JP2012070350A - Radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high confidentiality to an external eavesdropper while efficient transmission of network coding is realized by performing a coding operation on an input signal to obtain an output signal and effectively changing a frequency of the output signal in accordance with a prescribed rule in a relay node.SOLUTION: In each relay node, a frequency change pattern in which a use frequency is set at every time is stored as a pattern-time table, and a link-pattern corresponding table where the frequency change pattern to be used is set at every link is stored. When the input signal originated from an origination source node is inputted, the coding operation for multiplying a coding matrix is performed and the output signal is obtained (ST31). The use frequency of the output signal is obtained by referring to the link-pattern corresponding table and the pattern-time table (ST33, 34), and the use frequency is changed in accordance with an output link and the present time.

Description

  The present invention relates to a wireless communication method, and more particularly, to a wireless communication method for improving the confidentiality of transmission information and improving transmission efficiency by using a combination of network coding and frequency hopping.

  In network communication in which information is transmitted from a source to a destination in a network in which communication devices (nodes) are connected by a communication path (link), in conventional general packet communication, input information is desired at each relay node. Only the exchange process to output to the destination was performed. In the exchange processing, the user information in the packet is not processed only by distributing the packet toward the destination. On the other hand, in the network coding technique, not only exchange processing but also coding (encoding) is performed at each node, and it is devised so that efficient transmission can be performed as a whole network (for example, Non-Patent Document 1 and Patents). Reference 1).

  As another conventional communication method, in a network communication in which information is transmitted from a source to a destination in a network in which communication devices (nodes) are connected by a communication path (link), the frequency is changed according to a certain rule. Thus, frequency hopping has been proposed as a method for increasing resistance to noise, interference, interference, and the like (see, for example, Non-Patent Document 2 and Patent Document 2).

JP 2006-31693 A Special table 2001-520474 gazette

S-Y. R. Li et. Al., “Linear Network Coding,” IEEE, IEEE Transactions on Information Theory, vol. 49, no. 2, Feb. 2003, pp. 371-381 A. Goldsmith, translated by Takehiko Kobayashi, "Wireless Communication Engineering", Maruzen Co., Ltd., issued on August 10, 2007

  However, according to the conventional network coding technique described in Non-Patent Document 1 and Patent Document 1, only a method for obtaining an output signal by performing an encoding operation on an input signal at a relay node is proposed. Therefore, a method for effectively changing the frequency of the output signal has not been considered. Therefore, as a secondary characteristic of network coding, transmission information is subjected to coding (encoding) processing, and although there is a certain degree of confidentiality to external eavesdroppers, depending on the encoding function of each node There was a problem that transmission information could be seen.

  Further, according to the above-described conventional frequency hopping method as described in Non-Patent Document 2 and Patent Document 2, the frequency change rule is shared from the source to the destination, The frequency was the same and was not changed at the relay node. Therefore, if transmission information is observed for a long time at a certain frequency, there is a problem that the transmission information may be visible when the frequency is used.

  The present invention has been made to solve such a problem, and at the same time, an encoding operation is performed on an input signal at a relay node to obtain an output signal, and at the same time, the frequency of the output signal is effectively changed according to a certain rule. Accordingly, an object of the present invention is to obtain a wireless communication method having high secrecy against an external eavesdropper while achieving efficient transmission of network coding.

  The present invention is a wireless communication method for transmitting information from a source node to a destination node via one or more relay nodes in a network in which a plurality of nodes are connected by a link, and sets a use frequency for each time Storing a frequency change pattern as a pattern-time table, and storing a link-pattern correspondence table in which a frequency change pattern to be used is set for each link from among the frequency change patterns stored as the pattern-time table. When an input signal transmitted from the transmission source node is input, an output signal is generated by performing an encoding operation that multiplies the input signal and a predetermined encoding matrix for each node. And outputting the output signal of the link with reference to the link-pattern correspondence table. A step of obtaining a frequency change pattern corresponding to a link, a step of obtaining a use frequency corresponding to the current time in the obtained frequency change pattern with reference to the pattern-time table, and using the obtained use frequency And outputting the generated output signal to the output link at each relay node, so that when transmitting information from the source node to the destination node, A wireless communication method characterized by performing a network coding process for performing an encoding operation and performing a frequency hopping process for changing a use frequency in accordance with an output link and a current time.

  The present invention is a wireless communication method for transmitting information from a source node to a destination node via one or more relay nodes in a network in which a plurality of nodes are connected by a link, and sets a use frequency for each time Storing a frequency change pattern as a pattern-time table, and storing a link-pattern correspondence table in which a frequency change pattern to be used is set for each link from among the frequency change patterns stored as the pattern-time table. When an input signal transmitted from the transmission source node is input, an output signal is generated by performing an encoding operation that multiplies the input signal and a predetermined encoding matrix for each node. And outputting the output signal of the link with reference to the link-pattern correspondence table. A step of obtaining a frequency change pattern corresponding to a link, a step of obtaining a use frequency corresponding to the current time in the obtained frequency change pattern with reference to the pattern-time table, and using the obtained use frequency And outputting the generated output signal to the output link at each relay node, so that when transmitting information from the source node to the destination node, Since the wireless communication method is characterized by performing a network coding process for performing an encoding operation, and performing a frequency hopping process for changing a use frequency in accordance with an output link and a current time. To encode the input signal to obtain the output signal and at the same time set the frequency of the output signal to a certain rule. Accordingly By effectively changed, while achieving efficient transmission of network coding, to achieve high confidentiality against external eavesdroppers.

It is the figure which showed the example of the network model which the radio | wireless communication method which concerns on Embodiment 1 of this invention makes object. It is a flowchart which shows the procedure of the encoding calculation of normal network coding. It is a figure which shows the encoding operation of normal network coding. It is a figure which shows the table which shows the relationship between the frequency of normal frequency hopping, and time. It is a flowchart which shows the procedure of normal frequency hopping. It is the network diagram which added the frequency change pattern to the link in the radio | wireless communication method which concerns on Embodiment 1 of this invention. It is a figure which shows the table which shows a response | compatibility with a link number and a frequency change pattern in the radio | wireless communication method which concerns on Embodiment 1 of this invention. It is a figure which shows the table which shows the relationship between a frequency change pattern and time in the radio | wireless communication method which concerns on Embodiment 1 of this invention. It is a flowchart which shows the procedure of the network coding and the output frequency determination in the node of this invention in the radio | wireless communication method which concerns on Embodiment 1 of this invention. It is a figure which shows the table which shows the relationship between a frequency and time in the radio | wireless communication method which concerns on Embodiment 1 of this invention. It is a figure which shows pattern ep1 of the frequency-time table of FIG. It is a figure which shows pattern ep2 of the frequency-time table of FIG. It is a figure which shows pattern ep3 of the frequency-time table of FIG. It is a figure which shows pattern dp1 of the frequency-time table of FIG. It is a figure which shows pattern dp2 of the frequency-time table of FIG. It is a figure which shows pattern dp3 of the frequency-time table of FIG. It is a figure which shows pattern dp4 of the frequency-time table of FIG. It is a figure which shows pattern dp5 of the frequency-time table of FIG. It is a figure which shows the table which shows the comparison of normal frequency hopping, normal network coding, and the frequency hopping network coding of this invention. It is a network diagram which shows the mode of the transmission efficiency improvement of network coding in the radio | wireless communication method which concerns on Embodiment 1 of this invention. It is the figure which showed the example of the network model which the radio | wireless communication method which concerns on Embodiment 2 of this invention makes object. In the radio | wireless communication method which concerns on Embodiment 2 of this invention, it is the network diagram which described the frequency change pattern in the node. It is a figure which shows the table which shows a response | compatibility with a node number and a frequency change pattern in the radio | wireless communication method which concerns on Embodiment 2 of this invention. It is a figure which shows the table which shows the relationship between a frequency change pattern and time in the radio | wireless communication method which concerns on Embodiment 2 of this invention. It is a flowchart which shows the procedure of the network coding and the output frequency determination in the node of this invention in the radio | wireless communication method which concerns on Embodiment 2 of this invention. It is a figure which shows the table which shows the relationship between a frequency and time in the radio | wireless communication method which concerns on Embodiment 2 of this invention. It is a figure which shows pattern ep1 of the frequency-time table of FIG. It is a figure which shows pattern ep2 of the frequency-time table of FIG. It is a figure which shows pattern ep3 of the frequency-time table of FIG. It is a figure which shows pattern ep4 of the frequency-time table of FIG. It is a figure which shows pattern ep5 of the frequency-time table of FIG. It is a figure which shows pattern ep6 of the frequency-time table of FIG. It is a figure which shows pattern ep7 of the frequency-time table of FIG. It is a figure which shows pattern ep8 of the frequency-time table of FIG. FIG. 27 is a diagram in which the frequency change pattern-time table of FIG. 24 and the frequency-time table of FIG. 26 are combined. It is a figure which shows the table which shows the comparison of normal frequency hopping, normal network coding, and the frequency hopping network coding of this invention. It is a network diagram which shows the mode of the transmission efficiency improvement of network coding in the radio | wireless communication method which concerns on Embodiment 2 of this invention. It is a figure which shows the table which shows the relationship between a frequency change pattern and time in the radio | wireless communication method which concerns on Embodiment 3 of this invention. It is a flowchart which shows the procedure of the network coding and the output frequency determination in the node of this invention in the radio | wireless communication method which concerns on Embodiment 3 of this invention. It is a figure which shows the table which shows the relationship between a frequency and time in the radio | wireless communication method which concerns on Embodiment 3 of this invention. It is a figure which shows the table which shows the relationship between a frequency and time in the radio | wireless communication method which concerns on Embodiment 4 of this invention. It is a figure which shows the table which shows the relationship between a frequency change pattern and time in the radio | wireless communication method which concerns on Embodiment 5 of this invention. It is a flowchart which shows the procedure of the network coding and the output frequency determination in the node of this invention in the radio | wireless communication method which concerns on Embodiment 5 of this invention. It is a figure which shows the table which shows the relationship between a frequency and time in the radio | wireless communication method which concerns on Embodiment 5 of this invention. It is a flowchart which shows the procedure of the network coding and the output frequency determination in the node of this invention in the radio | wireless communication method which concerns on Embodiment 6 of this invention. It is a figure which shows the table which shows the relationship between a frequency and time in the radio | wireless communication method which concerns on Embodiment 6 of this invention. It is a figure which shows the table which shows the relationship between a frequency change pattern and time in the radio | wireless communication method which concerns on Embodiment 7 of this invention. It is a flowchart which shows the procedure of the network coding and the output frequency determination in the node of this invention in the radio | wireless communication method which concerns on Embodiment 7 of this invention.

Embodiment 1 FIG.
The present invention efficiently transmits information when performing communication for transmitting information from a source node to a destination node in a network in which communication devices (nodes) for wireless communication are connected by a communication path (link). For this reason, it is possible to improve the transmission efficiency and improve the confidentiality of transmission information by using a combination of network coding, which is a technology used for this purpose, and frequency hopping that changes the communication frequency every time. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an example of a network model targeted by the present invention. In FIG. 1A, 10 is a network model, N is a node that is a communication device, and L is a link that is a communication path. In the figure, when it is necessary to specify individual nodes N and links L, subscripts such as N1 and L1 are added. In the present invention, as shown in FIG. 1A, consider a network in which each node N is connected to each other by a directed link L. In the present invention, it is assumed that there is a special node called a source node NS1 (S: Source) among a plurality of nodes N, and one or a plurality of destination nodes NT among the plurality of nodes N. Suppose there is a special node called (T: Target).

  Now, as shown in FIG. 1B, it is assumed that a plurality of network models corresponding to the network model 10 shown in FIG. 1A are gathered to form one network model. Network models 10_1, 10_2,..., 10_n shown in FIG. 1B correspond to the network model 10 shown in FIG. A combination of a plurality of network models is referred to as a multi-frequency network model 10MF (MF: Multi-Frequency). Normally, in the multi-frequency network model 10MF, different frequencies f1, f2,..., Fn are used in each of the network models 10_1, 10_2,.

  Conventionally, different frequencies f1, f2,..., Fn are used for each of the network models 10_1, 10_2,..., 10_n as described above, but in the first embodiment of the present invention, each network model is used. A different frequency is used for each link L in 10_1, 10_2, ..., 10_n. In addition, the frequency is assumed to change sequentially to different frequencies for each link L based on different frequency change patterns for each link L. Details will be described later.

  Next, a conventional normal network coding encoding operation procedure at the node N will be described with reference to FIGS. Here, the node N is a node that performs an encoding operation as an intermediate relay node when transmitting information from the source node NS1 to the destination node NT1.

  FIG. 2 is a flowchart showing the procedure of the encoding operation at the node N as such a relay node. As shown in FIG. 2, when the signal transmitted from the source node NS1 is input to the node N directly or via another relay node N, the node N first receives the input signal in step ST11. Is multiplied by the encoding matrix of node N to calculate the output signal. Next, in step ST12, the calculated output signal is transmitted to each output link L. The procedure of FIG. 2 will be described in more detail with reference to the example of FIG.

  FIG. 3 is a diagram illustrating an encoding operation at the node N. As shown in FIG. 3A, in the node N, the number of links L entering the node N is h1, and the number of links L leaving the node N is h2. At this time, data flows through the h1 links L and enters the node N. At this time, as shown in FIG. 3B, the data (input signal) flowing through the link L entering the node N is represented by an h1 dimensional vector VT2, and the h1 dimensional vector VT2 (input) is expressed as in equation (1). Signal) is multiplied by a matrix MT2 (encoding matrix) of h2 rows and h1 columns to obtain an h2D vector VTD2. This process is step ST11 in FIG. The components of the h2D vector VTD2 obtained in this way are data (output signals) flowing through the link L exiting from the node N, so the components of the h2D vector VTD2 are transmitted to the h2 links L. . This process is step ST12 in FIG. Conventionally, the frequency at this time is a frequency set in advance for each of the network models 10_1, 10_2,..., 10_n, and is common to each link. Output is not performed at each node N. In the example of FIG. 3, h1 = 4 (book) and h2 = 2 (book) are used, and the coding matrix MT2 is taken as an appropriate example. Note that the encoding matrix of each node N is set in advance for each node N.

  Assuming that the route to be visited is not present in the network model 10, the data shown in FIGS. 2 and 3 are sequentially repeated at each node N, whereby the data flowing through each link L is sequentially determined.

  In this way, data (reception information) transmitted from the transmission source node NS1 is transmitted via one or more relay nodes N and reaches the destination node NT1 determined at the time of transmission. The destination node NT1 decrypts the received information and restores the transmission information from the source node NS1.

  Next, a conventional normal frequency hopping procedure will be described with reference to FIGS. FIG. 4 is a diagram showing a pattern-time table FTtab0 (F: Frequency, T: Time) showing the relationship between the frequency and time of conventional normal frequency hopping, and FIG. 5 is a diagram showing conventional normal frequency hopping. It is a flowchart which shows a procedure.

  4, the horizontal axis AT represents time, the vertical axis AF represents frequency, t1, t2,..., T8 represent times 1, 2,..., 8 respectively, and f1, f2,. 2,... In the table FTtab0 shown in FIG. 4, the time at which a specific frequency is used is marked. For example, since f8t5 of the pattern-time table FTtab0 is marked, for example, the frequency f8 is used at time t5. Similarly, frequency f2 is used at time t1, frequency f4 at time t2, frequency f3 at time t3, frequency f6 at time t4, frequency f5 at time t6, frequency f7 at time t7, and frequency f1 at time t8.

  In the conventional normal frequency hopping, as shown in FIG. 4, a table FTtab0 indicating the relationship between the frequency hopping frequency and time is prepared in advance, and as shown in FIG. The pattern-time table FTtab0 in FIG. 4 is referred to, and the use frequency corresponding to the current time is obtained. Next, in step ST21, communication is performed at the obtained use frequency.

  In the conventional normal frequency hopping, as shown in FIG. 4, the rule of frequency change is common to all links from the source node to the destination node, and the frequency of a session at a certain time is the same. Therefore, if transmission information is observed for a long time at a certain frequency, there is a problem that the transmission information may be visible when the frequency is used. In contrast, in the first embodiment of the present invention, communication is performed as follows.

  The coding operation and frequency hopping procedure of frequency hopping network coding at node N according to Embodiment 1 of the present invention will be described with reference to FIGS. 6, 7, 8, and 9. FIG. 6 is a network diagram in which a frequency change pattern is added to a link, FIG. 7 is a table showing the correspondence between the link number of each link L and the frequency change pattern, and FIG. 8 is a table showing the relationship between frequency and time in the frequency change pattern. FIG. 9 is a flowchart showing a procedure of encoding operation by network coding at node N and output frequency determination by frequency hopping in Embodiment 1 of the present invention.

  6A and 6B, in the network model shown in the network diagram of FIG. 1, the frequency change patterns ep1, ep2, and ep3 are assigned to the links L1, L2, L3, L4, L5, L6, and L7, respectively. , Ep1, ep2, ep3, ep1 are appended, and in each of the links L1, L2, L3, L4, L5, L6, L7, these frequency change patterns ep1, ep2, ep3, ep1, ep2, ep3, respectively. It shows that ep1 is used.

  The correspondence between the links L1 to L7 and the frequency change patterns ep1 to ep3 is shown in a link-pattern correspondence table LPtab (L: Link, P: Pattern) which is a link-pattern correspondence table of FIG. As shown in FIG. 7, in the correspondence table LPtab, the link numbers LNo of the links L1 to L7 and the pattern numbers PNo of the frequency change patterns set for the links are stored in association with each other. The correspondence table LPtab is stored in advance in a storage device (illustrated) provided in the node N.

  Further, which frequency is used at each time in each frequency change pattern is stored for each frequency change pattern in the pattern-time table PTtab (P: Pattern, T: Time) in FIG. 8, the horizontal axis AT represents time, the vertical axis AP represents the pattern number of the frequency change pattern, t1, t2,..., T8 represent times 1, 2,..., 8, respectively, ep1 to ep3, dp1 to dp5. Each represents a frequency change pattern. Which frequency is used at each time in each frequency change pattern will be described in detail using the frequency change pattern ep1 of the table PTtab as an example. Looking at the row of the frequency change pattern ep1 of the table PTtab, it can be seen that ep1t1 is f2, and therefore the frequency f2 is used at time t1. Similarly, since ep1t2 of the bank is f4, it can be seen that the frequency f4 is used at time t2. This table PTtab is stored in advance in a storage device (illustrated) or the like provided in the node N.

  As described above, in the first embodiment, the correspondence table LPtab shown in FIG. 7 and the table PTtab shown in FIG. 8 are prepared in advance and stored in the storage device (illustrated) of the node N that is a relay node. deep. Then, when the node N receives the input signal, as shown in FIG. 9, the node N first calculates the output signal by multiplying the input signal by the encoding matrix of the node N in step ST31. . The calculation method at this time may be as shown in FIG. 3, and the encoding matrix of each node N is set in advance for each node. Next, in step ST32, it is determined whether or not the output signals and frequencies of all the output links L have been determined. If not determined, the process proceeds to step ST33, and if determined, the process proceeds to step ST36. In step ST33, the frequency change pattern of the output link L is obtained with reference to the correspondence table LPtab of FIG. In step ST34, the frequency of the output link L corresponding to the current time is obtained with reference to the table PTtab of FIG. In step ST35, the next output link L of the node N is considered and the process returns to step ST32. In this way, when the processing from steps ST32 to ST35 is repeated and the output signals and frequencies of all the output links L are determined, in step ST36, each output link L is obtained for each link in step ST34. The output signal obtained in step ST31 is transmitted using the determined frequency.

  Next, the relationship between frequency and time in the first embodiment of the present invention will be described with reference to FIGS. 10 and 11 to 18. FIG. 10 shows a table FmTtab (F: Frequency, m: multi, T: Time) showing the relationship between frequency and time in the first embodiment of the present invention. 10A, the horizontal axis AT is time, the vertical axis AF is frequency, t1, t2,..., T8 represent times 1, 2,..., 8, respectively, f1, f2,. Represent frequencies 1, 2,..., 8, respectively. In the table FmTtab shown in FIG. 10, the time at which each frequency pattern ep1, ep2, ep3, dp1, dp2, dp3, dp4, dp5 is used is the frequency pattern ep1, ep2, ep3, dp1, dp2, dp3. Marked by the symbols attached to dp4 and dp5. See FIG. 10B for the symbols. 10A, for example, in the row of the frequency f8 of the table FmTtab, the time t1 is ep2 (f8t1), the time t2 is the frequency pattern dp4 (f8t2), the time t3 is the frequency pattern dp5 (f8t3), and the time t4 is the frequency. It can be seen that the pattern dp3 (f8t4), the time t5 is the frequency pattern ep1 (f8t5), the time t6 is the frequency pattern dp2 (f8t6), the time t7 is the frequency pattern ep3 (f8t7), and the time t8 is the frequency pattern dp1 (f8t8). .

  As shown in FIG. 10B, the frequency change patterns ep1, ep2, and ep3 are frequency change patterns for effective information EIF used in any of the links L1 to L7 in FIG. On the other hand, the frequency patterns dp1, dp2, dp3, dp4, dp5 are frequency change patterns for dummy information DIF which are not used in FIG. The dummy information DIF is inserted to confuse the eavesdropper. For example, if the eavesdropper eavesdrops on the frequency f8 in FIG. 10, the frequency patterns ep2, dp4, dp5, dp3, ep1, dp2, ep3, dp1 are obtained at times t1, t2,. Of these, ep2 at time t1, ep1 at time t5, and ep3 at time t7 are effective. However, since these signals are mixed with dummy signals, it is difficult to extract an effective signal. Here, if the dummy information DIF is larger than the effective information EIF, it is difficult to extract the effective signal EIF, but the utilization efficiency of communication resources is lowered. Conversely, if the effective information EIF is larger than the dummy information DIF, the utilization efficiency of communication resources is increased, but the effective signal EIF can be easily extracted. Therefore, in Embodiment 1 of the present invention, each node N is provided with a ratio setting means (ratio setting step) for setting the ratio between the effective information EIF and the dummy information DIF, and the transmission efficiency is changed by changing the ratio. And trade-off trade-offs. That is, an appropriate ratio is appropriately selected based on the available bandwidth at the time of use and the confidentiality requirement of the user. Further, as an extreme case, since the frequency pattern is changed according to the time even if no dummy information DIF is inserted, the effect of confusing an eavesdropper can be obtained only by the effective information EIF. The dummy information DIF is transmitted by constructing another link other than the links L1 to L7 in FIG.

  11 to 18 show the frequency change patterns extracted from FIG. 11 is a diagram showing the frequency change pattern ep1 in FIG. 10, FIG. 12 is a diagram showing the frequency change pattern ep2 in FIG. 10, and FIG. 13 is a diagram showing the frequency change pattern ep3 in FIG. 14 shows the frequency change pattern dp1 in FIG. 10, FIG. 15 shows the frequency change pattern dp2 in FIG. 10, and FIG. 16 shows the frequency change pattern dp3 in FIG. 17 is a diagram showing the frequency change pattern dp4 in FIG. 10, and FIG. 18 is a diagram showing the frequency change pattern dp5 in FIG.

  When the correspondence table LPtab of FIG. 7 and FIGS. 11 to 18 are combined, the links L1 and L7 transmit with the frequency change pattern of FIG. 11, and the links L2 and L5 transmit with the frequency change pattern of FIG. It can be seen that transmission is performed on the links L3 and L6 with the frequency change pattern of FIG. Further, if necessary, another link is constructed, and the dummy information DIF is transmitted using a part or all of the frequency change patterns of FIGS.

  FIG. 19 shows a table FHNCtab (FH: Frequency Hopping, NC: Network Coding) that summarizes comparison of conventional normal frequency hopping, conventional normal network coding, and frequency hopping network coding according to Embodiment 1 of the present invention. FIG. As shown in the figure, in normal frequency hopping, the frequency is changed every time, but the output frequency is not changed for each relay node. Also, the encoding operation at the relay node is not performed. In normal network coding, encoding operation is performed at the relay node, but the frequency is not changed every time. On the other hand, in the frequency hopping network coding according to Embodiment 1 of the present invention, encoding operations are performed at the relay nodes, and the output frequency is sequentially changed at each relay node in accordance with the output link and the current time. Thereby, the confidentiality of the transmission information with respect to an eavesdropper by the frequency hopping for every link improves, improving the transmission efficiency by the effect of network coding. As an example of the encoding operation at the relay node, the input signal may be output as it is as the output signal.

  Next, FIG. 20 shows that the frequency hopping network coding scheme according to the first embodiment of the present invention is highly likely to improve not only the secrecy of an eavesdropper but also the transmission efficiency of network coding.

  FIG. 20 is a network diagram showing a state of improving the transmission efficiency of frequency hopping network coding according to Embodiment 1 of the present invention. In network coding, it is generally said that the transmission efficiency improves as the configuration of the network topology becomes more complicated. In the frequency hopping network coding system according to the first embodiment of the present invention, as shown by 10 MFb in FIG. 20, the configuration of the network topology becomes complicated due to the use of a plurality of frequencies. There is a great potential for improvement.

  As described above, according to the first embodiment of the present invention, the network coding and the frequency hopping are combined, the frequency conversion for each output link is performed together with the encoding operation in the relay node, and the dummy information is also mixed. As a result, the confidentiality of transmission information with respect to an eavesdropper from outside can be improved, and the transmission efficiency can be improved due to the effect of network coding by making the network topology complicated by using multiple frequencies.

  In the above description, as shown in FIG. 6, the example in which the common frequency change patterns ep1 to ep3 are used in the corresponding links between the network models 10_1, 10_2,. That is, the example in which the link L1 of the network model 10_1, the link L1 of the network model 10_2,..., And the link L1 of the network model 10_8 use the same frequency has been described. However, the present invention is not limited to this, and a correspondence table LPtab shown in FIG. 7 is created separately for each network model 10_1, 10_2,..., 10_8, and corresponding links between the network models 10_1, 10_2,. If different frequency change patterns are used, eavesdropping becomes more difficult, and the secrecy of the eavesdropper is improved. Further, if the number of frequency change patterns (variations) is further increased, the confidentiality of the eavesdropper is further improved.

Embodiment 2. FIG.
FIG. 21 is a diagram showing another example of the network model targeted by the present invention. In FIG. 21A, 10 is a network model, N is a node that is a communication device, and L is a link that is a communication path. In the figure, when it is necessary to specify individual nodes N and links L, subscripts such as N1 and L1 are added. Also in the present embodiment, as in the first embodiment, consider a network in which each node N is connected to each other by a directed link L as shown in FIG. Also in the present embodiment, as in the first embodiment, it is assumed that there is a special node called a source node NS1 (S: Source) among a plurality of nodes N, and a plurality of nodes It is assumed that there is a special node called one or a plurality of destination nodes NT1, NT2 (T: Target) in N.

  Now, as shown in FIG. 21B, it is assumed that a plurality of network models corresponding to the network model 10 shown in FIG. 21A are gathered to form one multi-frequency network model 10MF. In FIG. 21B, network models 10_1, 10_2,..., 10_n respectively correspond to the network model 10 shown in FIG.

  In the first embodiment, different frequencies are used for the respective links L in the network models 10_1, 10_2,..., 10_n, but in the second embodiment, the network models 10_1, 10_2,. , 10_n, a different frequency is used for each node N. In addition, the frequency changes to a different frequency sequentially for each node N based on different frequency change patterns for each node N. Details will be described later.

  Note that the conventional network coding encoding operation procedure at the node N is as described above with reference to FIGS. 2 and 3, and the conventional normal frequency hopping procedure is as described above with reference to FIGS. 4 and 5. Therefore, although not described here, in the conventional normal frequency hopping, as shown in FIG. 4, the frequency change rule is common to all links from the source node to the destination node, Since the frequency of a session at a certain point in time is the same, if transmission information is observed for a long time at a certain frequency, the transmission information may be visible when the frequency is used. In contrast, in the second embodiment of the present invention, communication is performed as follows.

  The coding operation and frequency hopping procedure of frequency hopping network coding at node N according to Embodiment 2 of the present invention will be described with reference to FIG. 22, FIG. 23, FIG. 24, and FIG. FIG. 22 is a network diagram showing that different frequency change patterns are used depending on the node, FIG. 23 is a table showing the correspondence between the node number of each node N and the frequency change pattern, and FIG. 24 is the frequency and time in the frequency change pattern. FIG. 25 is a flowchart showing the procedure of coding operation by network coding at node N and output frequency determination by frequency hopping in Embodiment 2 of the present invention.

  22A and 22B, in the network model shown in the network diagram of FIG. 21, the frequency change patterns ep1, ep2, and ep7 are used in the nodes NS1, N2, and N7 (NT2), respectively. Show.

  The correspondence between the nodes NS1, N2, N3, N4, N5, N6 (NT1), N7 (NT2) and the frequency change patterns ep1 to ep7 is the node-pattern correspondence table NPtab (node-pattern correspondence table in FIG. 23). N: Node, P: Pattern). As shown in FIG. 23, in the correspondence table NPtab, the link numbers NNo of the nodes N1 to N7 and the pattern numbers PNo of the frequency change patterns set for the nodes are stored in association with each other. This correspondence table NPtab is stored in advance in a storage device (illustrated) or the like provided in the node N, or is described in a header or the like and notified to each node.

  Also, which frequency is used at each time in each frequency change pattern is stored for each frequency change pattern in the pattern-time table PTtab (P: Pattern, T: Time) in FIG. 24, the horizontal axis AT is the time, the vertical axis AP is the pattern number of the frequency change pattern, t1, t2,..., T8 represent times 1, 2,..., 8, respectively, and ep1 to ep8 are respectively This represents a frequency change pattern. Which frequency is used at each time in each frequency change pattern will be described in detail using the frequency change pattern ep1 of the table PTtab as an example. Looking at the row of the frequency change pattern ep1 of the table PTtab, it can be seen that ep1t1 is f2, and therefore the frequency f2 is used at time t1. Similarly, since ep1t2 of the bank is f4, it can be seen that the frequency f4 is used at time t2. This table PTtab is stored in advance in a storage device (not shown) or the like provided in the node N.

  As described above, in the second embodiment, the correspondence table NPtab shown in FIG. 23 and the table PTtab shown in FIG. 24 are prepared in advance and stored in a storage device (not shown) of the node N that is a relay node. Remember. Then, when the node N receives the input signal, as shown in FIG. 25, the node N first calculates the output signal by multiplying the input signal by the encoding matrix of the node N in step ST41. . The calculation method at this time may be as shown in FIG. 3, and the encoding matrix of each node N is set in advance for each node. Next, in step ST42, the frequency change pattern of the node N is obtained with reference to the correspondence table NPtab of FIG. In step ST43, the output frequency of the node N corresponding to the current time is obtained with reference to the table PTtab of FIG. In step ST44, an output signal is transmitted using the obtained output frequency.

  Next, the relationship between frequency and time in the second embodiment of the present invention will be described with reference to FIG. 26 and FIGS. FIG. 26 shows a table FmTtab (F: Frequency, m: multi, T: Time) showing the relationship between frequency and time in Embodiment 2 of the present invention. In FIG. 26 (a), the horizontal axis AT represents time, the vertical axis AF represents frequency, t1, t2,..., T8 represent times 1, 2,. Represent frequencies 1, 2,..., 8, respectively. In the table FmTtab shown in FIG. 26, the time at which each frequency pattern ep1, ep2, ep3, ep4, ep5, ep6, ep7, ep8 is used is the frequency pattern ep1, ep2, ep3, ep4, ep5, ep6. Marked by symbols attached to ep7 and ep8. For the symbols, refer to FIG. In FIG. 26A, for example, in the row of the frequency f8 of the table FmTtab, the time t1 is ep2 (f8t1), the time t2 is the frequency pattern ep7 (f8t2), the time t3 is the frequency pattern ep8 (f8t3), and the time t4 is the frequency. It can be seen that the pattern ep6 (f8t4), the time t5 is the frequency pattern ep1 (f8t5), the time t6 is the frequency pattern ep5 (f8t6), the time t7 is the frequency pattern ep3 (f8t7), and the time t8 is the frequency pattern ep4 (f8t8). .

  27 to 34 show the frequency change patterns extracted from FIG. 27 is a diagram showing the frequency change pattern ep1 in FIG. 26, FIG. 28 is a diagram showing the frequency change pattern ep2 in FIG. 26, and FIG. 29 is a diagram showing the frequency change pattern ep3 in FIG. 30 shows the frequency change pattern ep4 in FIG. 26, FIG. 31 shows the frequency change pattern ep5 in FIG. 26, and FIG. 32 shows the frequency change pattern ep6 in FIG. FIG. 33 is a diagram showing the frequency change pattern ep7 in FIG. 26, and FIG. 34 is a diagram showing the frequency change pattern ep8 in FIG.

  FIG. 35 shows diagrams corresponding to FIG. 24 and FIG. 26 side by side, and shows the same thing as FIG. 24 to FIG.

  When the correspondence table NPtab of FIG. 23 is combined with FIGS. 27 to 34 and FIG. 35, in the second embodiment, transmission is performed with different frequency patterns in all nodes. However, the same frequency pattern may be used when the nodes are sufficiently separated and do not cause interference.

  FIG. 36 shows a table FHNCtab (FH: Frequency Hopping, NC: Network Coding) that summarizes comparison of conventional normal frequency hopping, conventional normal network coding, and frequency hopping network coding according to Embodiment 2 of the present invention. FIG. As shown in the figure, in normal frequency hopping, the frequency is changed every time, but the output frequency is not changed for each relay node. Also, the encoding operation at the relay node is not performed. In normal network coding, encoding operation is performed at the relay node, but the frequency is not changed every time. On the other hand, in frequency hopping network coding according to Embodiment 2 of the present invention, encoding operations are performed at relay nodes, and output frequencies are sequentially changed at each relay node in accordance with the current time. Thereby, the confidentiality of the transmission information with respect to an eavesdropper by the frequency hopping for every link improves, improving the transmission efficiency by the effect of network coding. As an example of the encoding operation at the relay node, the input signal may be output as it is as the output signal.

  Next, FIG. 37 shows that the frequency hopping network coding scheme according to the first embodiment of the present invention has a high possibility of improving not only the confidentiality of an eavesdropper but also the transmission efficiency of network coding.

  FIG. 37 shows a plurality of adjacent nodes in the frequency hopping network coding according to the second embodiment of the present invention due to radio broadcast performance around each of NS1 of network model 10_1, N3 of network model 10_2, and network model 10_n. It is a network diagram which shows a mode that a transmission signal reaches | attains simultaneously. In network coding, it is generally said that the transmission efficiency is further improved by considering wireless broadcast performance. In the frequency hopping network coding system according to the first embodiment of the present invention, as shown in 10MFC in FIG. 37, since a plurality of frequencies are used in addition to the use of wireless broadcasting, transmission efficiency can be improved. The nature is great.

  As described above, according to the second embodiment of the present invention, transmission information is concealed from an eavesdropper from the outside by combining network coding and frequency hopping and performing frequency conversion together with encoding operation at a relay node. In addition, the transmission efficiency can be improved due to the effect of network coding.

Embodiment 3 FIG.
In the present embodiment, as an example of a target network model, the one illustrated in FIG. 21 will be described as in the second embodiment. Since the reference numerals in FIG. 21 are as described above, the description thereof is omitted here. In the present embodiment, as in the second embodiment, consider a network in which each node N is connected to each other by a directed link L as shown in FIG. Similarly to the second embodiment, it is assumed that there is a special node called a source node NS1 (S: Source) in the plurality of nodes N, and one or more in the plurality of nodes N It is assumed that there are special nodes called a plurality of destination nodes NT1, NT2 (T: Target).

  In the present embodiment, as in the second embodiment, as shown in FIG. 21B, a plurality of network models corresponding to the network model 10 shown in FIG. Assume that a network model 10MF is formed.

  Further, a different frequency is used for each node N in each network model 10_1, 10_2,. In addition, the frequency changes to a different frequency sequentially for each node N based on different frequency change patterns for each node N. Details will be described later.

  The conventional network coding encoding operation procedure at the node N is as described with reference to FIGS. 2 and 3, and the conventional normal frequency hopping procedure is described with reference to FIGS. However, in the conventional normal frequency hopping, as shown in FIG. 4, the frequency change rule is common to all links from the source node to the destination node. Since the frequency of a session at a certain point in time is the same, if transmission information is observed for a long time at a certain frequency, the transmission information may be visible when the frequency is used.

  On the other hand, in the second embodiment, as described above, by combining network coding and frequency hopping and performing frequency conversion together with encoding operation at the relay node, transmission information for an eavesdropper from the outside can be obtained. Improves confidentiality.

  In the second embodiment, the time for staying at each time, that is, the time for which a certain frequency is continuously used (hereinafter referred to as the stay time) is constant. The time is variable. Hereinafter, this embodiment will be described.

  First, in the present embodiment, how long a single frequency is continuously used at each time is called a residence time DT, and a time-residence time table TDTtab (T: Time, shown in FIG. 38). (DT: Dwell Time) is stored in advance. In the time-dwell time table TDTtab, the dwell times dt1 to dt7 are stored in association with each other at each time t1 to t7. This time-staying time table TDTtab is stored in advance in a storage device (not shown) or the like provided in the node N, or is described in a header or the like and notified to each node.

  The dwell time DT stored in the time-dwell time table TDTtab may be the value of the time itself such as 50 μsec, 10 seconds, 5 minutes, etc., but may also be a key value (one or more) that can uniquely identify the dwell time. Good. For example, when the dwell time is a random value (seconds) based on a predetermined pseudo-random number sequence, the random number seed and the random number are indicated.

  In this embodiment, first, as in the second embodiment, the correspondence table NPtab shown in FIG. 23 and the table PTtab shown in FIG. 24 are prepared in advance, and a storage device (not shown) of the node N that is a relay node ) Etc. Then, when the node N receives the input signal, as shown in FIG. 39, the node N first multiplies the input signal by the encoding matrix of the node N in step ST41 to calculate the output signal. . The calculation method at this time may be as shown in FIG. 3, and the encoding matrix of each node N is set in advance for each node. Next, in step ST42, the frequency change pattern of the node N is obtained with reference to the correspondence table NPtab of FIG. Next, in step ST43, the frequency of the node N corresponding to the current time is obtained with reference to the table PTtab of FIG. The processing so far is the same as that in the second embodiment, but in this embodiment, the dwell time at the current time is obtained with reference to the time-dwell time table TDTtab in step ST45A. Next, in step ST44A, the elapsed time from the current time is measured, and when the residence time determined in step ST45A has elapsed, an output signal is transmitted using the frequency determined in step ST43.

  Next, the relationship between frequency and time in the present embodiment will be described with reference to FIG. FIG. 40 shows a table FmTtab_A1 (F: Frequency, m: multi, T: Time) indicating the relationship between frequency and time in the present embodiment. 40 (a), the horizontal axis AT is time, the vertical axis AF is frequency, t1, t2,..., T8 represent times 1, 2,..., 8, respectively, f1, f2,. Represent frequencies 1, 2,..., 8, respectively. In the table FmTtab_A1 shown in FIG. 40, the time at which each frequency pattern ep1, ep2, ep3, ep4, ep5, ep6, ep7, ep8 is used is the frequency pattern ep1, ep2, ep3, ep4, ep5, ep6. Marked by symbols attached to ep7 and ep8. See FIG. 40B for the symbols. 40A, for example, in the row of the frequency f8 of the table FmTtab_A1, the time t1 is ep2 (f8t1), the time t2 is the frequency pattern ep7 (f8t2), the time t3 is the frequency pattern ep8 (f8t3), and the time t4 is the frequency. It can be seen that pattern ep6 (f8t4), time t5 is frequency pattern ep1 (f8t5), time t6 is frequency pattern ep5 (f8t6), time t7 is frequency pattern ep3 (f8t7), and time t8 is frequency pattern ep4 (f8t8). .

  In FIG. 40 of the present embodiment, unlike FIG. 26 of the above-described second embodiment, the intervals (that is, the residence time) between the times t1, t2,..., T8 are not constant. These intervals are designated by residence times dt1, dt2,..., Dt8 described in the time-staying time table TDTtab of FIG. Thereby, the confidentiality with respect to the third party who does not know residence time increases.

  Here, in order to simultaneously convert the frequency at all nodes in the network at the time when the specified residence time has elapsed, it is necessary that the times of all the nodes be synchronized with accuracy in consideration of the residence time interval. is there. In general frequency hopping, the frequency is often changed in a short cycle of 1 second or less, but in order to manage the dwell time with microsecond order accuracy, it is necessary for all nodes to be synchronized in time with accuracy commensurate with it. is there. However, in the method of the present embodiment, even if the residence time at one frequency is not such a short interval, there is an effect of improving secrecy even at intervals of several seconds, several tens of minutes, or more, and time synchronization The accuracy of can be appropriate.

  Note that when the correspondence table NPtab of FIG. 23 is combined with FIGS. 24 and 26, in the second embodiment, transmission is performed with different frequency patterns in all nodes. However, the same frequency pattern may be used when the nodes are sufficiently separated and do not cause interference.

  FIG. 36 is a table FHNCtab (FH: Frequency Hopping, NC: Network Coding) that summarizes comparison of conventional normal frequency hopping, conventional normal network coding, and frequency hopping network coding according to the third embodiment of the present invention. FIG. As shown in the figure, in normal frequency hopping, the frequency is changed every time, but the output frequency is not changed for each relay node. Also, the encoding operation at the relay node is not performed. In normal network coding, encoding operation is performed at the relay node, but the frequency is not changed every time. On the other hand, in the frequency hopping network coding according to the third embodiment, the encoding operation is performed at the relay node, and the output frequency is sequentially changed corresponding to the current time at each relay node. Thereby, the confidentiality of the transmission information with respect to an eavesdropper by the frequency hopping for every link improves, improving the transmission efficiency by the effect of network coding. As an example of the encoding operation at the relay node, the input signal may be output as it is as the output signal.

  As described above, according to the third embodiment of the present invention, the network coding and the frequency hopping are combined, the frequency conversion is performed together with the encoding operation at the relay node, and the residence time using one frequency is made variable. Thereby, the confidentiality of the transmission information with respect to an eavesdropper from the outside is further improved.

Embodiment 4 FIG.
In the present embodiment, a method of managing the variable residence time shown in FIG. 40 of the above-described third embodiment using a time division multiple access (TDMA) time slot will be described. The relationship between frequency and time in the fourth embodiment will be described with reference to FIG. FIG. 41 shows a table FmTtab_A1a (F: Frequency, m: multi, T: Time) indicating the relationship between frequency and time in the present embodiment. 41, the horizontal axis AT represents time, the vertical axis AF represents frequency, ts1, ts2,..., Ts7 represent TDMA time slots, and tt1,..., Tt6 represent sub-times constituting each time slot. Represents a slot. Thus, in this embodiment, each time slot ts1, ts2,..., Ts7 is composed of a plurality of sub time slots tt1,. In addition, f1, f2,..., F7 represent frequencies 1, 2,. In addition, the time slot ts1 portion of the frequency f7 is referred to as f7ts1, and the time slot ts2 portion of the frequency f7 is referred to as f7ts2,.

  In the table FmTtab_A1a shown in FIG. 41, the sub time slot to be used is shown in gray. In time slot ts1, f3t1 of frequency f3 is used, and in time slot ts1, f1t2 of frequency f1 is used. In time slots ts1 and ts2, one frequency is assigned to one time slot. This is called 1-hop allocation.

  Next, in the time slots ts3 and ts4, two frequencies are assigned to one time slot. This is called 2-hop allocation. In the time slot ts3, the first half uses f2t3 having the frequency f2, and the second half uses f6t3 having the frequency f6. In the time slot ts4, the first half uses f4t4 with the frequency f4, and the second half uses f7t4 with the frequency f7.

  Next, in the time slots ts5 and ts6, three frequencies are assigned to one time slot. This is called 3-hop allocation. In time slot ts5, f2t5 of frequency f5 is used for the first two sub time slots, f3t5 of frequency f3 is used for the next two sub time slots, and f1t5 of frequency f1 is used for the last two sub time slots. In time slot ts6, f2t6 of frequency f2 is used for the first two sub time slots, f6t6 of frequency f6 is used for the next two sub time slots, and f7t6 of frequency f7 is used for the last two sub time slots.

  Next, in the time slot ts7, 6 frequencies are assigned to one time slot. This is called 6-hop allocation. In time slot ts7, the first sub time slot tt1 is f6t7 of frequency f6, the next sub time slot tt2 is f5t7 of frequency f5, the next sub time slot tt3 is f1t7 of frequency f1, and the next sub time slot tt4 is frequency f3. f3t7, f7t7 of frequency f7 is used as the next sub time slot tt5, and f4t7 of frequency f4 is used as the last sub time slot tt6.

  A method of synchronizing all the nodes for each TDMA time slot ts1, ts2,..., Ts7 has already been established and is generally used. According to the method of the present embodiment using the TDMA time slot, in which the dwell time is changed using the, the dwell time can be changed even in the case of a frequency change on the order of microseconds.

  As described above, according to the fourth embodiment of the present invention, the network coding and the frequency hopping are combined, the frequency conversion is performed together with the encoding operation in the relay node, and the time slot is further divided into sub time slots. By using this to make the residence time using one frequency variable, the confidentiality of the transmission information to an eavesdropper from the outside is further improved.

Embodiment 5 FIG.
In the above-described second embodiment, the time spent at each time, that is, the time during which a certain frequency is continuously used (stay time) is constant, and the bandwidth of each frequency is also constant. In the third and fourth embodiments, the residence time is variable. In this embodiment, the residence time is constant and the frequency band is variable. How much frequency is used for each frequency is called a bandwidth FW, and is stored for each frequency in a frequency-bandwidth table FFWtab (F: Frequency, FW: Frequency Band Width) shown in FIG. As shown in FIG. 42, in the frequency-bandwidth table FFWtab, the bandwidths fw1 to fw7 are stored in association with the respective frequencies f1 to f7. The frequency-bandwidth table FFWtab is stored in advance in a storage device (not shown) or the like provided in the node N, or is described in a header or the like and notified to each node.

  The bandwidth FW stored in the frequency-bandwidth table FFWtab of FIG. 42 may be a bandwidth value such as 2 kHz or 10 MHz, but may be a key value (one or a plurality) that can uniquely identify the bandwidth. Good. For example, when the dwell time is a random value (seconds) based on a predetermined pseudo-random number sequence, the random number seed and the random number are indicated.

  In the present embodiment, first, similarly to the second embodiment described above, the correspondence table NPtab shown in FIG. 23 and the table PTtab shown in FIG. 24 are prepared in advance, and a storage device (see FIG. (Not shown). Then, when the node N receives the input signal, as shown in FIG. 43, the node N first calculates the output signal by multiplying the input signal by the encoding matrix of the node N in step ST41. . The calculation method at this time may be as shown in FIG. 3 described above, and the encoding matrix of each node N is set in advance for each node. Next, in step ST42, the frequency change pattern of the node N is obtained with reference to the correspondence table NPtab of FIG. In step ST43, the frequency of the node N corresponding to the current time is obtained with reference to the table PTtab of FIG. The processing so far is the same as that of the second embodiment, but in the present embodiment, the bandwidth at the current frequency is obtained by referring to the frequency-bandwidth table FFWtab in step ST47A. Next, in step ST44B, an output signal having the obtained frequency bandwidth is transmitted.

  Next, the relationship between frequency and time in the present embodiment will be described with reference to FIG. FIG. 44A shows a table FmTtab_A2 (F: Frequency, m: multi, T: Time) indicating the relationship between frequency and time in the present embodiment. 44A, the horizontal axis AT is time, the vertical axis AF is frequency, t1, t2,..., T8 represent times 1, 2,. Represent frequencies 1, 2,..., 8, respectively. In the table FmTtab_A2 shown in FIG. 44, the time at which each frequency pattern ep1, ep2, ep3, ep4, ep5, ep6, ep7, ep8 is used is the frequency pattern ep1, ep2, ep3, ep4, ep5, ep6. , Ep7, ep8 are marked by symbols. Refer to FIG. 44B for the symbols. In FIG. 44A, for example, in the row of the frequency f8 of the table FmTtab_A1, the time t1 is ep2 (f8t1), the time t2 is the frequency pattern ep7 (f8t2), the time t3 is the frequency pattern ep8 (f8t3), and the time t4 is the frequency. It can be seen that the pattern ep6 (f8t4), the time t5 is the frequency pattern ep1 (f8t5), the time t6 is the frequency pattern ep5 (f8t6), the time t7 is the frequency pattern ep3 (f8t7), and the time t8 is the frequency pattern ep4 (f8t8). .

  44 of the present embodiment, unlike FIG. 26 of the second embodiment, the bandwidths of the frequencies f1, f2,..., F8 are not constant. These bandwidths are specified by bandwidths fw1, fw2,... Fw8 described in the frequency-bandwidth table FFWtab of FIG. This increases confidentiality for third parties who do not know the bandwidth.

  As described above, according to the fifth embodiment of the present invention, the network coding and the frequency hopping are combined, the frequency conversion is performed together with the encoding operation at the relay node, and the bandwidth at each frequency is made variable. Thereby, the confidentiality of the transmission information with respect to the eavesdropper from the outside improves further.

Embodiment 6 FIG.
In Embodiment 2 described above, the time spent at each time, that is, the time using a certain frequency is constant, and the bandwidth of each frequency is also constant. In the third and fourth embodiments described above, the residence time at each time, that is, the residence time in which one frequency is continuously used is made variable. Furthermore, in the above-described fifth embodiment, the residence time is constant and the frequency band is variable. In the sixth embodiment, the residence time DT and the bandwidth FW at each frequency are variable. The dwell time DT is stored in advance in the time-dwell time table TDTtab (T: Time, DT: Dwell Time) of FIG. The bandwidth FW is stored in advance in the frequency-bandwidth table FFWtab (F: Frequency Band Width) of FIG. The structures of the time-staying time table TDTtab in FIG. 38 and the table FFWtab in FIG. 42 are the same as those in the third and fifth embodiments, respectively. These correspondence tables TDTtab and FFWtab are stored in advance in a storage device (not shown) or the like provided in the node N, or are described in a header or the like and notified to each node.

  In this embodiment, first, similarly to the above-described second embodiment, the correspondence table NPtab shown in FIG. 23 and the table PTtab shown in FIG. 24 are prepared in advance, and a storage device (not shown) of the node N as a relay node is shown. Etc.) in advance. Then, when the node N receives the input signal, as shown in FIG. 45, the node N first calculates the output signal by multiplying the input signal by the encoding matrix of the node N in step ST41. . The calculation method at this time may be as shown in FIG. 3, and the encoding matrix of each node N is set in advance for each node. Next, in step ST42, the frequency change pattern of the node N is obtained with reference to the correspondence table NPtab of FIG. In step ST43, the frequency of the node N corresponding to the current time is obtained with reference to the table PTtab of FIG. In the present embodiment, in step ST45A, the time-dwell time table TDTtab is referred to determine the dwell time at the current time, and in step ST47B, the frequency-bandwidth table FFWtab is referred to The bandwidth at the frequency of Next, when the residence time obtained in step ST45A has elapsed in step ST44C, an output signal having the frequency bandwidth obtained in step ST47B is transmitted.

  Next, the relationship between frequency and time in this embodiment will be described with reference to FIG. FIG. 46A shows a table FmTtab_A3 (F: Frequency, m: multi, T: Time) indicating the relationship between frequency and time in the present embodiment. In FIG. 46 (a), the horizontal axis AT represents time, the vertical axis AF represents frequency, t1, t2,..., T8 represent times 1, 2,. Represent frequencies 1, 2,..., 8, respectively. In the table FmTtab_A3 shown in FIG. 46, the time when each frequency pattern ep1, ep2, ep3, ep4, ep5, ep6, ep7, ep8 is used is the frequency pattern ep1, ep2, ep3, ep4, ep5, ep6. , Ep7, ep8 are marked by symbols. For the symbols, refer to FIG. 46A, for example, in the row of the frequency f8 of the table FmTtab_A1, the time t1 is ep2 (f8t1), the time t2 is the frequency pattern ep7 (f8t2), the time t3 is the frequency pattern ep8 (f8t3), and the time t4 is the frequency. It can be seen that the pattern ep6 (f8t4), the time t5 is the frequency pattern ep1 (f8t5), the time t6 is the frequency pattern ep5 (f8t6), the time t7 is the frequency pattern ep3 (f8t7), and the time t8 is the frequency pattern ep4 (f8t8). .

  In FIG. 46 of the present embodiment, unlike FIG. 26 of the second embodiment, the intervals of the times t1, t2,..., T8 are not constant, and at the same time, the bandwidths of the frequencies f1, f2,. Is not constant. The intervals between the times t1, t2,..., T8 are designated by the residence times dt1, dt2,... Dt8 described in the time-stay time table TDTtab of FIG. The intervals between the frequencies f1, f2,..., F8 are designated by the bandwidths fw1, fw2,... Fw8 described in the frequency-bandwidth table FFWtab of FIG. By making both the residence time and the bandwidth variable, the confidentiality for a third party who does not know the residence time or bandwidth is increased.

  Here, in order to simultaneously convert the frequency at all nodes in the network at the time when the specified residence time has elapsed, it is necessary that the times of all the nodes be synchronized with accuracy in consideration of the residence time interval. is there. In general frequency hopping, the frequency is often changed in a short cycle of 1 second or less, but in order to manage the dwell time with microsecond order accuracy, it is necessary for all nodes to be synchronized in time with accuracy commensurate with it. is there. However, in the method of the present invention, the dwell time at one frequency is not limited to such a short interval, but is effective even at intervals of several seconds, several tens of minutes, or more, and the accuracy of time synchronization is commensurate with it. It doesn't matter.

  The residence time may be managed by using the method using the TDMA time slot shown in the fourth embodiment.

  As described above, according to the sixth embodiment of the present invention, the network coding and the frequency hopping are combined, the frequency conversion is performed together with the encoding operation in the relay node, and the residence time using one frequency is made variable. In addition, by changing the bandwidth at each frequency, the confidentiality of the transmission information with respect to an eavesdropper from the outside is further improved.

Embodiment 7 FIG.
In the above-described sixth embodiment, the residence time and the bandwidth are variable with reference to the two tables of the time-retention time table TDTtab in FIG. 38 and the frequency-bandwidth table FFWtab in FIG. In the present embodiment, both the residence time and the bandwidth are stored in one time-residence time / bandwidth table TDTFWtab shown in FIG. As shown in FIG. 47, in the table TDTWFWtab, the residence times dt1 to dt7 and the bandwidths fw1 to fw7 are stored in association with each other at each time t1 to t7. The correspondence table TDTFFWtab is stored in advance in a storage device (not shown) or the like provided in the node N, or is described in a header or the like and notified to each node.

  In the present embodiment, first, similarly to the second embodiment described above, the correspondence table NPtab shown in FIG. 23 and the table PTtab shown in FIG. 24 are prepared in advance, and a storage device (see FIG. (Not shown) or the like. Then, when the node N receives the input signal, as shown in FIG. 48, first, in step ST41, the node N multiplies the input signal by the encoding matrix of the node N to calculate the output signal. . The calculation method at this time may be as shown in FIG. 3, and the encoding matrix of each node N is set in advance for each node. Next, in step ST42, the frequency change pattern of the node N is obtained with reference to the correspondence table NPtab of FIG. In step ST43, the frequency of the node N corresponding to the current time is obtained with reference to the table PTtab of FIG. Further, in the present embodiment, in step ST48A, the time-dwell time / bandwidth table TDTFFWtab is referred to determine both the dwell time and the bandwidth corresponding to the current time. Next, when the obtained residence time has elapsed in step ST44D, an output signal is transmitted using the obtained frequency bandwidth.

  The relationship between frequency and time in the seventh embodiment of the present invention is the same as that described in the sixth embodiment with reference to FIG.

  As described above, according to the seventh embodiment of the present invention, the network coding and the frequency hopping are combined, the frequency conversion is performed together with the encoding operation at the relay node, and the residence time using one frequency is made variable. In addition, by changing the bandwidth at each frequency, the confidentiality of the transmission information with respect to an eavesdropper from the outside is further improved.

  The present invention can be widely applied to various networks such as a wireless ad hoc network.

  10, 10_1, 10_2, 10_n network model, 10MF, 10MFb multi-frequency network model, AF vertical axis, AT horizontal axis, ep1, ep2, ep3, ep4, ep5, ep6, ep7, ep8 frequency change pattern, f1, f2, fn Frequency, L, L1, L2, L3, L4, L5, L6, L7 link, LPtab link-pattern correspondence table, N node, NS, NS1 Source node, NPtab node-pattern correspondence table, NT, NT1, NT2 Destination node PTtab pattern-time table.

Claims (8)

A wireless communication method for transmitting information via one or more relay nodes from a source node to a destination node in a network in which a plurality of nodes are connected by links,
Storing a frequency change pattern in which a use frequency is set for each time as a pattern-time table;
Storing a link-pattern correspondence table in which a frequency change pattern to be used is set for each link from the frequency change patterns stored as the pattern-time table;
When an input signal transmitted from the source node is input, performing an encoding operation of multiplying the input signal and a predetermined encoding matrix for each node to generate an output signal;
Obtaining a frequency change pattern corresponding to an output link that outputs the output signal out of the links with reference to the link-pattern correspondence table;
With reference to the pattern-time table, obtaining a use frequency corresponding to the current time in the obtained frequency change pattern;
Performing the step of outputting the generated output signal to the output link using the determined use frequency at each of the relay nodes,
When transmitting information from the source node to the destination node, each relay node in the middle performs a network coding process that performs an encoding operation, and also uses a frequency corresponding to the output link and the current time. A radio communication method characterized by performing frequency hopping processing to be changed. The wireless communication method transmits dummy information in addition to effective information for actual communication,
Storing in the pattern-time table a frequency change pattern for dummy information in which a use frequency used for transmission of the dummy information is set for each time;
A frequency change pattern to be used is set for each link from the dummy information frequency change patterns stored in the pattern-time table, and stored in the link-pattern correspondence table;
Similarly to the effective information, the dummy information is subjected to network coding processing for performing coding operation at each relay node, and frequency hopping processing for changing the use frequency in accordance with the output link and the current time. The wireless communication method according to claim 1, wherein:   The wireless communication method according to claim 2, further comprising a step of setting a ratio between effective information to be transmitted and dummy information. A wireless communication method for transmitting information via one or more relay nodes from a source node to a destination node in a network in which a plurality of nodes are connected by links,
Storing a frequency change pattern in which a use frequency is set for each time as a pattern-time table;
Storing a node-pattern correspondence table in which a frequency change pattern to be used is set for each node from among the frequency change patterns stored as the pattern-time table;
When an input signal transmitted from the source node is input, performing an encoding operation of multiplying the input signal and a predetermined encoding matrix for each node to generate an output signal;
Obtaining a frequency change pattern corresponding to the node with reference to the node-pattern correspondence table;
With reference to the pattern-time table, obtaining a use frequency corresponding to the current time in the obtained frequency change pattern;
By using each of the relay nodes to output the generated output signal using the determined use frequency,
When transmitting information from the source node to the destination node, each intermediate relay node performs a network coding process that performs an encoding operation, and changes the frequency used according to the current time. The wireless communication method characterized by performing the process. Each said relay node
Storing a residence time indicating how long one frequency is used at each time in a time-residence time table for each time;
A step of obtaining a dwell time corresponding to the current time with reference to the time-dwell time table;
5. The wireless communication method according to claim 4, wherein each of the relay nodes executes the step of outputting the output signal after the determined residence time has elapsed. The wireless communication method according to claim 5, wherein the residence time is managed using a time division multiple access (TDMA) time slot. Each said relay node
Storing a bandwidth indicating how much frequency band to use at each frequency in a frequency-bandwidth table for each used frequency;
A step of obtaining a bandwidth corresponding to the use frequency obtained in the step of obtaining the use frequency with reference to the frequency-bandwidth table;
The wireless communication method according to any one of claims 4 to 6, wherein each relay node outputs an output signal having the obtained bandwidth in the step of outputting the output signal. Each said relay node
Set how long one frequency is used at each time as a dwell time for each time and how much frequency band is used for each frequency for each time, and set dwell Storing time and bandwidth for each time as a time-dwell time / bandwidth table;
A step of obtaining a dwell time and a bandwidth corresponding to the current time with reference to the time-dwell time / bandwidth table;
5. The wireless communication method according to claim 4, wherein each of the relay nodes executes the step of outputting the output signal with the output signal having the determined bandwidth after the determined residence time has elapsed.

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