JP2018182575A - Wireless base station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio base station capable of acquiring sufficient diversity gain even when beamforming is applied in a physical downlink control channel for machine-type communication. SOLUTION: The eNB 100 has an index acquisition unit 170 that acquires the PMI of the optimum precoding vector applied to the MPDCCH and the corresponding PDSCH from a plurality of user devices, and precoding applied to the MPDCCH from the acquired plurality of PMIs. It includes a precoding unit 120 that determines a vector and applies the determined precoding vector to the MPDCCH, and a radio signal transmission / reception unit 140 that transmits the MPDCCH on which the precoding has been executed. [Selection diagram] Fig. 3

Description

  The present invention relates to a radio base station that transmits a physical downlink control channel for machine-type communication.

  The 3rd Generation Partnership Project (3GPP) has specified Long Term Evolution (LTE) and specified LTE-Advanced (hereinafter referred to as LTE including LTE-Advanced) in order to further accelerate LTE. Further, in 3GPP, a specification of a successor system of LTE called 5G New Radio (NR) or the like is further studied.

  In Release 13 or later of LTE, categories for inexpensive terminals (user apparatuses) such as Internet of Things (IoT) modules are defined. Specifically, categories M1 and M2 (hereinafter, Cat. M) are specified for the bandwidth reduced low complexity UE (BL UE).

  As Cat.M has limited available physical resource blocks (PRBs), physical downlink control for machine type communication as a new physical downlink control channel for machine type communication (MTC) A channel (MPDCCH) is defined (for example, Non-Patent Document 1).

  For MPDCCH, user equipment (UE) specific demodulation reference signal (DM RS) is set. That is, in MPDCCH, demodulation is performed using DM RS, so that beam forming can be applied to UEs (BL UEs) individually.

3GPP TS 36.300 V 14.2.0 Section 5.1.3 Physical downlink control channels, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 14), 3GPP, March 2017

  As described above, in MPDCCH, it is possible to apply beamforming to each UE. However, Cat.M is different from the conventional category in the number of PRBs (up to 6 PRBs, in the case of Cat.M1) and the scheduling method of the UE.

  Furthermore, in Cat.M, coverage extension (CE) may be applied to which Repetition for repeatedly transmitting the same data and frequency hopping are applied.

  For this reason, it is necessary to apply beamforming so that sufficient diversity gain can be obtained while taking into consideration such special situations.

  Therefore, the present invention has been made in view of such a situation, and it is an object of the present invention to provide a radio base station capable of acquiring sufficient diversity gain even when beamforming is applied to a physical downlink control channel for machine type communication. I assume.

  One aspect of the present invention is a radio base station (eNB 100) for transmitting a physical downlink control channel (MPDCCH) for machine type communication to a user apparatus (UE 200A, 200B), wherein the physical downlink control channel for machine type communication And an index acquisition unit (index acquisition unit 170) for acquiring an index (PMI) of an optimal precoding vector applied to the corresponding physical downlink shared channel (PDSCH) from the plurality of user apparatuses, and the index acquisition unit The precoding vector to be applied to the physical downlink control channel for machine type communication is determined using the plurality of acquired indexes, and the determined precoding vector is used as the physical downlink control channel for machine type communication. A precoding unit (precoding unit 120) to be applied; Comprising a radio transmitter for transmitting the machine type communication for the physical downlink control channel recoding has been performed and (radio signal transceiver 140).

  One aspect of the present invention is a radio base station that transmits a physical downlink control channel for machine type communication to a user apparatus, and is applied to the physical downlink shared channel corresponding to the physical downlink control channel for machine type communication. Acquiring an index acquisition unit that acquires an index of the optimal precoding vector from the plurality of user devices, and assist information used to correct the index acquired by the index acquisition unit according to a communication state The physical downlink for the machine type communication based on the assist information acquisition unit (assist information acquisition unit 180), the index acquired by the index acquisition unit, and the assist information acquired by the assist information acquisition unit The precody applied to the control channel It includes a precoding unit configured to determine a Gubekutoru, and a radio transmitting unit that transmits the machine type communication for the physical downlink control channel precoding is performed.

  According to the above-described radio base station, sufficient diversity gain can be obtained even when beamforming is applied to the physical downlink control channel for machine type communication.

FIG. 1 is an overall schematic configuration diagram of a wireless communication system 10. FIG. 2 is a diagram showing an example of the configuration of the physical downlink channel. FIG. 3 is a functional block configuration diagram of the eNB 100. FIG. 4 is a diagram showing a beamforming operation flow by the eNB 100. FIG. 5 is a diagram showing an operation flow of changing a precoding vector by the eNB 100. FIGS. 6A and 6B are diagrams showing an adjustment operation image of the phase rotation amount of the precoding vector by the eNB 100. FIG. FIG. 7 is a diagram illustrating an example of a hardware configuration of the eNB 100.

  Hereinafter, embodiments will be described based on the drawings. In addition, the same or similar reference numerals are given to the same functions or configurations, and the description thereof is appropriately omitted.

(1) Overall Schematic Configuration of Wireless Communication System FIG. 1 is an overall schematic configuration diagram of a wireless communication system 10 according to the present embodiment. The radio communication system 10 is a radio communication system according to Long Term Evolution (LTE), and includes a radio base station 100 (hereinafter, eNB 100) and user apparatuses 200A, 200B (hereinafter, UE 200A, 200B).

  The wireless communication system 10 is not necessarily limited to LTE (E-UTRA). For example, the wireless communication system 10 may be a wireless communication system according to 5G New Radio (NR).

  The eNB 100, the UE 200A, and the UE 200B execute wireless communication according to the LTE (E-UTRA) scheme. In the present embodiment, the UE 200A and the UE 200B are bandwidth reduced low complexity UEs (BL UEs), and belong to Cat. M (specifically, the category M1).

  The eNB 100 transmits a physical downlink control channel (PDCCH) and a physical downlink control channel for machine-type communication (MPDCCH) and a physical downlink shared channel (PDSCH) to the UE 200A and the UE 200B.

  The eNB 100 performs precoding in which a different precoding vector (antenna weight) is multiplied and transmitted for each transmission layer (stream) of the PDSCH. As a result, the PDSCH transmitted from the eNB 100 has directivity by beamforming as indicated by the beam B1 and the beam B2.

  Also, in the present embodiment, the eNB 100 also performs precoding on the MPDCCH. Specifically, the eNB 100 notifies a reference signal for demodulation of the MPDCCH by means of a demodulation reference signal (DM RS) specific to the UE, and applies beamforming using the precoding vector to the MPDCCH.

  Furthermore, in the present embodiment, the eNB 100 may determine the precoding vector to be applied to the MPDCCH using the index of the precoding vector reported from the UE 200A (UE 200B), specifically, the Precoding Matrix Index (PMI). it can. That is, in this embodiment, beam forming is applied in MPDCCH using PMI fed back from a plurality of UEs (UEs 200A and 200B).

  FIG. 2 shows a configuration example of a physical downlink channel related to the present embodiment. As shown in FIG. 2, in the normal LTE UE category, channel scheduling is performed in the same subframe.

  On the other hand, as mentioned above, Cat.M is a category defined for low cost and low power consumption chips (terminals) such as MTC, and the transmittable / receivable bandwidth is up to 6 PRBs (physical resource blocks) ( A mass of 6 PRBs is called Narrowband). Therefore, the Cat. M UE can receive up to 6 PRBs (2 PRBs and 4 PRBs are also possible) and can not receive PDCCH.

  Therefore, MPDCCH is supported as a physical downlink control channel dedicated to Cat.M. That is, the eNB 100 transmits the MPDCCH using a predetermined number (up to 6 PRBs) of physical resource blocks.

  In Cat. M, as shown in FIG. 2, cross subframe scheduling in which MPDCCH is scheduled across subframes is applied. Furthermore, with MPDCCH, coverage extension (CE) is possible in which Repetition for repeatedly transmitting the same data and frequency hopping are applied.

  In Cat.M, single reception (1 Rx) is used, and only QPSK and 16 QAM are supported as modulation schemes. In addition, half duplex communication (Half duplex) is an option. With such a specification, Cat.M has a maximum throughput of 1 Mbps (also DL / UL).

(2) Functional Block Configuration of Wireless Communication System Next, a functional block configuration of the wireless communication system 10 will be described. Specifically, the functional block configuration of the eNB 100 will be described. FIG. 3 is a functional block configuration diagram of the eNB 100.

  As shown in FIG. 3, the eNB 100 includes a layer mapping unit 110, a precoding unit 120, a radio resource assignment unit 130, a radio signal transmission / reception unit 140, an antenna element 150, an index acquisition unit 170, and an assist information acquisition unit 180.

  The layer mapping unit 110 maps modulated transmission data (control data and user data) to one or several transmission layers.

  Specifically, the layer mapping unit 110 acquires modulated transmission data, and maps the transmission data on a predetermined transmission layer according to the number of antenna elements 150 to be used, the number of spatial multiplexing, and the like.

  The precoding unit 120 applies a precoding vector (antenna weight) to the block of channel data of PDCCH, MPDCCH and PDSCH output from the layer mapping unit 110 for each transmission layer. Specifically, precoding section 120 determines a precoding vector to be applied to MPDCCH using PMI reported from UE 200A (UE 200B).

  More specifically, the precoding unit 120 uses the PMI acquired by the index acquisition unit 170 to determine the precoding vector to be applied to the MPDCCH. Also, the precoding unit 120 applies the determined precoding to the MPDCCH.

  In addition, when MPDCCH and PDSCH are transmitted in different bands, different precoding may be applied to MPDCCH and PDSCH.

  Also, when the PMIs reported from a plurality of UEs (UEs 200A and 200B) multiplexed into the same PRB set are different, the precoding unit 120 applies a precoding vector different from the reported PMI to the MPDCCH.

  In addition, PMI is an index of the said matrix with which UE200A (UE200B) selects the optimal matrix from the candidates (codebook) of the precoding weight matrix decided beforehand, and it feeds back to eNB100.

  Also, the precoding vector is, for example, a Precoding Matrix defined in 3GPP TS 36.211 Table 6.3.4.2.3-1 etc., and the precoding unit 120 precodes a precoding vector (Precoding Matrix) for each PRB. It can apply.

The precoding unit 120 is configured to receive the precoding matrix (for example, W ₁ , W ₂ , W ₃ , W ₄ ), W ₁ , W ₂ , W ₃ , W _{4 with} a phase difference of 90 degrees, etc. Appropriate selection is made for each element 150.

  The precoding unit 120 may also determine a precoding vector to be applied to the MPDCCH based on not only the PMI but also the PMI acquired by the index acquisition unit 170 and the assist information acquired by the assist information acquisition unit 180. it can.

  In the present embodiment, as described later, the assist information is the Doppler frequency of the hybrid automatic retransmission request (HARQ), the intermittent transmission state (DTX), and the UE 200A (UE 200B).

  The precoding unit 120 can also determine a precoding vector to be applied to the MPDCCH based on channel quality information (Channel Quality Indicator (CQI)) notified from the UEs 200A and 200B.

  Specifically, the precoding unit 120 can apply, to the MPDCCH, a precoding vector corresponding to the PMI acquired from the UE with the highest CQI. That is, for the UE, when it is determined that the reported precoding vector is optimal and the UE is prioritized, application of such a precoding vector can be considered.

  Alternatively, the precoding unit 120 may apply the precoding vector corresponding to the PMI acquired from the UE with the lowest CQI to the MPDCCH. That is, for the UE, it is judged that minimum communication can be performed by using the reported precoding vector, and application of such precoding vector is performed when maintaining the current channel quality of the UE. Is considered.

  Furthermore, the precoding unit 120 may apply, to the MPDCCH, a precoding vector corresponding to the largest number of PMIs acquired from a plurality of UEs. Alternatively, the precoding unit 120 may apply, to the MPDCCH, a precoding vector corresponding to the average value of PMI acquired from a plurality of UEs. By applying such precoding vectors, a certain degree of fairness among multiple UEs can be maintained.

  Moreover, the precoding part 120 may apply the precoding vector selected at random to MPDCCH, when the predetermined time passes, after the index acquisition part 170 acquires PMI from UE200A (UE200B).

  Furthermore, when the acknowledgment (ACK) or negative acknowledgment (NACK) of HARQ is acquired by the assist information acquisition unit 180, the precoding unit 120 can maintain the precoding vector applied to the MPDCCH. On the other hand, precoding section 120 can change the precoding vector applied to MPDCCH, when it is acquired that UE 200A (UE 200B) is in the intermittent transmission state (DTX).

  Also, the precoding unit 120 may apply, to the MPDCCH, a new precoding vector obtained by rotating the phase of the precoding vector corresponding to the reported PMI. Furthermore, at this time, the precoding unit 120 may determine the amount of rotation of the phase of the precoding vector according to the Doppler frequency of the UE 200A (UE 200B) acquired by the assist information acquisition unit 180.

  The radio resource assignment unit 130 assigns blocks of channel data of PDCCH, MPDCCH and PDSCH output from the precoding unit 120 to a radio resource. In particular, in the present embodiment, the radio resource assignment unit 130 maps enhanced control channel elements (ECCEs) to the PRB with respect to the MPDCCH.

  The radio signal transmission / reception unit 140 transmits the PDCCH, the MPDCCH, and the PDSCH using the radio resource (PRB) allocated by the radio resource allocation unit 130. Specifically, the wireless signal transmission / reception unit 140 maps the channel data to an OFDM symbol, and generates an ODFM signal for each antenna port AP. In the present embodiment, the radio signal transmission / reception unit 140 configures a radio transmission unit that transmits the MPDCCH on which precoding has been performed.

  In particular, in the present embodiment, the radio signal transmission / reception unit 140 can transmit the MPDCCH using a predetermined number of PRBs for which precoding has been performed by the precoding unit 120. The antenna ports 107 and 109 defined in 3GPP TS 36.211 are used for MPDCCH transmission. An antenna element 150 is connected to the antenna port AP.

  That is, in MPDCCH, since antenna port AP is shared by multiple UEs, common precoding must be applied between the UEs. In addition, it is possible to apply different precoding between antenna ports AP or to change a precoding vector on a per PRB basis.

  The index acquisition unit 170 acquires PMI fed back from the UEs 200A and 200B. Specifically, the index acquisition unit 170 acquires PMI, which is the index of the optimal precoding vector to be applied to the PDSCH, from a plurality of UEs. As mentioned above, it is an index of the matrix concerned which UE chooses the optimal precoding weight matrix and feeds it back to eNB100.

  Also, as described above, in this embodiment, the precoding vector to be applied to the MPDCCH is determined using the PMI of the PDSCH. That is, the index acquisition unit 170 acquires PMI of the optimal precoding vector applied to the PDSCH corresponding to the MPDCCH from the UEs 200A and 200B.

  The assist information acquisition unit 180 acquires assist information that assists in the determination of the precoding vector to be applied to the MPDCCH. Specifically, the assist information acquisition unit 180 acquires assist information used to correct the PMI acquired by the index acquisition unit 170 according to the communication state. In other words, the assist information assists the correction according to the PMI communication state acquired by the index acquisition unit 170.

  In the present embodiment, the assist information acquisition unit 180 acquires the following information as the assist information.

  Specifically, the assist information acquisition unit 180 acquires ACK or NACK of PDSCH. That is, it is a target of HARQ of PDSCH, and the assist information acquisition part 180 acquires ACK or NACK of PDSCH from UE200A, 200B.

  In addition, the assist information acquisition unit 180 acquires from the UE 200A (UE 200B) that the UE 200A (UE 200B) is in the Discontinuous Transmission state (DTX) in which transmission of the physical uplink channel is stopped.

  Based on these pieces of assist information, it can be determined whether the UE 200A (UE 200B) has successfully received the MPDCCH.

  Furthermore, the assist information acquisition unit 180 can also acquire a precoding vector that has been applied to the PDSCH in the past. Further, the assist information acquisition unit 180 can also acquire the UE 200A (UE 200B) Doppler frequency. The Doppler frequency can be estimated, for example, from the reception state of sounding reference signals (SRS) or Physical Uplink Shared Channel (PUSCH) transmitted from the UE 200A (UE 200B).

(3) Operation of Radio Communication System Next, the operation of the radio communication system 10 will be described. Specifically, the application operation of the precoding vector to the MPDCCH will be described.

(3.1) Operation example 1
In this operation example, a method of determining a precoding vector to be applied to MPDCCH using PMI fed back from UEs 200A and 200B is shown.

  As described above, the eNB 100 selects an appropriate precoding vector to be applied to the MPDCCH based on the PMI fed back from the UEs 200A and 200B.

  Here, as a situation of UEs sharing the same MPDCCH, specifically, the same PRB set (for example, 6 PRBs) in the MPDCCH, the following case is assumed.

Case 1: Single MPDCCH utilization by one UE Case 2: MPDCCH sharing by multiple UEs in which the same PMI is optimal Case 3: MPDCCH sharing by multiple UEs in which the same PMI is not optimal Here, Case 1 and 2 May select an appropriate precoding vector to be applied to MPDCCH based on the PMI simply fed back.

  On the other hand, for Case 3, the following options can be considered regarding the choice of PMI used to apply the precoding vector.

-Option 1: Select the PMI of the highest CQI UE-Option 2: Select the PMI of the lowest CQI UE-Option 3: Select the PMI with the highest number of feedback-Option 4: Multiple feedback with multiple PMI Select a PMI close to the corresponding phase average
Option 1 may be selected when giving priority to the UE of good channel quality.

  Option 2 is determined to be able to perform the minimum communication with the current precoding vector, and can be selected when maintaining the current channel quality of the UE, that is, when continuing the communication of the UE. This is because changing to another PMI in this state is likely to make it difficult for the UE to continue communication.

  Options 3 and 4 can be selected when emphasizing a certain degree of fairness among multiple UEs.

  Next, selection of precoding vector using PMI and selection operation of precoding vector based on other criteria will be described.

  FIG. 4 shows a beamforming operation flow by the eNB 100. FIG. 4 assumes application to Case 1 and 2 described above.

  As shown in FIG. 4, the eNB 100 executes scheduling of the UE in the PDSCH (MPDSCH) (S10). Moreover, eNB100 maps the said UE to MPDCCH (PRB) based on the scheduling of UE in PDSCH (S20). Thereby, UE starts the communication using MPDCCH and PDSCH.

  Then, the eNB 100 determines whether PMI is fed back from the UEs 200A and 200B, and whether the state of the MPDCCH corresponds to Case 1 or Case 2 described above (S30).

When PMI is fed back and falls under Case 1 or Case 2, eNB 100 uses the PMI to apply precoding vectors (eg, W ₁ , W ₂ , W ₃ , W ₄ described above) to be applied to MPDCCH. To determine Furthermore, the eNB 100 applies the determined precoding vector to the MPDCCH to perform beam forming of the MPDCCH (S40).

  On the other hand, when PMI is not fed back and does not correspond to Case 1 or Case 2, eNB 100 performs beamforming of MPDCCH based on random precoding vector without performing beam forming of MPDCCH based on PMI. (S50).

  Specifically, the eNB 100 switches precoding vectors at predetermined timings based on a predetermined standard, without using information to be fed back in particular, or uses arbitrarily selected precoding vectors. Perform random beamforming of MPDCCH.

  The eNB 100 transmits the beamformed MPDCCH-modulated radio signal to the UEs 200A and 200B (S60).

  As shown in FIG. 4, eNB 100 performs beamforming of MPDCCH based on PMI, but eNB 100 may use fed back PMI if one or more of the following conditions are satisfied: Good.

-When PMI is set to be fed back-When PMI is common to the same PRB set that configures MPDCCH-When within the predetermined time after the latest PMI is fed back such conditions If not, the eNB 100 may perform random beamforming of MPDCCH as described above.

(3.2) Operation example 2
In this operation example, PMI fed back from the UEs 200A and 200B is not simply used, but assist information is also used to realize more appropriate beamforming according to the communication situation.

  As described above, the HARQ information (ACK / NACK) of PDSCH is used as the assist information. When the eNB 100 can not receive an ACK or NACK for the PDSCH designated by the MPDCCH from the UE, it can be assumed that the UE can not correctly receive the MPDCCH.

  FIG. 5 shows an operation flow of changing the precoding vector by the eNB 100. As shown in FIG. 5, the eNB 100 acquires PMI fed back from the UEs 200A and 200B (S110).

  The eNB 100 determines whether an ACK or NACK for the PDSCH is normally received from the UE (S120).

  If the ACK or NACK is successfully received, the eNB 100 does not change the precoding vector currently applied to the MPDCCH (S130). That is, the eNB 100 maintains the precoding vector currently applied to the MPDCCH.

  On the other hand, when the ACK or NACK can not be received normally, that is, when the DTX state is detected, the eNB 100 determines the change of the precoding vector currently applied to the MPDCCH (S140). Specifically, the eNB 100 corrects the precoding vector applied to MPDCCH, substantially PMI, by adding phase rotation to the precoding vector applied to MPDCCH in the past.

  That is, the eNB 100 determines to apply, to the MPDCCH, a new precoding vector obtained by rotating the phase of the precoding vector that has been applied to the MPDCCH in the past.

  The eNB 100 applies the new precoding vector to the MPDCCH to perform beam forming of the MPDCCH (S150).

  For example, if the PMI with 0 degree phase and the PMI with 90 degree phase have been received normally in the past, the eNB 100 changes to a PMI with 270 degree phase that is 180 degrees out of phase. In addition, when the PMI with the phase of 180 degrees and the PMI with the phase of 270 degrees have been received normally in the past, the eNB 100 changes the PMI of the phase of 0 degrees, which is 180 degrees out of phase.

  That is, the eNB 100 can change to a PMI that is neither the past PMI nor the latest PMI. Basically, the eNB 100 may use the latest PMI reported. The aim of such a PMI change is based on the PMI when it was successfully received in the past because the PMI applied is not optimal if the environment of the MPDCCH changes during the period when the PMI is not reported. By correcting the PMI, it is to get closer to the optimal PMI.

  Furthermore, the eNB 100 may adjust the phase rotation amount of the precoding vector according to the Doppler frequency of the UE 200A (UE 200B) when changing the PMI, that is, the precoding vector applied to the MPDCCH.

  Specifically, when it is determined that the moving speed of the UE is high based on the Doppler frequency, the eNB 100 sets the maximum phase rotation (180 degrees) for the UE. On the other hand, when it is determined that the moving speed is low, the eNB 100 makes a small phase rotation (90 degrees) for the UE.

  Also, even if such adjustment is performed, the eNB 100 may gradually decrease (or increase) the phase rotation amount of the precoding vector when the UE can not continue to receive the MPDCCH normally.

  FIGS. 6A and 6B show adjustment operation images of the phase rotation amount of the precoding vector by the eNB 100. FIG. Specifically, FIG. 6 (a) shows the phase of the applied precoding vector. FIG. 6 (b) shows a specific adjustment example of the phase rotation amount of the precoding vector.

As shown in FIG. 6A, here, four precoding vectors (antenna weights) of W ₁ (0 degrees), W ₂ (180 degrees), W ₃ (90 degrees), and W ₄ (270 degrees). Is used.

  In FIG. 6B, the horizontal axis represents time, and the vertical axis represents phase. The curve shown in FIG. 6 (b) indicates the phase of the optimal precoding vector (PMI) according to the movement state and position of the UE (here, UE 200A).

  As shown in FIG. 6 (b), the eNB 100 (not shown in FIG. 6 (b)) receives PMI fed back from the UE 200A (not shown in FIG. 6 (b)) (long dashed arrow in the figure) . The eNB 100 adjusts the precoding vector applied to the MPDCCH based on the received PMI (solid arrow in the figure).

Here, since the eNB 100 receives the PDSCH ACK / NACK, the eNB 100 determines that the UE 200A has successfully received the MPDCCH, and does not change the precoding vector (W ₃ ).

Then, with the transition of the optimal precoding vector for UE 200A indicated by the curve from W ₃ to W ₂ , UE 200A can not detect MPDCCH and is in the DTX state.

  When the eNB 100 detects the DTX state of the UE 200A, it determines to change the precoding vector. The eNB 100 recognizes that the optimal precoding vector according to the movement state and position of the UE 200A is a curve as shown in FIG. 6 (b) due to the Doppler frequency of the UE 200A and the like.

Thus, the eNB 100 changes the precoding vector applied to the MPDCCH to W ₂ (180 degrees).

After that, as time passes, the eNB 100 detects the DTX state of the UE 200A again, and changes the precoding vector applied to the MPDCCH to W ₁ (0 degrees). The eNB 100 repeats the adjustment operation of the phase rotation of such precoding vector.

(4) Operation and Effect According to the embodiment described above, the following operation and effect can be obtained. Specifically, the eNB 100 (precoding unit 120) determines the precoding vector to be applied to the MPDCCH using the PMI obtained from the UEs 200A and 200B, and applies the determined precoding vector to the MPDCCH.

  Therefore, when there is a high possibility that the UE has not successfully received the MPDCCH, changing the directions of the beams B1 and B2 (see FIG. 1) can increase the reception probability of the MPDCCH. Thus, even when beamforming is applied in MPDCCH, sufficient diversity gain can be obtained. Further, as a result, since the probability of successful reception of MPDCCH is improved, the communication quality can be greatly improved also for UEs having a limited communication capability, such as a Cat.M UE.

  Further, in the present embodiment, since feedback (PMI) from the UEs 200A and 200B is used, more accurate Closed-loop beamforming can be realized in MPDCCH.

  In the present embodiment, in addition to the PMI, assist information can be used to assist the matching between the PMI of the precoding vector applied to the MPDCCH and the PMI fed back from the UEs 200A and 200B. For this reason, it is possible to realize a more accurate Closed-loop beamforming.

  In this embodiment, the eNB 100 can apply the precoding vector corresponding to the PMI acquired from the UE with the highest CQI to the MPDCCH. According to such an operation, it is possible to prioritize the communication of the UE determined that the current precoding vector is optimal.

  Moreover, eNB100 can apply the precoding vector corresponding to PMI acquired from UE with the lowest CQI to MPDCCH. According to such an operation, the communication of the UE can be continued while maintaining the current channel quality of the UE determined to be able to perform the minimum communication by the current precoding vector.

  Furthermore, the eNB 100 can apply, to the MPDCCH, a precoding vector corresponding to the largest number of PMIs acquired from a plurality of UEs. Moreover, eNB100 can apply the precoding vector corresponding to the average value of PMI acquired from several UE to MPDCCH. According to such an operation, a certain degree of fairness among multiple UEs can be maintained.

  In the present embodiment, the eNB 100 can apply a randomly selected precoding vector to the MPDCCH when a predetermined time has elapsed since acquiring the PMI. That is, even if the precoding vector is determined using the old PMI when the predetermined time has elapsed, the optimum phase may change with the lapse of time, so the possibility that the UE can receive MPDCCH normally Is low. In such a case, by using a randomly selected precoding vector, the reception probability of MPDCCH can be increased.

  In this embodiment, the hybrid automatic retransmission request (HARQ), the intermittent transmission state (DTX), and the Doppler frequency of the UE can be used as assist information used to correct the acquired PMI according to the communication state.

  The assist information contributes to the determination of the actual communication state of the UE, and by using such assist information, more accurate Closed-loop beamforming can be realized.

(5) Other Embodiments The contents of the present invention have been described above according to the embodiments, but the present invention is not limited to these descriptions, and various modifications and improvements are possible. It is obvious to the trader.

  For example, in the embodiment described above, two antenna ports AP (107, 109) are used, but the number and number of antenna ports AP are not particularly limited. Furthermore, the above-described embodiment is not limited to precoding as defined in 3GPP TS 36.211 Table 6.3.4.2.3-1 as an example of Precoding Matrix.

  Further, the block configuration diagram (FIG. 3) used in the description of the embodiment described above shows functional blocks. These functional blocks (components) are realized by any combination of hardware and / or software. Moreover, the implementation means of each functional block is not particularly limited. That is, each functional block may be realized by one physically and / or logically coupled device, or directly and / or indirectly two or more physically and / or logically separated devices. It connects (for example, wired and / or wirelessly), and may be realized by a plurality of these devices.

  Furthermore, the eNB 100 described above may function as a computer that performs the process of the present invention. FIG. 7 is a diagram illustrating an example of a hardware configuration of the eNB 100. As shown in FIG. 7, the device may be configured as a computer device including a processor 1001, a memory 1002, a storage 1003, a communication device 1004, an input device 1005, an output device 1006, a bus 1007 and the like.

  Each functional block (see FIG. 3) of the eNB 100 is realized by any hardware element of the computer apparatus or a combination of the hardware elements.

  The processor 1001 operates, for example, an operating system to control the entire computer. The processor 1001 may be configured by a central processing unit (CPU) including an interface with a peripheral device, a control device, an arithmetic device, a register, and the like.

The memory 1002 is a computer readable recording medium, and may be, for example, a ROM (Read).
The memory may be configured of at least one of an Only Memory), an EPROM (Erasable Programmable ROM), an EEPROM (Electrically Erasable Programmable ROM), and a RAM (Random Access Memory). The memory 1002 may be called a register, a cache, a main memory (main storage device) or the like. The memory 1002 can store a program (program code) capable of executing the method according to the above-described embodiment, a software module, and the like.

  The storage 1003 is a computer readable recording medium, and for example, an optical disc such as a CD-ROM (Compact Disc ROM), a hard disc drive, a flexible disc, a magneto-optical disc (eg, a compact disc, a digital versatile disc, a Blu-ray A (registered trademark) disk, a smart card, a flash memory (for example, a card, a stick, a key drive), a floppy (registered trademark) disk, a magnetic strip, and the like may be used. The storage 1003 may be called an auxiliary storage device. The above-mentioned recording medium may be, for example, a database including the memory 1002 and / or the storage 1003, a server or other appropriate medium.

  The communication device 1004 is hardware (transmission / reception device) for performing communication between computers via a wired and / or wireless network, and is also called, for example, a network device, a network controller, a network card, a communication module, or the like.

  The input device 1005 is an input device (for example, a keyboard, a mouse, a microphone, a switch, a button, a sensor, and the like) that receives an input from the outside. The output device 1006 is an output device (for example, a display, a speaker, an LED lamp, etc.) that performs output to the outside. The input device 1005 and the output device 1006 may be integrated (for example, a touch panel).

  Also, each device such as the processor 1001 and the memory 1002 is connected by a bus 1007 for communicating information. The bus 1007 may be configured by a single bus or may be configured by different buses among the devices.

  In addition, notification of information is not limited to the above-described embodiment, and may be performed by another method. For example, notification of information may be physical layer signaling (for example, Downlink Control Information (DCI), Uplink Control Information (UCI)), upper layer signaling (for example, RRC signaling, MAC (Medium Access Control) signaling, broadcast information (MIB (for example)). Master Information Block), SIB (System Information Block), other signals, or a combination thereof, or RRC signaling may be referred to as an RRC message, eg, RRC Connection Setup message, RRC It may be a Connection Reconfiguration message or the like.

  Furthermore, the input / output information may be stored in a specific place (for example, a memory) or may be managed by a management table. Information to be input or output may be overwritten, updated or added. The output information may be deleted. The input information may be transmitted to another device.

  The sequences, flowcharts, and the like in the above-described embodiments may be rearranged as long as there is no contradiction.

  Also, in the embodiment described above, the specific operation performed by the eNB 100 may be performed by another network node (device). Moreover, the function of eNB100 may be provided by the combination of several other network nodes.

  The terms described in the present specification and / or the terms necessary for the understanding of the present specification may be replaced with terms having the same or similar meanings. For example, the channels and / or symbols may be signals, where relevant. Also, the signal may be a message. Also, the terms "system" and "network" may be used interchangeably.

  Furthermore, the parameter or the like may be represented by an absolute value, may be represented by a relative value from a predetermined value, or may be represented by another corresponding information. For example, radio resources may be indexed.

  The eNB 100 (base station) can accommodate one or more (eg, three) cells (also referred to as sectors). If the base station accommodates multiple cells, the entire coverage area of the base station can be divided into multiple smaller areas, each smaller area being a base station subsystem (eg, a small base station RRH for indoor use: Remote Communication service can also be provided by Radio Head.

  The terms "cell" or "sector" refer to a portion or all of the coverage area of a base station and / or a base station subsystem serving communication services in this coverage. Furthermore, the terms "base station" "eNB", "cell" and "sector" may be used interchangeably herein. A base station may also be called in terms of a fixed station (Node station), NodeB, eNodeB (eNB), gNodeB (gNB), access point (access point), femtocell, small cell, and so on.

  UEs 200A, 200B are subscriber stations, mobile units, subscriber units, wireless units, remote units, mobile units, wireless devices, wireless communication devices, remote devices, mobile subscriber stations, access terminals, mobile terminals, by those skilled in the art. It may also be called a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable term.

  As used herein, the phrase "based on" does not mean "based only on," unless expressly stated otherwise. In other words, the phrase "based on" means both "based only on" and "based at least on."

  Also, the terms "including," "comprising," and variations thereof are intended to be inclusive as well as "comprising." Furthermore, it is intended that the term "or" as used in the present specification or in the claims is not an exclusive OR.

  Any reference to an element using the designation "first," "second," etc. as used herein does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient way of distinguishing between two or more elements. Thus, reference to the first and second elements does not mean that only two elements can be taken there, or that in any way the first element must precede the second element.

  Throughout the present specification, when articles are added by translation, such as a, an, and the in English, for example, these articles are not clearly indicated by the context. , Including several things.

  While the embodiments of the present invention have been described above, it should not be understood that the statements and drawings that form a part of this disclosure limit the present invention. Various alternative embodiments, examples and operation techniques will be apparent to those skilled in the art from this disclosure.

10 Wireless Communication System
100 eNB
110 Layer Mapping Unit
120 precoding unit
130 Radio Resource Allocation Unit
140 Wireless Signal Transmitter / Receiver
150 antenna elements
170 Index Acquisition Department
180 Assist Information Acquisition Unit
AP antenna port
200A, 200B UE
B1, B2 beam

Claims (10)

A radio base station for transmitting a physical downlink control channel for machine type communication to a user apparatus, comprising:
An index acquisition unit that acquires an index of an optimal precoding vector applied to a physical downlink shared channel corresponding to the physical downlink control channel for machine type communication from a plurality of user apparatuses;
The precoding vector to be applied to the physical downlink control channel for machine type communication is determined using the plurality of indexes acquired by the index acquisition unit, and the determined precoding vector is used as the physical for the machine type communication. A precoding unit applied to the downlink control channel;
And a radio transmitting unit for transmitting the physical downlink control channel for machine communication in which precoding has been performed.   The radio base station according to claim 1, wherein the precoding unit applies a precoding vector corresponding to the index acquired from a user apparatus with the highest channel quality information to the physical downlink control channel for machine type communication.   The radio base station according to claim 1, wherein the precoding unit applies a precoding vector corresponding to the index acquired from a user apparatus with the lowest channel quality information to the physical downlink control channel for machine type communication.   The radio base station according to claim 1, wherein the precoding unit applies a precoding vector corresponding to the largest number of indexes acquired from the plurality of user apparatuses to the physical downlink control channel for machine type communication.   The radio base station according to claim 1, wherein the precoding unit applies a precoding vector corresponding to an average value of the indexes acquired from the plurality of user apparatuses to the physical downlink control channel for machine type communication.   The precoding unit applies a randomly selected precoding vector to the physical downlink control channel for machine-type communication when a predetermined time has elapsed since the index acquisition unit acquires the index from the user apparatus. The radio base station according to claim 1. A radio base station for transmitting a physical downlink control channel for machine type communication to a user apparatus, comprising:
An index acquisition unit that acquires an index of an optimal precoding vector applied to a physical downlink shared channel corresponding to the physical downlink control channel for machine type communication from a plurality of user apparatuses;
An assist information acquisition unit that acquires assist information used to correct the index acquired by the index acquisition unit according to a communication state;
A pre-decision for determining the precoding vector to be applied to the physical downlink control channel for machine type communication based on the index acquired by the index acquisition unit and the assist information acquired by the assist information acquisition unit A coding unit,
And a radio transmitting unit for transmitting the physical downlink control channel for machine communication in which precoding has been performed. The target of the hybrid automatic retransmission request of the physical downlink shared channel,
The assist information acquisition unit acquires, as the assist information, an acknowledgment or a negative response of the physical downlink shared channel or an intermittent transmission state of the user apparatus from the user apparatus.
The precoding unit
The precoding vector applied to the physical downlink control channel for machine type communication is maintained when the acknowledgment or the negative acknowledgment is acquired by the assist information acquisition unit,
The radio base station according to claim 7, wherein when the user apparatus is acquired in the intermittent transmission state, the precoding vector applied to the physical downlink control channel for machine type communication is changed. The assist information acquisition unit acquires, as the assist information, a precoding vector that has been applied to the physical downlink shared channel in the past,
The precoding unit according to claim 7, wherein the precoding unit applies a new precoding vector obtained by rotating the phase of the precoding vector acquired by the assist information acquisition unit to the physical downlink control channel for machine type communication. Wireless base station. The assist information acquisition unit acquires a Doppler frequency of the user device as the assist information,
The radio base station according to claim 9, wherein the precoding unit determines a rotation amount of the phase of the precoding vector according to the Doppler frequency acquired by the assist information acquisition unit.

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