CN1213573C - Physical layer encryption method based on time-varying MPSK modulation in wireless local area network - Google Patents

Abstract

The present invention relates to a physical layer cryptographic method based on time-varying MPSK modulation in a wireless local area network, and belongs to the technical field of information transmission safety for a wireless local area network. The present invention is characterized in that under the precondition that a traditional random PN sequence continuously changes phase offset, a fixed modulation mode with a lower scale of QPSK or 8PSK is adopted so as to greatly enhance the performance of a system bit error rate BER on the basis of greatly enhancing the system safety. Moreover, compared with an MPSK modulation mode with a fixed random MPSK modulation mode and a lower scale, the present invention has obvious advantages in an SNR zone or a high SNR zone with a low signal-to-noise ratio.

Description

In the WLAN (wireless local area network) based on the time become the encryption in physical layer method of MPSK modulation

Technical field

In the WLAN (wireless local area network) based on the time become the MPSK modulation the encryption in physical layer method belong to wireless local area information transmission security technical field.

Background technology

As the important component part of wireless communication networks, wireless lan (wlan) has become the main developing direction of following radio communication, particularly wireless access technology.Along with the continuous improvement of performance, interoperability and the ease of manageability of WLAN, fail safe has become assembles WLAN (wireless local area network) on a large scale and presses for one of problem of solution.Because WLAN (wireless local area network) is used the wireless mode transmission of data signals, transmission medium is open, so be vulnerable to attack.On the other hand, the physics controlled range of WLAN (wireless local area network) is uncertain, and this is because radio wave can penetrate wall and dividing plate, propagates into sometimes outside the application region, makes the hacker have an opportunity to intercept and capture electric wave and enter in the not protected local area network (LAN).Because these difference of network infrastructure, the fail safe that causes WLAN (wireless local area network) and wired network is not in same level.

At present, the IEEE802.11 committee has recognized the safety defect that WLAN (wireless local area network) is intrinsic, thereby has introduced WEP (WiredEquivalent Privacy) algorithm.But the WEP algorithm also has defective and the weakness of self, can not guarantee the validity of encrypted transmission fully, also can't guarantee the fail safe of WLAN.

Introduce our invention the time modified tone system mode encryption in physical layer algorithm before, be necessary simply to introduce traditional MPSK modulation system.MPSK is with a kind of multi-system digital modulation mode of carrier phase as the parameter of the information of carrying.In M system (for example: M=8, expression octal system) phase shift keyed signal, carrier phase has M kind value, and the pairing M kind duration is T _sSymbol can be expressed as:

$S_i\left(t\right)=\sqrt{\frac{2E_s}{T_s}}\cos ({\mathrm{\ω}}_{c}t+{\mathrm{\φ}}_i)0\≤t\≤T_s,i=\mathrm{0,1},\·\·\·,M-1---\left(1\right)$

Here, E _sBe the signal energy of unit symbol, promptly at 0≤t≤T _sSignal energy in the time interval; ω _CBe carrier angular frequencies; φ _iBe phase place, M kind value is arranged.

The theoretical Bit Error Rate Computation formula of mpsk signal is as follows:

During M=2, $P_{b,\mathrm{BPSK}}=Q\left(\sqrt{\frac{2E_b}{N_0}}\right)---\left(2\right)$

During M=4, $P_{b,\mathrm{QPSK}}=2Q\left(\sqrt{\frac{2E_b}{N_0}}\right)[1-\frac{1}{4}Q\left(\sqrt{\frac{2E_b}{N_0}}\right)]---\left(3\right)$

During M=8, $P_{b,8\mathrm{PSK}}=2Q\left(\sqrt{\frac{{6\mathrm{<figure-callout\; id="0"\; label="E\; b\; N"\; filenames="C0314595000152.png"\; state="\{\{state\}\}">E</figure-callout>}}_b}{N_{}}}\sin \frac{\mathrm{\&pi;}}{8}\right)---\left(4\right)$

During M=16, $P_{b,16\mathrm{PSK}}=2Q\left(\sqrt{\frac{{8\mathrm{<figure-callout\; id="0"\; label="E\; b\; N"\; filenames="C0314595000152.png"\; state="\{\{state\}\}">E</figure-callout>}}_b}{N_{}}}\sin \frac{\mathrm{\&pi;}}{16}\right)---\left(5\right)$

Here, Q represents the Q function, and its mathematics implication is: $Q\left(a\right)={\&Integral;}_a^{\&infin;}\frac{1}{\sqrt{2\mathrm{\&pi;}}}{e}^{\frac{x^2}{2}}\mathrm{dx},$ It is the tail area of Gaussian Profile density function.E _bRepresent but the energy of bit signal N ₀The power spectral density of expression noise.

Under normal conditions, the M value that the MPSK modulation system is adopted is constant, phase deviation φ _iSpan also be constant.Like this, in a single day the signal after the modulation is intercepted and captured, and just easily by demodulation, causes leakage of information.For this reason, when proposing, we become the modulation system of MPSK, to increase the security performance of system.Further, for the error rate that reduces system and the complexity of realization, we also to the time MPSK modulation system that becomes make some and improve, to increase the availability of this method.

Summary of the invention

The object of the present invention is to provide a kind of can on the basis of improving security of system greatly, keep than in the wireless local area of low error rate based on the time become the encryption in physical layer algorithm of MPSK.

Based on the time become the MPSK modulation system the encryption in physical layer basic idea be: produces two PN pseudo random sequences, constantly change the value of multi-system M according to first PN sequence, while value and second PN sequence according to M constantly changes phase deviation φ _iValue.Each M and φ _iChange a back modulating data once.Like this, the signal after the modulation is at M and φ _iAll do not have statistical law to say on two parameters, have very strong confidentiality, reached the purpose of encrypting.Concrete condition, referring to Fig. 1, existing based on the time MPSK modulation system that becomes the encryption in physical layer algorithm be expressed as follows:

(1) generation of random PN sequence

(i) { 0, the 1} sequence is used for the M value of selected MPSK modulation system to PN1:2bits, and its corresponded manner is as shown in table 1 at random.

(ii) PN2:log ₂{ 0, the 1} sequence is used for selected phase deviation φ to M bits at random _iValue, its corresponded manner is as follows:

With log ₂M bits { 0, the 1} sequence is regarded a binary number as, is designated as (PN2) ₂, be converted into decimal number after, be designated as (PN2) ₁₀Then:

${\mathrm{\&phi;}}_i=2\mathrm{\&pi;}\frac{{\left(\mathrm{PN}2\right)}_{10}}{M}---\left(6\right)$

(2) (Encode) encrypted in modulation

Simplify modulating mode, utilize the planisphere of MPSK modulation system to come the mark enciphered data, data encrypted is selected on the unit circle.

For MPSK modulation system and selected M, enciphered data m should satisfy: 0≤m≤M-1 has:

$\mathrm{SIGNAL}=m,\mathrm{ENCODE}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{m}{M}+{\mathrm{\&phi;}}_i)]---\left(7\right)$

(3) demodulation deciphering (Decode)

(i) deciphering foundation

Adopt complex plane, mark constellation point on unit circle.Because phase deviation φ _iExistence, constellation point can rotate skew.The mark mode of constellation point is as follows:

$\mathrm{CONSTELLATIONPOINTS}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{K}{M}+{\mathrm{\&phi;}}_i)]---\left(8\right)$

$(K=\mathrm{0,1,2},\&CenterDot;\&CenterDot;\&CenterDot;,M-1)$

The data (RECEIVE) that receive are compared with each constellation point, and nearest point is as the value of these data;

That is to say, will with data point on complex plane the nearest pairing K value of constellation point as decrypted data.

(ii) decryption method

Get M constellation point CP ₁, CP ₂..., CP _MThe corresponding K=0 of difference, 1,2 ..., this M of M-1 point, decryption method is as follows:

IF|RECEIVE-CP _K|＝Min(RECEIVE-CP ₁，...，RECEIVE-CP _M)

(9)

THEN DECODE＝K

Should be noted that, though said method improves a lot on security of system, but because BPSK, QPSK, 8PSK and these 4 kinds of modulation systems of 16PSK all occur with 1/4 probability, the complexity that causes whole system to realize increases, the error rate is also higher, thereby limited the range of application of system, promptly required the signal to noise ratio of system higher (greater than 12dB).For this reason, we will become some improvement of do on the MPSK modulation system encryption in physical layer algorithm when existing, to enlarge its scope of application.

The invention is characterized in: it be a kind of adopt fixing QPSK modulation system the time become the encryption in physical layer method of MPSK, contain following steps successively:

1. the generation of random PN sequence

4 01 sequences at random.Selected phase deviation φ _iValue, its corresponded manner is as follows:

01 sequence binary number representation with 4 is designated as PN ₂, be converted into decimal number after, be designated as PN ₁₀Then:

${\mathrm{\&phi;}}_i=2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="10"\; label="P\; N"\; filenames="C0314595000151.png,C0314595000152.png"\; state="\{\{state\}\}">P</figure-callout>}{N}_{}{}_{10}}{16}.$

2. (Encode) encrypted in modulation

Come the mark enciphered data with planisphere, data encrypted is selected on the unit circle, selected enciphered data is represented with m.M should satisfy: 0≤m≤3.Then:

$\mathrm{SIGNAL}=m,{\mathrm{ENCODE}}_{\mathrm{QPSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="4"\; label="m"\; filenames="C0314595000161.png"\; state="\{\{state\}\}">m</figure-callout>}}{4}+{\mathrm{\&phi;}}_i)].$

3. demodulation deciphering (Decode)

Adopt complex plane, mark constellation point on unit circle.Mark mode is as follows:

$\mathrm{CONSTELLATION}{\mathrm{POINTS}}_{\mathrm{QPSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="C0314595000161.png"\; state="\{\{state\}\}">K</figure-callout>}}{4}+{\mathrm{\&phi;}}_i)],(K=\mathrm{0,1,2},3);$

Will with data point on complex plane the nearest pairing K value of constellation point as decrypted data.

Feature of the present invention also is: it be a kind of adopt 8PSK modulation mode the time become the encryption in physical layer method of MPSK, contain following steps successively:

1. the generation of random PN sequence

4 01 sequences at random.Selected phase deviation φ _iValue, its corresponded manner is as follows:

01 sequence binary number representation with 4 is designated as PN ₂, be converted into decimal number after, be designated as PN ₁₀Then:

${\mathrm{\&phi;}}_i=2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="10"\; label="P\; N"\; filenames="C0314595000151.png,C0314595000152.png"\; state="\{\{state\}\}">P</figure-callout>}{N}_{}{}_{10}}{16}.$

2. (Encode) encrypted in modulation

Come the mark enciphered data with planisphere, data encrypted is selected on the unit circle, selected enciphered data is represented with m.M should satisfy: 0≤m≤7.Then:

$\mathrm{SIGNAL}=m,{\mathrm{ENCODE}}_{8\mathrm{PSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="8"\; label="m"\; filenames="C0314595000152.png,C0314595000161.png"\; state="\{\{state\}\}">m</figure-callout>}}{8}+{\mathrm{\&phi;}}_i)].$

3. demodulation deciphering (Decode)

Adopt complex plane, mark constellation point on unit circle.Mark mode is as follows:

$\mathrm{CONSTELLATION}{\mathrm{POINTS}}_{8\mathrm{PSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="8"\; label="K"\; filenames="C0314595000152.png,C0314595000161.png"\; state="\{\{state\}\}">K</figure-callout>}}{8}+{\mathrm{\&phi;}}_i)],(K=\mathrm{0,1,2},\&CenterDot;\&CenterDot;\&CenterDot;,7);$

Will with data point on complex plane the nearest pairing K value of constellation point as decrypted data.

L-G simulation test proves: on the basis of improving the system safety performance greatly, can improve error rate of system BER performance greatly with the MPSK modulation system of hanging down system.

Description of drawings

Fig. 1 existing based on the time become the theory diagram of the encryption in physical layer/decryption method of MPSK modulation system

Fig. 2 improved based on the time become the theory diagram of the encryption in physical layer/decryption method of MPSK modulation system

The constellation point diagram of Fig. 3 16PSK modulation system

Become the simulation flow of MPSK encryption in physical layer algorithm during Fig. 4

Become the theoretical BER performance curve of MPSK modulation system during Fig. 5

Become the theoretical BER performance curve of MPSK modulation system during Fig. 6

Become the actual emulation BER performance curve of MPSK modulation system during Fig. 7

Become the actual emulation BER performance curve of MPSK modulation system during Fig. 8

Become the theoretical BER performance of MPSK modulation system and the comparison of actual emulation BER performance during Fig. 9

Embodiment

To the time become the improved basic thought of MPSK modulation system encryption in physical layer algorithm and be: system does not adopt random PN sequence to change the value of M, and adopts fixing QPSK or 8PSK modulation mode; But, phase deviation φ _iRemain randomly changing and φ in its randomness and the former method _iRandomness be suitable.Like this, owing to there be not the existence of 16PSK modulation system in system, the complexity of system and the error rate all reduce greatly; And since the modulation after signal at φ _iDo not have statistical law on this parameter, still have suitable confidentiality.Concrete condition, referring to Fig. 2, based on the time become MPSK modulation system encryption in physical layer algorithm improvement be expressed as follows:

(1) generation of random PN sequence

{ 0, the 1} sequence is selected phase deviation φ to PN:4bits at random _iValue, its corresponded manner is as follows:

With 4bits { 0, the 1} sequence is regarded a binary number as, is designated as PN ₂, be converted into decimal number after, be designated as PN ₁₀Then:

${\mathrm{\&phi;}}_i=2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="10"\; label="P\; N"\; filenames="C0314595000151.png,C0314595000152.png"\; state="\{\{state\}\}">P</figure-callout>}{N}_{}{}_{10}}{16}---\left(10\right)$

(2) (Encode) encrypted in modulation

Simplify modulating mode, utilize planisphere to come the mark enciphered data, data encrypted is selected on the unit circle.

For the QPSK modulation system, enciphered data m should correspondingly satisfy: 0≤m≤3 have:

${\mathrm{SIGNAL}}_{\mathrm{QPSK}}=m,{\mathrm{ENCODE}}_{\mathrm{QPSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="4"\; label="m"\; filenames="C0314595000161.png"\; state="\{\{state\}\}">m</figure-callout>}}{4}+{\mathrm{\&phi;}}_i)]---\left(11\right)$

For 8PSK modulation mode, enciphered data m should correspondingly satisfy: 0≤m≤7 have:

$\mathrm{<figure-callout\; id="8"\; label="S\; IGNAL"\; filenames="C0314595000152.png,C0314595000161.png"\; state="\{\{state\}\}">S</figure-callout>}{\mathrm{IGNAL}}_{}{}_{8\mathrm{PSK}}=m,{\mathrm{ENCODE}}_{8\mathrm{PSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="8"\; label="m"\; filenames="C0314595000152.png,C0314595000161.png"\; state="\{\{state\}\}">m</figure-callout>}}{8}+{\mathrm{\&phi;}}_i)]---\left(12\right)$

(3) demodulation deciphering (Decode)

Adopt complex plane, mark constellation point on unit circle.Because phase deviation φ _iExistence, constellation point can rotate skew.For QPSK, the mark mode of constellation point is as follows:

$\mathrm{CONSTELLATION}{\mathrm{POINTS}}_{\mathrm{QPSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="C0314595000161.png"\; state="\{\{state\}\}">K</figure-callout>}}{4}+{\mathrm{\&phi;}}_i)](K=\mathrm{0,1,2,3})---\left(13\right)$

For 8PSK, the mark mode of constellation point is as follows:

$\mathrm{CONSTELLATION}{\mathrm{POINTS}}_{8\mathrm{PSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{\mathrm{<figure-callout\; id="8"\; label="k"\; filenames="C0314595000152.png,C0314595000161.png"\; state="\{\{state\}\}">k</figure-callout>}}{8}+{\mathrm{\&phi;}}_i)](K=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,7)---\left(14\right)$

The data and each constellation point that receive are compared, and nearest point is as the value of these data; That is to say, will with data point on complex plane the nearest pairing K value of constellation point as decrypted data.

Compare with existing encryption in physical layer algorithm, the encryption in physical layer algorithm major advantage after the improvement is as follows:

(1) form of signal appearance is identical, and the two has all adopted the planisphere (as shown in Figure 3) of 16PSK modulation system, and user profile contained in the signal is protected.

(2) owing to adopt fixing MPSK modulation system (8PSK or QPSK), so the demodulating process of received signal, just decrypting process is more simple.

(3) owing to adopted than the MPSK modulation system of hanging down system, so the error rate of system reduces greatly.

But, be at random mixing MPSK modulation system because existing encryption in physical layer algorithm adopts, and the algorithm after improving has changed fixing MPSK modulation system into, so on encryption performance, compare slightly loss with original method.

From the bit error rate formula of MPSK modulation system, the bit error rate of mpsk signal depends primarily on M and E _b/ N ₀Value.Usually, M is big more, and the bit error rate of signal is just high more, and the complexity of simultaneity factor is also just high more, and when M was excessive, system can can't realize because of complexity is too high.Simultaneously, E _b/ N ₀Big more, the bit error rate of signal is just low more, works as E _b/ N ₀In the time of fully big, channel trends towards not having the ideal communication channel of noise, and the difference that different M values is brought will be no longer obvious.So for the influence of these two factors for the algorithm availability is discussed, we only consider MPSK modulation system commonly used and E generally _b/ N ₀Scope is carried out Monte Carlo emulation.

System emulation

By the comparison of Monte Carlo emulation and simulation result, our invention the time become MPSK modulation system encryption in physical layer algorithm and have very strong application potential.In the experiment simulation, we consider AWGN (Additive White Gauss Noise, additive white Gaussian noise) channel, pass through E _b/ N ₀Value noise energy is controlled; Then noise (NOISE) is superimposed upon above the coded signal (ENCODE) as received signal (RECEIVE), the initial data that obtains sending by deciphering at last.Definition

Span be 5dB ~ 15dB.The flow process principle of experiment simulation as shown in Figure 4.

About the control of generating noise and noise energy, concrete grammar is expressed as follows:

(1) generating noise

Produce white multiple noise, i.e. n=n ₁+ jn ₂Note the normalization of mould, promptly noise is zero-mean equally again, and variance is 1 white noise.

So, if n ₁, n ₂Be zero-mean, variance is 1 white noise, has:

$n=\frac{1}{\sqrt{2}}(n_1+j\&CenterDot;n_2)---\left(15\right)$

(2) to the control of noise energy

According to formula: $\mathrm{SNR}={\log }_{2}M\&CenterDot;\frac{{\mathrm{<figure-callout\; id="0"\; label="E\; b\; N"\; filenames="C0314595000152.png"\; state="\{\{state\}\}">E</figure-callout>}}_b}{N_{}}=\frac{E_s}{E_n},$ And signal energy E _s=1.Input

Then:

$\frac{E_s}{E_n}=\mathrm{SNR}={\log }_{2}M\&CenterDot;{10}^{\frac{{\left(\frac{E_b}{N_0}\right)}_{\mathrm{dB}}}{10}}---\left(16\right)$

Have:

$E_n=\frac{E_s}{\mathrm{SNR}}=\frac{1}{\mathrm{SNR}}---\left(17\right)$

(3) in sum: received signal RECEIVE=ENCODE+NOISE

Wherein:

$\mathrm{NOISE}=\frac{n}{\sqrt{\mathrm{SNR}}},\mathrm{SNR}={\log }_{2}M\&CenterDot;{10}^{\frac{{\left(\frac{E_b}{E_0}\right)}_{\mathrm{<figure-callout\; id="10"\; label="dB"\; filenames="C0314595000151.png,C0314595000152.png"\; state="\{\{state\}\}">dB</figure-callout>}}}{10}},n=\frac{1}{\sqrt{2}}(n_1+j\&CenterDot;n_2).$

In order to compare, we have listed theoretic mpsk signal BER performance in simulation result.At first, we consider Fig. 5 and Fig. 6, and it has provided 16PSK, and 8PSK and QPSK BER performance in theory relatively.As can be seen, when M reduced, the corresponding error rate also reduced greatly, that is to say, the MPSK modulation system of low system can improve the BER performance of system greatly.For example, when ${\left(\frac{E_b}{N_0}\right)}_{\mathrm{dB}}=7\mathrm{dB}$ The time, the bit error rate of 16PSK, 8PSK, QPSK is respectively 5.42%, 1.20%, 0.15%.In addition, along with E _b/ N ₀Increase, the MPSK modulation system of low system trends towards the BER performance of ideal communication channel at faster speed.So, still be high SNR district no matter in low SNR district, the difference of 3 kinds of MPSK modulation systems all is tangible.

Fig. 7 and Fig. 8 are the Monte Carlo simulation results of 200,000 characters on computers, and it has provided MPSK at random, and 8PSK and QPSK BER performance in actual applications relatively.As can be seen, adopt the fixedly MPSK modulation system of hanging down system can improve the BER performance of system greatly.In addition, along with E _b/ N ₀Increase, the fixedly MPSK modulation system of low system trends towards the BER performance of ideal communication channel at faster speed.So, still be high SNR district no matter in low SNR district, the MPSK modulation system all is tangible with the difference of fixing low system MPSK modulation system at random.

When having provided, Fig. 9 becomes the theoretical BER performance of MPSK modulation system and the comparison of actual emulation BER performance.As can be seen, adopt the BER performance of the BER performance of MPSK modulation system at random and 16PSK modulation system very approaching.Can draw thus, for the time become the BER performance of MPSK modulation system, 16PSK modulation system decisive role.That is to say, because the existence of 16PSK modulation system makes the bit error rate of whole system increase greatly.Therefore, in system, adopt the fixedly MPSK modulation system of low system, can improve the BER performance of whole system widely.In addition, the simulation curve of 8PSK and QPSK and theoretical curve are very identical, have also further confirmed the correctness of simulation result.

PN1	00	01	10	11
					M	2	4	8	16
MPSK	BPSK	QPSK	8PSK	16PSK

The selection corresponding relation of table 1 PN1 random sequence and modulation system

Claims (2)

1, in the WLAN (wireless local area network) based on the time become the encryption in physical layer method of MPSK modulation system, adopt random PN sequence constantly to change phase deviation φ _iValue, it is characterized in that: it be a kind of adopt fixing QPSK modulation system the time become the encryption in physical layer method of MPSK, contain following steps successively:

The generation of step 1. random PN sequence

4 01 sequences at random, selected phase deviation φ _iValue, its corresponded manner is as follows:

01 sequence binary number representation with 4 is designated as PN ₂, be converted into decimal number after, be designated as PN ₁₀, then:

${\mathrm{\&phi;}}_i=2\mathrm{\&pi;}\frac{P{N}_{10}}{16}.$

Step 2. modulation is encrypted

Come the mark enciphered data with planisphere, data encrypted is selected on the unit circle, selected enciphered data represents that with m m should satisfy: 0≤m≤3, then:

SIGNAL＝m， ${\mathrm{ENCODE}}_{\mathrm{QPSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{m}{4}+{\mathrm{\&phi;}}_i)]\&CenterDot;$

Step 3. demodulation deciphering

Adopt complex plane, mark constellation point on unit circle, mark mode is as follows:

$\mathrm{CONSTELLATIONPOINT}{S}_{\mathrm{QPSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{K}{4}+{\mathrm{\&phi;}}_i)],K=\mathrm{0,1,2,3};$

Will with data point on complex plane the nearest pairing K value of constellation point as decrypted data.

2, in the WLAN (wireless local area network) based on the time become the encryption in physical layer method of MPSK modulation system, adopt random PN sequence constantly to change phase deviation φ _iValue, it is characterized in that: it be a kind of adopt 8PSK modulation mode the time become the encryption in physical layer method of MPSK, contain following steps successively:

The generation of step 1. random PN sequence

4 01 sequences at random, selected phase deviation φ _iValue, its corresponded manner is as follows:

01 sequence binary number representation with 4 is designated as PN ₂, be converted into decimal number after, be designated as PN ₁₀, then:

${\mathrm{\&phi;}}_i=2\mathrm{\&pi;}\frac{{\mathrm{PN}}_{10}}{16}.$

Step 2. modulation is encrypted

Come the mark enciphered data with planisphere, data encrypted is selected on the unit circle, selected enciphered data represents that with m m should satisfy: 0≤m≤7, then:

SIGNAL＝m， ${\mathrm{ENCODE}}_{8\mathrm{PSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{m}{8}+{\mathrm{\&phi;}}_i)]\&CenterDot;$

Step 3. demodulation deciphering

Adopt complex plane, mark constellation point on unit circle, mark mode is as follows:

${\mathrm{CONSTELLATIONPOINTS}}_{8\mathrm{PSK}}=\exp [j\&CenterDot;(2\mathrm{\&pi;}\frac{K}{8}+{\mathrm{\&phi;}}_i)],K=\mathrm{0,1,2},...,7;$

Will with data point on complex plane the nearest pairing K value of constellation point as decrypted data.

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