JP2018182472A - Radio terminal, base station, and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve throughput characteristics.SOLUTION: A base station 10 includes: a transmission unit 12 capable of transmitting a first reference signal 41 used in a first communication mode 31; and a control unit 13 for switching to a second communication mode 32 to use a second reference signal 42 with a radio resource different from the first reference signal 41 if the first reference signal 41 and another signal 43 may collide in radio resources allocated to a radio terminal 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wireless terminal, a base station, and a communication control method.

  In 3GPP (Third Generation Partnership Project) LTE (Long Term Evolution) standard, multiple transmission modes (TM: Transmission Mode) are defined. Conditions such as suitability of transmission diversity, suitability of spatial multiplexing (closed loop / open loop), suitability of beamforming, transport block size, etc. are set for each TM.

  For example, in TM3 and TM4 (hereinafter, TM3 / 4), up to four layers of spatial-multiplex (MIMO: Multiple-Input and Multiple-Output) communication are allowed. Moreover, in TM3 / 4, CRS (Cell-specific Reference Signal) is used for decoding of the data transmitted by PDSCH (Physical Downlink Shared Channel).

  In TM9 and TM10 (hereinafter, TM9 / 10), up to eight layers of spatial multiplexing (MIMO) communication are allowed. Further, in TM9 / 10, data transmitted by PDSCH and DRS (Demodulation Reference Signal) used for decoding the data are transmitted as a set. Note that CRS is also transmitted in TM9 / 10. In the present specification, CRS may be described as CSRS, and DRS may be described as DMRS.

  CRS is a cell-specific reference signal, and DRS is a user-specific reference signal. Using DRS enables fine-grained beam directivity control, and high-speed DL (Downlink) data transmission can be realized by spatial multiplexing of up to eight layers.

  In the LTE standard, PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal) are defined as signals for the wireless terminal to know the base station at startup. The PSS / SSS is assigned to a specific subframe together with a Physical Broadcast Channel (PBCH). For example, PSS / SSS is arranged in subframe # 0 of each frame, and PBCH is further arranged in subframe # 0.

RP-160549, "RP-160549 rev RP-160421 36213 CR0548 (Rel-13 Rev-3) PDSCH collision v2", Huawei, HiSilicon, NTT DOCOMO, SoftBank, Ericsson, Panasonic R1-084660, "R1-084660 DRS handling 36 213 CR0167 REV1", Nokia, Nokia Siemens Networks R1-154323, "Clarifications for scheduling behavior related to the collision between port 5, 7-14 DMRS and PSS / SSS / PBCH", Huawei, HiSilicon R1-163790, "Collision between PSS / SSS / PBCH and MPDCCH / PDSCH for MTC", Ericsson, Samsung

  In the LTE standard, the arrangement of each signal is defined such that CRS and PSS / SSS are not allocated to the same RB (Resource Block). Therefore, in TM3 / 4, even in a subframe to which PSS / SSS is assigned, data transmitted on PDSCH can be decoded using CRS. On the other hand, in TM9 / 10, part of PSS / SSS is allocated to RB to which DRS is allocated. Therefore, DRS and part of PSS / SSS collide.

  If the collision occurs in a subframe to which PSS / SSS / PBCH is allocated, DRS can not be transmitted, and data transmission by TM9 / 10 is limited in a subcarrier in which PSS / SSS is transmitted. Therefore, in the current LTE standard, when a wireless terminal of TM9 / 10 (hereinafter referred to as a TM9 / 10 terminal) is assigned to a subframe in which PSS / SSS / PBCH is arranged, performance loss occurs due to the above-mentioned collision. Do.

  According to one aspect, an object of the present invention is to provide a wireless terminal, a base station, and a communication control method capable of improving throughput characteristics. Note that although TM3 / 4 and TM9 / 10 of the LTE standard are described as an example for convenience of explanation, the same problem as described above may occur in non-LTE standards and other TMs. The solution of such problems may also be included in the object of the present invention.

  According to one aspect, the transmitter capable of transmitting the first reference signal used in the first communication mode and the radio resource allocated to the wireless terminal may collide with the first reference signal and another signal. In the case, there is provided a base station having a control unit for switching to a second communication mode using a second reference signal with a radio resource different from the first reference signal.

  Throughput characteristics can be improved.

It is a figure showing an example of the radio communications system concerning a 1st embodiment. It is a figure showing an example of the radio communications system concerning a 2nd embodiment. It is a figure for demonstrating downlink transmission mode (TM). It is a block diagram showing an example of the hardware which a base station has. It is a block diagram showing an example of the hardware which a wireless terminal has. It is the block diagram which showed an example of the function which the base station which concerns on 2nd Embodiment has. It is a figure for demonstrating mapping information. It is a figure for demonstrating the switching method of transmission mode. It is a figure for demonstrating the antenna port of a downlink. It is the block diagram which showed an example of the function which the radio | wireless terminal which concerns on 2nd Embodiment has. It is the flowchart which showed the flow of the process by the base station which concerns on 2nd Embodiment. It is the flowchart which showed the flow of the process by the radio | wireless terminal which concerns on 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the attached drawings. In the present specification and drawings, elements having substantially the same function may be omitted to avoid redundant description by attaching the same reference numerals.

<1. First embodiment>
The first embodiment will be described with reference to FIG. The first embodiment relates to a technology that autonomously switches the communication mode to enable data transmission when there is a subframe in which a reference signal used for decoding data in a specific communication mode and another signal collide with each other. FIG. 1 is a diagram showing an example of a wireless communication system according to the first embodiment. The wireless communication system 5 illustrated in FIG. 1 is an example of the wireless communication system according to the first embodiment.

  As shown in FIG. 1, the wireless communication system 5 includes a base station 10 and a wireless terminal 20. Although only one wireless terminal (wireless terminal 20) is described in the example of FIG. 1 for convenience of explanation, the number of wireless terminals included in the wireless communication system 5 may be two or more.

  The base station 10 includes an antenna group 11 including at least one antenna, a transmitter 12, and a controller 13. On the other hand, the wireless terminal 20 has an antenna 21. Although the wireless terminal 20 having one antenna (antenna 21) is described in the example of FIG. 1 for convenience of explanation, the number of antennas included in the wireless terminal 20 may be two or more.

The transmission unit 12 is, for example, a transmission circuit including a digital to analog (DA) conversion circuit, a frequency conversion circuit, an encoding circuit, a modulation circuit, and the like.
The DA conversion circuit converts a digital signal into an analog signal. The frequency conversion circuit frequency-converts a signal (BB signal) in a BB (Base-Band) band to a signal (RF signal) in an RF (Radio Frequency) band. The encoding circuit encodes the bit string to generate encoded data. The modulation circuit performs modulation processing such as QPSK (Quadrature Phase Shift Keying) or 16 QAM (Quadrature Amplitude Modulation). In addition, the transmission unit 12 may have a plurality of phase shifters for shifting the phase of the RF signal transmitted from each antenna of the antenna group 11.

  The control unit 13 is a processor such as a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), and a field programmable gate array (FPGA). The control unit 13 includes, for example, a storage device such as a random access memory (RAM), a hard disk drive (HDD), a solid state drive (SSD), or a flash memory. For example, the control unit 13 can control the transmission unit 12 to perform beam forming, MIMO transmission, and the like by the antenna group 11.

  The base station 10 and the wireless terminal 20 can communicate in the first communication mode 31 or the second communication mode 32. The first communication mode 31 is a communication mode in which the first reference signal 41 is used for communication. The second communication mode is a communication mode in which a second reference signal 42 different from the first reference signal 41 is used for communication. The DMRS, which is a reference signal specific to the user (wireless terminal 20), is an example of the first reference signal 41. CSRS, which is a reference signal specific to a cell formed by the base station 10, is an example of the second reference signal 42.

  The transmitter 12 can transmit the first reference signal 41. The control unit 13 can autonomously switch the first communication mode 31 to the second communication mode 32. For example, when another signal 43 is assigned to the radio resource of the first reference signal 41 in a subframe having an assignment to the radio terminal 20 communicating in the first communication mode 31, the control unit 13 performs the first communication The mode 31 is switched to the second communication mode 32.

  Note that PSS / SSS periodically transmitted is an example of another signal 43. When the first reference signal 41 is DMRS and the other signal 43 is PSS / SSS, a collision between the first reference signal 41 and the other signal 43 may occur in a specific subframe. In such a case, the control unit 13 performs switching from the first communication mode 31 to the second communication mode 32.

  FIG. 1A shows, as an example, resource allocation such as DMRS, CSRS, PDSCH, PSS / SSS, PBCH, and PCFICH (Physical Control Format Indicator Channel) in subframes in which the collision occurs. Note that, for example, in addition to the PCFICH, the PCFICH etc includes a PDCCH (Physical Downlink Control Channel), a PHICH (Physical HARQ Indicator Channel), and the like. The horizontal axis is time (in symbol units), and the vertical axis is frequency (in subcarrier units).

  Among the resource allocations illustrated in FIG. 1 (A), PSS / SSS is placed in the range of (a), and PBCH is placed in the range of (b). The range of (a) includes DMRS, and part of RBs in which PSS / SSS is allocated collides with DMRS. The base station 10 and the radio terminal 20 hold information of resource allocation as shown in FIG. 1 (A). Therefore, each of the base station 10 and the radio terminal 20 can know the subframe in which the PSS / SSS and the DMRS collide, based on the held information.

  In the current LTE standard, when there is a subframe as shown in FIG. 1 (A), the DMRS can not be received by the TM9 / 10 terminal in the RB where there is the above collision, so data transmission on the PDSCH in the subcarrier where the RB is present Is constrained.

  On the other hand, when the technique of the first embodiment is applied to the example of FIG. 1 (A), the control unit 13 is in a collision subframe, as shown in FIG. 1 (B). Change from 10) to the communication mode (TM3 / 4) that uses CSRS. That is, the control unit 13 suppresses the transmission of the DMRS in this subframe, and transmits the data by the PDSCH in the RB in which the collision occurs. Since the wireless terminal 20 can decode data using CSRS, data transmission becomes possible.

  As described above, by applying the technology of the first embodiment, it becomes possible to effectively utilize radio resources that were not utilized in the current LTE standard, for example, to reduce the performance loss in the TM9 / 10 terminal. can do. In addition, as in the case of switching from TM9 / 10 to TM3 / 4, it is not necessary to formulate a new control signal by effectively using the existing communication mode, and processing complexity and processing load may be reduced. Throughput characteristics can be improved without causing an increase.

  In the description, although resource allocation in the LTE standard and switching from TM9 / 10 to TM3 / 4 have been exemplified, the application scope of the technology according to the first embodiment is not limited to this. That is, the same applies to a wireless communication system adopting specifications and settings that differ in the switching source and the switching destination communication mode, the type of signal colliding with the reference signal, and the type of signal allocated to a subframe. The technology of the first embodiment can be applied to Such a modification naturally belongs to the technical scope of the first embodiment.

The first embodiment has been described above.
<2. Second embodiment>
Next, a second embodiment will be described. The second embodiment relates to a technique for autonomously switching the communication mode to enable data transmission when there is a subframe in which a reference signal used to decode data in a specific communication mode and another signal collide with each other.

[2-1. system]
The wireless communication system 50 will be described with reference to FIG. FIG. 2 is a diagram showing an example of a wireless communication system according to the second embodiment. The wireless communication system 50 illustrated in FIG. 2 is an example of the wireless communication system according to the second embodiment.

As shown in FIG. 2, the wireless communication system 50 includes a base station 100 and wireless terminals 201 and 202. Note that the number of wireless terminals included in the wireless communication system 50 may be three or more.
In the wireless communication system 50, multiple transmission modes (TM) may be utilized. As an example, a list of downlink transmission modes is shown in FIG. FIG. 3 is a diagram for explaining the downlink transmission mode (TM). The ten types of TM illustrated in FIG. 3 are an example, and other TMs having different conditions may be used in the wireless communication system 50.

  In the list illustrated in FIG. 3, the mode number of TM is described in the column of Mode. For example, when the column of Mode is 1, the line corresponding to that column corresponds to the setting content of TM1 (the column of Purpose, the column of Uplink feedback). TM1 allows single antenna transmission and requests feedback of CQI (Channel Quality Indicator) in uplink.

As an example, the setting contents 303 of TM3 / 4 and the setting contents 304 of TM9 / 10 will be further described.
TM3 allows open loop spatial multiplexing and requests feedback of CQI and RI (Rank Indicator) in uplink. TM4 allows closed loop spatial multiplexing, and requests feedback of CQI, RI, and PMI (Precoding Matrix Indicator) in uplink. TM9 allows up to 8 layers of spatial multiplexing and requests uplink CQI feedback. The TM 10 permits CoMP (Coordinated Multiple Point) transmission and requests CQI feedback in the uplink. However, in TM 9/10, feedback of RI and PMI in the uplink is defined as a configurable item.

  In TM3 / 4, CSRS is used for channel estimation. In TM9 / 10, DMRS is used for channel estimation. CSRS is a reference signal specific to the cell formed by base station 100. The DMRS is a reference signal used for channel detection for performing synchronous detection of a PUSCH (Physical Uplink Shared Channel) and a PUCCH (Physical Uplink Control Channel), which are transmitted together with the DMRS. Note that beamforming is applied to DMRS transmission.

  For example, when the base station 100 and the wireless terminal 201 transmit downlink data using TM9 / 10, as shown in the RB map 301 of FIG. 2, the base station 100 performs DMRS in a subframe in which a wireless resource is allocated to the wireless terminal 201. Send CSRS is also transmitted in that subframe. On the other hand, when the base station 100 and the wireless terminal 202 transmit downlink data using TM3 / 4, as shown in the RB map 302 of FIG. 2, the base station 100 performs CSRS in a subframe in which wireless resources are allocated to the wireless terminal 202 And the DMRS does not.

  The time axis of the RB maps 301 and 302 is in symbol units. Also, the frequency axis of the RB maps 301 and 302 is in subcarrier units. The rectangles included in the RB maps 301 and 302 represent RBs. For example, in the RB map 301, data transmitted on a PDSCH placed after the DMRS is decoded using a result (channel matrix) of channel estimation based on the DMRS. On the other hand, in TM3 / 4, data is decoded using a channel matrix estimated using CSRS.

Hereinafter, the description will be given by taking the above-described wireless communication system 50 as an example.
(Hardware of base station 100)
The base station 100 has, for example, hardware as shown in FIG. FIG. 4 is a block diagram showing an example of hardware included in a base station.

  As shown in FIG. 4, the base station 100 includes an antenna group 100a, an RF circuit 100b, a BB circuit 100c, an NIF (Network Interface) circuit 100d, a CPU 100e, and a memory 100f.

  Antenna group 100a includes a plurality of antennas. The RF circuit 100b performs processing such as modulation / demodulation and frequency conversion on a signal (RF signal) in a wireless band. The RF circuit 100b includes, for example, a plurality of phase shifters that control the phases of a plurality of RF signals simultaneously transmitted and received through a plurality of antennas to switch the directivity of a beam formed by the antenna group 100a.

  The BB circuit 100c performs encoding / decoding processing, AD (Analog to Digital) / DA conversion processing, and the like on a baseband signal (BB signal). For example, the BB circuit 100c performs a process of suppressing inter-stream interference in the case of transmitting a plurality of streams in parallel and applying precoding for improving reception quality to the BB signal. The NIF circuit 100d is a communication circuit connected to the core network.

  The CPU 100 e controls the operation of the base station 100 using a program or data stored in the memory 100 f. For example, the CPU 100e performs control such as TM switching, radio resource allocation, application of precoding to a BB signal, application of beam forming by phase control of an RF signal, and the like. The CPU 100 e is an example of a processor, and can be replaced with a DSP, an ASIC, an FPGA, or the like.

  The memory 100 f is, for example, an HDD, an SSD, a RAM, a ROM (Read Only Memory), or the like. The memory 100 f stores, for example, information on resource block mapping such as the RB maps 301 and 302.

(Hardware of wireless terminal 201)
The wireless terminal 201 has, for example, hardware as shown in FIG. FIG. 5 is a block diagram showing an example of hardware included in the wireless terminal.

  As illustrated in FIG. 5, the wireless terminal 201 includes an antenna 201a, an RF circuit 201b, a BB circuit 201c, a CPU 201d, and a memory 201e. The number of antennas included in the wireless terminal 201 may be two or more.

  The RF circuit 201b performs processing such as modulation / demodulation and frequency conversion on an RF signal. The BB circuit 201c performs encoding / decoding processing, AD / DA conversion processing, etc. on the BB signal. The CPU 201 d controls the operation of the wireless terminal 201 using a program or data stored in the memory 201 e. For example, the CPU 201 d performs processing such as TM switching and channel estimation based on a reference signal.

  The CPU 201 d is an example of a processor, and can be replaced with a DSP, an ASIC, an FPGA, or the like. The memory 201 e is, for example, an HDD, an SSD, a RAM, a ROM, or the like. Further, since the hardware of the wireless terminal 202 is substantially the same as the wireless terminal 201, the description of the hardware of the wireless terminal 202 will be omitted.

[2-2. function]
Hereinafter, the functions of the base station 100 and the wireless terminal 201 will be described. In addition, since the wireless terminals 201 and 202 have the same function, the description of the function of the wireless terminal 202 is omitted.

(Function of base station 100)
The base station 100 has a function as shown in FIG. FIG. 6 is a block diagram showing an example of functions of the base station according to the second embodiment.

  As shown in FIG. 6, the base station 100 includes a storage unit 101, a transmission control unit 102, a collision detection unit 103, and an assignment control unit 104. The function of the storage unit 101 can be realized by the memory 100 f described above. The functions of the transmission control unit 102, the collision detection unit 103, and the assignment control unit 104 can be realized by the above-described CPU 100e or the like.

  The storage unit 101 stores the mapping information 101a. The mapping information 101a is information regarding resource block mapping for each subframe as shown in FIG. FIG. 7 is a diagram for explaining the mapping information.

  As an example, FIG. 7 shows an RB map in the case where the base station 100 and the radio terminal 201 transmit downlink data using TM9 / 10. In this example, for downlink data transmission to the wireless terminal 201, DMRSs are arranged in subframes # 0 and # 1. However, PSS / SSS / PBCH is allocated to subframe # 0. At this time, a part of PSS / SSS is allocated to the same RB as the DMRS allocated to subframe # 0. That is, part of PSS / SSS collides with DMRS.

  In the current LTE standard, when PSS / SSS and DMRS collide, not all DMRS is transmitted in a subframe in which PSS / SSS / PBCH is transmitted (in this example, subframe # 0). If the DMRS is not transmitted, data to be decoded using the DMRS will not be received. However, the base station 100 according to the second embodiment has a function of enabling data reception in subframes in which PSS / SSS and DMRS collide, by switching control of TM described later.

  Refer again to FIG. The transmission control unit 102 performs transmission control according to the TM. For example, in the case of TM9 / 10, the transmission control unit 102 transmits the DMRS based on the mapping information 101a. The collision detection unit 103 detects a collision between the PSS / SSS and the DMRS with reference to the mapping information 101a when the TM is TM9 / 10. The collision detection unit 103 also performs control to switch data to a decodable TM without using the DMRS. The assignment control unit 104 controls assignment of DMRS, PDSCH, and the like according to the TM.

  Here, with reference to FIG. 8, a method of switching TM in the case where a collision between PSS / SSS and DMRS is detected will be described. FIG. 8 is a diagram for describing a transmission mode switching method.

  In the example of FIG. 8, one frame is formed of ten subframes. PSS / SSS is arranged in subframes # 0 and # 5 of each frame, and PBCH is further arranged in subframe # 0. These are arranged in six RBs at the center of the system band. When the TM is TM9 / 10, the collision detection unit 103 detects a collision between DMRS and PSS / SSS in subframes # 0 and # 5 with reference to the mapping information 101a. Then, the collision detection unit 103 autonomously controls the transmission control unit 102 and the assignment control unit 104 so as to switch the TM to the transmission mode (corresponding to TM3 / 4) corresponding to TM9 / 10 to TM3 / 4.

On the other hand, in subframes # 1 to # 4 in which DMRS and PSS / SSS do not collide, TM is set to TM9 / 10 as shown in FIG.
For example, the collision detection unit 103 switches the TM from the equivalent of TM3 / 4 to TM9 / 10 when transitioning from subframe # 0 to subframe # 1, and transitions from subframe # 4 to subframe # 5 as TM9. Switch the TM from 10/10 to TM3 / 4 equivalent. Similarly, when transitioning from subframe # 5 to subframe # 6, the collision detection unit 103 switches the TM from the equivalent of TM3 / 4 to TM9 / 10, and transitions from subframe # 9 to subframe # 0 of the next frame. Switch the TM from TM9 / 10 to TM3 / 4 equivalent.

The transmission control unit 102 stops the transmission of the DMRS in a subframe in which data is transmitted by a TM equivalent to TM3 / 4.
Allocation control section 104 selects a radio terminal having the lowest rank based on RI fed back from radio terminals to be subjected to downlink data transmission, and transmits data of the selected radio terminal using TM equivalent to TM3 / 4. Allocated to RBs of subframes to be Also, the assignment control unit 104 assigns the PDSCH to antenna ports equal to or less than the maximum number of antenna ports (4 ports) defined by TM3 / 4. For example, the assignment control unit 104 assigns PDSCH to antenna ports # 0 to # 3 or antenna ports # 15 to # 18.

  In addition, as for the antenna port, the setting content is prescribed | regulated like the list | wrist illustrated in FIG. FIG. 9 is a diagram for explaining a downlink antenna port. In the list illustrated in FIG. 9, the column of Ant port indicates the port number of the antenna port, and the column of Application indicates the setting contents. In addition, the setting content of the antenna port in LTE specification is illustrated for convenience of description.

  Single antenna transmission and transmission diversity and spatial multiplexing by a plurality of antennas (2 antennas / 4 antennas) are set to the antenna ports # 0 to # 3 as applicable conditions (setting content 305). MBMS (Multimedia Broadcast and Multicast Service) is set to antenna port # 4, and beamforming is set to antenna port # 5.

  Application of PRS (Positioning Reference Signals) to antenna port # 6 is set, and beamforming of a plurality of layers and spatial multiplexing by 8 antennas are set to antenna ports # 7 to # 14. Application of CSI (Channel State Information) -RS is set to the antenna ports # 15 to # 22 as an applicable condition (setting content 306). In addition, application of Enhanced Physical Downlink Control Channel (EPDCCH) is set for antenna ports # 107 to # 110.

  As described above, when transmitting data using TM equivalent to TM3 / 4, the assignment control unit 104 selects up to four antenna ports from among these antenna ports as assignment destinations of PDSCH. When a PDSCH assignment destination is selected from antenna ports # 15 to # 22, CSI-RS can be used for channel estimation.

  When transmitting data using a TM equivalent to TM3 / 4, the transmission control unit 102 uses the latest RI or PMI fed back from the wireless terminal (for example, the wireless terminal 201) to which the RB is assigned by the assignment control unit 104. Apply precoding to the BB signal. For example, RI is used to make the setting equivalent to TM3, and RI and PMI are used to make the setting equivalent to TM4 (see setting contents 303 and 304 in FIG. 3).

  When transmitting data with TM3 / 4 equivalent TM by the above method, the RB allocation method of TM3 / 4 can be diverted and the CSI feedback of TM9 / 10 can be used, so TM3 / 4 can be created without designing a new signal. A considerable TM can be realized. Then, in a subframe where DMRS and PSS / SSS collide, data transmission equivalent to TM3 / 4 by the TM9 / 10 terminal becomes possible, and improvement in throughput can be expected.

(Function of wireless terminal 201)
In order to realize the data transmission equivalent to TM3 / 4 described above, the wireless terminal 201 has a function as shown in FIG. FIG. 10 is a block diagram showing an example of functions of the wireless terminal according to the second embodiment.

  As illustrated in FIG. 10, the wireless terminal 201 includes a storage unit 211, a reception control unit 212, a mode recognition unit 213, and a decoding processing unit 214. The function of the storage unit 211 can be realized, for example, by the memory 201 e described above. The functions of the reception control unit 212, the mode recognition unit 213, and the decoding processing unit 214 can be mainly realized by the CPU 201d.

  The storage unit 211 stores mapping information 211 a. The mapping information 211a is information on resource block mapping for each subframe (see FIG. 7). The reception control unit 212 performs reception control according to the TM. For example, in the case of TM9 / 10, the reception control unit 212 receives the DMRS based on the mapping information 211a.

The mode recognition unit 213 recognizes that data transmission using TM corresponding to TM3 / 4 is being performed.
For example, the mode recognition unit 213 refers to the mapping information 211 a and specifies a subframe in which PSS / SSS is to be transmitted. Further, when the PDSCH addressed to the wireless terminal 201 is allocated to the center 6 RBs of the system band for the identified subframe, the mode recognition unit 213 recognizes that the DMRS is not transmitted in the corresponding RB. Further, the mode recognition unit 213 recognizes that data transmission with TM equivalent to TM3 / 4 is performed, and autonomously switches TM from TM9 / 10 to TM3 / 4 equivalent.

  When the TM is switched to TM3 / 4 equivalent, the reception control unit 212 receives CSRS or CSI-RS of four antenna ports preset as an allocation destination of PDSCH in the TM equivalent to TM3 / 4. For example, in the case of antenna ports # 0 to # 3, CSRS is received, and in the case of antenna ports # 15 to # 18, CSI-RS is received.

  When the TM is equivalent to TM3 / 4, the decoding processing unit 214 calculates a channel matrix by channel estimation based on CSRS or CSI-RS. Also, the decoding processing unit 214 calculates the reception weight based on the latest RI and PMI fed back to the base station 100. For example, RI is used to make the setting equivalent to TM3, and RI and PMI are used to make the setting equivalent to TM4 (see setting contents 303 and 304 in FIG. 3). Also, the decoding processing unit 214 decodes the data to be transmitted on the PDSCH using the above-mentioned reception weight.

The mode recognition unit 213 switches the TM to TM9 / 10 in the next subframe of the subframe in which the PSS / SSS collides with the DMRS.
For example, as shown in FIG. 8, the mode recognition unit 213 switches the TM from the equivalent of TM3 / 4 to TM9 / 10 when transitioning from subframe # 0 to subframe # 1. Also, the mode recognition unit 213 switches TM from TM9 / 10 to TM3 / 4 equivalent when transitioning from subframe # 4 to subframe # 5. Similarly, mode transition section 213 autonomously performs switching of TM when transitioning from subframe # 9 to subframe # 0 of the next frame when transitioning from subframe # 5 to subframe # 6. .

  When transmitting data with TM3 / 4 equivalent TM by the above method, the RB allocation method of TM3 / 4 can be diverted and the CSI feedback of TM9 / 10 can be used, so TM3 / 4 can be created without designing a new signal. A considerable TM can be realized. Then, in a subframe where DMRS and PSS / SSS collide, data transmission equivalent to TM3 / 4 by the TM9 / 10 terminal becomes possible, and improvement in throughput can be expected.

The functions of the base station 100 and the wireless terminal 201 have been described above.
As described above, in the second embodiment, the radio resource is effectively used by the base station 100 and the radio terminal 201 autonomously switching the TM without performing special signaling. Therefore, it is possible to avoid complicated work such as formulation of a new signal and system complication, and it is possible to improve the throughput characteristics of TM 9/10 with a simple method.

[2-3. Processing flow]
Next, the flow of processing by the base station 100 and the wireless terminal 201 will be described.
(Processing by base station 100)
A flow of processing by the base station 100 transmitting data by TM 9/10 will be described with reference to FIG. FIG. 11 is a flow diagram showing a flow of processing by the base station according to the second embodiment.

(S101) The collision detection unit 103 refers to the mapping information 101a, and determines whether or not there is PSS / SSS transmission in the current subframe (current SF).
If there is PSS / SSS transmission in the current subframe, the process proceeds to S102. On the other hand, when there is no PSS / SSS transmission in the current subframe, the process proceeds to S106. That is, the collision detection unit 103 autonomously switches processing according to the type of signal mapped to a subframe, without using signaling between the base station 100 and the wireless terminal 201.

  (S102) The allocation control unit 104 selects six RBs having the lowest rank (RANK) at the center of the system band among the candidates for the wireless terminal (the current SF assignment candidate) to be assigned to the current subframe (S102). Allocated to the center 6 RBs of the system band: allocated RBs). For example, the assignment control unit 104 selects a wireless terminal to be assigned to the center 6 RBs of the system band based on the latest RI fed back from the assignment candidate of the current SF.

  As will be described later, in the current subframe where there is a PSS / SSS transmission, data is transmitted using a TM corresponding to TM3 / 4. Therefore, data transmission in the current subframe has a limitation that the maximum number of layers is 4, etc., which is a disadvantage as compared to other subframes which can transmit data without limitation by TM9 / 10. In consideration of such circumstances, a method of assigning a wireless terminal with a low rank to a current subframe with PSS / SSS transmission and preferentially assigning a wireless terminal with a high rank to subframes that can transmit data with TM 9/10 It is adopted.

(S103) The assignment control unit 104 cancels the mapping of the DMRS to the assigned RB. Then, the transmission control unit 102 cancels the transmission of DMRS in the current subframe.
(S104) The transmission control unit 102 performs precoding on the PDSCH of the allocation RB based on the latest RI and PMI fed back from the wireless terminal (the allocation-destination wireless terminal) allocated to the current subframe.

  (S105) The assignment control unit 104 assigns a PDSCH to antenna ports less than or equal to the maximum number of antenna ports (4 ports) defined by TM3 / 4 (PDSCH resource mapping). For example, the assignment control unit 104 assigns PDSCH to antenna ports # 0 to # 3 or antenna ports # 15 to # 18. When the process of S105 is completed, the series of processes shown in FIG.

  The processing of S103 to S105 is equivalent to TM3 / 4. That is, when there is PSS / SSS transmission in the current subframe, the collision detection unit 103 switches TM from TM9 / 10 to TM3 / 4 equivalent. Then, resource allocation equivalent to TM3 / 4 is performed as in S103 to S105.

  (S106) The assignment control unit 104 performs PDSCH assignment in the processing normally performed by TM9 / 10. When PSS / SSS is not transmitted in the current subframe, a collision between PSS / SSS and DMRS does not occur, so that DMRS can be transmitted, and decoding of PDSCH based on the result of channel estimation by DMRS is possible. Therefore, PDSCH is allocated as usual, and data transmission with TM9 / 10 is performed. When the process of S106 is completed, the series of processes shown in FIG.

(Processing by wireless terminal 201)
Next, the flow of processing by the wireless terminal 201 that receives data in TM9 / 10 will be described with reference to FIG. FIG. 12 is a flow diagram showing the flow of processing by the wireless terminal according to the second embodiment.

  (S201, S202) The decoding processing unit 204 decodes the PDCCH. Then, the decoding processing unit 204 determines whether or not there is an RB addressed to the own terminal (wireless terminal 201) in the current subframe (current SF). If there is an RB addressed to the own terminal, the process proceeds to S203. On the other hand, when there is no RB addressed to the own terminal, the series of processing shown in FIG. 12 ends.

(S203) The mode recognition unit 213 refers to the mapping information 211a and determines whether PSS / SSS is transmitted in the current subframe (current SF).
If there is PSS / SSS transmission in the current subframe, the process proceeds to S204. On the other hand, when there is no PSS / SSS transmission in the current subframe, the process proceeds to S209. That is, without using signaling between the base station 100 and the wireless terminal 201, the mode recognition unit 213 autonomously switches processing according to the type of signal mapped to a subframe.

  (S204) The mode recognition unit 213 determines whether the PDSCH addressed to the own terminal (the wireless terminal 201) is in the center 6 RBs of the system band. If the PDSCH addressed to the own terminal is in the center 6 RBs of the system band, the process proceeds to S205. On the other hand, when the PDSCH addressed to the own terminal is not in the center 6 RBs of the system band, the process proceeds to S209.

  (S205, S206) The mode recognition unit 213 recognizes that the DMRS is not transmitted in the allocation RB (an RB to which the wireless terminal 201 is allocated). Also, the mode recognition unit 213 recognizes that data transmission equivalent to TM3 / 4 is performed for the allocation RB, and recognizes that the maximum number of antenna ports of the allocation RB is 4 (maximum antenna port number of TM3 / 4). .

  (S207, S208) The decoding processing unit 204 calculates a channel matrix by channel estimation based on CSRS or CSI-RS (received CSRS / CSI-RS) received in the current subframe. Also, the decoding processing unit 204 performs decoding of the PDSCH in up to four layers using the calculated channel matrix. When the process of S208 is completed, the series of processes shown in FIG.

  The processing of S207 and S208 is mainly equivalent to TM3 / 4. That is, when there is PSS / SSS transmission in the current subframe, the mode recognition unit 213 switches TM from TM9 / 10 to TM3 / 4 equivalent. Then, as in S207 and S208, a decoding process equivalent to TM3 / 4 is performed.

  (S209) The decoding processing unit 204 performs PDSCH decoding in the processing that is normally performed in TM9 / 10. When PSS / SSS is not transmitted in the current subframe, a collision between the PSS / SSS and the DMRS does not occur, so that the DMRS can be received, and the PDSCH can be decoded based on the result of channel estimation by the DMRS. When the process of S209 is completed, the series of processes shown in FIG.

The flow of processing by the base station 100 and the wireless terminal 201 has been described above.
If the above method is applied, the TM3 / 4 RB allocation method can be diverted when transmitting data with TM3 / 4 equivalent TM, and the TM9 / 10 CSI feedback can also be used, so that new signals are formulated etc. It is not necessary. Also, data transmission equivalent to TM3 / 4 by the TM9 / 10 terminal becomes possible in subframes in which DMRS and PSS / SSS collide, and improvement in throughput can be expected.

The second embodiment has been described above.
In addition, although TM3 / 4 and TM9 / 10 were demonstrated to the example for convenience of explanation, the application range of the technique which concerns on 2nd Embodiment is not limited to the kind of TM mentioned above, or LTE specification.

  According to the second embodiment, for example, when there are a plurality of TMs transmitted in different RBs with reference signals used to decode data, the reference signals of some of the TMs are defined signals (such as periodically transmitted signals). In the case of a collision, it is possible to realize a mechanism in which the transmitting and receiving sides autonomously switch the TM with reference to the RB map. That is, the technology according to the second embodiment can be widely applied not only to the LTE standard, TM3 / 4, and TM9 / 10, but also to a radio communication system that transmits a plurality of decoding signals with different radio resources. Naturally, such an application example also belongs to the technical scope of the second embodiment.

<3. Appendices>
The following appendices will be further disclosed regarding the embodiment described above.
(Supplementary Note 1) A transmitter capable of transmitting a first reference signal used in the first communication mode,
A second communication mode using a second reference signal with a radio resource different from the first reference signal when the first reference signal and another signal may collide in a radio resource allocated to a wireless terminal And a control unit for switching to the base station.

(Supplementary Note 2) The base station according to Supplementary Note 1, wherein the control unit controls the transmission unit to suppress transmission of the first reference signal when switching to the second communication mode.

(Supplementary Note 3) The control unit limits the maximum number of antenna ports used for downlink data transmission to the number of antenna ports available in the second communication mode when switching to the second communication mode. The base station according to 2.

(Supplementary Note 4) The base station according to any one of Supplementary notes 1 to 3, wherein the information on the position of the radio resource to which the first reference signal is transmitted is held by both the base station and the radio terminal.

(Supplementary Note 5) The first reference signal is a reference signal specific to the wireless terminal,
The base station according to any one of appendices 1 to 4, wherein the second reference signal is a reference signal specific to a cell managed by the base station.

(Supplementary Note 6) A receiver capable of receiving a first reference signal used in the first communication mode,
A second communication mode using a second reference signal with a radio resource different from the first reference signal when the first reference signal and another signal can collide in a radio resource allocated to the own terminal And a control unit for switching to a wireless terminal.

(Supplementary Note 7) In a radio resource allocated to a wireless terminal, the base station is different from the first reference signal when the first reference signal used in the first communication mode may collide with another signal. Switching to a second communication mode using a second reference signal in radio resources;
A communication control method, wherein the wireless terminal switches to the second communication mode.

(Supplementary Note 8) The base station according to Supplementary note 1, wherein the control unit returns from the second communication mode to the first communication mode in a section in which the first reference signal and the other signal do not collide.

(Supplementary Note 9) The wireless terminal according to Supplementary note 6, wherein the control unit returns from the second communication mode to the first communication mode in a section in which the first reference signal and the other signal do not collide.

(Supplementary note 10) The base station and the wireless terminal return from the second communication mode to the first communication mode in a section in which the first reference signal and the other signal do not collide. Communication control method.

(Supplementary note 11) The base station according to supplementary note 1, wherein the control unit controls the transmission unit to transmit decodable downlink data based on the second reference signal.

(Supplementary note 12) The first reference signal is transmitted after performing precoding.
The base station according to appendix 1, wherein the second reference signal is transmitted without the precoding.

(Supplementary note 13) The base station according to supplementary note 1, wherein the number of streams that can be simultaneously transmitted in the first communication mode is larger than the number of streams that can be simultaneously transmitted in the second communication mode.

(Supplementary Note 14) The control unit, when switching to the second communication mode, has a better reception condition among a plurality of wireless terminals that can be allocated to a section in which the first reference signal and the other signal may collide. The base station according to appendix 11, wherein a radio terminal to be assigned to the section is selected in order of absence, and the downlink data is transmitted to the selected radio terminal.

5 wireless communication system 10 base station 11 antenna group 12 transmitting unit 13 control unit 20 wireless terminal 21 antenna 31 first communication mode 32 second communication mode 41 first reference signal 42 second reference signal 43 other signal

Claims (7)

A transmitter capable of transmitting a first reference signal used in the first communication mode;
A second communication mode using a second reference signal with a radio resource different from the first reference signal when the first reference signal and another signal may collide in a radio resource allocated to a wireless terminal And a control unit for switching to the base station. The base station according to claim 1, wherein the control unit controls the transmission unit to suppress transmission of the first reference signal when switching to the second communication mode. The control unit, when switched to the second communication mode, limits the maximum number of antenna ports used for downlink data transmission to the number of antenna ports available in the second communication mode. Base station. The base station according to any one of claims 1 to 3, wherein the information on the position of the radio resource to which the first reference signal is transmitted is held by both the base station and the radio terminal. The first reference signal is a reference signal specific to the wireless terminal,
The base station according to any one of claims 1 to 4, wherein the second reference signal is a reference signal specific to a cell managed by the base station. A receiver capable of receiving a first reference signal used in the first communication mode;
A second communication mode using a second reference signal with a radio resource different from the first reference signal when the first reference signal and another signal can collide in a radio resource allocated to the own terminal And a control unit for switching to a wireless terminal. In the radio resource allocated to the wireless terminal, if the base station may collide with the first reference signal used in the first communication mode and another signal, the first reference signal may be transmitted using a different radio resource than the first reference signal. Switch to the second communication mode using the second reference signal,
A communication control method, wherein the wireless terminal switches to the second communication mode.

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