CN101902265A - Safe transmission method of physical layer in wireless communication - Google Patents

Abstract

The invention discloses a safe transmission method of a physical layer in wireless communication, which is characterized by comprising the following steps of: a single-antenna desired user firstly transmits unencrypted request information to a multi-antenna base station; the base station receives the request information and estimates a signal path between the base station and the desired user with a frequency piloting sequence; the base station modulates bit to be transmitted into a constellation point symbol b (n) with a known phase position modulating mode, designs a fast-variable weighting coefficient, weights the constellation point symbol b (n) to be transmitted, and transmits the weighted symbol on selected Jrand antennas according appointed gross power; the desired user receives the weighted symbol, i.e. a weighting symbol, and decodes with a maximum likelihood method; and a wiretap user fast changes the weighting coefficient due to the process of the base station, can not decode with a blind equalization method, and can not decode with the maximum likelihood method, so that the method finally realizes the safe transmission.

Description

Safe transmission method of physical layer in the radio communication

Technical field

The present invention relates to wireless communication system, the safe transmission method of physical layer in particularly a kind of wireless communication system.

Background technology

In recent years, various wireless communication technologys emerge in an endless stream, and the appearance of these technology has terminal equipments such as computer, mobile phone and moves the ability that inserts, and have solved the line restriction of traditional wired access, and the access scheme of various efficient high-speeds is provided for the user.Along with improving constantly of the message transmission rate of wireless communication system support, wireless user's scale constantly enlarges, and wireless communication system progressively replaces the inexorable trend that traditional wired communication system has become Communication Development aspect a lot.Simultaneously, along with radio communication extensively popularizing aspect civilian, the secure wireless communication problem that relates to trade secret becomes more and more important.

In wireless communication system, because the broadcast characteristic of electromagnetic signal propagation and the opening of wireless channel, signal is propagated arbitrarily in the space by radio wave, lost the constraint of " wired ", make the receiver be in arbitrarily in the coverage just can receive the information that transmitter is launched by any line, other users that the communication information very easily is supposed to beyond the user obtain.In this sense, wireless communication system has bigger potential safety hazard than traditional wired communication system, how to prevent the wireless leakage of information, ensures that the fail safe of radio communication is also just more important.

At in May, 2007 JOURNAL OF COMMUNICATIONS, VOL.2, a kind of aerial array redundancy of utilizing, the wireless security transmission method that carries out random weighting to transmitting are proposed in the article of delivering on the NO.3 that is entitled as " Using Antenna Array Redundancy and Channel Diversity for SecureWireless Transmissions ".The design criterion of weight coefficient W is H ^HW=||H||, wherein H is that transmitting terminal arrives the channel that expectation receives the user.Under this criterion, select to obey the W of a certain distribution at random, make and can directly use maximum-likelihood decoding to obtain information to received signal at the desired user end.Because transmitting terminal is different from the desired user channel to eavesdropping user's channel, the W of change at random can make it to obtain information from disorder reception planisphere, thereby guarantee safe transmission eavesdropping signal constellation which that the user receives scramble at random.Yet, the subject matter of this random weighting method is that power utilization is too low, this is because the randomization of array weight coefficient causes the excessive dispersion of transmit signal power in the space, and the signal power that finally causes arriving desired user is not enough, has reduced the communication quality of desired user.

Summary of the invention

The design that the present invention is directed to above-mentioned random weighting coefficient causes the low excessively problem of power utilization, a kind of radio physical layer safe transmission method of selecting transmitting antenna is at random proposed, this method make signal that the base station sends at the desired user place all the time with superimposed to obtain the highest transmitting gain, power utilization is very high; For the eavesdropping user, demodulating information effectively, thus reach the purpose of secure communication.

For reaching above purpose, the present invention adopts following technical scheme to be achieved:

It is right that safe transmission method of physical layer in a kind of radio communication, the model of communication system of employing are communicate by letter as expectation in cover multi-antenna base station and a single antenna mobile terminal, and another many antennas mobile terminal is characterized in that as eavesdropping the user, comprises the steps:

A) the single antenna desired user at first sends the unencrypted solicited message to the base station, and this solicited message comprises the pilot frequency sequence that is used for channel estimating simultaneously, and pilot frequency sequence is all known symbol of receiving-transmitting sides;

B) base station receives solicited message, utilizes pilot frequency sequence to estimate channel h between them _AB(n), channel estimating adopts the channel estimation methods of existing band pilot tone, considers that time division duplex and channel become slowly, and the base station is identical with desired user to the channel of base station direction to the channel of desired user direction, is h _AB(n);

C) the base station bit that will send utilizes known a kind of phase modulation method to be modulated to constellation point symbol b (n), n=1,2,3 ..., preceding at each emission b (n), need be from all J root antennas picked at random J _RandThe root antenna, J _Rand＜J utilizes this J _RandThe channel I of root antenna _Rand(n) h _AB(n), design weight coefficient

Weight coefficient is changed fast, be weighted, at last the J that is choosing according to the symbol after specifying gross power with weighting to sent constellation point symbol b (n) _RandLaunch on the root antenna.I wherein _Rand(n) be the selection matrix at random of a J * J dimension, wherein I _Rand(n) random arrangement J on the diagonal _RandIndividual 1, all the other elements are 0;

D) desired user receives the symbol after the weighting, and promptly the weighting symbol utilizes the maximum likelihood method decoding;

E) the eavesdropping user receives the symbol after the weighting, makes weight coefficient change fast because handle the base station, and the eavesdropping user can't utilize the blind balance method decoding, if also utilize the maximum likelihood method decoding, then the error rate is 50%, has finally realized safe transmission.

In the said method, in the described step b), the channel estimation methods of existing band pilot tone is LS channel estimating, MMSE channel estimating or its improved method.

In the described step c), adopt the Ditital modulation method of BPSK (two-phase PSK) or QPSK (quarternary phase-shift keying (QPSK)) when phase modulation method; Then in the step d), desired user utilizes maximum likelihood method decoding simplified formula to be

Wherein x (n) expression is corresponding to a kind of constellation point of phase modulation method, and y (n) represents the signal that desired user receives.

Compare with the method for existing guarantee secure wireless communication, the invention has the beneficial effects as follows:

1, under the environment that channel becomes slowly, can stop the eavesdropping user to obtain information, reach safety so that equivalent channel changes fast.The tradition beamforming algorithm can form the wave beam that points to desired user, other directions is formed suppress.Yet its weight coefficient is along with channel variation, and under channel change situation slowly, weight coefficient is also constant substantially, and the listener-in just can utilize blind balance method to obtain the information of making a start.The present invention introduces on the basis of traditional beamforming algorithm and selects aerial array at random, even channel becomes slowly, because the different antenna array of each selection, therefore cause the equivalent channel of communicating pair to change fast, thereby make blind equalization algorithm lose efficacy, the eavesdropping user can't obtain the emission symbol of base station, thereby has guaranteed secure communication.

2, transmitting at the desired user place with superimposed of base station reaches higher power utilization.In the described article of background technology, mentioned the safing method of weight coefficient that designs at random, but the randomization of array weight coefficient causes the excessive dispersion of transmit signal power in the space in this method, the signal power that finally causes arriving desired user is not enough, has reduced the communication quality of desired user.The present invention launches to reach the fast-changing at random purpose of equivalent channel by the some antennas of each picked at random, the selection of weight coefficient adopts distributed launching beam to form, make signal that each array element sends at the desired user place all the time with superimposed to obtain the highest transmitting gain.This is to focus on same acceptance point transmitting at the desired user place with superimposed essence, and power utilization is very high.

3, under the situation of base station same transmit gross power, this patent method can reach higher signal to noise ratio at the desired user end, thereby the decoding performance of desired user is improved.

Description of drawings

Fig. 1 is the system model of the related safe transmission of the inventive method.

Fig. 2 is the weighting of base station symbol of the present invention and sends schematic diagram.

Fig. 3 is that the base station is selected the aerial array schematic diagram at random.

Fig. 4 is the error rate and transmit power curve contrast figure in existing method and the inventive method wireless transmission.

Fig. 5 is signal to noise ratio and transmit power curve contrast figure in existing method and the inventive method wireless transmission.

Embodiment

The present invention is described further below in conjunction with accompanying drawing and instantiation.

The system model that the present invention relates to safe transmission as shown in Figure 1, base station Alice has many antennas, desired user Bob uses single antenna, eavesdropping user Eve sets up many antennas in order to obtain information.Here choose base station J=8 antenna in concrete the enforcement, desired user 1 antenna, eavesdropping user 4 antennas.The meaning of secure communication is that the symbol of the base station user that only wishes to be supposed to obtains, and does not wish that being eavesdropped the user obtains.Here it is passive eavesdropping the user, i.e. its eavesdropping information is not to the spatial emission signal.In addition, generally require the transceiver channel can reciprocity in this wireless security mode, when channel became slowly, this reciprocity can be fully guaranteed by time division duplex (TDD).In the communication process, Bob at first sends pilot frequency sequence to Alice, estimates channel h between the two for Alice _AB(n).Alice estimates channel h _AB(n) after, the bit that will send utilizes known a kind of phase modulation method to be modulated to constellation point symbol b (n), n=1,2,3 ..., design weight coefficient then, be assigned to each antenna after constellation point symbol b (n) is weighted and launch, the modulation system of employing is BPSK or QPSK.That adopt in the present embodiment is QPSK, and concrete weighting and transmission flow are as shown in Figure 2.The method for designing of weight coefficient: also become slowly for fear of weight coefficient when channel becomes slowly, Alice need be in all J antennas picked at random J _Rand=4 antennas utilize this J then _RandThe channel design weight coefficient of root antenna, concrete formula is as follows

$w\left(n\right)=\frac{I_{\mathrm{rand}}\left(n\right)h_{\mathrm{AB}}\left(n\right)}{\left|\right|I_{\mathrm{rand}}\left(n\right)h_{\mathrm{AB}}\left(n\right)\left|\right|}---\left(1\right)$

I _Rand(n) be the selection matrix at random of a J * J dimension, wherein I _Rand(n) random arrangement J on the diagonal _RandIndividual 1, all the other elements are 0.I _Rand(n) effect makes that equivalent channel all changes, thereby has avoided Eve to obtain information when sending each symbol b (n).Particularly, select the aerial array schematic diagram at random as shown in Figure 3, when sending n symbol, select certain J at random _RandRoot antenna (J _Rand＜J), when sending next symbol, select J again at random _RandThe root antenna, by that analogy.Change along with sending symbol n among Fig. 3, the aerial array of selection also changes.After generating weight coefficient, Alice is assigned to J to the symbol b (n) that is mapped as constellation point _RandLaunch behind the weight coefficient by the weighting respective antenna on the root antenna.If total transmitting power is P, through behind the wireless channel, the symbol that desired user Bob receives is

$x_{\mathrm{Bob}}\left(n\right)=b\left(n\right)P\frac{I_{\mathrm{rand}}\left(n\right)h_{\mathrm{AB}}^H\left(n\right)}{\left|\right|I_{\mathrm{rand}}\left(n\right)h_{\mathrm{AB}}\left(n\right)\left|\right|}{h}_{\mathrm{AB}}\left(n\right)+v_{\mathrm{Bob}}\left(n\right)=b\left(n\right)P\left|\right|I_{\mathrm{rand}}\left(n\right)h_{\mathrm{AB}}\left(n\right)\left|\right|+v_{\mathrm{Bob}}\left(n\right)---\left(2\right)$

ν _Bob(n) for the noise of Bob end, suppose the noise Gaussian distributed.Remove The noise, the phase place of receiving symbol does not have deviation, the estimated value that Bob can directly utilize the method for maximum-likelihood decoding to obtain launching symbol b (n)

Because the channel h between base station and the eavesdropping user _AE(n) be different from the direct channel h of base station and desired user _AB(n), signal is through h _AE(n) symbol of back arrival eavesdropping user side is

$x_{\mathrm{Eve}}\left(n\right)=b\left(n\right)P\frac{I_{\mathrm{rand}}\left(n\right)h_{\mathrm{AB}}^H\left(n\right)}{\left|\right|I_{\mathrm{rand}}\left(n\right)h_{\mathrm{AB}}\left(n\right)\left|\right|}{h}_{\mathrm{AE}}\left(n\right)+v_{\mathrm{Eve}}\left(n\right)---\left(3\right)$

v _Eve(n) noise of holding for Eve.Even do not consider noise, the information that Eve receives is the scramble at random to amplitude and the phase place of former symbol b (n), this makes Eve can not use as the maximum likelihood of desired user Bob and directly deciphers, also can't use the such blind equalization algorithm of CMA (constant modulus algorithm) to obtain information, thereby guarantee the safe transmission of information.What Eve we can be interpreted as can not be utilized the CMA blind balance method to obtain information:

Suppose that blind equalization algorithm needs iteration N step to restrain, this just requires Eve will receive N symbol at least, and if channel remains unchanged in the duration substantially at L symbol at most, then the algorithm necessary condition that can restrain is N≤L.In other words, Eve just can't correctly estimate channel when L＜N.Because Alice selects J at random in J root antenna at every turn _RandRoot uses, and channel just has

Plant different possibilities, wherein The expression number of combinations.For iterative algorithm can be restrained, at first to guarantee in N step iteration, to use with a kind of channel, promptly Eve need receive

Individual symbol.If guarantee that channel exists

Individual symbol changed in the duration, promptly

Eve just can't correctly estimate channel so.Therefore, as long as the antenna number of using is abundant, just can make

Enough big, thus make

Final assurance listener-in can't acquisition of information.

Fig. 4 is the comparison diagram of the error rate of this patent method and background technology method (reference method) under the different transmission power with transmit power curve.Along with the increase of transmitting power, the error rate of Bob can significantly reduce, and this patent method can obtain the error rate lower than reference method under the identical situation of transmitting power.

For what being interpreted as under the same transmit gross power, the this patent method can be obtained the performance better than reference method (Bob has the lower error rate), and Fig. 5 provides this patent method and the signal to noise ratio contrast of reference method at different receiving terminals under identical total transmitting power.As can be seen from the figure, using this patent method why can allow Bob obtain the lower error rate is because this method makes the received signal to noise ratio of Bob compare reference method improve a lot (5dB), because two kinds of methods all do not have to do particular processing at Eve, the received signal to noise ratio of Eve is identical under these two kinds of situations.

So far, can verify the useful effect of the safe transmission of this patent method during ensureing radio communication from technical scheme and simulation result.

Claims (3)

1. the safe transmission method of physical layer in the radio communication, the model of communication system that adopts be a cover multi-antenna base station with a single antenna mobile terminal communicate by letter as expectation right, another many antennas mobile terminal is characterized in that as the eavesdropping user, comprises the steps:

A) the single antenna desired user at first sends the unencrypted solicited message to the base station, and this solicited message comprises the pilot frequency sequence that is used for channel estimating simultaneously, and pilot frequency sequence is all known symbol of receiving-transmitting sides;

B) base station receives solicited message, utilizes pilot frequency sequence to estimate channel h between them _AB(n), channel estimating adopts the channel estimation methods of existing band pilot tone, considers that time division duplex and channel become slowly, and the base station is identical with desired user to the channel of base station direction to the channel of desired user direction, is h _AB(n);

C) the base station bit that will send utilizes known a kind of phase modulation method to be modulated to constellation point symbol b (n), n=1,2,3 ..., preceding at each emission b (n), need be from all J root antennas picked at random J _RandThe root antenna, J _Rand＜J utilizes this J _RandThe channel I of root antenna _Rand(n) h _AB(n), design weight coefficient

Weight coefficient is changed fast, be weighted, at last the J that is choosing according to the symbol after specifying gross power with weighting to sent constellation point symbol b (n) _RandLaunch on the root antenna.I wherein _Rand(n) be the selection matrix at random of a J * J dimension, I _Rand(n) random arrangement J on the diagonal _RandIndividual 1, all the other elements are 0;

D) desired user receives the symbol after the weighting, and promptly the weighting symbol utilizes the maximum likelihood method decoding;

E) the eavesdropping user receives the symbol after the weighting, makes weight coefficient change fast because handle the base station, and the eavesdropping user can't utilize the blind balance method decoding, if also utilize the maximum likelihood method decoding, then the error rate is 50%, has finally realized safe transmission.

2. the safe transmission method of physical layer in the radio communication as claimed in claim 1 is characterized in that, in the described step b), the channel estimation methods of existing band pilot tone is LS channel estimating, MMSE channel estimating or its improved method.

3. the safe transmission method of physical layer in the radio communication as claimed in claim 1 is characterized in that, in the described step c), adopts the Ditital modulation method of BPSK or QPSK when phase modulation method; Then in the step d), desired user utilizes maximum likelihood method decoding simplified formula to be

Wherein x (n) expression is corresponding to a kind of constellation point of phase modulation method, and y (n) represents the signal that desired user receives.

Images