JP2000165410A - Communication system and polling communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the communication system where entry processing is completed in a shorter standby time even when entry processing by polling communication is concentrated and to provide a polling communication method. SOLUTION: In the communication system consisting of a master station 1 that can transmit a control frequency and a plurality of outgoing channel frequency and a plurality of slave stations 4 in a communication area of the master station 1 and setting up a communication channel with the master station 1 by receiving a polling signal addressed to each identification code specific to each slave station from the master station, each slave station 4 controls a frequency to receive the polling signal from the master station 1 according to an outgoing channel frequency indicated by the control frequency. Furthermore, various information sets consisting of information relating to each of slave stations 4 whose communication channels are not set up and included in slave station management data including outgoing channel frequencies of the slave stations are rearranged on the basis of the identification code specific to each slave station 4 and a prescribed number of groups depending on the specific identification code are set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device and a polling communication method for performing multi-channel wireless communication by time division or the like.

[0002]

2. Description of the Related Art When one base station communicates with a plurality of terminal stations controlled by the base station, when a new terminal station starts communication, for example, the terminal station first obtains a communication right from the base station. Entry processing must be performed.

FIG. 7 is an explanatory view schematically showing an entry process according to the prior art. As shown in FIG. 7, the base station sequentially polls the registered terminal stations and grants a communication right by permitting transmission of a response.

As shown in FIG. 7, when a base station sequentially polls all terminal stations using one transmission frequency, the polling cycle becomes longer as the number of terminal stations increases, and the terminal station becomes longer. Increases the average time required for entry processing.

To solve such a problem, if the base station polls the terminal station using a plurality of transmission frequencies, the number of transmission lines used increases as the number of terminal stations increases. However, the polling cycle can be made constant.

[0006]

However, in this case, the terminal station cannot know at which frequency the own station is polled. Therefore, it is necessary to sequentially search all frequencies that may be used by the base station and determine whether or not the own station is polled at each frequency. Therefore, also in this case, as the number of frequencies that the base station may use increases, the average time required for the terminal station to perform the entry process increases.

When such communication is performed, a large number of terminal stations are simultaneously operated after the service is temporarily stopped, immediately after the failure of the base station and the radio line is restored, or when the terminal station whose power is turned off at night is turned on the next morning. May require entry processing. In such a case, the time required for the entry process is inevitably increased.

The present invention has been made under such a background, and provides a communication apparatus and a polling communication method capable of completing entry processing in a short standby time even when entry processing in polling communication is concentrated. It is intended to be.

[0009]

According to a first aspect of the present invention, a master station capable of transmitting a control frequency and a plurality of downlink frequencies is provided. And a slave station that establishes a communication line with the master station by receiving polling from the master station for a unique identification code for each of which may exist in the communication area.
The master station is slave station registration data including information on each of the plurality of slave stations registered as communicable, and slave station including information on each of the slave stations for which a communication line is not established and the downlink frequency for the slave station. And slave control means having management data. Further, according to the invention described in claim 2, claim 1
Wherein the slave station includes frequency control means for controlling a frequency for receiving polling from the master station to the downlink frequency indicated by the control frequency. Further, in the invention according to claim 3, in the communication device according to claim 2, the slave station control means transmits various kinds of information included in the slave station management data to each of the slave stations, By rearranging based on the value of the identification code, a predetermined number of groups are set according to the value of the unique identification code, and the master station belongs to the group for each of the predetermined number of groups using the control frequency. The upper limit and the lower limit of the value of the unique identification code and the information of the downlink frequency assigned to the group are transmitted, and the frequency control means transmits the value of the unique identification code from the received signal of the control frequency. Extract the information of the upper limit and lower limit and the downlink frequency, and when the value of the unique identification code given to the own station is a value between the upper limit and the lower limit, the main station Or And controlling the on downlink frequency obtained by extracting a frequency to receive the poll. Also, in the invention according to claim 4, in the communication apparatus according to claim 3, the slave control unit is a boundary between the groups so that the slaves are equally distributed to the groups. The value of the unique identification code is determined. Also, in the invention according to claim 5, in the communication device according to any one of claims 3 and 4, the master station sets an upper limit value of the value of the unique identification code for each group. The information of the lower limit value and the information of the downlink frequency allocated to the group are sequentially and repeatedly transmitted at the same control frequency. Further, in the invention according to claim 6, in the communication apparatus according to any one of claims 3 to 5, the slave station uses the downlink frequency indicated by the control frequency. The polling from the master station is received, a response signal to the polling is transmitted using an uplink frequency, and the master station establishes a communication line with the slave station when receiving a response signal from the slave station by the uplink frequency. It is characterized by doing.
In the invention according to claim 7, a master station capable of transmitting a control frequency and a plurality of downlink frequencies, a plurality of master stations can exist in a communication area of the master station, and a unique identification is provided for each. In a communication device including a slave station that establishes a communication line with the master station by receiving polling from the master station for a code, the slave station determines a frequency for receiving polling from the master station by the control frequency. It is controlled to the designated downlink frequency. According to the invention of claim 8, in the polling communication method of claim 7, the slave station management includes information on each of the slave stations for which a communication line is not established and the downlink frequency for the slave station. Various types of information included in the data are rearranged based on the value of the unique identification code given to each of the slave stations, and a predetermined number of groups are set according to the value of the unique identification code. In the invention according to claim 9, claim 8
In the polling communication method described in the above, the master station, using the control frequency, for each of the predetermined number of groups, the upper limit value and the lower limit value of the value of the unique identification code belonging to the group, and the assigned to the group Transmit the downlink frequency information, the slave station extracts the upper limit value and the lower limit value of the value of the unique identification code and the downlink frequency information from the received control frequency signal, and is given to the own station. When the value of the unique identification code is between the upper limit value and the lower limit value, the frequency for receiving polling from the master station is controlled to the extracted downlink frequency. According to the tenth aspect of the present invention, in the polling communication method according to the ninth aspect, the master station is a boundary between the groups so that the slave stations are equally distributed to the groups. The value of the unique identification code is determined. Claim 11
In the polling communication method according to any one of the ninth and tenth aspects, the master station may include:
An upper limit value and a lower limit value of the value of the unique identification code for each group and information on the downlink frequency assigned to the group are sequentially and repeatedly transmitted at the same control frequency. Claim 12
In the polling communication method according to any one of claims 9 to 11, in the invention according to any one of claims 9 to 11, the slave station transmits a signal from the master station using the downlink frequency indicated by the control frequency. Receiving a polling signal, transmitting a response signal to the polling using an uplink frequency, and, upon receiving a response signal from the slave station with the uplink frequency, establishing a communication line with the slave station. And

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. FIG. 1 is a block diagram illustrating a schematic configuration of a multi-channel wireless communication network to which a communication device according to an embodiment of the present invention is applied. As shown in FIG. 1, base station 1 according to the present embodiment has a plurality of antennas 2 _-1 and 2 _-2 .

These 2 _-1 and 2 _-2 antennas each have a predetermined directivity and are installed in predetermined different directions (azimuths and elevation angles), whereby a plurality of different communication zones 3 _-1 and 3 _-2 are respectively provided. _3-2 .

In the communication zones 3 _-1 and 3 _-2 , a plurality of terminal stations 4 _-1 , 4 _-2 ... 4 _-4 , 4 _-5. 4, etc.), and the terminal stations 4 _-1 , 4 _-2 ... 4 _-4 belonging to the same communication zone 3 _-1 or 3 _-2 . , 4 _-5
Can use the same frequency.

Communication between the base station 1 and the terminal stations 4... Belonging to any of the communication zones 3 _-1 or 3 _-2 includes a plurality of downlinks from the base station 1 to the terminal stations 4. This is performed via a plurality of uplinks from the terminal station 4 to the base station 1.

One uplink frequency is assigned to a plurality of terminal stations 4.
.. if used, TDMA (Time Division Multiple Access)
Share the same frequency. Note that the configuration shown in FIG. 1 is a basic configuration to which the present invention is applied, in which a plurality of base stations 1 are installed, or in which the base station 1 is provided with more antennas. It may be.

FIG. 2 is a block diagram showing an example of the internal configuration of the base station 1 shown in FIG. Reference numeral 101 of the base station 1 denotes a protocol control unit, which is an IP (Internet Protocol).
And an interface with an external communication network 5 such as an ATM (Asynchronous Transfer Mode) communication network.

Reference numeral 102 denotes a packetizing unit which converts data input from the protocol control unit 101 into a packet format handled on a wireless line, and also has a function of buffering the data. 103
Is a router that distributes each packet converted by the packetizing unit 102 to a downlink used by the destination terminal station 4.

Reference numeral 104 denotes a terminal station control unit, which holds the used frequency and status of the terminal station 4 under its control, and creates and outputs a control message for entry processing of the terminal under its control. The above-mentioned router 103 refers to the used frequency information on the terminal station 4 which the terminal station control unit 104 has.

Reference numeral 115 denotes a control unit, and a plurality of modulators 108, 108,
.. And manages and monitors the frequency and information rate set in the modulator / demodulator 118 composed of the demodulators 110, 110.

Reference numeral 105 denotes a synchronization control unit. The synchronization control unit 105 generates a reference clock serving as a reference for frame synchronization between the own station and the terminal station 4 under the control thereof, and outputs a frame synchronization signal serving as a reference for frame synchronization of the terminal station 4.

.. Are synthesizing units. The combining unit 106 includes a data packet output by the router 103 and a control message output by the terminal station control unit 104.
Then, the frame and the frame synchronization signal output from the synchronization control unit 105 are combined by time division multiplexing.

Are encoders for encoding the output of the synthesizing unit 106, and 108, 108 ... are modulators for modulating the output of the encoder 107. Note that these combining section 106, encoder 107, and modulator 108 are provided for each downlink (transmission frequency).

Reference numeral 109 denotes a transmitting / receiving apparatus provided with the above-mentioned antenna 2 _-1 (2 _-2 ). Synthesis units 106, 106
··· are encoder 107 and modulator 108, respectively
This transmission / reception device 1 that covers each communication zone via
09 is transmitted.

On the other hand, the uplink signal received by transmitting / receiving apparatus 109 is demodulated by demodulator 110,
After being decoded by the decoder 111, the separating unit 1
12 is supplied.

Separating section 112 separates the received uplink information into a control message and a data packet. The demodulator 110, the decoder 111, and the separation unit 11
2 is provided for each uplink (reception frequency). The control message separated by separation section 112 is supplied to terminal station control section 104, while the data packet is supplied to synthesis section 113.

Combining section 113 multiplexes data packets for all uplink frequencies. The multiplexed data packet is transmitted to the external communication network 5 by the data reconfiguration unit 114.
After being restored to the format processed in and buffered, it is sent to the external communication network 5 via the protocol control unit 101.

FIG. 3 is a block diagram showing an example of the internal configuration of the terminal station 4. As shown in FIG. In FIG. 3, a transmitting / receiving device 409 is wirelessly connected to the transmitting / receiving device 109 of the base station 1 described above.

Reference numeral 410 denotes a demodulator, and a transmitting / receiving device 409
Demodulates the received downlink signal. A decoder 411 decodes the output of the demodulator 410. 41
Reference numeral 2 denotes a separation unit that separates downlink information output from the decoder 411 into data, a frame synchronization signal, and a control message.

The separating section 412 supplies the separated data to the data reconstructing section 414, supplies a control message to the terminal station control section 404, and supplies a frame synchronization signal to the synchronization control section 405.

The data reconstruction unit 414 to which the data has been supplied.
Restores data received on the downlink to a format that the terminal device 6 can handle, and
To supply. This protocol control unit 401 is a terminal device 6
Control the interface with the Note that this terminal device 6
Is, for example, a PPP (Point-t
o-Point Protocol).

Reference numeral 404 denotes a terminal station control unit that creates a response message to the control message transmitted by the base station 1. The terminal station control section 404 recognizes the downlink reception frequency and the uplink transmission frequency used by its own station according to the control message transmitted by the base station 1, and sets the same in the demodulator 410 and the modulator 408.

Reference numeral 402 denotes a packetizing unit that converts data input via the protocol control unit 401 into a packet format to be transmitted and received on a wireless line and buffers the packet.

A synthesizing unit 424 buffers the control response message output from the terminal station control unit 404 and the data output from the packetizing unit 402 in a FIFO (First-In First-Out memory) format.

Reference numeral 405 denotes a synchronization control unit. The synchronization control unit 405 establishes frame synchronization with a reference station based on the frame synchronization signal separated by the separation unit 412, and establishes TDMA transmission synchronization of the own station.

The transmission control section 426 generates a transmission signal from the output of the synthesizing section 424 based on the transmission synchronization established by the synchronization control section 405.
07 and the transmission / reception device 409 via the modulator 408.

FIG. 4 shows a terminal station control unit 104 in the base station 1.
FIG. 4 is an explanatory diagram showing an example of terminal station management data stored by the server. The terminal station control unit 104 is registered with the base station 1 but still have a list of entries and non terminal station 4, 4, ..., this terminal station number as shown in FIG. 4 N _um ...
It holds a terminal station number sort table rearranged according to.

The above-mentioned terminal station number N _um is _assigned to each terminal station 4, 4
.. Are assigned to the terminal numbers N at the time of manufacture or when installed in various places.
_um is set. Also, when the terminal station 4 is installed in various places,
This terminal station number _Num is registered in the base station 1.

The number of terminal stations on the terminal station number sort table indicates that the terminal station is newly registered or that communication with the terminal station whose entry has been completed is disconnected for some reason, and that this terminal station is in an unentry state. Increase when going back,
Decreases when the terminal station completes entry. The terminal station number sort table is rearranged each time there is an increase or decrease in terminal stations.

Also, as shown in FIG.
Reference numeral 4 denotes a terminal station number sorting table for ending the entry, constantly monitoring the number of terminal stations using each downlink frequency, and allocating terminal stations equally to each frequency. Create a downlink frequency designation message addressed to.

For example, in FIG. 4, the terminal station number "0031"
To “0808” are assigned to Group 1 and “0C
Group 12 from "12" to "12EA", group 3 from "1440" to "1A06"
And so on.

This grouping is performed in such a manner that the number of terminal stations is determined for a fixed number of groups.
The number of groups may be increased / decreased in accordance with the number of terminal stations, or the history of polling may be statistically weighted to reduce the number of terminal stations to be allocated to a group in which terminal stations having a high polling frequency exist.

FIG. 5 is an explanatory diagram showing an example of a downlink frequency designation message. FIG. 5A shows a downlink frequency designation message for group 1 in FIG.
5 (b) shows a downlink frequency designation message for group 2 and FIG. 5 (c) shows a downlink frequency designation message for group 3.

The downlink frequency designation message includes a broadcast address and a message type for the group, the minimum and maximum terminal numbers in the group, and information on the downlink frequency used by this group.

The above broadcast address is an address that can be received by all terminal stations as the destination terminal station number. The minimum terminal station number in the group and the maximum terminal station number in the group are the smallest terminal station number and the largest terminal station number in the terminal station group using the same downlink frequency.

The base station 1 transmits these downlink frequency designation messages using one predetermined control downlink frequency. On the other hand, when each terminal station 4 is installed in various places, a control downlink frequency used by the base station 1 to which the terminal station 4 belongs is set. This control downlink frequency is also used simultaneously for normal data transmission.

FIG. 6 is an explanatory diagram showing an example of a terminal station entry process according to the present embodiment. Here, the polling for the terminal station 4 to which "1586" is given as the terminal station number will be described as an example.

Base station 1 uses control downlink frequency F _0D to transmit a downlink frequency designation message for group 1 shown in FIG. 5A and a downlink frequency designation message for group 2 shown in FIG. Downlink frequency designation message for group 3 shown in FIG.
・ Send sequentially.

At this time, the terminal station 4 given the terminal station number "1586" receives all of these plurality of downlink frequency designation messages. However, the fact that the terminal number "1586" given to the own station is included between the minimum terminal number and the maximum terminal number in the transmitted downlink frequency designation message is shown in FIG. It is only a downlink frequency designation message for group 3.

[0048] Thus the terminal station 4 that given terminal station number "1586" processes the downlink frequency designation message to the group 3 as an active, switching the reception frequency F _3D included in the downlink frequency designation message.

The terminal station 4 described above, may receive the polling to its own station at the time of switching the reception frequency F _3D. In this case, a response message is returned using the uplink frequency (for example, F _1U ) specified in the polling message, and the entry processing ends here.

The base station 1 repeats polling of the terminal station in the non-entry state, using the downlink frequency designated for each terminal station group by the downlink frequency designation message.

As an application example of the above-described embodiment, as a frequency used for the terminal station to be notified of the communication downlink frequency first, a line having a narrow band different from the normal downlink for data communication. Are used. Only the notification message of the data communication downlink frequency is broadcast to this other line. In this case, an increase or decrease in the number of terminal stations requiring entry processing does not affect the actual line capacity of data communication.

[0052]

As described above, according to the present invention, a master station capable of transmitting a control frequency and a plurality of downlink frequencies, a plurality of master stations can exist in a communication area of the master station, and each of the plurality of master stations has a unique In a communication device including a slave station that establishes a communication line with the master station by receiving polling from the master station for the identification code of the slave station, the slave station is instructed by the control frequency to receive a polling signal from the master station. A value of a unique identification code given to each of the slaves to control the downlink frequency and to provide information on each of the slaves for which a communication line has not been established and various information included in slave management data including the downlink frequency for the slaves. And a predetermined number of groups are set according to the value of the unique identification code. Also, the master station transmits information on the upper limit value and the lower limit value of the value of the unique identification code belonging to the group and the downlink frequency assigned to the group for each of the predetermined number of groups using the control frequency, and the slave station receives The information of the upper limit value and lower limit value of the unique identification code as well as the downlink frequency information is extracted from the signal of the control frequency, and the value of the unique identification code given to the own station is between the upper limit value and the lower limit value. If the value is a value, the frequency for receiving polling from the main station is controlled to the extracted downlink frequency. Further, the master station determines the value of the unique identification code that is a boundary between the groups so that the stations are equally assigned to the groups. Also,
The master station sequentially and repeatedly transmits information on the upper and lower limits of the value of the unique identification code for each group and the downlink frequency assigned to the group at the same control frequency. Also, the slave station receives polling from the master station using the downlink frequency indicated by the control frequency, transmits a response signal to the polling using the uplink frequency, and the master station responds from the slave station using the uplink frequency. When a signal is received, a communication line with the slave station is established.
As a result, it is possible to realize a communication device and a polling communication method capable of completing entry processing in a short standby time even when entry processing in polling communication is concentrated.

That is, according to the present invention, a plurality of lines are used as downlinks used by a terminal station for entry processing, and the number of terminal stations is evenly distributed to each downlink. The increase in time can be reduced.

Although a plurality of downlinks are used for the entry process, the downlink frequency used by each terminal for the entry process is notified to the terminal station using one predetermined downlink frequency. Each terminal station does not need to search for a plurality of downlink frequencies, and the entry time is omitted.

Further, a message for notifying the terminal station of the downlink frequency for entry processing is transmitted for each terminal station group composed of a plurality of terminal stations using the same downlink. The effect extended by the increase in the number of terminal stations can also be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a multi-channel wireless communication network to which a communication device according to an embodiment of the present invention is applied.

FIG. 2 is a block diagram illustrating an example of an internal configuration of a base station 1 illustrated in FIG.

FIG. 3 is a block diagram showing an example of an internal configuration of a terminal station 4.

FIG. 4 is an explanatory diagram showing an example of terminal station management data stored by a terminal station control section 104 in the base station 1.

FIG. 5 is an explanatory diagram showing an example of a downlink frequency designation message.

FIG. 6 is an explanatory diagram showing an example of a terminal station entry process in the embodiment.

FIG. 7 is an explanatory diagram showing an outline of an entry process according to a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Base station (master station) 2 _-1 , 2 _-2 antenna 3 _-1 , 3 _-2 Communication zone (communication area) 4, 4 _-1 , 4 _-2 ... Terminal station (slave station) 5 External communication network 6 Terminal device 101 Protocol control unit 102 Packetization unit 103 Router 104 Terminal station control unit (slave control unit) 105 Synchronization control unit 106, 106 ... Combining unit 107, 107 ... Encoder 108, 108 ... Modulator 109 Transmitter / receiver 110, 110 ... Demodulator 111, 111 ... Decoder 112, 112 ... Separation unit 113 Combining unit 114 Data reconstruction unit 115 Control unit 118 Modulation / demodulation unit 401 Protocol control unit 402 Packetization unit 404 Terminal station Control unit (frequency control unit) 405 Synchronization control unit 407 Encoder 408 Modulator 409 Transmitter / receiver 410 Demodulator 411 Decoder 4 2 separating portion 414 the data reconstruction unit 424 combining unit 426 transmission control unit N _um, N _um ··· terminal station number F _0D control downlink frequency (control _{frequency) F 1D, F 2D, F} 3D ··· Downlink Frequency F _1U Uplink frequency

Claims (12)

[Claims] 1. A master station (1) capable of transmitting a control frequency (F _0D ) and a plurality of downlink frequencies (F _1D , F _2D , F _3D ...), And a communication area (3 _-1 , 3 _-2 ), and a slave station (4, 4 _-1) that establishes a communication line with the master station by receiving polling from the master station for a unique identification code for each. , 4 _-2 , 4 _-3 ...), Wherein the master station is slave station registration data including information on each of the plurality of slave stations registered as communicable, and the slave station has no communication line established. A communication apparatus comprising: a slave station control unit (104) having information on each slave station and slave management data including the downlink frequency for the slave station. 2. The slave station further comprises frequency control means (404) for controlling a frequency for receiving polling from the master station to the downlink frequency indicated by the control frequency. 2. The communication device according to 1. 3. The slave station control means reorders various information included in the slave station management data based on a value of a unique identification code given to each of the slave stations, and according to the value of the unique identification code. A predetermined number of groups, and the master station is assigned to the group by using the control frequency for each of the predetermined number of groups, the upper limit value and the lower limit value of the value of the unique identification code belonging to the group and the group. Transmitting the downlink frequency information, the frequency control unit extracts upper and lower limit values of the unique identification code value and the downlink frequency information from the received control frequency signal, When the value of the unique identification code given to is a value between the upper limit value and the lower limit value, a downlink frequency from which a frequency for receiving polling from the master station is extracted. The communication device according to claim 2, wherein the number is controlled to a number. 4. The apparatus according to claim 3, wherein the slave station control means determines the value of the unique identification code serving as a boundary between the groups so that the slave stations are equally distributed to the groups. The communication device as described. 5. The master station sequentially and repeatedly transmits information on an upper limit value and a lower limit value of the value of the unique identification code for each group and information on the downlink frequency assigned to the group by the same control frequency. The communication device according to claim 3, wherein: 6. The slave station receives polling from the master station using the downlink frequency indicated by the control frequency, transmits a response signal to the polling using an uplink frequency, and The communication device according to any one of claims 3 to 5, wherein, upon receiving a response signal from the slave station at the uplink frequency, establishes a communication line with the slave station. 7. A master station capable of transmitting a control frequency and a plurality of downlink frequencies, and a plurality of master stations capable of being present in a communication area of the master station and polling for identification codes unique to each of the master stations. A polling communication method in a communication device including a slave station that establishes a communication line with the master station by receiving the slave station, wherein the slave station is instructed by the control frequency to receive a polling frequency from the master station. A polling communication method comprising controlling the downlink frequency. 8. The information relating to each of the slave stations for which a communication line has not been established, and various types of information included in the slave station management data including the downlink frequency for the slave station can be obtained by using a unique identification code assigned to each of the slave stations. 8. The polling communication method according to claim 7, wherein the sorting is performed based on the values, and a predetermined number of groups are set according to the values of the unique identification codes. 9. The base station, using the control frequency, for each of the predetermined number of groups, an upper limit value and a lower limit value of the unique identification code belonging to the group, and the downlink frequency allocated to the group. The slave station extracts upper limit value and lower limit value of the value of the unique identification code and information of the downlink frequency from the received signal of the control frequency, and obtains the unique information given to the own station. If the value of the identification code is between the upper limit value and the lower limit value, the frequency for receiving polling from the master station is controlled to the extracted downlink frequency, The polling communication method described. 10. The apparatus according to claim 9, wherein the master station determines the value of the unique identification code serving as a boundary between the groups so that the slave stations are equally distributed to the groups. Polling communication method. 11. The master station sequentially and repeatedly transmits the upper limit value and the lower limit value of the value of the unique identification code for each group and the information of the downlink frequency allocated to the group using the same control frequency. The polling communication method according to claim 9, wherein: 12. The slave station receives polling from the master station using the downlink frequency indicated by the control frequency, transmits a response signal to the polling using an uplink frequency, and The polling communication method according to any one of claims 9 to 11, wherein upon receiving a response signal from the slave station at the uplink frequency, a communication line with the slave station is established.