JP2012010278A - Base station and radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform communication in a state of being distributed to a plurality of base stations without concentrating on one base station.SOLUTION: The radio communication system comprises a first base station having a first radio area, a second base station having a second radio area which is provided in the first radio area and smaller than the first area, and a mobile station capable of performing radio communication with both the base stations. The first base station assigns a radio communication channel in response to a connection request from the mobile station, notifies the mobile station of information indicating the radio communication channel assigned to, and transmits a radio signal of a predetermined transmission output at the same timing as that for the assigned radio communication channel.

Description

  The present invention relates to a radio communication system capable of distributing mobile station connections to a plurality of base stations without concentrating the mobile station connections on one base station.

  There is a wireless communication system in which a mobile station is connected to either a macro cell base station having a cell radius of several kilometers or a micro base station having a cell radius of several hundred meters. In such a wireless communication system, a plurality of micro base stations are installed in the service area of the macro cell base station. A mobile station in the service area of the micro base station connects to the micro base station. A mobile station that is in the service area of the macro cell base station but is not in the service area of the micro base station connects to the macro base station.

JP-A-8-186866

  However, in the radio communication system as described above, since the radio signal transmission output is set according to the cell radius of the base station, the radio signal transmission output from the macro base station is larger than that of the micro base station. For this reason, when the mobile station connects to the base station, it is determined that the macro base station having a larger transmission output has a better communication environment, and as a result, the connection concentrates on the macro base station. Therefore, in order to avoid the concentration of connections to the macro base station, in Patent Document 1, when it is determined that the macro base station has high traffic, a part of the frequency allocated to this area is disabled. Thus, a plurality of micro base stations are used in this area.

  This is because when there is a connection to either a macro base station or a micro base station, the connection is concentrated on the macro base station because it is often connected to a macro base station having a higher radio field strength than the micro base station. Because. Therefore, when it is determined that the macro base station has high traffic, the mobile station becomes connected to the micro base station by disabling a part of the frequency allocated to this area. A plurality of micro base stations are used.

  As described above, in this mobile communication system, traffic concentrates on the macrocell base station, so that the capabilities of the system such as the transfer rate cannot be fully exhibited. Furthermore, a mobile station that is within the coverage area of the macro cell base station and outside the coverage area of the micro cell base station cannot be connected to any base station when the macro cell base station cannot be connected in a high traffic state. There is.

  The present invention has been made in view of such problems, and an object of the present invention is to distribute connection of mobile stations to a plurality of base stations without concentrating the connection of mobile stations to one base station. A communication system and a radio base station are provided.

  In order to achieve the above object, a wireless communication system of the present invention includes a first base station having a first wireless area, and a second wireless area that is installed in the first wireless area and is narrower than the first area. And a mobile station that can be wirelessly connected to any base station, wherein the first base station responds to a connection request from the mobile station. A first wireless communication channel is assigned, and information indicating the assigned wireless communication channel is notified to the mobile station, and a wireless signal having a predetermined transmission output is transmitted at the same timing as the assigned wireless communication channel. The control part is provided.

  Further, the predetermined transmission output is set according to the number of the second base stations installed in the first radio area.

  Further, when the mobile station receives information indicating the assigned radio communication channel from the first base station, the mobile station performs carrier sense on the radio communication channel, and an electric field level in the radio communication channel is equal to or higher than a specified level. In this case, the wireless communication system includes a second control unit that refuses wireless communication with the first base station and performs communication control so as to perform wireless communication with the first base station when the level is less than a predetermined level.

  The second base station is connected to the first base station via a network, and the second base station responds to a connection request from the mobile station in a wireless communication environment with the mobile station. If the acquired wireless communication environment does not satisfy preset conditions, wireless communication with the mobile station is performed. If the conditions are satisfied, wireless communication with the mobile station is not performed. A third control unit is provided.

  The third control unit in the second base station transmits information about the wireless communication environment to the first base station via the network, and the first control unit in the first base station If the acquired wireless communication environment satisfies the condition, do not transmit a wireless signal of the predetermined transmission output at the same timing for a wireless communication channel assigned to a subsequent connection request from the mobile station. It is characterized by.

  The third control unit in the second base station acquires information about the wireless communication environment when a connection request from the mobile station reaches a preset number of times.

  A base station having a first radio area, another base station installed in the first radio area and having a second radio area narrower than the first area, and a mobile station that can be wirelessly connected to any base station And a first base station in a wireless communication system comprising: information that assigns a wireless communication channel to a connection request from the mobile station and indicates the assigned wireless communication channel to the mobile station And a first control unit that transmits a radio signal having a predetermined transmission output at the same timing as the assigned radio communication channel.

  ADVANTAGE OF THE INVENTION According to this invention, the connection of a mobile station can be disperse | distributed to several base stations, without concentrating the connection of a mobile station to one base station.

1 is a diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention. It is a block diagram which shows the structure of the macrocell base station concerning embodiment of this invention. It is a block diagram which shows the structure of the mobile station and microcell base station concerning embodiment of this invention. It is a figure which shows the communication channel connection sequence of the radio | wireless communications system of this invention. 3 is a flowchart illustrating an operation in a mobile station in the wireless communication system of the present invention. 3 is a flowchart illustrating an operation in a macro cell base station in the wireless communication system of the present invention. It is a table | surface which shows the corresponding | compatible relationship between the installation number of the microcell base station installed in the radio | wireless area of the macrocell base station of this invention, and radio wave intensity. 5 is a flowchart illustrating an operation in a microcell base station of the wireless communication system of the present invention. 3 is a flowchart illustrating an operation in a macro base station of the wireless communication system of the present invention.

  Next, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a wireless communication system according to an embodiment of the present invention. As shown in FIG. 1, the wireless communication system 1 includes a macro cell base station 10, a micro cell base station 30, and a mobile station 20. The macrocell base station 10 covers the radio area 10A. The microcell base station 30 covers the radio area 30A. The microcell base station 30 is mainly installed in the radio area 10A so that the radio area 30A to be covered and the radio area 10A of the macrocell base station 10 overlap. In this way, by installing the macro cell base station 10 and the micro cell base station 30 so as to overlap each other, a radio area that cannot be covered by the micro cell base station 30 like the radio area 10C of FIG. Can be covered by station 10. The mobile station 20 performs wireless communication by wirelessly connecting to either the macrocell base station 10 or the microcell base station 30.

  When starting the wireless communication, the mobile station 20 compares the radio field intensity of the radio signal transmitted from each base station and determines which base station to connect to. At this time, a base station with a wider radio area generally has a higher radio signal transmission output. Therefore, in the wireless communication system 1 as shown in FIG. 1, wireless connections are concentrated toward the macrocell base station 10. Therefore, the macrocell base station 10 allocates a radio signal having a predetermined transmission output when transmitting link channel allocation information including information on a radio communication channel to be allocated in response to a link channel allocation request (connection request) of the mobile station 20. Transmit for a predetermined period at the same timing as the wireless communication channel. Here, the predetermined transmission output (radio wave intensity) means that the mobile station 20 existing within a certain distance from the macrocell base station 10 performs carrier sense for the assigned wireless communication channel after receiving the link channel assignment information. Means a transmission output having such a magnitude that the interference wave level is high and link channel allocation is rejected.

  For this reason, the mobile station 20 existing within a certain distance from the macrocell base station 10 attempts to establish a wireless connection to the microcell base station 30 rather than the macrocell base station 10 that refuses to allocate a link channel. . Thereby, concentration of wireless connection to the macrocell base station 10 can be avoided. In addition, the connection impossible area 10B in FIG. 1 is a connection to the macro base station 10 due to the influence of a radio signal having a predetermined transmission output transmitted at the same timing when the link channel allocation information is transmitted from the macro cell base station 10. It means an area that cannot.

  Further, the predetermined transmission output (radio wave intensity) may take into account the number of installed microcell base stations 30 present in the radio area 10 </ b> A of the macrocell base station 10. As shown in FIG. 7, the macro cell base station 10 increases the transmission output (radio wave intensity) as the number of installed micro base stations 30 increases, and decreases the transmission output (radio wave intensity) as the number of installed micro base stations 30 decreases. Also good. When the number of installed micro cell base stations 30 in the radio area 10A is large, there are many radio areas 30A covered by the micro base stations 30, and there are few areas not covered. Therefore, in the macrocell base station 10, the mobile station 20 that is present at the cell edge (wireless area 10D shown in FIG. 1) and is difficult to connect to the base station by setting the transmission output large and expanding the wireless area 10A. Can be wirelessly connected with priority over the macrocell base station 10. On the other hand, when the number of installed micro cell base stations 30 in the radio area 10A is small, the area covered by the micro base station 30 is also reduced, so in the macro cell base station 10, by reducing the transmission output (radio wave intensity), A mobile station 20 existing in an area (radio area 10C shown in FIG. 1) that is relatively close to the macro cell base station 10 but not covered by the micro cell base station 30 can also be connected to the macro cell base station 10. be able to.

  FIG. 2 is a block diagram showing a configuration of the macro cell base station according to the embodiment of the present invention. As shown in FIG. 2, the macro cell base station 10 includes an antenna 11, a communication processing unit 12, a signal processing unit 13, and a control unit 14.

  The antenna 11 receives a radio signal transmitted from the mobile station 20, and transmits a radio signal to the mobile station 20. The antenna 11 includes a directional antenna having directivity, an omnidirectional antenna having no directivity, an adaptive array antenna including a plurality of antennas, and the like.

  The communication processing unit 12 transmits or receives a radio signal using the antenna 11. The wireless processing unit 12 includes a reception system (LNA, down converter and A / D converter), a transmission system (D / A converter, up converter and power amplifier) and the like. The communication processing unit 12 converts the baseband signal from the signal processing unit 13 into an analog signal at the time of signal transmission. The communication processing unit 12 upconverts and amplifies the analog signal to generate a radio signal, and transmits the generated radio signal from the antenna 11. Further, the communication processing unit 12 controls the transmission output of the radio signal according to the instruction from the control unit 14.

  The communication processing unit 12 converts the radio signal into a baseband signal by amplifying, down-converting, and A / D converting the radio signal from the antenna 11 when receiving the signal. The baseband signal is input to the signal processing unit 13.

  The signal processing unit 13 demodulates user data from the baseband signal and performs error correction decoding at the time of signal reception. The signal processing unit 13 modulates user data and performs error correction coding using a modulation class instructed by the control unit 14 at the time of signal transmission.

  The control unit 14 is realized as one function of the CPU, and controls the operation of the macrocell base station 10 using a program stored in a storage unit (not shown). The control unit 14 includes a carrier sense unit 141, a channel assignment unit 142, and a communication control unit 143.

  The carrier sense processing unit 141 detects signal power of a radio signal that may cause interference in each radio communication channel, and outputs a detection result (carrier sense result) to the channel allocation unit 142.

  The channel assignment unit 142 assigns a radio communication channel to the mobile station 20 that has requested the link channel assignment according to the detection result of the carrier sense processing unit 141.

  In response to the link channel allocation request from the mobile station 20, the communication control unit 143 sends link channel allocation information including information on the radio communication channel allocated by the channel allocation unit 142 via the communication processing unit 12. Send to. In addition, the communication processing unit 12 is instructed to transmit output when performing wireless communication with the mobile station 20, and the signal processing unit 13 is instructed to specify a modulation class when transmitting data.

  Further, the communication control unit 143 causes the communication processing unit 12 to transmit a radio signal having a predetermined transmission output at the same timing as the radio communication channel allocated by the channel allocation unit 143 in response to the link channel allocation request. The radio signal having the predetermined transmission output is preferably a radio communication channel having the same frequency as the assigned radio communication channel or an adjacent frequency band.

  FIG. 3 is a block diagram showing configurations of a mobile station and a microcell base station according to the embodiment of the present invention. As shown in FIG. 3A, the mobile station 20 includes an antenna unit 21, a transmission / reception unit 22, a baseband processing unit 23, a control unit 24, an input unit 25, and a carrier sense unit 26. Is provided. When starting the wireless communication, the control unit 24 transmits a link channel assignment request to the base station and receives the link channel assignment information, and then performs carrier sense of the assigned wireless communication channel to the carrier sense unit 26. In accordance with the carrier sense result, it is determined whether or not to perform wireless communication with the base station using the assigned wireless communication channel. Note that the mobile station 20 has a known configuration, and the effects of this patent can be achieved without particularly changing the hardware and software.

  As shown in FIG. 3B, the microcell base station 30 includes an antenna unit 31, a communication processing unit 32, a signal processing unit 33, and a control unit 34. The antenna unit 31, the communication processing unit 32, and the signal processing unit 33 are the same as the macro cell base station 10 and will not be described.

  The control unit 34 is realized as one function of the CPU, and controls the operation of the macrocell base station 10 using a program stored in a storage unit (not shown). The control unit 14 detects the signal power of a radio signal that may cause interference in each radio communication channel. The control unit 15 allocates a radio communication channel to the mobile station 20 that has requested the link channel allocation from the detection result (carrier sense result). Further, the control unit 15 transmits link channel allocation information including information on the allocated radio communication channel to the mobile station 20 via the communication processing unit 32. In addition, the communication processing unit 12 is instructed to transmit output when performing wireless communication with the mobile station 20, and the signal processing unit 13 is instructed to specify a modulation class when transmitting data.

  Next, the flow from when the mobile station 20 connects to the macrocell base station 10 to start wireless communication will be described with reference to FIG. FIG. 4 is a sequence diagram showing the process until the mobile station 20 wirelessly connects to the macrocell base station 10 and starts wireless communication. When the mobile station 20 starts wireless communication, a link channel allocation request 61 is sent to the macrocell base station 10. The macrocell base station 10 performs carrier sense and assigns an unused radio communication channel to the mobile station 20. The macrocell base station 10 transmits information on the assigned radio communication channel to the mobile station 20 as link channel assignment information 62. Further, the macrocell base station 10 outputs a radio signal 60B with a predetermined transmission output α at the same timing as the assigned radio communication channel. The mobile station 20 receives the link channel assignment information 62. The mobile station 30 that has received the link channel assignment information 62 performs carrier sense on the assigned radio communication channel, and determines whether the electric field level of the assigned radio communication channel is equal to or higher than a specified level. When the electric field level is equal to or higher than the specified level, the link channel allocation request 61 is sent again to the macro cell base station 10. On the other hand, if the electric field level is less than the specified level, it is determined that the wireless communication channel is unused, and wireless communication using the assigned wireless communication channel is started with respect to the macro cell base station 10.

  Next, a process until the mobile station 20 connects to the macrocell base station 10 and starts wireless communication will be described with reference to FIG. FIG. 7 is a flowchart showing operations until the mobile station 20 starts wireless communication. When the mobile station 20 starts wireless communication, a link channel assignment request is sent to the macrocell base station 10 (step S80). The mobile station 20 receives link channel assignment information (step S81). The mobile station 30 that has received the link channel assignment information performs carrier sense for the assigned radio communication channel (step S82), and determines whether the electric field level of the assigned radio communication channel is less than a specified level (step S82). S83: If the electric field level is less than the specified level, it is determined that the wireless communication channel is unused (corresponding to step S83 Yes), and the wireless communication using the assigned wireless communication channel is started for the macrocell base station 10. On the other hand, if the electric field level is equal to or higher than the specified level (corresponding to No in step S83), the link channel allocation request 61 is sent again to the macrocell base station 10. Here, for example, this link channel Even if the allocation request is made a predetermined number of times, the macro cell base station 10 If you can not continue, with ends the wireless connection process to the macrocell base station 10, another base station, i.e., attempts a wireless connection to the micro cell base station 30.

  Next, the processing of the macrocell base station 10 will be described with reference to the flowchart of FIG. When receiving the link channel assignment request from the mobile station 20 (step S90), the macro cell base station 10 performs carrier sense (step S91). After the carrier sense is executed, the macro cell base station 10 assigns a radio communication channel to the mobile station 20 (step S92). Next, the macrocell base station 10 transmits link channel allocation information to the mobile station 20 (step S93), and simultaneously transmits a radio signal with a predetermined transmission output at the same timing as the allocated radio communication channel (step S94). ).

  Next, processing in the wireless communication system 1 after the mobile station 20 in the wireless communication system 1 cannot wirelessly connect to the macrocell base station 10 will be described with reference to the flowcharts of FIGS. FIG. 8 is a flowchart showing the operation of the microcell base station 30. As a result of the processing for the macro cell base station 10 described above, if the wireless connection cannot be established, the mobile station 20 in the wireless area covered by the micro cell base station 30 tries the wireless connection to the micro cell base station 30, and the micro cell base station 30 receives the link channel request (step S10). However, when the radio communication environment between the mobile station 20 and the microcell base station 30 is not very good, the mobile station attempts a handover to the micro base station 30 in the vicinity. At this time, the control unit 34 of the microcell base station 30 that is a handover destination candidate determines whether or not the mobile station 20 that requested the handover has reached a preset number of times (for example, five times) in which the handover is set in advance. (Step S11). Then, when the number of handovers of the mobile station 20 is less than the set number (corresponding to Step S11 No), the mobile station 20 performs the wireless connection process by the handover of the mobile station 20 to itself (Step S12). ). On the other hand, when the number of handovers is equal to or greater than the set number of times and is equal to or greater than 5 (corresponding to step S11 Yes), the control unit 34 of the microcell base station 30 selects a radio communication environment with the mobile station 20, for example, one of the radio communication environments. Information about the RSSI level to be shown and the reception timing is acquired, and the acquired information is transmitted to the macrocell base station 10 via the backhaul line (step S13). The microcell base station 30 determines from the acquired information based on determination conditions such as whether the RSSI level is 0 dBμ or less and the reception timing is shifted by 5 symbols or more (step S14). As a result of the determination, if any information (or both) satisfies the determination condition (corresponding to step S14 Yes), the wireless connection process with the macrocell base station 10 is prioritized over the connection with the micro base station 30. Thus, wireless communication with the mobile station is not performed (step S15). On the other hand, when the determination condition is not satisfied (corresponding to step S14 No), the mobile station 20 directly connects to the microcell base station 30 (step S12).

  FIG. 9 is a flowchart showing the operation of the macrocell base station 10. The macro cell base station 10 receives information from the micro cell base station 30 (step S20). The macro cell base station 10 determines whether the RSSI level is 0 dBμ or less or the reception timing is shifted by 5 symbols or more from the acquired information. Determination is made (step S21). As a result of the determination, if any information (or both) satisfies the above-described determination condition (corresponding to step S21 Yes), the macrocell base station 10 stores the identification ID of the mobile station 20 that satisfies the determination condition in advance in the storage unit (illustrated). Not stored) (step S22). On the other hand, when the determination condition is not satisfied (corresponding to NO in step S21), the process is terminated as it is. When a link channel assignment request (handover request) is received from the mobile station 20 (step S23), link channel assignment information indicating a radio communication channel assigned to the mobile station 20 is transmitted, and at this time, at the same timing. A radio signal having a predetermined transmission output is not transmitted (step S24). As a result, the mobile station 20 can determine that the allocated radio communication channel is unused even if carrier sense is performed on the allocated radio communication channel. Therefore, the mobile station 20 uses the allocated radio communication channel. Wireless communication. As a result, the mobile station 20 that is performing radio communication while moving at high speed can perform stable radio communication because there is no need to repeatedly perform handover.

DESCRIPTION OF SYMBOLS 10 ... Macro cell base station, 20 ... Mobile station, 30 ... Micro cell base station, 10A ... Connection possible area, 10B ... Connection impossible area, 11, 21, 31 ... Antenna, 12, 32 ... Communication processing part, 13, 33 ... Signal processing unit, 14 ... control unit, 141 ... carrier sense unit, 142 ... channel allocation unit, 143 ... communication control unit, 21 ... antenna, 22 ... transmission / reception unit, 23 ... baseband processing unit, 24 ... control unit, 25 ... User interface section, 26... Carrier sense section, 34.

Claims (7)

A first base station having a first radio area, a second base station installed in the first radio area and having a second radio area narrower than the first area, and wireless to any base station A wireless communication system comprising a connectable mobile station,
The first base station is
A wireless communication channel is assigned to the connection request from the mobile station, information indicating the assigned wireless communication channel is notified to the mobile station, and predetermined transmission is performed at the same timing as the assigned wireless communication channel. A wireless communication system comprising a first control unit for transmitting an output wireless signal.   The radio communication system according to claim 1, wherein the predetermined transmission output is set according to the number of the second base stations installed in the first radio area. The mobile station
When receiving information indicating the assigned radio communication channel from the first base station, carrier sense for the radio communication channel is executed, and when the electric field level in the radio communication channel is equal to or higher than a specified level, the first base 3. The radio according to claim 1, further comprising a second control unit that rejects radio communication with a station and performs communication control so as to perform radio communication with the first base station when the level is less than a predetermined level. Communications system. The second base station is connected to the first base station via a network;
In response to the connection request from the mobile station, the second base station acquires information related to a wireless communication environment with the mobile station, and the acquired wireless communication environment does not satisfy a preset condition. 4. The wireless communication system according to claim 1, further comprising a third control unit that performs wireless communication with the mobile station and does not perform wireless communication with the mobile station when the condition is satisfied. 5. Wireless communication system. A third control unit in the second base station transmits information on the wireless communication environment to the first base station via the network;
The first control unit in the first base station is:
When the acquired wireless communication environment satisfies the condition, the wireless signal having the predetermined transmission output is not transmitted at the same timing with respect to the wireless communication channel allocated to the subsequent connection request from the mobile station. The wireless communication system according to claim 4.   The third control unit in the second base station acquires information about the wireless communication environment when a connection request from the mobile station reaches a preset number of times. Item 6. The wireless communication system according to Item 4 or 5. A base station having a first radio area, another base station installed in the first radio area and having a second radio area narrower than the first area, and a mobile station that can be wirelessly connected to any base station A first base station in a wireless communication system comprising:
A wireless communication channel is assigned to the connection request from the mobile station, information indicating the assigned wireless communication channel is notified to the mobile station, and predetermined transmission is performed at the same timing as the assigned wireless communication channel. A base station comprising a first control unit for transmitting an output radio signal.

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