JP4757140B2 - Radio frequency assignment device, radio communication system, and radio frequency assignment method - Google Patents

Description

  The present invention relates to a radio frequency allocation device, a radio communication system, and a radio frequency allocation method for controlling radio channel allocation in a radio communication system that performs autonomous distributed asynchronous digital radio transmission that performs virtual carrier sense.

  In a wireless LAN system, which is a typical current wireless communication system, an access point (AP) is fixedly installed, and the AP is connected to the backbone by wire.

  Since the terminal always communicates via the AP when performing communication, the radio is used only for one hop between the terminal and the AP.

  On the other hand, a wireless mesh network in which APs are connected by a wireless link has been proposed and technology development is progressing. In a wireless mesh network, it is possible to assign the same channel (frequency) to all the wireless links connecting the APs, but there is a problem that the throughput decreases due to various factors.

  This problem is alleviated by appropriately assigning a plurality of channels to each radio link. However, since the number of channels is limited, in some cases, it may not be possible to properly assign channels to all radio links.

Further, in a wireless mesh network, when packet communication is performed at the same frequency simultaneously on links that are somewhat distant from each other, there is a problem called “exposed terminal problem” in which bandwidth reservation fails and packet loss occurs. As shown in FIG. 1, the “exposed terminal” is a result of the radio station 1 and the radio station 2 exchanging RTS (transmission request signal) and CTS (request confirmation signal) for bandwidth reservation. 3 indicates a wireless station 3 that is in a transmission suppression state in order to avoid interference with the wireless station 2, and does not return any response even when a transmission request is received from the wireless station 4. In such a situation, even if the RTS from the wireless station 4 is retransmitted, no response is received from the wireless station 3, which causes packet loss. If the RTS / CTS exchange is not performed and the wireless station 1 transmits a packet to the wireless station 2 and transmits a packet from the wireless station 4 to the wireless station 3 almost simultaneously, as shown in FIG. The ACK (response) packet from 2 or 3 becomes interference in the wireless station 3 or 2, respectively, and packet loss occurs. As described above, the exposed terminal problem causes packet loss although the process is different regardless of whether or not RTS / CTS is used. This problem can be avoided by assigning different frequencies to a link set in which such an exposed terminal problem occurs.
Centralized Channel Allocation Technology to Alleviated Exposed Terminal Problem in CSMA / CA Based Mesh Networks: IEICE Transaction on Communications Vol. E88-B No. 3, pp. 958-964

  However, the background art described above has the following problems.

  In order to improve throughput in a wireless mesh network, it is effective to allocate multiple channels appropriately to each wireless link, but the number of channels required for performance improvement is larger than the given number of channels. In some cases, channel allocation that satisfies the constraints cannot be performed. In such a case, it is possible to allow a certain amount of interference and assign a channel to each radio link, but at the same time, there is a demand to reduce the interference as much as possible.

  Therefore, if the use of a radio link that interferes with another radio link is prohibited, the interference does not occur in the first place, so that the interference can be reduced. However, in such a case, the network may be disconnected by prohibiting the use of some wireless links. In order to prevent this problem, it is not desirable to prohibit the use of radio links that are important for maintaining network connectivity.

  Therefore, in the present invention, in the wireless mesh network, when a plurality of channels are allocated to each wireless link, when the number of channels required is larger than the given number of channels, the interference rate is reduced and the connection rate is maintained. An object of the present invention is to provide a radio frequency allocating device, a radio communication system, and a radio frequency allocating method that can allocate channels while performing the above.

In order to solve the above-described problem, the radio frequency allocation device of the present invention includes:
In a radio frequency allocation device in a radio communication system that performs radio band allocation control by virtual carrier sense:
Collection means for collecting information on nodes that can be directly transmitted;
Neighboring node information creation means for obtaining, as an interference relationship, links in which exposed terminal problems occur based on the node information and node information in other nodes;
Assign different frequencies to links that cause interference due to the exposed terminal problem, and if the number of frequencies required for frequency allocation to all links is greater than the number of available frequencies, duplicate available frequencies Means for assigning radio channels;
An edge interval degree calculating means for obtaining an edge interval degree for a link to which frequencies that can be used in the radio channel assigning means are assigned in an overlapping manner;
A link determination means for prohibiting the use of a predetermined link based on the average value and the standard deviation of the side interval degrees;
Equipped with a,
The edge interval calculating means, the set s of the node, the shortest path pst of t, with one of the features that you calculate the number of pairs, such as through the appropriate link.

  By configuring in this way, it is possible to select a link that suppresses communication based on the degree of edge spacing, and to reduce the degree of exposure terminal problems while suppressing a decrease in network connectivity and reducing packet loss. Can be reduced.

The wireless communication system of the present invention includes:
In a radio communication system that performs radio band allocation control by virtual carrier sense:
Collection means for collecting information on nodes that can be directly transmitted;
Neighboring node information creation means for obtaining, as an interference relationship, links in which exposed terminal problems occur based on the node information and node information in other nodes;
Assign different frequencies to links that cause interference due to the exposed terminal problem, and if the number of frequencies required for frequency allocation to all links is greater than the number of available frequencies, overlap the available frequencies Means for assigning radio channels;
An edge interval degree calculating means for obtaining an edge interval degree for a link to which frequencies that can be used in the radio channel assigning means are assigned in an overlapping manner;
A link determination means for prohibiting the use of a predetermined link based on the average value and the standard deviation of the side interval degrees;
Equipped with a,
The edge interval calculating means, the set s of the node, the shortest path pst of t, with one of the features that you calculate the number of pairs, such as through the appropriate link.

  With this configuration, the radio station can select a link that suppresses communication based on the degree of edge spacing, and can reduce the degree of exposure terminal problems while suppressing a decrease in network connectivity. Packet loss can be reduced.

The radio frequency allocation method of the present invention includes:
In a radio frequency allocation method in a radio communication system that performs radio band allocation control by virtual carrier sense:
A collecting step for collecting information of nodes that can be directly transmitted;
Neighboring node information creation step for obtaining, as an interference relationship, links where the exposed terminal problem occurs based on the node information and the node information in other nodes;
When assigning different frequencies to the links where interference due to the exposed terminal problem occurs, if the number of frequencies required for frequency allocation to all links is greater than the number of usable frequencies, the usable frequencies Assigning radio channels in duplicate;
A side interval degree calculating step for obtaining a side interval degree for a link to which frequencies that can be used in the wireless channel assigning unit are assigned in an overlapping manner;
A link determination step for prohibiting use of a predetermined link based on an average value and a standard deviation of the degree of side spacing;
I have a,
One of the characteristics is that the side interval degree calculating step calculates the number of sets such that the shortest path pst of the node sets s and t passes through the corresponding link .

  In this way, it is possible to select a link that suppresses communication based on the degree of edge spacing, and to reduce the degree of exposure terminal problems while suppressing a decrease in network connectivity and reducing packet loss. it can.

  According to an embodiment of the present invention, in a wireless mesh network, when the number of channels required when assigning a plurality of channels to each wireless link is larger than the given number of channels, the interference rate is reduced and the connection rate is reduced. It is possible to realize a radio frequency allocating device, a radio communication system and a radio frequency allocating method that can allocate channels while maintaining the above.

Next, embodiments of the present invention will be described with reference to the drawings.
In all the drawings for explaining the embodiments, the same reference numerals are used for those having the same function, and repeated explanation is omitted.

  In order to prevent a decrease in throughput in a wireless mesh network, it is known that it is effective to allocate a plurality of channels to each wireless link while satisfying certain constraints while avoiding interference.

  However, since the number of channels is finite, channel assignment may not be possible with the given number of channels. In such a case, in the present embodiment, channel allocation with reduced interference is realized by the following method while maintaining a high connection rate. Specifically, when channel allocation satisfying the constraint cannot be performed with a given number of channels, a channel that does not satisfy the constraint is allocated to a radio link that cannot allocate a channel. At the same time, a wireless link having a low edge interval is selected from these wireless links, and its use is prohibited during path control.

  The configuration of the mesh network according to the embodiment of the present invention will be described with reference to FIG. The mesh network according to the present embodiment performs radio band allocation control by virtual carrier sense. Here, the method using virtual carrier sense establishes communication with each other by exchanging a “transmission request signal” and a “preparation completion signal” between wireless stations performing transmission and reception. In addition, other wireless stations that have received these signals postpone transmission of the “transmission request signal” based on the “transmission prohibited period” included in these received signals.

The mesh network according to the present embodiment is composed of a plurality of radio stations. FIG. 3 shows a mesh network including _six radio stations 100 (100 ₁ , 100 ₂ , 100 ₃ , 100 ₄ , 100 ₅ , 100 ₆ ) as an example. In FIG. 3, a radio link (link) between the radio station 100 _k and the radio station 100 _l is indicated by L _kl (k and l are positive integers).

Each wireless station forms a mesh-connected network by establishing a link with a communicable wireless station. When a CSMA / CA (Carrier Sense Multiple Access Collision Detection) method is used as a wireless access control method (MAC) as in a wireless LAN system, a set of links according to a specific rule (in FIG. 3, the wireless station 100 ₁ and a link _{L 12} of the radio station 100 _2, the including links _{L 35} of the radio station 100 ₃ and the radio station 100 ₅₎ communicates simultaneously exposed problem occurs called terminal problem, a communication quality degradation such as packet loss (For example, refer nonpatent literature 1).

  That is, the exposed terminal problem refers to a problem in which communication cannot be started despite being far enough not to interfere.

  Next, the radio station 100 according to the present embodiment will be described with reference to FIG.

  The radio station 100 according to the present embodiment includes a radio frequency allocation device. The radio frequency allocation device is connected to the transmission / reception unit 102, the control unit 104 connected to the transmission / reception unit 102, and controls each unit of the radio frequency allocation device, and the control unit. 104 includes a wireless channel setting unit 110, an adjacent node information collection unit 106, and an adjacent node information creation unit 108 connected to the network 104. The radio channel setting unit 110 includes a radio channel assignment unit 112, a side interval degree calculation unit 114, and a link determination unit 116.

The adjacent node information creation unit 108 of each wireless station 100 (100 ₁ , 100 ₂ , 100 ₃ , 100 ₄ , 100 ₅ and 100 ₆ ) creates information related to its own wireless station, for example, a wireless station, in order to create adjacent node information. Broadcast a packet including the ID, frequency used, and adjacent node information. Other wireless stations that have received the broadcast packet collect adjacent node information in the adjacent node collection unit 106. In addition, in the adjacent node information creation unit 108, the wireless station 100 adds the adjacent node information of the own wireless station to the received packet, and broadcasts a packet including information related to the own wireless station and adjacent node information. By repeating the above process, the adjacent node information collection unit 106 of each wireless station can collect the adjacent node information collected by the adjacent node.

  Further, each wireless station creates a color graph in the adjacent node information creation unit 108 based on the collected adjacent node information of the adjacent nodes, and estimates a combination of communication paths in which the exposed terminal problem occurs. The coloring graph will be described later. More specifically, “communication of a transmission / reception station of a certain communication channel (referred to as communication channel A) recognized based on adjacent node information and another wireless station (referred to as wireless station B) recognized based on adjacent node information. If it is out of range, it is estimated based on the point at which an exposure terminal problem occurs in “communication between the local station and the wireless station B during communication on the communication path A”.

  For example, as illustrated in FIG. 5, the adjacent node information creation unit 108 generates a graph in which a link is a section of a graph and a pair of links generated by an exposed terminal is an edge. It is known that the problem of preventing the exposed terminal problem is equivalent to the “point coloring problem” in which connected nodes are colored so as not to have the same color. In the example shown in FIG. 5, since the coloring graph can be divided into two colors, it can be seen that two channels are sufficient to prevent the exposed terminal problem.

  Here, the color graph will be described in detail. The colored graph is a diagram representing communication paths in which exposure problems occur between the communication paths (links) as a connection relationship between the communication paths.

  For a given node (terminal) k, l, m, and n, an exposed terminal problem occurs between the communication path Ck, l between the node k and the node l and the communication path Cm, n between the node m and the node n. The criteria for determining whether to do this will be described with reference to FIG.

When determining whether or not it is a pair of exposed communication channels in bidirectional communication in TCP, whether carrier sense is possible or not differs between terminals k and l, or between terminals m and n Judgment is made based on whether the carrier sense status is different. If the status of carrier sense from the terminal m to the terminal k is expressed as S (k, m), If [{S (k, m) or
S (k, n)} ≠
{S (l, m) or S (l, n)}] or [{S (k, m) or S (l, m)} ≠ {S (k, n) or S (l, n)}] = Determine whether TRUE or FALSE.

  For example, (1) When terminal k cannot perform carrier sense from terminals m and n, but terminal l can perform carrier sense from terminals m or n, the transmission prohibition period is accompanied by transmission of a signal from terminal k to l. Terminal m and n cannot know, so that a terminal problem occurs when a signal is transmitted from terminal m or n to terminal l.

  (2) If the terminal m cannot perform carrier sense from the terminals k and l, but the terminal n can perform carrier sense from the terminal k or l, the transmission prohibition period is increased along with transmission of a signal from the terminal m to n. Since the terminals k and l cannot know, an exposure terminal problem occurs when a signal is transmitted from the terminal k or l to the terminal n.

  Therefore, if the exposed terminal problem occurs in any communication according to the above (1) and (2) (the conditional expression is TRUE), the terminal problem is exposed by exposing the relationship between the communication paths Ck, l and Cm, n in the coloring graph. It is assumed that there is an interference relationship as a generated communication path. Here, the interference refers to a relationship between radio stations in which the exposed terminal problem occurs.

  On the other hand, if either of the transmission and reception stations can know the transmission prohibition period, or if neither of the transmission and reception stations knows the transmission prohibition period, that is, if neither of the transmission and reception stations can communicate (conditional expression is FALSE), The relationship between Ck, l and Cm, n is exposed, and there is no interference relationship as a communication path where no terminal is generated. By performing this determination for all communication paths, the connection relationship between the communication paths can be represented by a colored graph. The present invention is not limited to TCP and can be applied to other protocols. Needless to say, the present invention is not limited to bidirectional communication, and any one of the above conditional expressions may be satisfied when applied to unidirectional communication.

  The radio channel setting unit 110 assigns a channel to each radio link in the radio channel assignment unit 112 based on the color graph created in the adjacent node information creation unit 108. For example, the radio channel setting unit 110 assigns different frequencies to be assigned to the links that cause the connected exposed terminal problem. In this way, by creating a coloring graph from the connection relationship of the wireless mesh network and assigning the channel to each wireless link from the result of coloring the coloring graph using some graph coloring algorithm, the communication quality due to the exposed terminal problem Decline can be prevented.

  As a result of such channel assignment, let N be the number of channels necessary for channel assignment to all radio links, and let M be the given number of channels, that is, the number of usable channels (M and N are positive integers). ). The wireless channel assignment unit 112 represents the color (channel) number from 1 to M. If N> M, a set of radio links to which channels M + 1 to N are assigned is represented by V ′. Of the 1st to Mth channels, one with less interference is assigned to the V ′ radio link. That is, when the number of frequencies necessary for frequency allocation to all links is larger than the number of usable frequencies, there is less interference among the usable frequencies for links other than the links to which the usable frequencies are allocated. Assign a frequency. In other words, the usable frequency is assigned to a link other than the link to which the usable frequency is assigned.

The edge interval degree calculation unit 114 calculates the edge interval degree for each wireless link of V ′. The edge interval degree is an index indicating the importance of the link network, and is calculated as follows. Let G = (V, E) be the network graph structure. Where V is a set of nodes and E is a set of edges. For two vertices s, t and an edge e∈E, the edge interval degree eb _{(s, t)} (e) of e in s, t is the number of shortest paths sp _{(s, t)} between _{s, t.} This indicates the ratio of the shortest path number sp _{(s, t)} (e) passing through e. The side center distance ebc _{(s, t)} (e) of the side eεE is the total of the side distances at any two vertices of e. Hereinafter, the side center interval degree is referred to as a side interval degree and is used in this sense. The edge spacing is calculated as follows.

辺間隔度は「メッシュネットワークの無線局の組ｓ，ｔの最短経路ｐ_ｓｔが該当するリンクを通るような組の数」と定義される。

The degree of edge spacing is defined as “the number of pairs in which the shortest path p _st of the wireless network set s, t of the mesh network passes through the corresponding link”.

As an example, a case where a mesh network connection relationship as shown in FIG. 7 is given will be described. FIG. 7 shows a mesh network including radio stations 100 ₁ , 100 ₂ , 100 ₃ , 100 ₄ , 100 ₅ , 100 ₆ , 100 ₇ , 100 ₈ and 100 ₉ . Further, FIG. 7 shows the calculation results of the degree of edge spacing in all links in the mesh network (numerical values in the figure).

  The link determination unit 116 calculates the average value ave and standard deviation sd of the edge interval degrees in the wireless link of V ′ obtained by the edge interval degree calculation unit 114, and obtains the threshold T using ave and sd. For example, any one of ave−2sd, ave−sd, ave, ave + sd, and ave + 2sd is used as the threshold T.

  The link determination unit 116 disconnects a link whose side interval degree of the V ′ radio link is smaller than the threshold value T. By doing in this way, interference can be suppressed, suppressing the fall of the connection rate in a mesh network.

  Next, the operation of the radio station according to the present embodiment will be described with reference to FIG.

  Each wireless station broadcasts its own wireless station ID (step S602). The adjacent node collection unit 106 receives the ID of the radio station broadcast from each radio station, and the adjacent node information creation unit 108 of each radio station creates adjacent node information (step S604), and the ID and creation of the own radio station The neighboring node information thus broadcast is broadcast to other wireless stations (step S606). The wireless station that has received the ID of the other wireless station and the adjacent node information creates adjacent node information of the adjacent node, that is, adjacent node information collected by the adjacent node (step S608).

  Next, the adjacent node information creation unit 108 calculates a condition for causing the exposed terminal problem. That is, a chromatic graph is created (step S610).

  Next, the radio channel assignment unit 112 determines whether or not the number of channels (N) necessary for all the radio links is larger than the given number of channels (M), that is, the number of usable channels (step S612). .

  When it is determined that the number of channels required for all the radio links is not larger than the given number of channels, that is, the number of usable channels, that is, when it is judged that the given number of channels is larger (step S612: NO) The radio channel assignment unit 112 assigns usable channels to all the radio links (step S614). For example, among the usable channels (frequencies), a channel with less (small) interference is allocated to all radio links.

  On the other hand, when it is determined that the number of channels necessary for all the radio links is larger than the given number of channels, that is, the number of usable channels (step S612: YES), the radio channel allocating unit 112 is allocated with usable frequencies. Of the usable frequencies, a frequency with less interference is assigned to a link other than the existing link (step S616). For example, among the channels corresponding to No. 1 to No. M, channels with less interference are assigned to the radio links corresponding to No. M + 1 to No. N.

  Next, the edge interval degree calculation unit 114 obtains the edge interval degree for the wireless links corresponding to the M + 1th to Nth (step S618).

  Next, the link determination part 116 calculates | requires the average value and standard deviation using the edge distance degree calculated | required in the edge distance degree calculation part 114 (step S620).

  Next, the link determination unit 116 prohibits the use of a radio link that is equal to or lower than the threshold value according to the threshold value obtained from the average value and the standard deviation of the edge interval degrees (step S622).

  As described above, in the present embodiment, this selection is performed using an index called the edge interval degree when determining a radio link that is prohibited from being used. None of the existing channel allocation schemes in mesh networks use information on the degree of edge spacing. In this embodiment, each wireless link has a measure of edge interval, and a link with a high edge interval plays an important role in maintaining high network connectivity. In other words, the network connectivity is easily maintained without using a wireless link with a small degree of edge spacing, but the network is likely to be disconnected if the use of a wireless link with a large degree of edge spacing is prohibited. Therefore, by prohibiting the use of links with a low degree of side spacing, interference can be reduced while maintaining connection.

  According to the present embodiment, it is possible to realize channel assignment to the wireless mesh network while simultaneously satisfying the reduction of interference and the maintenance of the connection rate.

  With reference to FIG. 7 and FIG. 8, the results obtained based on the assumptions in Table 1 regarding the connection rate and the interference rate when channel assignment is performed according to the above-described embodiment will be described. . Here, the connection rate indicates an average value of the ratio of the number of wireless station pairs connected to each other with respect to the total number of wireless station (node) pairs when channel assignment is performed a plurality of times by the above-described method. . This includes not only the case where all the radio stations are directly connected but also the case where the target radio station is connected via another radio station.

  The interference rate indicates a ratio of link pairs to which the same channel is allocated among link pairs to which different channels must be allocated.

  In FIG. 9 and FIG. 10, the horizontal axis represents the communication range.

図９および図１０において、ｃａｓｅ１はリンクの除去を行わない、すなわちリンクの使用を禁止しない場合であり、ｃａｓｅ２は辺間隔度がａｖｅ−２ｓｄ以下となるリンクを除去する場合であり、ｃａｓｅ３は辺間隔度がａｖｅ−ｓｄ以下となるリンクを除去する場合であり、ｃａｓｅ４は辺間隔度がａｖｅ以下となるリンクを除去する場合であり、ｃａｓｅ５は辺間隔度がａｖｅ＋ｓｄ以下となるリンクを除去する場合であり、ｃａｓｅ６は辺間隔度がａｖｅ＋２ｓｄ以下となるリンクを除去する場合である。

In FIG. 9 and FIG. 10, case 1 is a case where the link is not removed, that is, the use of the link is not prohibited, case 2 is a case where a link whose side interval degree is ave−2sd or less is removed, and case 3 is a side This is a case of removing a link whose interval degree is ave-sd or less, case 4 is a case of removing a link whose edge interval degree is ave or less, and case 5 is a case of removing a link whose edge interval degree is ave + sd or less. Case 6 is a case where a link whose side interval degree is ave + 2sd or less is removed.

  That is, case 4 is a result of using a selection criterion that prohibits the use of a radio link whose side interval degree is ave or less among the radio links of V ′.

  According to FIG. 9 and FIG. 10, it can be seen that the interference rate can be reduced while keeping the connection rate high by selecting the link whose use is prohibited by introducing the edge interval degree.

  The radio frequency allocation device, radio communication system, and radio frequency allocation method according to the present invention can be applied to an autonomous distributed digital radio transmission system that performs virtual carrier sense.

It is explanatory drawing which shows an exposed terminal problem. It is explanatory drawing which shows an exposed terminal problem. It is explanatory drawing which shows the structure of the mesh network concerning one Example of this invention. It is a partial block diagram which shows the radio station concerning one Example of this invention. It is explanatory drawing which shows an example of a coloring graph. It is explanatory drawing which shows the setting method of a channel. It is explanatory drawing which shows an example of the calculation result of a side interval degree. It is a flowchart which shows operation | movement of the radio station concerning one Example of this invention. It is a characteristic view which shows the effect of one Example of this invention. It is a characteristic view which shows the effect of one Example of this invention.

Explanation of symbols

100, 100 ₁ , 100 ₂ , 100 ₃ , 100 ₄ , 100 ₅ , 100 ₆ , 100 ₇ , 100 ₈ , 100 ₉ Radio station 102 Transmitter / receiver 104 Control unit 106 Adjacent node information collection unit 108 Adjacent node information creation unit 110 Radio Channel setting unit 112 Wireless channel allocating unit 114 Side interval degree calculating unit 116 Link determining unit

Claims (4)

In a radio frequency allocation device in a radio communication system that performs radio band allocation control by virtual carrier sense:
Collection means for collecting information on nodes that can be directly transmitted;
Neighboring node information creation means for obtaining, as an interference relationship, links in which exposed terminal problems occur based on the node information and node information in other nodes;
Assign different frequencies to links that cause interference due to the exposed terminal problem, and if the number of frequencies required for frequency allocation to all links is greater than the number of available frequencies, duplicate available frequencies Means for assigning radio channels;
An edge interval degree calculating means for obtaining an edge interval degree for a link to which frequencies that can be used in the radio channel assigning means are assigned in an overlapping manner;
A link determination means for prohibiting the use of a predetermined link based on the average value and the standard deviation of the side interval degrees;
Equipped with a,
The edge interval calculating means, the set s of the node, the shortest path pst of t, the radio frequency allocation and wherein that you calculate the number of pairs, such as through the appropriate link. In the radio frequency allocating device according to claim 1,
The radio frequency allocating apparatus according to claim 1, wherein the link determination unit obtains a standard deviation of the side interval degree and prohibits use of a predetermined link based on a threshold value calculated from the average value and the standard deviation. In a radio communication system that performs radio band allocation control by virtual carrier sense:
Collection means for collecting information on nodes that can be directly transmitted;
Neighboring node information creation means for obtaining, as an interference relationship, links in which exposed terminal problems occur based on the node information and node information in other nodes;
Assign different frequencies to links that cause interference due to the exposed terminal problem, and if the number of frequencies required for frequency allocation to all links is greater than the number of available frequencies, overlap the available frequencies Means for assigning radio channels;
An edge interval degree calculating means for obtaining an edge interval degree for a link to which frequencies that can be used in the radio channel assigning means are assigned in an overlapping manner;
A link determination means for prohibiting the use of a predetermined link based on the average value and the standard deviation of the side interval degrees;
Equipped with a,
The edge interval calculation means, a wireless communication system set s of the node, the shortest path pst of t, which is characterized that you calculate the number of pairs, such as through the appropriate link. In a radio frequency allocation method in a radio communication system that performs radio band allocation control by virtual carrier sense:
A collecting step for collecting information of nodes that can be directly transmitted;
Neighboring node information creation step for obtaining, as an interference relationship, links where the exposed terminal problem occurs based on the node information and the node information in other nodes;
When assigning different frequencies to the links where interference due to the exposed terminal problem occurs, if the number of frequencies required for frequency allocation to all links is greater than the number of usable frequencies, the usable frequencies Assigning radio channels in duplicate;
A side interval degree calculating step for obtaining a side interval degree for a link to which frequencies that can be used in the wireless channel assigning unit are assigned in an overlapping manner;
A link determination step for prohibiting use of a predetermined link based on an average value and a standard deviation of the degree of side spacing;
I have a,
The side interval degree calculating step calculates the number of sets such that the shortest path pst of the node sets s and t passes through the corresponding link .

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