SU-MIMO (Single User-Multiple Input Multiple Output) mode. A communication unit that communicates, and a resource allocation unit that allocates a first resource for the MU-MIMO mode and a second resource for the SU-MIMO mode, and the first resource and the second resource A base station is provided that notifies the mobile station of information for identifying the resource.

  The first resource and the second resource may be in a predetermined frequency range.

  The first resource and the second resource may be predetermined resource blocks.

  The MU-MIMO mode and the SU-MIMO mode may be dynamically switched.

  The information may be transmitted via RRC signaling.

  The information may be received via system information.

  In the first resource, first reference information for the MU-MIMO mode is transmitted, and in the second resource, second reference information for the SU-MIMO mode is transmitted. Also good.

  The second resource may be allocated more than the first resource.

  The number of streams that the communication unit transmits to one mobile station may be different between the MU-MIMO mode and the SU-MIMO mode.

  The number of streams transmitted to one mobile station in the SU-MIMO mode may be four times the number of streams transmitted to one mobile station in the MU-MIMO mode.

  In order to solve the above problem, according to another aspect of the present invention, either MU-MIMO (Multi User-Multiple Input Multiple Output) mode or SU-MIMO (Single User-Multiple Input Multiple Output) is used. Receiving information for identifying a communication unit that communicates in a communication mode, a first resource for the MU-MIMO mode allocated by a base station, and a second resource for the SU-MIMO mode; A mobile station is provided.

  As described above, according to the present invention, switching between MU-MIMO and SU-MIMO can be realized.

It is explanatory drawing which showed the structure of the radio | wireless communications system by embodiment of this invention. It is explanatory drawing which showed an example of the multiplication order of the weight for transmission. It is explanatory drawing which showed the relationship between V1 and V2. It is explanatory drawing which showed the determination method by the comparative example of transmission weight V1 and V2_MU. It is explanatory drawing which showed the determination method by the comparative example of the weight for transmission in case MU-MIMO and SU-MIMO coexist. It is explanatory drawing which showed the structure of the base station by embodiment of this invention. It is explanatory drawing which showed the structure of the weight multiplication part. It is explanatory drawing which showed the structure of the weight multiplication part by a modification. It is explanatory drawing which showed the structure of the mobile station by this embodiment. It is explanatory drawing which showed the 1st Embodiment of this invention. It is explanatory drawing which showed the 2nd Embodiment of this invention. It is explanatory drawing which showed the 3rd Embodiment of this invention. It is explanatory drawing which showed the example of resource allocation of CSI_RS rather than V1 * CSI_RS by 4th Embodiment. It is explanatory drawing which showed the specific example of the resource allocation by 5th Embodiment. It is explanatory drawing which showed the specific example of the resource allocation by 6th Embodiment. It is explanatory drawing which showed the specific example of the resource allocation by 7th Embodiment. 3 is a flowchart illustrating an operation of a base station according to an embodiment of the present invention. 5 is a flowchart illustrating an operation of a mobile station according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In the present specification and drawings, a plurality of components having substantially the same functional configuration may be distinguished by adding different alphabets after the same reference numeral.

  For example, a plurality of configurations having substantially the same functional configuration are distinguished as mobile stations 20A, 20B, and 20C as necessary.

  However, when it is not necessary to particularly distinguish each of a plurality of constituent elements having substantially the same functional configuration, only the same reference numerals are given. For example, when it is not necessary to distinguish the mobile stations 20A, 20B, and 20C, they are simply referred to as the mobile station 20.

Further, the “DETAILED DESCRIPTION OF THE INVENTION” will be described according to the following item order.
1. 1. Outline of wireless communication system 1-1. Configuration of wireless communication system 1-2. Transmission weight (V1 and V2)
1-3. Feedback weight feedback system 1-4. Dynamic switching 1-5. Comparative Example 2 2. Basic configuration of base station 3. Basic configuration of mobile station Description of each embodiment 4-1. First embodiment 4-2. Second Embodiment 4-3. Third embodiment 4-4. Fourth embodiment 4-5. Fifth embodiment 4-6. Sixth embodiment 4-7. 7. Seventh embodiment 5. Operation of base station and mobile station Summary

<1. Overview of Wireless Communication System>
Currently, standardization of 4G wireless communication systems is underway in 3GPP. Since the embodiment of the present invention can be applied to this 4G wireless communication system as an example, the outline of the 4G wireless communication system will be described first.

[1-1. Configuration of wireless communication system]
FIG. 1 is an explanatory diagram showing a configuration of a wireless communication system 1 according to an embodiment of the present invention. As shown in FIG. 1, the wireless communication system 1 according to the embodiment of the present invention includes a base station 10 and a plurality of mobile stations 20. The base station 10 may be a wireless communication device such as an eNodeB in 4G, a relay node, or a Home eNodeB that is a small home base station. The mobile station 20 may be a 4G relay node or a radio communication device such as a UE.

  The base station 10 controls communication with the mobile station 20 in the cell. In addition, as shown in FIG. 1, for example, the base station 10 is operated in three sectors so that each sector has an angle of 120 degrees. Furthermore, the base station 10 includes a plurality of antennas, and multiplies transmission signals from the antennas by a transmission weight V1, which will be described later, in a plurality of directions in each sector (four directions in the example shown in FIG. 1). Directivity can be formed.

  For this reason, the base station 10 can spatially separate and multiplex the mobile stations 20A and 20B existing in different directions when viewed from the base station 10. That is, the base station 10 can communicate with a plurality of mobile stations 20 by MU-MIMO. Note that the base station 10 can also communicate with the mobile station 20 by SU-MIMO.

  The mobile station 20 is a wireless communication device that communicates with the base station 10 by MU-MIMO or SU-MIMO. The mobile station 20 moves as the user or a vehicle such as a vehicle moves. In the present embodiment, the mobile station 20 will be described as an example of a wireless communication device that wirelessly communicates with the base station 10, but the present embodiment can also be applied to a wireless communication device that is fixedly installed.

[1-2. Transmission weight (V1 and V2)]
In 4G, in order to realize MU-MIMO, the use of a transmission weight of V2 in addition to V1 described above (double codebook method) is being studied. V1 is a transmission weight that realizes directivity as described above. This V1 has characteristics such as covering a wide frequency range and having a lower update frequency than V2.

  On the other hand, V2 is an omnidirectional transmission weight whose main purpose is to adjust the phase. More specifically, V2 is used to maximize the received power by adjusting the phase of each path between the mobile station 20 and the base station 10 antenna. Further, this V2 has characteristics such as covering a narrow frequency region and having a higher update frequency than V1.

  The base station 10 according to the present embodiment realizes MU-MIMO by multiplying the transmission data by the transmission weights V1 and V2. The base station 10 may multiply the transmission data by transmission weights in the order of V2 and V1 as shown in FIG. 2, or may multiply the transmission data by transmission weights in the order of V1 and V2. .

  FIG. 3 is an explanatory diagram showing the relationship between V1 and V2. As shown in FIG. 3, when the base station 10 has eight antennas, these antennas operate as linear array antennas 4A and 4B composed of two sets of four elements. Each linear array antenna 4A and 4B operates as an array antenna having the same directivity as shown in FIG.

  V2 acts to distribute two codewords of transmission data to two sets of linear array antennas 4A and 4B while changing the phase. That is, V2 acts to change the phase of the transmission signal supplied to the linear array antennas 4A and 4B that transmit in the same direction. On the other hand, V1 is applied to each antenna as shown in FIG. 3, and the linear array antennas 4A and 4B act so as to form directivity.

  Below, the specific example of V1 and V2 mentioned above is shown. In Equation 1 indicating V1, d indicates the distance from the reference antenna, λ indicates the wavelength, θ indicates the beam direction, and i indicates the antenna number. Further, H in Formula 2 representing V2 represents a channel matrix.

  As shown in Equation 2, V2 is a transmission weight represented by plus / minus 1 or plus / minus j. J represents an imaginary number. Therefore, the load for multiplying a specific matrix by V2 is small. On the other hand, since V1 is a transmission weight described by a directional vector, it is not a matrix represented by plus / minus 1 or plus / minus j. For this reason, the calculation load increases in the calculation using V1.

  If the transmission data of the base station 10 is S and the reception data of the mobile station 20 is R, the reception data R of the mobile station 20 is expressed as the following Equation 3 or Equation 4.

[1-3. Feedback weight feedback method]
As a MIMO feedback method for determining the transmission weights V1 and V2, there are three possible methods: Implicit Feedback, Explicit Feedback, and SRS-based Feedback. In 4G, it is decided to use Implicit Feedback as a MIMO feedback method for determining the transmission weights V1 and V2 because the load on the feedback line is small. Hereinafter, for reference, each feedback method in 3.9G (LTE) will be described.

(1) Implicit Feedback
The base station prepares 16 types of transmission weights (V1) to (V16) (pre coding) in a pre-designed bookbook. The mobile station that has received the reference signal from the base station acquires a channel matrix H between the base station and the mobile station. Then, the mobile station tentatively determines which of the HV (1), HV (2),..., HV (16) has the highest received power. Thereafter, the mobile station feeds back an index number indicating V that maximizes received power to the base station. The base station transmits data using V corresponding to the fed back index.

(2) Exclusive Feedback
The mobile station that has transmitted the reference signal from the base station and has received the reference signal from the base station acquires the channel matrix H between the base station and the mobile station, as in the case of Implicit Feedback. Then, the mobile station feeds back the channel matrix H to the base station as it is. The base station calculates and creates a desired transmission weight from the downlink channel matrix H fed back from the mobile station. Then, the base station transmits data using the created transmission weight. In this explicit feedback, since the channel matrix H is transmitted as it is at the time of feedback, there is a problem that the resources consumed for feedback are larger than the implicit feedback.

(3) SRS-based Feedback
The base station that has transmitted the reference signal from the mobile station and has received the reference signal from the mobile station acquires an uplink channel matrix between the mobile station and the base station. When channel reversibility is established (in the case of TDD mode), the base station can create a virtual downlink channel matrix from this channel matrix. A method for creating a virtual downlink channel matrix in this way is SRS-based Feedback. In this SRS-based Feedback, the reversibility of the uplink and downlink channels (channel matrix including the characteristics of the analog circuit) is required unless calibration is performed to correct variations in the analog circuit of the base station. There is a problem that does not hold.

[1-4. Dynamic switching]
In 4G (LTE-Advanced), it is considered to dynamically switch the MIMO setting between MU-MIMO and SU-MIMO. In 4G MU-MIMO, the use of 8 streams has been studied. In the case of 8 streams, one matrix for phase adjustment like V2 described in “1-2. Transmission weights (V1 and V2)” is used.

  In the above, the example which implement | achieves MU-MIMO combining V1 which is a 4x4 matrix and V2 which is a 2x2 matrix was demonstrated. On the other hand, for SU-MIMO, only V2 which is an 8 × 8 matrix is used. Each element of 8 × 8 V2 is represented by plus / minus 1 and plus / minus j, similarly to 2 × 2 V2. J represents an imaginary number.

  Thus, since V2 different between MU-MIMO and SU-MIMO is used, in this specification, V2 for MU-MIMO is referred to as V2_MU, and a weight for SU-MIMO is referred to as V2_SU. Are distinguished from each other.

[1-5. Comparative example]
In 4G and this embodiment, as described in “1-3. Feedback Weight Feedback Method”, the transmission weights V1 and V2_MU are determined by the Implicit Feedback. Here, in order to clarify the technical significance of the present embodiment, a determination method according to a comparative example of the transmission weights V1 and V2_MU will be described with reference to FIG.

  FIG. 4 is an explanatory diagram showing a method of determining transmission weights V1 and V2_MU according to a comparative example. In FIG. 4, the horizontal axis indicates time. The CSI is CSI_RS (Channel State Information Reference Signal).

  As shown in FIG. 4, the base station transmits CSI_RS (step 1), and the mobile station acquires a channel matrix H from CSI_RS received from the base station. Then, the mobile station evaluates which V1 is optimal from the four types of V1 candidates for the acquired channel matrix H. For example, the mobile station selects V1 that maximizes received power from among four types of V1 candidates. Further, the mobile station evaluates and selects an optimal V2_MU. Thereafter, the mobile station feeds back Index_V1 indicating the selected V1 and Index_V2 indicating V2_MU to the base station (step 2). The base station determines V1 and V2_MU based on feedback from the mobile station.

  When V1 and V2_MU are determined, the base station and the mobile station update only V2_MU a plurality of times (step 3), and then update V1 and V2_MU (step 4). Thus, the update frequency of V2_MU is higher than the update frequency of V1.

  Here, the mobile station performs a calculation using a plurality of types of V1 when selecting V1. As described in “1-2. Transmission weights (V1 and V2)”, since the calculation using V1 is heavier than the calculation using V2_MU, the load on the mobile station when selecting V1 is growing.

  On the other hand, when V2 is selected, it seems that the calculation using V1 becomes unnecessary. However, this idea is incorrect, and the mobile station performs an operation using V1 when selecting V2. This is because the mobile station acquires the channel matrix H from the newly received CSI_RS, multiplies the channel matrix H by the determined V1, and evaluates the optimum V2_MU for the channel matrix H multiplied by V1. It is. As described above, in the transmission weight determination method according to the comparative example, since the mobile station needs to perform calculation using V1 in both cases of updating V1 and V2, the calculation amount of the mobile station increases. .

  Next, a determination method according to a comparative example of transmission weights when MU-MIMO and SU-MIMO are mixed will be described with reference to FIG.

  FIG. 5 is an explanatory diagram showing a method for determining a transmission weight according to a comparative example when MU-MIMO and SU-MIMO coexist. As shown in FIG. 5, when MU-MIMO and SU-MIMO are mixed, the base station and the mobile station update V2_SU for all CSI_RSs in addition to V1 and V2_MU. For this reason, the calculation load in the mobile station further increases as V2_SU is updated. However, in order to realize dynamic switching between MU-MIMO and SU-MIMO, it is important that both V2_MU and V2_SU are constantly evaluated.

The transmission weight determination method according to the comparative example described above is summarized as follows.
(1) The calculation load in the mobile station is high Reason: As described with reference to FIG. 4, when V2_MU is evaluated, an operation using the determined V1 is performed.
(2) If dynamic switching between MU-MIMO and SU-MIMO is to be realized, the computational load on the mobile station further increases.
Reason: As described with reference to FIG. 5, both V2_MU and V2_SU are always evaluated.

  Further, when dynamic switching is performed in a communication system using a plurality of subcarriers such as an OFDM modulation scheme, there has been no frequency subcarrier allocation method that can effectively reduce the amount of calculation.

  Then, it came to create embodiment of this invention from the above circumstances. According to each embodiment of the present invention, it is possible to suppress the calculation load in the mobile station 20 for determining the transmission weight. Hereinafter, each embodiment of the present invention will be described in detail.

<2. Basic configuration of base station>
The present invention can be implemented in various forms, as will be described in detail in “4-1. First Embodiment” to “4-7. Seventh Embodiment” as an example. The base station 10 according to each embodiment is
A: a communication unit (antenna 110, analog processing unit 120, etc.) that transmits a reference signal (CSI_RS);
B: a first multiplier (V1 multiplier 154) that multiplies a first transmission weight (V1) determined based on reception of a reference signal by a communication partner (mobile station 20);
C: a second multiplier (V2_MU multiplier 156) for multiplying a second transmission weight (V2_MU) determined based on reception of the reference signal by the communication partner;
Is provided. further,
D: After determining the first transmission weight, the communication unit transmits a weighted reference signal (V1 * CSI_RS) obtained by multiplying the reference signal and the first transmission weight.

  In the following, first, a basic configuration common to such base stations 10 according to the respective embodiments will be described with reference to FIGS.

  FIG. 6 is an explanatory diagram showing the configuration of the base station 10 according to the embodiment of the present invention. As shown in FIG. 6, the base station 10 according to the embodiment of the present invention includes a plurality of antennas 110, a switch SW 116, an analog processing unit 120, an AD / DA conversion unit 124, a demodulation processing unit 128, A layer signal processing unit 132, a scheduler 136, a modulation processing unit 140, and a weight multiplication unit 150 are provided.

  The antennas 110 </ b> A to 110 </ b> N convert a radio signal transmitted from the mobile station 20 into an electrical reception signal and supply it to the analog processing unit 120, and a transmission signal supplied from the analog processing unit 120 as a radio signal It functions as a transmitting unit that converts the data into the mobile station 20 and transmits it to the mobile station 20. Note that the number of antennas 110 is not particularly limited, and may be, for example, eight or sixteen.

  The switch SW 116 is a switch for switching between transmission operation and reception operation by the base station 10. When the antennas 110A to 110N are connected to the transmission circuit of the analog processing unit 120 via the switch SW116, the base station 10 performs a transmission operation, and the antennas 110A to 110N receive the circuit of the analog processing unit 120 via the switch SW116. When connected to the base station 10, the base station 10 performs a receiving operation.

  The analog processing unit 120 includes a transmission circuit that performs analog processing on a transmission signal and a reception circuit that performs analog processing on a reception signal. In the transmission circuit, for example, up-conversion, filtering, gain control, and the like of an analog transmission signal supplied from the AD / DA conversion unit 124 are performed. In the reception circuit, for example, down-conversion and filtering of the reception signal supplied from the antenna 110 via the switch SW116 are performed.

  The AD / DA conversion unit 124 performs AD (Analogue Digital) conversion of the received signal supplied from the analog processing unit 120 and DA (Digital Analogue) conversion of the transmission signal supplied from the weight multiplication unit 150.

  The demodulation processing unit 128 performs demodulation processing on the reception signal supplied from the AD / DA conversion unit 124. The demodulation processing performed by the demodulation processing unit 128 may include OFDM demodulation processing, MIMO demodulation processing, error correction, and the like.

  The upper layer signal processing unit 132 performs processing for inputting / outputting transmission data and reception data to / from the upper layer, control processing for the scheduler 136, the modulation processing unit 140, and the weight multiplication unit 150, and from the mobile station 20. Each transmission weight is determined based on the feedback information.

  Further, as will be described in detail later, the base station 10 according to the present embodiment determines the transmission weight V1 based on feedback information from the mobile station 20, and then adds CSI_RS and V1 to CSI_RS (reference signal). V1 * CSI_RS (weighted reference signal) obtained by multiplication is transmitted. Upper layer signal processing section 132 includes a function as a reference signal management section that manages resources for transmitting CSI_RS and V1 * CSI_RS. Then, upper layer signal processing section 132 controls weight multiplication section 150 so that CSI_RS or V1 * CSI_RS is transmitted in the allocated resource.

  The scheduler 136 allocates resources for data communication to each mobile station 20. The resource allocated by the scheduler 136 is notified to each mobile station 20 through the control channel, and each mobile station 20 performs uplink or downlink data communication using the notified resource.

  The modulation processing unit 140 performs modulation processing such as mapping based on constellation on the transmission data supplied from the upper layer signal processing unit 132. The transmission signal modulated by the modulation processing unit 140 is supplied to the weight multiplication unit 150.

  The weight multiplication unit 150 multiplies the transmission signal supplied from the modulation processing unit 140 by the transmission weights V1 and V2_MU determined by the higher layer signal processing unit 132 when performing MU-MIMO. On the other hand, the weight multiplication unit 150 multiplies the transmission signal supplied from the modulation processing unit 140 by the transmission weight V2_SU determined by the higher layer signal processing unit 132 when performing SU-MIMO. Further, the weight multiplier 150 multiplies CSI_RS by V1 in the resource allocated to transmit V1 * CSI_RS (* is complex multiplication) by the higher layer signal processor 132. Hereinafter, the configuration of the weight multiplication unit 150 will be described in more detail with reference to FIG.

  FIG. 7 is an explanatory diagram showing the configuration of the weight multiplication unit 150. As illustrated in FIG. 7, the weight multiplication unit 150 includes selectors 151, 157, and 158, a V2_SU multiplication unit 152, a V1 multiplication unit 154, and a V2_MU multiplication unit 156.

  The selector 151 supplies the transmission signal supplied from the modulation processing unit 140 to the V2_MU multiplication unit 156 or the V2_SU multiplication unit 152. More specifically, the selector 151 supplies the transmission signal to the V2_MU multiplication unit 156 when the MIMO setting is MU-MIMO, and the transmission signal V2_SU multiplication when the MIMO setting is SU-MIMO. To the unit 152.

  The V2_SU multiplier 152 multiplies the transmission signal supplied from the selector 151 by V2_SU determined by the upper layer signal processor 132.

  On the other hand, the V2_MU multiplier 156 multiplies the transmission signal supplied from the selector 151 by V2_MU determined by the upper layer signal processor 132. Further, the V1 multiplier 154 multiplies the transmission signal multiplied by V2_MU by V1.

  The selector 157 selectively outputs the multiplication result by the V1 multiplication unit 154 or the multiplication result by the V2_SU multiplication unit 152. More specifically, the selector 157 outputs the multiplication result by the V1 multiplier 154 when the MIMO setting is MU-MIMO, and the V2_SU multiplier 152 when the MIMO setting is SU-MIMO. Outputs the multiplication result.

  The selector 158 supplies CSI_RS to the front stage or the rear stage of the V1 multiplier 154. More specifically, the selector 158 supplies CSI_RS to the subsequent stage of the V1 multiplier 154 in the resources allocated for transmission of CSI_RS. In this case, the base station 10 transmits CSI_RS that is not multiplied by V1.

  On the other hand, the selector 158 supplies CSI_RS to the preceding stage of the V1 multiplier 154 in the resources allocated for transmission of V1 * CSI_RS. In this case, since CSI_RS is multiplied by V1 in V1 multiplication section 154, base station 10 transmits V1 * CSI_RS.

  7 illustrates an example in which the V1 multiplication unit 154 is arranged at the subsequent stage of the V2 multiplication unit 156, but the configuration of the weight multiplication unit 150 is not limited to such an example. For example, as will be described below with reference to FIG. 8, the V1 multiplier 154 can be arranged before the V2 multiplier 156.

  FIG. 8 is an explanatory diagram showing a configuration of a weight multiplication unit 150 ′ according to a modification. As shown in FIG. 8, the weight multiplication unit 150 ′ according to the modification includes selectors 151, 155, 157 and 159, a V2_SU multiplication unit 152, a V1 multiplication unit 154, and a V2_MU multiplication unit 156.

  In the weight multiplication unit 150 ′ according to the modification, as illustrated in FIG. 8, the V1 multiplication unit 154 is disposed in front of the V2_MU multiplication unit 156. In the weight multiplication unit 150 ′ according to the modification, the selector 159 supplies CSI_RS to the preceding stage of the V1 multiplication unit 154 or the subsequent stage of the V2_MU multiplication unit 156.

  More specifically, the selector 159 supplies CSI_RS to the subsequent stage of the V2_MU multiplier 156 in resources allocated for transmission of CSI_RS. In this case, the base station 10 transmits CSI_RS that is not multiplied by V1.

  On the other hand, the selector 159 supplies CSI_RS to the preceding stage of the V1 multiplier 154 in the resources allocated for transmission of V1 * CSI_RS. In this case, CSI_RS is multiplied by V1 in the V1 multiplier 154, and V1 * CSI_RS as a multiplication result is supplied from the selector 155 to the selector 157 so as to bypass the V2_MU multiplier 156. As a result, the base station 10 transmits V1 * CSI_RS.

  As described above, the base station 10 according to the present embodiment starts transmission of V1 * CSI_RS after determining the transmission weight V1. With this configuration, it is possible to suppress a calculation load such as V2_MU in the mobile station 20 described below.

<3. Basic configuration of mobile station>
FIG. 9 is an explanatory diagram showing the configuration of the mobile station 20 according to the present embodiment. As shown in FIG. 9, the mobile station 20 according to the present embodiment includes a plurality of antennas 210, a switch SW216, an analog processing unit 220, an AD / DA conversion unit 224, a demodulation processing unit 228, and an upper layer. A signal processing unit 232, a modulation processing unit 240, a channel matrix acquisition unit 244, and a weight determination unit 248 are provided.

  The antennas 210A and 210B convert a radio signal transmitted from the base station 10 into an electrical reception signal and supply it to the analog processing unit 220, and a transmission signal supplied from the analog processing unit 120 as a radio signal It functions as a transmission unit that converts the signal into the base station 10 and transmits it to the base station 10. Note that the number of antennas 210 is not particularly limited, and may be four or eight, for example.

  The switch SW216 is a switch for switching between transmission operation and reception operation by the mobile station 20. When the antennas 210A and 210B are connected to the transmission circuit of the analog processing unit 220 via the switch SW216, the mobile station 20 performs transmission operation, and the antennas 210A and 210B receive the circuit of the analog processing unit 220 via the switch SW216. Mobile station 20 performs a receiving operation.

  The analog processing unit 220 includes a transmission circuit that performs analog processing on a transmission signal and a reception circuit that performs analog processing on a reception signal. In the transmission circuit, for example, up-conversion, filtering, gain control, and the like of an analog transmission signal supplied from the AD / DA conversion unit 224 are performed. In the receiving circuit, for example, down-conversion and filtering of the received signal supplied from the antenna 210 via the switch SW216 are performed.

  The AD / DA conversion unit 224 performs AD conversion of the reception signal supplied from the analog processing unit 220 and DA conversion of the transmission signal supplied from the modulation processing unit 240.

  The demodulation processing unit 228 performs demodulation processing on the reception signal supplied from the AD / DA conversion unit 224. The demodulation processing performed by the demodulation processing unit 228 may include OFDM demodulation processing, MIMO demodulation processing, error correction, and the like.

  The upper layer signal processing unit 232 performs processing for inputting / outputting transmission data and reception data to / from an upper layer. Further, the upper layer signal processing section 232 supplies feedback information indicating the transmission weight determined by the weight determination section 248 to the modulation processing section 240 as transmission data.

  The modulation processing unit 240 performs modulation processing such as mapping based on constellation on the transmission data supplied from the upper layer signal processing unit 232. The transmission signal modulated by the modulation processing unit 240 is supplied to the AD / DA conversion unit 224.

  When the CSI_RS is received from the base station 10, the channel matrix acquisition unit 244 acquires the channel matrix H between the base station 10 and the mobile station 20.

  The weight determination unit 248 determines transmission weights such as V1, V2_MU, and V2_SU based on the channel matrix H acquired by the channel matrix acquisition unit 244. Here, as described with reference to FIG. 4, when updating the V2_MU based on the channel matrix H acquired from the CSI_RS, the mobile station according to the comparative example multiplies the channel matrix H by the determined V1. , V2_MU is evaluated for the channel matrix H multiplied by V1. For this reason, in the mobile station according to the comparative example, calculation using V1 is performed even when V2_MU is updated.

  On the other hand, in the present embodiment, after determining V1, V1 * CSI_RS that is CSI_RS multiplied by V1 is received from the base station 10. The channel matrix H acquired by the channel matrix acquisition unit 244 from this V1 * CSI_RS has already been multiplied by V1. Therefore, the weight determination unit 248 can update V2_MU without performing an operation using V1 based on the channel matrix H acquired from V1 * CSI_RS. As a result, it is possible to significantly reduce the calculation load on the mobile station 20 for updating V2_MU.

<4. Description of each embodiment>
The basic configurations of the base station 10 and the mobile station 20 according to the embodiments of the present invention have been described above. Subsequently, each embodiment of the present invention will be described in detail.

[4-1. First Embodiment]
FIG. 10 is an explanatory diagram showing the first embodiment of the present invention. As shown in FIG. 10, when V1 is determined by transmitting CSI_RS, the base station 10 transmits V1 * CSI_RS for updating (determination) of V2_MU. As described above, the mobile station 20 that has received V1 * CSI_RS can evaluate the optimum V2_MU without performing an operation using V1.

  And the base station 10 transmits CSI_RS for the update of V1, after transmitting V1 * CSI_RS several times. Thereafter, the base station 10 transmits V1 * CSI_RS for updating V2_MU.

  FIG. 10 shows an example in which the update frequency of V2 is about 4 to 5 times the update frequency of V1, but the relationship of the update frequencies is not limited to this example. Actually, it is assumed that the update frequency of V1 exceeds 10 times the update frequency of V2.

[4-2. Second Embodiment]
As described in the first embodiment, if the base station 10 transmits V1 * CSI_RS, the mobile station 20 can evaluate the optimum V2_MU without performing calculation using V1. Here, in order to realize dynamic switching between MU-MIMO and SU-MIMO, the mobile station 20 needs to acquire V2_SU. However, it is difficult for the mobile station 20 to evaluate V2_SU from V1 * CSI_RS.

  Therefore, the upper layer signal processing section 132 of the base station 10 according to the second embodiment allocates resources for transmitting V1 * CSI_RS for V2_MU update (determination), and allocates resources for transmitting CSI_RS to V2_SU. Assign for update (decision). The operation of the base station 10 according to the second embodiment will be specifically described with reference to FIG.

  FIG. 11 is an explanatory view showing a second embodiment of the present invention. As shown in FIG. 11, after determining V1, the base station 10 according to the second embodiment transmits V1 * CSI_RS for updating V2_MU and transmits CSI_RS for updating (determination) of V2_SU. To do. With this configuration, V2_MU is obtained based on V1 * CSI_RS, and V2_SU is obtained based on CSI_RS. Therefore, dynamic switching between MU-MIMO and SU-MIMO can be realized.

Note that the mobile station 20 can determine whether the radio signal received from the base station 10 is CSI_RS or V1 * CSI_RS by, for example, the following method.
(1) The base station 10 notifies the mobile station 20 of the timing or order of transmitting CSI_RS or V1 * CSI_RS in advance via RRC signaling.
(2) The base station 10 notifies the mobile station 20 of the timing or order of transmitting CSI_RS or V1 * CSI_RS by broadcasting system information.
(3) The base station 10 transmits CSI_RS and V1 * CSI_RS with identification information indicating whether it is CSI_RS or V1 * CSI_RS.

[4-3. Third Embodiment]
As described in “1-4. Dynamic switching”, SU-MIMO performs MIMO transmission of, for example, 8 independent streams. On the other hand, in MU-MIMO, for example, two independent streams are MIMO transmitted to each of four different mobile stations 20. Therefore, V2_SU is for 8 streams, whereas V2_MU is for 2 streams.

  In this case, since higher accuracy is required for V2_SU for 8 streams, it is effective to make the update frequency of V2_SU higher than the update frequency of V2_MU.

  Therefore, the upper layer signal processing section 132 of the base station 10 according to the third embodiment transmits CSI_RS for updating (determining) V2_SU rather than transmitting V1 * CSI_RS for updating (determining) V2_MU. Allocate more resources to The operation of the base station 10 according to the third embodiment will be specifically described with reference to FIG.

  FIG. 12 is an explanatory view showing a third embodiment of the present invention. As shown in FIG. 12, the base station 10 according to the third embodiment, after determining V1, sets CSI_RS for updating (determining) V2_SU rather than V1 * CSI_RS for updating (determining) V2_MU. Sends frequently in the time direction. With this configuration, it is possible to acquire V2_SU with high accuracy while suppressing the calculation load on the mobile station 20 when updating the V2_MU.

[4-4. Fourth Embodiment]
In 3rd Embodiment, in order to make the update frequency of V2_SU higher than the update frequency of V2_MU, it demonstrated that the base station 10 transmitted CSI_RS in the time direction more frequently than V1 * CSI_RS. In the fourth embodiment, as in the third embodiment, in order to make the V2_SU update frequency higher than the V2_MU update frequency, V1 * CSI_RS and CSI_RS are arranged in the frequency direction in the OFDM subcarrier. Devised. Hereinafter, an example of resource allocation according to the fourth embodiment will be described in detail with reference to FIG.

  FIG. 13 is an explanatory diagram showing an example of V1 * CSI_RS and CSI_RS resource allocation according to the fourth embodiment. As illustrated in FIG. 13, the upper layer signal processing section 132 of the base station 10 according to the fourth embodiment arranges CSI_RSs more densely in the frequency direction than V1 * CSI_RS. Thus, by creatively arranging the arrangement of V1 * CSI_RS and CSI_RS in the frequency direction, as in the third embodiment, the calculation load on the mobile station 20 at the time of updating V2_MU is suppressed, and a high load is achieved. It becomes possible to acquire accurate V2_SU.

[4-5. Fifth Embodiment]
In the fifth embodiment, resource allocation for data communication using transmission weights after determination of transmission weights will be described.

  FIG. 14 is an explanatory diagram showing a specific example of resource allocation according to the fifth embodiment. The horizontal axis in FIG. 14 indicates time, and the vertical axis indicates frequency. Further, the time width of the rectangular block in FIG. 14 may be one resource block or one subframe. Further, the frequency width of the square block may be one resource block (for 12 subcarriers) or may be another bandwidth.

  As illustrated in FIG. 14, when the base station 10 first transmits CSI_RS, the mobile station 20 acquires V1, V2_MU, and V2_SU for each frequency based on reception of the CSI_RS. Then, the mobile station 20 feeds back V1, V2_MU, and V2_SU to the base station 10.

  After that, as shown in FIG. 14, the scheduler 136 of the base station 10 uses the bottom four resource blocks included in the frequency range B for MU-MIMO (first scheme) with the mobile stations 20A to 20C. assign. On the other hand, as shown in FIG. 14, the scheduler 136 of the base station 10 allocates the top two resource blocks included in the frequency range A for SU-MIMO (second scheme) with the mobile station 20D.

  Here, the scheduler 136 according to the fifth embodiment keeps the resource blocks included in the frequency range B as a region for MU-MIMO, and keeps the resource blocks included in the frequency range A as a region for SU-MIMO.

  Therefore, the scheduler 136 according to the fifth embodiment, for example, when dynamically switching the MIMO setting of the mobile station 20C from MU-MIMO to SU-MIMO, as shown in FIG. 14, is a resource block allocated to the mobile station 20C. Are moved to resource blocks included in the frequency range A.

  As described above, according to the fifth embodiment, MU-MIMO and SU-MIMO dynamic switching can be realized by moving the resource block of the mobile station 20 in the frequency direction.

[4-6. Sixth Embodiment]
FIG. 15 is an explanatory diagram showing a specific example of resource allocation according to the sixth embodiment. As shown in FIG. 15, the upper layer signal processing section 132 according to the sixth embodiment, after determining V1, determines the resource blocks included in the frequency range B for MU-MIMO described in the fifth embodiment. Assign for transmission of V1 * CSI_RS. Further, the upper layer signal processing section 132 allocates resource blocks included in the SU-MIMO frequency range A described in the fifth embodiment for transmission of CSI_RS.

  With this configuration, V2_MU can be updated in frequency range A while V2_MU is updated while suppressing the amount of calculation in mobile station 20. For this reason, the frequency range B can be used for communication by MU-MIMO, and the frequency range A can be used for communication by SU-MIMO.

[4-7. Seventh Embodiment]
In the fifth embodiment and the sixth embodiment described above, the example in which the frequency range for MU-MIMO and the frequency range for SU-MIMO are fixed has been described. However, the seventh embodiment will be described below. It is also possible to dynamically change the frequency range for MU-MIMO and the frequency range for SU-MIMO.

  FIG. 16 is an explanatory diagram showing a specific example of resource allocation according to the seventh embodiment. As shown in FIG. 16, it is assumed that resource blocks in frequency range Z and frequency range X are allocated for transmission of CSI_RS at time t1, and resource blocks in frequency range Y are allocated for transmission of V1 * CSI_RS. .

  Here, V1, V2_MU, and V2_SU can be acquired at the frequency at which CSI_RS is transmitted. On the other hand, at the frequency at which V1 * CSI_RS is transmitted, V2_MU can be acquired, but it is difficult to acquire V2_SU. That is, the frequency at which V1 * CSI_RS is transmitted can be used for MU-MIMO, and the frequency at which CSI_RS is transmitted can be used for either MU-MIMO or SU-MIMO.

  Therefore, the scheduler 136 according to the seventh embodiment handles the resource blocks in the frequency range X and the frequency range Z in which CSI_RS is transmitted as a switchable region for SU-MIMO and MU-MIMO. On the other hand, the scheduler 136 treats resource blocks in the frequency range Y in which V1 * CSI_RS is transmitted as a MU-MIMO dedicated area.

  For example, as shown in FIG. 16, the scheduler 136 allocates resource blocks in the frequency range X for communication by SU-MIMO at time t2, and allocates resource blocks in the frequency range Y and frequency Z by MU-MIMO. Assign for communication. After that, the scheduler 136 switches the resource block in the frequency range Z from MU-MIMO for SU-MIMO and switches the resource block in the frequency range X from SU-MIMO to MU-MIMO at time t3. Is possible.

<5. Operation of base station and mobile station>
The embodiments of the present invention have been described above. Next, operations of the base station 10 and the mobile station 20 according to the embodiment of the present invention will be described with reference to FIGS. 17 and 18.

  FIG. 17 is a flowchart illustrating an operation of the base station 10 according to the embodiment of the present invention. FIG. 17 particularly corresponds to the operation of the base station 10 according to the seventh embodiment.

  As shown in FIG. 17, the base station 10 first determines the update frequency in the time direction of V1 and V2_MU (S304). Subsequently, the base station 10 determines the update frequency in the time direction of V2_SU (S308).

  Thereafter, the base station 10 determines the resource for MU-MIMO and the density of the resource for SU-MIMO in the frequency direction (S312). Further, the base station 10 determines the ratio in the frequency direction between the MU-MIMO dedicated area and the dynamic switching possible area shown in FIG. 16 (S316). In the example shown in FIG. 16, the ratio of the MU-MIMO dedicated area and the dynamic switching possible area in the frequency direction is 1: 2, and the resource for MU-MIMO and the resource for SU-MIMO The density ratio in the frequency direction is 2: 1.

  Subsequently, the base station 10 allocates resources for transmitting CSI_RS and resources for transmitting V1 * CSI_RS (S320). More specifically, the base station 10 allocates V1 * CSI_RS for transmission of the frequency resource determined as the MU-MIMO dedicated area in S316, and allocates the frequency resource determined as the dynamic switching capable area for transmission of the CSI_RS. Assign for. Also, the base station 10 allocates resources in the time direction to V1 * CSI_RS and CSI_RS based on the determination results of S304 and S308. And the base station 10 transmits CSI_RS and V1 * CSI_RS according to the determined resource.

  FIG. 18 is a flowchart showing the operation of the mobile station 20 according to the present embodiment. As shown in FIG. 18, when the mobile station 20 receives a radio signal from the base station 10 (S404), when this radio signal is CSI_RS (S408), the mobile station 20 acquires a channel matrix H from the reception result of CSI_RS ( S412). Then, the mobile station 20 determines transmission weights such as V1, V2_MU, and V2_SU based on the channel matrix H acquired in S412 (S416). Further, the mobile station 20 feeds back V1, V2_MU, and V2_SU to the base station 10 (S420).

  On the other hand, when the received radio signal is V1 * CSI_RS (S408), the mobile station 20 acquires the channel matrix H multiplied by V1 from the reception result of V1 * CSI_RS (S424). Then, the mobile station 20 determines V2_MU based on the channel matrix H multiplied by V1 without performing an operation using V1 (S428). Further, the mobile station 20 feeds back V2_MU to the base station 10 (S432).

  If the received radio signal is a data signal (S408), the mobile station 20 demodulates the data signal and acquires data transmitted from the base station 10 (S436).

<6. Summary>
As described above, the base station 10 according to the embodiment of the present invention starts transmission of V1 * CSI_RS after determining the transmission weight V1. With this configuration, it is possible to suppress a calculation load such as V2_MU in the mobile station 20 described below. Furthermore, the base station 10 according to the embodiment of the present invention also continues to transmit CSI_RS. With this configuration, the mobile station 20 can determine V2_SU based on reception of CSI_RS. As a result, it is possible to realize dynamic switching between MU-MIMO and SU-MIMO.

  Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, two or more of the first to seventh embodiments may be combined. Specifically, resource allocation in the time direction described in the third embodiment, resource allocation in the frequency direction described in the fifth embodiment, SU-MIMO and MU-MIMO described in the sixth embodiment It is also possible to combine resource allocations for.

  In addition, each step in the processing of the base station 10 or the mobile station 20 in this specification does not necessarily have to be processed in time series in the order described as a flowchart. For example, each step in the processing of the base station 10 or the mobile station 20 may be processed in an order different from the order described as the flowchart, or may be processed in parallel.

  In addition, it is possible to create a computer program for causing hardware such as a CPU, ROM, and RAM incorporated in the base station 10 or the mobile station 20 to perform the same functions as the components of the base station 10 or the mobile station 20 described above. It is. A storage medium storing the computer program is also provided.

10 Base station 20, 20A, 20B Mobile station 110, 210 Antenna 116, 216 Switch SW
120, 220 Analog processing unit 124, 224 AD / DA conversion unit 128, 228 Demodulation processing unit 132, 232 Upper layer signal processing unit 136 Scheduler 140, 240 Modulation processing unit 150 Weight multiplication unit 152 V2_SU multiplication unit 154 V1 multiplication unit 156 V2_MU Multiplier 244 Channel matrix acquisition unit 248 Weight determination unit

Claims (10)

A communication unit that communicates in either MU-MIMO (Multi User-Multiple Input Multiple Output) mode or SU-MIMO (Single User-Multiple Input Multiple Output) communication mode;
A resource allocation unit that allocates a first resource for the MU-MIMO mode and a second resource for the SU-MIMO mode;
With
Allocating resources from common resources that can be used as both the first resource and the second resource,
The communication unit transmits first reference information for the MU-MIMO mode and second reference information for the SU-MIMO mode, and the first reference information in the mobile station and the A base station that transmits information for enabling identification of second reference information .   The base station according to claim 1, wherein the first resource and the second resource are in a predetermined frequency range.   The base station according to claim 1, wherein the first resource and the second resource are predetermined resource blocks.   The base station according to claim 1, wherein the MU-MIMO mode and the SU-MIMO mode are dynamically switched. The base station according to claim 1, wherein the information is transmitted via RRC signaling. The base station according to claim 1, wherein the information is received via system information.   The base station according to claim 1, wherein the second resource is allocated more than the first resource.   The base station according to claim 1, wherein the number of streams that the communication unit transmits to one mobile station differs between the MU-MIMO mode and the SU-MIMO mode. The base station according to claim 8 , wherein the number of streams transmitted to one mobile station in the SU-MIMO mode is four times the number of streams transmitted to one mobile station in the MU-MIMO mode. . It has a communication unit that communicates in either MU-MIMO (Multi User-Multiple Input Multiple Output) mode or SU-MIMO (Single User-Multiple Input Multiple Output) communication mode.
Communicate on resources allocated from common resources that can be used for both the MU-MIMO mode and the SU-MIMO mode,
First reference information for the MU-MIMO mode and second reference information for the SU-MIMO mode are transmitted from a base station,
A mobile station that identifies the first reference information and the second reference information based on identification information received from the base station.

Images