JP4541308B2 - Autonomous distributed frequency allocation method - Google Patents

Description

  The present invention relates to an autonomous distributed frequency allocation method for autonomously distributing the frequency of a link formed between wireless stations capable of communicating in a wireless communication system that can use a plurality of frequencies.

  A wireless ad hoc network can be constructed flexibly and easily by realizing multi-hop communication. In other words, the wireless LAN (Local Area Network) protocol of IEEE (Institute of Electrical and Electronics Engineers) 802.11 supports an ad hoc mode. In the ad hoc mode, data communication is performed directly between nodes without using an access point. Even if the other party's wireless station is at a remote location and cannot communicate directly, if the data can be relayed between the wireless stations, communication with that wireless station is possible by data transfer. A wireless ad hoc network can easily construct such a network system. Such a network system has excellent expandability, and is a technology suitable for temporary communication infrastructure in the military, police, and disasters, construction of a wireless home network, and expansion of a wireless LAN area. Application to is being considered.

  However, in such a conventional network system, a so-called hidden terminal problem occurs. The problem of this hidden terminal will be described with reference to FIGS.

  In the wireless LAN, CSMA / CA (Carrier Sense Multiple Access With Collision Avoidance) control is performed. In CSMA / CA, a wireless station that needs to transmit first determines whether another station is communicating or not, and starts transmitting a signal if the condition that it is not communicating (idle) is satisfied. To do. Carrier sense is performed to determine whether communication is in progress. When no carrier is detected, it is determined that the vehicle is in an idle state, and transmission is started.

  When transmission is started, an RTS (Request to Send) is sent from the transmitting radio station. Then, the reception-side radio station transmits CTS (Clear to Send) when preparation for reception is completed. Then, other wireless stations in the vicinity read the duration indicated in CTS or RTS, and during that time, transmission is prohibited regardless of carrier sense (NAV: Network Allocation Vector).

  For example, as shown in FIG. 11, it is assumed that radio stations T101 to T105 are arranged. Then, as shown in FIG. 11, it is assumed that a communication range is set for each of the radio stations T101 to T105.

  Here, it is assumed that data transmission is performed from the wireless station T102 to the wireless station T101. In this case, the radio station T102 performs carrier sense, and if no carrier is detected, transmits an RTS as shown in FIG. When the radio station T101 receives the RTS from the radio station T102, the radio station T101 transmits a CTS indicating that preparation for reception is completed, as shown in FIG. Further, when the radio station T103 receives the RTS from the radio station T102, the radio station T103 becomes NAV as shown in FIG. When the wireless station T102 receives the CTS from the wireless station T101, the wireless station T102 starts transmission of data (DATA) toward the wireless station T101 as shown in FIG.

  Here, it is assumed that data transmission from the wireless station T105 to the wireless station T104 is performed while data is being transmitted from the wireless station T102 to the wireless station T101. In this case, the radio station T105 performs carrier sense, and if it is idle, transmits an RTS as shown in FIG.

  When the radio station T104 receives the RTS from the radio station T105, the radio station T104 transmits a CTS indicating that preparation for reception is completed. However, in the wireless station T103, as shown in FIG. 12C, a collision occurs between the data (DATA) from the wireless station T102 and the CTS from the wireless station T104. Cannot receive CTS.

  When receiving the CTS from the wireless station T104, the wireless station T105 starts transmission of data (DATA) toward the wireless station T104 as shown in FIG.

  When the data transmission of the wireless station T102 is completed, the wireless station T101 determines whether or not the data can be received without an error. If the data can be received without an error, the wireless station T101 is wireless as shown in FIG. ACK (acknowledge) is transmitted to the station T102.

  As described above, since the radio station T103 cannot receive the CTS from the radio station 104, the radio station T103 does not detect data transmission from the radio station T105 to the radio station T104. For this reason, as shown in FIG. 12C, when the wireless station T103 determines that transmission from the wireless station T102 to the wireless station T101 has ended, a backoff is performed following the transmission signal interval (IFS: Inter Frame Space). The carrier sense is performed for a time called BO, and if it is continuously idle during that time, the transmission right is obtained and the RTS is transmitted. Accordingly, in the radio station T104, as shown in FIG. 12D, a collision between the RTS from the radio station T103 and the data (DATA) from the radio station T105 occurs.

  As described above, in this example, communication is performed using the link between the radio station T101 and the radio station T102 and the link between the radio station T104 and the radio station T105, but there is a radio station T103 that is not related to this. Cause hidden terminal problems. In this case, the link between the terminal T103 and the terminal T102 and the link between the terminal T105 and the terminal T104 are hidden terminal problem links.

  As described above, when this standard is applied to a wireless ad hoc network at a single frequency, there is a problem of a hidden terminal, which causes a problem that throughput is deteriorated.

  On the other hand, in the autonomous distributed frequency allocation method in a wireless ad hoc network in which a plurality of frequencies can be used, a frequency arrangement condition for avoiding the hidden terminal problem is defined. A radio station that forms a link (target link) that performs frequency allocation exchanges link information (a pair of the set frequency with a radio station that the connectable radio station forms a link) with the connectable radio station. Thus, the frequency allocation status of the peripheral links (links formed by radio stations capable of direct communication) is grasped, and the number of links that violate the frequency allocation conditions in the peripheral links, that is, the number of links that cause the hidden terminal problem is minimized. Frequency to be assigned to the target link.

  In FIG. 13, when the target link is L1, the radio stations that can directly communicate with the target radio stations T1 and T2 forming the target link L1 are T2 and T4 in T1, and T1, T3, and T5 in T2. In the wireless station T1, by exchanging link information with directly communicable wireless stations T2 and T4, the peripheral links grasped by T1 are L1, L2, L3, L4, L6 and L7 (a set of link information of T2 and T4). Thus, the links that can be the hidden terminal problem link grasped by T1 are L6 and L7. At this time, the link information of T1 is L1, L2, the link information of T2 is L1, L3, L4, and the link information of T4 is L2, L6, L7. The links that can be hidden terminal problem links are links: L6 and L7 obtained by excluding the links of the link information of T1 and T2 that are target wireless stations from the peripheral links that T1 grasps. Similarly, in the radio station T2, by exchanging link information with directly communicable radio stations T1, T3, T5, the peripheral links grasped by T2 are L1, L2, L3, L4, L5, L6, L8, L9. The links that can be hidden terminal problem links grasped by T2 are L5, L6, L8, and L9.

  The link that may cause the hidden terminal problem for the target link is a link that excludes the common link from the links that can be the hidden terminal problem link that the target wireless station grasps. This corresponds to one of the frequency arrangement conditions (described later (b)). This is done by exchanging link information that can be a hidden terminal problem link known by the target radio stations T1 and T2. At this time, since the common link is L6, the links excluding this link can be hidden terminal problem links with respect to the target link L1: L5, L7, L8, and L9. Further, the peripheral links are links L1 to L9 obtained by adding a link to be a hidden terminal problem link recognized by the other target wireless station to a set of peripheral links recognized by the own station. When the frequency of the link which can become a target link and a hidden terminal problem link overlaps, it becomes a hidden terminal problem link. By exchanging links that can become a hidden terminal problem link between the target wireless stations, link information of a link that can be a hidden terminal problem link and a peripheral link that is recognized by the target wireless station is shared.

  Here, the frequency allocation condition for avoiding the hidden terminal problem is to assign a frequency different from the link that may generate the hidden terminal problem link to the target link. Therefore, in the autonomous distributed frequency allocation method in a wireless ad hoc network in which a plurality of frequencies can be used, the target link L1 allocates a frequency that minimizes the number of hidden terminal problem links in the peripheral links.

In addition, in order to make it difficult to converge to a frequency arrangement that is a local solution, a frequency arrangement prediction method that predicts a frequency arrangement in a peripheral link and assigns a frequency that minimizes the number of hidden terminal problem links under the predicted arrangement has been proposed. (Non-patent document 1, Non-patent document 2).
Shimizu et al. “Characteristics Evaluation of Autonomous Distributed Frequency Allocation Method in Wireless Ad Hoc Networks (Part 2) {Society Conference of the Telecommunications Society, B-24-44, 2005” Shimizu et al. “Channel allocation Algorithm to Reduce Hidden Terminal Problem for Wireless Ad-hoc Network”, IWS 2005 / WPMC'05

  However, in the conventional autonomous distributed frequency allocation method, when the network scale increases due to the increase in the number of radio stations, links other than the peripheral links, links L10 to L12 in FIG. 13 increase, and are not considered in determining the frequency of the target link. Since the number of links increases, it may be easy to converge to a frequency arrangement that is a local solution.

  In order to make it difficult to converge to a frequency arrangement that is a local solution, a frequency arrangement prediction method that predicts a frequency arrangement in a peripheral link and assigns a frequency that minimizes the number of hidden terminal problem links under the predicted arrangement (Non-Patent Document 1, Non-Patent Document 1, Although there is a patent document 2), if there are hidden terminal problem links in the network and no frequency change occurs in those links, the frequency arrangement of the entire network does not change. At this time, if this frequency arrangement is a local solution, the present method cannot deviate from the frequency arrangement that becomes a local solution.

  FIG. 14 shows an arrangement success rate for each network in the conventional frequency arrangement prediction algorithm. Here, the network model as shown in FIGS. 15A and 15B is used to evaluate the characteristics of the frequency allocation prediction method when the network scale increases. The target link is selected at random, and 1000 patterns are implemented with different seeds. Here, the placement success rate is (number of patterns in which frequency placement for avoiding the hidden terminal problem is realized / total number of patterns (1000 times)).

  FIG. 15A is a network model in which (4 × 4) “16” radio stations are arranged in a grid pattern, and FIG. 15B is a (5 × 5) “25” radio station. This is a network model arranged in a grid. The communication range of the radio station is an adjacent station and a diagonal station. At this time, the total number of links is “42” in the case of FIG. 15A and “72” in the case of FIG. 15B. Moreover, in order to realize the frequency allocation for avoiding the hidden terminal problem, both networks need 5 channels by the total frequency allocation search.

  As shown by characteristic A101 in FIG. 14, in the network of (4 × 4) shown in FIG. 15A, the placement success rate reaches 1.0, and the frequency for avoiding the hidden terminal problem in all patterns Arrangement has been realized. However, as shown by the characteristic A102 in FIG. 14, in the network of (5 × 5) shown in FIG. 15B, a pattern that saturates with an arrangement success rate of 0.827 and converges to a frequency arrangement that becomes a local solution. You can see that it exists. From these comparisons, there is a problem that the conventional method tends to converge to a frequency arrangement that becomes a local solution when the network scale increases.

  In view of the above-mentioned problems, the present invention is capable of improving the success rate of arrangement to a frequency arrangement that does not cause a hidden terminal problem without converging to a frequency that becomes a local solution even if the network scale increases. An object is to provide a frequency allocation method.

  In order to solve the above-mentioned problem, the invention according to claim 1 is an autonomous distributed frequency assignment for autonomously selecting a frequency of a link formed between wireless stations capable of communicating in a wireless system capable of using a plurality of frequencies. In the method, when the frequency arrangement of the target link is set by the frequency setting algorithm, and the set frequency arrangement becomes a hidden terminal problem link, it is detected whether the set frequency arrangement has not changed over a specified period, The autonomous distributed frequency allocation method is characterized in that when the set frequency has not changed over a prescribed period, it is regarded as convergence to a local solution, and processing for changing the frequency arrangement is performed.

  In the invention of claim 2, the frequency setting algorithm determines whether there is a frequency satisfying the frequency allocation condition in the usable frequency as the setting frequency of the target link, and the frequency satisfying the frequency allocation condition in the usable frequency. The number of links that do not satisfy the frequency allocation condition for each usable frequency when there are no frequencies that satisfy the frequency allocation condition for all available frequencies. And the frequency that minimizes the number of links that do not satisfy the frequency allocation condition is set as the frequency of the target link.

  In the invention of claim 3, the frequency setting algorithm performs a target link determination process for determining whether or not there is a frequency arrangement in which the target link does not become a hidden terminal problem link. If the frequency that satisfies the allocation condition is the frequency of the target link and the target link becomes a hidden terminal problem link regardless of the usable frequency, select the frequency prediction link from the peripheral links of the target link, and select the target All the frequency allocation prediction patterns that can be taken within the usable frequency are derived from the link and the prediction link, and among the frequency allocation prediction patterns and the peripheral links, the link that does not belong to the target link or the prediction link is set as the current set frequency. By creating a frequency allocation pattern for the peripheral links, the frequency allocation for the peripheral links is created. Extracting a pattern number hidden terminal problem link in the arrangement pattern is minimized, characterized in that as the frequency of the target link frequency corresponding to the target link of the pattern.

  The invention of claim 4 is characterized in that the specified period is a fixed value. The invention according to claim 5 is characterized in that the specified period is a variable value.

  The invention of claim 6 is characterized in that in the process of changing the frequency arrangement, the change frequency is determined and the frequency change link is selected. The invention according to claim 7 is characterized in that the frequency change link is selected by selecting a target link. In the invention of claim 8, the selection of the frequency change link is performed by selecting a plurality of links including the target link.

  According to the present invention, when the set frequency arrangement becomes a hidden terminal problem link, it is detected whether or not the set frequency arrangement has changed beyond the specified period, and as a result of this detection, the set frequency arrangement is specified. When it has not changed over the period, it is regarded as convergence to a local solution, and processing for changing the frequency setting is performed. For this reason, even if the network scale increases, it does not converge to a frequency that becomes a local solution, and the success rate of arrangement to a frequency arrangement that does not cause a hidden terminal problem can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration example of a radio station according to the embodiment of the present invention. As shown in FIG. 1, the radio station according to the embodiment of the present invention has a plurality of transmission / reception processing units 14 each including a data processing unit 11, a modulation / demodulation unit 12, and a high frequency unit 13, and each is assigned a different frequency.

  Input data from an upper layer is distributed by the transmission / reception control unit 15 to the transmission / reception processing unit 14 corresponding to transmission to the next-hop wireless station by selecting the next-hop wireless station from the transmission destination. At this time, a header including the next hop destination is added to the packet. The transmission / reception control unit 15 specifies a distribution destination transmission / reception processing unit 14 by acquiring link information that is a pair of a link with a next-hop wireless station and its set frequency from the frequency allocation processing unit 16, and performs the corresponding transmission / reception. Output to the processing unit 14. Data input to the transmission / reception processing unit 14 is packetized by the data processing unit 11, modulated by the modulation / demodulation unit 12, and transmitted from the high frequency unit 13. The data processing unit 11 performs data transmission / reception processing based on the CSMA / CA control method. In addition, signals from other radio stations are received by the high frequency unit 13, demodulated by the modem unit 12, and sent to the data processing unit 11. Processing such as error detection is performed in the data processing unit 11, and data is output from the data processing unit 11 to the transmission / reception control unit 15. The transmission / reception control unit 15 transfers the data to the upper layer if it is addressed to the own station, and outputs it to the transmission / reception processing unit 14 corresponding to the next-hop wireless station if the data is transferred to another station. The frequency allocation processing unit 16 determines the frequency of the link with the radio station that can communicate directly from the exchange of link information. The transmission / reception processing unit 14 to be used is determined by determining the frequency.

  FIG. 2 is a functional block diagram of the frequency allocation processing unit 16. In FIG. 2, the link information exchange unit 21 outputs link information of the own station and link information that can be a hidden terminal problem link grasped by the own station to the transmission / reception control unit 15 and link information from other radio stations. Link information that can be a hidden terminal problem link that other wireless stations grasp is input from the transmission / reception control unit 15. A link that can be a hidden terminal problem link is determined based on the frequency allocation condition of the frequency allocation condition setting unit 23. The link information is information on the radio stations forming the link and the set frequency used in the link. The link information of the own station is output to the corresponding transmission / reception processing unit 14 periodically using a common channel or in response to a request from another radio station, and broadcast. Link information that can be a hidden terminal problem link grasped by the own station is output to the transmission / reception processing unit 14 corresponding to the common channel or the communication channel and transmitted to the target radio station. Based on the link information acquired from the surrounding radio stations, link information of the peripheral link and link information of a link that can be a hidden terminal problem link are generated for each target link and stored in the link information setting unit 22. .

  The frequency allocation condition setting unit 23 is set with frequency allocation conditions for preventing the hidden terminal problem from occurring. The frequency arrangement conditions include the following.

(A) The frequency of the target link is a frequency different from the set frequency of the link that can be a hidden terminal problem link.

(B) Assuming that the radio stations forming the target link are A and B, and the radio stations forming the link that can be a hidden terminal problem link of the target link are C and D, the radio station A, the radio station C, and the radio station B When a link can be formed by the wireless station D, or when a link can be formed by the wireless station A and the wireless station D, or by the wireless station B and the wireless station C, the link formed by the wireless station C and the wireless station D is the target link. It is not regarded as a link that can be a hidden terminal problem link, and the frequency of the target link is a frequency different from the set frequency of the link that can be a hidden terminal problem link.

  If any one of the above frequency allocation conditions is satisfied, the hidden terminal problem is not caused at the same frequency, and the hidden terminal problem can be avoided.

  In the frequency allocation conditions listed here, when communication is possible between two radio stations, the radio station forming the target link for frequency allocation can communicate with either the target radio station or the target radio station. Wireless stations are adjacent wireless stations. A link that can be a hidden terminal problem link is a communicable link that is formed with a radio station whose adjacent radio station is not the target radio station.

  Further, the frequency allocation conditions listed here are only examples, and other frequency allocation conditions for preventing the hidden terminal problem are conceivable. The links that can become the hidden terminal problem link differ depending on the conditions. In addition, the range of link information for grasping links that can be hidden terminal problem links also differs.

  The frequency determination unit 25 acquires link information of links that can be a link around the target link to be frequency-assigned and a hidden terminal problem link from the link information for each target link set in the link information setting unit 22, and a frequency setting algorithm Is used to determine a frequency at which the hidden terminal problem does not occur or the hidden terminal problem can be minimized. Then, the transmission / reception control unit 15 is notified, and the transmission / reception processing unit 14 of the target link is set based on this frequency.

  In the first embodiment of the present invention, a local solution detection counter 26 is provided. This local solution detection counter 26 is prepared for each target link, and is incremented when there is a hidden terminal problem in the target link and there is no change in the frequency arrangement. In the first embodiment of the present invention, it is detected from the count value of the local solution detection counter 26 that the set frequency has not changed over a specified period, and thereby it is determined whether or not the local solution has fallen. The When the frequency arrangement condition is not satisfied, it is determined whether the local solution detection counter 26 has reached a predetermined value or more. When the local solution detection counter 26 has reached a predetermined value or more, the local solution detection counter 26 has reached the local solution. Therefore, the process of changing the set frequency is performed.

  3 and 6 are flowcharts showing the processing of the first embodiment of the present invention. In FIG. 3, a frequency setting process is performed (step S101). In the first embodiment of the present invention, this frequency setting process is performed by a static allocation algorithm.

  When the frequency is set, it is determined whether the target link is a hidden terminal problem link (step S102). Whether or not the link is a hidden terminal problem link can be determined by whether or not the above-described frequency arrangement condition is satisfied.

  If it is not a hidden terminal problem link, the local solution detection counter 26 is initialized (step S103), and the frequency arrangement of the current peripheral link is stored as the frequency arrangement at the time of the previous processing (step S104).

  On the other hand, if it is a hidden terminal problem link in step S102, the frequency arrangement of the peripheral links of the target link is compared with the frequency arrangement at the time of the previous process (step S106). At this time, if there is a change in the frequency arrangement, it is not regarded as convergence to the local solution, the local solution detection counter 26 is initialized (step S103), and the frequency arrangement of the current peripheral link is stored as the frequency arrangement at the time of the previous processing. (Step S104).

  On the other hand, if there is no change in the frequency arrangement, the local solution detection counter 26 is incremented (step S107). Then, the count value of the local solution detection counter 26 is compared with a specified value for determining convergence to the local solution (step S108). If the count value of the local solution detection counter 26 is less than the specified value, it is not regarded as convergence to the local solution, the process goes to step S104, and the frequency arrangement of the current peripheral link is stored as the frequency arrangement at the previous processing.

  Here, when there is no change in the frequency arrangement in the link with the hidden terminal problem, the value of the local solution detection counter 26 is increased by repeating the loop of steps S102, S106, S107, S108, and S104. . If the frequency arrangement is not changed for the specified period or longer, the local solution detection counter 26 becomes the specified value or more. Thus, when there is no frequency change and the local solution detection counter 26 is equal to or greater than the specified value, there is a high possibility that the local solution has converged.

Therefore, when the value of the local solution detection counter 26 is equal to or larger than the specified value, it is regarded as convergence to the local solution, and the frequency arrangement changing process is performed (step S109).
In the frequency arrangement changing process, the frequency determining unit 25 determines the frequency changing link and the changing frequency, and notifies the link information exchanging unit 21 of the frequency changing link. The link information exchange unit 21 creates a frequency change notification based on the changed frequency for the radio stations forming the corresponding frequency changed link, and outputs the frequency change notification to the transmission / reception control unit 15. On the other hand, when the link information exchange unit 21 receives a frequency change notification from another radio station, the frequency determination unit 25 notifies the frequency determination unit 25 of the frequency change for the notified link.

  If it is determined that the convergence to the local solution is made, in step S109, the change frequency is determined and the frequency change link is selected. The change frequency is a frequency that minimizes the number of hidden terminal problem links of the peripheral links among the usable frequencies excluding the set frequency of the target link. In addition, the selection of the frequency change link includes a method of selecting a target link and a method of selecting a plurality of links including the target link. When selecting a plurality of links, (1) a case where all links of a wireless station (target wireless station) forming the target link are selected, and (2) a target link is formed between the target link and (1). There is a case where a link is formed between radio stations (common adjacent radio stations) that can directly communicate with each other. 4 and 5 show examples of selecting a frequency change link in the cases (1) and (2), respectively.

  Further, the specified value for determining convergence to the local solution in step S108 can take a fixed value or a fluctuation value. The fixed value is regarded as convergence to a local solution when the frequency change of the peripheral link does not occur continuously for a fixed number of times. On the other hand, the fluctuation value is a specified value, a fluctuation element, and the frequency change processing frequency implemented according to the present invention is introduced, and (fixed value × the frequency change frequency) or (fixed value × 2 ^ (the frequency change frequency− 1)) etc. That is, a frequency change processing counter is provided, and this frequency change processing counter is incremented every time the frequency change processing is performed in step S109. The count value of this frequency change processing counter is introduced to set a prescribed value for determining convergence to a local solution.

When the processing for changing the frequency arrangement is performed in step S109 in FIG. 3, the local solution detection counter 26 is initialized (step S110). Then, the frequency arrangement after the frequency change is stored as the frequency arrangement at the time of the previous process (step S111), and the process is terminated.
In addition, this process (step S101-S111) is implemented periodically. However, it may be performed aperiodically when there is a change in topology accompanying the appearance of a new radio station or the removal of an existing radio station.

  FIG. 6 shows frequency setting processing by the static allocation algorithm in step S101. As shown in FIG. 6, a usable frequency is set as a set frequency candidate (step S201), a set frequency is selected from the candidate (step S202), and it is determined whether or not a set frequency exists (step S203). If the set frequency exists, it is determined whether the set frequency satisfies the frequency allocation condition for frequency allocation (step S204). If the frequency allocation condition is satisfied, the allocated frequency is set as the set frequency (step S205). ).

  When the frequency allocation condition is not satisfied, the set frequency and the number of links that do not satisfy the frequency allocation condition are stored (step S206), the set frequency is excluded from the set frequency candidates (step S207), and the set frequency is again set. Make a selection. When the set frequency cannot be selected, that is, when there is no set frequency candidate, the frequency that minimizes the number of links that do not satisfy the frequency arrangement condition is set as the assigned frequency (step S208).

(Second Embodiment)
7 to 9 are flowcharts showing the process of the second embodiment of the present invention. In the first embodiment described above, a static allocation algorithm is used as the frequency setting algorithm. This algorithm does not take into account changes that occur in the peripheral links. On the other hand, in the second embodiment, a frequency allocation prediction algorithm is used that predicts frequency changes of peripheral links and minimizes the number of hidden terminal problem links under the predicted frequency allocation.

  In FIG. 7, a frequency setting process is performed (step S301). In the second embodiment of the present invention, this frequency setting process is performed by a frequency allocation prediction algorithm.

  When the frequency is set, it is determined whether the target link is a hidden terminal problem link (step S302). Whether or not the link is a hidden terminal problem link can be determined by whether or not the above-described frequency arrangement condition is satisfied.

  If it is not a hidden terminal problem link, the local solution detection counter 26 is initialized (step S303), and the frequency arrangement of the current peripheral link is stored as the frequency arrangement at the time of the previous processing (step S304).

  On the other hand, if it is a hidden terminal problem link in step S302, the frequency allocation of the peripheral links of the target link is compared with the frequency allocation in the previous process (step S306). At this time, if the frequency arrangement is changed, it is not regarded as convergence to the local solution, the local solution detection counter 26 is initialized (step S303), and the frequency arrangement of the current peripheral link is stored as the frequency arrangement at the previous processing. (Step S304).

  On the other hand, if there is no change in the frequency arrangement, the local solution detection counter 26 is incremented (step S307). Then, the count value of the local solution detection counter 26 is compared with a specified value for determining convergence to the local solution (step S308). If the count value of the local solution detection counter 26 is less than the specified value, the processing is not regarded as convergence to the local solution, the process goes to step S304, and the frequency arrangement of the current peripheral link is stored as the frequency arrangement at the previous processing.

  Here, when there is no change in the frequency arrangement on the link with the hidden terminal problem, the value of the local solution detection counter 26 is increased by repeating the loop of steps S302, S306, S307, S308, and S304. . If the frequency arrangement is not changed for a specified period or more, the local solution detection counter 26 becomes equal to or greater than a specified value. Thus, when there is no frequency change and the local solution detection counter 26 is equal to or greater than the specified value, there is a high possibility that the local solution has converged.

  Therefore, when the value of the local solution detection counter 26 is equal to or greater than the specified value, it is regarded as convergence to the local solution, and a frequency changing process is performed (step S309). This frequency changing process is performed as described in the first embodiment.

When the frequency is changed, the local solution detection counter 26 is initialized (step S310). Then, the frequency arrangement after the frequency change is stored as the frequency arrangement at the time of the previous process (step S311), and the process is terminated.
This process (steps S301 to S311) is periodically performed. However, it may be performed aperiodically when there is a change in topology accompanying the appearance of a new radio station or the removal of an existing radio station.

  FIG. 8 shows frequency setting processing by the frequency allocation prediction algorithm in step S301.

  In FIG. 8, target link determination processing is performed (step S401), and it is determined whether the target link is a hidden terminal problem link (step S402). If there is a frequency that does not become a hidden terminal problem link for the target link, the frequency is set as an assigned frequency (step S403). When the target link becomes a hidden terminal problem link using any of the usable frequencies, a frequency prediction link is selected from the peripheral links of the target link (step S404), and the target link and the prediction link can be used. Deriving all frequency allocation prediction patterns that can be taken within a frequency, and combining each frequency allocation prediction pattern with a frequency allocation that uses a link that does not belong to the target link or prediction link among the peripheral links as the current set frequency. Thus, a frequency arrangement pattern of peripheral links is created (step S405). Then, a pattern that minimizes the number of hidden terminal problem links is extracted from the frequency arrangement patterns of the peripheral links, and a frequency corresponding to the target link of the pattern is set as an assigned frequency (step S406).

  The target link determination process in step S401 in FIG. 8 is performed as shown in FIG. In FIG. 9, the usable frequency is set as a set frequency candidate (step S501), a set frequency is selected from the candidates (step S502), and it is determined whether the set frequency exists (step S503). If the set frequency exists, it is determined whether the set frequency satisfies the frequency allocation condition for frequency allocation (step S504). If the frequency allocation condition is satisfied, it is determined that the target link is not a hidden terminal problem link (step S505). If the frequency allocation condition is not satisfied, the set frequency and the number of links that do not satisfy the frequency allocation condition are stored (step S506), the set frequency is excluded from the set frequency candidates (step S507), and the set frequency is again set. Make a selection. If the set frequency cannot be selected, that is, if there is no set frequency candidate, it is determined that the target link is a hidden terminal problem link (step S508).

  FIG. 10 compares the placement success rate of the embodiment of the present invention with the placement success rate in the case of the conventional method.

  As a network model, “25” wireless stations (see FIG. 15B) arranged in a (5 × 5) lattice shape were used. The communication range of the radio station is an adjacent station and a diagonal station. This example shows a placement success rate (second embodiment) in the frequency placement prediction algorithm. Here, the placement success rate is the number of patterns / the total number of patterns realizing the frequency placement that avoids the hidden terminal problem. Note that. The usable frequency is “5”, the target link is randomly selected, and 1000 patterns are implemented by changing the seed. Also. The specified value for determining convergence to the local solution is a fixed value × the number of frequency change processing according to the present invention and a fixed value of 5. The frequency change link is a link formed between the target link and the target radio station and the common adjacent radio station. .

  As can be seen from FIG. 10, in the conventional frequency allocation prediction algorithm (indicated by characteristic A1), the allocation success rate is saturated at 0.827, and there is a pattern that converges to the frequency allocation that is a local solution. On the other hand, when the frequency changing method according to the present invention is used, the allocation success rate reaches 1.0 as shown by the characteristic A2, and the frequency allocation that avoids the hidden terminal problem in all patterns can be realized.

In the above embodiment, the wireless station has a plurality of transmission / reception processing units 14 and different frequencies are set as an example, but transmission / reception is performed based on the frequency determination in the frequency allocation processing unit 16. It is also possible to change the frequency of the processing unit 14. (Thus, for example, it is possible to have a plurality of transmission / reception processing units 14 having the same frequency.)
The present invention is not limited to the above-described embodiments, and various modifications and applications can be made without departing from the gist of the present invention.

  The present invention can be applied to a radio system constructed by a plurality of radio stations, and is particularly suitable for use in a wireless ad hoc network.

It is a block diagram which shows the structure of the radio station which can apply this invention. It is a functional block diagram which shows the structure of the frequency setting part in the radio station which can apply this invention. It is a flowchart used for description of the 1st Embodiment of this invention. It is explanatory drawing of selection of a frequency change link. It is explanatory drawing of selection of a frequency change link. It is a flowchart used for description of a static allocation algorithm. It is a flowchart used for description of the 2nd Embodiment of this invention. It is a flowchart used for description of a frequency arrangement | positioning prediction algorithm. It is a flowchart used for description of the judgment process of the object link in a frequency arrangement | positioning prediction algorithm. It is a graph used for the comparison with the arrangement success rate in the case of the conventional method and the arrangement success rate by the embodiment of the present invention. It is explanatory drawing of generation | occurrence | production of a hidden terminal problem. It is a timing diagram used for description of generation | occurrence | production of a hidden terminal problem. It is a specific explanatory view of a peripheral link. It is a graph which shows the arrangement success rate in the conventional autonomous distributed frequency allocation method. It is explanatory drawing of a network model.

Explanation of symbols

11: Data processing unit 12: Modulation / demodulation unit 13: High frequency unit 21: Link information exchange unit 22: Link information setting unit 23: Frequency arrangement condition setting unit 25: Frequency determination unit 26: Local solution detection counter

Claims (8)

In an autonomous distributed frequency allocation method for autonomously selecting a frequency of a link formed between wireless stations capable of communicating in a wireless system capable of using a plurality of frequencies,
Set the frequency allocation of the target link by the frequency setting algorithm,
When the set frequency becomes a hidden terminal problem link, it is detected whether the set frequency arrangement has not changed over a specified period,
An autonomous distributed frequency allocation method characterized in that when the set frequency arrangement has not changed over a prescribed period, it is regarded as convergence to a local solution, and processing for changing the frequency arrangement is performed. The frequency setting algorithm is:
Determine whether there is a frequency that satisfies the frequency allocation condition among the available frequencies as the set frequency of the target link.
When there is a frequency that satisfies the frequency allocation condition in the usable frequencies, the frequency satisfying the frequency allocation condition is set as the frequency of the target link.
When there are no frequencies that satisfy the frequency allocation condition for all available frequencies, the number of links that do not satisfy the frequency allocation condition is calculated for each available frequency, and the frequency that minimizes the number of links that do not satisfy the frequency allocation condition The autonomous distributed frequency allocating method according to claim 1, characterized in that the frequency of the target link is used. The frequency setting algorithm is:
Perform the target link determination process to determine whether there is a frequency allocation that does not cause the target link to become a hidden terminal problem link,
If the target link does not become a hidden terminal problem link, the frequency satisfying the frequency allocation condition is set as the frequency of the target link,
If the target link is a hidden terminal problem link using any of the available frequencies, select the frequency prediction link from the peripheral links of the target link,
All frequency allocation prediction patterns that can be taken within the usable frequency are derived from the target link and the prediction link, and among the frequency allocation prediction patterns and peripheral links, the link that does not belong to the target link or the prediction link is the currently set frequency. Create a frequency allocation pattern for peripheral links by combining
2. The pattern in which the number of hidden terminal problem links is minimized among the frequency arrangement patterns of peripheral links, and the frequency corresponding to the target link of the pattern is set as the frequency of the target link. The autonomous decentralized frequency allocation method described in 1.   The autonomous distributed frequency allocation method according to claim 1, wherein the specified period is a fixed value.   The autonomous distributed frequency allocation method according to claim 1, wherein the specified period is a variable value.   2. The autonomous distributed frequency allocation method according to claim 1, wherein in the process of changing the frequency arrangement, a change frequency is determined and a frequency change link is selected.   The autonomous distributed frequency allocation method according to claim 6, wherein the frequency change link is selected by selecting a target link.   The autonomous distributed frequency allocation method according to claim 6, wherein the frequency change link is selected by selecting a plurality of links including a target link.

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