JP6075751B2 - Wireless communication system and calibration method - Google Patents

Description

  The present invention relates to a radio communication system including a base station capable of radio communication using a MIMO (Multiple Input Multiple Output) system and a mobile terminal capable of radio communication using the MIMO system and having an adaptive array function, and The present invention relates to a calibration method for a portable terminal.

  Wireless communication capable of performing MIMO (Multiple Input Multiple Output) wireless communication in both uplink and downlink between mobile terminals and base stations, such as WiMAX using TDD-OFDMA and WLAN using CSMA / CA-OFDM The system is widespread. In addition, portable terminals having an adaptive array function have become widespread. An adaptive array is a technique for controlling the directivity of a radio wave by adjusting the phase of the radio wave using a plurality of antennas.

  Usually, a portable terminal having an adaptive array function is calibrated to form optimum directivity at the time of factory shipment. Specifically, in the calibration, a difference in transmission characteristics of the transmission / reception circuit in the portable terminal is measured, and a correction value based on the difference in transmission characteristics is stored in a correction table. When executing the adaptive array function, the mobile terminal calculates a transmission weight using the correction value stored in the correction table, and forms a beam and a null.

  However, since the characteristics of the mobile terminal change from the time of shipment from the factory due to aging and temperature change, it is required to perform calibration not only at the time of shipment from the factory but also after the start of use. Patent Document 1 discloses a technique for performing calibration by measuring a difference in transmission characteristics of a transmission / reception circuit by transmitting a known signal from one antenna among a plurality of antennas of a mobile terminal and receiving the signal from the remaining antennas. Is disclosed. In Patent Document 2, a desired wave and an interference wave are transmitted from a base station to a mobile terminal, and a transmission weight calculated based on these signals is used for directivity control of an adaptive array function to transmit a beam and a null to the base station. A technique for performing calibration based on such a beam and null is disclosed.

JP 2008-166866 A JP 2005-328571 A

  In the technique of the above-mentioned Patent Document 1, it is necessary to perform calibration by sequentially changing the combination of antennas, so that calibration takes time. In addition, signals cannot be received simultaneously with all antennas, and the accuracy of calibration is reduced as compared with a case where calibration is performed by simultaneously receiving signals with all antennas. The fact that the transmitting antenna and the receiving antenna are very close also makes it difficult to form a directivity pattern, which also reduces the accuracy. Furthermore, since transmission and reception are performed between antennas in the mobile terminal, it is necessary to perform transmission power control so that the reception circuit is not saturated, which complicates calibration. On the other hand, in the technique of the above-mentioned Patent Document 2, the intra-cell throughput of the base station is reduced during calibration.

  The present invention has been made in view of the above problems, and a wireless communication system capable of calibrating a mobile terminal having an adaptive array function without causing a decrease in intra-cell throughput of the base station, and its An object is to provide a calibration method for a portable terminal.

  In order to solve the above-described problems, a typical configuration of the present invention includes a base station capable of wireless communication using a MIMO (Multiple Input Multiple Output) method, wireless communication using a MIMO method, and an adaptive array function. In the wireless communication system including the mobile terminal, the mobile terminal includes a terminal wireless communication unit having a plurality of antennas, and a correction table that stores a correction value used for calculating a transmission weight of the adaptive array function, Includes a base station radio communication unit having a plurality of antennas, and the base station radio communication unit receives a correction value calibration request from a mobile terminal and requests an unused empty OFDM subcarrier defined for MIMO. The terminal wireless communication unit receives the desired wave and the jamming wave by a plurality of antennas, and transmits the calculated wave and the jamming wave to the mobile terminal. The transmission weight calculated based on the reception weight between the tenors and the current correction value is used for the directivity control of the adaptive array function, and the beam of the adaptive array function is used with the unused empty OFDM subcarrier defined for MIMO. When the ratio between the received signal strength of the beam and the received signal strength of the null is less than a predetermined value, the base station wireless communication unit transmits the change of the current correction value to the mobile terminal. It is characterized by instructing.

  If the ratio between the received signal strength of the beam and the received signal strength of the null is less than a predetermined value, the base station sets a new correction value stored in the correction table based on the received signal strength of the beam and the received signal strength of the null. It is preferable that a weight correction value calculation unit for calculating the correction value is further provided, and the base station radio communication unit transmits a new correction value to the mobile terminal.

  In order to solve the above problems, another typical configuration of the present invention is to calibrate a mobile terminal capable of wireless communication with a base station using a MIMO (Multiple Input Multiple Output) method and having an adaptive array function. In this method, the base station receives a calibration request for a correction value used for calculating the transmission weight of the adaptive array function from the mobile terminal, and transmits a desired wave with an unused empty OFDM subcarrier defined for MIMO. The mobile terminal transmits the interference wave to the mobile terminal, the mobile terminal receives the desired wave and the interference wave by a plurality of antennas, obtains the reception weight between the antennas, and the transmission weight calculated based on the reception weight and the current correction value Is used for the directivity control of the adaptive array function, and is used for unused unused OFDM subcarriers defined for MIMO. When the ratio of the beam received signal strength and the null received signal strength is less than the predetermined value, the base station transmits the change of the current correction value to the mobile terminal. It is characterized by instructing.

  According to the present invention, there is provided a radio communication system capable of calibrating a portable terminal having an adaptive array function without causing a decrease in intra-cell throughput of the base station, and a calibration method for the portable terminal. be able to.

It is a block diagram which shows schematic structure of the radio | wireless communications system concerning this embodiment. It is a block diagram which shows schematic structure of the radio | wireless part shown in FIG. 3 is a flowchart illustrating a calibration method for the mobile terminal shown in FIG. 1.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

[Wireless communication system]
FIG. 1 is a block diagram illustrating a schematic configuration of a wireless communication system 100 according to the present embodiment. As shown in FIG. 1, the wireless communication system 100 includes a base station 102 and a mobile terminal 104. The base station 102 can perform wireless communication using a MIMO (Multiple Input Multiple Output) scheme. Further, the mobile terminal 104 is capable of wireless communication by the MIMO method and has an adaptive array function.

  The portable terminal 104 includes a terminal control unit 106 that includes a central processing unit (CPU), and a terminal memory 108 that includes a ROM, a RAM, a flash memory, and the like. The terminal control unit 106 executes a program stored in the terminal memory 108 to control and manage the mobile terminal 104. The terminal memory 108 stores programs and various data. In the present embodiment, the terminal memory 108 includes a correction table 110 that stores correction values used for calculating transmission weights of the adaptive array function. The correction value is for correcting a difference in transmission characteristics of the transmission / reception circuit in the portable terminal 104. In addition, the portable terminal 104 includes an internal temperature measurement unit 154 that measures the temperature inside the terminal.

  The mobile terminal 104 includes a terminal wireless communication unit 114 having a plurality of antennas 112a, 112b, 112c. The terminal wireless communication unit 114 includes wireless units 116a, 116b, 116c,... 116N for each antenna 112a, 112b, 112c,. FIG. 2 is a block diagram illustrating a schematic configuration of the wireless unit 116a. As shown in FIG. 2, the radio unit 116a includes a transmission circuit including a transmission unit 118 and a D / A converter 120, and a reception circuit including a reception unit 122 and an A / D converter 124, and includes an antenna. The connection to 112a is switched by the switch 126. In addition, although illustrated about the radio | wireless part 116a here, it is the same also about the radio | wireless parts 116b, 116c ... 116N.

  As shown in FIG. 1, the mobile terminal 104 includes an OFDM modulation / demodulation unit 128 that performs modulation and demodulation. The OFDM modulation / demodulation unit 128 includes a signal strength detection unit 130 that detects reception signal strength (RSSI), and a reception weight acquisition unit 132 that acquires reception weights between the antennas 112a, 112b, 112c,. In this embodiment, the terminal control unit 106 performs a carrier sense determination unit 134 that performs carrier sense determination based on the received signal strength (RSSI), and an adaptive array function based on the reception weight and the correction value stored in the correction table 110. It functions as a transmission weight setting unit 136 that calculates and sets a transmission weight.

  The base station 102 includes a base station control unit 138 that includes a central processing unit (CPU), and a base station memory 140 that includes a ROM, a RAM, a flash memory, and the like. The base station control unit 138 executes a program stored in the base station memory 140 to control and manage the base station 102. The base station 102 also includes a backbone backbone line unit 156 that connects to the line network.

  The base station 102 includes a base station wireless communication unit 144 having a plurality of antennas 142a, 142b, 142c. The base station radio communication unit 144 includes radio units 146a, 146b, 146c,... 146N for each antenna 142a, 142b, 142c,. The radio units 146a, 146b, 146c,... 146N are respectively similar to the radio unit 116a and the like, with a transmission circuit composed of a transmission unit and a D / A converter, and a reception circuit composed of a reception unit and an A / D converter. And the connection to the antenna is switched by a switch.

  The base station 102 includes an OFDM modulation / demodulation unit 148 that performs modulation and demodulation. The OFDM modulation / demodulation unit 148 includes a signal strength detection unit 150 that detects received signal strength (RSSI). In this embodiment, the base station control unit 138 determines that the ratio between the received signal strength of the beam transmitted from the mobile terminal 104 and the received signal strength of null is a predetermined value when the mobile terminal 104 having the adaptive array function is calibrated. It functions as a ratio determination unit 152 that determines whether or not it is less than the value. In addition, when the ratio between the beam reception signal strength and the null reception signal strength is less than a predetermined value, the base station control unit 138 corrects the mobile terminal 104 based on the beam reception signal strength and the null reception signal strength. It functions as a weight correction value calculation unit 158 that calculates a new correction value stored in the table 110.

[Calibration method]
FIG. 3 is a flowchart illustrating a calibration method of the mobile terminal 104. Hereinafter, according to the flowchart of FIG. 3, the calibration method of the portable terminal 104, that is, the calibration method of the correction value of the adaptive array function will be specifically described. Here, after determining whether or not calibration is possible when the adaptive array function is activated, calibration is performed when necessary. However, the calibration is not limited to this, and calibration may be performed periodically.

  In the wireless communication system 100, when the use of the mobile terminal 102 is started (step S200), carrier sense is performed as needed after completion of location registration (step S202). From this state, when a data communication request is generated in the portable terminal 104 (step S204), the terminal control unit 106 determines whether to activate the adaptive array function (step S206). In step S206, for example, the interference level is determined from the received signal strength to determine whether to activate the adaptive array function.

  When starting the adaptive array function (Yes in step S206), the terminal control unit 106 determines that the difference between the temperature inside the terminal at the previous calibration and the current temperature inside the terminal measured by the internal temperature measurement unit 154 is greater than or equal to a predetermined value. It is determined whether or not (step S208). The temperature inside the terminal at the time of the previous calibration is stored in the terminal memory 108, for example.

  If the internal temperature difference is not greater than or equal to the predetermined value (No at Step S208), the terminal control unit 106 determines whether or not a predetermined time has elapsed since the previous calibration (Step S210). The time from the previous calibration is calculated by, for example, holding the previous calibration in the terminal memory 108 or the correction table 110, and the terminal control unit 106 acquires and calculates the current date and time.

  If the predetermined time or more has not elapsed since the calibration (step S210 No), the adaptive array function is executed without calibration and data communication is established (step S232). If the adaptive array function is not activated (No at step S206), data communication is established using a normal radio wave transmission / reception method instead of the adaptive array function (step S230).

  On the other hand, in the case of step S208 Yes or step S210 Yes, the terminal control unit 106 controls the terminal radio communication unit 114 to transmit a calibration request to the base station 102 (step S212). In the base station 102 that has received the calibration request, when the base station control unit 138 enters a communication state in which it is not necessary to perform MIMO, the mobile terminal uses a free OFDM subcarrier that is defined for MIMO but is not always used. The base station radio communication unit 144 is controlled to transmit the desired wave and the disturbing wave to 104 (Yes at Step S214, Step S216). If there is no empty OFDM subcarrier for MIMO (No in step S214), the portable terminal 104 is allowed to establish data communication without calibration (step S232).

  After step S216, in the mobile terminal 104, when the terminal wireless communication unit 114 receives the desired wave and the interference wave by the plurality of antennas 112a, 112b, 112c,... 112N, the reception weight acquisition unit 132 acquires the reception weight between the antennas. . The transmission weight setting unit 136 calculates and sets a transmission weight based on the reception weight and the current correction value stored in the correction table 110. The terminal control unit 106 uses this transmission weight for the directivity control of the adaptive array function, and a beam of the adaptive array function (forms adaptive beamforming) and null with an unused unused OFDM subcarrier defined for MIMO. The terminal radio communication unit 114 is controlled to transmit (form adaptive null steering) to the base station 102 (for example, mutually) (step S218).

  After step S218, in the base station 102, the ratio determining unit 152 determines whether or not the ratio between the received signal strength of the beam and the received signal strength of null is less than a predetermined value (step S220). If it is not less than the predetermined value (step S220 No), the base station control unit 138 controls the base station radio communication unit 144 to instruct the mobile terminal 104 that the current correction value stored in the correction table 110 is not changed. (Step S226). After step S226, the portable terminal 104 executes the adaptive array function without changing the current correction value, and establishes data communication (step S228).

  On the other hand, when the ratio is less than the predetermined value (Yes in step S220), the weight correction value calculation unit 158 newly stores the correction table 110 of the mobile terminal 104 based on the received signal strength of the beam and the received signal strength of null. A correct correction value is calculated. Then, the base station control unit 138 controls the base station wireless communication unit 144 to transmit a new correction value to the mobile terminal 104 (step S222). After step S222, the portable terminal 104 writes the new correction value received by the terminal control unit 106 into the correction table 110 as the current correction value, executes the adaptive array function using this correction value, and performs data communication. Establish (step S224).

  Here, the weight correction value calculation unit 158 calculates a new correction value to be stored in the correction table 110 of the mobile terminal 104. However, the correction value may be calculated or determined by another method or the terminal side. Good. That is, when the ratio is less than the predetermined value, the base station radio communication unit 144 does not need to transmit a new correction value, and at least instructs the portable terminal 104 to change the current correction value.

[effect]
According to the wireless communication system 100 described above, calibration of the mobile terminal 104 having an adaptive array function can be performed as appropriate, and calibration can be performed with high accuracy in a short time. Furthermore, since calibration is performed using empty OFDM subcarriers that are defined for MIMO but are not always used, it is possible to avoid a decrease in intra-cell throughput of the base station.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention relates to a radio communication system including a base station capable of radio communication using a MIMO (Multiple Input Multiple Output) system and a mobile terminal capable of radio communication using the MIMO system and having an adaptive array function, and It can be used for a calibration method of a portable terminal.

DESCRIPTION OF SYMBOLS 100 ... Wireless communication system, 102 ... Base station, 104 ... Portable terminal, 106 ... Terminal control part, 108 ... Terminal memory, 110 ... Correction table, 112a, 112b, 112c, 112N ... Antenna, 114 ... Terminal wireless communication part, 116a 116b, 116c, 116N ... wireless unit, 118 ... transmission unit, 120 ... D / A converter, 122 ... reception unit, 124 ... A / D converter, 126 ... switch, 128 ... OFDM modulation / demodulation unit, 130 ... signal strength Detection unit, 132 ... reception weight acquisition unit, 134 ... carrier sense determination unit, 136 ... transmission weight setting unit, 138 ... base station control unit, 140 ... base station memory, 142a, 142b, 142c, 142N ... antenna, 144 ... base Station wireless communication unit, 146a, 146b, 146c, 146N ... wireless unit, 148 ... OFDM modulation / demodulation unit, 50 ... signal strength detection unit, 152 ... ratio determination unit, 154 ... internal temperature measuring unit, 156 ... Backbone line portion, 158 ... weight correction value calculation unit

Claims (5)

In a wireless communication system including a base station capable of wireless communication with a MIMO (Multiple Input Multiple Output) scheme and a mobile terminal capable of wireless communication with a MIMO scheme and having an adaptive array function,
The portable terminal includes a terminal wireless communication unit having a plurality of antennas,
A correction table for storing a correction value used for calculating the transmission weight of the adaptive array function,
The base station includes a base station wireless communication unit having a plurality of antennas,
The base station radio communication unit receives a calibration request for the correction value from the mobile terminal, and transmits a desired wave and an interfering wave to the mobile terminal using unused unused OFDM subcarriers defined for MIMO. ,
The terminal radio communication unit uses a transmission weight calculated based on a reception weight between antennas calculated by receiving the desired wave and the interference wave by the plurality of antennas and the current correction value, Transmit a beam and a null to the base station on the unused empty OFDM subcarrier,
The base station wireless communication unit instructs the portable terminal to change the current correction value when a ratio of the received signal strength of the beam and the received signal strength of the null is less than a predetermined value. Wireless communication system. When the ratio of the received signal strength of the beam and the received signal strength of the null is less than a predetermined value, the base station stores in the correction table based on the received signal strength of the beam and the received signal strength of the null. A weight correction value calculation unit for calculating a new correction value to be
The wireless communication system according to claim 1, wherein the base station wireless communication unit transmits the new correction value to the mobile terminal. A mobile terminal calibration method capable of wireless communication with a base station using a MIMO (Multiple Input Multiple Output) scheme and having an adaptive array function and a terminal wireless communication unit having a plurality of antennas,
The base station receives a calibration request for a correction value used for calculating the transmission weight of the adaptive array function from the mobile terminal, and receives a desired wave and an interfering wave using unused unused OFDM subcarriers defined for MIMO. To the mobile device,
The portable terminal receives the desired wave and the interference wave by the plurality of antennas, acquires a reception weight between the antennas, and transmits a transmission weight calculated based on the reception weight and the current correction value to the adaptive array. Used for directivity control of the function, transmit the beam and null of the adaptive array function to the base station on unused unused OFDM subcarriers defined for MIMO,
The base station instructs the portable terminal to change the current correction value when the ratio of the received signal intensity of the beam and the received signal intensity of the null is less than a predetermined value. . In a base station capable of wireless communication by MIMO (Multiple Input Multiple Output) system,
A base station wireless communication unit having a plurality of antennas,
The base station wireless communication unit receives a correction value calibration request from a mobile terminal, and transmits a desired wave and an interfering wave to the mobile terminal using an unused unused OFDM subcarrier defined for MIMO,
The portable terminal uses the transmission weight calculated based on the reception weight between antennas calculated by receiving the desired wave and the interference wave and the current correction value, and uses the unused empty OFDM sub When transmitting a beam and null to the base station on the carrier,
The base station radio communication unit is a base station that instructs the portable terminal to change the current correction value when the ratio of the received signal intensity of the beam and the received signal intensity of the null is less than a predetermined value. In a mobile terminal capable of wireless communication by MIMO (Multiple Input Multiple Output) method and having an adaptive array function,
A terminal wireless communication unit having a plurality of antennas;
A correction table for storing a correction value used for calculating the transmission weight of the adaptive array function,
When a base station capable of wireless communication with the MIMO scheme transmits a desired wave and an interfering wave to the mobile terminal using an unused empty OFDM subcarrier defined for MIMO,
The terminal radio communication unit uses a transmission weight calculated based on a reception weight between antennas calculated by receiving the desired wave and the interference wave by the plurality of antennas and the current correction value, A mobile terminal that transmits a beam and a null to the base station on the unused empty OFDM subcarrier.

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