Method for identifying hidden terminals in a wireless communication network

Abstract

To provide a communication terminal capable of recognizing the presence of a hidden terminal prior to wireless data communication.SOLUTION: In a wireless communication network 100 including an aggregation station 10 and a plurality of communication terminals 20, a communication terminal 20 operates as a search terminal 20A and aggregates, in an aggregation station 10, demodulable communication terminal data D1 for detecting demodulable communication terminals capable of demodulating communication data with other communication terminals 20, creates demodulation possible or impossible communication terminal aggregation data D2 from the demodulable communication terminal data D1 aggregated by the aggregation station 10, and transmits the data D2 to the communication terminals 20. The search terminal 20A acquires the number of carrier-senseable communication terminals, calculates hidden terminal estimated number data D3 based on the demodulation possible or impossible communication terminal aggregation data D2, sets an intermediate communication terminal 20B, and specifies hidden terminal specifying data D5 in which terminals of the same number as the estimated number of hidden terminals are specified as hidden terminals 20C from the hidden terminal candidate data D4 for identifying hidden terminal candidate data in ascending order of RSSI values which are signal intensifies of data communication.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a method for identifying hidden terminals in a wireless communication network.

Background Art

[0002] A wireless communication system having an aggregation station and a plurality of communication terminals capable of wireless communication with the aggregation station is known. In such a wireless communication system, an invention for improving the wireless communication performance of communication terminals is disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2017-98687), even when there are hidden terminals in the wireless communication network called hidden terminals.

[0003] According to the wireless communication apparatus and the wireless communication method disclosed in Patent Document 1, it is possible to improve the wireless communication performance in a communication terminal even in a wireless communication environment where hidden terminals exist.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the wireless communication apparatus and the wireless communication method disclosed in Patent Document 1, since wireless communication is performed in a state where the presence of hidden terminals cannot be grasped, data collisions cannot be avoided, and there is a problem that there is room for improving the quality of wireless data communication.

Means for Solving the Problems

[0006] Therefore, the present invention is for solving the above problems, and its object is to realize a wireless communication network in which data collision does not occur by grasping the existence of hidden terminals prior to the wireless data communication of communication terminals, and to provide a method for specifying hidden terminals in a wireless communication network.

[0007] As a result of intensive research by the inventor of the present invention to solve the above problems, the following configuration was conceived. That is, the present invention is a method for specifying hidden terminals in a wireless communication network having an aggregation station and a plurality of communication terminals that can communicate wirelessly with the aggregation station and are arranged in a state where their positions with respect to the aggregation station are fixed. Each of the communication terminals serves as a search terminal and detects a demodulable communication terminal that transmits a communication signal having a signal strength equal to or greater than a signal strength at which demodulation of communication data is possible with each of the other communication terminals, creates demodulable communication terminal data that is a list of the detected demodulable communication terminals, and transmits the demodulable communication terminal data to the aggregation station. The aggregation station aggregates the demodulable communication terminal data transmitted from all of the communication terminals, creates demodulable communication terminal aggregation data that distinguishes between the demodulable communication terminals and the non-demodulable communication terminals among all of the communication terminals, and transmits the demodulable communication terminal aggregation data to each of the communication terminals. Each of the communication terminals serves as a search terminal and acquires the number of communication terminals that can only perform carrier sense with each of the other communication terminals as the number of carrier senseable communication terminals, calculates the difference between the number of non-demodulable communication terminals based on the demodulable communication terminal aggregation data and the number of carrier senseable communication terminals as the estimated number of hidden terminals, each of the communication terminals serves as a search terminal and sets any one of the demodulable communication terminals for the search terminal as an intermediate communication terminal, specifies a communication terminal that is a non-demodulable communication terminal for the search terminal and for which demodulation of the communication data is possible for the intermediate communication terminal as a hidden terminal candidate, and specifies the hidden terminal candidates as hidden terminals in ascending order of the signal strength of the communication data for the same number as the estimated number of hidden terminals. This is a method for specifying hidden terminals in a wireless communication network.

[0008] Thus, before the communication terminal performs wireless data communication, the presence of hidden terminals can be grasped, so that it is possible to realize a wireless communication network in which data collisions are less likely to occur.

[0009] Also, when each of the communication terminals serves as the search terminal and specifies the hidden terminals in ascending order of the signal strength of the communication data for the same number as the estimated number of hidden terminals among the hidden terminal candidates, if the cumulative number of specified hidden terminals exceeds the estimated number of hidden terminals due to the presence of a plurality of hidden terminal candidates with the same signal strength of the communication data, among the plurality of hidden terminal candidates specified last as the hidden terminals, for each of the hidden terminal candidates with the same signal strength of the communication data, it is preferable to specify the hidden terminals in ascending order of the number of communication terminals capable of demodulating the communication data for any of the search terminal and the hidden terminal candidates.

[0010] Thus, even when the cumulative number of specified hidden terminal candidates exceeds the estimated number of hidden terminals due to the presence of a plurality of hidden terminal candidates with the same signal strength of the communication data, the cumulative number of specified hidden terminals does not exceed the estimated number of hidden terminals.

[0011] Also, the intermediate communication terminal is preferably the communication terminal having the maximum or minimum signal strength of the communication data with respect to the search terminal.

[0012] In the above, if the intermediate communication terminal with the maximum signal strength is selected, since the hidden terminal candidates are specified using an intermediate communication terminal whose wireless communication environment is similar to that of the search terminal, the hidden terminal candidates can be specified accurately. On the other hand, when the intermediate communication terminal with the minimum signal strength is selected, since the hidden terminal candidates are specified using an intermediate communication terminal whose wireless environment is similar to that of the hidden terminal candidates, the hidden terminal candidates can be specified accurately.

Advantages of the Invention

[0013] According to the method for identifying hidden terminals in a wireless communication network in the present invention, since the presence of hidden terminals can be grasped prior to the communication terminals performing wireless data communication, communication data collisions in the aggregation station do not occur, and it becomes possible to realize a wireless communication network with high data communication efficiency.

Brief Description of the Drawings

[0014]

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Embodiments for Carrying Out the Invention

[0015] Hereinafter, an embodiment of the wireless communication network 100 according to the present invention will be described with reference to FIGS. 1 and 2. The wireless communication network 100 in this embodiment has a plurality of communication terminals 20 that can communicate wirelessly with the aggregation station 10 and the aggregation station 10. The aggregation station 10 has at least an aggregation station antenna 12, an aggregation station operation control unit 14, and an aggregation station storage unit 16. The aggregation station operation control unit 14 is for causing the aggregation station 10 to execute a specific operation based on an aggregation station operation control program (not shown) stored in the aggregation station storage unit 16. Each communication terminal 20 has at least a terminal antenna 22 that can communicate wirelessly with the aggregation station antenna 12 of the aggregation station 10, a terminal operation control unit 24, and a terminal storage unit 26. The terminal operation control unit 24 is for causing the communication terminal 20 to execute a specific operation based on a communication terminal operation control program (not shown) stored in the terminal storage unit 26.

[0016] In the wireless communication network 100 in this embodiment, each communication terminal 20 is pre-assigned an identifier, and these identifiers do not overlap within the wireless communication network 100. The aggregation station 10 can identify each communication terminal 20 by the identifier represented by the identification number. Also, the installation position of each communication terminal 20 is fixed. Note that the numbers 1 to 6 attached to the screen portions of the respective communication terminals 20 in FIG. 1 are the identification numbers assigned to the respective communication terminals 20.

[0017] Hereinafter, the specific processing content of the hidden terminal identification method in the wireless communication network according to the present invention will be described with reference to FIGS. 3 and 4 and the like. Note that the hidden terminal 20C in this specification means a signal non-detection terminal that exists outside the carrier sense range of a certain communication terminal 20 (search terminal 20A) and cannot be detected as existing from a certain communication terminal 20.

[0018] First, a search terminal 20A (since the configuration of the search terminal 20A is the same as that of the communication terminal 20, it will be described using the symbols used in the configuration of the communication terminal 20) selected from each of the communication terminals 20 belonging to the wireless communication network 100 detects a communication terminal 20 capable of demodulating communication data with other communication terminals 20 excluding the search terminal 20A (S-1). Specifically, the terminal operation control unit 24 in the sequentially selected search terminal 20A may measure the signal strength (RSSI value) of the communication data from other communication terminals 20 received by its own terminal antenna 22. The terminal operation control unit 24 detects a communication terminal 20 whose communication signal strength (RSSI value) of the communication data measured by its own terminal antenna 22 is equal to or greater than the signal strength (RSSI value) of the communication data that can be demodulated, which is set in advance, as a demodulable communication terminal.

[0019] Next, the terminal operation control unit 24 creates demodulable communication terminal data D1 in which a list of identifiers of the communication terminals 20 detected as demodulable communication terminals is paired with its own (search terminal 20A) identifier, and stores it in its own terminal storage unit 26 (S-2). FIG. 5 is a list of the demodulable communication terminal data D1 created in each communication terminal 20. The terminal operation control unit 24 transmits the demodulable communication terminal data D1 stored in its own terminal storage unit 26 from the terminal antenna 22 to the aggregation station 10 (S-3).

[0020] At the aggregation station 10, the aggregation station operation control unit 14 stores the demodulable communication terminal data D1 from all the search terminals 20A (equal to all the communication terminals 20) received by the aggregation station antenna 12 in the aggregation station storage unit 16 (S-4). The aggregation station operation control unit 14 can grasp the total number of communication terminals 20 belonging to itself (aggregation station 10) based on the demodulable communication terminal data D1 stored in the aggregation station storage unit 16. Subsequently, the aggregation station operation control unit 14 aggregates the demodulable communication terminal data D1 stored in the aggregation station storage unit 16 (S-5). Specifically, the aggregation station operation control unit 14 creates demodulation-available / unavailable communication terminal aggregation data D2 (see FIG. 6) that distinguishes between demodulable communication terminals and non-demodulable communication terminals among all communication terminals 20, and stores it in the aggregation station storage unit 16 (S-6).

[0021] The demodulation-possible communication terminal aggregated data D2 is a list in which an '○' is assigned to each communication terminal 20 detected as a demodulation-possible communication terminal in each communication terminal 20, and a '△' is assigned to each communication terminal 20 that is not detected as a demodulation-possible communication terminal but is detected as a demodulation-impossible communication terminal. Then, the aggregation station operation control unit 14 transmits the demodulation-possible communication terminal aggregated data D2 stored in the aggregation station storage unit 16 from the aggregation station antenna 12 to each search terminal 20A (communication terminal 20) (S-7).

[0022] Each search terminal 20A (communication terminal 20) stores the demodulation-possible communication terminal aggregated data D2 transmitted from the aggregation station 10 from the terminal antenna 22 in the terminal storage unit 26 (S-8). After that, the terminal operation control unit 24 in each search terminal 20A obtains the number of demodulation-possible communication terminals for itself (search terminal 20A) and the number of carrier sense-only possible communication terminals that can only perform carrier sense from the signal strength (RSSI value) of the communication data received by the terminal antenna 22 from other communication terminals 20 when performing carrier sense every data transmission period T of itself (search terminal 20A) (S-9). As shown in FIG. 7, the acquisition of the number of demodulation-possible communication terminals and the number of carrier sense-only possible communication terminals can be integerized under preset conditions by using the average number of communication terminals 20 that can only perform carrier sense, which is the average value of the number of communication terminals 20 that can only perform carrier sense within a preset time (an integer multiple of the data transmission period T). Here, the average number of communication terminals 20 that can only perform carrier sense, which is the average value of the number of communication terminals 20 that can only perform carrier sense within three times (3T) the data transmission period T (which is 2 in FIG. 7), is used as the number of carrier sense-only possible communication terminals. Then, based on the demodulation-possible communication terminal aggregated data D2, the terminal operation control unit 24 of the search terminal 20A calculates, as the hidden terminal estimated number data D3, the difference between the number of demodulation-impossible communication terminals and the number of carrier sense-only possible communication terminals, as shown in FIG. 7 (S-10). The terminal operation control unit 24 of the search terminal 20A stores the hidden terminal estimated number data D3 in the terminal storage unit 26 (S-11).

[0023] Next, the terminal operation control unit 24 of the search terminal 20A sets one of the communication terminals 20 capable of demodulation with respect to the search terminal 20A as the intermediate communication terminal 20B (since the configuration of the intermediate communication terminal 20B is the same as that of the communication terminal 20, it will be described using the symbols used in the configuration of the communication terminal 20) (S-12). The setting of the intermediate communication terminal 20B may be any communication terminal 20 capable of data demodulation with respect to the search terminal 20A, but it is preferable to set as the intermediate communication terminal 20B the communication terminal 20 having the maximum or minimum signal strength (RSSI value) of the communication data with respect to the search terminal 20A. In the present embodiment, as shown in FIG. 8, the communication terminal 20 having the maximum signal strength (RSSI value) of the communication data with respect to the search terminal 20A (located at the closest distance from the search terminal 20A) is set as the intermediate communication terminal 20B. By setting the communication terminal 20 having the maximum signal strength (RSSI value) of the communication data as the intermediate communication terminal 20B in this way, it is advantageous in that the wireless communication environment between the search terminal 20A and the intermediate communication terminal 20B can be made comparable. Note that FIG. 8 illustrates a form of the wireless communication network 100 different from the wireless communication network 100 shown in FIG. 1. The same applies to FIGS. 9 and below.

[0024] Next, the terminal operation control unit 24 of the intermediate communication terminal 20B refers to the demodulation possible / impossible communication terminal aggregation data D2 stored in the terminal storage unit 26, and identifies as hidden terminal candidates the communication terminals 20 that are impossible to demodulate at the search terminal 20A and are capable of demodulating the communication data with respect to the intermediate communication terminal 20B (S-13). The terminal operation control unit 24 of the intermediate communication terminal 20B creates hidden terminal candidate data D4 and stores the hidden terminal candidate data D4 in the terminal storage unit 26 of the intermediate communication terminal 20B (S-14). Then, as shown in FIG. 9(A), the terminal operation control unit 24 of the intermediate communication terminal 20B specifies as the hidden terminal 20C the hidden terminal candidates extracted in ascending order of the RSSI value, which is the signal strength of the data communication (in the order of difficulty of demodulating the communication data), from among the hidden terminal candidate data D4, in the same number as the numerical value (estimated number of hidden terminals) of the hidden terminal estimated number data D3 stored in the terminal storage unit 26.

[0025] Next, the terminal operation control unit 24 of the intermediate communication terminal 20B creates hidden terminal identification data D5 as shown in Fig. 9(B) in which the identifier of the identified hidden terminal 20C is associated with the identification of the search terminal 20A, and stores it in the terminal storage unit 26 of the intermediate communication terminal 20B (S-15). Then, the terminal operation control unit 24 of the intermediate communication terminal 20B transmits the hidden terminal identification data D5 from the terminal antenna 22 of the intermediate communication terminal 20B to the aggregation station 10 (S-16).

[0026] The aggregation station operation control unit 14 (aggregation station 10) receives the hidden terminal identification data D5 transmitted from all the search terminals 20A (all communication terminals 20) with the aggregation station antenna 12, and stores the hidden terminal identification data D5 in the aggregation station storage unit 16 (S-17). The aggregation station operation control unit 14 aggregates all the hidden terminal identification data D5 stored in the aggregation station storage unit 16 to create hidden terminal identification aggregated data D6 as shown in Fig. 10, and stores the hidden terminal identification aggregated data D6 in the aggregation station storage unit 16 (S-18). The aggregation station operation control unit 14 transmits the hidden terminal identification aggregated data D6 stored in the aggregation station storage unit 16 from the aggregation station antenna 12 to all the communication terminals 20 (S-19).

[0027] After the communication terminal 20 receives the hidden terminal identification aggregated data D6 transmitted from the aggregation station 10 with the terminal antenna 22, the terminal operation control unit 24 stores the hidden terminal identification aggregated data D6 in the terminal storage unit 26 (S-20). By executing the processes of (S-1) to (S-20) described above, the process of identifying and sharing the hidden terminal 20C in all the communication terminals 20 in the wireless communication network 100 in the present embodiment is completed (END).

[0028] As described above, by storing the hidden terminal identification aggregated data D6 in the terminal storage unit 26 of each of all the communication terminals 20 belonging to the wireless communication network 100, each of all the communication terminals 20 belonging to the wireless communication network 100 can grasp the hidden terminal 20C. Thereby, when the communication terminal 20 performs data communication, information regarding the hidden terminal 20C can be obtained by referring to the hidden terminal identification aggregated data D6, collisions in data communication at the aggregation station 10 can be prevented, and it becomes possible to provide the wireless communication network 100 with high reliability in data communication.

[0029] In the present embodiment, as shown in FIG. 9(A), the same number as the numerical value (estimated number of hidden terminals) of the hidden terminal estimated number data D3 can be specified from the hidden terminal candidate data D4 in ascending order of the RSSI value which is the signal strength of the communication data (in the order in which demodulation of the communication data is difficult). However, there may be cases where such specification cannot be performed. Specifically, since the hidden terminal candidate data D4 includes a plurality of hidden terminal candidates having the same RSSI value which is the signal strength of the communication data, when specifying the hidden terminal 20C in ascending order of the RSSI value which is the signal strength of the data communication from the hidden terminal candidates, it is assumed that the number of hidden terminal candidates having the same RSSI value is larger than the number of the hidden terminal 20C to be specified last. A method for specifying the hidden terminal 20C in this case will be described.

[0030] As shown in FIG. 11, when there are a plurality of hidden terminal candidates with the same RSSI value, which is the signal strength of communication data, and if all of them are specified as the hidden terminal 20C and the numerical value of the hidden terminal estimation number data D3 is exceeded, among the plurality of hidden terminal candidates with the same RSSI value, which is the signal strength of the communication data, a hidden terminal specifying additional process is performed to specify the hidden terminal 20C in ascending order of the number of two-way connection terminals, which is the number of communication terminals 20 capable of demodulating communication data for both the search terminal 20A and the hidden terminal candidates. Thereby, among a plurality of hidden terminal candidates with the same RSSI value (same difficulty level of demodulating communication data), the communication terminal 20 with a small number of communication terminals 20 capable of data demodulation (located at a position far from other communication terminals 20) can be specified as the last one or a plurality of hidden terminals 20C.

[0031] Although the present invention has been described in detail based on the above embodiments, the technical scope of the present invention is not limited to the above embodiments. For example, in the above embodiments, the selection of the intermediate communication terminal 20B is exemplified by selecting the communication terminal 20 with the maximum RSSI value, which is the signal strength in data communication, among the communication terminals 20 capable of demodulating data with the search terminal 20A, but it is not limited to this form. The selection of the intermediate communication terminal 20B can also adopt a form of selecting the communication terminal 20 with the minimum RSSI value (the longest distance from the search terminal 20A), which is the signal strength in data communication, among the communication terminals 20 capable of demodulating data with the search terminal 20A. According to this form, it is advantageous in that the wireless communication environment of the intermediate communication terminal 20B can be made comparable to that of the hidden terminal candidates. Furthermore, a form of selecting the communication terminal 20 with the average value or the median value of the RSSI value, which is the signal strength in data communication, among the communication terminals 20 capable of demodulating data with the search terminal 20A as the intermediate communication terminal 20B can also be adopted.

[0032] Also, as described in this embodiment, among the communication terminals 20 capable of demodulating data with the search terminal 20A, the communication terminal 20 with the maximum RSSI value, which is the signal strength in data communication, is selected as the intermediate communication terminal 20B, and the hidden terminal identification aggregated data D6 generated thereby, and the communication terminal 20 with the minimum RSSI value, which is the signal strength in data communication, among the communication terminals 20 capable of demodulating data with the search terminal 20A is selected as the intermediate communication terminal 20B, and the hidden terminal identification aggregated data D6 generated thereby may be used in combination to identify the hidden terminal 20C. According to this form, among a plurality of hidden terminal candidates with the same RSSI value, which is the signal strength in data communication as shown in FIG. 11 (the difficulty level of demodulating communication data is the same), the cumulative number of identified hidden terminals 20C can be prevented from exceeding the estimated number of hidden terminals without performing the hidden terminal identification additional process of identifying the hidden terminal 20C in ascending order of the number of two-way connection terminals, which is the number of communication terminals 20 capable of demodulating communication data for both the search terminal 20A and the hidden terminal candidates.

[0033] Furthermore, a form in which the embodiments and modification examples described above are appropriately combined may be adopted.

Explanation of Signs

[0034] 10: Aggregation station 12: Aggregation station antenna, 14: Aggregation station operation control unit, 16: Aggregation station storage unit 20: Communication terminal, 20A: Search terminal, 20B: Intermediate communication terminal, 20C: Hidden terminal, 22: Terminal antenna, 24: Terminal operation control unit, 26: Terminal storage unit 100: Wireless communication network D1: Demodulable communication terminal data, Demodulation possible / impossible communication terminal aggregated data D2, D3: Estimated number of hidden terminal data, D4: Hidden terminal candidate data, D5: Hidden terminal identification data, D6: Hidden terminal identification aggregated data

Claims

1. In a wireless communication network having an aggregation station and a plurality of communication terminals that are wirelessly communicable with the aggregation station and are arranged in a state where their positions with respect to the aggregation station are fixed, a method for identifying hidden terminals within the wireless communication network for identifying hidden terminals between each of the communication terminals, comprising: Each of the communication terminals, as a search terminal, detects a demodulable communication terminal that transmits a communication signal having a signal strength equal to or greater than a signal strength at which demodulation of communication data is possible with each of the other communication terminals, creates demodulable communication terminal data that is a list of the detected demodulable communication terminals, and transmits the demodulable communication terminal data to the aggregation station. The aggregation station aggregates the demodulable communication terminal data transmitted from all of the communication terminals, creates demodulation-available / unavailable communication terminal aggregation data that distinguishes between the demodulable communication terminals and the non-demodulable communication terminals among all of the communication terminals, and transmits the demodulation-available / unavailable communication terminal aggregation data to each of the communication terminals. Each of the communication terminals, as a search terminal, obtains the number of communication terminals that are only carrier sense capable with each of the other communication terminals as the number of carrier sense capable communication terminals, and calculates the difference between the number of non-demodulable communication terminals based on the demodulation-available / unavailable communication terminal aggregation data and the number of carrier sense capable communication terminals as the estimated number of hidden terminals. Each of the communication terminals, as a search terminal, sets any one of the demodulable communication terminals with respect to the search terminal as an intermediate communication terminal, and identifies, as a hidden terminal candidate, a communication terminal that is a non-demodulable communication terminal with respect to the search terminal and is demodulable with respect to the intermediate communication terminal, and among the hidden terminal candidates, identifies hidden terminals in ascending order of the signal strength of the communication data for the same number as the estimated number of hidden terminals. A method for identifying hidden terminals within a wireless communication network, characterized by this.

2. When each of the communication terminals, as a search terminal, identifies hidden terminals in ascending order of the signal strength of the communication data for the same number as the estimated number of hidden terminals among the hidden terminal candidates, if the cumulative number of identified hidden terminals exceeds the estimated number of hidden terminals due to the presence of a plurality of hidden terminal candidates having the same signal strength of the communication data. Among the plurality of hidden terminal candidates that are finally specified as the hidden terminals, for each of the hidden terminal candidates having the same signal strength of the communication data, the number of the communication terminals capable of demodulating the communication data for any of the search terminal and the hidden terminal candidates is small. The method for specifying a hidden terminal in a wireless communication network according to claim 1, wherein the hidden terminal is specified in ascending order.

3. The intermediate communication terminal is the communication terminal having the maximum or minimum signal strength of the communication data with respect to the search terminal. The method for specifying a hidden terminal in a wireless communication network according to claim 1 or 2, characterized in that.

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