JP2006174507A - Wireless lan slave station and wireless lan system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a slave station to realize the most satisfactory communicating circumstances with a master station without adjusting the physical position of a receiving antenna in a wireless LAN system mainly using the milliwave band of an electromagnetic wave. <P>SOLUTION: A slave station side is provided with an antenna means 1 for dynamically changing directional characteristics at the time of receiving an electric wave from a master station, a means 2 for transmitting a control frame to the master station before starting communication and a means 3 for changing the directional characteristics of the means 1, and for retrieving directional characteristics maximizing the receiving electric field strength of a carrier wave from the master station. The master station side is provided with a means 5 for starting the transmission of the carrier wave corresponding to the reception of the control frame. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a local area network (LAN), and more particularly, in a wireless LAN system mainly using millimeter-wave band electromagnetic waves, without adjusting the physical position of a receiving antenna on the wireless LAN slave station side. It is related with the communication quality optimization system for implement | achieving the best communication condition between.

  In recent years, LANs have become increasingly popular, and data handled on LANs has also increased. Furthermore, communication functions of data terminals such as personal computers have been enhanced and miniaturized, and demands for use in mobile environments have increased, and wireless LAN systems have attracted attention.

  Until now, the wireless LAN system has used the radio wave band of about 1 to 3 GHz called the ISM band for the wireless LAN. However, this band is used for industrial or microwave ovens, and since there are many noises, it is necessary to suppress the influence of noise using a spread spectrum method etc., and the system becomes complicated, In this radio wave band, there is a drawback that a sufficient band for high-speed transmission cannot be secured.

Therefore, the millimeter wave band of 50 to 70 GHz, which is also an unused band, has been attracting attention for data communication, and the use of this band is being approved for data communication.
As characteristics of electromagnetic waves in this band, it is strong in straightness and relatively easy to be absorbed by oxygen, glass, etc. For example, when used in an office environment, there is little possibility of electromagnetic waves leaking to the outside. It is valid. Furthermore, because it is an unused band, unlike the case of using the ISM band, it is not necessary to use a spread spectrum method, etc., and the system can be simplified correspondingly, and the band necessary for high-speed transmission can be secured sufficiently. This is a very promising band at the present time when the speed of LAN exceeds 100Mbps.

  However, in the millimeter-wave wireless LAN system, the master station antenna usually has a relatively broad radiation directivity to widen the communication range, but the slave station antenna has a strong millimeter-wave linearity and is easily absorbed by oxygen. In order to obtain a good communication environment due to interference between slave stations or multipath effects, it is necessary to set the radiation directivity characteristics to be sharp directivity rather than broad, and to point accurately toward the master station antenna. There wasn't. Furthermore, the adoption of the diversity method or the spread spectrum method for avoiding these effects is difficult to realize in the millimeter wave band, and even if it is adopted, the system becomes complicated.

  A wireless LAN system using millimeter wave band electromagnetic waves has the following problems. The first problem is that the communication situation deteriorates rapidly due to subtle fluctuations in the position and direction of the antenna of the slave station. That is, as described above, in the millimeter wave band, the master station antenna needs to have a broad radiation characteristic in order to widen the communication range. On the other hand, in the millimeter wave band, which has strong characteristics of straight travel and is easily absorbed by oxygen, the radiation characteristics of the slave station antenna cannot be broadened due to multipath effects, etc. A good communication state cannot be obtained unless the radiation directivity of the antenna is sharpened and the direction of the antenna does not accurately face the direction of the master station. That is, in order to maintain a good communication state, there has been a problem that the radiation pattern of the slave station antenna must be made extremely sharp and the direction thereof must always be accurately directed toward the master station antenna.

  The second problem is to use a diversity antenna as a method to avoid multipath or interference between slave stations, or to introduce a spread spectrum method, but these are difficult to realize in the millimeter wave band, The system becomes complicated.

  In view of the above-mentioned problems, an object of the present invention is to employ an active phased planar array antenna that can dynamically change its directivity as a slave station antenna, and transmit only a carrier wave from the master station side. Accordingly, the communication quality in the wireless LAN is optimized by searching for the antenna directivity that maximizes the received electric field strength.

  FIG. 1 is a block diagram showing the principle of the present invention. FIG. 1 is a block diagram showing the basic configuration of a wireless LAN system that is connected to a backbone LAN and includes a wireless LAN master station that supports communication between subordinate slave stations and a wireless LAN slave station. The master station and the slave station are transmission / reception apparatuses that can transmit and receive as communications with the other party.

In FIG. 1, antenna means 1, control frame transmission means 2, and antenna directivity control means 3 are provided on the slave station 4 side, and carrier wave transmission means 5 is provided on the master station 6 side.
The antenna means 1 can dynamically change its directivity when receiving radio waves from the master station. The control frame transmission means 2 transmits a control frame to the master station side before the start of communication with the master station or another slave station or when the communication status deteriorates after the start of communication. .

  The antenna directivity control means 3 changes the directivity characteristics of the antenna means 1, for example, an active phased planar array antenna, so that the received electric field strength of the carrier wave transmitted from the master station side corresponding to the control frame is maximized. It searches for a directional characteristic.

  The carrier transmission means 5 starts transmission of a carrier in response to reception of a control frame from the slave station side. In general, LAN data has a characteristic of being concentrated and communicated at a certain point in time in bursts. Generally, when there is no data to be communicated, the parent station side of the LAN system transmits a carrier wave as well as a data frame. I did not go well. Therefore, in the present invention, the control frame is transmitted to the master station side by the control frame transmitting means 2 on the slave station side, and the master station 6 transmits only the carrier wave by the carrier transmitting means 5 in response to the reception of the control frame. At the start, while the carrier wave is being transmitted, the directivity characteristic of the antenna means 1 is searched by the antenna directivity characteristic control means 3 so that the received electric field strength of the carrier wave is maximized.

  In the present invention, when the control frame transmitting means 2 transmits a control frame, only one element is used among a plurality of elements as an array of active phased planar array antennas constituting the antenna means 1. By transmitting a control frame, the directivity characteristics of the antenna means 1 on the slave station side can be broadened. Also, in this case, by increasing the power supplied to only this one element, the control frame can be reliably sent to the master station side without reducing the transmission power of the control frame as compared with the case where all elements are used. Can do.

  Furthermore, in the present invention, a directivity characteristic that maximizes the received electric field strength of the carrier wave transmitted from the slave station side is searched, and after the directivity characteristic of the antenna means 1 is fixed in that direction, Data frame transmission / reception as communication is started, but after that, the antenna directivity characteristics are searched again as necessary.

  For example, when an error of a data frame received from the master station, for example, a frame check sequence error is detected and the number of detected error frames exceeds a predetermined value, the control frame transmission means 2 transmits a control frame, When the carrier wave transmission means 5 starts transmission of the carrier wave and the antenna directivity characteristic control means 3 searches for the directivity characteristics, the communication quality in the wireless LAN is optimized again.

  As described above, according to the present invention, by adopting an active phased planar array antenna, the best communication with the master station can be achieved without adjusting the physical position of the antenna on the slave station side. The situation can be realized.

  According to the present invention, in a wireless LAN system mainly using millimeter waves, an active phased planar array antenna that can freely change its radiation directivity is adopted as a slave station antenna, and a control frame is transmitted from the slave station. The direction of the antenna directivity that allows the master station to receive the carrier wave transmitted from the parent station with the maximum intensity by changing the feeding phase to the antenna element and the slave station starting transmission of the carrier wave correspondingly. By searching for and fixing the directivity characteristics of the slave station antenna in that direction, it is possible to ensure an optimal communication state without adjusting the position of the data terminal, slave station, or slave station antenna.

  Furthermore, a condition is set for the number of error frames received on the slave station side or the received field strength of the data frame, and the optimum antenna directivity pattern is searched again when the condition no longer holds. Therefore, it is possible to automatically cope with the deterioration of the communication status due to the movement of the data terminal or the slave station or the positional deviation of the antenna, and always provide the best communication quality.

  In addition, by reducing the strength of the transmission carrier wave from the master station during the search operation compared to the normal data communication, it becomes possible to save power on the master station side. From the above, it is possible to construct a robust and flexible wireless LAN system, which contributes to the practical application of a high-speed wireless LAN system that uses an unused millimeter-wave band allocated for table communication. large.

FIG. 2 is a basic configuration diagram of a wireless LAN system in which the communication quality optimization method of the present invention is realized.
In FIG. 2, the wireless LAN system includes, for example, a wireless LAN master station 12 connected to a wired backbone LAN 11 and a plurality of wireless LAN slave stations 15 connected to data terminals 14. The antenna of the wireless LAN master station 12 has a broad radiation directivity characteristic 13, whereas the slave station antenna 16 of the wireless LAN slave station 15 has a sharp radiation directivity characteristic 17.

  In general, in a LAN system, data is often transmitted in bursts. For example, when there is no data to be transmitted, the wireless LAN master station 12 does not transmit a carrier wave. For this reason, in this embodiment, the slave station 15 sends a control frame different from a normal LAN data frame at the time of activation, activation of the data terminal 14 such as a connected personal computer, or communication start of the data terminal 14. 12 and the master station 12 receives it and starts transmitting only the carrier wave. The slave station 15 searches the direction in which the carrier wave transmitted from the master station can be received with the maximum intensity by the active phased planar array antenna 15 whose dynamic characteristics can be dynamically changed. Good communication quality is ensured by matching the direction of the radiation beam of the antenna, that is, the radiation directivity.

  In FIG. 2, as the format of the wireless LAN slave station 15, various types such as a PC card type, a terminal built-in type, and a separate case type are used. Further, the slave station 15 and the antenna 16 include an integrated type, and the type in which the antenna 16 is connected to the slave station 15 through a signal line. Particularly, the configuration and shape of the slave station 15 and the antenna 16 are limited. Not. Further, the antenna 16 may be one that performs transmission and reception with one antenna, or one that performs transmission and reception with separate antennas. In the present embodiment, description will be made assuming that the transmitting antenna and the receiving antenna are different.

  FIG. 3 is an explanatory diagram of an active phased planar array antenna as an example of the slave station antenna 16 of FIG. In the figure, the active phased planar array antenna 21 is composed of a plurality of patch elements, here, nine patch elements 22. An x phase shifter 23 and a y phase shifter 24 are provided corresponding to each patch element. The x phase shifter 23 changes the feeding phase to the side parallel to the y axis of the patch element in order to change the directivity in the xz plane, and the y phase shifter 24 goes to the side parallel to the x axis. This is for changing the feeding phase. Each x phase shifter 23 is connected to an x phase shifter excitation controller 25, and each y phase shifter 24 is connected to an y phase shifter excitation controller 26.

  The active phased planar array antenna 21 in FIG. 3 has an antenna array composed of nine patch elements, but the number of elements is not particularly limited to this. Furthermore, although the shape of the element is a square patch element, it is natural that any of the four corners of the square, such as a shape obtained by cutting two corners that are not at both ends of one side, a circle, or a dipole shape may be used. It is.

  FIG. 4 is an explanatory diagram of a change in radiation directivity when the active phased planar array antenna is viewed from the y direction. In the figure, it can be seen that the direction of the radiation directivity of the whole antenna changes on the xz plane by the control of the x phase shifter 23 for each patch element 21.

  FIG. 5 is a block diagram showing the configuration of the slave station. In the figure, a reception antenna 32 and a transmission antenna 33 are connected to the slave station 31. The slave station 31 is roughly divided into a radio unit 34, a control unit 35, a LAN function unit 36, and a timer 37.

The radio unit 34 is connected to the reception antenna 32 and the transmission antenna 33, and includes a modulator / demodulator, a phase shifter, a phase shifter controller, an antenna feeding circuit, a burst switch circuit, and the like.
The LAN function unit 36 includes a data transmission / reception control function, a carrier detection function, an FCS (frame check sequence) error detection function, a co-region detection function, a preamble addition function, and a terminal interface.

  The control unit 35 includes a search function control unit 41, an antenna directivity control 42, a reception control unit 43, an electric field strength detection / storage unit 44, a control frame generation unit 45, a feed power control unit 46, a transmission control unit 47, and an FCS error frame. It comprises a detector / counter 48.

  FIG. 6 is an explanatory diagram of the configuration and operation of the search function control unit 41 of FIG. In the figure, the search function control unit 41 is provided with a search state storage / instruction unit 51. For example, when an error is detected by the reception control unit 43 for a control frame returned from the master station side, When the electric field intensity detection / storage unit 44 detects that the electric field intensity of the carrier wave received from the station side does not satisfy the conditions described later, an error with respect to a normal data frame is detected by the FCS error frame detection unit / counter 48. When it is detected many times or when a data terminal activation signal is input, a signal instructing the start of search is sent to the control frame generator 45 or the like.

  FIG. 7 is an explanatory diagram of the configuration and operation of the antenna directivity control unit 42. In the figure, the antenna directivity control unit 42 includes a directivity instruction unit 52 and a use element instruction unit 53.

  Here, the control by the antenna directivity control unit will be further described. As described above, the LAN slave station uses an active phased planar array antenna that can freely and continuously change its radiation directivity as a receiving antenna. As described with reference to FIG. 4, the direction of the radiation directivity characteristic can be freely changed on the xz plane by changing the feeding phase to the patch element 21 using the phase shifter corresponding to each patch element 21. it can. The same can be done in the yz plane. By changing the feed phase by the x phase shifter 23 and the y phase shifter 24, the direction of the radiation directivity characteristic can be freely changed in the hemisphere on the antenna surface. Can be made.

  Here, the active phased planar array antenna will be further described. This antenna is a plurality of antenna elements, that is, an antenna in which patch elements are two-dimensionally (planar) arranged on a dielectric substrate. The phaser continuously changes the excitation phase of each patch antenna and activates the radiation direction of electromagnetic waves, that is, the radiation directivity characteristics without changing the physical direction of the antenna. For example, it is used for radar. Further, by arranging a large number of patch elements, an antenna having a sharp radiation directivity characteristic can be configured. Conversely, a broad radiation directivity characteristic with a half-value angle of 90 ° to 120 ° or more can be obtained with only one patch element.

  FIG. 8 is an explanatory diagram of a search method for the radiation directivity of the slave station antenna, that is, a search method for the master station direction. As described in FIG. 3, the slave station receiving antenna 32 has nine patch elements 22 arranged two-dimensionally and has a sharp radiation directivity characteristic. A search is performed so that the radiation directivity characteristic is directed to the direction 54 of the master station.

  First, by moving the radiation directivity characteristic on the xy plane, the θ angle is determined 55 by searching on the horizontal plane. Thereafter, the φ angle is determined 56 by searching in the z-α plane. As a result, the radiation directivity characteristic 57 of the slave station antenna faces the direction 54 of the master station.

  FIG. 9 is an explanatory diagram of a method of sending a control frame to the master station before starting the antenna direction search. In the figure, among the plurality of patch elements constituting the slave station transmission antenna 33, for example, only the central patch element 58 is used, and the control frame is transmitted to the master station side. At this time, by using only one patch element, the radiation directivity characteristic 59 becomes broad, the control frame 60 is transmitted in a wide direction, and the master station controls the master station in any direction. The frame can be received.

  The directivity instruction unit 52 in FIG. 7 holds the values of θ and φ as the antenna directivity characteristic search results, and notifies the radio unit 34 of the values, and the radiation directivity of the transmission antenna 33 and the reception antenna 32. Fix the characteristics. That is, during normal data communication, both the transmitting and receiving antennas are oriented in the direction determined by the optimum values of θ and φ. In response to the search start instruction signal from the search function control unit 41, the use element instruction unit 53 transmits a command to send a control frame to the radio unit 34 using only one element of the transmission antenna 33. .

  FIG. 10 is an explanatory diagram of the configuration and operation of the reception control unit 43 in FIG. In the figure, the reception control unit 43 includes a control frame FCS error check unit 64, a data switch unit 65, and a random backoff timer 66.

  The control frame FCS error check unit 64 receives a data input from the radio unit 34, and when an error is detected in the control frame returned on the master station side, for example, a normal data frame sent from another slave station And the search function control unit 41 is instructed to perform the search again after the random backoff. The data switch unit 65 uses the data from the radio unit 34 as a control frame as data when searching in the antenna direction, and the data is sent to the LAN function unit 36 and the electric field as a data frame during communication of a normal data frame. The random back-off timer 66 is a timer for randomly determining the waiting time for transmission until retransmission of the control frame after detection of the co-region. .

FIG. 11 is an explanatory diagram of the configuration and operation of the electric field intensity detection / storage unit 44. In the figure, the electric field strength detection / storage unit 44 is composed of an electric field strength detection unit 68 and a storage unit 69.
The electric field strength detection unit 68 detects the electric field strength of the carrier wave transmitted from the master station when searching for the antenna direction, and notifies the storage unit 69 of the angle of the radiation directivity at that time. If the detected electric field strength is not more than a preset threshold even when the angle is changed, the search function control unit 41 is instructed to execute the search again. Also, during normal data communication, the received field strength of a normal data frame is monitored, and when the value is below a preset threshold, the search function control unit 41 is similarly searched for re-execution of the antenna directivity. Instruct.

  The storage unit 69 receives the output from the electric field strength detection unit 68 and stores the values of the angles θ and φ if the maximum reception strength during the search is a predetermined minimum value, that is, a threshold value or more, and the antenna directivity characteristics The control unit 42 is notified, and the antenna directivity is fixed in the directions of the angles θ and φ.

  FIG. 12 is an explanatory diagram of the configuration of the control frame generation unit 45 and its operation. In the figure, the control frame storage ROM 71 receives a search start instruction from the search function control unit 41 and outputs a control frame burned in the ROM to the transmission control unit 47.

  FIG. 13 is an explanatory diagram of the configuration and operation of the feed power control unit 46. In the figure, upon receiving a search start instruction from the search function control unit 41, the power enhancement instruction unit 72 increases the power supplied to only one antenna element, that is, the patch element, used for transmitting the control frame. An instruction is sent to the wireless unit 34, and an instruction is given to return to normal power supply after transmission of the control frame. As described with reference to FIG. 9, only one patch element is used for the purpose of broadening the radiation directivity during transmission of the control frame, and the transmission power from the antenna becomes small. This is to increase the value.

  FIG. 14 is an explanatory diagram of the configuration of the transmission control unit 47 and its operation. In the figure, the data switch unit 73 sends the control frame input from the control frame generation unit 45 to the radio unit 34 when searching for the antenna directivity according to the instruction from the search function control unit 41, and the LAN for normal data communication. A switch function for sending a normal data frame from the function unit 36 to the radio unit 34 is executed.

  FIG. 15 is an explanatory diagram of the configuration and operation of the FCS error frame detector / counter. In the figure, the FCS error count / storage unit 74 receives an input from the LAN function unit 36 and counts the number of data frames in which an error is detected by the LAN function unit 36 during normal data communication. When the set number of frames is received, a search start instruction is sent to the search function control unit 41.

  Alternatively, the timer 37 is instructed to start the timer when the error frame is first received, and the search function control unit 41 is instructed to start the search when a predetermined number of error frames are received before the timeout. Send. Such an operation will be further described later.

  FIG. 16 is a block diagram showing the configuration of the LAN master station. In the figure, a receiving antenna 82 and a transmitting antenna 83 are connected to the master station 81. The master station 81 is roughly composed of a radio unit 84, a control unit 85, and a LAN function unit 86.

  The radio unit 84 includes a modem, a phase shifter, a phase shifter controller, an antenna power supply circuit, a burst switch circuit, and the like. A control unit 85 includes a search function control unit 87, a frame determination unit 88, and a power supply power control unit 89. It is composed of Furthermore, the LAN function unit 86 includes a data transmission / reception control function, a carrier detection function, a co-region detection function, a preamble addition function, a data loopback function, a backbone interface, and the like.

  FIG. 17 is an explanatory diagram of the configuration and operation of the search function control unit 87 of FIG. In the figure, when the search function control unit 87 is notified from the frame determination unit 88 that the control frame has been received, the search function control unit 87 instructs the radio unit 84 to transmit a carrier wave. In order to save power at this time, an instruction is given to the feed power control unit 89 to lower the transmission power of the carrier wave.

  FIG. 18 is an explanatory diagram of the configuration and operation of the frame discriminating unit 88. In the figure, a control frame discriminating unit 91 discriminates whether or not the received frame from the radio unit 84 is a control frame, and outputs the result to the switch unit 92. If it is a control frame, the switch unit 92 notifies the search function control unit 87 that the control frame has been received. If it is not a control frame, the switch unit 92 sends the received frame to the LAN function unit 86.

  FIG. 19 is an explanatory diagram of the configuration and operation of the feed power control unit 89. In the figure, the power adjustment unit 93 reduces the power supply power in accordance with an instruction from the search function control unit 87 when transmitting a carrier wave, and supplies the power to the radio unit 84.

  In the above, the outline of the operation has been described focusing on the configuration of the LAN slave station and the LAN master station. Hereinafter, the communication quality optimization method in the present embodiment will be described in more detail.

  First, on the LAN slave station 31 side, as described above, for example, when the slave station is activated, a control frame transmission instruction is given from the search function control unit 41 to the control frame generation unit 45, and a control frame different from a normal LAN data frame is generated. The data is transmitted to the master station side via the communication control unit 47 and the radio unit 34. At this time, since the radiation directivity characteristic of the transmission antenna 33 of the slave station is not necessarily directed to the direction of the master station, in order to ensure that the master station receives the control frame, this control frame has a broad radiation directivity characteristic. It is necessary to transmit using.

  Therefore, by transmitting the signal using only one patch element as described in FIG. 9 under the control of the antenna directivity control unit 42, the control frame can be reliably received on the master station side. It is not always necessary to use the central patch element 58 as shown in FIG. In addition, since the radiated electromagnetic field strength is weak in the transmission by only one element, the feeding power to the patch element 58 is transmitted by the feeding power control unit 46 in order to make the master station receive the control frame reliably. Increase transmission from time to time.

  The LAN master station 81 receives the control frame transmitted from the slave station side by the receiving antenna 82, confirms that the frame received by the frame discrimination unit 88 via the radio unit 84 is a control frame, and performs search function control. Under the control of the unit 87, the radio unit 84 starts transmission of only the carrier wave. At this time, the control frame is not transferred from the master station 81 to the backbone LAN, for example.

  Even if a data frame is transmitted from the backbone LAN side or another child station while the parent station is transmitting a carrier wave, it is upstream, that is, from the child station to the parent station, and downstream, that is, from the parent station to the child station. The transmission frequency is different and the electric field strength is constant, and there is no effect on the slave station that is searching for the antenna directivity. That is, the slave station that is searching for the antenna directivity only receives a carrier wave transmitted from the master station at this time, and no frame co-region (collision) occurs. However, as described later, when a slave station transmits a control frame, a co-region occurs when a control frame or a normal data frame is transmitted simultaneously via the backbone LAN or by another slave station.

  At this time, the control frame transmitted from the slave station side needs to be clearly distinguished from the normal data frame. FIG. 20 shows an example of the format of this control frame. As shown in the figure, for example, by setting all the bits indicating the end point address and the start point address of the frame to “0”, the master station side can clearly distinguish the control frame from the normal data frame. In particular, by using the MAC (physical) address portion at the beginning of the frame as shown in this figure, the master station can instantaneously perform control frame discrimination. The starting point address field is a part for setting a unique address in each data terminal, and a method of setting all starting point addresses to “1” may be used. Alternatively, a method may be used in which a control frame is distinguished from a normal data frame by using a part other than the MAC address part. That is, the control frame format may be any format as long as it can be distinguished from a normal data frame.

  Further, as shown in FIG. 20, for example, in the case of Ethernet (registered trademark), padding, that is, an 8-bit unit bit string of arbitrary contents is embedded as a PAD in the data field of the control frame, and further frame check sequence data is embedded. If the control frame length is 512 bits as the shortest frame length in Ethernet (registered trademark) and a normal data frame and co-region occur, the slave station searching for antenna directivity and data transmission are performed. It is possible to recognize that a co-region has occurred in both terminals.

  As a result, even if there is a slave station that is searching for directivity characteristics, normal data communication is not affected. On the other hand, the slave station that is searching is interrupted and invalidated. For example, after the random buffer is turned off, the control unit 41 transmits a control frame again to perform a search operation.

  Following transmission of the control frame, the slave station is transmitted from the master station while changing the directivity characteristics of the receiving antenna by changing the phase of the feed power by the phase shifter as described in FIGS. The reception field strength of the carrier wave is detected by the field strength detection / storage unit 44, and the search in the direction of the master station is started. At this time, the carrier wave received from the master station is not output from the reception control unit 43 to the LAN function unit 36. That is, the level (amplitude) of the carrier wave is smaller than the level (amplitude) of the data, and the reception control unit 43 detects data using a threshold larger than the level of the carrier wave, so that the carrier wave is output to the LAN function unit 36. Absent.

  In the search for the antenna directivity, first, as described in FIG. 8, the angle θ at which the carrier wave from the master station can be received most strongly over 360 degrees on a plane parallel to the antenna plane is detected. The angle φ is detected by a search over 180 degrees in the vertical plane.

  When searching for the antenna directivity, the search procedure is re-executed if necessary according to the detected maximum value and minimum value of the electric field strength. First, the minimum limit value of the electric field strength of the carrier wave transmitted from the master station is set in the electric field strength detection / storage unit 44 in advance, and if the electric field strength exceeding the minimum limit value is not detected during the search, the search is performed again. The procedure is performed to determine the optimum direction of the radiation beam of the slave station antenna.

  Here, the minimum limit value of the received electric field strength means a received electric field strength that is weak enough to affect normal communication. As a specific value, for example, in the prototype stage of the commercialization process of a wireless LAN system, Such a limit value is determined by actual measurement and set in the system, or the value is considered to depend on the characteristics of the system itself, that is, characteristics such as components used and transmission power. It is conceivable to use a method such as setting to or determining the error frame occurrence rate.

  Further, the minimum value of the difference between the maximum value and the minimum value of the received field strength of the carrier wave transmitted from the master station is stored in the field strength detection / storage unit 44 of the slave station, and the antenna directivity characteristics are searched. If the carrier wave cannot be received in a state where the difference is greater than the minimum value, the search procedure is executed again from the beginning to determine the direction of the optimum directivity characteristic of the slave station antenna.

  FIG. 21 is an explanatory diagram when the search is considered successful / failed depending on whether the minimum value of the difference between the maximum value and the minimum value of the received electric field strength reaches a preset value. In FIG. 8A, for example, when the coordinates are changed on a plane parallel to the antenna plane of FIG. 8, the difference between the maximum value and the minimum value of the actually measured received electric field strength is larger than the preset minimum value. In this case, the search is considered successful. On the other hand, FIG. 5B shows a case where the difference between the maximum value and the minimum value of the received electric field strength is smaller than the preset minimum value and is regarded as a search failure.

  Further, when the maximum value and the minimum value of the received electric field strength of the carrier wave from the master station are detected at the time of searching the directivity characteristics of the slave station antenna in this way, the ratio between the maximum value and the minimum value, that is, “maximum value / The ratio of the “minimum value” is stored in the electric field strength detection / storage unit 44, and if a search exceeding the ratio cannot be performed during the search, the search procedure is executed again from the beginning, and the optimal slave station antenna radiation is obtained. The direction of the beam can also be determined. Or, conversely, the ratio “minimum value / maximum value” is stored in the electric field strength detection / storage unit 44, and if a search below the ratio cannot be performed during the search, the search procedure can be executed again from the beginning. .

  Next, the re-execution of the search after the search is finished and the direction of the optimum directivity characteristic of the slave station antenna is fixed and the normal data transmission / reception, that is, the transmission / reception of the data frame with the master station is started will be described. To do.

  The slave station stores, in the electric field strength detection / storage unit 44, the received data frame strength of a data frame that starts to interfere with normal communication with the master station, and stores the received field strength of a normal data frame received from the master station. Detection is performed. When the received electric field strength of the data frame transmitted from the master station falls below a preset threshold due to movement of the data terminal or a slave station connected to the data terminal, antenna positional deviation, etc. As described above, a search start instruction is sent from the search function control unit 41 to the control frame generation unit 45, and a search operation can be started to ensure an optimum communication environment again.

  At this time, for example, if the electric field strength exceeding the minimum value of the received electric field strength of the carrier wave from the master station stored in advance as described above cannot be detected during the search operation, the search procedure is executed again. Can do. With respect to the minimum value of the difference between the maximum value and the minimum value, the ratio between the maximum value and the minimum value, and the ratio between the minimum value and the maximum value, the same processing as described above can be executed.

  Further, regarding the intensity of the carrier wave received from the master station, not only the electric field intensity but also the magnetic field intensity may be used as a reference, and in the infrared wireless LAN system, the infrared intensity can be used as a reference.

  Another condition for resuming the search after the start of transmission / reception of a normal data frame with the master station is a data frame error. The slave station is provided with an FCS error frame detector / counter 48 as shown in FIG. When an error is detected in a frame received from the master station, the number of frames is counted, and when the preset number of frames is reached, the search function control unit 41 instructs the start of search in the same manner as described above, and again A search for antenna directivity to ensure an optimal communication environment is performed. At this time, as described above, the same processing is performed regarding the minimum value of the electric field strength, the minimum value of the difference between the maximum value and the minimum value, the ratio of the maximum value to the minimum value, and the ratio of the minimum value to the maximum value, and does not meet the conditions. In that case, you can start the search again.

  As for the error frame count, the search can be performed again in the same manner as described above when the number of error frames continuously received from the master station reaches a preset number. Alternatively, the timer 37 may be started when the first error frame is received, and the antenna directivity characteristics may be searched again when the number of error frames received before the timer 37 times out reaches a preset number. it can. If the preset number of error frames is not received before the timer 37 times out, the counter is cleared after the time-out, and the processing after starting the timer 37 may be repeated when the error frame is received again. it can.

  Alternatively, the timer 37 can be activated when an error frame is received, and the search for antenna directivity can be started when the number of continuously received error frames reaches a predetermined number. Even if several consecutive error frames are received after the timer 37 is started, if a normal frame is received again before reaching a preset number, the counter and timer are reset. When the timer 37 times out, the counter is cleared.

  Even when the timer 37 is started in this way, the minimum value of the received electric field strength of the carrier wave transmitted from the master station, the minimum value of the difference between the maximum value and the minimum value, the ratio of the maximum value to the minimum value, the minimum value and the maximum value With respect to the ratio of the values, it is also possible to perform the same process as described above and perform a search again for the antenna directivity.

  Next, as an operation on the master station side, when a control frame is received from the slave station and a carrier wave is transmitted to the slave station side in response to the control frame, when a normal data frame is transmitted by the feed power control unit 89 of FIG. It is also possible to transmit the carrier wave with lower transmission power. This makes it possible to save power.

  In this way, a data frame was transmitted from another slave station or backbone LAN while the master station transmitted a carrier wave with a lower transmission power than during normal data communication and the slave station was searching for antenna directivity. In this case, the electric field strength detection / storage unit 44 of the slave station is expected to detect a discontinuous and rapid increase in electric field strength. In such a case, since it is impossible to search for the optimum direction of normal antenna directivity, the slave station interrupts the search, clears the results of the previous search, and when transmission of the data frame ends, Alternatively, for example, it is possible to transmit the control frame again after a certain time determined by the random backoff algorithm, transmit the carrier wave to the master station, and search for the antenna directivity.

It is a block diagram which shows the principle structure of this invention. 1 is a basic configuration diagram of a wireless LAN system in which a communication quality optimization method of the present invention is realized. It is explanatory drawing of the active phased planar array antenna as an example of a slave station antenna. It is explanatory drawing of the change of the radiation directivity characteristic in an active phased planar array antenna. It is a block diagram which shows the structural example of a wireless LAN slave station. It is explanatory drawing of the structure of the search function control part of FIG. 5, and its operation | movement. It is explanatory drawing of a structure and operation | movement of an antenna directivity characteristic control part. It is explanatory drawing of the search method of the radiation directivity characteristic of a slave station antenna. It is a figure explaining the method of sending a control frame to the master station side prior to the search start of antenna radiation directivity characteristics. FIG. 6 is an explanatory diagram of the configuration and operation of the reception control unit in FIG. 5. It is explanatory drawing of a structure and operation | movement of an electric field strength detection / storage part. It is explanatory drawing of a structure and operation | movement of a control frame production | generation part. FIG. 6 is an explanatory diagram of a configuration and operation of a power feeding power control unit in FIG. 5. It is explanatory drawing of a structure and operation | movement of a transmission control part. It is explanatory drawing of a structure and operation | movement of a FCS error frame detection part / counter. It is a block diagram which shows the structural example of a wireless LAN base station. It is explanatory drawing of a structure of the search function control part of FIG. 16, and its operation | movement. It is explanatory drawing of a structure and operation | movement of a flame | frame discrimination | determination part. It is explanatory drawing of a structure and operation | movement of the electric power feeding control part of FIG. It is a figure which shows the example of a format of a control frame. It is a figure explaining the determination of the success / failure of the search by the difference of the highest value and the lowest value of electromagnetic field intensity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna means 2 Control frame transmission means 3 Antenna directivity control means 5 Carrier transmission means 11 Backbone LAN
12 wireless LAN master station 14 data terminal 15 wireless LAN slave station 16 slave station antenna 21 active phased planar array antenna 22 patch element 23 x phase shifter 24 y phase shifter 25 x phase shifter excitation controller 26 y phase shifter Excitation controller 31 Slave station 34 Radio unit 36 LAN function unit 41 Search function control unit 42 Antenna directivity control unit 43 Reception control unit 44 Electric field intensity detection / storage unit 45 Control frame generation unit 46 Feed power control unit 47 Transmission control 48 FCS error frame detector / counter 81 Master station 87 Search function controller 88 Frame discriminator 89 Power feed controller

Claims (2)

In a wireless LAN slave station that supports wireless communication with a master station,
Antenna means capable of dynamically changing the directivity when receiving radio waves from the master station;
Control frame transmitting means for transmitting a control frame to the master station prior to the start of communication;
An antenna directivity control means for changing the directivity of the antenna means and searching for the directivity so that the received electric field strength of the carrier wave transmitted from the master station side is maximized corresponding to the control frame;
With
A wireless LAN slave station that searches again when an error is detected in a control frame that is turned back on the master station side. In a wireless LAN system that supports wireless communication between a master station and a plurality of slave stations,
In the slave station,
Antenna means capable of dynamically changing the directivity when receiving radio waves from the master station;
Control frame transmitting means for transmitting a control frame to the master station prior to the start of communication;
An antenna directivity control means for changing the directivity of the antenna means and searching for the directivity so that the received electric field strength of the carrier wave transmitted from the master station side is maximized corresponding to the control frame;
With
A wireless LAN system which searches again when an error is detected in a control frame turned back at a master station side.

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