JP6577358B2 - Ad hoc network - Google Patents

Description

  The present invention relates to an ad hoc network that constructs a communication path for its own device up to an end point relay device by transmitting and receiving route information stored in each of a plurality of relay devices to each other.

  In this ad hoc network, as described in Patent Document 1 below, each of a plurality of transmission / reception stations stores transmission relay information for communication path setting stored therein (for example, a partner station (end point relay)). Based on the received relay information for transmission and reception, the relay information (the station number of the partner station, the next communication partner station in the communication path to the partner station) A station number and the number of relays (hops) to the other station on this communication path are created and stored, and are communicated with each other via a communication path corresponding to the stored relay information. In this case, in principle, each transmitting / receiving station creates relay information so that the number of transmitting / receiving stations (transmitting / receiving stations functioning as a relay station) included in the communication path, that is, the number of hops (number of relays) is minimized.

  By the way, in a wireless communication system using an ad hoc network, as in the wireless communication system (regional crime prevention system) disclosed by the applicant of the present application as the background art in the following Patent Document 2, the call of a repeater (transmission / reception station) is usually performed. At the time (when transmission is performed), carrier sense is executed to check the presence / absence of another carrier (whether or not another carrier having a predetermined carrier sense level or higher is detected). When there is no other carrier (when no other carrier of the carrier sense level or higher is detected), the transmission is performed after a random waiting time generated by a random number (that is, transmission is performed by the CSMA / CA method), and waiting. The occurrence of collision (collision) between a plurality of repeaters is avoided.

JP 2000-324125 A (page 3-6, FIG. 1-10) JP 2009-104457 A (page 3)

  However, the ad hoc network has the following problems to be improved. That is, in this ad hoc network, when each relay station performs a transmission operation, it can avoid collision between transmission waves (carrier collision) by performing transmission by the CSMA / CA method as described above. However, in two repeaters in which the reception level of each other's transmission wave is less than the carrier sense level, one of the two repeaters has a third repeater located between the two repeaters. When the transmission operation is executed as the other party, the other relay device of the two relay devices performs the transmission operation (for example, each of the relay devices described above (the two relay devices and the third relay device described above). A transmission operation with another relay device different from that of the other relay device is executed. In this case, in the third repeater, the reception level of the transmission wave from the one repeater that is the communication partner and the reception level of the transmission wave from the other repeater described above There arises a problem to be improved that the ratio may be equal to or lower than a predetermined signal-noise ratio (SNR) (that is, interference may occur).

  In order to improve this problem, for example, it is conceivable to select a repeater having the shortest separation distance (that is, a repeater having the strongest received electric field strength) as the counterpart station. There arises a new problem that the number of hops in the case of transmitting the possessed information of the own device to another relay device as a device via a communication path created in advance greatly increases.

  The present invention has been made to improve such a problem, and mainly provides an ad hoc network that can communicate with an end point repeater with a smaller number of hops while greatly reducing the occurrence of interference in the repeater. Objective.

In order to achieve the above object, the ad hoc network according to claim 1 includes a plurality of relay devices, one of the plurality of relay devices as an end point relay device, and another relay device as a start point relay device. It is configured to be able to execute transmission processing for transmitting the possessed information held by itself to the end point relay device, and the start point relay device performs route information request processing for broadcasting a route information request by the CSMA / CA method, and the route Performing route information creation processing for creating route information including the number of hops to the end point relay device based on route response information received from the other relay device responding to the information request and recording the route information in the route table, and In the transmission process, the ad hoc network transmits the possessed information based on the route information, and the start point repeater measures a received electric field strength when receiving the route response information. This is when the field strength measurement process is executed and the received field strength measured in the field strength measurement process is equal to or higher than a reference field strength determined in advance based on the field strength E1 calculated by the following formula (1). When the route information is not created, the route information created by executing the route information creation process is recorded in the route table, and the route information is when the received electric field strength is greater than or equal to the reference field strength. Is already created, the number of hops contained in the new route information created by executing the route information creation process is less than the number of hops contained in the created route information. The route table is updated with new route information.
E1 = CS + B × log ₁₀ (1 + 10 ^{SNR / B} ) (1)
However, CS is a carrier sense level that is a fixed value in the above-described CSMA / CA system, B is a fixed value that is determined based on the antenna height of the repeater, and SNR indicates that interference at the repeater is slight. This is a fixed value of the S / N ratio.

In addition, the ad hoc network according to claim 2 is composed of a plurality of relay devices, one of the plurality of relay devices is an end point relay device, and another relay device is owned by the own device as a start point relay device. A transmission process for transmitting the retained information to the destination relay station, and the source relay station responds to the path information request and a path information request process for broadcasting a path information request in the CSMA / CA scheme. Route information creation processing for creating route information including the number of hops to the end point relay device based on the route response information received from the other relay device and recording the route information in a route table. An ad hoc network that transmits the possessed information based on route information, wherein the start point repeater measures a received electric field strength when receiving the route response information And when the received electric field strength measured in the electric field strength measurement process is equal to or higher than a reference electric field strength determined in advance based on the electric field strength E2 calculated by the following formula (2). When the information is not created, the route information created by executing the route information creation process is recorded in the route table, and the route information is already created when the received electric field strength is equal to or higher than the reference electric field strength. When the number of hops contained in the new route information created by executing the route information creation process is less than the number of hops contained in the created route information, the new route Update the routing table with information.
E2 = CS + B × log ₁₀ (1 + 10 ^{SNR / B} ) + Z (2)
However, CS is a carrier sense level that is a fixed value in the above-described CSMA / CA system, B is a fixed value that is determined based on the antenna height of the repeater, and SNR indicates that interference at the repeater is slight. Is a fixed value of the S / N ratio, and Z is the other value that the start point repeater responds to when the repeater other than the other repeater that responds is a hidden terminal when viewed from the start point repeater This is an attenuation amount of the received electric field intensity received from the repeater other than the repeater due to an obstacle existing between the repeaters.

  Further, in the ad hoc network according to claim 3, in the ad hoc network according to claim 1 or 2, the SNR is determined in consideration of an improvement degree of the SN ratio by error correction decoding performed by the start point repeater. It is a fixed value.

  According to the ad hoc network according to claim 1, in the repeater that can be the start point repeater, the processing unit has the path information when the measured value of the received electric field strength measured in the electric field strength measurement process is equal to or higher than the reference electric field strength. Is not created, the route information created by executing the route information creation process is recorded in the route table, and when the received field strength measurement value is equal to or higher than the reference field strength and the route information is already created, the route information In order to update the route table with this new route information when the number of hops included in the new route information created by executing the information creation process is less than the number of hops included in the already created route information, It is possible to communicate with a repeater as an end point repeater with a smaller number of hops while greatly reducing the occurrence of interference in the repeater.

  According to the ad hoc network according to claim 2, the reference electric field strength is determined based on the electric field strength (reception electric field strength) calculated by the above formula (2), so that even in the presence of a hidden terminal, As in the case of the ad hoc network described in 1, the occurrence of interference in the repeater can be reliably avoided while significantly reducing the occurrence of interference in the repeater.

  According to the ad hoc network described in claim 3, even if the SNR changes according to the error correction decoding used in the ad hoc network, an appropriate reference electric field strength can be determined based on the SNR.

1 is a configuration diagram of an ad hoc network 1. FIG. It is a block diagram of the relay machine STR. It is a data structure figure of transmission information. It is a data structure figure of route response information. It is a data structure figure of the route information recorded on the route table RT. It is explanatory drawing for demonstrating the determination procedure of the reference electric field strength Er when repeater STRs and STRa are exposed and it is terminal related. It is explanatory drawing for demonstrating the determination procedure of the reference electric field strength Er when relay machine STRs and STRa are hidden terminal relations. It is explanatory drawing for demonstrating the routing information recorded on the routing table RT of relay machine STR2. It is explanatory drawing for demonstrating the routing information recorded on the routing table RT of relay machine STR3. It is explanatory drawing for demonstrating the routing information recorded on the routing table RT of relay machine STR4. It is explanatory drawing for demonstrating the routing information recorded on the routing table RT of relay machine STR5.

  Embodiments of an ad hoc network will be described below with reference to the accompanying drawings.

  First, the configuration of the ad hoc network 1 will be described with reference to the drawings.

  As shown in FIG. 1, the ad hoc network 1 as an ad hoc network includes a plurality of relay devices STR1 to STR5 (hereinafter, also referred to as “relay device STR” when not distinguished). It is configured. Further, as shown in FIG. 2, each repeater STR is configured by a transmission unit 2, a reception unit 3, and a computer, for example, and controls the operation of the transmission unit 2 and the reception unit 3, and retained information transmission processing (described later) Transmission processing), route information request processing to be described later, route information response processing to be described later, route information creation processing to be described later and electric field strength measurement processing to be described later, and a processing unit 4 that executes various processing such as route information request to be described later. A storage unit 5 is provided for storing possession information to be described later, identification information of the own device, a route table RT to be described later, field strength information to be described later, and reference field strength Er to be described later.

  In addition, the number of relay units STR is not particularly limited, and may be composed of several tens to thousands. In addition, in FIG. 1, the relay stations STR that are associated with each other with a solid arrow line are in a positional relationship that allows direct communication with each other (exposed terminal relationship that does not require relaying by other relay devices STR). It is assumed that the relay stations STR associated with each other in an arrow line are in a positional relationship (hidden terminal relationship) where they cannot communicate directly with each other. In addition, among the relay stations STR associated with each other with a solid arrow line, the relay stations STR associated with each other with a thick solid arrow line (for example, between the relay stations STR1, STR2, etc.) The relay STRs that are in a positional relationship in which the measured value of ES is equal to or greater than the reference electric field strength Er and that are associated with each other by the thin solid arrow line (for example, between the relays STR1 and STR5) measure the received electric field strength ES. It is assumed that the value is higher than a carrier sense level CS, which will be described later, and has a positional relationship that is less than the reference electric field strength Er.

  In the ad hoc network 1, the relay STR1 functions as a master unit for the other relays STR2 to STR5, and is connected to a server (not shown) via a communication infrastructure (not shown) such as the Internet. Further, the other relay machines STR2 to STR5 use the possessed information held by the own machine as a start point relay machine (hereinafter also simply referred to as “start point machine”) as a parent machine (end point relay machine. Hereinafter, also simply referred to as “end point machine”). ) Or relaying the possessed information from another repeater STR that has transmitted the possessed information of its own device as a starting point device.

  As a result, the possession information held by the repeaters STR2 to STR5 includes the own device possession information about the own device acquired (or created) by the repeater STR and the possession information received from another repeater STR. Thus, there is relay possession information to be relayed to another relay station STR. Each repeater STR2 to STR5 stores (stores) its own possession information including its own identification information (its own ID (a code for identification identification)), and also retains this own possession of relay possession information. The information is saved (stored) including the own device identification information of the relay device that has acquired the information. Further, each of the relay units STR2 to STR5 configures and transmits the possessed information into transmission information having a data structure as shown in FIG. The counterpart device identification information in the transmission information is the identification information of the next hop destination repeater (hereinafter also referred to as “hop destination device”) STR in the communication path to be described later. In this example, as an example, the identification information of each relay STR is described with the same code (“STR”) as the code of each relay STR. Therefore, the identification information of the relays STR1, STR2, STR3, STR4, STR5 is represented by the codes STR1, STR2, STR3, STR4, STR5, respectively.

  The transmission unit 2 is controlled by the processing unit 4 in a CSMA / CA (with Carrier Sense Multiple Access / Collision Avoidance) with Ack method based on a predetermined carrier sense level CS, and is not illustrated via an antenna (not illustrated). Various types of information are wirelessly transmitted to the child device (mobile terminal) and other relay device STR.

  The receiving unit 3 constantly monitors the presence / absence of a transmission signal from the transmitting unit 2 of another relay STR by carrier sense. Specifically, the receiving unit 3 measures the reception electric field strength ES of the transmission signal, determines that there is a transmission signal when the reception electric field strength ES is equal to or higher than the carrier sense level CS, and determines the carrier sense signal. While outputting to the process part 4, the information (various information transmitted from other relay machine STR, a subunit | mobile_unit etc.) contained in a transmission signal is received, and it outputs to a process part 4 as reception information. In addition, the reception unit 3 outputs the measured value of the received electric field strength ES to the processing unit 4 as electric field strength information.

  Regarding the processing unit 4, the operation contents are different between the processing unit 4 of the relay station STR1, which is an end machine, and the processing units 4 of the other relay machines STR2 to STR5. Therefore, first, the processing unit 4 of the relay stations STR2 to STR5 will be described. When detecting the output of the carrier sense signal from the receiving unit 3, the processing unit 4 acquires the reception information and the electric field strength information output from the receiving unit 3 and stores them in the storage unit 5. In this case, as a general rule, the received information is the information addressed to the own device (the transmitted device information (the transmitted device information (see the transmitted information (see FIG. 3) described above) or the route response information (see FIG. 4) described later) Only the information about the own device, which is identification information of the own device), is stored in the storage unit 5. Also, regarding the electric field strength information, only the electric field strength information when the information addressed to the own device is received is addressed to the own device. Is stored in the storage unit 5 in correspondence with the identification information of the transmission source of the information (own device identification information included in the transmission information (see FIG. 3) and the route response information (see FIG. 4)) (field strength) However, as an exception, the route information in which the transmitted information (received information output from the receiving unit 3) is broadcast from another relay STR (transmitted without specifying the receiving party) Is a request Kiniwa always stores the transmission source identification information transmitted together with the path information request and the route information request to the storage unit 5.

  In addition, when the processing unit 4 obtains (creates) new own device possession information or receives new relay possession information from another relay device STR, the processing unit 4 executes retained information transmission processing. In the possession information transmission process, the processing unit 4 reads out these new possession information stored in the storage unit 5 and records them in the route table RT (see FIG. 5) stored in the storage unit 5. Route information (end machine identification information (identification information STR1 in this example), hop destination machine identification information in the communication path from the own machine to the end machine, and the number of relays of this communication path (hereinafter also referred to as hop count) ) To the other relay station STR (partner machine) indicated by the hop destination machine identification information as transmission information having the data structure shown in FIG.

  Further, the processing unit 4 executes a route information request process and a route information creation process immediately after startup and periodically thereafter. In this route information request process, the processing unit 4 broadcasts a route information request together with its own device identification information via the transmission unit 2. Further, the processing unit 4 receives the route response information (see FIG. 4) transmitted from another relay STR that has responded to this route information request (executed the route information response processing in response to the route information request). When the route response information is received, the measured value of the received electric field strength ES indicated by the electric field strength information stored in the storage unit 5 and the reference electric field strength Er stored in the storage unit 5 are received. When the measured value of the received electric field strength ES is greater than or equal to the reference electric field strength Er, the path information creation process is executed. As shown in FIG. 4, the route response information includes counterpart device identification information (identification information sent together with the route information request (identification information of the relay device STR that is the source of the route information request)), and own device identification. Information (identification information of the relay STR responding to the path information request), end-point machine identification information (identification information STR1), and a communication path from the relay STR responding to the path information request to the relay (master) STR1 Data structure information including the number of relays (number of hops).

  In this route information creation process, the processing unit 4 creates new route information based on the received route response information. Specifically, the processing unit 4 uses the own device identification information included in the route response information as the hop destination device identification information (hop destination device identification information), and is included in the route response information. The number of times of adding 1 to the number of times of relaying (the number of hops) is set as the number of times of relaying (the number of hops), and the route information shown in FIG. 5 including the end machine identification information (identification information STR1 in this example) is created. In this case, when the route information is not created, the processing unit 4 records the created route information in the route table RT. On the other hand, when the route information is already created, the processing unit 4 includes the number of hops included in the newly created route information. The route table RT is updated by recording new route information in the route table RT only when is less than the number of hops included in the already created route information recorded in the route table RT.

  Note that the processing unit 4 stores and stores the measured value of the received electric field strength ES even when the route response information transmitted from another relay STR responding to the route information request is received via the reception unit 3. As a result of comparison with the reference electric field strength Er stored in the unit 5, when the measured value of the received electric field strength ES is less than the reference electric field strength Er, the route information creation processing is not executed (that is, the creation of new route information is not performed). Not performed).

  The processing unit 4 records the route information in the route table RT stored in the storage unit 5 when the route information response processing is received when a route information request broadcast from another relay station STR is received. When this is done, it is executed in response to this route information request. In this route information response processing, the processing unit 4 has been transmitted together with the route information request together with the number of relays (the number of hops), the own device identification information, and the end device identification information included in the route information recorded in the route table RT. The information of the data structure shown in FIG. 4 including the identification information as the counterpart device identification information is created as route response information and transmitted via the transmission unit 2. Even when the route information request is received, the processing unit 4 does not execute the route information response process because there is no information to be transmitted when the route information is not recorded in the route table RT (this information) Do not respond to routing information requests).

  Next, the processing unit 4 of the relay STR1 that functions as a master unit will be described. The processing unit 4 does not execute the above-described electric field strength measurement processing, route information request processing, and route information creation processing. In the possession information transmission process, the processing unit 4 transmits the possession information to the server via the communication infrastructure when new possession information about the other relays STR2 to STR5 is received. In addition, since the routing table RT does not exist in the relay STR1, the processing unit 4 identifies the own device to the other relay STR that has transmitted the routing information request in the routing information response processing when the routing information request is received. Information STR1 is transmitted via the transmission unit 2 as route response information. Therefore, this route response information is information of a data structure including the counterpart device identification information and the own device identification information (identification information STR1), although not shown.

  Next, a procedure for determining the reference electric field strength Er stored in the storage unit 5 will be described.

It is generally known that the radio wave propagation characteristic between the base station and the mobile station (between the repeater STR in this example) is expressed by the Okumura-Kashiwa curve (the following propagation loss approximation formula (1)). (Known).
Propagation loss L = A + B × log (d) −a (hm) + C (1)
Here, A is a parameter (fixed value) related to the radio wave frequency and the base station antenna height, and B is a parameter related to the base station antenna height, where the base station antenna height is h. , B = 44.9−6.55 × log (h), C is a parameter (fixed value) related to the frequency of the radio wave, and a (hm) is the frequency of the radio wave And a parameter (fixed value) related to the mobile station antenna height, and d is the distance (km) between the repeaters STR. The bottom of the log is “10”. Same in the following.

  In this ad hoc network 1, as shown in FIG. 6, the relay STRs serving as the start relays are the first relays (next) that configure the communication path to the end relays in order to transmit the retained information to the end relays. In a state where communication is performed with the relay STRp, which is a hop destination of), the relay STRa present at a position where the received electric field strength at the relay STRs is less than the carrier sense level CS in the CSMA / CA scheme described later is transmitted. When the operation is started, interference may occur in the relay station STRp. The occurrence of this interference is highest when the relay STRa is on a straight line connecting the relays STRs and STRp, as shown in the figure, on the opposite side of the relay STRs with the relay STRp as a reference. It is time to position.

In such a positional relationship and when the relays STRs and STRa are exposed and in a terminal relationship, the propagation loss for the relay STRs in the relay STRp is Ls, and the relay in the relay STRp When the propagation loss for STRa is La and the difference (La−Ls) between the two propagation losses is calculated based on the above equation (1), it is expressed as the following equation (2).
La−Ls = A + B × log (da) −a (hm) + C
− (A + B × log (ds) −a (hm) + C)
= B * (log (da) -log (ds))
= B × log (da / ds) (2)

In consideration of this, when the received electric field strength ESa for the relay STRa in the relay STRp is obtained with reference to the received electric field strength ESs for the relay STRs in the relay STRp, the following equation (3) is obtained. It is expressed as follows.
ESa = ESs−B × log (da / ds) (3)

Similarly, when the received electric field strength ESa1 for the relay STRa in the relay STRs is obtained with reference to the received electric field strength ESs for the relay STRs in the relay STRp, the following equation (4) is obtained. expressed.
ESa1 = ESs−B × log ((da + ds) / ds) (4)
Here, assuming that the carrier sense level of each relay STR is CS, the boundary of presence / absence of interference (not generated) in the relay STRp for the received electric field strength ESa1 is when the received electric field strength ESa1 = CS. Therefore, the following equation (5) is established based on the above equation (4). As for the carrier sense level CS, in an ad hoc network in which the provision of carrier sense is required, any one value within a range defined by this ad hoc network can be selected as a fixed value. In an ad hoc network in which provision of carrier sense is not required, any one value can be selected as a fixed value without limitation.
CS = ESs−B × log ((da + ds) / ds)
= ESs−B × log (1 + da / ds) (5)

If the lower limit value of the signal-to-noise ratio at which interference does not occur in each relay STR is SNR, the following formula (6) needs to be established in the relay STRp.
SNR = ESs−ESa (6)

And based on said Formula (3), (6), following Formula (7) is formed.
SNR = B × log (da / ds) (7)
Furthermore, the following equation (8) is derived from this equation (7).
da / ds = 10 ^{SNR / B} (8)

Further, the above equation (5) is transformed into an equation for obtaining ESs, and the following equation (9) is derived by substituting the above equation (8) into this equation.
ESs = CS + B × log (1 + 10 ^{SNR / B} ) (9)

Equation (9) derived in this way indicates that the relay STRs as the start point relays communicate with the end point relays in order to transmit the retained information to the end point relays (the relay STR1 in the configuration of FIG. 1). When selecting the first repeater STR (hop destination) constituting the route, the repeater in which the received electric field strength ES at the repeater STRs is larger than the carrier sense level CS by B × log (1 + 10 ^{SNR / B} ) or more. By selecting from the STR, it is shown that the occurrence of interference in the first repeater STR (hop destination machine) can be surely avoided.

On the other hand, as shown in FIG. 7, when the relay STRa is located on a straight line connecting the relays STRs and STRp and on the opposite side of the relay STRs with respect to the relay STRp, When STRa is in a hidden terminal relationship, even if it is under the same conditions as in the exposed terminal relationship that the received electric field strength ES for the relay STRa at the relay STRs is less than the carrier sense level CS, the relay STRp In the relay station STRa, the received electric field strength ESa is higher than that of the terminal-related terminal. That is, as indicated by a broken line in the figure, the relay station STRa has a positional relationship that is closer to the relay station STRp only equivalently. In consideration of the increase (value Z) of the received electric field strength ESa for the relay STRa in the relay STRp, the above equation (5) is expressed as the following equation (5a).
CS + Z = ESs−B × log (1 + da / ds) (5a)
Moreover, said Formula (9) is represented like the following formula (9a).
ESs = CS + B × log (1 + 10 ^{SNR / B} ) + Z (9a)
However, Z is when Z is a hidden terminal when a relay station STRa other than the other relay station STRp that responds is viewed from the start-point relay station (relay station STRs that communicates with the other relay station STRp that responds). Of the received electric field strength received from the repeater STRa by the start point repeater of the first and second relays due to an obstacle (not shown) existing between the repeaters STRa and STRs.

Equation (9a) derived in this way is the first that configures the communication path to the end point repeater in order for the relay unit STRs as the start point relay unit to transmit the retained information to the end point relay unit (relay unit STR1). When selecting the next relay STR (next hop destination), the received signal strength ES at the relay STRs becomes larger than the carrier sense level CS by (B × log (1 + 10 ^{SNR / B} ) + Z) or more. This indicates that the occurrence of interference in the first repeater STR can be reliably avoided even in the presence of a hidden terminal.

The ad hoc network 1 of this example has a configuration in which hidden terminals exist as shown in FIG. Further, the value E2 (= CS + B × log (1 + 10 ^{SNR / B} ) + Z) on the right side of the above equation (9a) represents the carrier sense level CS, the lower limit value SNR and the value Z of the signal-to-noise ratio at each repeater STR. It is a fixed value in the determined state. Therefore, in the ad hoc network 1, this value E2 is calculated (determined) in advance and stored as the reference electric field strength ESr in the storage unit 5 of each of the repeaters STR2 to STR5 that can be the start point repeater. This value Z can be determined in advance by simulation or experiment. If there is no hidden terminal (a configuration in which all the relay stations STR are exposed terminals), the value E1 (= CS + B × log (1 + 10 ^{SNR / B} )) on the right side of the above equation (9) is calculated in advance ( And is stored as the reference electric field strength ESr in the storage unit 5 of each of the repeaters STR2 to STR5 that can be the start point repeater.

  From the viewpoint of surely avoiding the occurrence of interference, as in this example, the above-described value E1 and value E2 (hereinafter also referred to as “value E1 etc.”) are used as the most preferable configuration as the reference electric field strength ESr. Instead, a value slightly smaller than the value E1 or the like within the range in which the condition that the value is greater than the carrier sense level CS is satisfied, or a value slightly larger than the value E1 or the like is set as the reference electric field strength ESr. It is also possible to adopt the configuration as follows.

  The reason for adopting the former configuration (a configuration having a value slightly smaller than the value E1 or the like) of the two configurations will be described. The above-described configuration described with reference to FIG. 6 is a configuration in which the occurrence of interference is highest in the relay STRp (a configuration in which the relays STRs, STRp, and STRa are arranged in a straight line in this order). In the network 1, most of the relay units STRa deviate from the straight line connecting the relay units STRs and STRp, like the relay unit STRa indicated by a broken line in FIG. In this case, even if the distance between the relays STRs and STRa is the same (ds + da), the distance between the relays STRp and STRa becomes longer and the received electric field strength ESa decreases, so the value E1 is made smaller. Even if it does, it is because generation | occurrence | production of interference can be avoided. However, since the positional relationship among the relays STRs, STRp, and STRa is various, it is preferable to stop the value for correcting the value E1 at the value −5 dB in order to prevent the occurrence of interference more reliably. Even if the value E1 is slightly reduced in this way, the frequency of occurrence of interference is greatly reduced as compared with the conventional method in which the reception electric field strength ES is selected from among the relays STR having the carrier sense level CS or higher. It becomes possible.

  Next, the reason for adopting the latter configuration (a configuration having a value slightly larger than the value E1 etc.) of the two configurations described above will be described. For example, when the relay STRa is present at a position closer to the relay STRs (position P1 indicated by the broken line) than the position of the relay STRa indicated by a solid line in FIG. 6, the relay STRs creates a communication path. In addition, for example, an obstacle is temporarily located between the relay STRs and the relay STRa, so that the received electric field strength for the relay STRa at the relay STRs is temporarily lower than the carrier sense level CS. When the state becomes smaller, the relay STRs selects the relay STRp as the hop destination. In this case, in the normal state where the obstacle that was temporarily present between the repeater STRs and the repeater STRa no longer exists, the difference between the two received electric field strengths ESs and ESa at the repeater STRp (ESs− Since ESa) falls below the SNR, interference occurs at the relay STRp.

  On the other hand, when the reference electric field strength ESr is set to a value slightly larger than the value E1 or the like, the relay STRs have a higher reception field strength (for example, the relay STRp indicated by the solid line in FIG. 6). Also, the relay station STRp) present at the position P2 closer to the relay station STRs is selected as the hop destination. In this case, since the reception field strength ESs at the relay STRp increases and the reception field strength ESa decreases, the difference between the two reception field strengths ESs and ESa (ESs−ESa) exceeds the SNR. As a result, the occurrence of interference in the relay STRp can be greatly reduced.

  However, when the reference electric field strength ESr is set to a value slightly larger than the value E1, etc., a configuration of increasing to +10 dB is adopted in order to more surely achieve a significant reduction in the occurrence of interference in the repeater STRp. However, as the distance increases, the distance to the hop-destination relay STR is shortened, and as a result, the number of hops to the end-point relay is increased. For this reason, it is considered to be preferably +5 dB in consideration of a significant reduction in the occurrence of interference in the relay station STRp and an increase in the number of hops.

  Next, the operation of the ad hoc network 1 will be described.

  After the installation, in each of the repeaters STR1 to STR5, the reception unit 3 starts an operation of constantly monitoring the presence / absence of a transmission signal from the transmission unit 2 of the other relays STR1 to STR5 by carrier sense. In each relay station STR2 to STR5, route information is not recorded in the route table RT stored in the storage unit 5. For this reason, in each of the repeaters STR2 to STR5, the processing unit 4 executes a route information request process in order to create route information.

  In this case, when the processing unit 4 of the relay STR1 receives a route information request via the receiving unit 3 of its own device, the processing unit 4 always executes the route information response process in response to the route information request, thereby The identification information STR1 of the own device is transmitted as route information to the other relay device STR that has transmitted the information request via the transmission unit 2. On the other hand, the processing unit 4 of each of the repeaters STR2 to STR5 receives the route information request via the receiving unit 3, and the route information is recorded in the route table RT stored in the storage unit 5. The route information response process is executed only in response to this route information request. Therefore, immediately after the installation, the processing unit 4 of each relay station STR2 to STR5 in which the path information is not recorded in the routing table RT does not execute the path information response process, and only the processing unit 4 of the relay station STR1 responds to the path information response. Execute the process.

  In this ad hoc network 1, the relay STR1 can directly communicate with relays STR2, STR3, and STR5 other than the relay STR4 as shown in FIG. For this reason, the processing unit 4 of the relay STR1 receives the route information request from the relays STR2, STR3, STR5, and executes a route information response process for the relays STR2, STR3, STR5. As a result, the relay device STR1 receives route response information including the counterpart device identification information (identification information STR2) and the own device identification information (identification information STR1), the counterpart device identification information (identification information STR3), and the own device identification information ( Route response information consisting of identification information STR1) and route response information consisting of counterpart device identification information (identification information STR5) and own device identification information (identification information STR1) are transmitted.

  In this case, in each of the repeaters STR2, STR3, and STR5, the processing unit 4 first detects the output of the carrier sense signal from the receiving unit 3, and is addressed to the own unit in the transmission information output from the receiving unit 3. Is stored in the storage unit 5 and the field strength information output from the reception unit 3 is also acquired, and the storage unit is associated with the identification information STR1 of the transmission source relay STR1. 5 is stored (electric field strength measurement processing is executed).

  Next, in each of the repeaters STR2, STR3, and STR5, the processing unit 4 receives the route response information and the measured value of the received electric field strength ES indicated by the electric field strength information stored in the storage unit 5 and the storage unit 5 Is compared with the reference electric field strength Er stored in the, and only when the measured value of the received electric field strength ES is equal to or higher than the reference electric field strength Er, the route information creation process is executed. The correct route information.

  In this ad hoc network 1, as shown in FIG. 1, the measured value of the received electric field strength ES at the repeater STR2 closer to the repeater STR1 than the repeaters STR3 and STR5 is equal to or higher than the reference electric field strength Er, and the repeaters STR3 and STR5 The measured value of the received electric field strength ES is less than the reference electric field strength Er. For this reason, in the relay STR2, the processing unit 4 executes the route information creation process based on the fact that the measured value of the received electric field strength ES is equal to or higher than the reference electric field strength Er and the route information has not been created. Information is created and this route information is recorded in the route table RT. Accordingly, the processing unit 4 includes the identification information STR1 of the end point relay STR1, the identification information of the next hop destination (in this case, the identification information STR1 because the next hop destination is the relay STR1, and the relay STR1). A set of up to the number of hops (in this case, a numerical value “1”) is created as route information and recorded in the route table RT of the own device as shown in FIG.

  On the other hand, in the relay units STR3 and STR5, the processing unit 4 does not execute the route information creation process even if the route information is not created because the measured value of the received field strength ES is less than the reference field strength Er. For this reason, in the relay devices STR3 and STR5, the state in which route information is not created continues.

  Thereafter, in the relay stations STR3 and STR5, the processing unit 4 executes the route information request process again. In this ad hoc network 1, the relays STR3 and STR5 can directly communicate with all of the other relays STR1 to STR4 as shown in FIG. 1, but route information is stored in the route table RT of the relays STR3 and STR4. Since it is not recorded, only the processing unit 4 of the relays STR1 and STR2 executes the route information response process. As a result, the processing unit 4 of the relay STR1 receives the path information request from the relays STR3 and STR5, and executes the path information response process for the relays STR3 and STR5, whereby the counterpart machine identification information (identification information STR3 ) And own device identification information (identification information STR1), and route response information consisting of counterpart device identification information (identification information STR5) and own device identification information (identification information STR1). In addition, the processing unit 4 of the relay STR2 receives the route information request from the relays STR3 and STR5, executes a route information response process for the relays STR3 and STR5, and receives counterpart device identification information (identification information STR3). , Route response information including own device identification information (identification information STR2), end device identification information (identification information STR1) and number of relays (hop count: 1), counterpart device identification information (identification information STR5), own device identification information (Identification information STR2), destination machine identification information (identification information STR1), and route response information including the number of relays (hop count: 1) are transmitted.

  In this case, in the relay station STR3, the processing unit 4 first detects the output of the carrier sense signal from the receiving unit 3, and the transmission information (route) addressed to the own unit among the transmission information output from the receiving unit 3 Response information) is stored in the storage unit 5 and the electric field strength information output from the reception unit 3 is also acquired and stored in the storage unit 5 in correspondence with the identification information STR of the transmission source relay STR (electric field). Perform intensity measurement process). In this case, since the relay device STR3 receives the transmission information from the two relay devices STR1 and STR2, the storage unit 5 stores the electric field strength information about the relay device STR1 and the electric field strength information about the relay device STR2. Is done. Further, in relay station STR5, processing unit 4 first detects the output of the carrier sense signal from receiving unit 3, and among the transmission information output from receiving unit 3, the transmission information addressed to itself (path response) Information) is stored in the storage unit 5 and the electric field strength information output from the receiving unit 3 is also acquired and stored in the storage unit 5 in association with the identification information STR of the transmission source relay STR (electric field strength). Perform measurement process). In this case, since the transmission information from the two relays STR1 and STR2 is received at the relay STR5, the field strength information about the relay STR1 and the field strength information about the relay STR2 are stored in the storage unit 5. Is done.

  Next, in the relay units STR3 and STR5, the processing unit 4 stores the measured value of the received electric field strength ES indicated by the electric field strength information stored in the storage unit 5 when the route response information is received and the storage unit 5. New route information based on this route response information by comparing the reference electric field strength Er and executing the route information generation process only when the measured value of the received electric field strength ES is equal to or higher than the reference electric field strength Er. Create

  In the ad hoc network 1, as described above, the measured value of the received electric field strength ES for the relay STR1 in the relay STR3 and the measured value of the received electric field strength ES for the relay STR1 in the relay STR5 are the reference electric field strength. As shown in FIG. 1, the measured value of the received electric field strength ES for the relay STR2 closer to the relays STR3 and STR5 than the relay STR1 is equal to or higher than the reference electric field strength Er. In this case, in the repeater STR3, the processing unit 4 executes the route information creation process based on the fact that the measured value of the received electric field strength ES is equal to or higher than the reference electric field strength Er and the route information has not been created. Information is created and this route information is recorded in the route table RT. Specifically, the processing unit 4 receives the route response information (partner device identification information (identification information STR3), own device identification information (identification information STR2), end device identification information (identification information) received from the relay device STR2. STR1) and the number of relays (hop count: 1)) are used as the identification information of the hop destination machine (hop destination machine identification information), and the number of relays included in this route response information The number of hops 2 plus 1 is set as the number of relays (the number of hops), and the route information having the end point machine identification information as the identification information STR1 is created, as shown in FIG. Record. Further, in the repeater STR5, the processing unit 4 executes the route information creation process based on the fact that the measured value of the received electric field strength ES is equal to or higher than the reference electric field strength Er and the route information has not been created. And the route information is recorded in the route table RT. Specifically, the processing unit 4 receives the route response information (partner device identification information (identification information STR5), own device identification information (identification information STR2), end device identification information (identification information) received from the relay device STR2. STR1) and the number of relays (hop count: 1)) are used as the identification information of the hop destination machine (hop destination machine identification information), and the number of relays included in this route response information The number of relays (the number of hops) obtained by adding 1 to (the number of hops) is set as the number of relays (the number of hops), and the route information having the end machine identification information as the identification information STR1 is created. Record.

  In the repeater STR3, the processing unit 4 receives the route response information (partner device identification information (identification information STR3), own device identification information (identification information STR5), and end device identification information (identification information STR1) received from the relay STR5. ) And the number of relays (hop count: 2)) are used as the identification information (hop destination machine identification information) of the hop destination machine, and the number of relays ( Route information based on the route response information received from the relay device STR2 described above is route information in which the number of hops (1) plus 1 is the number of relay times (hop count) and the destination device identification information is the identification information STR1. However, if the route information is first created based on the route response information received from the repeater STR5 and this route information is recorded in the route table RT, For towards the hop count of the route information based on the route response information received from the relay device STR2 created is small, the routing table RT is updated with this route information. On the other hand, if the route information based on the route response information received from the repeater STR2 is first created and this route information is recorded in the route table RT, the route received from the later created repeater STR5. Since the number of hops of the route information based on the response information is larger, the route table RT is not updated, and the route information based on the route response information received from the relay station STR2 is maintained. Accordingly, the route information having the contents shown in FIG. 9 is recorded in the route table RT of the relay station STR3 as described above.

  Thereafter, in the relay device STR4 in which the route information is not created, the processing unit 4 performs the route information request processing and the electric field strength measurement processing in the same manner as the processing unit 4 of the relay devices STR2, STR3, STR5 described above, The route response received from the relay STR3 by executing the route information creation processing based on the route response information transmitted from the relays STR2, STR3, STR5 responding to the route information request transmitted in the route information request processing Own device identification information included in information (partner device identification information (identification information STR4), own device identification information (identification information STR3), end device identification information (identification information STR1), and number of relays (hop count: 2)) Is the identification information of the hop destination machine (hop destination machine identification information), and the number of relays (hop count) included in this route response information plus 1 And the number of relays (number of hops), creates a route information for the endpoint device identification information and the identification information STR 1, recorded in the routing table RT of its own as shown in FIG. 10.

  In the relay station STR4, the processing unit 4 also sends route response information (partner machine identification information (identification information STR4), own machine identification information (identification information STR2), end machine identification information (identification information STR1) from the relay machine STR2. If this route response information is used, route information with a smaller number of relays (hops) can be created. Since the measured value of the received electric field strength ES is less than the reference electric field strength Er, the route information creation process using the route response information from the relay STR2 is not executed. Therefore, the route information RT shown in FIG. 10 is recorded in the route table RT of the relay STR4 as described above.

  Thereby, the recording of the route information to the route table RT is completed in each of the repeaters STR2 to STR5, and in the ad hoc network 1, the relay is performed from the repeater STR5 via the repeater STR2 as shown by a one-dot chain line in FIG. Two communication paths are constructed: a communication path R1 leading to the machine STR1 and a communication path R2 leading from the relay machine STR4 to the relay machine STR1 via the relay machine STR3 and the relay machine STR2.

  Therefore, after that, in each of the repeaters STR2 to STR5, when the processing unit 4 acquires (creates) new own device possession information or receives new relay possession information from another repeater STR, An information transmission process is executed, and the possessed information is transmitted via the transmission unit 2. Specifically, in the possession information transmission process, the processing unit 4 reads out these new possession information stored in the storage unit 5 and records them in the route table RT stored in the storage unit 5. Based on the route information (end machine identification information (identification information STR1), hop destination machine identification information in the communication path from the own machine to the end machine, and the number of relays of this communication path (hereinafter also referred to as hop count)), Transmit to another relay STR (adjacent repeater located on the upstream side (master unit side) in the communication path including the above-described communication paths R1 and R2) indicated by the hop destination machine identification information .

  In this transmission, the processing unit 4 controls the transmission unit 2 by the CSMA / CA method based on the measurement value of the received electric field strength ES indicated by the electric field strength information output from the reception unit 3 and the carrier sense level CS. Thus, the retained information is transmitted via the transmission unit 2 while avoiding the occurrence of collision (collision) between the transmission signals.

  Further, in this ad hoc network 1, each relay STR is connected to the relay STR that receives a transmission signal with a reference electric field strength Er that is greater (stronger) than the carrier sense level CS in the CSMA / CA scheme as the next hop destination. For example, as shown in FIG. 1, in two relay devices STR1 and STR4 that are in a hidden terminal relationship with each other, a relay device STR3 that communicates with the relay device STR4 is assumed to be a transmission signal from the relay device STR4. Even if the relay STR1 transmits a transmission signal while receiving the signal, the ratio between the reception level of the transmission signal from the relay STR4 and the reception level of the transmission signal from the relay STR1 is defined in advance. Occurrence of a situation where the SNR or less (that is, interference in the relay STR3) is avoided.

  Thus, according to this ad hoc network 1, in each of the repeaters STR2 to STR5 that can be the start point relay STR, the processing unit 4 uses the measured value of the received electric field strength measured in the electric field strength measurement process as the reference electric field strength Er. In the above case, when the route information is not created, the route information created by executing the route information creation process is recorded in the route table RT, and the measured value of the received electric field strength is equal to or higher than the reference electric field strength Er. When the route information has already been created, the new hop number included in the new route information created by executing the route information creation process is less than the number of hops contained in the already created route information. Since the route table RT is updated with the route information, it is possible to communicate with the repeater STR1 as the end point repeater with a smaller number of hops while greatly reducing the occurrence of interference in the repeater STR. .

  Further, according to this ad hoc network 1, by determining the reference electric field strength ESr based on the received electric field strength ESs calculated by the above equation (10a), even in the presence of a hidden terminal, It is possible to reliably avoid the occurrence of interference at the relay STR while greatly reducing the occurrence of interference.

  The SNR that is the lower limit of the signal-to-noise ratio at which no interference occurs in each relay STR varies depending on the error correction decoding performed by the relay STR. It can also be determined in consideration. According to the ad hoc network 1 having this configuration, even if the SNR changes according to the error correction decoding used in the ad hoc network 1, an appropriate reference electric field strength ESr can be determined based on the SNR.

1 Ad hoc network ESr Standard electric field strength STR repeater

Claims (3)

It is composed of a plurality of repeaters, and one of the plurality of repeaters is used as an end point repeater, and another relay device transmits the retained information held by itself as the start point repeater to the end point repeater. The start point repeater is configured to be able to execute a transmission process, and the start point repeater broadcasts a route information request in the CSMA / CA method, and a route response received from another relay device that responds to the route information request. Route information creation processing for creating route information including the number of hops to the end-point relay device based on the information and recording the route information in a route table, and transmitting the possessed information based on the route information in the transmission processing An ad hoc network,
The start point repeater performs an electric field strength measurement process for measuring a received electric field strength at the time of receiving the route response information, and the received electric field strength measured in the electric field strength measurement process is expressed by the following formula (1). When the route information is not created yet when it is equal to or higher than a reference field strength determined in advance based on the calculated field strength E1, the route information created by executing the route information creation process is stored in the route table. When the received field strength is greater than or equal to the reference field strength and the route information has already been created, the hops included in the new route information created by executing the route information creation process An ad hoc network that updates the route table with the new route information when the number is less than the number of hops included in the created route information.
E1 = CS + B × log ₁₀ (1 + 10 ^{SNR / B} ) (1)
However, CS is a carrier sense level that is a fixed value in the above-described CSMA / CA system, B is a fixed value that is determined based on the antenna height of the repeater, and SNR indicates that interference at the repeater is slight. This is a fixed value of the S / N ratio. It is composed of a plurality of repeaters, and one of the plurality of repeaters is used as an end point repeater, and another relay device transmits the retained information held by itself as the start point repeater to the end point repeater. The start point repeater is configured to be able to execute a transmission process, and the start point repeater broadcasts a route information request in the CSMA / CA method, and a route response received from another relay device that responds to the route information request. Route information creation processing for creating route information including the number of hops to the end-point relay device based on the information and recording the route information in a route table, and transmitting the possessed information based on the route information in the transmission processing An ad hoc network,
The start point repeater performs an electric field strength measurement process for measuring a received electric field strength at the time of receiving the route response information, and the received electric field strength measured in the electric field strength measurement process is expressed by the following formula (2). When the route information is not created yet and the reference field strength determined in advance based on the calculated electric field strength E2, the route information created by executing the route information creation process is stored in the route table. When the received field strength is greater than or equal to the reference field strength and the route information has already been created, the hops included in the new route information created by executing the route information creation process An ad hoc network that updates the route table with the new route information when the number is less than the number of hops included in the created route information.
E2 = CS + B × log ₁₀ (1 + 10 ^{SNR / B} ) + Z (2)
However, CS is a carrier sense level that is a fixed value in the above-described CSMA / CA system, B is a fixed value that is determined based on the antenna height of the repeater, and SNR indicates that interference at the repeater is slight. Is a fixed value of the S / N ratio, and Z is the other value that the start point repeater responds to when the repeater other than the other repeater that responds is a hidden terminal when viewed from the start point repeater This is an attenuation amount of the received electric field intensity received from the repeater other than the repeater due to an obstacle existing between the repeaters.   The ad hoc network according to claim 1 or 2, wherein the SNR is a fixed value determined in consideration of an improvement degree of the SN ratio by error correction decoding performed by the start point repeater.

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