MIMO cross-layer secure communication system and method based on spatial modulation and upper-layer key stream
Technical Field
The invention belongs to the technical field of wireless communication system safety, and particularly relates to a MIMO cross-layer safety communication system and method based on spatial modulation and upper-layer key stream.
Background
The openness and the broadcast of a wireless channel enable communication information of a legal user to be easily monitored or intercepted by an illegal user and an eavesdropper, and because the traditional safety communication is established on a physical layer and is based on the calculation of a password-unbreakable safety measure, even though the current development of the safety transmission research of the physical layer is inexhaustible, the communication system has great dependence on the environment, has the statistical property that the safety performance with the probability of 1 cannot be ensured, and cannot meet the safety requirement of an actual system; therefore, cross-layer enhanced security techniques for wireless communication have become a research hotspot.
The Multiple Input Multiple Output (MIMO) technology adopts a plurality of antennas to transmit a plurality of data streams in parallel, and can greatly increase the capacity of a channel and the utilization rate of a frequency spectrum on the premise of not increasing the bandwidth; however, in the MIMO system, due to wireless dispersion, mutual interference between multipath and channels, and difficulty in synchronization, the error code rate of the receiver is increased sharply when decoding the transmitted information, and the reliability of communication is poor due to high cost and overhead.
The spatial modulation technology well makes up the defects of an MIMO system, and is different from the traditional space-time code in that the antenna serial number is used as an extra carrier for bearing information bits; only one transmitting end antenna in the same time slot is in an activated state and used for transmitting the modulated residual information, and a receiving end needs to complete the estimation of the activated antenna serial number and the demodulation of a transmission symbol; the spatial modulation avoids the problems of inter-channel interference generated when a plurality of antennas transmit signals simultaneously and synchronization of the transmitting antennas, greatly improves the frequency spectrum utilization rate and also saves the system cost; as shown in fig. 1, which is a schematic diagram of conventional spatial modulation, a part of a binary signal source sequence is used for digital signal modulation, and another part is used for antenna sequence number mapping, and due to randomness of a wireless communication channel, a receiving end correctly decodes a transmitted information stream through differences between channels; the method has the advantages of ICI and IAS elimination, low error rate, low cost, high energy efficiency and the like; the spatial modulation can be combined with large MIMO with hundreds of antennas at the future transmitting end, and can be used in the future 5G wireless communication system.
However, the MIMO spatial modulation technique still has certain defects in information security, and ensuring the information security of the MIMO spatial modulation system becomes a problem to be solved.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a MIMO cross-layer secure communication system and a method based on spatial modulation and an upper-layer key stream.
The purpose of the invention is realized by the following technical scheme: the MIMO cross-layer secure communication system based on spatial modulation and upper key stream comprises a transmitting end, a receiving end, a control sequence generating end and a wireless channel;
the control sequence generating terminal is used for generating an antenna control sequence ZNTAnd a symbol control sequence Fmod;
The wireless channel is used for data transmission between the transmitting end and the receiving end;
the transmitting terminal comprises an information source, an SM safety modulation module, a digital-to-analog conversion module and a radio frequency transmitting module; the signal source is used for inputting a signal sequence for the SM security modulation module; the SM safety modulation module is used for controlling the sequence Z according to the antennaNTAnd a symbol control sequence FmodPerforming cross-layer spatial modulation on an input signal sequence to obtain an antenna mapping serial number and modulation data; the digital-to-analog conversion module is used for performing digital-to-analog conversion on the modulation data; the radio frequency transmitting module is used for activating the corresponding antenna according to the antenna mapping serial number and transmitting the data after the digital-to-analog conversion to a wireless channel;
the receiving end comprises a radio frequency receiving module, an analog-to-digital conversion module, a signal detection and estimation module and an SM safety demodulation module; the radio frequency receiving module is used for receiving data from a wireless channel; the analog-to-digital conversion module is used for performing analog-to-digital conversion on the received data, and the signal detection and estimation module is used for detecting and estimating the data obtained by the analog-to-digital conversion; the SM safety demodulation module is used for controlling the sequence Z according to the antennaNTAnd a symbol control sequence FmodAnd performing cross-layer spatial demodulation on the data obtained by detection and estimation, and outputting the data.
The antenna control sequence ZNTAnd a symbol control sequence FmodAn upper layer key stream pre-shared by both parties of legal communication; the two communication parties select to be a transmitting end or a receiving end according to requirements.
The SM safety modulation module comprises a serial-parallel conversion submodule, an antenna sequence number mapping submodule and a digital modulation submodule; the serial-parallel conversion sub-module is used for dividing the signal sequence from the signal source into two groups of sequences of antenna information and transmission information,outputting the antenna information to an antenna sequence number mapping submodule and outputting the transmission information to a digital modulation submodule; the antenna sequence number mapping submodule is used for mapping the antenna sequence number according to the antenna control sequence ZNTMapping the antenna serial number of the antenna information; the digital modulation submodule is used for controlling the sequence F according to the symbolmodThe transmission information is subjected to conventional digital modulation or modified digital modulation.
The SM safety demodulation module comprises an antenna serial number demapping submodule, a digital demodulation submodule and a parallel-serial conversion submodule; the antenna sequence number demapping submodule is used for demapping the estimated antenna sequence number according to the antenna control sequence to obtain antenna information; the digital demodulation submodule is used for carrying out conventional digital demodulation or deformation digital demodulation on the data after detection and estimation according to the symbol control sequence to obtain transmission information; and the parallel-serial conversion sub-module is used for recombining and outputting the antenna information and the transmission information.
The information source is a binary information source.
The method for carrying out communication in the MIMO cross-layer secure communication system based on the spatial modulation and the upper layer key stream comprises the following steps:
s1, generating an antenna control sequence Z by a control sequence generating endNTAnd a symbol control sequence FmodAnd sharing the generated sequence to the transmitting end and the receiving end;
s2, the transmitting end information source generates a binary information source sequence, and the SM safety modulation module generates a binary information source sequence according to an antenna control sequence ZNTAnd a symbol control sequence FmodPerforming cross-layer spatial modulation on the binary source sequence to obtain an antenna mapping serial number and modulation data;
s3, activating a corresponding antenna by the radio frequency transmitting module according to the antenna mapping sequence number;
s4, the digital-to-analog conversion module performs digital-to-analog conversion on the modulation data, transmits analog signals obtained through conversion to the radio frequency transmitting module, and transmits the analog signals to a wireless channel through an activated antenna;
s5, a radio frequency receiving module of a receiving end receives signals from a wireless channel and performs analog-to-digital conversion on the received signals;
s6, the signal detection and estimation module carries out channel estimation and signal detection and estimation to obtain an antenna serial number and estimation data;
s7.SM Security demodulation Module according to antenna control sequence ZNTAnd a symbol control sequence FmodAnd performing cross-layer spatial demodulation on the antenna serial number and the estimation data, and outputting the data.
The step S2 includes the following sub-steps:
s21, the information source generates a binary information source sequence, and the serial-parallel conversion sub-module divides the binary information source sequence into two groups of sequences of antenna information and transmission information;
s22, in a frame time slot, the antenna serial number mapping submodule detects the antenna control sequence value z at the momentiAnd according to the detection result, the antenna information x is detected1=(a1,a2,…ak) Mapping an antenna sequence number l:
(1) if z isi=0,l=[2k-1,2k-2,…2,1]·x1 T+1;
(2) If z isi=1,l=Nt-[2k-1,2k-2,…2,1]·x1 T;
Wherein k is the number of elements in the antenna information, x1 TFor antenna information x1Transpose of (N)tThe number of the antennas in the radio frequency transmitting module; then, according to the mapping result, sending a signal to a radio frequency transmitting module to activate a number I antenna;
s23, in each symbol period in the same frame time slot as step S22, the digital modulation submodule detects the symbol control sequence value fjAnd transmitting information x for the symbol period according to the detection result2=(ak+1,ak+2,…ak+d) And (3) modulation:
(1) if fjIf the value is 0, carrying out BPSK/QPSK/QAM conventional digital modulation;
(2) if fjIf the signal is 1, performing BPSK/QPSK/QAM conventional digital modulation, and then deforming the obtained symbol to make the mapping bit completely opposite, namely the Hamming distance of the signal is maximum;
wherein d is the number of elements in the transmission information; the modulated data is then input to a digital-to-analog conversion module.
The step S7 includes the following sub-steps:
s71, in a frame time slot, the antenna sequence number demapping submodule checks an antenna control sequence value z at the momentiAnd de-mapping the estimated antenna serial number according to the checking result to obtain the antenna information y1=(b1,b2,…bk):
(1) If z isiDemapping l-1 to binary bits when equal to 0;
(2) if z isi1, adding Nt-l demapping into binary bits;
s72. in each symbol period in the same frame slot as in step S61, the digital demodulation sub-module detects the symbol control sequence value fjAnd demodulating the estimated data of the symbol period according to the checking result to obtain the transmission information y2=(bk+1,bk+2,…bk+d);
(1) If fjIf the value is 0, carrying out BPSK/QPSK/QAM conventional digital demodulation;
(2) if fjIf it is 1, firstly carrying out BPSK/QPSK/QAM conventional digital demodulation, and then deforming the obtained symbol to make the mapping bit completely opposite, i.e. maximum Hamming distance of signal;
s73, the parallel-serial conversion submodule converts the antenna information y1And transmit information y2And (5) recombining and outputting.
The antennaControl sequence ZNTAnd a symbol control sequence FmodAntenna control sequence 1 for upper layer key stream pre-shared by both parties of legal communicationNTControl of mapping/demapping rules of antenna sequence numbers, symbol control sequence FmodRules governing digital modulation/demodulation.
The invention has the beneficial effects that: (1) the MIMO cross-layer secure communication system and method based on spatial modulation and upper-layer key stream combination are provided, and the noise characteristic of a channel is fully utilized by designing a spatial modulation scheme and combining with an upper-layer cryptographic technology under the MIMO spatial modulation system, so that an enhanced wireless communication encryption mode is realized, and information leakage is prevented.
(2) By combining two control sequences shared by both legal communication parties, the spatial domain mapping and the digital modulation are subjected to double cross-layer encryption simultaneously, so that an illegal user is effectively prevented from eavesdropping or intercepting information, and the communication reliability is greatly improved.
(3) Using the key stream as a control sequence to respectively control the mapping/de-mapping rule of the antenna serial number and the rule of digital modulation/demodulation; the legal receiver knows the specific form of the key stream and can judge to adopt a reasonable demodulation algorithm to decode correct transmitting information; however, an illegal eavesdropper does not know that the spatial modulation is cross-layer encrypted, adopts a conventional spatial demodulation method, or guesses two control sequences completely to decode according to a demodulation algorithm similar to that of a legal receiver, and is difficult to recover correct transmitted information.
(4) The invention has good receiving performance for legal users under the condition that the signal-to-noise ratio and the digital modulation mode are changed, and simultaneously, the eavesdropper has stable bit error rate and frame error rate.
Drawings
FIG. 1 is a diagram of a conventional spatial modulation scheme;
FIG. 2 is a schematic block diagram of the system of the present invention;
fig. 3 is a functional block diagram of an SM security modulation module;
FIG. 4 is a functional block diagram of an SM Security demodulation module;
FIG. 5 is a flow chart of a method of the present invention;
fig. 6 is a mapping spatial modulation constellation of a 4-antenna QPSK modulation Gray code;
FIG. 7 is an antenna sequence number mapping table according to an embodiment;
fig. 8 is a schematic diagram illustrating mapping constellation and selection of a warped signal constellation of the Gray code for QPSK modulation according to the first embodiment;
fig. 9 is a mapping table of Gray codes and a mapping table of deformed signals for QPSK modulation according to an embodiment.
FIG. 10 is a diagram of FER performance simulation of a four-transmission four-reception BPSK/QPSK/8PSK modulation system in accordance with the first embodiment;
FIG. 11 is a diagram of BER performance simulation of a four-transmission four-reception BPSK/QPSK/8PSK modulation system in the first embodiment;
fig. 12 is a BER performance simulation diagram of a four-transmission four-reception BPSK/QPSK/8PSK MIMO conventional spatial modulation system according to an embodiment.
Detailed Description
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.
The invention fully utilizes the dual modulation mode of the spatial modulation system to design the controlled spatial modulation; both legal communication parties share a key stream formed by two binary pseudorandom sequences in advance, one key stream is used as an antenna control sequence to control an antenna sequence number mapping/de-mapping rule, and the other key stream is used as a symbol control sequence to control a digital modulation/demodulation rule; the legal receiver knows the specific form of the key stream and can use a reasonable demodulation algorithm to decode the correct transmitted information.
As shown in fig. 2, the MIMO cross-layer secure communication system based on spatial modulation and upper layer key stream includes a transmitting end, a receiving end, a control sequence generating end and a wireless channel;
the control sequence generating end is used for generating a binary pseudorandom antenna control sequence ZNTAnd a symbol control sequence Fmod;
The wireless channel is used for data transmission between the transmitting end and the receiving end;
the transmitting terminal comprises an information source, an SM safety modulation module, a digital-to-analog conversion module and a radio frequency transmitting module; the signal source is used for inputting a signal sequence for the SM security modulation module; the SM safety modulation module is used for controlling the sequence Z according to the antennaNTAnd a symbol control sequence FmodPerforming cross-layer spatial modulation on an input signal sequence to obtain an antenna mapping serial number and modulation data; the digital-to-analog conversion module is used for performing digital-to-analog conversion on the modulation data; the radio frequency transmitting module is used for activating the corresponding antenna according to the antenna mapping serial number and transmitting the data after the digital-to-analog conversion to a wireless channel;
the receiving end comprises a radio frequency receiving module, an analog-to-digital conversion module, a signal detection and estimation module and an SM safety demodulation module; the radio frequency receiving module is used for receiving data from a wireless channel; the analog-to-digital conversion module is used for performing analog-to-digital conversion on the received data, and the signal detection and estimation module is used for detecting and estimating the data obtained by the analog-to-digital conversion; the SM safety demodulation module is used for controlling the sequence Z according to the antennaNTAnd a symbol control sequence FmodAnd performing cross-layer spatial demodulation on the data obtained by detection and estimation, and outputting the data.
The antenna control sequence ZNTAnd a symbol control sequence FmodAn upper layer key stream pre-shared by both parties of legal communication; the two communication parties select to be a transmitting end or a receiving end according to requirements.
As shown in fig. 3, the SM security modulation module includes a serial-to-parallel conversion sub-module, an antenna sequence number mapping sub-module, and a digital modulation sub-module;
the serial-parallel conversion submodule is used for dividing a signal sequence from an information source into two groups of sequences of antenna information and transmission information, outputting the antenna information to the antenna sequence number mapping submodule and outputting the transmission information to the digital modulation submodule; the antenna sequence number mapping submodule is used for mapping the antenna sequence number according to the antenna control sequence ZNTMapping antenna serial numbers of the antenna information to obtain antenna mapping serial numbers, and sending the antenna mapping serial numbers to a radio frequency transmitting module to activate corresponding antennas (the radio frequency transmitting module comprises a plurality of transmitting antennas); the digital modulation submodule is used for controlling the sequence F according to the symbolmodThe transmission information is subjected to conventional digital modulation or deformation digital modulation, and a signal obtained by modulation is transmitted to a wireless channel through an activated antenna after passing through a digital-to-analog conversion module.
As shown in fig. 4, the SM security demodulation module includes an antenna serial number demapping sub-module, a digital demodulation sub-module, and a parallel-serial conversion sub-module;
after receiving the signal from the wireless channel, the rf receiving module (including multiple receiving antennas) performs analog-to-digital conversion on the signal, and then obtains the antenna serial number and the estimated data (i.e., the received transmission information) through the signal detection and estimation module.
The antenna sequence number demapping submodule is used for demapping the estimated antenna sequence number according to the antenna control sequence to obtain antenna information; the digital demodulation submodule is used for carrying out conventional digital demodulation or deformation digital demodulation on the data after detection and estimation according to the symbol control sequence to obtain transmission information; and the parallel-serial conversion sub-module is used for recombining and outputting the antenna information and the transmission information.
The information source is a binary information source.
As shown in fig. 5, the method for performing communication in the MIMO cross-layer secure communication system based on spatial modulation and upper layer key stream includes the following steps:
s1, generating an antenna control sequence Z by a control sequence generating endNTAnd symbol control sequenceFmodAnd sharing the generated sequence to the transmitting end and the receiving end;
s2, the transmitting end information source generates a binary information source sequence, and the SM safety modulation module generates a binary information source sequence according to an antenna control sequence ZNTAnd a symbol control sequence FmodPerforming cross-layer spatial modulation on the binary source sequence to obtain an antenna mapping serial number and modulation data;
s3, activating a corresponding antenna by the radio frequency transmitting module according to the antenna mapping sequence number;
s4, the digital-to-analog conversion module performs digital-to-analog conversion on the modulation data, transmits analog signals obtained through conversion to the radio frequency transmitting module, and transmits the analog signals to a wireless channel through an activated antenna;
s5, a radio frequency receiving module of a receiving end receives signals from a wireless channel and performs analog-to-digital conversion on the received signals;
s6, the signal detection and estimation module carries out channel estimation and signal detection and estimation to obtain an antenna serial number and estimation data;
s7.SM Security demodulation Module according to antenna control sequence ZNTAnd a symbol control sequence FmodAnd performing cross-layer spatial demodulation on the antenna serial number and the estimation data, and outputting the data.
The step S2 includes the following sub-steps:
s21, the information source generates a binary information source sequence, and the serial-parallel conversion sub-module divides the binary information source sequence into two groups of sequences of antenna information and transmission information;
s22, in a frame time slot, the antenna serial number mapping submodule detects the antenna control sequence value z at the momentiAnd according to the detection result, the antenna information x is detected1=(a1,a2,…ak) Mapping an antenna sequence number l:
(1) if z isi=0,l=[2k-1,2k-2,…2,1]·x1 T+1;
(2) If z isi=1,l=Nt-[2k-1,2k-2,…2,1]·x1 T;
Wherein k is the number of elements in the antenna information, x1 TFor antenna information x1Transpose of (N)tThe number of the antennas in the radio frequency transmitting module; then, according to the mapping result, sending a signal to a radio frequency transmitting module to activate a number I antenna;
s23, in each symbol period in the same frame time slot as step S22, the digital modulation submodule detects the symbol control sequence value fjAnd transmitting information x for the symbol period according to the detection result2=(ak+1,ak+2,…ak+d) And (3) modulation:
(1) if fjIf the value is 0, carrying out BPSK/QPSK/QAM conventional digital modulation;
(2) if fjIf the signal is 1, performing BPSK/QPSK/QAM conventional digital modulation, and then deforming the obtained symbol to make the mapping bit completely opposite, namely the Hamming distance of the signal is maximum;
wherein d is the number of elements in the transmission information; the modulated data is then input to a digital-to-analog conversion module.
The step S7 includes the following sub-steps:
s71, in a frame time slot, the antenna sequence number demapping submodule checks an antenna control sequence value z at the momentiAnd de-mapping the estimated antenna serial number according to the checking result to obtain the antenna information y1=(b1,b2,…bk):
(1) If z isiDemapping l-1 to binary bits when equal to 0;
(2) if z isi1, adding Nt-l demapping into binary bits;
s72, in step S61, each symbol period in the same frame time slot, digital demodulation submodelBlock detection symbol control sequence value fjAnd demodulating the estimated data of the symbol period according to the checking result to obtain the transmission information y2=(bk+1,bk+2,…bk+d);
(1) If fjIf the value is 0, carrying out BPSK/QPSK/QAM conventional digital demodulation;
(2) if fjIf it is 1, firstly carrying out BPSK/QPSK/QAM conventional digital demodulation, and then deforming the obtained symbol to make the mapping bit completely opposite, i.e. maximum Hamming distance of signal;
s73, the parallel-serial conversion submodule converts the antenna information y1And transmit information y2And (5) recombining and outputting.
The antenna control sequence ZNTAnd a symbol control sequence FmodAntenna control sequence 1 for upper layer key stream pre-shared by both parties of legal communicationNTControl of mapping/demapping rules of antenna sequence numbers, symbol control sequence FmodRules governing digital modulation/demodulation.
In the first embodiment, for the conventional spatial modulation of 4 transmitting antennas and gray code mapping of QPSK modulation, the constellation diagram is as shown in fig. 6, spatial domain, real part, and imaginary part three-dimensional modulation is formed, the first 2 bits of 4-bit information are mapped into the antenna sequence number, and the second 2 bits are mapped into the complex domain by QPSK modulation.
Taking a communication system with 4 transmitting and 4 receiving antennas, QPSK modulation, and a flat rayleigh fading channel (assuming that the channel characteristics are not changed in one symbol transmission period and the channel characteristics between adjacent symbols are completely uncorrelated), the method for performing communication in the MIMO cross-layer secure communication system based on spatial modulation and upper layer key stream in the present application includes the following steps:
s001: the source generates a transmission in which each packet has 2000 frames, and each frame has 50 symbol sequences, each symbol comprising 4 bits x ═ a1,a2,a3,a4);
S002: obtaining x after serial-to-parallel conversion1=(a1,a2) And x2=(a3,a4);
S003: control sequence generation end generates antenna control sequence ZNT=(z1,z2,…zi,…z2000),zi∈ GF (2), symbol control sequence Fmod=(f1,f2,…fj,…f100000),fj∈GF(2);
S004: in a frame time slot, the antenna serial number mapping submodule detects the antenna control sequence value z at the momentiFor antenna information x1=(a1,a2) Mapping the antenna number l is performed, as shown in fig. 7:
if z isi=0,l=[2,1]·x1 T+1;
If z isi=1,l=Nt-[2,1]·x1 T;
Then, sending a signal to a radio frequency transmitting module to activate a No. I antenna;
s005: in each symbol period in the frame time slot in the last step, the digital modulation submodule detects a symbol control sequence value fj:
If fjWhen x is equal to 0, then x is paired2=(a3,a4) QPSK modulation is performed to obtain a symbol s, where s is {0,1,2,3} which is a QPSK modulation constellation signal set;
if fjWhen 1, then x2=(a3,a4) The symbol s obtained by QPSK modulation is turned over by 180 degrees in the corresponding constellation diagram, that is
sopt=ej π*s
The euclidean distance of the two symbols before and after the deformation is maximized as shown in fig. 8; meanwhile, the hamming distance is the largest, as shown in fig. 9, thereby maximizing the bit error rate and the worst performance of the eavesdropper.
S006: setting the i-th frame slot, the j-th symbol slot, and the transmission symbol generated in step S005 asThe transmission matrix can be expressed as:
wherein,the position is the l column, which indicates that the symbol is transmitted on the l transmitting antenna.
S007: through the flat rayleigh fading channel, the symbols received by the receiving end are as follows:
Y=HX+n
wherein n is [ n ]1,n2,n3,n4]Is random white gaussian noise, and the flat rayleigh channel matrix H is a complex matrix with dimension 4 × 4, which can be expressed as:
the elements are independent and identically distributed (i.i.d) zero-mean complex Gaussian variables, namely hmn∈N(0,1),m,n∈{1,2,3,4}。
S008: at the receiving end, because the transmitted information bits come from two parts, one part is a complex value symbol after digital modulation, and the other part is hidden in the serial number of the transmitting antenna, the demodulation needs to be carried out in three steps:
s0081: the symbols g on the transmit antennas are estimated for the received signal, and the MMSE algorithm is used for signal detection estimation.
Wherein, I is an identity matrix, and σ is a variance of gaussian white noise, so as to more accurately estimate a symbol matrix g sent by a transmitting terminal:
s0082: finding out the symbol position l with the maximum amplitude as the serial number of the time slot transmitting antenna,
g=[g1,g2,g3,g4]
the legal receiver and the sender share the antenna control sequence, so the antenna control sequence value z at the moment is detected firstiAnd the estimated antenna serial number is demapped according to the rule in fig. 7 to obtain antenna information y1=[b1,b2]:
If z isiConverting l-1 to binary bit as 0;
if z isi1, adding Nt-l is converted into binary bits;
s0083: at the same time, the symbol g on this transmitting antennalI.e. digitally modulated symbols, constellation point quantization
To obtainIn the formula, Q (-) is an equation for quantization of constellation points;
the legal receiver and the sender share the symbol control sequence, so the symbol control sequence value f at the moment is detected againjAnd for the estimated dataDemodulating according to the rule of FIG. 9 to obtain the transmission information y2=[b3,b4]:
If fjIf 0, performing conventional QPSK demodulation;
if fjWhen 1, the symbol is first markedTurned over by 180 deg. in the corresponding constellation diagram, i.e.
Then, carrying out conventional QPSK demodulation;
s009: will y1=[b1,b2]And y2=[b3,b4]The parallel-serial conversion successfully recovers the original bit stream y ═ b1,b2,b3,b4]。
The eavesdropper does not know the control sequence ZNTAnd FmodUnder the condition of not knowing a cross-layer safety communication scheme, cross-layer safety space demodulation similar to a legal user is carried out according to a traditional space demodulation method or two control sequences are completely guessed; because the key stream is very long, the probability of the occurrence values of 0 and 1 is 0.5, an eavesdropper has half of possibility to guess the control sequence value incorrectly; is takingIn the BPSK/QPSK/8PSK digital modulation scheme, the simulation verification result shows that the eavesdropper can detect the frame error rate close to 100% as shown in fig. 10 and the bit error rate of about 0.5 as shown in fig. 11.
The results of fig. 10 and fig. 11 verify the performance of spatial modulation cross-layer secure communication, and ensure that a legitimate user has good receiving performance; on one hand, under the condition that a transmitting end transmits a large amount of data, the frame error rate and the bit error rate of a legal user are continuously reduced along with the improvement of SNR; under the same signal-to-noise ratio condition, along with the change of the modulation order, the receiving performance QPSK performance of the system is the best, BPSK is the second and close to QPSK, and 8PSK performance is the worst; this is because after a constellation point of 8PSK is inverted by 180 °, the corresponding codeword is not bit-inverted to achieve the maximum hamming distance of 3, but only 2-bit inverted. On the other hand, the decoding performance of the eavesdropper is resisted, the eavesdropper can not easily find that the eavesdropper maintains about 0.5 of bit error rate and 0.9-1 of frame error rate under different SNR conditions and three modulation modes, and effective information cannot be overheard at all; fig. 12 shows that the cross-layer enhanced security technique of the present invention based on the MIMO conventional spatial modulation system does not affect the performance of the legitimate user at all, and can implement secure communication with a probability of 1.