Communication system, communication device, and communication method

Abstract

To increase the safety of a communication.SOLUTION: A communication system according to an embodiment includes a first communication device and a second communication device. The first communication device repeatedly performs a first modulation system control including selecting a first modulation system used to transmit data from a plurality of modulation systems including a modulation system which does not use the power of 2 and setting an offset used for a modulation by the first modulation system, and performs the modulation based on the first modulation system and the offset to transmit transmission data. The second communication device repeatedly performs a second modulation system control including selecting a second modulation system used to receive data from the plurality of modulation systems and setting a threshold value used for a demodulation by the second modulation system, and demodulates a signal from the first communication device on the basis of the second modulation system and the threshold value to obtain reception data. The second modulation system control is performed in synchronization with the first modulation system control.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a communication system, a communication device, and a communication method.

Background Art

[0002] In recent years, highly secure communication has been desired in the electromagnetic wave region. In data communication, security has been ensured by software-based methods, but due to the remarkable development of the computing power of computing devices, the security has been relatively decreasing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to provide a technology capable of improving communication security.

Means for Solving the Problems

[0005] A communication system according to an embodiment includes a first communication device and a second communication device. The first communication device repeatedly performs first modulation method control including selecting a first modulation method to be used for data transmission from among a plurality of modulation methods including a modulation method not based on a power of 2, and setting an offset to be used for modulation by the first modulation method. The first communication device further includes a first modulation method control unit, a modulation unit that performs modulation on a bit string based on transmission data according to the first modulation method and the offset, and a transmission unit that transmits a signal obtained by the modulation. The second communication device repeatedly performs second modulation method control including selecting a second modulation method to be used for data reception from among the plurality of modulation methods, and setting a threshold value to be used for demodulation by the second modulation method. The second communication device further includes a second modulation method control unit, a reception unit that receives the signal from the first communication device, and a demodulation unit that performs demodulation on the signal according to the second modulation method and the threshold value. The second modulation method control unit performs the second modulation method control in synchronization with the first modulation method control in the first modulation method control unit.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0007] Hereinafter, embodiments will be described with reference to the drawings.

[0008] (First Embodiment) FIG. 1 schematically shows a wireless communication system 100 according to the first embodiment. As shown in FIG. 1, the wireless communication system 100 includes a wireless communication device 110 and a wireless communication device 120. The wireless communication device 110 wirelessly communicates with the wireless communication device 120. Here, it is assumed that the wireless communication device 110 is on the data transmission side and the wireless communication device 120 is on the data reception side. In FIG. 1, the components related to data transmission are shown in the wireless communication device 110, and the components related to data reception are shown in the wireless communication device 120. Each of the wireless communication devices 110 and 120 may include both components related to data transmission and components related to data reception. Data transmission may be performed by any of unicast, multicast, and broadcast.

[0009] The wireless communication device 110 includes, as hardware components, a CPU (Central Processing Unit) 10 as a processor, a memory (not shown), and a communication module 11. The wireless communication device 110 may be movable. For example, the wireless communication device 110 may be a terminal device (e.g., a smartphone) carried by a person, or a moving body (e.g., a drone) equipped with a moving mechanism.

[0010] The wireless communication device 110 includes an error correction code adding unit 111, a modulation method control unit 112, a code conversion unit 113, an interleaving unit 114, a modulation unit 115, a mixer 116, a carrier oscillator 117, a transmission unit 118, and an antenna 119. In the present embodiment, these are implemented in the communication module 11. In other embodiments, the processing performed in some of these may be realized by the CPU 10. For example, when the CPU 10 executes a program stored in the memory, it functions as the error correction code adding unit 111 and the like.

[0011] The error correction code adding unit 111 adds an error correction code to the transmission data generated in the CPU 10, and sends the transmission data including the error correction code to the code conversion unit 113. For example, the error correction code adding unit 111 generates an error correction code based on the transmission data, and adds the generated error correction code to the transmission data. As the error correction code, for example, a cyclic redundancy checking (CRC) code, a forward error correction (FEC) code, etc. can be used.

[0012] The modulation method control unit 112 controls the modulation method used for data transmission (communication with the wireless communication device 120). Specifically, the modulation method control unit 112 repeatedly performs modulation method control including a process of determining the modulation method used for data transmission. The modulation method control unit 112 performs modulation method control, for example, at a predetermined time interval. The modulation method control unit 112 includes an initial value generation unit 1121, a pseudo-random number generation unit 1122, a modulation method selection unit 1123, and an offset calculation unit 1124.

[0013] The initial value generation unit 1121 generates an initial value (seed value) used for generating an M-sequence pseudo-random number. The initial value is synchronized between the wireless communication devices 110 and 120. That is, the same initial value is generated in the wireless communication devices 110 and 120. As a non-limiting example, at the initial stage in the communication between the wireless communication devices 110 and 120, the initial value generation unit 1121 transmits synchronization data for synchronizing between the wireless communication devices 110 and 120 to the wireless communication device 120. The synchronization data may include data used for generating the initial value and data indicating the timing for performing modulation method control. The synchronization data is transmitted via the error correction code adding unit 111, the code conversion unit 113, the interleaving unit 114, the modulation unit 115, the mixer 116, the transmission unit 118, and the antenna 119. The initial value generation unit 1121 generates an initial value from the synchronization data, and the wireless communication device 120 generates an initial value from the synchronization data received from the wireless communication device 110.

[0014] The pseudo-random number generation unit 1122 generates a plurality of M-sequence pseudo-random number codes having a predetermined bit length based on the initial value generated by the initial value generation unit 1121 and a predetermined M-sequence pseudo-random number generation algorithm. For example, the pseudo-random number generation unit 1122 calculates an M-sequence pseudo-random number from the initial value according to a predetermined M-sequence pseudo-random number generation algorithm, and extracts a plurality of M-sequence pseudo-random number codes having a predetermined bit length from the calculated M-sequence pseudo-random number. In an example where the bit length of the M-sequence pseudo-random number code is 14, the pseudo-random number generation unit 1122 extracts the 1st to 14th bits of the M-sequence pseudo-random number as the 1st M-sequence pseudo-random number code, extracts the 15th to 28th bits of the M-sequence pseudo-random number as the 2nd M-sequence pseudo-random number code, ···, extracts the (14(N - 1)+1)th to (14N)th bits of the M-sequence pseudo-random number as the Nth M-sequence pseudo-random number code, thereby obtaining N M-sequence pseudo-random number codes. That the M-sequence pseudo-random number generation algorithm is predetermined may mean that the same M-sequence pseudo-random number generation algorithm used in the wireless communication device 120 which is the communication partner is implemented in the wireless communication device 110. For example, the same recurrence formula is used in the wireless communication device 110 and the wireless communication device 120.

[0015] Each M-sequence pseudo-random number code has its first part used by the modulation method selection unit 1123 and its second part used by the offset calculation unit 1124. For example, as shown in FIG. 2, the upper 2 bits of the M-sequence pseudo-random number code are used by the modulation method selection unit 1123, and the lower 12 bits of the M-sequence pseudo-random number code are used by the offset calculation unit 1124.

[0016] Referring to FIG. 1 again, the modulation method selection unit 1123 selects a modulation method to be used for data transmission from a plurality of predetermined modulation methods based on the first part of the M-sequence pseudo-random number code generated by the pseudo-random number generation unit 1122. Specifically, the modulation method selection unit 1123 selects, from a plurality of predetermined modulation methods, the modulation method corresponding to the first part of the M-sequence pseudo-random number code as the modulation method to be used for data transmission. For example, four digital modulation methods, namely, binary phase shift keying (BPSK), ternary phase shift keying (TPSK), quadrature phase shift keying (QPSK), and 16-position quadrature amplitude modulation (16QAM), can be used. BPSK, QPSK, and 16QAM are examples of phase modulation methods based on powers of 2, and TPSK is an example of a phase modulation method not based on powers of 2. A modulation method not based on powers of 2 is a modulation method that assigns information bits to a number of symbols (signal points) not equal to a power of 2. For example, when the upper two bits of the M-sequence pseudo-random number code are "00", the modulation method selection unit 1123 selects BPSK; when the upper two bits are "01", it selects TPSK; when the upper two bits are "10", it selects QPSK; and when the upper two bits are "11", it selects 16QAM. Not only can the modulation method be selected, but the M-sequence pseudo-random number code can also be applied to the modulation method itself. For example, in the case of differential code transmission using a phase difference such as differential quadrature phase shift keying (DPQSK), the phase difference offset can be determined based on a part of the M-sequence pseudo-random number code to change (add or subtract) the phase difference.

[0017] Note that the number of modulation schemes is not limited to four, and may be two, three, or five or more. For example, when three modulation schemes, namely BPSK, TPSK, and QPSK, can be used, the modulation scheme selection unit 1123 may select BPSK when the upper two bits of the M-sequence pseudo-random number code are "00", select TPSK when the upper two bits of the M-sequence pseudo-random number code are "01", and select QPSK when the upper two bits of the M-sequence pseudo-random number code are "10" or "11".

[0018] The offset calculation unit 1124 calculates an offset for use in primary modulation (specifically, mapping) based on the second part of the M-sequence pseudo-random number code generated by the pseudo-random number generation unit 1122. The offset indicates the amount of shift from the origin of the IQ plane, which is a complex plane, and includes an offset of the I (In-phase) axis and an offset of the Q (Quadrature phase) axis. For example, the offset calculation unit 1124 calculates the I-axis offset based on the middle 6 bits (the 3rd bit to the 8th bit) of the M-sequence pseudo-random number code, and calculates the Q-axis offset based on the lower 6 bits (the 9th bit to the 14th bit) of the M-sequence pseudo-random number code. As an example, the offset calculation unit 1124 holds a conversion table associating a bit string with a bit length of 6 with an offset value, and obtains the I-axis offset by converting the middle 6 bits of the M-sequence pseudo-random number code into an offset value using the conversion table, and obtains the Q-axis offset by converting the lower 6 bits of the M-sequence pseudo-random number code into an offset value using the conversion table.

[0019] The code conversion unit 113 receives transmission data including an error correction code from the error correction code addition unit 111, and performs code conversion on the transmission data to obtain encoded data. The code conversion includes, for example, bit rate limitation and convolutional coding.

[0020] The interleaving unit 114 receives the encoded data from the code conversion unit 113, and performs interleaving on the encoded data.

[0021] The modulation unit 115 modulates the bit sequence output from the interleaving unit 114 based on the modulation method selected by the modulation method selection unit 1123 and the offset calculated by the offset calculation unit 1124 to generate a complex signal. The complex signal includes two-channel electrical signals also referred to as the I signal and the Q signal. Specifically, the modulation unit 115 performs primary modulation including mapping to the IQ plane obtained by shifting the origin of the IQ plane where signal points corresponding to the modulation method selected by the modulation method selection unit 1123 are arranged by the offset calculated by the offset calculation unit 1124 on the bit sequence. Shifting the origin of the IQ plane by the offset corresponds to shifting each signal point on the IQ plane by the reciprocal of the offset. Let the I-axis offset be O I , and the Q-axis offset be O Q . Then, in QPSK, for example, the information "11" is mapped to the signal point (1 - O I , 1 - O Q ), the information "01" is mapped to the signal point (-1 - O I , 1 - O Q ), the information "10" is mapped to the signal point (1 - O I , -1 - O Q ), and the information "00" is mapped to the signal point (-1 - O I , -1 - O Q ). In this case, the I signal is a signal that changes with two values corresponding to 1 - O I、 - 1 - O I , and the Q signal is a signal that changes with two values corresponding to 1 - O Q , -1 - O Q .

[0022] The mixer 116 generates a modulated signal from the complex signal using the carrier wave generated by the carrier oscillator 117. For example, the mixer 116 includes a first multiplier, a second multiplier, and a combiner, multiplies the carrier wave by the I signal in the first multiplier, multiplies the carrier wave with its phase shifted by 90 degrees by the Q signal in the second multiplier, and synthesizes the output of the first multiplier and the output of the second multiplier in the combiner.

[0023] The transmission unit 118 wirelessly transmits the modulation signal generated by the mixer 116. For example, the transmission unit 118 performs secondary modulation including an inverse fast Fourier transform (IFFT) on the modulation signal to generate a wireless signal, and transmits the wireless signal via the antenna 119.

[0024] The wireless communication device 120 receives the wireless signal transmitted by the wireless communication device 110. The wireless communication device 120 performs processing complementary to the processing executed by the wireless communication device 110. The wireless communication device 120 includes, as hardware components, a CPU 20, a memory (not shown), and a communication module 21. The wireless communication device 120 may be movable.

[0025] The wireless communication device 120 includes an error correction unit 121, a modulation method control unit 122, a de - coding unit 123, an interleaving unit 124, a demodulation unit 125, a mixer 126, a carrier oscillator 127, a reception unit 128, and an antenna 129. In the present embodiment, these are implemented in the communication module 21. In other embodiments, the processing performed in some of these may be realized by the CPU 20. For example, when the CPU 20 executes a program stored in the memory, it functions as the error correction unit 121 and the like.

[0026] The reception unit 128 receives the wireless signal from the wireless communication device 110 via the antenna 129. The reception unit 128 performs secondary demodulation including a fast Fourier transform (FFT) on the wireless signal to generate a demodulated signal.

[0027] The mixer 126 generates a complex signal from the demodulated signal generated by the reception unit 128 using the carrier wave generated by the carrier oscillator 127. For example, the mixer 126 includes a splitter, a first multiplier, and a second multiplier. The mixer 126 bifurcates the demodulated signal in the splitter, multiplies one of the demodulated signals by the carrier wave in the first multiplier to generate an I signal, and multiplies the other demodulated signal by the carrier wave with a 90 - degree phase shift in the second multiplier to generate a Q signal.

[0028] The modulation method control unit 122 controls the modulation method used for data reception (communication with the wireless communication device 110). For example, the modulation method control unit 122 repeatedly performs modulation method control including a process of determining the modulation method used for data reception. The modulation method control unit 122 includes an initial value generation unit 1221, a pseudo-random number generation unit 1222, a modulation method selection unit 1223, and a threshold setting unit 1224. The initial value generation unit 1221, the pseudo-random number generation unit 1222, and the modulation method selection unit 1223 each perform the same processes as the initial value generation unit 1121, the pseudo-random number generation unit 1122, and the modulation method selection unit 1123 of the wireless communication device 110. Therefore, detailed descriptions of the initial value generation unit 1221, the pseudo-random number generation unit 1222, and the modulation method selection unit 1223 are omitted.

[0029] The initial value generation unit 1221 generates an initial value (seed value) used to generate an M-sequence pseudo-random number. For example, the initial value generation unit 1221 generates an initial value from the synchronization data transmitted by the wireless communication device 110. The initial value generation unit 1221 obtains the synchronization data from the wireless communication device 110 via the antenna 129, the reception unit 128, the mixer 126, the demodulation unit 125, the deinterleaving unit 124, the code inverse conversion unit 123, and the error correction unit 121.

[0030] The pseudo-random number generation unit 1222 generates a plurality of M-sequence pseudo-random number codes having a predetermined bit length based on the initial value generated by the initial value generation unit 1221 and a predetermined M-sequence pseudo-random number generation algorithm. The pseudo-random number generation unit 1222 uses the same initial value and M-sequence pseudo-random number generation algorithm as those used by the pseudo-random number generation unit 1122 of the wireless communication device 110, thereby obtaining the same M-sequence pseudo-random number codes as those generated by the pseudo-random number generation unit 1122.

[0031] The modulation method selection unit 1223 selects a modulation method to be used for data reception from a plurality of predetermined modulation methods based on the first part (for example, the upper 2 bits) of the M-sequence pseudo-random number code generated by the pseudo-random number generation unit 1222. The modulation method selection unit 1223 performs modulation method selection according to the same selection rule as the modulation method selection unit 1123 of the wireless communication device 110.

[0032] The threshold setting unit 1224 sets a plurality of thresholds (base values) to be used for primary demodulation (specifically, demapping) based on the modulation method selected by the modulation method selection unit 1223, based on the second part of the M-sequence pseudo-random number code generated by the pseudo-random number generation unit 1222. The threshold setting unit 1224 performs offset calculation according to the same calculation rule as the offset calculation unit 1124 of the wireless communication device 110 to obtain an offset, and subtracts the offset from the thresholds on the IQ plane corresponding to the modulation method selected by the modulation method selection unit 1223. The thresholds include the thresholds of the I-axis and the Q-axis, and the threshold setting unit 1224 subtracts the I-axis offset from each of the thresholds of the I-axis and subtracts the Q-axis offset from each of the thresholds of the Q-axis.

[0033] The modulation method control unit 122 of the wireless communication device 120 performs modulation method control in synchronization with the modulation method control unit 112 of the wireless communication device 110. For example, the modulation method control unit 122 performs modulation method control in the same cycle as the cycle in which the modulation method control unit 112 performs modulation method control and according to the same method as the modulation method control unit 112. Thereby, the wireless communication device 120 uses the same modulation method as the modulation method used by the wireless communication device 110 and thresholds that match the offset used by the wireless communication device 110 for primary demodulation.

[0034] The demodulation unit 125 demodulates the complex signal output from the mixer 126 based on the modulation method selected by the modulation method selection unit 1223 and the threshold value set by the threshold value setting unit 1224 to generate a bit sequence. For example, the demodulation unit 125 performs primary demodulation including demapping using the modulation method selected by the modulation method selection unit 1223 and the threshold value set by the threshold value setting unit 1224 on the complex signal. When soft decision decoding is performed in the subsequent inverse coding unit 123, the bit sequence output from the demodulation unit 125 includes soft decision values.

[0035] The deinterleaving unit 124 performs deinterleaving on the bit sequence output from the demodulation unit 125.

[0036] The inverse coding unit 123 performs inverse coding on the bit sequence output from the deinterleaving unit 124 to generate data. The inverse coding includes, for example, bit rate limitation and Viterbi decoding. For example, the inverse coding unit 123 performs soft decision Viterbi decoding according to the modulation method selected by the modulation method selection unit 1223.

[0037] The error correction unit 121 performs error correction on the data generated by the inverse coding unit 123 to obtain the received data.

[0038] Next, the operation of the wireless communication system 100 will be described.

[0039] Figure 3 schematically shows a data transmission method executed by the wireless communication device 110.

[0040] In step S31 of Figure 3, the modulation method control unit 112 generates N M-sequence pseudo-random number codes having a predetermined bit length. For example, the initial value generation unit 1121 generates an initial value, the pseudo-random number generation unit 1122 generates an M-sequence pseudo-random number using the generated initial value, and the generated M-sequence pseudo-random number is segmented to obtain N M-sequence pseudo-random number codes. The pseudo-random number generation unit 1122 assigns identifiers (1 to N) to the N M-sequence pseudo-random number codes.

[0041] In step S32, the modulation method control unit 112 initializes the variable i. For example, the modulation method control unit 112 sets the variable i to 1.

[0042] In step S33, the modulation method control unit 112 selects the M-sequence pseudo-random number code with the identifier i from among the N M-sequence pseudo-random number codes.

[0043] In step S34, the modulation method control unit 112 determines the modulation method and offset to be used for data transmission based on the M-sequence pseudo-random number code selected in step S33. For example, the modulation method selection unit 1123 selects the modulation method corresponding to the upper 2 bits of the M-sequence pseudo-random number code from among BPSK, TPSK, QPSK, and 16QAM. Further, for example, the offset calculation unit 1124 calculates the I-axis offset based on the middle 6 bits of the M-sequence pseudo-random number code and calculates the Q-axis offset based on the lower 6 bits of the M-sequence pseudo-random number code.

[0044] In step S35, the wireless communication device 110 performs data transmission using the modulation method and offset determined in step S34. For example, the code conversion unit 113 performs code conversion on the transmission data to obtain a bit sequence as encoded data, the interleaving unit 114 performs interleaving on the bit sequence output from the code conversion unit 113, the modulation unit 115 performs primary modulation on the bit sequence output from the interleaving unit 114 based on the modulation method and offset determined in step S34, the mixer 116 generates a modulated wave from the complex signal output from the modulation unit 115 using the carrier wave output from the carrier oscillator 117, and the transmission unit 118 converts the modulated wave into a radio signal and transmits it via the antenna 119. For example, the modulation unit 115 performs modulation including mapping to the IQ plane obtained by shifting the origin of the IQ plane having signal points corresponding to the modulation method determined in step S34 by the offset determined in step S34 on the bit sequence.

[0045] In step S36, the modulation method control unit 112 determines whether a predetermined time has elapsed since the process of step S43 was executed. If the predetermined time has not elapsed (step S36; No), the wireless communication device 110 continues data transmission. When the predetermined time has elapsed (step S36; Yes), the flow proceeds to step S37.

[0046] In step S37, the modulation method control unit 112 determines whether the variable i is equal to N. If the variable i is smaller than N (step S37; No), the flow proceeds to step S38, and the wireless communication device 110 increments the variable i by 1. Thereafter, the flow returns to step S33, and the processes after step S33 are repeated.

[0047] If the variable i is equal to N (step S37; Yes), the flow ends. For example, the flow shown in FIG. 3 is executed again.

[0048] In this way, the wireless communication device 110 performs data transmission while switching the modulation method from moment to moment.

[0049] FIG. 4 schematically shows a data reception method executed by the wireless communication device 120.

[0050] In step S41 of FIG. 4, the pseudo-random number generation unit 1222 generates N M-sequence pseudo-random number codes having a predetermined bit length, and assigns identifiers (1 to N) to the N M-sequence pseudo-random number codes.

[0051] In step S42, the modulation method control unit 122 sets the variable i to 1.

[0052] In step S43, the modulation method control unit 122 selects the M-sequence pseudo-random number code whose identifier is i from among the N M-sequence pseudo-random number codes.

[0053] In step S44, the modulation method control unit 122 determines the modulation method and threshold value to be used for data reception based on the M-sequence pseudo-random number code selected in step S43. For example, the modulation method selection unit 1223 selects a modulation method corresponding to the upper 2 bits of the M-sequence pseudo-random number code from among BPSK, TPSK, QPSK, and 16QAM. Further, for example, the threshold value setting unit 1224 calculates the I-axis offset based on the middle 6 bits of the M-sequence pseudo-random number code, shifts the threshold value of the I-axis corresponding to the modulation method selected by the modulation method selection unit 1223 by the reciprocal of the I-axis offset, calculates the Q-axis offset based on the lower 6 bits of the M-sequence pseudo-random number code, and shifts the threshold value of the Q-axis corresponding to the modulation method selected by the modulation method selection unit 1223 by the reciprocal of the Q-axis offset.

[0054] In step S45, the wireless communication device 120 performs data reception using the modulation method and offset determined in step S44. For example, the receiving unit 128 demodulates the wireless signal received via the antenna 129 to obtain a demodulated wave, the mixer 126 generates a complex signal from the demodulated wave using the carrier wave output from the carrier oscillator 127, the demodulating unit 125 performs demodulation based on the modulation method and threshold value determined in step S44 on the complex signal, the deinterleaving unit 124 performs deinterleaving on the bit sequence output from the demodulating unit 125, and the inverse coding unit 123 performs inverse coding on the bit sequence output from the deinterleaving unit 124 to obtain data. For example, the demodulating unit 125 performs demodulation including demapping using the threshold value determined in step S44 on the complex signal.

[0055] In step S46, the modulation method control unit 122 determines whether or not a predetermined time has elapsed since the processing of step S43 was executed. If the predetermined time has not elapsed (step S46; No), the wireless communication device 120 continues data reception. When the predetermined time has elapsed (step S46; Yes), the flow proceeds to step S47.

[0056] In step S47, the modulation method control unit 122 determines whether the variable i is equal to N. If the variable i is smaller than N (step S47; No), the flow proceeds to step S48, and the modulation method control unit 122 increments the variable i by 1. Thereafter, the flow returns to step S43, and the processes after step S43 are repeated.

[0057] If the variable i is equal to N (step S47; Yes), the flow ends. For example, the flow shown in FIG. 4 is executed again.

[0058] In this way, the wireless communication device 120 receives data while switching the modulation method from moment to moment. The data transmission method shown in FIG. 3 and the data reception method shown in FIG. 4 are executed synchronously with each other. For this reason, the wireless communication device 120 can correctly demodulate the radio signal transmitted by the wireless communication device 110.

[0059] As described above, the wireless communication device 110 transmits data while switching the modulation method from moment to moment, and the wireless communication device 120 receives data using the same modulation method as the modulation method used by the wireless communication device 110. Thereby, while the legitimate recipient, the wireless communication device 120, can correctly demodulate the radio signal transmitted by the wireless communication device 110, it becomes difficult for an eavesdropper, who is an unauthorized recipient, to demodulate. As a result, the security of wireless communication can be improved.

[0060] Generally, as a modulation method using phase modulation, a modulation method based on a power of 2 such as BPSK or QPSK is very often used. Therefore, if data transmission is performed by interweaving a modulation method not based on a power of 2 (for example, TPSK), the demodulation pattern increases dramatically, making it more difficult for an eavesdropper to demodulate. In the present embodiment, the modulation method is switched among a plurality of modulation methods including a modulation method not based on a power of 2. Thereby, the security of wireless communication can be further improved.

[0061] Furthermore, the wireless communication device 110 transmits data while changing the offset moment by moment, and the wireless communication device 120 receives data by changing the threshold value with the same offset value as the offset used by the wireless communication device 110. Therefore, the wireless communication device 120 can correctly demodulate the wireless signal transmitted by the wireless communication device 110. On the other hand, eavesdroppers will receive the wireless signal without being able to grasp the change in the threshold value, and the received IQ value is likely to deviate from the ideal concentric circle shape and result in a reception error. In this way, only legitimate receivers can easily return to the normal constellation. As a result, the security of wireless communication can be further improved.

[0062] A modification of the first embodiment will be described.

[0063] FIG. 5 schematically shows a wireless communication system 500 according to a modification of the first embodiment. In FIG. 5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate. As shown in FIG. 5, the wireless communication system 500 includes a wireless communication device 510 and a wireless communication device 520. Here, it is assumed that the wireless communication device 510 is on the data transmission side and the wireless communication device 520 is on the data reception side.

[0064] The wireless communication device 510 corresponds to the wireless communication device 110 shown in FIG. 1 with a signal point pattern selection unit 1125 added. The signal point pattern selection unit 1125 is included in the modulation method control unit 112 of the wireless communication device 510. With the addition of the signal point pattern selection unit 1125, the processing in some components is changed.

[0065] The pseudo-random number generation unit 1122 generates a plurality of M-sequence pseudo-random number codes having a predetermined bit length based on the initial value generated by the initial value generation unit 1121 and a predetermined M-sequence pseudo-random number generation algorithm. For example, assume that the bit length of the M-sequence pseudo-random number code is 16. Each M-sequence pseudo-random number code may have its first part used by the modulation method selection unit 1123, its second part used by the offset calculation unit 1124, and its third part used by the signal point pattern selection unit 1125. For example, the upper 2 bits of the M-sequence pseudo-random number code are used by the modulation method selection unit 1123, the middle 12 bits of the M-sequence pseudo-random number code are used by the offset calculation unit 1124, and the lower 2 bits of the M-sequence pseudo-random number code are used by the signal point pattern selection unit 1125.

[0066] The signal point pattern selection unit 1125 selects a signal point pattern corresponding to the third part of the M-sequence pseudo-random number code generated by the pseudo-random number generation unit 1122 from among a plurality of pre-prepared signal point patterns. The signal point pattern indicates a pattern regarding the arrangement (constellation) of signal points on the IQ plane. The plurality of pre-prepared signal point patterns include a plurality of signal point patterns for each modulation method. When the modulation method selection unit 1123 selects QPSK, the signal point pattern selection unit 1125 selects a signal point pattern corresponding to the third part of the M-sequence pseudo-random number code from among the plurality of signal point patterns regarding QPSK.

[0067] Multiple signal point patterns related to QPSK may include four multiple signal point patterns. As an example, in the first signal point pattern related to QPSK, the information "11" is associated with the signal point (1, 1), the information "01" is associated with the signal point (-1, 1), the information "10" is associated with the signal point (1, -1), and the information "00" is associated with the signal point (-1, -1). In the second signal point pattern related to QPSK, the information "11" is associated with the signal point (-1, 1), the information "01" is associated with the signal point (1, 1), the information "10" is associated with the signal point (-1, -1), and the information "00" is associated with the signal point (-1, 1). In the third signal point pattern related to QPSK, the information "11" is associated with the signal point (1, -1), the information "01" is associated with the signal point (-1, -1), the information "10" is associated with the signal point (1, 1), and the information "00" is associated with the signal point (1, -1). In the fourth signal point pattern related to QPSK, the information "11" is associated with the signal point (-1, -1), the information "01" is associated with the signal point (1, -1), the information "10" is associated with the signal point (-1, 1), and the information "00" is associated with the signal point (1, 1).

[0068] The modulation unit 115 modulates the bit sequence output from the interleaving unit 114 based on the modulation method selected by the modulation method selection unit 1123, the offset calculated by the offset calculation unit 1124, and the signal point pattern selected by the signal point pattern selection unit 1125 to generate a complex signal. Specifically, the modulation unit 115 performs primary modulation including mapping to the IQ plane obtained by shifting the origin of the IQ plane where the signal points corresponding to the modulation method selected by the modulation method selection unit 1123 are arranged in the signal point pattern selected by the signal point pattern selection unit 1125 by the offset calculated by the offset calculation unit 1124 on the bit sequence.

[0069] The wireless communication device 520 receives the wireless signal transmitted by the wireless communication device 510. The wireless communication device 520 performs processing complementary to the processing executed by the wireless communication device 510. The wireless communication device 520 corresponds to the one obtained by changing the threshold setting unit 1224 to the threshold setting unit 1225 in the wireless communication device 120 shown in FIG. 1. The threshold setting unit 1225 is included in the modulation method control unit 122 of the wireless communication device 520. With the addition of the threshold setting unit 1225, the processing in some components is changed.

[0070] The threshold setting unit 1225 sets a threshold for primary demodulation based on the modulation method selected by the modulation method selection unit 1223, based on the second and third parts of the M-sequence pseudo-random number code generated by the pseudo-random number generation unit 1122. For example, the threshold setting unit 1225 calculates an offset according to the same calculation rule as the offset calculation unit 1124 of the wireless communication device 510, and selects a threshold pattern corresponding to the third part of the M-sequence pseudo-random number code from among a plurality of pre-prepared threshold patterns. The plurality of threshold patterns are prepared according to the plurality of signal point patterns held in the wireless communication device 510. Specifically, each threshold pattern may include a plurality of thresholds (for example, soft decision thresholds) used to demodulate a signal modulated using the corresponding signal point pattern. Changing the threshold pattern corresponds to an operation of swapping thresholds, as shown in FIG. 6. In FIG. 6, the thresholds on the I-axis are shown, and the thresholds on the Q-axis are omitted. The threshold setting unit 1225 selects a threshold pattern corresponding to the third part of the M-sequence pseudo-random number code from among a plurality of threshold patterns related to the modulation method selected by the modulation method selection unit 1223, and changes the thresholds included in the selected threshold pattern according to the calculated offset.

[0071] Referring to FIG. 5 again, the demodulation unit 125 performs primary demodulation on the complex signal output from the mixer 126 based on the modulation method selected by the modulation method selection unit 1223 and the threshold set by the threshold setting unit 1225, and generates a bit sequence.

[0072] In a modification of the first embodiment, the wireless communication device 510 performs data transmission while changing the signal point pattern from moment to moment, and the wireless communication device 520 performs data reception using a threshold value that conforms to the signal point pattern used by the wireless communication device 110. Therefore, while the wireless communication device 520 can correctly demodulate the wireless signal transmitted by the wireless communication device 510, the possibility of reception error is even higher for eavesdroppers. As a result, the security of wireless communication can be further improved.

[0073] (Second Embodiment) The communication method described above is also applicable to an optical communication system.

[0074] FIG. 7 schematically shows an optical communication system 700 according to the second embodiment. As shown in FIG. 7, the optical communication system 700 includes an optical communication device 710 and an optical communication device 720. The optical communication device 710 is connected to the optical communication device 720 via an optical transmission line 730 such as an optical fiber. Here, it is assumed that the optical communication device 710 is on the data transmission side and the optical communication device 720 is on the data reception side. In FIG. 7, the components related to data transmission are shown in the optical communication device 710, and the components related to data reception are shown in the optical communication device 720. Each of the optical communication devices 710 and 720 may include both components related to data transmission and components related to data reception.

[0075] The optical communication device 710 includes a code conversion unit 711, a modulation method control unit 712, a modulation unit 713, an electrical amplification circuit 714, an E / O (Electrical / Optical) converter 715, an electrical amplification circuit 716, an E / O converter 717, and a coupler 718.

[0076] The modulation method control unit 712 performs the same processing as the modulation method control unit 112 shown in FIG. 1. For example, the modulation method control unit 712 generates an initial value used to generate an M-sequence pseudo-random number. The initial value is synchronized between the optical communication devices 710 and 720. For example, at the initial stage of communication between the optical communication devices 710 and 720, the modulation method control unit 712 transmits synchronization data for synchronization to the optical communication device 720 and generates an initial value from the synchronization data.

[0077] Based on the generated initial value and a predetermined M-sequence pseudo-random number generation algorithm, the modulation method control unit 712 generates a plurality of M-sequence pseudo-random number codes having a predetermined bit length. For example, assume that the bit length of the M-sequence pseudo-random number code is 14. Each M-sequence pseudo-random number code has its first part used for the selection of the modulation method and its second part used for offset calculation.

[0078] The modulation method control unit 712 selects, as the modulation method to be used for data transmission, the modulation method corresponding to the first part of the M-sequence pseudo-random number code from among a plurality of predetermined modulation methods.

[0079] Based on the second part of the M-sequence pseudo-random number code, the modulation method control unit 712 calculates the offset to be used for modulation. The offset indicates the amount by which the signal levels of the two-channel electrical signals output from the modulation unit 713 are shifted and includes the offset for each of the two channels. The offsets of the two channels are referred to as the I-axis offset and the Q-axis offset, respectively. The Q-axis offset corresponds to the amount by which the intensity of the optical signal output from the E / O converter 715 is shifted, and the I-axis offset corresponds to the amount by which the intensity of the optical signal output from the E / O converter 717 is shifted. For example, the modulation method control unit 712 calculates the I-axis offset based on the middle 6 bits (the 3rd bit to the 8th bit) of the M-sequence pseudo-random number code and calculates the Q-axis offset based on the lower 6 bits (the 9th bit to the 14th bit) of the M-sequence pseudo-random number code.

[0080] The code conversion unit 711 performs code conversion on the transmission data. The code conversion includes, for example, convolutional coding.

[0081] Based on the modulation method selected by the modulation method control unit 712 and the offset calculated by the modulation method control unit 712, the modulation unit 713 modulates the bit sequence output from the code conversion unit 711 to generate two-channel electrical signals also referred to as I signals and Q signals.

[0082] The electrical amplifier circuit 714 amplifies the Q signal, and the E / O converter 715 converts the Q signal into an optical signal having a first frequency. The electrical amplifier circuit 716 amplifies the I signal, and the E / O converter 717 converts the I signal into an optical signal having a second frequency different from the first frequency.

[0083] The coupler 718 combines the optical signal output from the E / O converter 715 and the optical signal output from the E / O converter 717. The optical signal output from the coupler 718 is sent to the optical transmission line 730.

[0084] FIG. 8 schematically shows the modulation process according to the second embodiment. Here, for simplicity of explanation, the offset is omitted. As shown in FIG. 8, the modulation unit 713 outputs an electrical signal having a signal level corresponding to the Q-axis coordinate value of the signal point as the Q signal, and the optical signal output from the E / O converter 715 has an intensity corresponding to the signal level of the Q signal. The modulation unit 713 outputs an electrical signal having a signal level corresponding to the I-axis coordinate value of the signal point as the I signal, and the optical signal output from the E / O converter 717 has an intensity corresponding to the signal level of the I signal.

[0085] Referring back to FIG. 7, the optical communication device 720 includes a code inverse conversion unit 721, a modulation method control unit 722, a demodulation unit 723, an O / E (Optical / Electrical) converter 724, a wavelength filter 725, an O / E converter 726, a wavelength filter 727, and a distributor 728.

[0086] The modulation method control unit 722 performs the same processing as the modulation method control unit 122 shown in FIG. 1. For example, the modulation method control unit 722 generates the same M-sequence pseudo-random number code as that generated in the modulation method control unit 712 of the optical communication device 720. The modulation method control unit 712 selects, as the modulation method to be used for data reception, the modulation method corresponding to the first part of the M-sequence pseudo-random number code from among a plurality of predetermined modulation methods. The modulation method control unit 722 calculates an offset based on the second part of the M-sequence pseudo-random number code, and sets a threshold value for demodulation based on the selected modulation method based on the calculated offset.

[0087] The distributor 728 receives an optical signal from the optical communication device 710 via the optical transmission line 730 and bifurcates the optical signal. The wavelength filter 725 extracts an optical signal having a first frequency from the optical signal output from the distributor 728, and the O / E converter 724 converts the optical signal extracted by the wavelength filter 725 into an electrical signal to obtain a Q signal. The wavelength filter 727 extracts an optical signal having a second frequency from the optical signal output from the distributor 728, and the O / E converter 726 converts the optical signal extracted by the wavelength filter 727 into an electrical signal to obtain an I signal.

[0088] The demodulation unit 723 performs the same processing as the demodulation unit 125 shown in FIG. 1. The demodulation unit 723 demodulates the pair of the Q signal output from the O / E converter 724 and the I signal output from the O / E converter 726 based on the modulation method selected by the modulation method control unit 122 and the threshold value set by the modulation method control unit 122. When soft decision decoding is performed in the subsequent code inverse conversion unit 721, the bit sequence output from the demodulation unit 723 includes soft decision values.

[0089] The code inverse conversion unit 721 performs code inverse conversion on the bit sequence output from the demodulation unit 723 to generate received data. The code inverse conversion includes, for example, Viterbi decoding. For example, the code inverse conversion unit 721 performs soft decision Viterbi decoding according to the modulation method selected by the modulation method control unit 122.

[0090] According to the optical communication system 700 according to the second embodiment, similar to the first embodiment, while the legitimate recipient, the optical communication device 720, can normally demodulate the optical signal transmitted by the optical communication device 710, it becomes difficult for an eavesdropper, who is an unauthorized recipient, to demodulate it. As a result, the security of optical communication can be improved.

[0091] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0092] 100…Wireless communication system, 110…Wireless communication device, 10…CPU, 11…Communication module, 111…Error correction coding unit, 112…Modulation method control unit, 1121…Initial value generation unit, 1122…Pseudo-random number generation unit, 1123…Modulation method selection unit, 1124…Offset calculation unit, 1125…Signal point pattern selection unit, 113…Symbol conversion unit, 114…Interleaver, 115…Modulation unit, 116…Mixer, 117…Carrier oscillator, 118…Transmission unit, 119…Antenna, 120…Wireless communication device, 20…CPU, 21…Communication module, 121…Error correction unit, 122…Modulation method control unit, 1221…Initial value generation unit, 1222…Pseudo-random number generation unit, 1223…Modulation method selection unit, 1224, 1225…Threshold setting unit, 123…Symbol inverse conversion unit, 124…Deinterleaver, 125…Demodulation unit, 126…Mixer, 127…Carrier oscillator, 128…Receiving unit, 129…Antenna, 500…Wireless communication system, 510, 520…Wireless communication device, 700…Optical communication system, 710…Optical communication device, 711…Symbol conversion unit, 712…Modulation method control unit, 713…Modulation unit, 714, 716…Electrical amplifier circuit, 715, 717…E / O converter, 718…Coupler, 720…Optical communication device, 721…Symbol inverse conversion unit, 722…Modulation method control unit, 723…Demodulation unit, 724, 726…O / E converter, 725, 727…Wavelength filter, 728…Divider, 730…Optical transmission line.

Claims

1. A communication system comprising a first communication device and a second communication device, wherein the first communication device, repeatedly performs first modulation method control including selecting a first modulation method to be used for data transmission from among a plurality of modulation methods including a modulation method not based on a power of 2, and setting an offset to be used for modulation by the first modulation method; a first modulation method control unit; a modulation unit that performs modulation based on the first modulation method and the offset on a bit string based on transmission data; a transmission unit that transmits the signal obtained by the modulation; and includes, wherein the second communication device, repeatedly performs second modulation method control including selecting a second modulation method to be used for data reception from among the plurality of modulation methods, and setting a threshold value to be used for demodulation by the second modulation method; a second modulation method control unit; a reception unit that receives the signal from the first communication device; a demodulation unit that performs demodulation based on the second modulation method and the threshold value on the signal; and includes, wherein the second modulation method control unit performs the second modulation method control in synchronization with the first modulation method control in the first modulation method control unit, a communication system.

2. The first modulation method control unit generates a plurality of first pseudo-random number codes, In the first modulation method control, the first modulation method control unit selects a first pseudo-random number code from among the plurality of first pseudo-random number codes, selects the first modulation method from among the plurality of modulation methods based on a first part of the first pseudo-random number code, and calculates the offset based on a second part of the first pseudo-random number code, The second modulation method control unit generates a plurality of second pseudo-random number codes identical to the plurality of first pseudo-random number codes, In the second modulation method control, the second modulation method control unit selects a second pseudo-random number code from among the plurality of second pseudo-random number codes, selects the second modulation method from among the plurality of modulation methods based on a first part of the first pseudo-random number code, and sets the threshold value based on a second part of the second pseudo-random number code. The communication system according to claim 1.

3. The modulation method not based on the power of 2 is three-phase phase modulation (TPSK). The communication system according to claim 1 or 2.

4. The offset is an offset indicating an amount of shifting the origin of the IQ plane, The modulation unit performs the modulation including mapping to an IQ plane obtained by shifting the origin of the IQ plane where signal points corresponding to the first modulation method are arranged by the offset for the bit sequence. The transmission unit wirelessly transmits the signal to the second communication device. The communication system according to any one of claims 1 to 3.

5. The first modulation method control further includes selecting a signal point pattern to be used for data transmission from among a plurality of signal point patterns. The modulation unit performs the modulation including mapping to an IQ plane obtained by shifting the origin of the IQ plane where the signal points corresponding to the first modulation method are arranged in the signal point pattern by the offset for the bit sequence. The communication system according to claim 4.

6. The modulation unit obtains a first electrical signal and a second electrical signal by the modulation. The transmitting unit performs electro-optical conversion on the first electrical signal to obtain a first optical signal having a first frequency, performs electro-optical conversion on the second electrical signal to obtain a second optical signal having a second frequency different from the first frequency, combines the first optical signal and the second optical signal to generate a third optical signal, and transmits the third optical signal to the second communication device. The communication system according to any one of claims 1 to 3.

7. A modulation method control unit that repeatedly performs modulation method control including selecting a modulation method to be used for data transmission from among a plurality of modulation methods including a modulation method not based on a power of 2, and calculating an offset to be used for modulation by the modulation method; A modulation unit that performs modulation on a bit string based on transmission data according to the modulation method and the offset; A transmitting unit that transmits a signal obtained by the modulation to another communication device; A communication device comprising:

8. A modulation method control unit that repeatedly performs modulation method control including selecting a modulation method to be used for data reception from among a plurality of modulation methods, and setting a threshold value to be used for demodulation by the modulation method; A receiving unit that receives a signal from another communication device; A demodulation unit that performs demodulation on the signal according to the modulation method and the threshold value; A communication device comprising:

9. The first communication device repeatedly performs first modulation method control including selecting a first modulation method to be used for data transmission from among a plurality of modulation methods including a modulation method not based on a power of 2, and setting an offset to be used for modulation by the first modulation method; The first communication device performs modulation on a bit string based on transmission data according to the first modulation method and the offset; The first communication device transmits a signal obtained by the modulation; The second communication device repeatedly performs second modulation method control including selecting a second modulation method to be used for data reception from among the plurality of modulation methods and setting a threshold value to be used for demodulation by the second modulation method. The second communication device receives the signal from the first communication device. The second communication device demodulates the signal based on the second modulation method and the threshold value. and comprises The second communication device performs the second modulation method control in synchronization with the first modulation method control in the first communication device. Communication method.

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