JP5527041B2 - Mobile radio communication system including handover destination cell selection function - Google Patents

Description

  The present invention relates to a mobile radio communication system including a handover destination cell selection function.

Currently, LTE (Long Term Evolution) standardization as the next generation mobile radio communication technology is 3
Considered by GPP (3rd Generation Partnership Project). In this examination, various techniques for improving the frequency utilization efficiency are discussed.

  In order to improve frequency utilization efficiency, it is represented by radio resources used for data communication in the form of packets between a radio base station apparatus (sometimes simply referred to as a base station) and a mobile station, that is, frequency and time. Control (scheduling) that efficiently allocates resources (which may be described as frequency-time resources or resource blocks (RBs)) to a large number of subordinate mobile stations is indispensable in a radio base station apparatus. is there.

  There is a technique for improving frequency utilization efficiency called one-cell frequency repetition that uses a plurality of the same frequencies (strictly speaking, frequency blocks or frequency groups) in all cells in the communication area. When this technology is adopted, the same frequency is used between adjacent cells, so there is a concern about the occurrence of inter-cell interference at the cell edge. The cell edge includes the vicinity of the cell edge.

In an LTE access network (E-UTRAN: Evolved UMTS Terrestrial Radio Access Network), a technique called Inter-cell Interference Coordination (ICIC) is used in order to realize inter-cell orthogonalization. In this technique, in addition to the fact that a plurality of the same frequencies are used in one cell frequency repetition in all cells by a partial frequency repetition FFR (Fractional Frequency Reuse) method, different frequencies for each cell at the cell edge, for example, Used with 3 cell frequency repetition.

In inter-cell interference coordination by FFR, a resource block as a radio resource for downlink packet access can be commonly used by a plurality of first radio resources that can be used only by each base station and by all base stations. Divided into a plurality of second radio resources. The first radio resource is allocated to a mobile station located at the cell edge (strictly speaking, wirelessly connected at the cell edge), and the second radio resource is assigned to a cell interior (cell interior other than the cell edge).
For example, mobile stations located near the base station and in the cell center area. By this inter-cell interference coordination, each mobile station located at the cell edge can communicate with less interference.

  As for intra-cell interference, in LTE E-UTRAN, each base station can perform uplink and downlink scheduling, thereby realizing intra-cell orthogonalization, that is, orthogonalization between users.

JP 2008-167413 A

3GPP TS 36.213 3GPP TS36.214 3GPP TS36.300 3GPP TS36.321 3GPP TS36.331 3GPP TS 36.401 3GPP TS36.423

  While adopting the above-described inter-cell interference coordination method by FFR and exchanging information using the X2 interface between base stations, mobile stations located at the cell edge (sometimes referred to as cell-edge mobile stations) Therefore, it is possible to dynamically determine a radio resource area for the mobile station and a radio resource area for a mobile station located outside the cell edge (sometimes referred to as a cell internal mobile station).

  However, even when such an inter-cell interference coordination method is adopted, all radio resource areas are used as allocation areas for cell edge mobile stations in order to limit total transmission power in the downlink and suppress interference. I can't. That is, this allocation area is unavoidable to be limited to about 1/3 from the viewpoint of radio resource allocation. As a result, the number of cell edge mobile stations that can communicate simultaneously is limited to a small number, and when there are a plurality of cell edge mobile stations that communicate at the same time, the communication rate of each cell edge mobile station decreases.

  In addition, even if the radio condition is equivalent to being determined as a cell edge mobile station, a radio resource area for a cell internal mobile station is allocated in a state where the radio resource area for the cell edge mobile station is insufficient. I must. In such a case, the cell edge mobile station to which the radio resource area for the cell internal mobile station is assigned cannot only avoid a decrease in throughput, but also the total throughput of the corresponding cell decreases.

  Therefore, in a mobile radio communication system that performs inter-cell interference coordination by FFR, radio resources that can be used by a cell-edge mobile station are limited, and therefore, a handover destination cell that is estimated to be optimal that more radio resources can be used. Is required to select.

  The problem is to provide a technique for selecting a handover destination cell that is estimated to be optimal so that more radio resources can be used.

  In order to solve the above-mentioned problem, a handover destination cell selection method in a radio base station apparatus that employs inter-cell interference coordination by partial frequency repetition is a report signal when radio quality equivalent to a mobile station located at a cell edge is achieved. Is transmitted in advance as a handover trigger condition; when the report signal is received, the mobile station is wirelessly connectable to the first throughput prediction information in the first cell to which the mobile station is wirelessly connected The second throughput prediction information in a plurality of adjacent second cells is selected, and the second cell having the highest value of the second throughput prediction information is selected; The execution of handover to the second cell is instructed.

  According to the disclosed technology, it is possible to increase the effective utilization rate of the entire radio resources of the mobile radio communication system employing inter-cell interference coordination by FFR, that is, it is possible to increase the transmission rate per frequency. In addition, the transmission rate of the mobile station located at the cell edge can be increased.

  Other objects, features and advantages will become apparent upon reading the detailed description set forth below when taken in conjunction with the drawings and the appended claims.

1 is a block diagram showing a configuration of a mobile radio communication system according to an embodiment. The figure for demonstrating radio | wireless resource allocation in the mobile radio | wireless communications system of one embodiment. The figure for demonstrating the interference coordination between cells by FFR in the mobile radio | wireless communications system of one embodiment. The block diagram which shows the structure of the radio base station apparatus applicable to the mobile radio | wireless communications system of one embodiment. The figure which shows the sequence of the information exchange which uses X2 interface in the mobile radio | wireless communications system of one Embodiment. The figure which shows the hand-over sequence in the mobile radio | wireless communications system of one embodiment. The figure which shows the format of the RRC Connection Reconfiguration message in the mobile radio | wireless communications system of one Embodiment. The flowchart which shows the judgment algorithm of the hand-over in the mobile radio | wireless communications system of one embodiment.

  Hereinafter, further detailed description will be given with reference to the accompanying drawings. The drawings show preferred embodiments. However, it can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein.

[Mobile radio communication system]
[System configuration]
Referring to FIG. 1 showing a system configuration in an embodiment, a mobile radio communication system SYS including a handover destination cell selection function that is estimated to be optimal includes a plurality of radio base station apparatuses eNB (evolved Node B) (# 1, # 2, # 3), a plurality of mobile stations UE (User Equipment) (# 1, # 2, # 3) which are wireless terminals used by users, and a management system EMS (Element Management System). In addition, the mobile radio communication system SYS actually constructed
Is provided with a large number of radio base station apparatuses eNB and mobile stations UE, but the illustration is simplified here.

  In this mobile radio communication system SYS, radio base station apparatuses eNB (# 1, # 2, # 3) are connected by a management interface to a management system EMS arranged in, for example, an operation management center. Neighboring or neighboring radio base station apparatuses eNB (# 1, # 2, # 3) are connected to each other via an X2 interface. The management interface and the X2 interface are interfaces in a wired transmission path.

  Also, the radio base station apparatuses eNB (# 1, # 2, # 3) are connected to a plurality of mobile stations UE located in a plurality (here, three) cells CL under their respective radio uu interfaces. . In this example, the radio base station apparatus eNB (# 1) is connected to three mobile stations UE (# 1, # 2, # 3) located in the cell CL (# 1) through radio uu interfaces, respectively. Indicates the state. As will be described in detail later, in the cell CL (# 1), the mobile station UE (# 1) is located inside the cell other than the cell edge, and the mobile stations UE (# 2, # 3) are located at the cell edge.

Each radio base station apparatus eNB communicates with each mobile station UE by a predetermined radio connection technology. The downlink (DL) signal from each radio base station apparatus eNB to each mobile station UE is
It is an Orthogonal Frequency Division Multiple Access (OFDMA) signal, and an uplink (UL: Up Link) signal from each mobile station UE to each radio base station apparatus eNB is a single carrier frequency division multiple access (SC). -FDMA: Single Carrier-Frequency Division Multiple Access signal.

[Wireless resource allocation]
The mobile radio communication system SYS adopting the above-described configuration is capable of realizing an LTE access network E-UTRAN, and includes cell coverage with three radio base station apparatuses eNB (# 1, # 2, # 3), That is, it covers the entire communication area.

  As shown in FIG. 2, the scheduler unit (not shown) in each radio base station apparatus eNB, for each of a plurality of subframes SF (# 1 to # 7) constituting the radio frame, The allocation number and allocation position (timing) to be allocated in units of resource blocks RB (# 1 to # 12...) Are dynamically determined. The resource block RB is configured by, for example, a set of 12 adjacent subcarriers in the frequency domain. In the time domain, two consecutive OFDM symbols (corresponding to one subframe) serve as a basic unit and constitute a resource block.

  Radio resource (RB) allocation information as scheduling determination information is transmitted using a downlink control channel (PDCCH: Physical Downlink Control Channel) arranged at the head of each subframe SF of the downlink DL.

  When using the PDCCH, the radio base station apparatus eNB can freely designate the mobile station UE, the number of RBs, and the RB position to be transmitted in a certain subframe SF. By executing the allocation according to the quality, it is possible to increase the utilization efficiency of radio resources.

  Desired user data is transmitted on a downlink shared channel (PDSCH).

On the other hand, although not shown, in the uplink UL, each mobile station UE performs multiple access using the required number of resource blocks RB as in the downlink. An uplink transmission time interval (TTI: Transmission Time Interval) is for each subframe as in the downlink. User data is an uplink shared channel (PUSCH: Physical Uplink Shared
Channel). The PUSCH capable of transmitting user data is four subframes after the notification of the radio resource allocation information by PDCCH.

The uplink control channel (PUCCH) is a channel quality indicator (CQI) and reception result information (ACK / NAC).
K) and other downlink reception status information is transmitted as uplink control information. The PUCCH is transmitted in a reserved band provided in the uplink frequency domain.

  Referring to FIG. 3, in a mobile radio communication system SYS that employs an inter-cell interference coordination method using partial frequency repetition FFR, a resource block RB as a radio resource for downlink packet access is allocated to each cell in the frequency domain. Divided into a plurality of first resource blocks that can be used only by CL (# 1 to # 9) and a plurality of second resource blocks that can be used in common by all cells CL (# 1 to # 9). .

For example, in the downlink DL radio resource shown in FIG. 2, the resource blocks RB1, 2, RB3, RB4, and RB5, 6 of the subframes SF # 1 to # 7 are stored in the cell CL (# 1,
This is a first resource block that can be used only by # 4, # 7), cell CL (# 2, # 5, # 8), and cell CL (# 3, # 6, # 9). The other resource blocks RB7 to RBn are second resource blocks that can be used in common in all the cells CL (# 1 to # 9).

  The first resource block is assigned to a mobile station (cell edge mobile station) UE located at the cell edge, and the second resource block is assigned to a mobile station (cell internal mobile station) UE located inside the cell other than the cell edge. It is done. Thereby, it is avoided that the resource block area | region allocated to the cell edge mobile station UE overlaps between adjacent cells, and reduces inter-cell interference.

  For example, in the cell CL (# 1) shown in FIG. 1, resource blocks RB1 and RB2 are allocated to the cell edge mobile stations UE (# 2 and # 3), and resource blocks are allocated to the cell internal mobile station UE (# 1). RB7 to RBn can be assigned.

  If the transmission power from the radio base station apparatus eNB is increased for the cell edge mobile station UE without dividing the resource block area, interference occurs between adjacent cells. If the resource block area is divided so as not to overlap, the resource block area for the cell edge mobile station UE of a certain cell is a resource block area for the cell internal mobile station UE of an adjacent cell, so the transmission power is increased. However, since it is a resource block area for the cell internal mobile station UE in the adjacent cell, it does not interfere with the cell internal mobile station UE located in the adjacent cell.

[Radio base station equipment]
FIG. 4 shows a detailed configuration of the radio base station apparatus eNB10 that can be applied to the mobile radio communication system SYS of the embodiment shown in FIG.

  Although not shown, the radio base station apparatus eNB10 selects a transmission unit that performs processing on a downlink signal, a reception unit that performs processing on an uplink signal, and a mobile station UE that is a communication target. In addition, a scheduler unit that manages (controls) allocation of radio resources is included.

  The transmission unit performs processing on a transmission data signal to the communication target mobile station UE determined by the scheduler unit according to a combination set (modulation format) of a modulation scheme and a coding rate. Here, the transmission unit generates and transmits an orthogonal frequency division multiplexing (OFDM) signal by multicarrier modulation.

The receiving unit performs processing on the received data signal transmitted from the mobile station UE determined by the scheduler unit. For example, LTE employs SC-FDMA as a wireless connection technology for uplink (UL) data communication. Since the OFDM modulated wave has a large PAPR (Peak to Average Power Ratio), the efficiency of the transmission amplifier of the mobile station UE is reduced, and the maximum transmission power is reduced or the power consumption is inevitably increased. This problem is avoided by adopting SC-FDMA.

  The scheduler unit included in the control unit that performs overall control of the overall operation of the radio base station apparatus eNB10 sends control information to a transmission unit that performs transmission processing for downlink signals and a reception unit that performs reception processing for uplink signals, By receiving the channel quality indicator (CQI) and the acknowledgment / negative acknowledgment signal (ACK / NACK) as the reception processing result in the reception unit, the mobile station UE to be communicated is selected, and radio resources are allocated. Control.

The radio base station apparatus eNB10 performs a handover destination cell selection process that is estimated to be optimal, which will be described in detail later, and includes a uu interface unit 11, an X2 interface unit 12, a management interface unit 13, an RRC (Radio Resource Control) message transmission / reception unit 14, management information transmission / reception unit 15, X2 message transmission / reception unit 16, mobile station (UE) connection management unit 17, mobile station (UE) information storage unit 18, own cell resource utilization rate measurement unit 19, own cell resource utilization rate notification unit 20, another cell resource utilization rate reception unit 21, a resource information storage unit 22, a handover (HO) condition change unit 23, and a handover (HO) determination unit 24.

  The control unit controls the overall operation of the radio base station apparatus eNB10 by executing a base station control program stored in advance in the storage unit.

[Mobile station]
The detailed configuration of the mobile station UE applicable to the mobile radio communication system SYS according to the embodiment shown in FIG. 1 is not shown.

  The mobile station UE wirelessly connected to the radio base station apparatus eNB receives a downlink signal (user data, control information) received from the radio base station apparatus eNB, and an uplink transmitted to the radio base station apparatus eNB Performs predetermined processing based on the results of demodulation and decoding in the transmission unit that processes signals (user data and quality information) and the reception unit, and instructs the transmission unit to perform transmission processing according to various received control information And a control unit. The control unit controls the overall operation of the mobile station by executing a mobile station control program stored in advance in the storage unit.

[Handover destination cell selection processing]
Next, an example of handover destination cell selection processing in the mobile radio communication system SYS of the embodiment shown in FIG. 1 will be described with reference to related drawings.

[Prerequisites]
In this mobile radio communication system SYS, the following items are included as preconditions in order to select a handover destination cell that is estimated to be optimal.

(1) The geographical and area coverage of the communication area under the control of the radio base station apparatus eNB (# 1, # 2, # 3) in the mobile radio communication system SYS is repeated by one cell frequency (reuse = 1)
).

  Referring to FIG. 1, in the mobile radio communication system SYS, a plurality of the same frequencies as radio resources are used in all cells in the communication area in order to improve the frequency utilization efficiency. When radio resource allocation according to LTE described above with reference to FIG. 2 is performed, the basic unit of the radio resource is a resource block of a frequency-time resource.

  (2) Inter-cell interference coordination by partial frequency repetition FFR is performed.

  When the one-cell frequency repetition method in the precondition (1) is adopted, the same frequency is used between adjacent cells, so that there is a possibility that inter-cell interference occurs at the cell edge (including the vicinity of the cell edge). In order to avoid this inter-cell interference, the inter-cell interference coordination by FFR described above with reference to FIG. 3 is adopted, and different frequencies are used for each cell at the cell edge. That is, at the cell edge, a technique equivalent to 3-cell frequency repetition (reuse = 3) is adopted.

  (3) Resource (radio resource) information is exchanged by the X2 interface.

  Referring to FIG. 5, as shown in the sequence for exchanging resource information through the X2 interface, resource information is notified between adjacent radio base station apparatuses eNB (# 1, # 2, # 3).

That is, the radio base station apparatus eNB (# 1) transmits a resource status request RSR1 (Resource Status Request) message to the adjacent radio base station apparatuses eNB (# 2, # 3) through the X2 interface, and periodically Request to transmit resource information (at a predetermined time interval t).

  The radio base station apparatus eNB (# 2, # 3) that has received the RSR1 message periodically transmits a resource status response RSR2 (Resource Status Response) message to the radio base station apparatus eNB (# 1) through the X2 interface. Thereby, the radio base station apparatus eNB (# 1) periodically receives the resource information for each cell under the control of each of the radio base station apparatuses eNB (# 2, # 3). In the resource state response message RSR2 in FIG. 6, the resource utilization rates of the cell edge region and the cell internal region are notified as a response to the resource state request message RSR1 shown in FIG.

  Since the radio base station apparatuses eNB (# 1, # 2, # 3) execute autonomous distributed inter-cell interference coordination, respectively, the radio base station apparatuses eNB (# 2, # 3) are mainly responsible for resources. Receive information regularly.

When exchanging resource information, in addition to resource information that can be exchanged according to the LTE standard, additional resource information for calculating a throughput prediction coefficient (efficiency) EFC, which will be described later, is also exchanged in inter-cell interference coordination. Here, the additional resource information includes the following elements.
l: Average delay time of radio resource allocation in cell edge region n: Number of cell edge mobile stations r: Average data transmission rate of cell edge mobile stations (4) Radio base station apparatuses eNB (# 1, # 2, # 3) When the mobile station UE (# 1, # 2, # 3) is instructed to measure the radio quality by a radio resource control connection RRC (RRC Connection Reconfiguration or RRC Connection Setup) message, a condition that becomes a radio environment of the cell edge mobile station Is set as a trigger for handover (HO).

  That is, as in the sequence illustrated in FIG. 6, the radio base station apparatus eNB (# 1) transmits the mobile stations UE (# 1, # 2, #) under the RRC message, here RRC Connection Reconfiguration, via the uu interface. 3) Instruct the handover trigger condition. At this time, the radio base station apparatus eNB (# 1) transmits a measurement report (MR) message to the mobile stations UE (# 1, # 2, # 3) when the radio quality of the cell edge mobile station is reached. To indicate an early handover trigger condition. An example of the format of this RRC message is shown in FIG. In this format, the part indicated by bold is a handover trigger condition instruction.

  Since the radio base station apparatuses eNB (# 1, # 2, # 3) execute autonomous distributed inter-cell interference coordination, respectively, the radio base station apparatuses eNB (# 2, # 3) are mainly responsible for the early stage. Indicates a handover trigger condition.

More specifically with reference to FIG. 6, the handover in the radio base station apparatus eNB (# 1) is started by the reception of an MR message notifying that the handover trigger condition has been reached from the mobile station UE. The handover trigger condition is that when the mobile station UE is connected, the radio base station apparatus eNB (# 1) “when the radio base station apparatus eNB (# 1) has a certain radio quality and the adjacent radio base station apparatus The eNB (# 2, # 3) is instructed in advance to report to at least one of “when a certain radio quality is obtained”.

  The radio base station apparatus eNB (# 1) that has received the MR message from the mobile station UE is a notification that conforms to the handover trigger condition, or whether handover is permitted for the handover destination reported from the mobile station UE Determine.

  As a result of the determination, when it is determined that the radio base station apparatus eNB (# 1) performs handover, the handover destination cell, that is, another cell under the radio base station apparatus eNB (# 1) or the radio base station apparatus eNB (# 2, # 3) Inquires the corresponding radio base station apparatus eNB whether to accept a handover to another cell under its control.

  When the handover destination cell is under the control of the adjacent radio base station apparatuses eNB (# 2, # 3), an inquiry is executed by a handover request message via the X2 interface. When the radio base station apparatus eNB (# 1) confirms that the radio base station apparatus eNB (# 2) subordinate to the handover destination cell accepts it by a Handover Request Acknowledgment (Handover Request ACK) message, the target mobile station The UE is instructed to execute handover by an RRC message.

  The mobile station UE that has received the handover execution instruction transmits and receives a normal message (Preamble, RACH response, RRC Connection Reconfiguration Complete) after performing synchronization processing with the target radio base station apparatus eNB (# 2). To complete the process.

[Process overview]
The radio base station apparatus eNB (# 1, # 2, # 3) in the mobile radio communication system SYS includes the following processing in order to perform handover destination cell selection.

  When there are a plurality of cells in which a mobile station (cell edge mobile station) UE located at the cell edge can be wirelessly connected (simply referred to as connection), the target cell edge mobile station UE The first throughput prediction coefficient EFC1 in the cell (own cell) and the second throughput prediction coefficient EFC2 in the cell (adjacent cell) to which the target cell edge mobile station UE can be connected, and the target cell edge mobile station A cell having the highest value of the second throughput prediction coefficient EFC2 for the UE is determined (selected). Here, the throughput prediction coefficient EFC is defined as a coefficient obtained by coefficientizing a predicted value of the maximum throughput theoretically possible when the target cell edge mobile station UE is connected to the cell.

  The first throughput prediction coefficient EFC1 of the own cell is calculated based on the resource information of the own cell and the radio quality of the own cell in the MR message reported from the mobile station UE. The second throughput prediction coefficient EFC2 of the neighboring cell is calculated based on the resource information of the neighboring cell acquired through the X2 interface and the radio quality of the neighboring cell in the MR message reported from the mobile station UE.

  In order to use the MR message from the mobile station UE, the radio base station apparatus eNB may be able to provide the mobile station UE with the cell edge before reaching the handover condition, that is, even when the radio level quality of its own cell is good. When the radio quality of the mobile station is reached, the mobile station UE is instructed in advance to transmit an MR message.

  As a result, when the second throughput prediction coefficient EFC2 in the adjacent cell is higher than the first throughput prediction coefficient EFC1 in the own cell, the target cell edge mobile station UE is instructed to execute early handover ( (See FIG. 6).

  (1) The radio base station apparatus eNB (# 1) is configured such that adjacent radio base station apparatuses eNB (# 2, # 3) are defined from the management system EMS via a management interface or are adjacent to each other. When eNB (# 2, # 3) is automatically detected, periodic update of resource information with neighboring radio base station apparatuses eNB (# 2, # 3) is started according to the sequence shown in FIG.

  (2) The radio base station apparatus eNB, when the mobile station UE is connected, or when the radio resource area (resource block) for the cell edge mobile station UE in its own cell is insufficient, the radio resource control connection message RRC1 To instruct MR message transmission earlier than the normal handover trigger. Furthermore, in order to cope with when the own cell is congested, the MR message from the mobile station UE is held for a predetermined time.

  (3) When receiving the MR message from the cell edge mobile station UE, the radio base station apparatus eNB compares the first throughput prediction coefficient EFC1 and the second throughput prediction coefficient EFC2 for the cell edge mobile station UE. When the throughput prediction coefficient EFC is higher when connected to another cell than the own cell, the radio base station apparatus eNB instructs execution of the handover.

  (4) When congestion occurs in the radio resource area for the cell edge mobile station UE, the radio base station apparatus eNB predicts throughput based on the current retained resource information obtained from the retained MR message. Recalculate the coefficient EFC. As a result of the recalculation, if there is a cell edge mobile station UE having a higher throughput prediction coefficient EFC when connected to another cell, n (n = 1 or larger) from the highest throughput prediction coefficient EFC. Instructs execution of handover.

[Processing details: Judgment of congestion]
The radio base station apparatus eNB includes an X2 interface unit 12, an X2 message transmission / reception unit 16, an own cell resource utilization rate measurement unit 19, an own cell resource utilization rate notification unit 20, an other cell resource utilization rate reception unit 21, and a resource information storage unit Through the cooperation of 22, the resource utilization rate of the radio resource area for the cell edge mobile station UE in the own cell or an adjacent cell is calculated based on the preset parameter and the resource information, and congestion is determined.

Congestion criteria:
The condition for determining the congestion of the own cell is when the resource usage rate of the own cell is equal to or greater than a predetermined threshold. Further, the condition for determining the congestion of the adjacent cell is when Expression 1 is satisfied.
(Formula 1) ... Resource utilization rate of adjacent cell <Resource utilization rate of own cell-α
Here, α is an offset value for avoiding equality at the time of comparison.

Preset parameters:
L: Allowable average delay time of radio resource allocation in the cell edge area N: Number of cell edge mobile stations with the minimum connection R: Minimum data transmission rate of cell edge mobile stations Additional resource information:
Each element of the additional resource information described in the precondition (3) is measured for each subordinate cell by each radio base station apparatus eNB. This measurement value is periodically exchanged between adjacent radio base station apparatuses eNB (# 1, # 2, # 3) via the X2 interface.
l: Average delay time of radio resource allocation in the cell edge region n: Number of cell edge mobile stations r: Average data transmission rate of cell edge mobile stations Calculation of resource utilization rate:
The radio base station apparatus eNB calculates the resource utilization rate using Equation 2. Let the delay time, the number of connected UEs, and the average rate per UE be one coefficient value.
(Expression 2)... Max (l−L, 0) / L + max (n−N, 0) /
N + | min (r−2R, 0) | / R
[Details of processing: Calculation of throughput prediction coefficient]
The radio base station apparatus eNB holds the MR message and scheduling information notified from the mobile station UE by the cooperation of the uu interface unit 11, the RRC message transmission / reception unit 14, the UE connection management unit 17, and the UE information storage unit 18. The throughput prediction coefficient EFC is calculated for each cell based on the information for link adaptation and the resource usage rate of the cell.

Here, the MR message notified from the mobile station UE includes the received power RSRP (Reference Signal Received Power) of the reference signal transmitted by the radio base station apparatus eNB and the reference signal transmitted by the radio base station apparatus eNB. Received quality RSRQ (Reference Signal Received Quality).

  The information that the radio base station apparatus eNB holds for each mobile station UE for link adaptation is PowerHeadRoom and a channel quality indicator (CQI). PowerHeadRoom is a surplus power of the transmission power of the mobile station UE. When this surplus power is eliminated, the maximum number of resource blocks to be allocated is limited. CQI is a value of reception quality that the mobile station UE notifies the radio base station apparatus eNB as feedback. The scheduler unit in the radio base station apparatus eNB determines MCS (Modulation and Coding Scheme) which is a set (modulation format) of a combination of modulation scheme and coding rate based on the reception quality value.

  The scheduler unit in the radio base station apparatus eNB converts the resource usage rate and the radio quality of the mobile station UE into coefficient values, and calculates a throughput prediction coefficient EFC (efficiency).

The first throughput prediction coefficient EFC1 in the cell (own cell) to which the target cell edge mobile station UE is connected is calculated by Equation 3.
(Formula 3) ... Own cell resource utilization rate x
{(PowerHeadRoom / cell edge mobile station resource block area) ×
((CQI + 1) / 16)}
Here, dividing by 16 is because the CQI value is a 16-step value.

The second throughput prediction coefficient EFC2 in a cell (adjacent cell) to which the target cell edge mobile station UE can be connected is calculated by Expression 4.
(Formula 4) ... Adjacent cell resource utilization rate x
{(PowerHeadRoom / cell edge mobile station resource block area) ×
((CQI + 1/16)} ×
(RSRQ of neighboring cell / RSRQ of own cell)
Here, dividing by 16 is because the CQI value is a 16-step value.

  For a mobile station UE that should be determined as a cell edge mobile station UE but cannot be assigned to a cell edge resource block area, an offset value β (β = 1 or more) is determined from the CQI value of the mobile station UE. (Integer) is subtracted. This subtraction is to correct the offset value β because the transmission power is small in the communication area inside the cell other than the cell edge.

[Processing details: Handover decision algorithm]
The handover determination unit 24 in the radio base station apparatus eNB (# 1) performs handover destination cell selection that is estimated to be optimal by the handover determination algorithm shown in FIG.

  When detecting that the own cell is congested (S80) and detecting that there is a non-congested cell in the neighboring cell (S81), the UE information storage unit 18 recently transmits an MR message. The selected mobile station UE is extracted as a handover candidate, and a mobile station UE that can be handed over to an adjacent cell that is not congested is selected from the candidates (S82).

  For the selected mobile station UE, a first throughput prediction coefficient EFC1 in its own cell and a second throughput prediction coefficient EFC2 in an adjacent cell as a handover destination candidate are calculated (S83).

  When there is a mobile station UE having a second throughput prediction coefficient EFC2 in the adjacent cell larger than the first throughput prediction coefficient EFC1 in the own cell, these mobile stations UE are extracted (S84).

  Among the extracted plurality of mobile stations UE, N (N = 1 or greater) mobile stations UE having a large difference in throughput prediction coefficient EFC are selected (S85), and handover is performed for the selected mobile stations UE. An instruction is given (S86). Here, the number of mobile stations UE to be selected is determined according to the congestion state of the own cell.

  Note that the handover determining unit 24 calculates the throughput prediction coefficient EFC when the MR message notified from the mobile station UE reaches the handover condition in a state where the own cell is not congested, and performs handover handover. Judgment is possible. As a result, handover to a congested adjacent cell can be suppressed.

[Modification]
The management system EMS in the mobile radio communication system SYS according to the embodiment shown in FIG. 1 collects resource information from each radio base station eNB via the management interface and gives instructions to adjust (change) the handover trigger condition. It is possible to give to the radio base station apparatus eNB. The HO condition change unit 23 in the radio base station apparatus eNB that has received the handover condition change instruction via the management interface unit 13 and the management information transmission / reception unit 15 inputs the change condition to the HO determination unit 24.

  Each process in the above-described embodiment may be performed by selecting and combining any plural or all of the processes.

  The processing in the above-described embodiment is provided as a computer-executable program, and can be provided via a recording medium such as a CD-ROM or a flexible disk, and further via a communication line.

[Others]
The following additional remarks are disclosed with respect to the above-described embodiment and modifications.

(Appendix 1)
A handover destination cell selection method in a radio base station apparatus adopting inter-cell interference coordination by partial frequency repetition;
Instructing in advance as a handover trigger condition to transmit a report signal when radio quality equivalent to a mobile station located at a cell edge is reached;
When the report signal is received, first throughput prediction information in a first cell to which the mobile station is wirelessly connected, and second information in a plurality of adjacent second cells to which the mobile station can be wirelessly connected Comparing with the throughput prediction information and selecting the second cell for which the second throughput prediction information has the highest value;
A handover destination cell selection method for instructing the mobile station to execute a handover to a selected second cell.

(Appendix 2)
The first and second throughput prediction information is obtained by coefficientizing a predicted value of the maximum throughput theoretically possible when the mobile station is wirelessly connected to the first and second cells. The handover destination cell selection method described.

(Appendix 3)
The first throughput prediction information is calculated based on the resource information of the first cell and the radio quality of the first cell in the report signal, and the second throughput prediction information is the first throughput prediction information. The handover destination cell selection method according to Supplementary Note 1 or 2, which is calculated based on resource information of two cells and radio quality of the second cell in the report signal.

(Appendix 4)
The handover destination cell selection method according to claim 1, 2 or 3, wherein an instruction to change the handover trigger condition is received via a management interface based on the collection of the resource information.

(Appendix 5)
A radio base station apparatus adopting inter-cell interference coordination by partial frequency repetition;
Means for instructing in advance as a handover trigger condition to transmit a report signal when radio quality equivalent to a mobile station located at a cell edge is reached;
When the report signal is received, first throughput prediction information in a first cell to which the mobile station is wirelessly connected, and second information in a plurality of adjacent second cells to which the mobile station can be wirelessly connected Means for comparing with the throughput prediction information and selecting the second cell for which the second throughput prediction information shows the highest value;
Means for instructing the mobile station to execute a handover to the selected second cell;
A radio base station apparatus comprising:

(Appendix 6)
The first and second throughput prediction information is obtained by coefficientizing a prediction value of the theoretically possible maximum throughput when the mobile station is wirelessly connected to the first and second cells. The radio base station apparatus described.

(Appendix 7)
The first throughput prediction information is calculated based on the resource information of the first cell and the radio quality of the first cell in the report signal, and the second throughput prediction information is the first throughput prediction information. The radio base station apparatus according to appendix 5 or 6, calculated based on resource information of two cells and radio quality of the second cell in the report signal.

(Appendix 8)
The radio base station apparatus according to appendix 5, 6 or 7, further comprising means for receiving, via a management interface, an instruction to change the handover trigger condition based on the collection of the resource information.

SYS mobile radio communication system eNB radio base station apparatus UE mobile station EMS management system CL cell

Claims (5)

A handover destination cell selection method in a radio base station apparatus adopting inter-cell interference coordination by partial frequency repetition;
Instructing in advance as a handover trigger condition to transmit a report signal early when radio quality equivalent to a mobile station located at a cell edge is reached;
When the report signal transmitted at an early stage is received, first throughput prediction information in a first cell to which the mobile station is wirelessly connected, and a plurality of adjacent second that can be wirelessly connected to the mobile station The second throughput prediction information in the cell of the second cell and select the second cell for which the second throughput prediction information has the highest value;
A handover destination cell selection method for instructing the mobile station to execute a handover to a selected second cell. The first and second throughput prediction information is obtained by coefficientizing a prediction value of a theoretically possible maximum throughput when the mobile station is wirelessly connected to the first and second cells. 2. The handover destination cell selection method according to 1. The first throughput prediction information is calculated based on the resource information of the first cell and the radio quality of the first cell in the report signal, and the second throughput prediction information is the first throughput prediction information. The handover destination cell selection method according to claim 1 or 2, calculated based on resource information of two cells and radio quality of the second cell in the report signal. The handover destination cell selection method according to claim 1, 2 or 3, wherein an instruction to change the handover trigger condition is received via a management interface based on collection of resource information of the first cell and the second cell . A radio base station apparatus adopting inter-cell interference coordination by partial frequency repetition;
Means for instructing in advance as a handover trigger condition that a report signal is transmitted early when radio quality equivalent to a mobile station located at a cell edge is reached;
When the report signal transmitted at an early stage is received, first throughput prediction information in a first cell to which the mobile station is wirelessly connected, and a plurality of adjacent second that can be wirelessly connected to the mobile station Means for comparing the second throughput prediction information in the cell and selecting the second cell showing the highest value in the second throughput prediction information;
Means for instructing the mobile station to execute a handover to the selected second cell;
A radio base station apparatus comprising:

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