JP2016096478A - Base station, offset value calculation method, and connection cell determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve desired signal reception quality in a peripheral cell which is a connection destination after connection switching in an off-load technique that makes a user device switch connection from a prescribed cell to the peripheral cell.SOLUTION: A base station is used in a mobile communication system that supports CRE technique to make a user device switch connection from a prescribed cell to a peripheral cell on the basis of a CRE offset value. The base station comprises: reception means for receiving first desired signal reception quality from the user device connected with the prescribed cell formed by the base station; and calculation means for calculating the CRE offset value so that second desired signal reception quality is larger than a prescribed threshold value on the basis of the first desired signal reception quality received by the reception means, the second desired signal reception quality being desired signal reception quality at a peripheral cell on the assumption that the user device connected with the peripheral cell.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a technique for offloading traffic of a user apparatus UE in a mobile communication system.

  In LTE, heterogeneous networks are being introduced. In the heterogeneous network, the capacity of the radio network is increased by offloading the traffic of the user apparatus UE in the macro cell to a small cell (eg, hot spot) with relatively small transmission power.

  FIG. 1 shows an example of a mobile communication system in which a small cell exists. As shown in FIG. 1, a base station eNB that forms a macro cell (hereinafter referred to as a macro eNB), a base station eNB that forms a small cell (hereinafter referred to as a small eNB), and a number of user apparatuses UE (hereinafter referred to as Called UE). Here, the small eNB may be a base station eNB that performs a cooperative operation such as CoMP with a macro eNB, or a remote antenna device (radio unit) connected to the macro eNB through an optical fiber or the like. A certain RRE (Remote Radio Equipment) may be used.

3GPP TS 36.214 V11.1.0 (2012-12)

  In order to promote offload of UE traffic from a macro cell to a small cell, there is a technique called CRE (Cell range expansion). In CRE, when a reception level (reception power) from a small cell satisfies a predetermined condition in a UE connected to the macro cell, the UE is handed over to the small cell.

Specifically, RSRP (Reference Signal Received Power) based on the reference signal from the macro cell is RSRP _macro , RSRP based on the reference signal from the small cell is RSRP _small, and Thr _CRE is called a predetermined threshold (CRE offset value). ), When a UE connected to the macro cell satisfies “RSRP _macro -RSRP _small <Thr _CRE ”, the UE is handed over to the _small cell.

That is, addition is performed on the RSRP _small by Thr _CRE , and the added value is compared with the RSRP _macro . As a result, as shown in FIG. 2, the size of the small cell is substantially expanded, and offloading of traffic to the small cell is promoted.

  However, in the conventional CRE, a uniform CRE offset value is applied to all UEs, and a connection to a small cell that is not the best cell (the cell with the highest reception level) is performed. There is a problem that the SINR (example of desired signal reception quality) of the UE may deteriorate. For this reason, for example, the detection error of the downlink control channel (PDCCH or the like) may increase, and the problem that the throughput of data (PDSCH) decreases may occur.

  The present invention has been made in view of the above points, and in an offload technology that allows a user apparatus to change connection from a predetermined cell to a neighboring cell, receiving a desired signal in a neighboring cell that is a connection destination after the connection is changed. The object is to provide a technology that can improve the quality.

According to an embodiment of the present invention, a base station used in a mobile communication system that supports CRE technology that allows a user apparatus to switch connection from a predetermined cell to a neighboring cell based on a CRE offset value. ,
Receiving means for receiving a first desired signal reception quality from a user apparatus connected to the predetermined cell formed by the base station;
Based on the first desired signal reception quality received by the receiving means, a second desired signal reception quality that is a desired signal reception quality in the peripheral cell when it is assumed that the user apparatus is connected to the peripheral cell. There is provided a base station comprising calculation means for calculating the CRE offset value such that is larger than a predetermined threshold.

Moreover, according to the embodiment of the present invention, a base station used in a mobile communication system,
Receiving means for receiving received power of the predetermined cell and received power of one or a plurality of neighboring cells from a user apparatus connected to the predetermined cell formed by the base station;
Based on the received power of each cell received by the receiving means, for each neighboring cell, calculating means for calculating the SINR in the neighboring cell when it is assumed that the user apparatus is connected to the neighboring cell;
There is provided a base station comprising connection control means for determining a neighboring cell corresponding to an SINR larger than a predetermined threshold among the SINRs calculated by the calculation means as a connection destination candidate of the user apparatus.

Moreover, according to the embodiment of the present invention, a base station used in a mobile communication system,
Receiving means for receiving the reception quality of the predetermined cell and the reception quality of one or a plurality of neighboring cells from a user apparatus connected to the predetermined cell formed by the base station;
Based on the reception quality of each cell received by the receiving means, for each neighboring cell, calculating means for calculating the SINR in the neighboring cell when it is assumed that the user apparatus is connected to the neighboring cell;
There is provided a base station comprising connection control means for determining a neighboring cell corresponding to an SINR larger than a predetermined threshold among the SINRs calculated by the calculation means as a connection destination candidate of the user apparatus.

Further, according to the embodiment of the present invention, a base station used in a mobile communication system that supports CRE technology that allows a user apparatus to switch connection from a predetermined cell to a neighboring cell based on a CRE offset value is provided. An offset value calculation method to be executed,
Receiving a first desired signal reception quality from a user apparatus connected to the predetermined cell formed by the base station;
Based on the first desired signal reception quality received in the reception step, a second desired signal reception quality that is a desired signal reception quality in the peripheral cell when it is assumed that the user apparatus is connected to the peripheral cell. An offset value calculation method is provided that includes a calculation step of calculating the CRE offset value such that is larger than a predetermined threshold value.

Moreover, according to the embodiment of the present invention, there is a connected cell determination method executed by a base station used in a mobile communication system,
A reception step of receiving the reception power of the predetermined cell and the reception power of one or a plurality of neighboring cells from a user apparatus connected to the predetermined cell formed by the base station;
Based on the received power of each cell received in the reception step, a calculation step for calculating the SINR in the neighboring cell when it is assumed that the user apparatus is connected to the neighboring cell for each neighboring cell;
There is provided a connected cell determination method comprising: a connection control step of determining a neighboring cell corresponding to an SINR larger than a predetermined threshold among the SINRs calculated in the calculation step as a connection replacement destination candidate of the user apparatus. The

  According to an embodiment of the present invention, in an offload technology that allows a user apparatus to change connection from a predetermined cell to a neighboring cell, it is possible to improve desired signal reception quality in a neighboring cell that is a connection destination after the connection is changed. The technology which enables is provided.

It is a figure which shows the example of the mobile communication system in which a small cell exists. It is a figure for demonstrating CRE. It is a block diagram of the communication system in embodiment of this invention. It is a figure for demonstrating the outline | summary of 1st Embodiment. It is a sequence diagram for demonstrating the process sequence in 1st Embodiment. It is a figure which shows the example of the relationship between SINR before offloading and a CRE offset value. It is a system configuration diagram in a specific example of the first embodiment. It is a figure which shows the CRE offset value of each UE. It is a figure which shows RSRP of each UE. It is a block diagram of the base station in 1st Embodiment. It is a figure for demonstrating the outline | summary of 2nd Embodiment. It is a sequence diagram which shows the process sequence in Example 2-1. It is a figure for demonstrating the characteristic of the SINR calculation method in Example 2-1. It is a sequence diagram which shows the process sequence in Example 2-2. It is a figure for demonstrating the characteristic of the SINR calculation method in Example 2-2. It is a sequence diagram which shows the process sequence in Example 2-3. It is a figure for demonstrating the characteristic of the SINR calculation method in Example 2-3. It is a block diagram of the base station in 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment. For example, the mobile communication system according to the present embodiment assumes a system based on LTE, but the present invention is not limited to LTE and can be applied to other systems. In this specification and claims, “LTE” is not only a communication method corresponding to Release 8 or 9 of 3GPP, but also communication corresponding to Release 10, 11, 12, 13 or later of 3GPP. It is used in a broad sense that can include methods.

  In addition, the term “offload” is used in the sense that traffic is transferred from one cell to another cell. However, for convenience, a UE connection such as “offload UE” is used. In some cases, it is used in the sense of moving the destination from one cell to another (similar to handover).

(System configuration)
FIG. 3 shows an example of the overall configuration of a communication system according to an embodiment of the present invention (common to the first embodiment and the second embodiment). The communication system according to the present embodiment includes a macro eNB that forms a macro cell, and a small eNB that is within the coverage area of the macro cell. FIG. 3 shows a plurality of UEs in the macro cell. The small eNB may be an RRE connected to the macro eNB through an optical fiber or the like, or may be a base station eNB that performs a cooperative operation with the macro eNB.

  In the communication system, macro coverage is ensured by a macro eNB in a low frequency band, and traffic in a small area (eg, hot spot) is absorbed by a small eNB in a high frequency band. Is just an example and is not limited to this.

  In the present embodiment, as a technique for solving the above-described problem that the SINR of a UE handed over from a macro cell to a small cell may deteriorate, the macro eNB may call the SINR (desired signal reception quality) in the macro cell in the UE. Based on the measurement report of each cell from the UE, the technology 1 for determining the CRE offset value for each UE based on the CRE offset, and connecting the UE to the small cell based on the CRE offset value, There is a technique 2 for calculating the SINR of each cell and connecting the UE to the small cell based on the SINR.

  Hereinafter, technology 1 will be described as the first embodiment, and technology 2 will be described as the second embodiment.

  In the first and second embodiments, since RSRP and RSRQ are used, RSRP and RSRQ will be described here.

  The RSRP measured by the UE is, for example, as defined in Non-Patent Document 1, and is an average of the power of the resource element that carries the reference signal (CRS) in the measured frequency band (considerated measurement frequency bandwidth). RSRQ is as defined in Non-Patent Document 1, for example, and is calculated (measured) by “N × RSRP / RSSI”. Here, N is the number of resource blocks in the RSSI measurement band (E-UTRA carrier RSSI measurement bandwidth). Also, RSRP and RSSI measurements in RSRQ are performed in the same set of resource blocks. RSSI is an abbreviation for Received Signal Strength Indicator, and is the sum of received power (reception level) of all signals such as a desired signal from a serving cell, an interference signal from a neighboring cell (neighboring cell), and a noise signal due to thermal noise.

(First embodiment)
As described above, in the first embodiment, for each UE connected to the macro cell, the macro eNB calculates a CRE offset value based on the SINR of the UE, and offloads the UE based on the CRE offset value. Make a decision. The graph on the left side of FIG. 4 shows an example of the reception level (RSRP) S ₁ at the macro cell and the reception levels S _{2 to} S _i at each small cell in the UE connected to the macro cell. In this case, since S _{2 to} S _i become interference for the UE connected to the macro cell, the SINR ₁ of the UE connected to the macro cell can be basically calculated as S ₁ / Σi ≠ 1 (S _i ). . Moreover, if, when the UE has moved to the small cell reception level _{S 2,} similarly, it can be calculated SINR ₂ (in FIG. 4 right). However, SINR ₂ needs to be a predetermined value or more. In the first embodiment, the CRE offset value is calculated based on such a concept. A specific calculation method will be described later.

  With reference to FIG. 5, an example of a processing procedure in the first embodiment will be described. Note that the calculation of the CRE offset value, the offload determination, and the like are performed for each UE connected to the macro cell, but FIG. 5 shows only processing related to a specific UE for the sake of illustration. .

  As shown in FIG. 5, a UE connected to a macro cell (macro eNB) (eg, a UE in an RRC connected state in the macro cell), for example, transmits a CQI (Channel Quality Indicator) in the macro cell to the macro eNB at a predetermined period. Report (step 101). In the present embodiment, the UE reports the CQI of the macro cell to the macro eNB, but the SINR itself may be reported.

  In step 102, the macro eNB obtains an SINR corresponding to the CQI received in step 101, and calculates a CRE offset value based on the SINR.

  The CQI is a value corresponding to the maximum data rate at which the error rate of received data in the UE is equal to or lower than a predetermined value. Basically, the CQI increases as the SINR increases. In the present embodiment, the macro eNB can uniquely calculate the SINR corresponding to the reported CQI for each UE. In calculating SINR, a table in which CQI and SINR are associated with each other may be stored and obtained by referring to the table, or CQI may be converted into SINR using a predetermined mathematical formula.

  In step 102, the macro eNB calculates the CRE offset value specific to the UE so as to satisfy, for example, the minimum SINR for PDCCH detection (the following constant T (dB)). Specifically, when the CRE offset value is x (linear value), x is determined as a value smaller than the value on the right side of the following CRE offset value calculation formula. That is, it is determined as a value whose upper limit is the value on the right side.

上記のＣＲＥオフセット値算出式の導き方は後述する。前述したように、ＲＳＲＰ_{ｓｍａｌｌ}が「ＲＳＲＰ_{ｍａｃｒｏ}‐ＲＳＲＰ_{ｓｍａｌｌ}＜Ｔｈｒ_ＣＲＥ」を満たす場合に、スモールセルへのトラフィックオフロードを行うことができるから、ｘ（上記Ｔｈｒ_ＣＲＥ）が大きいほどスモールセルへのオフロードがされ易くなり、ｘが小さいほど、スモールセルへのオフロードがされ難くなる。マクロｅＮＢは、例えば、マクロｅＮＢが混雑しており、積極的にスモールセルへのトラフィックオフロードを実施したい場合は、ｘとして上限値を採用することが考えられる、逆に、積極的にオフロードを実施する必要がない場合は、例えば、ｘとして上限値よりも所定の値だけ小さい値を採用することが考えられる。

A method for deriving the CRE offset value calculation formula will be described later. As described above, when RSRP _small satisfies “RSRP _macro -RSRP _small <Thr _CRE ”, traffic offload to the small cell can be performed. Therefore, the larger x (the above Thr _CRE ) is, the smaller the traffic to the small cell is. Offloading is easier, and the smaller x is, the more difficult it is to offload to a small cell. For example, when the macro eNB is congested and it is desired to actively perform traffic offload to a small cell, the macro eNB may adopt an upper limit value as x. In the case where it is not necessary to implement, for example, it is conceivable to adopt a value smaller than the upper limit value by a predetermined value as x.

  In step 103, the macro eNB uses the CRE offset value calculated in step 102 to determine whether or not there is a small cell that can perform offloading and determines whether to perform offloading.

Here, the UE, for example by measurement report (Measurement report), _{RSRP small} of _{RSRP macro} and each small cell in the macro cell (a certain size of the reception level of small cells) has been reported to a macro eNB, the macro eNB is If there is a small cell satisfying “RSRP _macro -RSRP _small <Thr _CRE ”, the small cell is determined as a traffic offload destination small cell candidate. If there is one small cell that satisfies the condition, the small cell is determined as a traffic offload destination small cell. When there are a plurality of small cells that satisfy the condition, for example, the small cell with the largest RSRP _small is selected. In addition, when there are a plurality of small cells that satisfy the condition, the small cell having the smallest congestion degree (for example, the number of connected UEs) may be determined as the traffic offload destination small cell.

  In Step 104, the macro eNB transmits a connection instruction (eg, RRC Connection Reconfiguration) to the UE to perform handover to the small cell determined in Step 103. In accordance with the instruction, the UE connects to the small cell and performs communication (step 105).

  FIG. 6 is a diagram showing the relationship between SINR (horizontal axis) and CRE offset value (vertical axis) before off-road. The upper curve shown in FIG. 6 corresponds to the value on the right side of the CRE calculation formula, and this curve is the upper limit (maximum) of the CRE offset value. The straight line (dotted line) below the lower limit (minimum) of the CRE offset value. As shown in the figure, the value between the maximum CRE curve and the dotted line is a possible CRE offset value.

<Derivation method of CRE offset calculation formula>
Here, a method for deriving the CRE offset calculation formula will be described. In the following, S ₁ is RSRP of the first cell (macro cell), and S ₂ is RSRP of the second cell (offload destination candidate small cell). Further, the SINR of an offload destination small cell is required to be larger than T (dB).

SINR ₁ that is the SINR before offloading can be expressed by the following equation (1).

上記の式（１）においてＮは熱雑音、Ｉは他セル干渉を示す。以下、同様である。ＣＲＥオフセット値（ｘ（線形値））の条件に基づいて、第２セルへのオフロードがなされた場合のＳＩＮＲ_２は、下記の式（２）で表すことができる。

In the above equation (1), N represents thermal noise, and I represents other cell interference. The same applies hereinafter. Based on the condition of the CRE offset value (x (linear value)), SINR ₂ when the offload to the second cell is performed can be expressed by the following equation (2).

上記のように、ＣＲＥオフセット値がｘであるとすると、下記の式（３）が得られる

As described above, when the CRE offset value is x, the following equation (3) is obtained.

式（３）を式（１）に代入することで、下記の式（４）が得られる。

By substituting equation (3) into equation (1), the following equation (4) is obtained.

式（３）と式（４）を式（２）に代入することで、下記の式（５）が得られる。

By substituting Equation (3) and Equation (4) into Equation (2), the following Equation (5) is obtained.

オフロード先の第２セルにおけるＳＩＮＲ_２はＴ（線形値）より大きいものとすると、下記の式（６）が得られる。

Assuming that SINR ₂ in the second cell to be offloaded is greater than T (linear value), the following equation (6) is obtained.

上記の式をｘ（線形値）で整理することで、下記のＣＲＥオフセット算出式が得られる。

By organizing the above expression with x (linear value), the following CRE offset calculation expression can be obtained.

＜具体例＞
以下、第１の実施の形態におけるより具体的な例を説明する。ここでは、図７に示すように、マクロｅＮＢ配下のマクロセルカバレッジ内に、スモールセル＃１（ＳＣ＃１と記述する）と、スモールセル＃２（ＳＣ＃２と記述する）が存在し、また、ＵＥ＃１とＵＥ＃２がマクロセルに接続されているものとする。

<Specific example>
Hereinafter, a more specific example in the first embodiment will be described. Here, as shown in FIG. 7, there are small cell # 1 (described as SC # 1) and small cell # 2 (described as SC # 2) in the macro cell coverage under the macro eNB, and Suppose UE # 1 and UE # 2 are connected to the macro cell.

  UE # 1 and UE # 2 each feed back CQI to the macro eNB, and the macro eNB obtains each SINR from the CQI. Here, as an example, it is assumed that the SINR of UE # 1 is −4 dB and the SINR of UE # 2 is 0 dB.

  The macro eNB determines the CRE offset value of each UE using the CRE offset calculation formula based on the SINR value. Here, as an example, it is assumed that the CRE offset value of UE # 1 is 2 dB and the CRE offset value of UE # 2 is determined as 5 dB. When this value is shown in the format of FIG. 6, it is as shown in FIG.

  The macro eNB determines a small cell as a traffic offload destination for each UE based on the above CRE offset value, and shifts the connection destination of each UE to the small cell (hands over each UE).

  Here, as an example, the RSRP of each cell in UE # 1 reported from UE # 1 to the macro eNB is as shown in FIG. 9A, and in UE # 2 reported from UE # 2 to the macro eNB. Assume that the RSRP of each cell is as shown in FIG.

For UE # 1, as shown in FIG. 9A, the macro eNB offloads SC # 1 having a larger RSRP among SC # 1 and SC # 2 satisfying “RSRP _macro -RSRP _small <2”. The UE is determined as the previous small cell, and UE # 1 is handed over to SC # 1.

As for UE # 2, as shown in FIG. 9B, the macro eNB determines SC # 2 satisfying “RSRP _macro- RSRP _small <5” as an offload destination small cell, and determines UE # 2 as SC #. 2 is handed over.

<Configuration example of base station eNB>
FIG. 10 shows a functional configuration diagram of a base station eNB used as a macro eNB in the present embodiment. As illustrated in FIG. 10, the base station eNB includes a UL signal reception unit 101, a DL signal transmission unit 102, a CRE offset value calculation unit 103, and an offload control unit 104. Note that FIG. 10 shows only functional units particularly related to the embodiment of the present invention in the base station eNB, and has at least a function (not shown) for performing an operation based on the LTE scheme. Further, the functional configuration shown in FIG. 10 is merely an example. As long as the operation according to the present embodiment can be performed, the function classification and the name of the function unit may be anything.

  The UL signal receiving unit 101 includes a function of receiving various uplink signals from the UE and acquiring higher layer information from the received physical layer signals. The DL signal transmission unit 102 includes a function of generating various signals of the physical layer from information on higher layers to be transmitted from the base station eNB and transmitting the signals to the UE. In the configuration shown in FIG. 10, the function of obtaining a measurement instruction to each UE and acquiring RSRP / RSRQ and the function of acquiring CQI from each UE are the UL signal receiving unit 101 / DL signal transmitting unit 102. Has.

  The CRE offset value calculation unit 103 calculates (determines) the CRE offset value for each UE by using a CRE offset calculation formula based on the RSRP of the macro cell received from each UE.

  Based on the CRE offset value calculated by the CRE offset value calculation unit 103 and the RSRP of each cell received from the UE, the offload control unit 104 determines a small cell that is a traffic offload destination of the UE for each UE. It includes a function of determining, creating an instruction signal for performing handover to the small cell, and transmitting from the DL signal transmission unit 102.

  As described above, in the present embodiment, a base station used in a mobile communication system that supports CRE technology that allows a user apparatus to switch connection from a predetermined cell to a neighboring cell based on the CRE offset value. And receiving means for receiving the first desired signal reception quality from the user equipment connected to the predetermined cell formed by the base station, and the first desired signal reception quality received by the receiving means. Based on the CRE offset value so that the second desired signal reception quality, which is the desired signal reception quality in the neighboring cell when it is assumed that the user apparatus is connected to the neighboring cell, is larger than a predetermined threshold value. There is provided a base station characterized by comprising calculation means for calculating.

  With the above configuration, in the offload technology that allows the user equipment to change the connection from a predetermined cell to a neighboring cell, a technology that can improve the desired signal reception quality in the neighboring cell that is the connection destination after the connection is changed. Is provided.

  The base station determines a neighboring cell to which the user apparatus is to be reconnected based on the received power of the predetermined cell received from the user apparatus, the received power of one or more neighboring cells, and the CRE offset value. A connection control means for determining and transmitting an instruction signal for connecting the user apparatus to the neighboring cell to the user apparatus may be further provided. With this configuration, it is possible to switch the connection to an appropriate peripheral cell.

  For example, the first desired signal reception quality is CQI or SINR, and the second desired signal reception quality is SINR. In this way, the present invention is applied to both the method of reporting CQI from the UE to the eNB and the method of reporting SINR from the UE to the eNB by using CQI or SINR as the first desired signal reception quality. can do.

  For example, the predetermined cell is a macro cell, and the neighboring cell is a small cell. With this configuration, in a heterogeneous network including macro cells and small cells, it is possible to improve desired signal reception quality in a small cell that is a connection destination after connection switching.

(Second Embodiment)
Next, a second embodiment will be described. In the second embodiment, the macro eNB receives the RSRP (or RSRQ) of each cell from the UE, calculates (estimates) the SINR in each small cell of the UE based on the received measurement value, and the SINR Based on the above, a small cell as an offload destination of the traffic of the UE is determined.

  In the second embodiment, three examples of Example 2-1, Example 2-2, and Example 2-3 will be described. As illustrated in FIG. 11, in Example 2-1, the SINR is estimated using RSRP without considering the load information (DL resource usage rate) in each cell. In Example 2-2, SINR is estimated using RSRP in consideration of the load information of each cell. In Example 2-3, SINR is estimated using RSRQ in consideration of the load information of each cell.

  In each example, the macro eNB compares, for each UE, the SINR of each small cell (cell other than the connected cell) with a predetermined threshold (eg, −7), and selects a cell with an SINR larger than the predetermined threshold. The small cell candidate of the offload destination. If there is one offload destination small cell candidate, the cell can be set as an offload destination. When there are a plurality of offload destination small cell candidates, for example, the cell having the largest SINR is determined as the offload destination cell. Moreover, it is good also as selecting preferentially a small cell with a small cell congestion degree (example: the number of connected UEs). Hereinafter, Example 2-1, Example 2-2, and Example 2-3 will be described.

<Example 2-1>
An example of a processing procedure in Example 2-1 will be described with reference to FIG. The macro eNB instructs measurement by transmitting measurement configuration information (Measurement configuration) to the UE (step 201). The measurement setting information includes, for example, the frequency of the cell to be measured, the measurement amount (RSRP, RSRQ, etc.), the reporting method (reporting periodically, etc.) and the like. The same applies to other examples. In this example, the UE measures the RSRP of the connected cell (macro cell) and each neighboring cell (small cell) based on the measurement setting information, and grasps that the measurement result is reported to the macro eNB. This report is made periodically, for example.

In step 202, the UE measures the RSRP of each cell based on the reference signal received from each cell. Then, in step 203, the UE transmits the measurement result (including the RSRP of each cell) to the macro eNB as a measurement report (Measurement report). In FIG. 12, the RSRP of the cell j is denoted as RSRP _j .

The macro eNB that has received the RSRP of each cell calculates SINR _j that is the SINR of cell j as described below (step 204).

上記の式は、該当セル（ｊ）における所望信号の受信レベル（ＲＳＲＰ_ｊ）を、当該セルｊの周辺セルｉ（ｉ≠ｊ）のＲＳＲＰの合計（所望信号に対する干渉）で割ることでＳＩＮＲ_ｊを求めるものである。

The above equation, SINR reception level of the desired signal in the corresponding cell _(j) (RSRP j), by dividing the sum of the RSRP of neighboring cells of the cell j i (i ≠ j) (interference to the desired signal) _j Is what you want.

  In step 204, the SINR of each small cell is calculated. In step 205, the macro eNB compares the SINR of each small cell calculated in step 204 with a predetermined threshold (eg, a value necessary for normally receiving PDCCH) and is larger than the predetermined threshold. A small cell of SINR is set as a small cell of an offload destination candidate. The macro eNB determines the small cell as an offload destination if there is one small cell as the offload destination candidate. If there are a plurality of offload destination candidate small cells, for example, the small cell having the largest SINR is determined as the offload destination cell. Thereafter, the UE is handed over to the small cell in the same manner as steps 104 and 105 in FIG. 5 in the first embodiment.

In Example 2-1, the total RSRP of neighboring cells i (i ≠ j) is calculated as an interference component without considering the load information of each cell. In other words, assuming that data is assigned to all cells, SINR _j is calculated on the safe side.

  FIG. 13 is a diagram for explaining the characteristics of the calculation method in Example 2-1. In the example shown in FIG. 13 (the same applies to FIGS. 15 and 17), the macro cell, the small cell SC # 1, and the small cell SC # 2 exist as in the case shown in FIG. As shown in FIG. 13, in each cell, a reference signal (CRS) to be measured by RSRP is mapped, and a downlink control channel (including PDCCH) region arrives for each subframe. Also, it is indicated that there are subframes with data (PDSCH) assignment and subframes with no assignment.

  Interference due to data transmission does not occur from a cell to which no data is allocated to other cells. However, since downlink control information is transmitted at subframe intervals for the downlink control channel, data (PDSCH) allocation is not performed. Regardless of the presence or absence, it causes interference to other cells. In Example 2-1, the SINR on the safe side can be calculated in consideration of such interference.

<Example 2-2>
An example of a processing procedure in Example 2-2 will be described with reference to FIG. The macro eNB instructs measurement by transmitting measurement configuration information (Measurement configuration) to the UE (step 301). Similar to Example 2-1, in this example, the UE measures the RSRP of the connected cell (macro cell) and each neighboring cell (small cell) based on the measurement setting information, and reports the measurement result to the macro eNB. To figure out. This report is made periodically, for example.

In step 302, the UE measures the RSRP of each cell based on the reference signal received from each cell. In step 303, the UE transmits the measurement result (including the RSRP of each cell) to the macro eNB as a measurement report (Measurement report). In FIG. 14, the RSRP of the cell j is denoted as RSRP _j .

  In this example, the macro eNB acquires the load information (resource usage rate information) of each small cell (step 304). The load information is acquired as resource usage rate information in the predetermined period, for example, every predetermined period (eg, every subframe). The load information is, for example, a ratio of allocated resources in PDSCH allocatable resources. As a more specific example, for example, if the resource that can be allocated to PDSCH is 100 RB in the predetermined period, and the resource used (with data allocation) is 10 RB, the load information is 0. .1 (10/100).

  When the small cell is formed by the base station eNB, the macro eNB can acquire the load information through inter-base station communication (X2 interface). When a small cell is formed by RRE, the macro eNB can acquire load information from scheduling information in each cell. The macro eNB also acquires load information of the own cell (macro cell). The contents of load information and the acquisition method are the same as in Example 2-3.

The macro eNB that has acquired the RSRP and load information of each cell calculates SINR _j that is the SINR of cell j as follows (step 305).

上記の式は、該当セル（ｊ）における所望信号の受信レベル（ＲＳＲＰ_ｊ）を、当該セルｊの周辺セルｉ（ｉ≠ｊ）におけるＲＳＲＰとロード情報との積の合計（所望信号に対する干渉）で割ることでＳＩＮＲ_ｊを求めるものである。

The above equation, the reception level of the desired signal in the corresponding cell (j) (RSRP _j), the sum of the product of the RSRP and the load information in the neighboring cell i of the cell j (i ≠ j) (interference to the desired signal) The SINR _j is obtained by dividing by.

  In step 305, the SINR of each small cell is calculated. In step 306, the macro eNB compares the SINR of each small cell calculated in step 305 with a predetermined threshold (eg, a value necessary for normally receiving PDCCH), and is larger than the predetermined threshold. A small cell of SINR is set as a small cell of an offload destination candidate. The macro eNB determines the small cell as an offload destination if there is one small cell as the offload destination candidate. If there are a plurality of offload destination candidate small cells, for example, the small cell having the largest SINR is determined as the offload destination cell. Thereafter, the UE is handed over to the small cell in the same manner as steps 104 and 105 in FIG. 5 in the first embodiment.

Since the load information may change frequently, a value obtained by averaging the plurality of pieces of load information acquired in a certain period may be used for calculating SINR _j .

In Example 2-2, the total RSRP of neighboring cells i (i ≠ j) is calculated as an interference component in consideration of the load information of each cell. Thereby, as shown in FIG. 15, it is possible to calculate SINR _j more accurately reflecting the influence of PDSCH.

<Example 2-3>
An example of a processing procedure in Example 2-3 will be described with reference to FIG. The macro eNB instructs measurement by transmitting measurement configuration information (Measurement configuration) to the UE (step 401). In this example, the UE measures (calculates) the RSRQ of the connected cell (macro cell) and each small cell based on the measurement setting information, and grasps that the measurement result is reported to the macro eNB. This report is made periodically, for example.

In step 402, based on the reference signal received from each cell, UE measures RSRP of each cell and measures total in-band power RSSI to obtain RSRQ (RSRP / RSRQ). In step 403, the UE transmits the measurement result (including the RSRQ of each cell) to the macro eNB as a measurement report (Measurement report). In FIG. 16, the RSRQ of the cell j is denoted as RSRQ _j .

  Further, as in Example 2-2, the macro eNB acquires the load information (resource usage rate information) of each small cell (and macro cell) (step 404). The contents of the load information and the acquisition method are the same as in Example 2-2.

The macro eNB that has acquired the RSRQ and load information of each cell calculates SINR _j that is the SINR of the cell j as described below (step 405).

上記の式は、ＲＳＲＱにおけるＲＳＳＩ成分に対してロード情報を加味してＳＩＮＲ_ｊを求めることに相当し、具体的には以下のようにして導出される。

The above equation corresponds to obtaining SINR _j by adding load information to the RSSI component in RSRQ, and is specifically derived as follows.

First, S _j is RSRP in cell j. Here, RSRP and RSSI measurements are considered in units of a 1 RB bandwidth (180 kHz) and a predetermined time width (eg, time width of a resource element). Two reference signals are included per RB, and RSRP is calculated as a value (that is, an average) obtained by dividing the total reception level of the two reference signals by two. Under such assumption, RSRQ _j can be expressed as in the following equation (11).

上記の式（１１）の右辺において、分母はＲＳＳＩを表す。２×Ｓ_ｊは該当セルに関しての参照信号の全受信レベルを示し、１０×Ｓ_ｊ×ｌｏａｄ_ｊは、ロード情報(リソース使用率)を考慮した、データ部分の全受信電力を示す。１ＲＢあたり、１２リソースエレメントとなるため、参照信号を除いた残りが１０リソースエレメントとなる。またΣの部分は、周辺セルについて上記と同様の計算を行って加算するものである。式（１１）を変形することで、下記の式（１２）、式（１３）が得られ、最終的にＲＳＲＱ_ｊが式（１４）として得られる。

On the right side of equation (11) above, the denominator represents RSSI. 2 × S _j indicates the total reception level of the reference signal for the corresponding cell, and 10 × S _j × load _j indicates the total reception power of the data portion in consideration of the load information (resource usage rate). Since there are 12 resource elements per RB, the remainder excluding the reference signal is 10 resource elements. Further, the part of Σ is added by performing the same calculation as above for the peripheral cells. By transforming equation (11), the following equations (12) and (13) are obtained, and finally RSRQ _j is obtained as equation (14).

ステップ４０５では、各スモールセルのＳＩＮＲが算出される。ステップ４０６において、マクロｅＮＢは、ステップ４０５で算出された各スモールセルのＳＩＮＲを所定の閾値（例：ＰＤＣＣＨを正常に受信するために必要な値）と比較して、当該所定の閾値よりも大きなＳＩＮＲのスモールセルをオフロード先候補のスモールセルとする。マクロｅＮＢは、当該オフロード先候補のスモールセルが１つであれば当該スモールセルをオフロード先として決定する。また、オフロード先候補のスモールセルが複数であれば、例えばＳＩＮＲが最も大きなスモールセルをオフロード先のセルとして決定する。その後は、第１の実施の形態における図５のステップ１０４、１０５と同様に、ＵＥを当該スモールセルにハンドオーバさせる。

In step 405, the SINR of each small cell is calculated. In step 406, the macro eNB compares the SINR of each small cell calculated in step 405 with a predetermined threshold (eg, a value necessary for normally receiving PDCCH), and is larger than the predetermined threshold. A small cell of SINR is set as a small cell of an offload destination candidate. The macro eNB determines the small cell as an offload destination if there is one small cell as the offload destination candidate. If there are a plurality of offload destination candidate small cells, for example, the small cell having the largest SINR is determined as the offload destination cell. Thereafter, the UE is handed over to the small cell in the same manner as steps 104 and 105 in FIG. 5 in the first embodiment.

Since the load information may change frequently, a value obtained by averaging the plurality of pieces of load information acquired in a certain period may be used for calculating SINR _j .

In Example 2-3, RSSI in RSRQ is calculated in consideration of the load information of each cell. Thereby, as shown in FIG. 17, it is possible to calculate SINR _j reflecting the influence of PDSCH and PDCCH (downlink control channel).

  In Example 2-3, it is not essential to use the load information. Similarly to Example 2-1, the load information may not be used.

<Configuration example of base station eNB>
FIG. 18 shows a functional configuration diagram of a base station eNB used as a macro eNB capable of executing the operations of Example 2-1, Example 2-2, and Example 2-3 in the present embodiment. As illustrated in FIG. 18, the base station eNB includes a UL signal reception unit 201, a DL signal transmission unit 202, a load information acquisition unit 203, a SINR calculation unit 204, and an offload control unit 205. FIG. 18 shows only functional units that are particularly related to the embodiment of the present invention in the base station eNB, and has at least a function (not shown) for performing an operation in conformity with the LTE scheme. Further, the functional configuration shown in FIG. 18 is merely an example. As long as the operation according to the present embodiment can be performed, the function classification and the name of the function unit may be anything.

  The UL signal receiving unit 201 includes a function of receiving various uplink signals from the UE and acquiring higher layer information from the received physical layer signals. The DL signal transmission unit 202 includes a function of generating various signals of the physical layer from information of higher layers to be transmitted from the base station eNB and transmitting the signals to the UE. In the configuration illustrated in FIG. 18, the UL signal receiving unit 101 / DL signal transmitting unit 102 has a function of issuing a measurement instruction to each UE and acquiring RSRP / RSRQ.

  The load information acquisition unit 203 has a function of acquiring the load information of each cell as described in Example 2-2 and Example 2-3. When the base station eNB is used in the operation of Example 2-1 alone, the load information acquisition unit 203 may not be provided. The SINR calculation unit 204 performs SINR calculation in step 204 of FIG. 12 when performing the operation of Example 2-1. Also, the SINR calculation unit 204 performs SINR calculation in Step 305 of FIG. 14 when performing the operation of Example 2-2. Also, the SINR calculation unit 204 performs SINR calculation in Step 405 of FIG. 16 when performing the operation of Example 2-3.

  The offload control unit 205 determines, for each UE, a small cell that is a traffic offload destination of the UE based on the SINR of each small cell calculated by the SINR calculation unit 204, and performs handover to the small cell. A function of creating an instruction signal to be performed and transmitting it from the DL signal transmission unit 202 is included.

  As described above, according to the present embodiment, the received power of the predetermined cell from the user equipment connected to the predetermined cell formed by the base station, which is a base station used in the mobile communication system. Assuming that the user apparatus is connected to the neighboring cell for each neighboring cell based on the receiving means for receiving the received power of one or a plurality of neighboring cells, and the received power of each cell received by the receiving means. And calculating means for calculating the SINR in the neighboring cell, and among the SINRs calculated by the calculating means, a neighboring cell corresponding to an SINR that is larger than a predetermined threshold is selected as a candidate for a connection change destination of the user apparatus. And a connection control means for determining as a base station.

  With the above configuration, in the offload technology that allows the user equipment to change the connection from a predetermined cell to a neighboring cell, a technology that can improve the desired signal reception quality in the neighboring cell that is the connection destination after the connection is changed. Is provided.

  The calculation unit calculates the SINR by using, for example, received power in each cell other than the neighboring cell assumed to be connected by the user apparatus as an interference component for the neighboring cell. With this configuration, it is possible to calculate the SINR corresponding to the case where data is always assigned to the resource, and it is possible to calculate the SINR considering the downlink control channel as interference.

  For example, the calculation unit calculates the SINR by using, as an interference component for the neighboring cell, received power that takes into account the resource usage state in each cell other than the neighboring cell assumed to be connected by the user apparatus. With this configuration, the SINR can be calculated in consideration of the status of data allocation to resources.

  Further, according to the present embodiment, a base station used in a mobile communication system, from a user apparatus connected to a predetermined cell formed by the base station, the reception quality of the predetermined cell and one or Receiving means for receiving reception quality of a plurality of neighboring cells, and the surroundings when it is assumed that the user apparatus is connected to the neighboring cell for each neighboring cell based on the receiving quality of each cell received by the receiving means Calculation means for calculating SINR in a cell, and connection control for determining a neighboring cell corresponding to an SINR larger than a predetermined threshold among the SINRs calculated by the calculation means as a candidate for a connection replacement destination of the user apparatus Means for providing a base station.

  With the above configuration, in the offload technology that allows the user equipment to change the connection from a predetermined cell to a neighboring cell, a technology that can improve the desired signal reception quality in the neighboring cell that is the connection destination after the connection is changed. Is provided.

  For example, the predetermined cell is a macro cell, and the neighboring cell is a small cell. With this configuration, in a heterogeneous network including macro cells and small cells, it is possible to improve desired signal reception quality in a small cell that is a connection destination after connection switching.

  Note that the technique described in this embodiment can not only improve downlink quality, but also improve uplink received power (received power from the UE to the eNB).

  Each user apparatus UE described in the present embodiment may include a CPU and a memory, and may be configured by a program being executed by a CPU (processor), or may be described in the present embodiment. The configuration may be realized by hardware such as a hardware circuit having the above logic, or a program and hardware may be mixed.

  Each base station eNB described in the present embodiment may include a CPU and a memory, and may be realized by a program being executed by a CPU (processor), or may be described in the present embodiment. The configuration may be realized by hardware such as a hardware circuit having the above logic, or a program and hardware may be mixed.

  Although the embodiments of the present invention have been described above, the disclosed invention is not limited to such embodiments, and those skilled in the art will understand various variations, modifications, alternatives, substitutions, and the like. I will. Although specific numerical examples have been described in order to facilitate understanding of the invention, these numerical values are merely examples and any appropriate values may be used unless otherwise specified. The classification of items in the above description is not essential to the present invention, and the items described in two or more items may be used in combination as necessary, or the items described in one item may be used in different items. It may be applied to the matters described in (if not inconsistent). The boundaries between functional units or processing units in the functional block diagram do not necessarily correspond to physical component boundaries. The operations of a plurality of functional units may be physically performed by one component, or the operations of one functional unit may be physically performed by a plurality of components. For convenience of explanation, the base station eNB has been described using a functional block diagram, but such an apparatus may be implemented in hardware, software, or a combination thereof. Software operated by the processor of the base station eNB according to the embodiment of the present invention includes random access memory (RAM), flash memory, read only memory (ROM), EPROM, EEPROM, register, hard disk (HDD), removable disk, It may be stored in any appropriate storage medium such as a CD-ROM, a database, a server, or the like.

  The present invention is not limited to the above embodiments, and various modifications, modifications, alternatives, substitutions, and the like are included in the present invention without departing from the spirit of the present invention.

eNB base station UE user apparatus 101 UL signal reception unit 102 DL signal transmission unit 103 CRE offset value calculation unit 104 offload control unit 201 UL signal reception unit 202 DL signal transmission unit 203 load information acquisition unit 204 SINR calculation unit 205 offload control Part

Claims (9)

A base station used in a mobile communication system that supports CRE technology that allows a user apparatus to perform connection switching from a predetermined cell to a neighboring cell based on a CRE offset value,
Receiving means for receiving a first desired signal reception quality from a user apparatus connected to the predetermined cell formed by the base station;
Based on the first desired signal reception quality received by the receiving means, a second desired signal reception quality that is a desired signal reception quality in the peripheral cell when it is assumed that the user apparatus is connected to the peripheral cell. And a calculating means for calculating the CRE offset value so that becomes larger than a predetermined threshold. Based on the received power of the predetermined cell received from the user apparatus, the received power of one or a plurality of neighboring cells, and the CRE offset value, determine the neighboring cell to which the user equipment is to be switched, and the user The base station according to claim 1, further comprising connection control means for transmitting an instruction signal for connecting a device to the neighboring cell to the user device. The base station according to claim 1 or 2, wherein the first desired signal reception quality is CQI or SINR, and the second desired signal reception quality is SINR. A base station used in a mobile communication system,
Receiving means for receiving received power of the predetermined cell and received power of one or a plurality of neighboring cells from a user apparatus connected to the predetermined cell formed by the base station;
Based on the received power of each cell received by the receiving means, for each neighboring cell, calculating means for calculating the SINR in the neighboring cell when it is assumed that the user apparatus is connected to the neighboring cell;
A connection control unit that determines a neighboring cell corresponding to an SINR larger than a predetermined threshold among the SINRs calculated by the calculation unit as a connection replacement destination candidate of the user apparatus. . The calculation unit according to claim 4, wherein the calculation unit calculates the SINR by using received power in each cell other than a neighboring cell assumed to be connected to the user apparatus as an interference component for the neighboring cell. base station. The calculation means calculates the SINR by using, as an interference component with respect to the neighboring cell, received power that takes into account the resource usage state in each cell other than the neighboring cell assumed to be connected by the user apparatus. The base station according to claim 4. A base station used in a mobile communication system,
Receiving means for receiving the reception quality of the predetermined cell and the reception quality of one or a plurality of neighboring cells from a user apparatus connected to the predetermined cell formed by the base station;
Based on the reception quality of each cell received by the receiving means, for each neighboring cell, calculating means for calculating the SINR in the neighboring cell when it is assumed that the user apparatus is connected to the neighboring cell;
A connection control unit that determines a neighboring cell corresponding to an SINR larger than a predetermined threshold among the SINRs calculated by the calculation unit as a connection replacement destination candidate of the user apparatus. . An offset value calculation method executed by a base station used in a mobile communication system that supports CRE technology that allows a user apparatus to change connection from a predetermined cell to a neighboring cell based on a CRE offset value,
Receiving a first desired signal reception quality from a user apparatus connected to the predetermined cell formed by the base station;
Based on the first desired signal reception quality received in the reception step, a second desired signal reception quality that is a desired signal reception quality in the peripheral cell when it is assumed that the user apparatus is connected to the peripheral cell. A calculation step of calculating the CRE offset value so that is larger than a predetermined threshold value. A connected cell determination method executed by a base station used in a mobile communication system, comprising:
A reception step of receiving the reception power of the predetermined cell and the reception power of one or a plurality of neighboring cells from a user apparatus connected to the predetermined cell formed by the base station;
Based on the received power of each cell received in the reception step, a calculation step for calculating the SINR in the neighboring cell when it is assumed that the user apparatus is connected to the neighboring cell for each neighboring cell;
A connected cell comprising: a connection control step of determining a neighboring cell corresponding to an SINR larger than a predetermined threshold among the SINRs calculated in the calculating step as a connection replacement destination candidate of the user apparatus. Decision method.

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