WO2015104839A1

WO2015104839A1 - Wireless communication system, base station, and cell selection control method

Info

Publication number: WO2015104839A1
Application number: PCT/JP2014/050341
Authority: WO
Inventors: 玉木　諭; 山本　知史; 仁志石田; 倫太郎片山; 栄里子武田
Original assignee: 株式会社日立製作所
Priority date: 2014-01-10
Filing date: 2014-01-10
Publication date: 2015-07-16

Abstract

A wireless communication system includes a plurality of base stations each of which wirelessly communicates with a user terminal and each of which holds group identification information and a wireless communication parameter. The plurality of base stations include a plurality of base station groups each having respective different group identification information. In each of the plurality of base station groups, the same group identification information and the same wireless communication parameter are shared. Each of the plurality of base stations transmits, to the user terminal, broadcast information including the group identification information and wireless communication parameter. In a group of base stations each having received, from the user terminal, a random access channel that complies with the wireless communication parameter transmitted by that base station, a base station, for which the received-signal power of the random access channel is the greatest in that group, connects to the user terminal.

Description

Wireless communication system, base station, and cell selection control method

The present invention relates to a radio communication system, a base station, and a cell selection control method.

With the increase in the bandwidth of wireless communication, a multi-carrier communication scheme is used in which transmission information is divided into a plurality of frequency bands called subcarriers for communication. Among multi-carrier communication systems, the OFDM (Orthogonal Frequency Division Multiplexing) system has improved resistance to delayed waves by narrowing the bandwidth per subcarrier. Furthermore, the OFDM system is used in a wide range of systems because it can realize high frequency utilization efficiency without using a guard band between subcarriers by utilizing the orthogonality of signals.

Also, OFDMA (Orthogonal Frequency Division Multiple Access) that divides OFDM radio resources into units called resource blocks having one or a plurality of subcarriers and a certain time width and performs multiple access. The system is adopted in a wireless communication system called WiMAX (Worldwide Interoperability of Microwave Access) or LTE (Long Term Evolution).

In a wireless communication system, user terminals can be installed in a wide range by installing base stations called macro cell base stations, which have high transmission power and have a coverage area per base station ranging from several hundred meters to several kilometers. Wireless communication can be performed. However, since radio waves used for wireless communication are attenuated by distance and are shielded by, for example, buildings, there are places where radio waves from the macro cell base station are weakened in the coverage area of the macro cell base station. Moreover, since the number of user terminals in the cover area increases as the coverage area of the macro cell base station increases, the radio resources available to each user terminal decrease.

For this purpose, a heterogeneous network is used in which base stations called small cell base stations having low transmission power and a small cover area per base station are installed at a plurality of locations in the cover area of the macro cell base station. The heterogeneous network can secure a radio resource that can be used by each user terminal by using radio resources of a small cell base station while covering a wide range of the macro cell base station as a whole system.

In a heterogeneous network, the number of small cell base stations can be increased, and a large number of user terminals can be connected to the small cell base stations to increase the radio resources of the entire system. However, on the other hand, since the cover area of the small cell base station is narrow, the connection destination cell is frequently switched as the user terminal moves. In addition, since a large number of small cell base stations are installed in the coverage area of the macro cell base station, there are a large number of base stations that are candidates for optimal connection destinations especially for user terminals connected to the macro cell base station. Furthermore, the processing load for the user terminal to detect the base station increases.

As background art of this technical field, for example, Non-Patent Document 1 describes a method of optimizing frequent connection destination cell switching accompanying movement of a user terminal, and processing load by controlling detection conditions of connection destination candidate base stations. Is described.

For example, in the method described in Non-Patent Document 1 for reducing the processing load by controlling the detection conditions of base stations that are connection destination candidates, there is a tradeoff between the ease of detecting an appropriate connection destination base station and the processing load. Therefore, there is a problem that the processing load cannot be reduced sufficiently if the connection destination base station is appropriately detected.

In order to solve the above-described problem, an object of the present invention is to determine an appropriate connection destination base station while reducing the load for each user terminal to detect a connection destination base station candidate, and to increase the system capacity of the wireless communication system. It is in.

One aspect of the present invention is as follows. Including a plurality of base stations that perform radio communication with user terminals, each of the plurality of base stations holding group identification information and radio communication parameters, and the plurality of base stations each having different group identification information A plurality of base station groups, each of the plurality of base station groups sharing the same group identification information and the same radio communication parameter, and each of the plurality of base stations is configured to transmit the group to the user terminal. Among the base stations that transmit the broadcast information including identification information and the wireless communication parameters, and have received the first random access channel according to the wireless communication parameters transmitted by the base station from the user terminal, A radio communication system in which a base station having the largest received signal power of the first random access channel is connected to the user terminal. .

According to one aspect of the present invention, it is possible to determine an appropriate connection destination base station while reducing the load for each user terminal to detect a connection destination base station candidate, and to increase the system capacity of the wireless communication system. it can.

It is explanatory drawing which shows the example of an outline | summary of the radio | wireless communications system in embodiment of this invention. It is a block diagram which shows the hardware structural example of the base station in embodiment of this invention. It is a block diagram which shows the hardware structural example of the connection management apparatus in embodiment of this invention. It is a sequence diagram which shows the 1st example of the cell selection process in embodiment of this invention. It is a sequence diagram which shows the 2nd example of the cell selection process in embodiment of this invention. It is a sequence diagram which shows the example of the hand-over process in embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that this embodiment is merely an example for realizing the present invention, and does not limit the technical scope of the present invention. In each figure, the same reference numerals are given to common configurations.

In the following embodiments, sequences and processes may be described in a specific order. However, unless there is a dependency on the order in which the result of one process is used in the next process, the order of the processes May be replaced, or processing may be performed in parallel. Further, even when the subsequent process uses the execution result of the previous process, the respective processes may be executed asynchronously, and the latest previous process execution result at the time of the subsequent process execution may be used for the subsequent process.

In the following embodiments, a base station that communicates with a wide range of terminals with relatively large transmission power is referred to as a macro cell base station, and a base station that communicates with terminals within a narrow range with low transmission power is referred to as a small cell base station. When there is no need to distinguish between a macro cell base station and a small cell base station, these are simply referred to as base stations.

Further, in the following embodiments, a plurality of constituent elements may be exemplified by specific numbers, but the number of the constituent elements may be different from the illustrated examples unless otherwise limited.

FIG. 1A is an explanatory diagram illustrating an example of a configuration of a wireless communication system in all the embodiments including the first embodiment. The wireless communication system includes a network 101 and a plurality of base stations 102-1 to 102-6 connected via the network 101.

The plurality of base stations include macro cell base stations 102-1 and 102-2, and small cell base stations 102-3, 102-4, 102-5, and 102-6. The wireless communication system also includes a user terminal 111-that communicates with the base station by wireless communication with the core network 103 and the connection management device 104 connected to the base stations 102-1 to 102-6 via the network 101. 1, 111-2.

Hereinafter, when the base stations 102-1 to 102-6 are not particularly distinguished, they are simply referred to as the base station 102. Further, when the user terminals 111-1 and 111-2 are not particularly distinguished, they are simply referred to as the user terminal 111. In FIG. 1A, two macro cell base stations 102-1 and 102-2 are shown. However, in this embodiment, the number of macro cell base stations is not limited to two, and any number of macro cell base stations may be provided. The same applies to the numbers of small cell base stations 102-3 to 102-6, user terminals 111, and connection management devices 104.

In the following, signals and communications from the base station 102 to the user terminal 111 are referred to as downlink signals and downlink communications, respectively. Conversely, signals and communications from the user terminal 111 to the base station 102 are referred to as uplink signals and uplink communications, respectively.

The base station 102 is connected to the core network 103 via the network 101. The base station 102 transmits a downlink signal to the user terminal 111 and receives an uplink signal transmitted by the user terminal 111. The range in which each of the base stations 102 communicates may be in an inclusive relationship between the plurality of base stations 102, or a part of the communication range may overlap.

Each base station 102 has one or a plurality of cell IDs, and transmits broadcast information including the cell IDs within the communication range. Here, a plurality of base stations 102 may have the same cell ID. For example, a plurality of small cell base stations in the vicinity of the same macro cell base station may have a common cell ID.

Note that the cell ID is an example of information for identifying the group of the base stations 102. The group of base stations 102 may be composed of one base station 102. For example, when the same cell ID is shared among a plurality of base stations 102, the user terminal 111 that has received broadcast information including the same cell ID from each of the plurality of base stations 102, Treat as one base station 102 without distinction. In addition to the cell ID, each base station 102 has base station identification information unique to each base station 102, and transmits random access reception information including the base station identification information to the connection management apparatus 104.

The core network 103 includes a mobility management function and a gateway function with other networks. The connection management device 104 assists the connection between the user terminal 111 and the base station 102. The connection management device 104 compares the random access reception information received from each base station 102, and notifies the connection management information to each base station 102 based on the comparison result.

The connection management device 104 may be an independent device connected to one or a plurality of base stations 102 via the network 101, or may be included in any of the base stations 102 as a function. In this case, the base station 102 performs both processing as the base station 102 and processing as the connection management device 104.

FIG. 1B is a block diagram illustrating a hardware configuration example of the base station 102 mainly including a processing unit including a DSP, a CPU, and a logic circuit in the present embodiment and the embodiments described later. The base station 102 includes a CPU / DSP module 401 that is an example of a processing unit, a memory 402 that is an example of a storage unit, a logic circuit module 403 that is an example of a processing unit, a network interface (I / F) 404, And an RF module 405 that is a wireless communication unit connected to one or a plurality of antennas, and each is connected via a bus 406.

The processing by the base station 102 in the present embodiment and in each embodiment described below is necessary for one or both of a program executed by the CPU / DSP module 401 serving as a processing unit and an arithmetic circuit in the logic circuit module 403, and / or necessary. For example, the memory 402 is used. In addition, the memory 402 holds information, programs, and the like that are required in each process of the present embodiment and each embodiment described later. Examples of the information include broadcast information 200, random access reception information 210, connection management information 211, connection auxiliary information 311, candidate base station information 320, interference cancellation information, and a cell selection bias value.

The network interface (I / F) 404 inputs and outputs control signals, transmission signals before signal processing, and reception signals after signal processing. The RF module 405 converts a transmission signal into a radio frequency band signal, transmits the signal via an antenna, and converts a signal received via the antenna into a baseband signal.

Note that each module and bus 406 are not necessarily single. For example, there may be a plurality of CPU / DSP modules 401 and a plurality of buses 406. When there are a plurality of buses 406, it is not always necessary that all the buses 406 are connected to all the modules. For example, in addition to the buses 406 connected to all the modules, the memory 402 and the logic circuit module 403. There may also be a bus 406 that connects only to.

FIG. 1C is a block diagram illustrating a hardware configuration example of the connection management apparatus 104 mainly including a processing unit including a DSP, a CPU, and a logic circuit in the present embodiment and the embodiments described later. The connection management apparatus 104 includes a CPU / DSP module 501 that is an example of a processing unit, a memory 502 that is an example of a storage unit, a logic circuit module 503 that is an example of a processing unit, and a network interface (I / F) 504. Are connected to each other via a bus 506. The memory 502 holds random access reception information 210, connection management information 211, connection auxiliary information 311, candidate base station information 320, and the like. The description of each configuration of the connection management device 104 is omitted because it is the same as the above description of each configuration corresponding to the base station 102.

Each user terminal 111 performs a cell selection process before starting communication and enters a connection state with any of the base stations 102. FIG. 2 is a sequence diagram illustrating a first example of cell selection processing for the user terminal 111 to be connected to the base station 102. In FIG. 2, processing by three base stations A, B, and C is shown as an example.

2, each base station 102 periodically transmits broadcast information 200 including a wireless communication parameter and a cell ID within the communication range of the base station. The wireless communication parameter is, for example, information indicating the timing at which the user terminal 111 transmits a random access channel to the base station 102. At this time, for example, the base station A and the base station B share the same cell ID and the same radio communication parameter in advance, and the same broadcast information including the cell ID and the radio communication parameter, for example, 200 is transmitted. In addition, the base station C has a cell ID different from that of the base station A and the base station B.

User terminal 111 receives broadcast information 200 transmitted from each base station 102, and selects broadcast information 200 having the highest received power, for example, from broadcast information 200 that could be received. The user terminal 111 transmits the random access channel 201 to the base station 102 that has transmitted the broadcast information 200 according to the wireless communication parameters included in the broadcast information 200.

Here, for example, when the base station A and the base station B share the cell ID and the wireless communication parameter, the received power of the broadcast information 200 from the base station A and the received power of the broadcast information 200 from the base station B The random access channel 201 transmitted by the user terminal 111 follows the same wireless communication parameter regardless of which received power is large.

Each base station 102 attempts to receive the random access channel 201 transmitted by the user terminal 111, and the base station 102 that has received the valid random access channel 201 measures the received power value of the random access channel 201. The random access channel 201 effective for each base station 102 is the random access channel 201 transmitted according to the wireless communication parameters included in the broadcast information 200 transmitted by the own base station. The base station 102 notifies the connection management apparatus 104 of random access reception information 210 including the received power value and the base station identification information of the base station 102.

Here, each base station 102 may also measure the received power value for the random access channel 201 not addressed to itself, and notify the connection management device 104 of the random access reception information 210 including the received power value. In this case, the random access reception information 210 transmitted by each base station 102 includes information for identifying whether or not the random access channel 201 received by each base station 102 is addressed to the own station.

The connection management device 104 compares the notified random access reception information 210 and notifies the base station 102 that transmitted the random access reception information 210 of the connection management information 211 based on the comparison result. At this time, the connection management apparatus 104 transmits connection management information 211 including a connection process continuation instruction to one base station 102 having the largest received power value of the random access channel 201. The connection management apparatus 104 transmits connection management information 211 including a connection processing interruption instruction to the other base stations 102.

For example, the received power of the random access channel 201 included in the random access reception information 210 notified from the base station B is higher than the received power value of the random access channel 201 included in the random access reception information 210 notified from the base station A. When the value is larger, the connection management device 104 transmits connection management information 211 including a connection processing continuation instruction to the base station B. In this case, the connection management apparatus 104 transmits connection management information 211 including a connection processing interruption instruction to the base station A.

The base station 102 instructed to interrupt the connection processing as the connection management information 211 from the connection management device 104 interrupts this processing. The base station 102 instructed to continue the connection process as the connection management information 211 from the connection management device 104 transmits a random access response 202 including communication resource allocation information such as transmission timing to the user terminal 111.

The user terminal 111 that has received the random access response 202 transmits a connection request 203 including a user terminal unique ID and the like to the base station 102 that has transmitted the random access response 202 using the allocated communication resource. The base station 102 that has received the connection request 203 transmits a connection setting 204 to the user terminal 111, and the user terminal 111 is connected to the base station 102.

Of the above processing, processing from when the user terminal 111 transmits the random access channel 201 to when the connection setting 204 is received is referred to as a random access sequence 250.

In this embodiment, since the user terminal 111 handles a plurality of base stations 102 sharing the same cell ID as one base station 102, the measurement targets of the connection candidate base stations 102 can be reduced. Therefore, the radio communication system according to the present embodiment can reduce the load for each user terminal 111 to detect the connection candidate base station 102, and thus increase the system capacity of the radio communication system.

Further, in this embodiment, even when a plurality of base stations 102 sharing the same cell ID receive the random access channel 201 from the user terminal 111, the connection management device 104 is based on the received power value of the random access channel 201. Then, an appropriate connection destination is determined from the plurality of base stations 102. Therefore, the wireless communication system of the present embodiment can determine a connection destination base station 102 appropriate for each user terminal 111.

In this embodiment, only the base station 102 instructed to continue the connection process transmits a random access response 202 to the user terminal 111. That is, it is not necessary for the other base station 102 to transmit the random access response 202, and radio waves transmitted by the entire wireless communication system can be reduced.

FIG. 3 is a sequence diagram showing a second example of cell selection processing for the user terminal 111 to be connected to the base station 102. In FIG. 3, similarly to FIG. 2, processing by three base stations A, B, and C is described as an example.

3, each base station 102 periodically transmits broadcast information 200 including a wireless communication parameter and a cell ID within the communication range of the base station. At this time, between the plurality of base stations, for example, the base station A and the base station B share the same cell ID and the same wireless communication parameter in advance, and the same notification including the cell ID and the wireless communication parameter Information 200 is transmitted. Further, the base station C has a cell ID different from that of the base station A and the base station B.

The user terminal 111 receives the broadcast information 200 transmitted from each base station, and selects the broadcast information 200 having the highest received power from the broadcast information 200 that can be received, for example. The user terminal 111 transmits the random access channel 201 including the cell ID included in the broadcast information 200 to the base station 102 that has transmitted the broadcast information 200 according to the radio communication parameter included in the broadcast information 200.

At this time, the random access channel transmitted by the user terminal 111 is the case where either the received power of the broadcast information 200 from the base station A or the received power of the broadcast information 200 from the base station B is large. 201 are the same.

Each base station 102 attempts to receive the random access channel 201 transmitted by the user terminal 111, and the base station 102 that has received the valid random access channel 201 measures the received power value of the random access channel 201. The base station 102 notifies the connection management apparatus 104 of random access reception information 210 including the received power value and the base station identification information of the base station 102.

Here, each base station 102 may also measure the received power value for the random access channel 201 that is not addressed to itself and notify the connection management device 104 as the random access reception information 210. At this time, the random access reception information 210 transmitted by each base station 102 includes information for identifying whether or not the random access channel 201 received by each base station 102 is addressed to the own station.

In addition, the base station 102 that has received the valid random access channel 201 does not wait for the connection management information 221 to be received from the connection management device 104, and receives a random access response including communication resource allocation information such as transmission timing to the user terminal 111. 202 is transmitted. For example, the base station 102 that has received the valid random access channel 201 may transmit the random access response 202 to the user terminal 111 in parallel with the notification of the random access reception information 210 to the connection management apparatus 104.

The user terminal 111 that has received the random access response 202 transmits a connection request 203 including a user terminal unique ID and the like to the base station 102 that has transmitted the random access response 202 using the allocated communication resource. The user terminal 111 that has received a plurality of random access responses 202 may transmit connection requests 203 corresponding to all the random access responses 202, for example. Further, the user terminal 111 that has received a plurality of random access responses 202 may transmit only some of the random access responses 202, for example, the connection request 203 corresponding to the random access response 202 having the largest received power.

The connection management device 104 compares the notified random access reception information 210 and notifies the base station 102 that transmitted the random access reception information 210 of the connection management information 211 based on the comparison result. At this time, the connection management apparatus 104 transmits connection management information 211 including a connection processing continuation instruction to the base station 102 having the largest received power value of the random access channel 201. The connection management apparatus 104 transmits connection management information 211 including a connection processing interruption instruction to the other base stations 102.

For example, the received power value of the random access channel 201 included in the random access reception information 210 notified from the base station B is higher than the received power value of the random access channel 201 included in the random access received information 210 notified from the base station A. If this is larger, the connection management device 104 transmits connection management information 211 including a connection process continuation instruction to the base station B. In this case, the connection management apparatus 104 transmits connection management information 211 including a connection processing interruption instruction to the base station A.

The base station 102 instructed to interrupt the connection processing as the connection management information 211 from the connection management device 104 interrupts this processing. The base station 102 instructed by the connection management device 104 to continue connection processing as the connection management information 211 and receives the connection request 203 from the user terminal 111 transmits a connection setting 204 to the user terminal 111, and the connection setting 204 Is connected to the base station 102.

Of the above processes, the process from when the user terminal 111 transmits the random access channel 201 to when the connection setting 204 is received is referred to as a random access sequence 260.

In the wireless communication system according to the present embodiment, the base station 102 that has received the valid random access channel 201 does not wait for the connection management information 211 to be received from the connection management device 104, and sends a random access response 202 to the user terminal 111. Send. Therefore, it is possible to shorten the time from when the user terminal 111 transmits the random access channel 201 to when the user terminal 111 receives the random access response 202.

FIG. 4 is a sequence diagram illustrating an example of a handover process for switching the base station 102 to which the user terminal 111 is connected. The user terminal 111 receives candidate base station information 320 including wireless communication parameters and cell IDs of candidate base stations 102 that are connection switching destination candidates from the connected base station 102. The user terminal 111 that has received the candidate base station information 320 receives the broadcast information 200 transmitted from the base station 102 included in the candidate base station information 320, and measures the received power value. Here, in the candidate base station information 320, the base station 102 having a common wireless communication parameter and cell ID is not distinguished and is treated as one base station 102.

For example, a predetermined condition such as a case where a difference obtained by subtracting the reception signal power of the notification information 200 from the connected base station 102 from the reception signal power of the notification information 200 from the candidate base station 102 is equal to or larger than a predetermined threshold. When satisfying, the user terminal 111 transmits a measurement result report 301 including the cell ID of the candidate base station 102 to the connected base station 102. The connected base station 102 that has received the measurement result report 301 determines whether or not handover is possible.

For example, the connected base station 102 determines to perform handover if the difference in received signal power described above is equal to or greater than a predetermined threshold, and determines not to perform handover if the difference is smaller than the threshold. Further, when the broadcast information 200 transmitted by the candidate base station 102 includes traffic information of the candidate base station 102, whether or not handover is possible may be determined as follows. For example, the connected base station 102 determines to perform handover if the difference obtained by subtracting the traffic congestion level of the candidate base station 102 from the traffic congestion level of the connected base station 102 is equal to or greater than a predetermined threshold value. If it is smaller, it is determined that handover is not performed.

When the connected base station 102 determines to perform handover, the connected base station 102 transmits a handover instruction 302 to the base station 102 having the cell ID to the user terminal 111.

The user terminal 111 that has received the handover instruction 302 executes the random access sequence 250 or the random access sequence 260 described above. The user terminal 111 that has received the handover instruction 302 switches the connection destination from the candidate base station 102 to the selected base station 102 and completes the handover. The switching destination base station 102 receives the completion of the handover, and transmits the handover end information 310 to the connection management device 104.

The connection management apparatus 104 that has received the handover end information 310 receives the random access channel received signal power at each base station 102 obtained from the random access reception information 210 received from each base station in the random access sequence 250 or the random access sequence 260. The connection assistance information 311 including information regarding the transmission is transmitted to the base station 102 that has transmitted the handover end information 310.

The base station 102 that has received the connection assistance information 311 may perform correction according to the connection assistance information 311 when determining a communication method with the user terminal 111. For example, when the base station 102 that has received the connection assistance information 311 has a difference obtained by subtracting the random access channel received signal power in the other base station 102 from the random access channel received signal power of the own base station being equal to or greater than a predetermined threshold. May preferentially select the transmission mode using the cell-specific reference signal.

Note that the base station 102 transmits a common reference signal (cell individual reference signal) to the user terminals 111 existing in the communication range of the base station 102 in the transmission mode using the cell individual reference signal. The transmission mode using the cell individual reference signal is more susceptible to interference between base stations than the transmission mode using the user terminal individual reference signal described later.

When the difference between the random access channel received signal power of the own base station and the random access channel received signal power of the other base station 102 is large, the signal of the own base station and the signal of the other base station may interfere with each other. Low. Therefore, in such a case, the base station 102 may select a transmission mode that uses a cell-specific reference signal.

Also, for example, when the base station 102 that has received the connection assistance information 311 has a difference obtained by subtracting the random access channel received signal power in the other base station 102 from the random access channel received signal power of the own base station smaller than a predetermined threshold value May preferentially select the transmission mode using the user terminal individual reference signal.

Note that, for example, the base station 102 that has measured the largest random access channel received signal power among the base stations 102 included in the connection auxiliary information 311 may be the other base station 102 described above. Further, for example, the average value of the random access channel received signal power at the base station 102 included in the connection assistance information 311 may be used as the random access channel received signal power at the other base station 102.

In addition, in the transmission mode using the user terminal individual reference signal, the base station 102 refers to a user terminal 111 that exists in the communication range of the base station 102, and a different reference for each user terminal 111, in addition to the cell individual reference signal. A signal (user terminal individual reference signal) is transmitted. At this time, since the base station 102 transmits the cell individual reference signal and the user terminal individual reference signal, the communication efficiency is lower than the transmission mode using the cell individual reference signal. However, transmission mode signals using user terminal individual reference signals transmitted by each base station 102 are unlikely to interfere with each other.

When the difference between the random access channel received signal power of the own base station and the random access channel received signal power of the other base station 102 is small, the signal of the own base station and the signal of the other base station 102 may interfere with each other. High nature. Therefore, in this case, the base station 102 may select a transmission mode using a user terminal individual reference signal in order to improve communication quality.

Also, there is a possibility that a plurality of base stations 102 having the same cell ID transmit the same cell individual reference signal. Therefore, the base station 102 that has received the connection assistance information 311 uses the random access reception signal power of the base station 102 having the same cell ID as that of the own base station as follows: The communication method may be corrected as compared with.

For example, the base station that has received the connection assistance information 311 has a difference obtained by subtracting the random access channel received signal power in the other base station 102 having the same cell ID as that of the own base station from the random access channel received signal power of the own base station. If it is equal to or greater than the predetermined threshold, the transmission mode using the cell individual reference signal may be selected with priority.

Also, for example, the base station 102 that has received the connection assistance information 311 subtracts the random access channel received signal power in the other base station 102 having the same cell ID as the own base station from the random access channel received signal power of the own base station. When the difference is equal to or smaller than a predetermined threshold, the transmission mode using the user terminal individual reference signal may be preferentially selected.

For example, among the base stations 102 having the same cell ID as that of the own base station and included in the connection auxiliary information 311, the base station 102 that has measured the largest random access channel received signal power is referred to as the above-described own base station. Other base stations 102 having the same cell ID may be used. Further, for example, the average value of the received signal power of the random access channel in the base station 102 included in the connection auxiliary information 311 and having the same cell ID as that of the own base station is determined as another base station having the same cell ID as that of the own base station. Random access channel received signal power at 102 may be used.

Also, the base station 102 that has received the connection auxiliary information 311 may correct the candidate base station information 320 according to the connection auxiliary information 311 when transmitting the candidate base station information 320 to the user terminal 111. For example, the base station 102 that has received the connection assistance information 311 may preferentially select the base station 102 whose random access channel received signal power is greater than or equal to a predetermined value as the base station 102 that includes the candidate base station information 320.

For example, the base station 102 that has received the connection assistance information 311 may exclude the base station 102 whose random access channel received signal power is below a certain level from the candidate base station information 320. Alternatively, for example, the base station 102 that has received the connection assistance information 311 may exclude the small cell base station 102 having a random access channel reception signal power of a certain value or less from the candidate base station information 320. In addition, the base station 102 that has received the connection assistance information 311 transmits again the candidate base station information 320 including the base station 102 excluded from the candidate base station information 320 to the user terminal 111 after a predetermined time has elapsed since the completion of the handover. May be.

As described above, the base station 102 corrects the connection candidate base station information 320 according to the connection auxiliary information 311 including the random access channel received signal power in the other base stations 102. By the correction, the measurement target of the handover candidate base station is reduced, and the user terminal 111 can be handed over to an appropriate base station 102.

The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for better understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

In addition, each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files that realize each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

Claims

Including a plurality of base stations that perform wireless communication with user terminals,
Each of the plurality of base stations holds group identification information and radio communication parameters,
The plurality of base stations include a plurality of base station groups having different group identification information,
In each of the plurality of base station groups, the same group identification information and the same wireless communication parameter are shared,
Each of the plurality of base stations is
Broadcast information including the group identification information and the wireless communication parameter is transmitted to the user terminal,
Among the base stations that have received the first random access channel according to the radio communication parameters transmitted by the base station from the user terminal, the base station with the highest received signal power of the first random access channel is the user. A wireless communication system connected to a terminal.
The wireless communication system according to claim 1,
A connection management device that is connected to the plurality of base stations via a network and manages connection between the user terminal and the plurality of base stations;
Each of the plurality of base stations is
Further holding base station identification information unique among the plurality of base stations,
When the first random access channel is received from the user terminal, random access reception information including the base station identification information and received signal power information of the first random access channel to the connection management device Send and
The connection management apparatus transmits a connection instruction with the user terminal to a first base station having the highest received signal power of the first random access channel among base stations that have transmitted the random access reception information. Wireless communication system.
The wireless communication system according to claim 2,
A wireless communication system in which a base station that has received the connection instruction from the connection management device responds to a user terminal that has transmitted the first random access channel.
The wireless communication system according to claim 2,
The connection management device transmits a connection processing interruption instruction with the user terminal to a base station other than the first base station,
The base station that has received the first random access channel responds to the user terminal that has transmitted the random access channel before receiving the connection instruction and the connection processing interruption instruction from the connection management apparatus. Wireless communication system.
The wireless communication system according to claim 2,
The connection management device transmits connection auxiliary information including received signal power information of the first random access channel in another base station to the first base station,
The group identification information indicates a cell ID of the base station,
The first base station is
A first transmission mode using a cell-specific reference signal based on a difference between a received signal power of the first random access channel in the own base station and a received signal power of the first random access channel in the other base station; And the radio | wireless communications system which selects the transmission mode selected from the 2nd transmission mode using a user terminal separate reference signal, and performs radio | wireless communication with the said user terminal in the said selected transmission mode.
The wireless communication system according to claim 5,
The wireless communication system, wherein the another base station is a base station that shares group identification information with the first base station.
The wireless communication system according to claim 2,
The connection management device transmits connection auxiliary information including received signal power information of the first random access channel in another base station to the first base station,
The plurality of base stations are
Holds information on candidate base stations to be handed over by user terminals connected to the base station,
When receiving the connection assistance information from the connection management device and the other base station includes the candidate base station, the candidate base station based on the received signal power of the first random access channel in the candidate base station A wireless communication system that corrects the information and transmits the corrected candidate base station information to the user terminal.
A base station that performs wireless communication with a user terminal,
Holding group identification information and wireless communication parameters,
Share the same group identification information and the same group identification information with all base stations in the base station group to which the base station belongs,
Broadcast information including the group identification information and the wireless communication parameter is transmitted to the user terminal,
Receiving a first random access channel according to a radio communication parameter transmitted by the base station from the user terminal; and receiving the first random access channel in the base station among base station groups to which the base station belongs. A base station connected to the user terminal when the signal power is the highest.
A cell selection control method in a radio communication system including a plurality of base stations that perform radio communication with a user terminal,
Each of the plurality of base stations holds group identification information and radio communication parameters,
The plurality of base stations include a plurality of base station groups having different group identification information,
In each of the plurality of base station groups, the same group identification information and the same wireless communication parameter are shared,
The method
Each of the plurality of base stations transmits broadcast information including the group identification information and the wireless communication parameter to the user terminal,
Among the base stations that have received the first random access channel according to the radio communication parameters transmitted by the base station from the user terminal, the base station with the highest received signal power of the first random access channel is the Connecting with a user terminal.