JP2012119768A - Radio communication method and radio communication device in cognitive radio system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid saturation of a control channel in an ad-hoc cognitive radio communication system.SOLUTION: A first radio communication device holds an initial control channel table defining which channel will be used to start communication among multiple initial control channels according to a location and time. The first radio communication device comprises the steps of: detecting available frequencies; obtaining location information and time information; establishing connection with a second radio communication device by means of an initial control channel to be determined based on the obtained location information and time information; establishing a dynamic control channel by exchanging information on the established initial control channel; and establishing a data channel by exchanging information on the established dynamic control channel. Because the initial control channel is released from establishing the dynamic control channel, the initial control channel can be occupied in a shorter time period.

Description

  The present invention relates to a radio communication technique in a cognitive radio system, and more particularly to a technique for establishing a radio connection and starting communication in an ad hoc cognitive radio network that does not have a predetermined control channel.

  In recent years, research and development of cognitive radio systems that detect and use unused frequency bands have been underway. The usable frequency band changes from time to time as well as spatially depending on the communication of the primary user (primary user) and the movement of the terminal. Therefore, it is important to quickly determine an appropriate frequency band to be used for communication.

  Research on such cognitive radio systems often presupposes the existence of a common control channel.

  For example, Non-Patent Document 1 proposes a method using a common spectrum coordination channel (CSCC). Each wireless node periodically broadcasts frequency usage information (for example, a user ID such as an IEEE MAC address, a used frequency band, transmission power, etc.) on the CSCC. Adjacent nodes observe these notifications so that newly active users create a spectrum activity map and select any available frequencies.

  Further, in a system in which a base station (BS) such as IEEE 802.22 exists, the BS allocates a frequency channel to each terminal based on the frequency usage situation detection result of each terminal. Since the control unit such as the BS assigns the frequency channel, it is not necessary to exchange the frequency channel used between the transmission and reception nodes when establishing the connection. In addition, when the radio wave condition changes during communication and the frequency channel to be used is switched, switching is easy because an instruction is sent from the BS.

  However, such a common control channel and a centralized control unit cannot be used in a wireless communication system that does not use an infrastructure (such as an access point) such as ad hoc wireless communication. In consideration of such a situation, the present inventors have already proposed a technique for performing communication using an available frequency in a situation where there is no fixed control channel or infrastructure (Patent Documents 1-3). ).

  In Patent Document 1, it is proposed that a wireless communication apparatus that is to start communication scans a frequency and notifies a connection request using any of the available frequencies (one, plural, or all). Yes. Thereby, communication can be started even in a situation where there is no predetermined fixed control channel.

In Patent Documents 2 and 3, the frequency range to be scanned is narrowed down based on position information and time information when detecting available control channels. According to this method, high-speed connection establishment can be realized. One reason is that the scan time is shortened by narrowing the scan range. Another reason is that if the position or time of the wireless communication device that is about to start communication changes, the frequency to be used is different, so that collision of the usage frequencies can be suppressed. After establishing the control channel, necessary data is exchanged through the control channel to determine the data channel. The data channel is available to both the sender and receiver, and a frequency is selected that can satisfy the application requirements. Even after establishing the data channel,
The sender / receiver exchanges information through the control channel, and switches the frequency to be used when the control channel and the data channel become unavailable. Thereby, it is possible to select an appropriate control channel and data channel frequency in accordance with a change in the situation after the start of communication.

JP 2009-200582 A JP 2010-136290 A JP 2010-136291 A

X. Jing, D. Raychaudhuri, “Spectrum Co-existence of IEEE 802.11b and 802.16a Networks using the CSCC Etiquette Protocol”, Proceedings of IEEE DySPAN 2005, Nov. 2005

  In Patent Documents 2 and 3, since a frequency range determined based on position information and time information is set as a scan target when establishing a control channel, wireless communication apparatuses that start communication at different positions or times are different. The frequency range will be scanned. Therefore, it can be avoided that the frequencies used as the control channel overlap.

  However, in the methods of Patent Documents 2 and 3, a wireless communication device that has started communication continues to use a control channel within a relatively narrow frequency range. Therefore, it is conceivable that all frequencies for the control channel are used (saturated) depending on the relationship between the frequency resources that can be used as the control channel and the number of wireless communication apparatuses that perform communication. When it approaches the saturation state, it becomes difficult to start a new communication, and when it is completely saturated, it becomes impossible to start a new communication.

  In consideration of such problems, the present invention establishes communication by selecting a frequency suitable for communication between transmitting and receiving nodes in a cognitive radio communication system in which no fixed control channel exists, and occupies the control channel. It aims at providing the technology which can use a frequency resource effectively, without doing.

  In order to achieve the above object, in the present invention, wireless communication in a cognitive wireless system is performed by the following means or processing.

  In the wireless communication method of the present invention, a predetermined initial control channel is established according to position and time, and necessary information is exchanged through the initial control channel to establish a dynamic control channel from available frequencies. . Thereafter, necessary data is exchanged through the dynamic control channel to establish a data channel.

  In this way, by shortening the period for using the predetermined initial control channel and selecting the dynamic control channel from the available frequencies, it is possible to occupy the initial control channel, which is a relatively valuable radio resource. Can be prevented. In addition, the predetermined initial control channel is not necessarily optimal, and efficient wireless communication can be realized by selecting a more appropriate frequency as the dynamic control channel.

More specifically, in the present invention, an initial control channel table that defines which of the plurality of initial control channels is used by the wireless communication devices constituting the cognitive radio system to start communication according to position and time have. Then, the first wireless communication device uses the step of detecting available frequencies, the step of acquiring position information and time information, and the initial control channel determined based on the acquired position information and time information. Establishing a connection with the second wireless communication device, exchanging information on the established initial control channel to establish a dynamic control channel, and exchanging information on the established dynamic control channel for data Establishing a channel. Here, it is preferable to release the initial control channel after the dynamic control channel is established.

  In the present invention, in the initial control channel table, which initial control channel is used to start communication is determined for each area and each time, and between the wireless communication apparatuses that start communication in different areas. It is preferable that the initial control channel used in the system is designed not to interfere.

  By designing in this way, wireless communication devices located in the same area at the same time use the same initial control channel and do not cause interference with wireless communication devices located in other areas.

  Further, the initial control channel table defines T allocation patterns of initial control channels according to the area, and communication is started using any initial control channel according to a different allocation pattern every predetermined switching time. Decide what to do. Here, the T is preferably a number obtained by dividing the communication continuation time in the initial control channel by the predetermined switching time.

  Since the communication continuation time on the initial control channel is T times the predetermined switching time, if there are at least T allocation patterns, a wireless communication device located in another area while a certain wireless communication device is communicating on the initial control channel Can prevent interference from the initial control channel.

  In the present invention, it is preferable that the initial control channel has a frequency lower than a frequency range of the dynamic control channel and the data channel.

  The lower the frequency, the more reliable and longer communication distance can be realized.

  In the present invention, it is preferable that the dynamic control channel and the data channel are selected from the same frequency range. Note that there is no need to set upper limits on the frequency ranges of the dynamic control channel and the data channel.

  By selecting the dynamic control channel and the data channel from a wide frequency range, many resources can be utilized. That is, since the frequency that can be used as the dynamic control channel or the data channel is increased, it is possible to avoid the frequency being exclusively used for other purposes. If the frequency range is widened, the scan target range is also widened. However, since the range to be scanned with each other can be narrowed down by exchanging information through the initial control channel, this is not a problem in the present invention.

  Further, in the present invention, in the step of establishing the dynamic control channel, based on a frequency that can be used by the first and second wireless communication devices and a distance between the first and second wireless communication devices, Preferably, the dynamic control channel is determined.

  By using a frequency having a communication distance according to the distance between transmission and reception as a dynamic control channel, it is possible to avoid interference with other communication pairs as much as possible and to efficiently use the frequency.

  Further, the step of establishing the dynamic control channel in the present invention includes the step of establishing a frequency range between the first and second wireless communication devices within a frequency range corresponding to a distance between the first and second wireless communication devices. Notifying the available frequency, and transmitting the probe packet by using the frequency that the first wireless communication device can use in both the first and second wireless communication devices; A step in which the second wireless communication apparatus transmits an acknowledgment at the frequency at which the probe packet is received; and a part of the frequency at which the first wireless communication apparatus has received the acknowledgment is selected as a dynamic control channel. Preferably including a step.

  Just because certain frequencies are available to each other, that is, not being used for other communications in the surroundings, it is not guaranteed that communications can actually be performed. Therefore, it is possible to establish a more reliable channel by selecting the dynamic control channel after confirming that communication is actually possible using the probe packet.

  Also, in the present invention, the frequency that can be used by the first and second wireless communication apparatuses is mutually notified via the dynamic control channel during communication, and the dynamic control channel or data channel that is used is used. It is preferable to further include a channel switching step of switching a frequency used as a dynamic control channel or a data channel when it becomes impossible or is predicted to become unavailable.

  If the radio wave status changes during communication, it is necessary to change the dynamic control channel and data channel, but by using the dynamic control channel to notify each other of available frequencies detected in advance. The channel can be switched quickly when it becomes necessary to switch the channel frequency.

  Further, the channel switching step in the present invention includes a step of detecting a frequency that each of the first and second wireless communication apparatuses can use in a frequency range suitable for a dynamic control channel and a data channel, A step of notifying the usage status of each frequency between the first and second wireless communication devices via a dynamic control channel, and the first wireless communication device is configured to transmit the first and second wireless communication devices. Transmitting a probe packet using a frequency that can be used in both, a step in which the second wireless communication apparatus transmits an acknowledgment at a frequency at which the probe packet is received, and the first wireless communication. Preferably, the apparatus includes a step of determining a frequency to which the dynamic control channel and the data channel are switched from among frequencies at which the device has received the acknowledgment.

  Just because certain frequencies are available to each other, i.e. not being used for other communications in the surroundings, it is not guaranteed whether or not communications are actually possible. Therefore, after confirming that communication can be actually performed using the probe packet, the channel can be switched more reliably by selecting the dynamic control channel or data channel to be switched to.

  Further, the channel switching step in the present invention further includes a step of notifying the second wireless communication device via the dynamic control channel of the frequency at which the first wireless communication device has received the confirmation response. Preferably, each of the first and second wireless communication devices determines a frequency to which a dynamic control channel and a data channel are switched from among frequencies at which an acknowledgment can be received according to a common policy. .

Further, in the present invention, when the dynamic control channel or the data channel cannot be used due to deterioration of communication quality or when it is predicted that the data channel cannot be used, switching to a lower frequency, and nodes other than the transmitting and receiving nodes perform communication. If the dynamic control channel or the data channel becomes unavailable or is expected to become unavailable due to the start, a policy of switching to a frequency suitable for communication quality can be considered.

  When the communication quality deteriorates, it is expected that the distance between the transmission and reception nodes is increased. Therefore, it is preferable to switch to a lower frequency with a longer reach distance. On the other hand, when other nodes start using, there is no such limitation, and therefore, a frequency suitable for the request may be selected from frequencies that can be used with each other.

  When the communication quality deteriorates, it is expected that the distance between the transmitting and receiving nodes is increased. Therefore, it is preferable to switch to a lower frequency band having a longer reach. On the other hand, when other nodes start using, there is no such limitation, and therefore, a frequency band suitable for the request may be selected from among the frequency bands that can be used with each other.

  The present invention can also be understood as a radio communication method in a cognitive radio system having at least a part of the above processing, or a program for realizing this method. Further, the present invention can also be understood as a wireless communication device having each means for executing the above processing. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

  According to the present invention, in a cognitive radio communication system in which there is no fixed control channel, a frequency suitable for communication is selected between transmission and reception nodes to establish communication, and frequency resources are allocated without using an initial control channel. It can be used effectively.

It is a figure which shows the functional block of the radio | wireless communication apparatus in the cognitive radio system which concerns on this embodiment. It is a figure explaining the outline | summary of the wireless connection establishment process in this embodiment. It is a figure explaining the frequency range of an initial control channel, a dynamic control channel, and a data channel. It is a figure which shows the example of an initial control channel table. It is a figure which shows the flow of a process at the time of initial control channel establishment. It is a figure which shows the flow of a process at the time of dynamic control channel establishment. It is a figure which shows the flow of a process at the time of data channel establishment. It is a figure explaining a frequency list. It is a figure which shows the process for the dynamic channel switching performed during communication. It is a figure explaining the switching policy in the case of dynamic channel switching.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

  The cognitive radio communication system according to the present embodiment includes a plurality of radio communication devices. The wireless communication device is mounted on a vehicle and forms a vehicle-to-vehicle communication wireless network. Communication between these terminals is performed while dynamically switching the frequency (frequency channel) to be used by detecting surrounding radio wave conditions. The wireless communication system is an ad hoc network in which wireless communication devices are connected to each other without intervention of an infrastructure such as an access point. Therefore, there is no control device that allocates a frequency band used for communication.

<Outline of configuration>
FIG. 1 is a schematic diagram illustrating a functional configuration of a wireless communication device that configures the cognitive wireless communication system according to the present embodiment. The wireless communication device 1 includes an antenna 2, a high frequency unit 3, an AD conversion unit 4, a digital signal processing unit 5, and a GPS device 6. The high-frequency unit 3 receives a radio signal and converts it to a frequency band that facilitates digital signal processing, or converts a transmission signal to a frequency that is actually transmitted. The AD conversion unit 4 converts the received analog signal into a digital signal, and converts the digital signal to be transmitted into an analog signal. Note that the wireless communication apparatus 1 collectively AD-converts a wideband signal (for example, 900 MHz to 5 GHz) received from the antenna 2 and realizes demodulation processing including channel selection in the digital signal processing unit 5. To do.

The digital signal processing unit 5 can be configured by a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), a dynamic reconfigurable processor, or the like. The digital signal processing unit 5 includes a communication control unit 51, a radio wave condition detection unit 52, a frequency list 53, and an initial control channel table 54 as functional units. The digital signal processing unit 5 requires other functional units for modulation / demodulation and the like, but these are well-known and will not be described in detail.

  The communication control unit 51 performs a connection establishment process, a data transmission / reception process, a process for notifying a communication partner of a channel usage status, a process for selecting a channel to be used, and the like.

The radio wave status detection unit 52 detects the radio wave status around the own node and determines whether each frequency is in use or unused (in other words, whether the own node is available). As a specific sensing technique, various known methods can be employed. The radio wave condition detection unit 52 performs energy detection, wavelet decomposition technique, pilot-based spectrum sensing, spectrum sensing based on eigenvalues, feature detection, a matched filter method, etc. according to the wireless communication method to be detected. Determine whether the frequency is in use or unused.

  The frequency list 53 stores the availability status (usage status of others) of each frequency for the own node and the communication partner node. The availability status of the own node can be updated from the detection result of the radio wave status detection unit 52. Further, the availability status of the communication partner can be obtained and updated through the control channels (initial control channel and dynamic control channel). Furthermore, as will be described later, it is possible to confirm that communication is possible using the frequency by transmitting a probe packet.

  The frequency list 53 cannot be used because other nodes are using the frequencies provided by each node (corresponding as hardware), and is not used by other nodes, but there is no response to the probe. The management is divided into three states: communication is impossible, and other nodes do not use and there is a response to the probe (communication is possible). However, it is not always necessary to grasp the usage status for all the equipment frequencies, and the usage status may be narrowed down to a frequency range that may be actually used.

  The initial control channel table 54 defines which one of a plurality of predetermined initial control channels is used for each area and each time. There are a plurality of initial control channels, and each frequency is predetermined. The size of each area is determined such that if two nodes are located in the same area, they can communicate with each other using any initial control channel. As will be described in detail later, while communicating using the initial control channel, interference occurs between a node that started communication in another area or a node that started communication at a different time in the same area. The allocation of the initial control channel is designed so that there is no.

The GPS device 6 receives a signal from a GPS satellite and acquires position information and time information. The acquisition of the position information and the time information is not limited solely to the GPS satellite signal, but various auxiliary means such as a gyroscope, an acceleration sensor, map (road) information, and a signal from a base station may be used. In the present embodiment, the GPS device 6 serves as both the position information acquisition unit and the time information acquisition unit. However, the time information may be acquired by another unit other than the GPS device 6.

  In the following description, a node that starts wireless communication is a transmitting node (corresponding to the first wireless communication device in the present invention), and a node that performs communication in response to a request from the transmitting node is a receiving node (second node in the present invention). Equivalent to a wireless communication device). Both the transmission node and the reception node have the functional configuration described above.

<Outline of processing>
The outline of the wireless communication method according to this embodiment will be described below. One of the features of this method is that two control channels, an initial control channel (ICC) and a dynamic control channel (DCC), are used. The initial control channel has a predetermined frequency and is used only at the start of communication. The dynamic control channel is appropriately selected from available frequencies. In this system, when communication is first established on the initial control channel, necessary information is exchanged on the initial control channel to establish a dynamic control channel. After establishing the dynamic control channel, the initial control channel is released. The data channel is established by exchanging necessary information through the dynamic control channel.

  In this way, by shortening the use time of the initial control channel having a predetermined frequency, it is possible to avoid saturation of the initial control channel even when the number of wireless communication devices increases, and to start communication. The probability of success is improved.

  In addition, information is exchanged on the initial control channel, and the frequency of the dynamic control channel is determined based on the information. For example, a frequency having an appropriate communication range according to the distance between transmission and reception is used as the dynamic control channel. You can choose. Thereby, useless interference can be suppressed and the use efficiency of the radio frequency can be improved.

  In addition, after the dynamic control channel and the data channel are determined, the frequency usage situation may change. Therefore, information is periodically exchanged using the dynamic control channel, and the dynamic control channel and the data channel are switched based on the result. Since information is regularly exchanged in this way, quick switching is possible when switching channels.

  Next, an overview of wireless communication according to the present embodiment will be described with reference to FIG. First, an initial control channel is established in accordance with an area where communication is to be started and time (step S1). Each node creates a frequency list 53 as appropriate. In other words, the usage status of the frequency (corresponding as hardware) installed in each node is detected, and the usage status is stored in the frequency list 53.

  Next, necessary information is exchanged via the initial control channel to establish a dynamic control channel (step S2). The location information and information regarding available frequencies are exchanged between the transmission / reception nodes, and a frequency corresponding to the distance between the transmission / reception nodes is selected as a dynamic control channel from the available frequencies. After determining the dynamic control channel, the initial control channel is released. In addition, after the dynamic control channel is determined, the frequency usage status is periodically exchanged using this channel.

  Next, based on the frequency list exchanged between the transmitting and receiving nodes, a frequency that can be used and satisfies the application request is determined as a data channel (step S3).

  Since the surrounding radio wave conditions change even after the dynamic control channel and data channel are determined, the frequency list is periodically exchanged to perform dynamic channel switching (step S4).

<Processing details>
Below, the detail of the radio | wireless communication method which concerns on this embodiment is demonstrated.

[Initial control channel table]
As shown in FIG. 3, the initial control channel has a lower frequency compared to the dynamic control channel and the data channel. This is because the initial control channel is used at the start of communication, and therefore it is preferable that communication is as reliable as possible and the reachable range is long.

  FIG. 4 is a diagram showing an outline of the initial control channel table. FIG. 4 shows an example in which 16 initial control channels (0 to F) are prepared. Here, the frequency of channel 0 is the lowest and the frequency of channel F is the highest. Therefore, the reach distance of channel 0 is the longest and the reach distance of channel F is the shortest.

  The numbers in FIG. 4 are attached and the square represents one area. Communication is performed between nodes located in the same area. Although the size of the area varies depending on application requirements, for example, the radius can be about 10 m to about 1000 m. In the inter-vehicle communication system related to the vehicle safety system, for example, a radius of about 100 m can be adopted as the size of the area. Thus, in order to satisfy the application requirements, it is necessary that the reach of the initial control channel has a sufficient distance to cover one area. Therefore, even when a plurality of initial control channels are assigned, not all frequencies are used depending on application requirements, but only initial control channels having a required reach and a predetermined frequency or less are used. May be.

  Here, of the two tables shown in FIGS. 4A and 4B, which table is to be used is determined for each predetermined switching time (hereinafter referred to as unit time). When measured in unit time, the table of FIG. 4A is used at odd times and FIG. 4B is used at even times. Note that the case where the communication continuation time using the initial control channel is within 2 unit hours is taken as an example. Therefore, when the communication continuation time is 3 unit hours or more, it is preferable to prepare a number of tables corresponding to the communication continuation time.

  Here, at an arbitrary time, the distance between areas in which the same frequency is designated is such that no interference occurs. For example, channel 0 is used in areas 41 and 42 at an odd time (FIG. 4A), and the distance 43 between the areas is designed to be equal to or less than the reach distance of channel 0.

  In addition, it is necessary to prevent interference between nodes that start communication at different times. Therefore, the distance between the areas where the same frequency is designated at the odd time and the even time is also set so as not to cause interference. For example, the distance 45 between the area 42 where the channel 0 is used at the odd time and the area 44 where the channel 0 is specified at the even time is designed to be equal to or less than the reach distance of the channel 0.

  In the example of FIG. 4, in all channels, the distance between areas using the same frequency within the same time and the distance between areas using the same frequency at different times are all designed to be equal. . Since the reach distance of channel 0 is the longest, if it is designed so that no interference occurs in channel 0, no interference occurs in any other channel.

Here, there are 16 initial control channels, and the communication duration in the initial control channel is 2
Although the case of unit time has been described as an example, it is preferable to allocate the initial control channel as follows in general. First, when the communication continuation time in the initial control channel is T unit time, it is preferable to prepare T allocation patterns and determine a control channel according to a different allocation pattern every time the unit time elapses. In other words, it is preferable to determine the initial control channel according to the allocation pattern corresponding to (current time mod T). And it is preferable that the initial control channel is allocated so that the distance between areas where the same channel is used is longer than the reach distance of the channel through all of the T allocation patterns. In this way, while a certain node is communicating on the initial control channel, it is possible to prevent interference from the initial control channel by nodes located in other areas.

  When the number of assigned patterns is reduced (when the switching time is increased), the time for using one pattern becomes longer, so the possibility that two or more nodes that start communication within the same area appear, The possibility of occurrence of interference increases. On the other hand, when the number of allocation patterns is increased (when the switching time is shortened), it may be difficult to design many patterns that do not cause interference.

  As a specific example of the initial control channel, the case where the number of initial control channels is 16 and there are two allocation patterns (FIGS. 4A and 4B) has been described, but it is possible to design an allocation pattern other than FIG. It will be easy for those skilled in the art. Also, even if the number of initial control channels and the number of allocation patterns are different, it will be easy for those skilled in the art to design an allocation pattern that satisfies the above conditions.

[Initial control channel establishment process]
Next, the initial control channel establishment process (step S1 in FIG. 2) will be described with reference to FIG. The following processing is performed by the communication control unit 51, and the communication control unit 51 corresponds to the initial control channel establishment means in the present invention.

  First, a wireless communication device (transmission node) that intends to start communication acquires position information and time information from the GPS device 6 (step S11). Next, the communication control unit 51 extracts an initial control channel corresponding to the acquired position information and time information from the initial control channel table 54 (step S12). The communication control unit 51 transmits a connection request on the initial control channel determined in this way (step S13). The wireless communication device (receiving node) that has received this connection request transmits a connection response (step S14), and the establishment of the initial control channel is completed. Thereafter, communication is started on the initial control channel (step S15), and a dynamic control channel establishment process is performed.

  Since the initial control channel is obtained only from the position and time, it can be quickly connected without scanning.

[Dynamic control channel establishment processing]
Detailed processing of the dynamic control channel establishment processing (step S2 in FIG. 2) will be described with reference to FIG. The following processing is performed by the communication control unit 51 controlling the radio wave condition detection unit 52 and the like, and the communication control unit 51 corresponds to the dynamic control channel establishment means in the present invention.

First, each of the transmission / reception nodes scans the radio wave condition around the own node by the radio wave condition detection unit 52 (steps S21 and S22). The radio wave status scan need not be performed after the initial control channel is established, and may be appropriately performed by each transmitting / receiving node. Or conversely, after the initial control channel is established, position information and the like are exchanged between the transmitting and receiving nodes, and the radio wave condition may be detected only for the frequency range determined based on the obtained information.

  Next, each of the transmitting / receiving nodes notifies the position information obtained from the GPS device 6 and the available frequencies to each other through the initial control channel (steps S23 and S24). As a result, the transmission / reception nodes can grasp each other's distance and the frequencies that can be used. In this process, first, only the position information may be notified first, and thereafter, an available frequency within an appropriate frequency range may be notified according to the distance between the transmitting and receiving nodes.

  Next, the transmitting node selects a frequency that can be used with each other and satisfies the requirements described below as a candidate for a dynamic control channel, and transmits a probe packet (step S25). Since it is desired that the dynamic control channel is stable, a low frequency is preferable. However, in order to avoid unnecessary interference, it is preferable that the radio control channel does not have an undesirably long radio wave reach. Therefore, a frequency having a frequency as high as possible is selected as a dynamic control channel from frequencies having a reach distance equal to or greater than a value obtained by adding a predetermined margin to the distance between the transmitting and receiving nodes.

  The probe packet is transmitted because it is not always available for communication just because the frequency can be used by both the transmitting and receiving nodes. The probe packet may be transmitted using only one frequency, but it is also preferable to transmit the probe packet using a plurality of frequencies suitable as a dynamic control channel.

  When the receiving node receives the probe packet (step S26), an ACK (acknowledgment response) is transmitted to the transmitting node in response (step S27). When a plurality of probe packets are received, it is preferable to transmit ACK at each frequency.

  When the transmitting node receives ACK, it can be seen that communication can be performed between the transmitting and receiving nodes using the frequency. Therefore, the dynamic control channel is selected from the frequencies where ACK can be received (step S28). If ACK can be received at a plurality of frequencies, any one may be selected. For example, the highest frequency may be selected as the dynamic control channel. If ACK cannot be received at any of the frequencies at which the transmitting node has transmitted the probe packet, it is sufficient to return to step S25 and transmit the probe packet at a different frequency.

  As a result of the above processing, a dynamic control channel is established between the transmitting and receiving nodes, and communication can be started (step S29). In the dynamic control channel, information necessary for establishing the data channel is exchanged. Specifically, frequency usage status, location information, and the like in each transmitting / receiving node are transmitted through the dynamic control channel. Note that the initial control channel is released after the dynamic control channel is established. As described above, since the time to occupy the initial control channel is only during the establishment of the dynamic control channel, even if the number of transmitting / receiving node pairs in communication is larger than the number of initial control channels, It is possible to start a new communication without saturating the control channel.

[Data channel establishment processing]
Next, detailed processing of the data channel establishment processing (step S3 in FIG. 2) will be described with reference to FIG. The following processing is performed by the communication control unit 51 by controlling the radio wave condition detection unit 52 and the like, and the communication control unit 51 corresponds to the data channel determination means in the present invention.

When the dynamic control channel is determined, frequency information is exchanged using the channel (step S31). The frequency information exchanged here includes a list of frequencies suitable for the required frequency and the equipment frequency of the terminal, frequencies that cannot be used by communication of the primary user or other users. Note that it is sufficient to notify the frequency information from the receiving node to the transmitting node, and it is not always necessary to share the information between the transmitting and receiving nodes. Also, a frequency that cannot be used temporarily may not necessarily be transmitted at this timing.

  When the exchange of frequency information is completed, the frequency range is narrowed and adjusted to determine the data channel. The range in which adjustment is actually performed in a wide frequency band is narrowed down by two indicators, the equipment frequency and the frequency range suitable for the required quality of the application. Among these, the “frequency band suitable for the required quality of the application” may differ depending on the application that performs communication. Such an index defines a scan range for data channel determination. Each transmitting / receiving node detects frequencies that can be used by the own node within this range (steps S32 and S33).

  Next, the transmitting node transmits a probe packet by using a frequency that can be used by the own node in the scan range (step S34). Here, the probe packet may be transmitted using all of the frequencies detected as being usable by the own node. However, the higher the frequency, the shorter the arrival distance, and thus the probe packet becomes difficult to reach. . Therefore, the range in which the probe packet can be reliably received is compared with the distance between transmission and reception obtained from the position information of the communication partner obtained from the dynamic control channel and the position information of the own node obtained from the GPS device 6 and the reach distance of each frequency. The probe packet is transmitted using only the frequency. This increases the efficiency of the data channel determination process.

  On the other hand, the receiving node receives a packet addressed to itself at a frequency that can be used by the node as a result of scanning (step S35), and transmits an ACK at each frequency at which the probe packet is received (step S36).

As a result of the above processing, it is found that the frequency band in which the ACK can be received on the transmitting node side can actually be used for communication between the transmitting and receiving nodes. The item of “state” in the frequency list 53 is updated from the reception status of the probe packet. Here, as shown in FIG. 8, the usage status of each frequency is classified into three, “1”, “0”, and “−1”. Each of the three states represents the following meaning.
1: Can receive ACK for probe packets = Can be used for communication at any time 0: No ACK is returned = Not within communication range, or used by primary users (primary users) or other users around the receiver Yes (may be available in the future)
-1: Used by primary users and other users around the sender = Not available for communication

  The transmitting node determines the frequency used for the data channel from the frequency at which the ACK can be received. (Step S37). In general, there may be a plurality of frequencies that can be used for data communication. In such a case, the number of data channels is determined according to the required quality and the surrounding situation. For example, if there are no other terminals in the vicinity, all available frequencies may be used for the data channel. In addition, when a plurality of terminals exist in the vicinity, a part of the frequencies may be used as a data channel. At this time, although it is actually necessary to determine the number of data channels in consideration of spectrum sharing, in the present embodiment, only one frequency is simply used as a data channel. In the example of FIG. 8, the highest frequency f6 among the frequencies f3, f5, and f6 that can be used for communication is determined as the data channel.

[Dynamic channel switching processing]
With the above processing, the dynamic control channel and the data channel are appropriately determined according to the situation, and efficient communication between the transmission / reception nodes becomes possible. However, as the terminal moves, the surrounding situation of each transmitting / receiving node frequently changes. Therefore, it is necessary to dynamically switch the dynamic control channel / data channel once determined according to the surrounding situation even during communication between the transmitting and receiving nodes.

  Hereinafter, the dynamic channel switching process (step S4 in FIG. 2) will be described with reference to FIGS. The following processing is performed by the communication control unit 51 by controlling the radio wave condition detection unit 52 and the like, and the communication control unit 51 corresponds to the channel switching means in the present invention.

  Even after the dynamic control channel and data channel are determined, the transmitting and receiving nodes regularly detect the radio wave conditions around the own node (steps S41 and S42). The scan range at this time includes a frequency band for the dynamic control channel and a frequency band for the data channel. Since the method for determining the scan range for each channel has been described in the description of the connection establishment process, it is omitted here.

  Based on the scan result, the transmitting node transmits a probe packet at a frequency that can be used by the own node (step S43), and the receiving node returns an ACK at the frequency at which the probe packet is received (steps S44 and 45). When transmitting a probe packet, the probe packet is not transmitted at a frequency that is known to be unavailable for the receiving node (frequency list state is “−1”), thereby improving processing efficiency. Can be achieved. On the other hand, if the frequency is available to the receiving node, the probe packet is transmitted regardless of whether the state is “1” or “0”.

  Then, the transmitting node updates the frequency list 53 from the reception status of the ACK for the probe packet (step S46), and notifies the receiving node of the updated frequency list 53 using the current dynamic control channel (step S47). ).

  Next, it is determined whether the frequency status changes and it is necessary to switch the dynamic control channel or the data channel (step S48). When the frequency state has not changed (S48-NO), the process returns to the radio wave state scanning process. When the frequency state changes and it is necessary to switch the dynamic control channel or the data channel (S48-YES), communication using a new frequency is performed (step S49).

  Note that the frequency of the switching destination is determined in advance periodically based on the communication status at that time so that the channel can be switched quickly. For example, when notifying the receiving node of the frequency list in step S49, the switching destination frequency candidates may be explicitly shown to the receiving node. Further, based on the frequency list, the switching destination frequency may be determined based on a policy common between the transmission and reception nodes (in this case, the switching destination frequency may be determined when the frequency list is notified to the receiving node. Can be considered pre-determined).

  The switching destination frequency is switched to the most suitable channel between the transmission / reception nodes based on the information of the frequency list 53 exchanged periodically as described above. Here, since information is shared between the transmission and reception via the dynamic control channel and the data channel is also managed, it is necessary to avoid disconnecting the control channel as much as possible. Therefore, it is preferable to switch the frequency to be used by detecting quality degradation before the communication is cut off. It is also preferable to determine a plurality of switching destination frequencies in advance and perform channel switching reliably. In the case of the data channel, the channel is switched to an appropriate channel by the same method as the dynamic control channel, but the channel change notification is performed using the dynamic control channel.

  Next, a specific frequency switching policy will be described. First, when a primary user or another communication is detected, the communication quality is not deteriorated. Therefore, it is only necessary to switch to the one suitable for the communication quality regardless of whether the frequency is high or low (FIG. 10A). On the other hand, when the communication quality is deteriorated, it is considered that the reach distance of the channel being used is shorter than the distance between transmission and reception, so the frequency is switched to a lower frequency having a longer reach distance (FIG. 10B).

  Note that the degradation of communication quality can be detected from the information on the number of times of frame retransmission. In addition, detection of communication quality degradation is based on the position information acquired from the GPS device, and the distance between the transmitting and receiving nodes is determined and compared with the arrival distance of each frequency to detect movement exceeding the arrival distance, and channel switching It is also possible to predict the timing in advance.

<Operation and effect of this embodiment>
According to the cognitive radio system in the present embodiment, the initial control channel can be determined only from the position and time at the start of communication, and it is not necessary to perform processing such as scanning, so that communication can be started quickly. Thus, the initial control channel that is guaranteed to be available is a valuable resource. In this embodiment, since the initial control channel is used only to establish the dynamic control channel, the time for using the valuable initial control channel can be shortened. That is, even when the number of node pairs that perform communication increases, saturation of the initial control channel does not occur. Therefore, even when the number of transmission / reception node pairs is increased as compared with the number of initial control channels, the initial control channel can be used by a node that newly starts communication.

  In addition, since the dynamic control channel is determined after various information is exchanged through the initial control channel, an appropriate frequency can be used as the dynamic control channel according to the situation. In the inter-vehicle communication system, the number of vehicles that are close to a certain vehicle is limited due to the characteristic that the vehicle travels on a road. When the inter-node distances are different, different dynamic control channels are used, so that no interference or collision occurs in communication between the transmission / reception node pairs. Further, since a high frequency is used as a dynamic control channel between a pair having a short distance between nodes, the same frequency can be used in other areas, and the spatial use efficiency of the high frequency is improved.

DESCRIPTION OF SYMBOLS 1 Wireless communication apparatus 5 Digital signal processing part 6 GPS apparatus 51 Communication control part 52 Radio wave condition detection part 53 Frequency list 54 Initial control channel table

Claims (24)

A first wireless communication apparatus having an initial control channel table that defines which of a plurality of initial control channels is used to start communication according to a position and time,
Detecting available frequencies; and
Obtaining position information and time information;
Establishing a connection with the second wireless communication device using an initial control channel determined based on the acquired position information and time information;
Establishing a dynamic control channel by exchanging information on the established initial control channel;
Establishing a data channel by exchanging information on the established dynamic control channel;
A wireless communication method in a cognitive radio system that executes After establishing the dynamic control channel, release the initial control channel,
A radio communication method in the cognitive radio system according to claim 1. In the initial control channel table, which initial control channel is used to start communication is determined for each area and each time, and the initial control channel is used with a wireless communication device that starts communication in a different area. Designed so that the control channel does not interfere,
A radio communication method in the cognitive radio system according to claim 1. In the initial control channel table, T patterns of initial control channel allocation patterns corresponding to the area are defined, and communication is started using any initial control channel according to a different allocation pattern every time a predetermined switching time elapses. Decide what to do,
The T is a number obtained by dividing the communication duration in the initial control channel by the predetermined switching time.
A wireless communication method in a cognitive radio system according to claim 3. The initial control channel is a frequency lower than the frequency range of the dynamic control channel and the data channel.
The radio | wireless communication method in the cognitive radio system in any one of Claims 1-4. The dynamic control channel and the data channel are selected from the same frequency range;
A radio communication method in a cognitive radio system according to claim 1. In the step of establishing the dynamic control channel, the dynamic control channel is determined based on a frequency available to the first and second wireless communication devices and a distance between the first and second wireless communication devices. To
The radio | wireless communication method in the cognitive radio system in any one of Claims 1-6. Establishing the dynamic control channel comprises:
Notifying available frequencies within a frequency range according to the distance between the first and second wireless communication devices between the first and second wireless communication devices;
The first wireless communication device transmits a probe packet using a frequency that can be used by both the first and second wireless communication devices;
The second wireless communication device transmitting an acknowledgment at the frequency at which the probe packet was received;
The first wireless communication device selecting at least a part of a frequency at which an acknowledgment can be received as a dynamic control channel;
The radio | wireless communication method in the cognitive radio system of Claim 7 containing this. When the first and second wireless communication apparatuses notify each other of available frequencies through the dynamic control channel during communication, and the dynamic control channel or data channel being used becomes unavailable or A channel switching step of switching a frequency to be used as a dynamic control channel or a data channel when it is predicted that it will become unavailable.
The radio | wireless communication method in the cognitive radio system in any one of Claims 1-8. The channel switching step includes
Each of the first and second wireless communication devices detecting an available frequency in a frequency range suitable for a dynamic control channel and a data channel;
Notifying the usage status of each frequency via the dynamic control channel between the first and second wireless communication devices;
The first wireless communication device transmits a probe packet using a frequency that can be used by both the first and second wireless communication devices;
The second wireless communication device transmitting an acknowledgment at the frequency at which the probe packet was received;
Determining a frequency to which the dynamic control channel and the data channel are switched from among the frequencies at which the first wireless communication apparatus has received the acknowledgment;
The radio | wireless communication method in the cognitive radio system of Claim 9 containing this. The channel switching step further includes
The first wireless communication device includes a step of notifying the second wireless communication device of a frequency at which the acknowledgment response can be received via a dynamic control channel;
Each of the first and second wireless communication devices determines a frequency to which a dynamic control channel and a data channel are switched from among frequencies at which an acknowledgment response can be received according to a common policy.
The radio | wireless communication method in the cognitive radio system of Claim 10. In the channel switching step,
If the dynamic control channel or data channel becomes unavailable or is expected to be unavailable due to degradation of communication quality, determine a lower frequency as the switching destination frequency,
When the primary user starts communication and the dynamic control channel or data channel becomes unavailable or is expected to become unavailable, the frequency suitable for the communication quality is determined as the switching destination frequency.
The radio | wireless communication method in the cognitive radio system of Claim 10 or 11. An initial control channel table that defines which of the initial control channels is used to start communication depending on the position and time;
Radio wave condition detection means for detecting available frequencies;
Position information acquisition means for acquiring position information;
Time information acquisition means for acquiring time information;
Initial control channel establishment means for establishing a connection with a communication partner using an initial control channel determined based on the acquired position information and time information;
Dynamic control channel establishment means for exchanging information on the established initial control channel to establish a dynamic control channel;
A data channel establishment means by exchanging information through the established dynamic control channel and a data channel;
A wireless communication device in a cognitive wireless system comprising: After establishing the dynamic control channel, release the initial control channel,
The wireless communication apparatus in the cognitive wireless system according to claim 13. In the initial control channel table, which initial control channel is used to start communication is determined for each area and each time, and the initial control channel is used with a wireless communication device that starts communication in a different area. Designed so that the control channel does not interfere,
The radio | wireless communication apparatus in the cognitive radio system of Claim 13 or 14. In the initial control channel table, T patterns of initial control channel allocation patterns corresponding to the area are defined, and communication is started using any initial control channel according to a different allocation pattern every time a predetermined switching time elapses. Decide what to do,
The T is a number obtained by dividing the communication duration in the initial control channel by the predetermined switching time.
The radio | wireless communication apparatus in the cognitive radio system of Claim 15. The initial control channel is a frequency lower than the frequency range of the dynamic control channel and the data channel.
The radio | wireless communication apparatus in the cognitive radio system in any one of Claims 13-16. The dynamic control channel and the data channel are selected from the same frequency range;
The radio | wireless communication apparatus in the cognitive radio system in any one of Claims 13-17. The dynamic control channel establishment means determines a dynamic control channel based on a frequency that can be used by the node and a communication partner and a distance between the node and the communication partner.
The radio | wireless communication apparatus in the cognitive radio system in any one of Claims 13-18. The dynamic control channel establishment means includes
Notify the communication partner of the frequency that can be used by the node within the frequency range according to the distance between the node and the communication partner, and receive from the communication partner the frequency that the communication partner can use within the frequency range. And
Send a probe packet using the frequency that can be used by both the local node and the communication partner,
Selecting at least a part of the frequency at which the acknowledgment response to the probe packet transmitted from the communication partner can be received as a dynamic control channel;
The radio | wireless communication apparatus in the cognitive radio system of Claim 19. Notifying the communication partner of frequencies that can be used by the own node via the dynamic control channel during communication, receiving the frequency that can be used by the communication partner from the communication partner, and using the dynamic control channel or Further comprising channel switching means for switching a frequency used as a dynamic control channel or a data channel when the data channel becomes unavailable or is predicted to become unavailable.
The radio | wireless communication apparatus in the cognitive radio system in any one of Claims 13-20. The channel switching means includes
Detect available frequencies in a frequency range suitable for dynamic control and data channels,
Notifying the communication partner of the usage status of each frequency via the dynamic control channel, receiving the usage status of each frequency on the communication partner side from the communication partner,
Send a probe packet using the frequency that can be used by both the own node and the communication partner,
Determining the frequency to which the dynamic control channel and the data channel are switched from among the frequencies in which the acknowledgment response to the probe packet transmitted from the communication partner can be received;
The wireless communication apparatus in the cognitive wireless system according to claim 21. The channel switching means further includes
Notify the communication partner via the dynamic control channel the frequency at which the acknowledgment was received,
Determine the frequency to which the dynamic control channel and data channel are switched from among the frequencies for which the acknowledgment response could be received according to the common policy with the communication partner.
23. A wireless communication device in a cognitive radio system according to claim 22. The channel switching means includes
If the dynamic control channel or data channel becomes unavailable or is expected to be unavailable due to degradation of communication quality, determine a lower frequency as the switching destination frequency,
When the primary user starts communication and the dynamic control channel or data channel becomes unavailable or is expected to become unavailable, the frequency suitable for the communication quality is determined as the switching destination frequency.
The radio | wireless communication apparatus in the cognitive radio system of Claim 22 or 23.

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