JP5026312B2 - Communication control method for base station apparatus and base station apparatus - Google Patents

Description

  The present invention relates to a transmission power control technique, and more particularly to a base station apparatus that controls transmission power of a terminal apparatus.

In cellular mobile communication systems, it is desired to maximize system capacity while maximizing communication quality. Generally, in order to maximize the communication quality, the transmission power may be increased. However, for example, excessive uplink transmission power from the terminal device interferes with neighboring base stations, and thus the system capacity may be reduced. Conventionally, transmission power between a base station apparatus and a terminal apparatus has been determined by ranging processing for such a problem (for example, see Non-Patent Document 1).
Takeshi Hattori, Masanobu Fujioka, Revised Wireless Broadband Textbook, High Speed IP Wireless, Impress R & D, Inc., June 21, 2006, p. 180-181

  In general, when performing wireless communication using a femtocell base station having a very small cell radius, transmission power control by ranging is performed between the femtocell base station and a terminal device. Here, if the transmission power from the terminal device becomes too large, it may cause interference with neighboring base stations other than the femtocell base station, and the communication quality deteriorates.

  This invention is made | formed in view of such a condition, The objective is to provide the technique which can suppress the interference to a periphery base station.

  In order to solve the above problems, a base station apparatus according to an aspect of the present invention includes a transmission power identification unit that identifies transmission power that enables wireless communication with another base station apparatus, and a transmission power identification unit. A transmission power control unit that controls transmission power to and from the terminal device with the specified transmission power as a limit, and a transmission power control unit that controls transmission power between the terminal device and the terminal device. And a wireless communication unit for performing wireless communication.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, it is possible to suppress interference with neighboring base stations.

  Before describing embodiments of the present invention specifically, an outline will be described first. Embodiments described herein relate generally to transmission power control in a femtocell base station. Transmission power control is control performed between a base station apparatus and a terminal device. This control maximizes the system capacity while maximizing the communication quality by increasing the transmission power within a range that does not interfere with other devices.

  A femto cell base station (Femto-Cell Base Station) is a small base station device intended to be placed in a specific premises or a place where radio waves from a base station such as a cell edge are difficult to reach. This femtocell base station is named because it has an extremely small cell radius compared to a normal base station (hereinafter referred to as “macrocell base station”). Further, the femtocell base station has a smaller number of terminals that can be accommodated and a lower transmission power than a normal base station. However, it is expected that a large number of femtocell base stations will be randomly installed due to the ease of installation and the fact that a stable radio wave environment can be obtained.

  Also in this femtocell base station, transmission power control is performed with the terminal device. However, even if transmission power control is performed between the femtocell base station and the terminal device, since the installation of the femtocell base station is often random, the uplink transmission power from the terminal device to the femtocell base station May interfere with macro cell base stations existing in the vicinity. Similarly, the transmission power from the femtocell base station to the terminal device can also interfere with the macrocell base station.

  Therefore, in the embodiment of the present invention, the femtocell base station derives a transmission power control amount that reduces the possibility of interference with the macrocell base station, and the maximum transmission power amount in wireless communication with the terminal device. We decided to use as. By such an aspect, it can suppress that the transmission power between a terminal device and a femtocell base station interferes with a macrocell base station.

  FIG. 1 is a diagram illustrating a configuration example of a communication system 100 according to an embodiment of the present invention. The communication system 100 includes a fixed base station 10, a wired network 20, a femtocell 30, and a first terminal device 60a and a second terminal device 60b represented by a terminal device 60. Hereinafter, the fixed base station 10 and the femtocell 30 are referred to as a macrocell base station 10 and a femtocell base station 30 in order to facilitate the distinction.

  The macrocell base station 10 performs wired communication with the femtocell base station 30 via the wired network 20. The wired network 20 is a wired communication network used for wired communication between base station apparatuses such as the macrocell base station 10 and the femtocell base station 30.

  Wired communication is performed when a terminal device under the macrocell base station 10 performs communication with another communication device. For example, when the second terminal device 60b exists under the control of the macro cell base station 10, the second terminal device 60b is connected to the first terminal device 60a via the macro cell base station 10, the wired network 20, and the femto cell base station 30. Communication with is performed.

  The femtocell base station 30 performs wireless communication with the first terminal device 60a, and also performs wired communication with the macrocell base station 10 and the like via the wired network 20. Prior to the wireless communication with the first terminal device 60a, the femtocell base station 30 performs a ranging process with the macrocell base station 10 via a wireless line.

  In general, the ranging process is a process performed in the base station to determine a correction value from the reference timing in the terminal device serving as a communication partner, an uplink transmission power amount, and the like. Here, in the OFDMA (Orthogonal Frequency Division Multiple Access) scheme, (1) First, the terminal device generates a random initial ranging code (Initial CDMA Ranging Code), and the CDMA (Code Division Multiple Acces base base station). Send. (2) In response to this, the base station returns a ranging response RNG-RSP (Ranging Response) to the terminal device. (3) The message exchange of (1) and (2) is repeated a plurality of times in order to adjust the transmission power between the base station and the terminal device. The transmission power at this time is corrected based on the correction value included in the received RNG-RSP. In addition, when the terminal apparatus cannot receive RNG-RSP normally in (2), the transmission power of the terminal apparatus in the next (1) is set with a predetermined adjustment. In the predetermined adjustment, for example, the previous transmission power may be increased by a predetermined value, or the previous transmission power may be used as it is. (4) When these adjustments are completed, the base station transmits an RNG-RSP indicating success (hereinafter also referred to as a success response) to the terminal device. (5) On the other hand, the terminal device transmits a ranging request RNG-REQ (Ranging Request) to the base station. (6) The base station assigns a connection identifier CID (Connection IDentifier) to the terminal device, and transmits an RNG-RSP including the CID to the terminal device.

  Also, in a scheme other than the OFDMA scheme, for example, the OFDM scheme, first, the terminal apparatus requests the base station to start ranging by transmitting an RNG-REQ. Upon receiving the request, the base station permits the terminal device to transmit the ranging slot. Further, the base station sends RNG-RSP to the terminal device. At this time, if the terminal device does not receive the RNG-RSP, the terminal device adjusts the transmission power to the base station (appropriately) and transmits the RNG-REQ. On the other hand, when the terminal device receives the RNG-RSP, one of the two processes is executed according to the parameter included in the RNG-RSP. (1) When the frame number is included in the RNG-RSP, the terminal apparatus considers that the transmission of the RNG-REQ to the base station has failed. Further, the terminal apparatus adjusts the transmission power to the base station using the correction value included in the RNG-RSP. (2) When the MAC address is included in the RNG-RSP, the terminal apparatus considers that the transmission of the RNG-REQ to the base station is successful. Further, the terminal apparatus adjusts the transmission power to the base station using the correction value included in the RNG-RSP.

  In the present embodiment, the macrocell base station 10 functions as a base station device in normal ranging processing, and the femtocell base station 30 functions as a terminal device. That is, the femtocell base station 30 changes to a terminal device and performs the ranging process on the macrocell base station 10. The ranging process is performed for the purpose of deriving a critical uplink transmission power amount (hereinafter referred to as a minimum transmission power amount) that enables communication with the macrocell base station 10.

  Specifically, the femtocell base station 30 repeats the transmission of the ranging slot while gradually increasing the transmission power level, and the transmission power amount when the RNG-RSP that is a successful response is received is set as the minimum transmission power amount. save. For example, in order to ensure that the signal reaches the macrocell base station 10, first, transmission is started with the maximum transmission power, and then the ranging slot is gradually decreased until the success response cannot be received while gradually decreasing the transmission slot. The minimum transmission power amount may be obtained by repeating the transmission.

  Next, the femtocell base station 30 performs a ranging process with the terminal device 60. In the ranging process at this time, the femtocell base station 30 is implemented as a base station apparatus. Here, the femtocell base station 30 adjusts the maximum uplink transmission power that should be permitted to the terminal device 60 in consideration of the already derived minimum transmission power.

  FIG. 2 is a diagram illustrating a configuration example of the femtocell base station 30 of FIG. The femtocell base station 30 includes a wired communication unit 32, a wireless communication unit 34, a ranging processing unit 36, and a transmission power control unit 38. The wired communication unit 32 performs wired communication with another base station device (not shown) or a fixed telephone via the wired network 20.

  Prior to the start of wireless communication with the terminal device 60, the wireless communication unit 34 performs wireless communication with the macrocell base station 10. In addition, the wireless communication unit 34 performs wireless communication processing with the terminal device 60 after the minimum transmission power to the terminal device 60 is determined.

  The ranging processing unit 36 requests the macro cell base station 10 for the ranging process via the wireless communication unit 34. This ranging process is originally requested by the terminal device to the base station. Therefore, in this stage, the femtocell base station 30 performs a ranging process with the femtocell base station 30 as a terminal device. The transmission power control unit 38 increases the transmission power of the signal toward the macrocell base station 10 until the ranging processing unit 36 can receive the RNG-RSP related to the success response.

  The transmission power when a successful response can be received can be said to be the lowest transmission power at which wireless communication processing with the macrocell base station 10 is possible. Here, the ranging processing unit 36 stores the minimum transmission power and notifies the transmission power control unit 38 of it. In addition, the ranging processing unit 36 causes the wireless communication unit 34 to end the ranging process with the macrocell base station 10. As the ranging process with the macrocell base station 10 ends, the femtocell base station 30 switches to an operation as a base station.

  The transmission power control unit 38 also performs the ranging process with the terminal device 60 when starting the wireless communication process with the terminal device 60. At this time, the transmission power amount of the terminal device is controlled in consideration of the minimum transmission power. Specifically, the transmission power control unit 38 controls the transmission power of the terminal device 60 so that the maximum transmission power from the terminal device 60 is smaller than a value obtained by subtracting a predetermined value from the minimum transmission power.

  The predetermined value is set in order to reduce the possibility that the uplink signal from the terminal device 60 to the femtocell base station 30 causes interference with the surrounding macrocell base station 10. Increasing the predetermined value can reduce the possibility of interference, but reduces the stability of wireless communication between the terminal device 60 and the femtocell base station 30. Therefore, the predetermined value takes into consideration both the improvement of the stability of the radio communication with the terminal device 60 by the femtocell base station 30 and the suppression of interference from the terminal device 60 to the macrocell base station 10. It may be determined.

  These configurations described above can be realized in hardware by a CPU, memory, or other LSI of an arbitrary computer, and in terms of software, it is realized by a program loaded in the memory. Describes functional blocks realized through collaboration. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 3 is a flowchart showing an operation example in the femtocell base station 30 of FIG. First, the femtocell base station 30 wirelessly transmits an RNG-REQ to the macrocell base station 10 and executes a ranging process (S10). Next, the femtocell base station 30 receives the RNG-RSP wirelessly transmitted from the macrocell base station 10 (S12). Here, when the received RNG-RSP indicates failure (N in S14), the macrocell base station 10 increases the transmission power (S16) and repeats S10 to S14.

  When the received RNG-RSP indicates success (Y of S14), the femtocell base station 30 determines the maximum transmission power of the terminal device by subtracting a predetermined value from the transmission power at that time. (S18). The femtocell base station 30 performs transmission power control on the terminal device 60 in consideration of the determined maximum transmission power (S20).

  As described above, a transmission power control amount that reduces the possibility of interference with the macro cell base station is derived, and is used as the maximum transmission power amount in wireless communication with the terminal device. Interference can be efficiently suppressed. By increasing the transmission power of the signal directed to the macrocell base station 10 until the RNG-RSP relating to the successful response can be received, the maximum transmission power amount in the wireless communication with the terminal device can be efficiently derived. By setting the minimum transmission power to be smaller than a value obtained by subtracting a predetermined value, interference with the macrocell base station 10 can be reliably suppressed.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  Next, a modified example will be described. The modified example aims to suppress interference with the macrocell base station, as in the above-described embodiment. In the above-described embodiment, the femtocell base station determines transmission power that does not interfere with the macrocell base station. However, in the modification, the terminal device determines the transmission power. Is different. In addition, about the structure similar to embodiment mentioned above, the same code | symbol is attached | subjected and description is simplified.

  The radio system according to the modification has a configuration similar to that illustrated in FIG. Here, the terminal device 60 in the modified example first performs a ranging process with the macro cell base station 10. Further, the terminal device 60 determines the transmission power with the femtocell base station 30 based on the ranging result with the macrocell base station 10. With such a configuration, interference with the macrocell base station 10 can be suppressed.

  This will be specifically described. FIG. 4 is a diagram illustrating a configuration example of the terminal device 60 according to the modification of the present invention. The terminal device 60 includes a wireless processing unit 62, a first ranging processing unit 64, a second ranging processing unit 66, and a control unit 68.

  The wireless processing unit 62 performs wireless communication with the macrocell base station 10 or the femtocell base station 30. Further, prior to the start of wireless communication with the femtocell base station 30, the wireless processing unit 62 performs an RNG on the macrocell base station 10 in order to perform a ranging process in accordance with an instruction from the first ranging processing unit 64. -REQ is transmitted, and RNG-RSP is received from the macrocell base station 10.

  The first ranging processor 64 performs a ranging process with the macrocell base station 10 via the wireless processor 62. In the ranging process, the transmission power is increased until the RNG-RSP related to the success response can be received from the macrocell base station 10 as in the above-described embodiment. Also, the first ranging processing unit 64 stores the transmission power when the RNG-RSP related to the success response has been received, and notifies the control unit 68 of the transmission power.

  When receiving the notification of the transmission power when the RNG-RSP related to the success response has been received, the control unit 68 determines the maximum transmission power with the femtocell base station 30 in consideration of the notified transmission power. To do. Specifically, for example, a value obtained by subtracting a predetermined value from the notified transmission power is determined as the maximum transmission power. In addition, the control unit 68 causes the second ranging processing unit 66 to start ranging processing with the femtocell base station 30 with the maximum transmission power as a limit. Further, the control unit 68 notifies the femtocell base station 30 of the maximum transmission power via the wireless processing unit 62.

  By the above aspect, between the femtocell base station 30 and the terminal device 60, interference with the macrocell base station 10 can be suppressed while performing wireless communication with appropriate transmission power.

  In the embodiment of the present invention, it has been described that the femtocell base station 30 controls the transmission power of the terminal device 60 in consideration of the minimum transmission power with the macrocell base station 10. However, the present invention is not limited to this. For example, the femtocell base station 30 may notify the terminal device of the specified transmission power before starting control of the transmission power with the terminal device 60. Thereby, since the terminal device 60 can know the maximum transmission power in advance, it is possible to suppress the interference to the macrocell base station 10 even in the initial stage of ranging.

  In the embodiment of the present invention, it has been described that the femtocell base station 30 controls the transmission power of the terminal device 60 in consideration of the minimum transmission power with the macrocell base station 10. However, the present invention is not limited to this. For example, the femtocell base station 30 performs a ranging process with a plurality of macrocell base stations 10, derives the minimum transmission power that is minimum among them, and sets the minimum transmission power to the terminal device. 60 may be the maximum transmission power. Thereby, regardless of the arrangement relationship between the existing macrocell base station 10 and the femtocell base station 30, it is possible to derive transmission power that does not interfere with any macrocell base station 10. Thereby, the system capacity can be increased.

It is a figure which shows the structural example of the communication system concerning embodiment of this invention. It is a figure which shows the structural example of the femtocell base station of FIG. It is a flowchart which shows the operation example in the communication system of FIG. It is a figure which shows the structural example of the terminal device concerning the modification of this invention.

Explanation of symbols

  100 communication system, 10 macrocell base station, 20 wired network, 30 femtocell base station, 60 terminal device, 32 wired communication unit, 34 wireless communication unit, 36 ranging processing unit, 38 transmission power control unit, 62 wireless processing unit, 64 A first ranging processing unit, 66 a second ranging processing unit, 68 a control unit.

Claims (5)

A transmission power identifying unit that identifies transmission power that enables wireless communication with another base station device by processing executed when wireless communication is performed by connecting to the other base station device ;
And the transmission power specified by the transmission power specifying unit to limit a transmission power controller for controlling transmission power of the terminal device,
A wireless communication unit that performs wireless communication with the terminal device while controlling the transmission power of the terminal device in the transmission power control unit;
A base station apparatus comprising:   The transmission power specifying unit gradually increases transmission power directed to the other base station device prior to wireless communication processing with the terminal device, thereby wirelessly communicating with the other base station device. The base station apparatus according to claim 1, wherein transmission power that enables communication is specified. The transmission power control unit controls the transmission power of the terminal device so as to be smaller than a value obtained by subtracting a predetermined value from the transmission power specified by the transmission power specifying unit. Or the base station apparatus of 2. The wireless communication unit, before the transmission power control unit starts controlling the transmission power of the terminal apparatus, claims and notifies the transmission power specified by the transmission power specifying unit to the terminal device Item 4. The base station apparatus according to any one of Items 1 to 3. The transmission power that enables wireless communication with other base station devices is specified by processing executed when wireless communication is performed by connecting to the other base station device,
Performing wireless communication with the terminal device while controlling the transmission power of the terminal device with the specified transmission power as a limit,
A communication control method for a base station apparatus.

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