JP2014014189A - Radio base station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless communication system capable of improving the throughput of a wireless terminal by appropriately distributing load.
A radio base station 100A transmits to the relay node 200 an instruction of either relay handover in which a relay node 200 switches a connection destination or terminal handover in which any of radio terminals 300E to 300G switches a connection destination. The relay node 200 executes the relay handover when receiving the relay handover instruction, and transmits the terminal handover instruction when receiving the terminal handover instruction.
[Selection] Figure 2

Description

  The present invention relates to a radio base station.

As a next-generation radio communication system to realize high speed communication than the third generation and 3.5G wireless communications system currently being operated, in 3GPP standards body of the radio communication system (3 ^rd Generation Partnership Project) There is standardized LTE (Long Term Evolution).

  Technical specifications of LTE have been determined as 3GPP Release 8, and Release 9 which is an improved version of Release 8 and LTE Advanced which is an advanced version of LTE are currently being studied. In LTE Advanced, adoption of relay transmission using a radio relay station called a relay node is scheduled (for example, see Non-Patent Document 1).

  The radio relay station is a low-power relay base station that is connected to a radio base station (macro base station) by radio. A wireless terminal connected to the wireless relay station communicates with the wireless base station via the wireless relay station. A radio relay station is installed at a cell edge of a radio base station or a coverage hole, and the radio terminal communicates indirectly with the radio base station via the radio relay station, so that the radio terminal directly communicates with the radio base station. It is possible to perform communication under conditions better than communicating with the network.

3GPP TR 36.814 V0.4.1, Chapter 9 “Relaying functionality”, February 2009

  Since the radio relay station relays communication between the radio base station and the radio terminal, the throughput between the radio terminal and the radio base station depends on the throughput between the radio base station and the radio relay station. For this reason, when the load of the radio base station to which the radio relay station is connected is high (for example, when there is a lot of traffic handled by the radio base station), the throughput between the radio base station and the radio relay station decreases, The throughput between the wireless terminal and the wireless base station is also reduced.

  Therefore, the wireless terminal connected to the wireless relay station has a problem that the throughput is lowered even when the wireless quality with the wireless relay station is good when the load on the wireless base station to which the wireless relay station is connected is high. is there.

  Therefore, an object of the present invention is to provide a wireless communication system, a wireless base station, a wireless relay station, and a handover control method that can improve the throughput of wireless terminals by achieving appropriate load distribution.

  In the radio communication system according to the present invention, a radio relay station (eg, relay node 200) is connected to a radio base station (eg, radio base station 100A), and at least one radio terminal (eg, radio terminals 300E to 300G) is connected to the radio relay station. ), And the wireless relay station relays communication between the wireless terminal and the wireless base station (for example, wireless communication system 1), and the wireless base station has a load on the wireless base station. When the base station load is over a first threshold (for example, threshold 1), either an instruction of either a relay station handover where the radio relay station switches the connection destination or a terminal handover where the radio terminal switches the connection destination Is transmitted to the radio relay station, and the radio relay station receives the relay station handover instruction from the radio base station. Run the Ndooba, when the instruction of the terminal handover is received from the radio base station to increase the transmission instruction of the terminal handover to the radio terminal.

  In the radio communication system according to the present invention, the radio base station determines whether to execute the relay station handover or the terminal handover when the base station load exceeds the first threshold, and the relay When it is determined to execute station handover, the relay station handover instruction is transmitted to the radio relay station, and when it is determined to execute terminal handover, the terminal handover instruction is transmitted to the radio relay station. To do.

  In the radio communication system according to the present invention, the radio base station gives priority to the relay station handover over the terminal handover.

  In the radio communication system according to the present invention, the radio base station receives a load notification indicating a load of the relay station handover candidate from a relay station handover candidate that is a handover destination candidate of the radio relay station, and the base station When the load exceeds the first threshold value, it is determined whether to execute the relay station handover based on the load notification received from the relay station handover candidate.

  In the radio communication system according to the present invention, the radio relay station transmits a first measurement result notification indicating a measurement result of radio quality of a signal received by the radio relay station to the radio base station, and the radio base station Determining the relay station handover candidate based on the first measurement result notification received from the radio relay station, and transmitting a load notification request for requesting transmission of the load notification to the determined relay station handover candidate .

  In the radio communication system according to the present invention, the radio base station is a relay that is a load given to the radio base station by the radio relay station and the radio terminal when the base station load exceeds the first threshold. Calculating a station load, predicting a load of the relay station handover candidate when the radio relay station executes the relay station handover based on the load of the relay station handover candidate and the relay station load, and Whether to execute the relay station handover is determined based on the predicted load of the relay station handover candidate.

  In the radio communication system according to the present invention, the radio base station receives a load notification indicating a load of the terminal handover candidate from a terminal handover candidate which is a handover destination candidate of the radio terminal, and the base station load is When it is determined that the terminal handover is to be executed when the first threshold value is exceeded, a radio terminal to execute the terminal handover is determined based on the load notification received from the terminal handover candidate.

  In the radio communication system according to the present invention, the radio relay station transmits a second measurement result notification indicating a radio quality measurement result of a signal received by the radio terminal to the radio base station, The terminal handover candidate is determined based on the second measurement result notification received from the radio relay station, and a load notification request for requesting transmission of the load notification is transmitted to the determined terminal handover candidate.

  In the radio communication system according to the present invention, the radio relay station calculates a terminal load that is a load that the radio terminal gives to the radio relay station when the base station load exceeds the first threshold, A load notification indicating the terminal load is transmitted to the radio base station, and the radio base station, based on the load of the terminal handover candidate and the load notification received from the radio relay station, the radio terminal The terminal handover candidate load when the terminal handover is executed and the base station load when the wireless terminal executes the terminal handover are predicted, the predicted terminal handover candidate load, and the predicted base Based on the load of the station load, a wireless terminal to execute the terminal handover is determined.

  In the radio communication system according to the present invention, the radio relay station transmits a battery notification indicating a remaining battery level of the radio terminal to the radio base station, and the radio base station has the base station load of the first threshold value. If it is determined that the terminal handover is to be executed, a radio terminal to execute the terminal handover is determined based on the battery notification received from the radio relay station.

  In the radio communication system according to the present invention, when the radio base station causes the relay station handover or the terminal handover to be executed due to the base station load exceeding the first threshold, the relay station handover or the terminal A notification regarding handover is transmitted to the handover destination of the radio relay station or the radio terminal.

  In the radio communication system according to the present invention, the radio base station performs the relay station handover or the terminal handover due to the base station load exceeding the first threshold, and then the base station load is second. When it becomes smaller than a threshold (for example, threshold 2), a notification regarding the base station load is transmitted to the handover destination of the radio relay station or the radio terminal.

  In the radio communication system according to the present invention, when the radio base station causes the relay station handover or the terminal handover to be executed due to the base station load exceeding the first threshold, the radio relay station or the radio A notification regarding the load at the handover destination is received from the handover destination of the terminal.

  The radio base station according to the present invention is a radio base station (for example, radio base station 100A) to which a radio relay station (for example, relay node 200) that relays communication with at least one radio terminal (for example, radio terminals 300E to 300G) is connected. A calculation unit (for example, a load calculation unit 131) that calculates a base station load that is a load of the radio base station, and the radio relay station is connected when the base station load exceeds a first threshold value The gist of the present invention is to include a transmission unit (for example, a transmission / reception unit 120) that transmits an instruction to either the relay station handover for switching the destination or the terminal handover for the wireless terminal to switch the connection destination.

  A radio relay station according to the present invention is a radio relay station (eg, relay node 200) that relays communication between at least one radio terminal (eg, radio terminals 300E to 300G) and a radio base station (eg, radio base station 100A). A reception unit (for example, a transmission / reception unit 230) that receives from the radio base station an instruction of either a relay station handover in which the radio relay station switches a connection destination or a terminal handover in which the radio terminal switches a connection destination; When the receiving unit receives the relay station handover instruction, the handover executing unit (for example, the handover executing unit 253) that executes the relay station handover and when the receiving unit receives the terminal handover instruction, the terminal handover A transmission unit (for example, a transmission / reception unit 240) that transmits the instruction to the wireless terminal The gist.

  The handover control method according to the present invention includes a step of connecting a radio relay station to a radio base station, a step of connecting at least one radio terminal to the radio relay station, and communication between the radio terminal and the radio base station. When the radio relay station relays, and when the base station load, which is the load of the radio base station, exceeds a first threshold, the radio relay station switches the connection destination, or the radio terminal A step of transmitting any instruction of terminal handover for switching connection destination from the radio base station to the radio relay station (for example, step S610), and the radio relay station receives the relay station handover instruction from the radio base station; The wireless relay station performs the relay station handover (for example, step S670), and the wireless relay station When a station receives an indication of the terminal handover from the radio base station, and summarized in that comprises a step (e.g., step S640) of transmitting an indication of said terminal handover from the radio relay station to the radio terminal.

  According to the present invention, it is possible to provide a radio communication system, a radio base station, a radio relay station, and a handover control method that can improve the throughput of radio terminals by achieving appropriate load distribution.

It is a figure which shows the structure of the radio | wireless communications system which concerns on embodiment of this invention. It is a figure for demonstrating the handover of the relay node which concerns on embodiment of this invention. It is a figure for demonstrating the hand-over of the radio | wireless terminal under the relay node which concerns on embodiment of this invention. It is a block diagram which shows the structure of the wireless base station which concerns on embodiment of this invention. It is a block diagram which shows the structure of the relay node which concerns on embodiment of this invention. It is a block diagram which shows the structure of the radio | wireless terminal which concerns on embodiment of this invention. It is a sequence diagram which shows the operation example 1 of the radio | wireless communications system which concerns on embodiment of this invention. It is a sequence diagram which shows the operation example 2 of the radio | wireless communications system which concerns on embodiment of this invention. It is a flowchart which shows the detail of step S490 of FIG.7 and FIG.8. It is a flowchart which shows the detail of step S550 of FIG.7 and FIG.8.

  A radio communication system according to an embodiment of the present invention will be described. Specifically, (1) the configuration of the wireless communication system, (2) the operation of the wireless communication system, (3) a modification of the embodiment, and (4) other embodiments will be described.

  In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) Configuration of radio communication system
First, the configuration of the wireless communication system according to the present embodiment will be described in the order of (1.1) overall configuration of the wireless communication system and (1.2) detailed configuration of the wireless communication system.

(1.1) Overall configuration of wireless communication system
FIG. 1 is a diagram illustrating a configuration of a wireless communication system 1 according to the present embodiment. The wireless communication system 1 has a configuration based on LTE-Advanced, which is positioned as a fourth generation (4G) mobile phone system, for example.

  The radio communication system 1 includes a radio base station 100A that forms a cell C1, and a radio base station 100B that forms a cell C2. The cell C1 is a communication area connectable to the radio base station 100A, and the cell C2 is a communication area connectable to the radio base station 100B. The radio base stations 100A and 100B are macro base stations that form cells C1 and C2 each having a radius of about several hundred meters, for example.

  The cells C1 and C2 are adjacent to each other in a partially overlapping state, and hereinafter, the radio base station 100B is appropriately referred to as “adjacent base station of the radio base station 100A”. In addition, although two radio base stations are illustrated in FIG. 1, other radio base stations may be installed adjacent to the two radio base stations.

  The radio base station 100A and the radio base station 100B are connected via a backhaul network (not shown) that is a wired communication network, and can directly perform communication between base stations. In LTE, such an inter-base station communication interface is referred to as an X2 interface.

  Wireless terminals 300A to 300D and relay node 200 are connected to wireless base station 100A wirelessly. The radio terminals 300A to 300D communicate directly with the radio base station 100A. The wireless terminal in the present embodiment is configured to be movable. The relay node 200 is installed at the end of the cell C1 and in the vicinity of the cell C2.

  Wireless terminals 300E to 300G are connected to the relay node 200 by radio. The relay node 200 is a radio relay station that relays communication between the radio terminals 300E to 300G and the radio base station 100A.

  The radio terminals 300E to 300G communicate indirectly with the radio base station 100A via the relay node 200. By such relay transmission, the radio terminals 300E to 300G can communicate with the radio base station 100A even outside the cell C1. Hereinafter, the wireless terminals 300E to 300G connected to the relay node 200 are appropriately referred to as “wireless terminals under the relay node 200”.

  Wireless terminals 300H and 300I are wirelessly connected to the wireless base station 100B. The radio terminals 300H and 300I communicate directly with the radio base station 100B. In the following, when the radio base stations 100A and 100B are not distinguished, they are simply referred to as “radio base station 100”, and when the radio terminals 300A to 300I are not distinguished, they are simply referred to as “radio terminals 300”.

  The radio base station 100A periodically calculates a base station load that is a load of the radio base station 100A. In this embodiment, the load is, for example, the consumption of radio resources (resource blocks) defined by frequency and time, or the amount of data (traffic amount) to be transmitted and received. However, the degree of interference received from the interference source may be included in the load. The base station load is an overall load of the radio base station 100A, regardless of whether it is an uplink load or a downlink load.

  The radio base station 100A determines whether to perform relay handover or terminal handover when the base station load exceeds the first threshold. The case where the base station load exceeds the first threshold means that the load on the radio base station 100A is increasing and it is difficult for the radio base station 100A to provide good communication.

  The relay handover (relay station handover) is a handover in which the relay node 200 switches the connection destination as shown in FIG. FIG. 2 illustrates a case where the relay node 200 performs a handover from the radio base station 100A to the radio base station 100B.

  The terminal handover is a handover in which a wireless terminal (in particular, a wireless terminal under the relay node 200) switches a connection destination as shown in FIG. FIG. 3 illustrates a case where the radio terminal 300E performs a handover from the radio base station 100A to the radio base station 100B.

  When it is determined that the relay handover is to be executed, the radio base station 100A transmits a relay handover instruction to the relay node 200. Further, when it is determined that the terminal handover is to be executed, the radio base station 100A transmits a terminal handover instruction to the relay node 200. The handover instruction (hereinafter referred to as “handover instruction” as appropriate) includes information specifying a node (wireless terminal or relay node) to be handed over and handover destination information specifying a handover destination.

  As described above, the radio base station 100A has the right to determine handover for the radio terminals 300A to 300D and the relay node 200 connected to the radio base station 100A and the right to determine handover for the radio terminals under the relay node 200. Yes.

  By performing processing and calculations related to handover mainly in the radio base station 100A, an increase in traffic in the radio section between the relay node 200 and the radio base station 100A can be avoided. Note that the radio base station 100B has a handover decision right for the radio terminals 300H and 300I connected to the radio base station 100B.

  When the relay node 200 receives a relay handover instruction from the radio base station 100A, the relay node 200 executes the handover. Specifically, the relay node 200 executes a handover to the handover destination corresponding to the handover destination information included in the handover instruction.

  When the relay node 200 receives a terminal handover instruction from the radio base station 100A, the relay node 200 transmits a terminal handover instruction to the radio terminals under the relay node 200. Specifically, relay node 200 transmits the handover instruction to the radio terminal corresponding to the handover destination information included in the handover instruction. The wireless terminal that has received the handover instruction from the relay node 200 executes a handover to the handover destination corresponding to the handover destination information included in the received handover instruction.

  As shown in FIG. 2, in the radio communication system 1, when the base station load exceeds the first threshold (that is, when the load on the radio base station 100A is high), the relay node 200 is caused to perform a relay handover. As a result, the connection destination of the relay node 200 is switched from the radio base station 100A to the radio base station 100B. Thereby, throughput improvement of the radio terminals 300E to 300G under the relay node 200 can be achieved. The radio base station 100A eliminates the load caused by each of the radio terminals 300E to 300G under the relay node 200, and the base station load is greatly reduced. Therefore, the throughput of the radio terminals 300A to 300D that communicate directly with the radio base station 100A Improvements can be made.

  As shown in FIG. 3, in the radio communication system 1, when the base station load exceeds the first threshold value (that is, when the load on the radio base station 100A is high), the handover to the radio terminal 300E under the relay node 200 is performed. By performing the above, it is possible to improve the throughput of the wireless terminal 300E. Also, the radio base station 100A is released from the load of the radio terminal 300E by the handover of the radio terminal 300E, and the base station load is reduced.

  Relay handover has a greater effect of reducing base station load than terminal handover. In addition, the relay node 200 is assumed to be installed at a cell edge or a coverage hole, and has a higher wireless communication function than a wireless terminal. Therefore, there is a high possibility that good communication can be realized even after handover.

  Accordingly, in the present embodiment, the radio base station 100A prioritizes the handover of the relay node 200 over the handover of the radio terminal under the relay node 200. Also, the radio base station 100A may prioritize the handover of the relay node 200 over the handover of the radio terminals 300A to 300D connected to the relay node 200.

  On the other hand, relay handover leads to a sudden increase in the load at the handover destination. In the example of FIG. 2, the load on the radio base station 100B increases rapidly due to relay handover. Therefore, under a situation where the load on the radio base station 100B is high, the radio base station 100A does not perform relay handover to the radio base station 100B, but instead executes terminal handover for each radio terminal under the relay node 200. When the terminal handover is executed, the radio base station 100A hands over at least one radio terminal from among the radio terminals under the relay node 200 so that the base station load of the radio base station 100A becomes a predetermined value or less.

  For example, the radio base station 100A sends a load notification indicating the load of the relay handover candidate from the relay handover candidate (the radio base station 100B in the example of FIG. 2) that is a handover destination candidate of the relay node 200 through inter-base station communication. Receive. Based on the load notification received from the relay handover candidate, the radio base station 100A determines whether to perform relay handover or terminal handover.

  When radio base station 100A causes relay handover to be executed because the base station load of radio base station 100A exceeds the first threshold value, radio base station 100A transmits a notification regarding relay handover to the handover destination of relay node 200. The notification regarding the relay handover is a notification for prompting the handover of the relay node 200 to the radio base station 100A, and includes, for example, information for identifying the relay node 200 and information for identifying the radio base station 100A. This is because the relay node 200 located in the cell C1 is preferably connected to the radio base station 100A and is preferably connected to the radio base station 100A in terms of radio quality.

  Similarly, when the radio base station 100A causes the radio terminal to execute handover due to the base station load of the radio base station 100A exceeding the first threshold, the radio base station 100A transmits a notification regarding the terminal handover to the handover destination of the radio terminal. May be. The notification regarding terminal handover is a notification for prompting handover of the radio terminal to the radio base station 100A, and includes, for example, information identifying the radio terminal and information identifying the radio base station 100A.

  Also, the radio base station 100A adds the load when the relay node 200 returns to the radio base station 100A to the base station load after the relay handover is executed due to the base station load exceeding the first threshold. When the value becomes smaller than the second threshold, a notification regarding the base station load of the radio base station 100A is transmitted to the handover destination of the relay node 200. Even when the relay node 200 returns to the radio base station 100A, the second threshold is a value that is the same as the first threshold or a value that is smaller than the first threshold. The notification regarding the base station load of the radio base station 100A is a notification for prompting the handover of the relay node 200 to the radio base station 100A, and information on the base station load of the radio base station 100A or information that can identify the information including. Alternatively, it may be information that the value obtained by adding the load when the relay node 200 returns to the radio base station 100A to the base station load of the radio base station 100A is smaller than the threshold 2. Similarly, when the base station load becomes smaller than the second threshold after the base station load has exceeded the first threshold and the base station load has become smaller than the second threshold after the base station load has exceeded the first threshold, the radio base station 100A May be transmitted to the handover destination of the wireless terminal.

  When the base station load of the radio base station 100A exceeds the first threshold value and the relay handover is executed, the radio base station 100A receives a notification regarding the handover destination load from the handover destination of the relay node 200. The notification regarding the load at the handover destination of the relay node 200 includes information on the load at the handover destination of the relay node 200 or information capable of specifying the load information. Similarly, when the radio base station 100A causes the radio terminal to perform terminal handover because the base station load of the radio base station 100A exceeds the first threshold value, the radio base station 100A performs handover of the radio terminal from the handover destination of the radio terminal. A notification regarding the previous load may be received.

(1.2) Detailed configuration of wireless communication system
Next, regarding the detailed configuration of the wireless communication system 1, (1.2.1) the configuration of the radio base station, (1.2.2) the configuration of the relay node, (1.2.3) the configuration of the radio terminal. explain.

(1.2.1) Configuration of radio base station
FIG. 4 is a block diagram showing a configuration of the radio base station 100A. The radio base station 100B has the same configuration as the radio base station 100A.

  As illustrated in FIG. 4, the radio base station 100A includes an antenna unit 110, a transmission / reception unit 120, a control unit 130, a backhaul interface (I / F) unit 140, and a storage unit 150.

  The transmission / reception unit 120 is configured using, for example, a radio frequency (RF) circuit, a baseband (BB) circuit, or the like, and transmits / receives a radio signal via the antenna unit 110. Further, the transmission / reception unit 120 performs encoding and modulation of the transmission signal and demodulation and decoding of the reception signal.

  The control unit 130 is configured using, for example, a CPU, and controls various functions provided in the radio base station 100A. The storage unit 150 is configured using, for example, a memory, and stores various types of information used for controlling the radio base station 100A. The backhaul I / F unit 140 communicates with other radio base stations 100 via a backhaul network.

  The control unit 130 includes a load calculation unit 131 and a handover control unit 132. The load calculation unit 131 calculates the base station load of the radio base station 100A and the load of another radio base station (for example, the radio base station 100B). The handover control unit 132 controls relay handover and terminal handover. Specifically, the handover control unit 132 performs various processes related to handover and generates a message related to handover. Details of the function of the handover control unit 132 will be described later. In the present embodiment, the transmission / reception unit 120 corresponds to a transmission unit that transmits an instruction for either relay handover or terminal handover to the relay node 200.

(1.2.2) Configuration of relay node
FIG. 5 is a block diagram showing a configuration of relay node 200. As illustrated in FIG. 5, the relay node 200 includes antenna units 210 and 220, transmission / reception units 230 and 240, a control unit 250, and a storage unit 260.

  The transmission / reception unit 230 is configured using, for example, an RF circuit, a BB circuit, or the like, and transmits / receives a radio signal to / from the radio base station 100. In addition, the transmission / reception unit 230 performs encoding and modulation of the transmission signal and demodulation and decoding of the reception signal. In the present embodiment, the transmission / reception unit 230 corresponds to a reception unit that receives an instruction for either relay handover or terminal handover from the radio base station 100.

  The transmission / reception unit 240 is configured using, for example, an RF circuit, a BB circuit, or the like, and transmits / receives a wireless signal to / from the wireless terminal 300. Further, the transmission / reception unit 240 performs encoding and modulation of the transmission signal and demodulation and decoding of the reception signal. In the present embodiment, the transmission / reception unit 240 corresponds to a transmission unit that transmits a terminal handover instruction to the radio terminal 300 when the transmission / reception unit 230 receives the terminal handover instruction.

  The control unit 250 is configured using a CPU, for example, and controls various functions provided in the relay node 200. The storage unit 260 is configured using, for example, a memory, and stores various types of information used for controlling the relay node 200 and the like.

  The control unit 250 includes a radio quality measurement unit 251, a load calculation unit 252, and a handover execution unit 253.

  The radio quality measurement unit 251 measures the radio quality of the radio signal received by the transmission / reception unit 230. As the radio quality of the radio signal, the received signal strength (RSSI) of the reference signal periodically transmitted by each radio base station 100, the carrier-to-interference noise ratio (CINR) of the reference signal, or the like can be used.

  The load calculation unit 252 calculates a terminal load that is a load that the wireless terminal under the relay node 200 gives to the relay node 200. When the transmission / reception unit 230 receives a relay handover instruction, the handover execution unit 253 executes the relay handover.

(1.2.3) Configuration of wireless terminal
FIG. 6 is a block diagram illustrating a configuration of the wireless terminal 300. As illustrated in FIG. 6, the wireless terminal 300 includes an antenna unit 310, a transmission / reception unit 320, a control unit 330, a storage unit 340, and a battery 350.

  The transmission / reception unit 320 is configured using, for example, an RF circuit, a BB circuit, or the like, and transmits / receives a radio signal to / from a radio base station or a relay node. The transmission / reception unit 320 performs encoding and modulation of the transmission signal and demodulation and decoding of the reception signal. In this embodiment, the transmission / reception unit 320 receives a terminal handover instruction from the relay node 200.

  The control unit 330 is configured using, for example, a CPU, and controls various functions included in the wireless terminal 300. The storage unit 340 is configured using, for example, a memory, and stores various types of information used for controlling the wireless terminal 300 and the like.

  The control unit 330 includes a radio quality measurement unit 331 and a handover execution unit 332.

  The radio quality measurement unit 331 measures the radio quality of the radio signal received by the transmission / reception unit 320. Here, as the radio quality of the radio signal, RSSI of the reference signal periodically transmitted by each radio base station or each relay node, CINR of the reference signal, or the like can be used.

  When the transmission / reception unit 320 receives a terminal handover instruction, the handover execution unit 332 executes terminal handover.

  The battery 350 stores power supplied to each block of the wireless terminal 300. The control unit 330 is configured to be able to detect the remaining amount of electric power stored in the battery 350 (hereinafter, the remaining battery amount).

(2) Operation of wireless communication system
Next, the operation of the wireless communication system 1 will be described in the order of (2.1) operation of the entire wireless communication system, (2.2) handover destination candidate determination processing, and (2.3) handover destination determination processing.

(2.1) Operation of the entire wireless communication system
Below, the operation examples 1 and 2 of the whole radio | wireless communications system 1 are illustrated. In LTE, a radio base station controls handover of a radio terminal according to a measurement result of radio quality of a signal received by the radio terminal. Also in this embodiment, the radio terminals 300E to 300G and the relay node 200 need to notify the radio base station of the measurement result of the radio quality.

  The operation example 1 is an operation example in which the radio terminals 300E to 300G and the relay node 200 notify the measurement result of the radio quality when a specific event occurs. The operation example 2 is an operation example in which the wireless terminals 300E to 300G and the relay node 200 periodically notify the measurement result of the wireless quality.

(2.1.1) Operation example 1
FIG. 7 is a sequence diagram showing an operation example 1 of the wireless communication system 1.

  The load calculation unit 131 of the radio base station 100A calculates a base station load. In step S350, the handover control unit 132 of the radio base station 100A compares the base station load calculated by the load calculation unit 131 with the threshold value 1. If the load on the radio base station 100A is equal to or greater than the threshold 1, the process proceeds to the subsequent processes.

  In step S <b> 370, the transmission / reception unit 120 of the radio base station 100 </ b> A transmits a measurement result request for requesting notification of the measurement result of the radio quality in the relay node 200 to the relay node 200. The transmission / reception unit 230 of the relay node 200 receives the measurement result request.

  The radio quality measurement unit 251 of the relay node 200 measures the radio quality of radio signals received by the transmission / reception unit 230 from the radio base station 100A and a base station adjacent to the radio base station 100A (such as the radio base station 100B). The transmission / reception unit 230 of the relay node 200 transmits a measurement result notification indicating the measurement result by the radio quality measurement unit 251 to the radio base station 100A (step S430).

  In step S390, the transmission / reception unit 120 of the radio base station 100A transmits to the relay node 200 a notification request for the measurement result of radio quality and a notification request for terminal load in the radio terminals 300E to 300G under the relay node 200. The transmission / reception unit 230 of the relay node 200 receives the notification request. When receiving the terminal load notification request, the load calculation unit 252 of the relay node 200 calculates the terminal load for each of the wireless terminals 300E to 300G.

  In step S410, the transmission / reception unit 240 of the relay node 200 transmits a measurement result request for requesting notification of the measurement result of the radio quality in the radio terminals 300E to 300G to the radio terminals 300E to 300G. The transmitting / receiving unit 320 of the wireless terminals 300E to 300G receives the measurement result request.

  When the measurement result request is received, the radio quality measurement unit 331 of each of the radio terminals 300E to 300G transmits the radio signal received by the transmission / reception unit 320 from the relay node 200, the radio base station 100A, and the adjacent base station (eg, the radio base station 100B). Measure radio quality. The transmission / reception unit 320 of the wireless terminals 300E to 300G transmits a measurement result notification indicating the measurement result by the wireless quality measurement unit 331 to the relay node 200 (step S450). The transmission / reception unit 240 of the relay node 200 receives the measurement result notification.

  In step S470, the transmission / reception unit 230 of the relay node 200 performs a load notification indicating each terminal load calculated by the load calculation unit 252, and a measurement result corresponding to the measurement result notification received by the transmission / reception unit 240 from the wireless terminals 300E to 300G. The notification is transmitted to the radio base station 100A. The load notification and the measurement result notification may be combined into one message or may be individual messages. The transceiver 120 of the radio base station 100A receives the load notification and the measurement result notification.

  In step S490, the handover control unit 132 of the radio base station 100A becomes a handover destination candidate for each of the relay node 200 and the radio terminals 300E to 300G based on the measurement result notification received by the transmission / reception unit 120 from the relay node 200. A radio base station (hereinafter, candidate base station) is determined. Here, it is assumed that the radio base station 100B is determined as a candidate base station. Details of step S490 will be described later.

  In step S510, the backhaul I / F unit 140 of the radio base station 100A transmits a load notification request for requesting notification of the load of the candidate base station (radio base station 100B) to the radio base station 100B. The backhaul I / F unit 140 of the radio base station 100B receives the load notification request.

  In step S530, the load calculation unit 131 of the radio base station 100B calculates the load of the radio base station 100B, and transmits a load notification indicating the calculated load to the radio base station 100A. The backhaul I / F unit 140 of the radio base station 100A receives the load notification.

  In step S550, the handover control unit 132 of the radio base station 100A determines a node (radio terminal or relay node) to be handed over and a handover destination radio base station from the relay node 200 and the radio terminals 300E to 300G. . Here, it is assumed that the radio base station 100B is determined as the handover destination radio base station. Details of step S550 will be described later.

  In step S570, the backhaul I / F unit 140 of the radio base station 100A transmits a handover request (handover request) to the handover destination radio base station (radio base station 100B), and a response to accept the handover. (Handover request response) is received from the radio base station 100B.

  In step S610, the transceiver unit 120 of the radio base station 100A transmits a handover instruction to the relay node 200. The transmission / reception unit 230 of the relay node 200 receives the handover instruction. Further, the backhaul I / F unit 140 of the radio base station 100A transfers untransmitted data addressed to the node to be handed over to the handover destination radio base station (radio base station 100B) (step S650).

  When the handover instruction received by the transmission / reception unit 230 of the relay node 200 is a handover instruction for any of the radio terminals 300E to 300G under the relay node 200 (step S630; NO), the transmission / reception unit 240 of the relay node 200 in step S640 Then, a handover instruction is transmitted to the corresponding wireless terminal.

  On the other hand, when the handover instruction received by the transmission / reception unit 230 of the relay node 200 is a handover instruction for the relay node 200 (step S630; YES), in step S670, the handover execution unit 253 of the relay node 200 Handover from the station 100A to the radio base station 100B is performed.

  The load calculation unit 131 of the radio base station 100A newly calculates the base station load. The base station load in this case may be the sum of the loads of the nodes that have been handed over, or the current load of the radio base station 100A. In step S690, the handover control unit 132 of the radio base station 100A compares the base station load newly calculated by the load calculation unit 131 with the threshold value 2. If the base station load is smaller than the threshold value 2, the backhaul I / F unit 140 of the radio base station 100A sends a load notification regarding the base station load newly calculated by the load calculation unit 131 in step S710 to the handover destination. Transmit to the radio base station (radio base station 100B).

  When receiving the load notification from the radio base station 100A, the radio base station 100B transmits, for example, a handover instruction to the radio base station 100A to the node that has been handed over from the radio base station 100A.

  Alternatively, when receiving the load notification from the radio base station 100A, the radio base station 100B may return information indicating the current load of the node that has been handed over to the radio base station 100B. Such a message transmission / reception may be performed, and the handed over node may be handed over from the radio base station 100B to the radio base station 100A to return to the original state. When the original state is optimal in terms of radio quality, it is desirable to return to the optimal state by returning to the original state when the load on the radio base station 100A becomes small.

  Further, the handover destination radio base station (radio base station 100B) periodically or irregularly changes the load information of its own base station with respect to the handover source base station (radio base station 100A). May be notified. In this way, it is possible to prompt the handover source base station whether to restore the handed over node.

(2.1.2) Operation example 2
FIG. 8 is a sequence diagram showing an operation example 2 of the wireless communication system 1.

  The radio terminals 300E to 300G under the relay node 200 periodically measure the radio quality, and periodically transmit a measurement result notification to the relay node 200 (step S310). In addition, the relay node 200 periodically measures the radio quality and periodically transmits a measurement result notification to the radio base station 100A (step S330).

  In the operation example 2, the relay node 200 always knows the radio quality in the radio terminals 300E to 300G under the relay node 200, and the radio base station 100A always knows the radio quality in the relay node 200. Processing such as step S370 described in Example 1 is omitted.

(2.2) Handover destination candidate determination process
Next, the handover destination candidate determination process, that is, step S490 in FIGS. 7 and 8 will be described.

  The relay node 200 transmits a measurement result notification (first measurement result notification) indicating the measurement result of the radio quality of the signal received by the relay node 200 to the radio base station 100A (step S430 in FIG. 7, FIG. 8). Step S330). In the handover destination candidate determination process, the radio base station 100A determines a handover destination candidate for the relay node 200 based on the measurement result notification received from the relay node 200. Thereby, the candidate of the handover destination of the relay node 200 can be appropriately determined, and the relay node 200 can perform good communication after the relay handover.

  The relay node 200 transmits a measurement result notification (second measurement result notification) indicating the measurement result of the radio quality of the signal received by the radio terminal to the radio base station 100A (step S470 in FIGS. 7 and 8). Based on the measurement result notification received from the relay node 200, the radio base station 100A determines a handover destination candidate for the radio terminal 300. Thereby, the candidate of the hand-over destination of the radio | wireless terminal 300 can be determined appropriately, and the radio | wireless terminal 300 can perform favorable communication after a terminal handover.

  FIG. 9 is a flowchart showing details of step S490.

  In step S491, the handover control unit 132 of the radio base station 100A determines the most wireless radio base station other than the radio base station 100A to which the relay node 200 is currently connected from the measurement result of the radio quality of the relay node 200. A radio base station having good quality is determined as a first candidate base station (candidate for relay handover) as a handover destination. If the radio quality cannot be measured for a radio base station other than the radio base station 100A to which the relay node 200 is currently connected, or if it can be measured but is below a predetermined quality, the first candidate base station is not included. .

  In step S492, the handover control unit 132 of the radio base station 100A identifies and enumerates handover candidate base stations (terminal handover candidates) of each radio terminal from the measurement results of radio quality of the radio terminals 300E to 300G under the relay node 200. To do. Specifically, each radio base station having the best radio quality for each radio terminal is set as a handover candidate base station. If the radio quality of a radio base station cannot be measured, or if it can be measured but is below a predetermined quality, there is no handover candidate base station for that radio terminal.

  In step S493, the handover control unit 132 of the radio base station 100A prioritizes the second candidate, the third candidate,..., The Nth candidate in order of good radio quality with respect to the handover candidate base stations listed in step S492. Add. The first candidate base station to the Nth candidate base station are determined by the processing of step S491 to step S493.

(2.3) Handover destination decision processing
Next, the handover destination determination process, that is, step S550 in FIGS. 7 and 8 will be described.

  When the base station load exceeds the first threshold, the radio base station 100A calculates a relay station load that is a load applied to the radio base station 100A by the relay node 200 and the radio terminals 300E to 300G, and Whether to predict the relay handover candidate load when the relay node 200 executes the relay handover based on the load and the relay station load, and whether to execute the relay handover based on the predicted relay handover candidate load To decide. As described above, the load after the relay handover is predicted in advance, and if the load after the relay handover is acceptable, the relay handover is executed. If the load after the relay handover is unacceptable, Relay handover can be prevented from being executed.

  Further, when it is determined not to execute relay handover, the radio base station 100A performs a terminal handover by the radio terminal 300 based on the terminal load notified from the relay node 200 and the load of terminal handover candidates. The terminal handover candidate load and the base station load when the wireless terminal executes the terminal handover are predicted. Then, the radio base station 100A determines a radio terminal to execute terminal handover based on the predicted load of the terminal handover candidate and the predicted load of the base station load. As a result, it is possible to predict in advance the load of the base station and the load of the handover destination after the terminal handover, and determine the radio terminal to be handed over so that the balance between the loads is optimal.

  FIG. 10 is a flowchart showing details of step S550.

  In step S551, the load calculation unit 131 of the radio base station 100A calculates a load by the relay node 200 (hereinafter, relay node load). The relay node load is a load of the entire relay node 200 including the wireless terminals 300E to 300G under the relay node 200.

  In step S552, the load calculation unit 131 of the radio base station 100A calculates a load (hereinafter, terminal load) by the radio terminals 300E to 300G under the relay node 200 from the load notification received from the relay node 200 in step S470. The terminal load is the load of each of the radio terminals 300E to 300G under the relay node 200 in the load of the radio base station 100A.

  In step S553, the load calculating unit 131 of the radio base station 100A loads the first candidate base station corresponding to the load notification received in step S530 and the load of the relay node 200 calculated in step S551 (relay node load). Based on the above, the load of the first candidate base station when the relay node 200 executes the handover to the first candidate base station is calculated.

  In step S554, the handover control unit 132 of the radio base station 100A determines whether or not the relay node 200 can be handed over to the first candidate base station based on the handover destination load calculated in step S553. For example, the handover control unit 132 allows a handover when the load of the first candidate base station calculated in step S553 is equal to or less than a predetermined value, and does not allow a handover in other cases.

  When it is determined that the first candidate base station can be handed over, the handover control unit 132 determines the first candidate base station as the handover destination of the relay node 200. When it is determined that the handover to the first candidate base station is not possible, the handover control unit 132 gives up the handover of the relay node 200 and performs handover determination for each wireless terminal in step S555 and subsequent steps.

  In step S555, the load calculation unit 131 of the radio base station 100A sets n indicating 2 as a candidate base station.

  In step S556, the load calculation unit 131 loads the terminal load of the wireless terminal corresponding to the nth candidate base station (here, the second candidate base station) and the load of the nth candidate base station corresponding to the load notification received in step S530. Based on the above, the load on the nth candidate base station when the wireless terminal corresponding to the nth candidate base station is handed over to the nth candidate base station is calculated.

  In step S557, the handover control unit 132 of the radio base station 100A performs handover of the radio terminal corresponding to the nth candidate base station to the nth candidate base station based on the load of the nth candidate base station calculated in step S556. Determine whether it is possible. For example, the handover control unit 132 allows handover when the load of the nth candidate base station calculated in step S556 is equal to or less than a predetermined value, and disables handover in other cases.

  When it is determined that the handover to the nth candidate base station is possible, the handover control unit 132 determines the nth candidate base station as a handover destination of the wireless terminal. In step S558, the handover control unit 132 determines whether or not the base station load of the radio base station 100A is equal to or less than a predetermined value when the radio terminal is handed over to the handover destination (nth candidate base station). . When the base station load is equal to or less than the predetermined value, the handover control unit 132 determines the node to which the wireless terminal is to be handed over, determines the nth candidate base station as the handover destination, and ends the process.

  On the other hand, when it is determined that the handover to the nth candidate base station is not possible, the handover control unit 132 sets n = n + 1 in step S559, and proceeds to the determination process for the next candidate base station.

  In step S560, the handover control unit 132 determines whether or not processing has been completed for all candidate base stations. If there is a candidate base station that has not completed processing, the processing returns to step S556. When the process is completed for all candidate base stations (step S560; NO), and when the handover destination is determined in the process so far, the handover control unit 132 corresponds to the determined handover destination. It is determined as a node to which the wireless terminal is handed over. If the processing is completed for all candidate base stations (step S560; NO), and if the handover destination has not been determined by the processing up to that point, the processing ends with no handover destination.

  If YES in step S558 and the process ends, the load on the radio base station 100A is equal to or less than the predetermined value. If NO in step S560 and the process ends, the load on the radio base station 100A is predetermined. It is not less than the value. At this time, the handover control unit 132 of the radio base station 100A may perform the same processing on the relay nodes other than the relay node 200 so that the load on the radio base station 100A becomes a predetermined value or less. The load on the radio base station 100A may be reduced by handing over the radio terminals 300A to 300D connected to the station 100A.

  When the radio terminals 300E to 300G under the relay node 200 are handed over to the radio base station 100A and the load on the relay node 200 is reduced, the relay node 200 can be handed over to another radio base station. You may do this.

(3) Modification of the embodiment
In this modification example, the wireless terminal 300 to be handed over is determined in consideration of the remaining battery level of the wireless terminal 300.

  The wireless terminal 300 transmits to the relay node 200 a battery notification indicating the battery level of the terminal itself. The relay node 200 transmits a battery notification to the radio base station 100A. For example, the relay node 200 may further transmit a battery notification to the radio base station 100A in step S470 of FIG.

  When the base station load of the radio base station 100A exceeds the first threshold, the handover control unit 132 of the radio base station 100A determines that the terminal handover is to be executed based on the battery notification received from the relay node 200. Thus, a wireless terminal to execute terminal handover is determined.

  For example, the handover control unit 132 may prioritize candidate base stations for handover based on the remaining battery level in step S493 of FIG. The wireless terminal 300 with a small remaining battery capacity can be connected to the relay node 200 that is closer to the wireless base station 100A, so that the transmission power is smaller, and the wireless terminal 300 with a small remaining battery capacity can be connected to battery saving. it can.

(4) Other embodiments
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in the above-described embodiment, the relay node 200 is a fixed type, but may be configured to be movable.

  In the above-described embodiment, the radio base station 100A determines a handover destination candidate according to the measurement result notification. However, when the relay node 200 is a fixed type, a handover destination candidate may be determined in advance.

  In the above-described embodiment, the case where the radio terminal under the relay node 200 performs handover from the relay node 200 to the radio base station is exemplified. However, the handover destination of the radio terminal under the relay node 200 is not limited to the radio base station, It may be a node. Moreover, although the case where the relay node 200 performs handover between radio base stations is illustrated, the handover destination of the relay node 200 is not limited to a radio base station, and may be a relay node.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 100A, 100B ... Wireless base station, 110 ... Antenna part, 120 ... Transmission / reception part, 130 ... Control part, 131 ... Load calculation part, 132 ... Handover control part, 140 ... Backhaul I / F part, DESCRIPTION OF SYMBOLS 150 ... Memory | storage part, 200 ... Relay node, 210, 220 ... Antenna part, 230, 240 ... Transmission / reception part, 250 ... Control part, 251 ... Wireless quality measurement part, 252 ... Load calculation part, 253 ... Handover execution part, 260 ... Storage unit, 300A to 300I ... wireless terminal, 310 ... antenna unit, 320 ... transmission / reception unit, 330 ... control unit, 331 ... wireless quality measurement unit, 332 ... handover execution unit, 340 ... storage unit, 350 ... battery

Claims (1)

A radio base station connected to a second radio node communicating with at least one first radio node,
For load balancing in the radio base station, an instruction of either the first handover in which the first radio node switches the connection destination or the second handover in which the second radio node switches the connection destination is sent to the second radio node. A radio base station including a transmission unit that transmits to a node.

Images