JP2019087915A - Base station, wireless communication system, parameter updating method and program - Google Patents

Abstract

To suppress throughput reduction in beam switching between base stations.SOLUTION: A base station includes an offset notification unit for notifying a wireless quality offset value to a terminal for switching from a first beam to a second beam on the basis of first wireless quality of the first beam which is pre-coded and transmitted by a first base station, second wireless quality of the second beam which is pre-coded and transmitted by a second base station, and a wireless quality offset value used for determination when switching from the first beam to the second beam. The base station further includes an offset update unit for increasing/decreasing the wireless quality offset value depending on whether wireless quality of the first and second base stations after beam switching due to the wireless quality offset value received from the terminal is greater than respective predetermined thresholds or not.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a base station, a wireless communication system, a parameter updating method and program.

  BACKGROUND In recent years, data traffic of mobile communication has been rapidly increasing due to the spread of smartphones and tablet terminals, and the spread of services involving large-volume data exchange such as video viewing. As a countermeasure, in addition to the conventional 6 GHz band or less, a method of utilizing a high frequency band of 28 GHz band or more is attracting attention. By utilizing the high frequency band, the bandwidth can be expanded from several hundred MHz to several GHz, so that realization of a large capacity can be expected.

  However, in the high frequency band, the attenuation of radio waves is larger than in the low frequency band. In order to compensate for this rapid attenuation, Massive Multiple Input Multiple Output (MIMO) beamforming is performed in a base station provided with a large number of antenna elements (see Patent Document 1). Massive MIMO beamforming is a technology for forming a beam with a strong signal strength in a specific direction by adjusting and superimposing the amplitudes and phases of radio waves from each antenna element. Massive MIMO beamforming can form a large number of narrow area beams with a large beam gain, so that beam attenuation can be compensated by utilizing the beams.

  As described above, in a wireless communication system environment where high frequency band Massive MIMO beamforming is introduced, high throughput can be expected while securing coverage. However, in order to continuously maintain high throughput, it is necessary to keep track of the movement of the user and continue to select an appropriate beam having a large received power from among a large number of beams. Patent Document 1 discloses a mobile communication system in which a beam can efficiently be made to follow the movement of a user. The base station apparatus of the same document transmits to the user apparatus a beam stream including a plurality of beams corresponding to a plurality of channel measurement reference signals precoded to the user apparatus. On the other hand, the user apparatus receives the plurality of beams, selects a beam with the highest received power from them, and notifies the base station apparatus. At that time, it is considered that the user apparatus can efficiently perform the beam following by receiving not only the beam currently in use but also the beam candidate that may be used after movement. ing.

  Patent Document 2 discloses a carrier switching technique in a multicarrier access network. Further, Patent Document 3 discloses a radio telephone apparatus capable of controlling an activation threshold of base station switching according to a base station environment at a place to be used.

Patent No. 6121931 gazette JP-A-2010-533999 JP 2001-251657 A

  The following analysis is given by the present invention. The urban area is a typical environment in which Massive MIMO base stations (hereinafter simply referred to as base stations) are installed, and a large number of base stations are installed to accommodate a large amount of traffic. In such an environment, it is necessary not only to switch beams within the same base station but also to switch beams frequently between different base stations.

  When beam switching between base stations is performed based on the technology disclosed in Patent Document 1, there is a problem that throughput temporarily decreases. This is because switching to the beam of the adjacent base station is performed after the received power of the beam at the connected base station is greatly reduced. Conversely, throughput may be reduced due to premature beam switching. In the same base station, the beams are transmitted continuously at a constant angle, but between the base stations, the beams are often separated from each other compared to the base station due to the restriction of the installation location, which means that the received power It is the cause of the decline. In addition, since a handover processing delay occurs between the base stations, the same base station is continuously connected until the switching is completed, which also causes a decrease in received power. Throughput decreases temporarily due to the decrease in received power.

  An object of the present invention is to provide a base station, a wireless communication system, a parameter updating method, and a program base station that can contribute to suppression of throughput reduction in inter-base station beam switching.

  According to the first aspect, the first radio quality of the first beam precoding and transmitting by the first base station, and the second radio signal precoding and transmitting by the second base station For a terminal that switches from the first beam to the second beam using the wireless quality of 2 and the wireless quality offset value used for determination when switching from the first beam to the second beam, A base station is provided that includes an offset notification unit that notifies the wireless quality offset value. The base station further determines whether the radio quality of the first and second base stations after beam switching based on the radio quality offset value received from the terminal is greater than a predetermined threshold. It has an offset update unit that increases or decreases the value.

  According to the second aspect, the first radio quality of the first beam precoding and transmitting by the first base station, and the second radio beam precoding and transmitting by the second base station A terminal for switching from the first beam to the second beam using the wireless quality of 2 and a wireless quality offset value used for determination when switching from the first beam to the second beam; The offset notification unit that notifies the terminal of the wireless quality offset value, and the wireless quality of the first and second base stations after beam switching by the wireless quality offset value received from the terminal respectively have predetermined threshold values. And a base station including an offset update unit that increases or decreases the radio quality offset value depending on whether the base station is larger or not.

  According to the third aspect, the first radio quality of the first beam precoding and transmitting by the first base station, and the second radio beam precoding and transmitting by the second base station For a terminal that switches from the first beam to the second beam using the wireless quality of 2 and the wireless quality offset value used for determination when switching from the first beam to the second beam, The radio quality offset value is notified, and the radio quality of the first and second base stations after beam switching according to the radio quality offset value received from the terminal is greater than a predetermined threshold. A parameter update method is provided to increase or decrease the wireless quality offset value. The method is tied to a particular machine, the base station, which informs the terminal of the radio quality offset value to use in the determination when switching from the first beam to the second beam.

  According to the fourth aspect, the first radio quality of the first beam transmitted by the first base station by precoding and the second radio signal transmitted by the second base station by the precoding For a terminal that switches from the first beam to the second beam using the wireless quality of 2 and the wireless quality offset value used for determination when switching from the first beam to the second beam, Depending on whether the wireless quality of the first and second base stations after beam switching according to the process of notifying the wireless quality offset value and the beam switching by the wireless quality offset value received from the terminal is greater than a predetermined threshold. A program is provided which causes a computer mounted on the first base station or the second base station to execute the process of increasing or decreasing the wireless quality offset value. Note that this program can be recorded on a computer readable (non-transitory) storage medium. That is, the present invention can also be embodied as a computer program product.

  According to the present invention, it is possible to suppress a decrease in throughput in inter-base station beam switching.

It is a figure which shows the structure of one Embodiment of this invention. It is a figure for demonstrating the operation | movement of one Embodiment of this invention. FIG. 6 is another diagram for explaining the operation of an embodiment of the present invention. It is a figure for demonstrating the structure and operation | movement of the radio | wireless communications system of the 1st Embodiment of this invention. It is a functional block diagram showing composition of a base station of a 1st embodiment of the present invention. It is a functional block diagram showing composition of a terminal of a 1st embodiment of the present invention. It is a flow chart showing operation of a terminal of a 1st embodiment of the present invention. It is a flow chart showing operation of a base station of a 1st embodiment of the present invention. It is a sequence diagram showing the whole operation of the radio communications system of a 1st embodiment of the present invention. It is a figure for demonstrating the update process (increase / decrease process) of the offset value in the base station of the 1st Embodiment of this invention. It is a flow chart showing operation of a base station of a 2nd embodiment of the present invention. It is a figure which shows the structure of the computer mounted in the base station of this invention.

  First, an outline of an embodiment of the present invention will be described with reference to the drawings. The reference numerals of the drawings appended to this summary are added for convenience to the respective elements as an example for aiding understanding, and the present invention is not intended to be limited to the illustrated embodiments. In addition, connection lines between blocks such as drawings referred to in the following description include both bidirectional and unidirectional directions. The unidirectional arrows schematically indicate the flow of main signals (data), and do not exclude bidirectionality.

  The present invention, in one embodiment, can be realized by a configuration including a base station 100a and a terminal 200a, as shown in FIG. More specifically, the terminal 200a transmits the first radio quality of the first beam that the first base station precodes and transmits, and the second beam that the second base station precodes and transmits A function of switching from the first beam to the second beam using the second wireless quality and the wireless quality offset value used for determination when switching from the first beam to the second beam; And a function of reporting, to the base station 100a, the wireless quality of the first and second base stations after beam switching by the wireless quality offset value.

  On the other hand, the base station 100a includes an offset notification unit 101a and an offset update unit 102a. Then, the offset notification unit 101a notifies the terminal 200a of the wireless quality offset value. Also, the offset update unit 102a determines whether the wireless quality of the first and second base stations after beam switching according to the wireless quality offset value received from the terminal 200a is greater than a predetermined threshold. Increase or decrease the wireless quality offset value.

  For example, when the switching from the beam of the first base station B1 to the beam of the second base station B2 is delayed, the terminal 200a performs the first and second base stations at the completion of the beam switching process of FIG. Report the wireless quality of B1 and B2. In this case, since the radio quality B1 of the first base station is lower than the predetermined threshold, the base station 100a determines that the switching is delayed, adds the predetermined value β1 to the offset value ΔP, and adds ΔP to the terminal 200a. Notice. Thereafter, since the terminal 200a determines that wireless quality B1 <wireless quality B2 + (ΔP + β1), switching timing is advanced, and as a result, beam switching is performed at an appropriate timing.

  Similarly, for example, when the beam from the first base station B1 is switched to the beam from the second base station B2 too early, the terminal 200a performs the first and second at the completion of the beam switching process of FIG. The radio quality of the base stations B1 and B2 of In this case, since the radio quality B2 of the second base station is lower than the predetermined threshold, the base station 100a determines that switching is premature, and subtracts the predetermined value β2 from the offset value ΔP, To notify. Thereafter, since the terminal 200a determines that wireless quality B1 <wireless quality B2 + (ΔP−β2), the switching timing is delayed, and as a result, beam switching is performed at an appropriate timing.

  Note that different values may be set for the first base station and the second base station as the threshold. Further, the values β1 and β2 to be added to or subtracted from the offset value ΔP may be the same value or different values. Further, instead of adding and subtracting the values β1 and β2, the offset value ΔP may be multiplied by a predetermined coefficient to increase or decrease the offset value ΔP.

First Embodiment
Subsequently, a first embodiment of the present invention will be described in detail with reference to the drawings. In the following description, in each drawing, the same reference numeral is given to the same element, and the repeated explanation is omitted except for the case of being necessary for the clarification of the explanation. In the following description, “A and / or B” is used to mean at least one of A and B.

  In this embodiment, the offset value used in inter-base station beam switching based on the received power of each beam and the offset value is updated. Specifically, the offset value is updated by comparing the received power in the latest beam switching using the statistical value of the received power in the past beam switching as a threshold. The updated offset value is used in beam switching to be performed later.

  FIG. 4 is a diagram for explaining the configuration and operation of the wireless communication system of the first embodiment of the present invention. The lower part of FIG. 4 shows the configuration of the wireless communication system according to the first embodiment of the present invention. In the present embodiment, the case where Long Term Evolution (LTE) / LTE-Advanced is applied as a wireless communication system will be described. The wireless communication system according to the present embodiment transmits and receives Massvie MIMO base station apparatuses 1-1 and 1-2 which transmit and receive in a high frequency band (for example, 28 GHz band) and several hundred antenna elements, and a terminal apparatus 2. It comprises. Hereinafter, the Massvie MIMO base station apparatus will be simply referred to as a "base station apparatus", and in particular, when the base station apparatuses 1-1 and 1-2 are not distinguished from one another, they will be referred to as a "base station apparatus 1". In FIG. 4, as an example, the case where there are two base station apparatuses 1 and one terminal apparatus 2 is illustrated. Each base station apparatus 1 performs beamforming toward a specific area by performing predetermined precoding on a beam reference signal.

  As shown in the middle part of FIG. 4, the base station apparatus 1 transmits beam reference signals beamformed in the horizontal direction and the vertical direction toward the respective front areas. The terminal device 2 is a device that communicates with the base station device 1. When the terminal device 2 moves the cover area of the base station apparatus 1 as shown in FIG. 4 (arrow in FIG. 4), the terminal device 2 selects a specific beam as it moves (a beam drawn in bold in FIG. 4) ).

  The upper chart in FIG. 4 shows an example of transition of received power while the terminal device 2 is moving. However, in FIG. 4, it is set as the reception power which emphasized the beam gain of each beam. As shown in FIG. 4, as the terminal device 2 moves, a beam with the largest received power is selected. The numbers of base station apparatuses 1 and terminal apparatuses 2 in FIG. 4 are merely an example, and the present invention is not limited to FIG. 4.

  FIG. 5 is a block diagram showing the configuration of the base station device 1 in the wireless communication system of the first embodiment of the present invention. The base station apparatus 1 includes an RF transmission / reception unit 101, a digital signal processing unit 102, a resource assignment unit 103, a base station wired transmission / reception unit 104, a channel estimation unit 105, an offset setting unit 106, and a beam switching unit 107. In addition, since the structure of all the base station apparatuses is the same, the description about the structure of the other base station apparatus 1 is abbreviate | omitted.

The RF transmission / reception unit 101 is connected to _NT (for example, 128) antenna elements, and in wireless communication with the terminal device 2, basic functions of wireless transmission / reception as a base station device in a general wireless communication system are provided. Prepare. Examples of this basic function include the following functions.
1) Transmission of downlink reference signals (beam RS (Reference Signal), cell-specific RS, etc.), downlink control signals (PDCCH: Physical Downlink Control CHannel, etc.) and downlink data signals (PDSCH: Physical Downlink Shared CHannel, etc.) function,
2) Reception functions for uplink reference signals (SRS: Sounding Reference Signal etc.), uplink control signals (PUCCH: Physical Uplink Control CHannel) and uplink data signals (PUSCH: Physical Uplink Shared CHannel),
3) Adjust the phase and amplitude of radio waves from each antenna element so that radio waves are concentrated and transmitted in a predetermined direction (horizontal and vertical directions) at a fixed interval (for example, 15 degrees). Analog beamforming function by overlaying.
The details of each function, including other functions included in the RF transmission / reception unit 101, are known matters to those skilled in the art, and thus the description thereof is omitted.

  The digital signal processing unit 102 performs digital precoding processing on data streams that are spatially multiplexed at the same time and in the same frequency block (referred to as resource block or resource block group in LTE). As a specific method of the digital precoding process, any one of various known techniques may be applied. For example, block diagonalization in which interference between terminal apparatuses is suppressed by null formation may be applied.

  The resource assignment unit 103 selects a terminal device to be subjected to spatial multiplexing and a data stream, and inputs the selected data processing unit 102 to the digital signal processing unit 102. As a specific method of selecting a terminal device and a data stream, any of various known techniques may be applied. For example, the throughput of each data stream is estimated based on the measurement result of channel quality, and the sum of throughputs The terminal device and the data stream that maximizes

  The base station wired transmission / reception unit 104 has a basic function of wired transmission / reception of a base station apparatus in a general wireless communication system in wireless communication with the terminal device 2. The base station wired transmission / reception unit 104 receives data addressed to the terminal device from the upper network via the wired line, and transmits data from the terminal device to the upper network via the wired line. The functions of the base station wired transmission / reception unit 104 are well known to those skilled in the art, and thus detailed description of each function will be omitted.

  The channel estimation unit 105 receives a radio wave transmitted from each antenna element of the terminal apparatus by each antenna element of the base station apparatus to obtain channel quality for a combination of each antenna element transmitted and received between the terminal apparatus and the base station apparatus. (Amplitude and phase change amount) are estimated. A channel matrix is formed from the obtained channel quality, and is input to the digital signal processing unit 102.

  The offset setting unit 106 has a function of updating an offset value used in beam switching, and a function (corresponding to an offset notification unit) of notifying all terminal devices connected to the base station apparatus of the offset value. The offset setting unit 106 updates the offset value using the received power of the beam RS reported from the terminal device 2 after performing the switching process of the base station. Therefore, in the present embodiment, the offset setting unit 106 functions as the offset updating unit 102 a in addition to the function as the offset setting unit 101 a described above.

  The beam switching unit 107 selects the switching destination beam based on the determination result of the beam switching performed by the terminal apparatus, and notifies the RF transmitting / receiving unit 101 of the selected beam.

  FIG. 6 is a block diagram showing the configuration of the terminal device 2 in the wireless communication system of the first embodiment of the present invention. The terminal device 2 includes an RF transmission / reception unit 201, a wireless quality measurement unit 202, an offset acquisition unit 203, and a beam switching determination unit 204. In addition, since the structure of all the terminal devices is the same, the description about the structure of the other terminal device 2 is abbreviate | omitted.

The RF transmission / reception unit 201 is connected to N _R (for example, two) antenna elements, and has a basic function of wireless transmission / reception for wireless communication with the base station device 1. Examples of basic functions include transmission functions of uplink reference signals (such as SRS), uplink control signals (such as PUCCH) and uplink data signals (such as PUSCH), downlink reference signals (such as beam RS and CRS), and downlink control signals. And a PDSCH reception function for downlink data signals. In the RF transmission / reception unit 201, beam forming may be performed in downlink reception and uplink transmission using _NR antenna elements. In addition, since the function with which the RF transmission / reception unit 201 is provided is a well-known matter of those skilled in the art, detailed description of each function is omitted.

  The wireless quality measurement unit 202 measures the wireless signal quality used for beam switching. As the radio signal quality, the received power of the beam RS is measured. The beam RS to be measured is not only the beam RS formed by the connected base station apparatus (for example, the base station apparatus 1-1) but also the beam RS formed by the adjacent base station apparatus (for example, the base station apparatus 1-2) Including. Regarding the latter beam RS, the correlating relationship between the Cell ID for identifying the adjacent base station apparatus and the beam ID for identifying the beam RS is known, and the measurement target is obtained by acquiring the Cell ID of the adjacent base station apparatus. The beam ID of the beam RS can be identified.

  The offset acquisition unit 203 acquires an offset value notified from the base station device 1.

  The beam switching determination unit 204 uses the received power of the beam RS and the acquired offset value to determine whether to switch the beam, and notifies the base station apparatus 1 of the determination result via the RF transmission / reception unit 201. The details of the beam switching operation will be described later.

  Subsequently, the operation of the present embodiment will be described in detail with reference to the drawings. Taking the beam switching at the time of switching the connection destination base station from the base station apparatus 1-1 to the base station apparatus 1-2 in FIG. 4 as an example, first, the beam switching operation in the terminal apparatus 2 will be described with reference to the flowchart of FIG. Explain with reference to.

As described above, the base station apparatus 1-1 and the base station apparatus 1-2 transmit the precoded beam RS using _NT transmit antennas. In step S301, the wireless quality measurement unit 202 of the terminal device 2 measures the received power of each precoded beam RS. The received power is periodically measured at each of the N _R reception antennas in the RF transmission and reception unit 201. In addition, transmission of the beam RS in each base station apparatus 1 is implemented, for example so that all beams RS may be sequentially transmitted by time division within a predetermined transmission section (for example, 10 msec).

In step S302, the beam switching determination unit 204 determines the necessity of beam switching from the connection source base station device 1-1 to the connection destination base station device 1-2. For the determination, for example, a determination equation such as equation (1) can be used. In the formula ^{_{(1), P k, i}} s denotes a reception power in the terminal device i beam RS _k being used in the base station apparatus 11 (in dBm). Also, P _j, ^{i n} denotes a reception power in the terminal device i closest beam _RSj to the base station apparatus 11 in the base station apparatus 1-2 (in dBm). ΔP indicates the offset value already acquired from the base station device 1 by the offset acquisition unit 203 before this step (unit: dB). In the present embodiment, ΔP is a value of 0 or more, and the larger the ΔP, the easier it is to satisfy the equation (1), so that beam switching can be performed more quickly. Conversely, beam switching is performed more slowly because the smaller ΔP, the harder it is to satisfy Equation (1). Also, the subscript s indicates that the base station apparatus 1-1, and the subscript n indicates that it is the received power of the beam from the base station apparatus 1-2.

In step S302, if equation (1) is satisfied (YES), it is determined that switching from beam RS _k to beam RS _j is necessary, and the process proceeds to step S303. On the other hand, if the equation (1) is not satisfied in step S302 (NO), it is determined that the beam switching is unnecessary, and the present operation is ended.

In step S303, it is determined that the beam switching from the beam RS _k of the base station device 1-1 to the beam RS _j of the base station device 1-2 is necessary because the equation (1) is satisfied. The terminal device 2 notifies the base station device 1-1 of the determination result so that the base station device 1-1 can start the beam switching process.

  Next, the update operation of the offset value in the offset setting unit 106 of the base station device 1-1 will be described using the flowchart of FIG. This operation is performed by collecting data required by the base station apparatus 1-1 after the beam switching determination operation in FIG. 7 is performed.

  In step S401, the notification of the determination result of the beam switching transmitted from the terminal device 2 in step S303 of FIG. 7 is received. Here, the terminal device 2 determines the beam switching from the base station device 1-1 to the base station device 1-2, and the terminal device 2 determines the base station device 1-1 after the beam switching, and the base station device 1 Description will be made assuming that the received power of −2 is transmitted.

In step S402, the base station device 1 determines whether to increase the offset value based on the received power. Specifically, the offset setting unit 106 receives the received power P _{k, i '} ^{s at} the terminal apparatus i' of the beam RS _k from the base station apparatus 1-1 at the time when the beam switching processing of this time is completed, The average value mean (P _k ^s ) of the received power of the beam RS _k measured in the implemented beam switching process is compared. This determination is expressed by the following equation (2). Here, the units of P ^s _{k, i ′} and mean (P ^s _k ) are both in dBm. In addition, _{i ′} in P ^s _{k, i ′} indicating the terminal device 2 is not necessarily the same as i. Also, α _up is a threshold, and the unit is dB. In addition, as the average value mean (P _k ^s ), for example, an average value of m reception power values in the past m times from the terminal apparatus which has performed the same beam switching can be used.

As a result of the determination in step S402, when the equation (2) is satisfied (YES), the received power of this time is largely dropped as compared with the past average received power of the beam RS _k . In this case, the offset setting unit 106 determines that it is necessary to start the switching process early next time, and proceeds to step S403 to increase the offset value ΔP. On the other hand, when Formula (2) is not satisfy | filled (NO), it transfers to step S404.

In step S403, the offset setting unit 106 increases the offset value by a fixed value β _up (in dB) on the basis of the determination result of the offset value increase.

In step S404, the base station device 1 determines whether to decrease the offset value based on the received power. Specifically, the offset setting unit 106 receives the received power P ⁿ _{j, i ′ at} the terminal device i ′ of the beam RS _j from the base station device 1-2 at the time when the beam switching process of this time is completed, The average value mean (P _j ⁿ ) of the received power of the beam RS _j measured in the implemented beam switching process is compared. This determination is expressed by the following equation (3). Here, the units of P ⁿ _{j, i ′} and mean (P ⁿ _j ) are both dBm. Further _{, i ′} in P ⁿ _{j, i ′} indicating the terminal device 2 is not necessarily the same as i. α _down is a threshold, and the unit is dB. Further, as the average value mean (P _j ⁿ ), for example, an average value of m reception power values in the past m times from the terminal apparatus which has performed the same beam switching can be used.

As a result of the determination in step S404, when the formula (3) is satisfied (YES), the current received power in the beam RS _j is largely dropped compared to the average received power in the past. In this case, the offset setting unit 106 determines that it is necessary to start the switching process later on the next time, and proceeds to step S405 in order to decrease the offset value ΔP. On the other hand, when the equation (3) is not satisfied (NO), the offset setting unit 106 determines that the offset value does not need to be updated, and ends this operation.

In step S405, the offset setting unit 106 reduces the offset value by a fixed value β _down (in dB) based on the determination result of the offset reduction. Note that β _down may have the same value as β _up , that is, the same step width.

  In step S406, when the offset value is updated, the offset setting unit 106 notifies all the terminal devices 2 connected to the base station device 1-1 of the updated offset value.

  Next, based on the operations of FIG. 7 and FIG. 8, the relationship between the operations of the terminal device 2 and the base station devices 1-1 and 1-2 will be described with reference to the sequence diagram of FIG. 9. Steps A501 to A503 correspond to beam switching in the same base station apparatus, and steps A504 to A53 correspond to beam switching across the base station apparatuses described with reference to FIGS. 7 and 8.

In step A501, the base station device 1-1 periodically transmits the beam RS. This includes the beams RS _k in FIGS. 7 and 8.

  In step A502, the terminal device 2 determines the necessity of beam switching in the base station device 1-1 based on the received power of each beam RS. Specifically, as the terminal device 2 moves, the terminal device 2 switches to the beam RS with the largest received power.

  In step A503, the terminal device 2 notifies the base station device 1-1 of the implemented determination result of the beam switching.

Step A504 shows periodic transmission of the beam RS by the adjacent base station device 1-2. This includes the beams RS _j in FIGS. 7 and 8.

  In step A505, as described in steps S302 and S303 in FIG. 7, the terminal device 2 determines that it is necessary to perform beam switching from the base station device 1-1 to 1-2.

  In step A506, as in the operation of step S303 in FIG. 7, the terminal device 2 notifies the base station device 1-1 of the determination result of beam switching.

  In step A507, the base station device 1-1 transmits a HO request message to the base station device 1-2 in order to carry out a handover (HO) process on the base station device side. The HO process is a process for switching the connection destination base station apparatus as the terminal apparatus 2 moves and enabling communication to be continued.

  In Step A508, the base station device 1-2 transmits to the base station device 1-1 a HO request confirmation message indicating that the HO request has been accepted.

  In step A 509, the base station device 1-1 transmits an HO process control message to the terminal device 2 in order to execute the HO process on the terminal device side.

  In step A510, the terminal device 2 transmits, to the base station device 1-2, an HO processing completion confirmation message indicating that the HO processing on the terminal device side has been completed.

In step A511, the terminal device 2 measures the reception power P ^s _k of the beam RS _k of the base station device 1-1 measured at the timing when the beam switching process including the HO process is completed with respect to the base station device 1-1. _{, i ′} and the received power P ⁿ _{j, i ′} of the beam RS _j of the base station device 1-2.

  In step A512, as described in FIG. 8, the received power of each base station is compared with the average value of the received power of each base station received in the past, and, if necessary, the base station apparatus 1-1. Updates the offset value ΔP.

  In step A513, when the base station device 1-1 updates the offset value, the base station device 1-1 notifies the terminal device of the updated offset value.

  The effects of this embodiment will be described with reference to FIG. FIG. 10A shows beam switching when the offset value is not used. That is, it corresponds to the case where it is determined that ΔP = 0 in the equation (1). FIG. 10 (b) shows the beam switching when the offset value is used and set appropriately. Each of FIGS. 10A and 10B shows the relationship between the position of the terminal device 2 and the received power with respect to the beam related to switching in the base station device 1-1 and the base station device 1-2.

  In FIG. 10A, since ΔP = 0, the beam switching process starts at a point where the reception powers of the beams of the base station apparatuses 1-1 and 1-2 intersect. After the HO processing delay of a fixed time, the beam switching processing is completed, and communication with the base station apparatus 1-2 is started. The HO processing delay, that is, the period from the start of beam switching processing to the completion of beam switching processing corresponds to the delay for implementing the sequence from step A506 to step A510 in FIG. Since the beam can not be switched during this HO processing delay, the received power of the beam of the base station apparatus 1-1 drops significantly. Although the case where the beams of the base station apparatuses 1-1 and 1-2 are relatively regularly arranged is taken as an example in FIG. 10A, it may be possible that they are not regularly arranged. In this case, the reduction in received power is further increased.

On the other hand, in FIG. 10 (b), since the received power of the beam (corresponding to the beam RS _j ) of the base station apparatus 1-2 becomes larger than the actual value due to the addition of the offset value, Become. As a result, the beam switching processing is completed near the point where the received power of the beam of the base station device 1-1 (corresponding to the beam RS _k ) and the beam of the base station device 1-2 cross, thereby reducing the received power of the beam. It can be avoided. Furthermore, as described in the present embodiment, optimization (update) of the offset value is performed using a report from the terminal device 2 after beam switching. Thereby, stabilization of received power before and after beam switching is achieved.

  As described above, in the present embodiment, it is possible to suppress a decrease in received power by switching to a beam having good received power in the adjacent base station before the received power of the beam in the connected base station is decreased. Thereby, it is possible to suppress a temporary decrease in throughput due to beam switching between base stations.

  Further, the procedure shown in FIG. 8 can be realized by causing a computer (9000 in FIG. 12) such as a microprocessor to execute a program for controlling the base station apparatus. Such a computer is exemplified by a configuration including a central processing unit (CPU) 9010, a communication interface 9020, a memory 9030, and an auxiliary storage device 9040 in FIG. That is, the base station control program may be executed by the CPU 9010 of FIG. 12, and the process of updating the offset value held in the auxiliary storage device 9040 or the like may be performed.

  In the present embodiment, although the received power of each beam RS is measured and used for updating the offset value, the measurement value that can be used for updating the offset value is not limited to this. For example, it may be reception quality (for example, SINR: Signal to Interference plus Noise Ratio, RSRQ: Reference Signal Received Quality) further considering interference power from the adjacent base station.

  Moreover, although the case where an average value was used as a statistical value of the received power of beam RS was demonstrated in above-mentioned Formula (2) and Formula (3), 50% value (median value), mode are also besides this, for example Statistical values such as minimum value may be used. Also, instead of these statistical values, thresholds calculated using a machine learning model or the like may be used.

  Further, in the present embodiment, the simple case in which the maximum and minimum values of the offset value ΔP are not set has been described, but the maximum and minimum values may be set in order to prevent the offset value from becoming excessive or excessively small.

  Further, in this embodiment, the offset is made using the ratio (difference in dBm unit) between the average value of the received power of the beam RS after beam switching performed in the past and the received power of the beam RS after beam switching performed this time Although the update of the value was determined, it may be determined using a difference (implemented in Watt units).

Second Embodiment
Subsequently, a second embodiment of the present invention will be described. The present embodiment differs from the first embodiment in the updating operation of the offset value. That is, in the first embodiment, the offset value is updated using the actual value of the received power of each beam RS when the beam switching processing is completed, but in this embodiment, the user rate for each beam at the same point is Use to update the offset value. Here, the user rate means the number of bits that can be transmitted per user per unit time. The present embodiment and the first embodiment are different only in the offset value updating operation, and the other configurations and operations are the same. Therefore, the difference will be mainly described.

  First, the update operation of the offset value in the offset setting unit 106 of the base station device 1-1 will be described using the flowchart of FIG. The difference from FIG. 8 in FIG. 11 is that steps S402 and S404 in FIG. 8 are replaced with steps S602 and S604, respectively. These steps are described below.

In step S602, the base station device 1 determines whether to increase the offset value based on the received user rate. Specifically, the offset setting unit 106 sets the user rate C ^s _{k, i ′ at} the terminal device i ′ of the beam RS _k from the base station device 1-1 at the time of completion of the beam switching process this time, and the past. The average value mean (C _k ^s ) of the user rate of the beam RS _k in the beam switching process performed in FIG. This determination is expressed by the following equation (4). Here _{, i ′} in C ^s _{k, i ′} indicating the terminal device 2 is not necessarily the same as i. Also, γ _up is a threshold. The user rate ^{C s} _{k, i 'is} the received power ^{P s} _k beams RS _{k, i'} a, the bandwidth B (unit GHz), the number of terminal devices connected to the base station apparatus 1-1 K _s, the thermal noise N (unit dBm) with, can be calculated as equation (5). As the mean value mean (C _k ^s ), for example, it is possible to use an average value of m user rates in the past calculated from information received from a terminal apparatus which has performed the same beam switching. Also, the units of C ^s _{k, i ′} and mean (C ^s _k ) are both bps (bit per second).

As a result of the determination in step S602, when the equation (4) is satisfied (YES), the current user rate is significantly reduced compared to the past average user rate of the beam RS _k . In this case, the offset setting unit 106 determines that it is necessary to start the switching process early next time, and proceeds to step S403 to increase the offset value ΔP. On the other hand, when Formula (4) is not satisfy | filled (NO), it transfers to step S604.

In step S604, the base station device 1 determines whether to decrease the offset value based on the received user rate. Specifically, the offset setting unit 106 sets the user rate C ⁿ _{j, i ′ at} the terminal device i ′ of the beam RS _j from the base station device 1-2 at the time when the beam switching processing this time is completed, The average value mean (C _j ⁿ ) of the user rate of the beam RS _j in the beam switching process performed in step (c) is compared. This determination is expressed by the following equation (6). Here _{, i ′} in C ⁿ _{j, i ′} indicating the terminal device 2 is not necessarily the same as i. Further, γ _down is a threshold. Note that the user rate ^{C n} _{j, i 'is} the received power ^{P n} _j of the beam RS _{j, i'} and the bandwidth B (unit GHz), the number of terminal devices connected to the base station apparatus 1-2 K _n, the thermal noise n (unit dBm) with, can be calculated as in equation (7). Also, K _n is notified from the base station apparatus 1-2 to the base station apparatus 1-1 via a wired line. As the average value mean (C _j ⁿ ), for example, an average value of m user rates in the past m times calculated from information received from a terminal apparatus that has performed the same beam switching can be used. Also, the units of C ⁿ _{j, i ′} and mean (C _j ⁿ ) are both bps.

As a result of the determination in step S604, when the equation (6) is satisfied (YES), the current user rate drops significantly compared to the past average user rate in the beam RS _j . In this case, the offset setting unit 106 determines that it is necessary to start the switching process later on the next time, and proceeds to step S405 in order to decrease the offset value ΔP. On the other hand, when the equation (6) is not satisfied (NO), the offset setting unit 106 determines that the offset value does not need to be updated, and ends this operation.

  As described above, according to the present embodiment in which the offset value is updated using the actual value of the user rate in each beam, the beam is an index having a high correlation with the actual throughput when using an application such as Web browsing or video viewing. The switching can be performed, and the temporary decrease in throughput can be suppressed more effectively.

  In the present embodiment, the user rate is calculated using Equation (5) or Equation (7), but the number of bits transmitted by the base station device 1 to each terminal device 2 in unit time is measured. The measured values may be used.

[Other Embodiments]
In the first and second embodiments, the case where the present invention is applied to the LTE / LTE-Advanced wireless communication system has been described, but the wireless communication system to which the present invention is applied is not particularly limited. . For example, the present invention can be applied to a future wireless access system such as 5G and a next system of a wireless LAN system such as IEEE 802.11ac / ad.

  Also, in the first and second embodiments, the configuration of the base station apparatus has been described for the case where all the functions are in the same base station apparatus as shown in FIG. 5, but the configuration is not limited to this, Some functions may be divided into different devices. For example, only the RF transmission / reception unit may be used as an antenna device, and may be separated from the base station device. By this means, an antenna can be installed closer to the terminal device, so that the effect of improving received power can be expected.

  As mentioned above, although each embodiment of the present invention was described, the present invention is not limited to the above-mentioned embodiment, and further modification, substitution, adjustment in the range which does not deviate from the basic technical idea of the present invention Can be added. For example, the network configuration shown in each drawing, the configuration of each element, and the form of expressing messages are merely examples for helping to understand the present invention, and the present invention is not limited to the configuration shown in these drawings.

Finally, the preferred form of the invention is summarized.
[First embodiment]
(Refer to the base station from the above first viewpoint)
[Second form]
The above-mentioned offset update unit of the base station
Preferably, the radio quality offset value is increased when the radio quality of the first base station received from the terminal falls below a predetermined offset increase threshold.
[Third form]
The above-mentioned offset update unit of the base station
It is preferable to use the average value of the radio quality of the first base station after the beam switching notified from the terminal as the threshold for offset increase.
[Fourth embodiment]
The above-mentioned offset update unit of the base station
It is also possible to use the statistical value (50% value (median value), mode, minimum value) of the radio quality of the first base station after the beam switching notified from the terminal as the threshold for increasing the offset. it can.
[Fifth embodiment]
The above-mentioned offset update unit of the base station
Preferably, the radio quality offset value is decreased when the radio quality of the second base station received from the terminal falls below a predetermined offset reduction threshold.
Sixth Embodiment
The above-mentioned offset update unit of the base station
It is preferable to use the average value of the radio quality of the second base station after the beam switching notified from the terminal as the threshold for offset reduction.
[Seventh embodiment]
The above-mentioned offset update unit of the base station
It is also possible to use the statistical value (50% value (median value), mode, minimum value) of the radio quality of the first base station after the beam switching notified from the terminal as the threshold for offset reduction. it can.
[Eighth embodiment]
An upper limit or a lower limit based on the maximum / minimum value of the offset value may be provided in the update of the wireless quality offset value by the offset update unit of the base station described above.
[Ninth form]
The above mentioned base station is
As the wireless quality used to update the wireless quality offset value, any one or more of received power, user rate, and received quality can be used.
[Tenth embodiment]
(Refer to the wireless communication system according to the above second aspect)
[Eleventh embodiment]
(Refer to the parameter update method from the above third viewpoint)
[Twelfth embodiment]
(Refer to the program from the above 4th viewpoint)
The above tenth to twelfth embodiments can be developed into second to ninth embodiments as in the first embodiment.

  The disclosures of the above-mentioned patent documents are incorporated herein by reference. Within the scope of the entire disclosure of the present invention (including the scope of the claims), modifications and adjustments of the embodiments or examples are possible based on the basic technical concept of the invention. In addition, various combinations or selections of various disclosed elements (including each element of each claim, each element of each embodiment or example, each element of each drawing, and the like) are possible within the scope of the present disclosure. It is. That is, the present invention of course includes the entire disclosure including the scope of the claims, and various modifications and alterations that can be made by those skilled in the art according to the technical concept. In particular, with regard to the numerical ranges described herein, it should be understood that any numerical value or small range falling within the relevant range is specifically described even if it is not otherwise described.

  The present invention is applicable to an inter-base station beam switching function implemented in an environment in which a number of Massive MIMO base stations are installed in mobile communication. Among other things, even if the user moves to a different base station, the drop in throughput is suppressed by continuously switching to a beam with large received power, and applications such as high definition moving images and VR (Virtual Reality) requiring high throughput. It is effective for the use which uses comfortably.

1-1, 1-2 Base station apparatus 2 Terminal apparatus 100a Base station 101 RF transmission / reception unit 101a Offset notification unit 102 Digital signal processing unit 102a Offset update unit 103 Resource allocation unit 104 Base station wired transmission / reception unit 105 Channel estimation unit 106 Offset setting Unit 107 Beam switching unit 200 a Terminal 201 RF transmission / reception unit 202 Wireless quality measurement unit 203 Offset acquisition unit 204 Beam switching determination unit 9000 Computer 9010 CPU
9020 Communication interface 9030 Memory 9040 Auxiliary storage device

Claims (10)

A first radio quality of a first beam that the first base station precodes and transmits, a second radio quality of a second beam that the second base station precodes and transmits, and The wireless quality offset value is notified to a terminal that switches from the first beam to the second beam using the wireless quality offset value used for determination when switching from one beam to the second beam. Offset notification unit,
Offset update for increasing or decreasing the wireless quality offset value depending on whether the wireless quality of the first and second base stations after beam switching by the wireless quality offset value received from the terminal is larger than a predetermined threshold value or not Department,
A base station comprising The offset update unit is
The base station according to claim 1, wherein the radio quality offset value is increased when the radio quality of the first base station received from the terminal falls below a predetermined offset increase threshold. The offset update unit is
The base station according to claim 2, wherein an average value of radio quality of the first base station after the beam switching notified from the terminal is used as the threshold for increasing the offset. The offset update unit is
The base station according to any one of claims 1 to 3, wherein the radio quality offset value is decreased when the radio quality of the second base station received from the terminal falls below a predetermined offset reduction threshold. The offset update unit is
The base station according to claim 4, wherein an average value of radio quality of the second base station after the beam switching notified from the terminal is used as the threshold for offset reduction.   The base station according to any one of claims 1 to 5, wherein any one or more of a reception power, a user rate and a reception quality is used as the radio quality used for updating the radio quality offset value. A first radio quality of a first beam that the first base station precodes and transmits, a second radio quality of a second beam that the second base station precodes and transmits, and The wireless quality offset value is notified to a terminal that switches from the first beam to the second beam using the wireless quality offset value used for determination when switching from one beam to the second beam. ,
The parameter that increases or decreases the wireless quality offset value depending on whether the wireless quality of the first and second base stations after beam switching by the wireless quality offset value received from the terminal is greater than a predetermined threshold. How to update   The method according to claim 7, wherein the wireless quality offset value is increased when the wireless quality of the first base station received from the terminal falls below a predetermined offset increase threshold.   The parameter updating method according to claim 8, wherein the average value of the radio quality of the first base station after the beam switching notified from the terminal is used as the threshold for increasing the offset.   The method according to any one of claims 7 to 9, wherein the wireless quality offset value is decreased when the wireless quality of the second base station received from the terminal falls below a predetermined offset reduction threshold.

Images