CN106211143A - A kind of safe transmission discrete power control method based on fountain codes - Google Patents

Abstract

The invention discloses a kind of safe transmission discrete power control method based on fountain codes, comprising the following steps: 1) each time slot transmitting terminal uses fountain codes to encode, and speed R (μ | γ) of maximum when obtaining transmit powers μ different under instantaneous signal-to-noise ratio γ according to the long L of bag of fountain codes；2) optimal varied rate λ of the speed that unit power is increased in each time slot under transmitting terminal calculates at power-limited condition according to the maximum rate R (μ | γ) when different signal to noise ratios^*With transmission number ω maximum in each time slot；3) system is according to the instantaneous signal-to-noise ratio γ of user feedback, determines to send number i of fountain codes packet, and distributes corresponding power μ.The inventive method takes full advantage of in fountain coding transmitting procedure without the transmitting feature retransmitted, it is designed with the power control scheme of beneficially lifting legitimate receipt end speed by receiving the instantaneous signal-to-noise ratio of validated user feedback at transmitting terminal, thus makes receiving terminal have the speed of maximum under the premise that security is guaranteed.

Description

A kind of safe transmission discrete power control method based on fountain codes

Technical field:

The invention belongs to wireless communication technology field, be specifically related to a kind of safe transmission discrete power control based on fountain codes Method processed, this control method utilizes fountain codes technology to reduce in wireless data transmission and eavesdrops the intercept probability of user and carry The efficiency of transmission of high transmitting terminal.

Background technology:

Compared with cable communication system, the opening of cordless communication network makes its safe transmission problem more thorny, this It is because listener-in and is prone to intercept the confidential data of wireless device end.The potential safety existed for listener-in in wireless network Risk, existing upper layer network protocol layer uses encryption technology to guarantee that data are not ravesdropping, but the realization of encryption technology is Based on listener-in's computing capability limited it is assumed that and when eavesdropping user side computing capability unrestricted, then safety cannot ensure. Additionally, key management mechanism is also difficult to realization for dynamic wireless network.

Meanwhile, fountain codes is as a kind of emerging transmitting technology received much concern, and it uses the side of random coded Formula, produces new fountain codes symbol continually, and each new fountain codes symbol carries certain useful information for receiving terminal, After user receives the most just acknowledgement decoding of enough fountain codes symbols, transmitting terminal just stops coding, then front relative to coding with regard to really For the forward error correction of constant bit rate, the code check of fountain codes is unfixed, and fountain codes is also known as no-rate codes.Therefore in wireless biography After defeated transmitting terminal introduces fountain codes, by utilizing two controllable parameters (degree and the selected information bag in fountain codes cataloged procedure Sequence number), be designed with beneficially promote validated user decoding rate verification packet encoder scheme, thus ensure validated user end prior to Eavesdropping end successfully decoded.Traditional fountain codes delivery plan, the state difference of validated user ratio eavesdropping when, have employed phase The power control scheme closed, it is ensured that the safety of data transmission；But validated user is better than eavesdropping User Status when, Do not take any measures to improve transmitting terminal transfer rate.

Summary of the invention:

It is an object of the invention to the shortcoming overcoming above-mentioned prior art, it is provided that a kind of safe transmission based on fountain codes Discrete power control method, the method can be effectively reduced the intercept probability of eavesdropping user and improve the transmission effect of transmitting terminal Rate.

For reaching above-mentioned purpose, the present invention adopts the following technical scheme that and realizes:

A kind of safe transmission discrete power control method based on fountain codes, carries out wireless data transmission using fountain codes Before, transmitting terminal first has to secret file to be passed is divided into k the fountain codes packet s being associated₁,s₂,...,s_k, and The a length of L of bag of each fountain codes, the method comprises the following steps:

1) each time slot transmitting terminal uses fountain codes coded method to complete the cataloged procedure of a fountain bag, and according to instantaneous Signal to noise ratio γ obtains maximum speed R under different transmit powers μ (μ | γ)；

2) when transmitting terminal calculates power limited according to the maximum rate R (μ | γ) under different signal to noise ratios in each time slot Speed optimal varied rate λ when unit power increases^*And transmission number ω that in each time slot, fountain codes is maximum；

3) system is according to the instantaneous signal-to-noise ratio γ of user feedback, calculates and sends different number when current instantaneous signal-to-noise ratio γ The subgradient of power corresponding to mesh fountain codes packet is interval, and judges iptimum speed rate of change λ^*Which it is belonging to send number The subgradient of mesh fountain codes power is interval, and transmitting terminal is according to λ^*Affiliated interval judgement sends number i of fountain codes packet, meter Calculate and send the power μ that i fountain bag needs to distribute⁽ⁱ⁾。

The present invention is further improved by, step 1) in obtain the tool of maximum rate R under different transmit power μ (μ | γ) Body step is as follows:

Bandwidth B that 1-1) first transmitting terminal is allocated according to user and the long L of bag of fountain codes, obtain specifying instantaneous noise The power needed than transmitting terminal when sending different number of fountain codes j under γ:

${\mathrm{\μ}}^{\left(j\right)}=\frac{1}{\mathrm{\γ}}(2^{\frac{jL}{BT}}-1)$

What now j represented is the number of the fountain codes packet sent, and the span of j is whole natural number；

1-2) under specifying instantaneous signal-to-noise ratio γ, the speed obtained of different transmit powersIt is (iL, μ^(j)) convex Combination, in order to maximize transmit power, is taken at speed R maximum in the case of identical transmit power (μ | γ), obtains:

$R\left(\mathrm{\&mu;}\right|\mathrm{\&gamma;})=\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}\mathrm{\&mu;},{\mathrm{\&mu;}}^{\left(j\right)}\&le;\mathrm{\&mu;}<{\mathrm{\&mu;}}^{(j+1)}$

The maximum number sending fountain bag in the most each time slot is not have conditional, and scope is whole natural number.

The present invention is further improved by, step 2) in iptimum speed rate of change λ^*With the maximum sent in each time slot What fountain codes number ω determined specifically comprises the following steps that

2-1) the Lagrangian formula of foundation maximization user's average speed:

$L(\mathrm{\&mu;},\mathrm{\&lambda;})={\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}R\left(\mathrm{\&mu;}\right|\mathrm{\&gamma;})p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}-\mathrm{\&lambda;}{\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}\mathrm{\&mu;}\left(\mathrm{\&gamma;}\right)p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}$

Maximize transfer rate and set up Lagrangian optimize formula time, power meets restrictive condition:

$E\&lsqb;\mathrm{\&mu;}\&rsqb;={\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}\mathrm{\&mu;}\left(\mathrm{\&gamma;}\right)p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}\&le;1$

The most normalized power is less than equal to mean power；

2-2) carry out numerical computations according to Lagrangian to solve and obtain, when increasing unit power, optimal speed change Rate λ^*；

2-3) according to maximum rate rate of change λ^*, obtain transmitting terminal transmission fountain codes packet and reach maximum channel capacity Time, transmission number ω that in each time slot, fountain codes is maximum.

The present invention is further improved by, step 3) determine that transmitting terminal sends the concrete of fountain codes packet number operation Step is as follows:

3-1) obtain the subgradient when different power μ according to rate equation R (μ) interval:

$\&part;R\left(\mathrm{\&mu;}\right)=\left\{\begin{array}{cc}\{\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\}& {\mathrm{\&mu;}}^{\left(j\right)}<\mathrm{\&mu;}<{\mathrm{\&mu;}}^{(j+1)}\\ \&lsqb;\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;},\frac{L\mathrm{\&gamma;}}{2^{\frac{(j-1)L}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\&rsqb;& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(j\right)},j=1,2,\mathrm{...}\mathrm{\&omega;}-1\\ (-\mathrm{\&infin;},\frac{L\mathrm{\&gamma;}}{2^{\frac{(j-1)L}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\&rsqb;& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(\mathrm{\&omega;}\right)}\\ \&lsqb;\frac{L\mathrm{\&gamma;}}{2^{\frac{L}{BT}}-1}-\mathrm{\&lambda;},+\mathrm{\&infin;})& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(0\right)}\end{array}\right.$

Wherein, j represent under not carrying out signal to noise ratio γ specified before power control the fountain bag that may send Number, the bag of what L represented is fountain bag is long, bandwidth that user is allocated that what B represented is, T is the slot length of flat fading channel, ω represents that maximum sends the minima of fountain bag number when reaching maximum channel capacity when specifying and wrapping long L, and transmitting terminal is sending The when of the number of different fountain bags, transmitting terminal can distribute corresponding power μ, and under different power, speed R (μ) has phase The subgradient answered is interval

3-2) judge λ^*Belong in the number j subgradient interval of the fountain codes sending how many numbers, according to λ^*Affiliated time ladder Degree interval, transmitting terminal determines to send number i of fountain codes packet, and what wherein i represented is transmitting terminal after overpower control Determine the number of the fountain bag sent, simultaneously to the transmitting terminal corresponding power of distribution:

${\mathrm{\&mu;}}^{\left(i\right)}=\frac{1}{\mathrm{\&gamma;}}(2^{\frac{iL}{BT}}-1)$

If 3-3) transmitting terminal receives Bob data and decoded feedback, then return to step 1)；Otherwise file not by Bob has decoded, and returns to 3-2).

Compared with traditional scheme, the present invention, validated user is better than eavesdropping User Status when, uses power to control Method, is different from traditional scheme and only sends a fountain bag.When the status information of validated user is good time, calculate legal use The noise γ gradient next time interval that family is currentThen optimal transmission rate λ is judged^*Fall interval in which subgradient, with This number i determining to send fountain bag, transmitting terminal calculates, according to number i of fountain bag, the power μ that transmitting terminal is allocated simultaneously⁽ⁱ⁾。 The number of the fountain bag sent in each time slot of the present invention is greater than equal to 1, and therefore the speed of traditional scheme is this The minimum-rate of the lower limit of bright speed, the i.e. present invention is exactly the speed of traditional scheme.When validated user and eavesdropping user can connect Receive a fountain bag, but the status information of validated user may insure that the when that validated user receiving at least 2 fountain bags, In traditional scheme, transmitting terminal only sends 1 fountain bag, validated user and eavesdropping user and all receives this fountain bag.And in the present invention, Validated user can receive 2 fountain bags, and eavesdropping user can only receive 1 fountain bag, and validated user was received before eavesdropping user To the number of the fountain bag that decoding needs, validated user can receive safely file.The present invention makes full use of the shape of validated user State information determines the number of the fountain codes that transmitting terminal is to be sent.Further increase in the case of the speed improving transmitting terminal The safety of system.Currently available technology is not involved with the technology of this respect.

Accompanying drawing illustrates:

Fig. 1 is the system model figure of the present invention；

Fig. 2 is the realization mechanism figure (operational flowchart) of the present invention；

Fig. 3 is that under the inventive method difference bag length, single time-slot throughput changes schematic diagram in K value；

Fig. 4 is single time-slot throughput comparison diagram under the long L of difference bag of the present invention；

Fig. 5 is that the inventive method L is not both intercept probability comparison diagram；

Fig. 6 is the intercept probability comparison diagram of the fountain bag number that the inventive method file is divided into；

Intercept probability comparison diagram when Fig. 7 is the inventive method Eve position difference.

Detailed description of the invention:

The present invention is described in further detail with being embodied as example below in conjunction with the accompanying drawings.

Fountain codes uses a kind of linear coding and decoding mode, and transmitting terminal can be allowed to produce coded identification continually, directly Just stop coding sending to receiving the feedback that user is properly received, be a kind of chnnel coding increasing transmission reliability.When wireless Transmission transmitting terminal use fountain codes coding after, transmitting terminal receive validated user be properly received file feedback just stop transmission Fountain codes packet.

The core concept of the present invention is that transmitting terminal uses fountain codes coded method to k letter in wireless data transmission Breath bag encodes, and is designed with beneficially lifting using the instantaneous signal-to-noise ratio of legitimate receipt end feedback as the foundation that power controls The scheme of transmission rate, thus ensure that validated user end is prior to eavesdropping end successfully decoded.Compared with the coded system of tradition fountain codes, The present invention program can be according to legal instantaneous signal-to-noise ratio, and the number that transmitting terminal sends in single time slot fountain codes is done in real time Ground adjusts, and can significantly improve the speed that in wireless data transmission, receiving terminal receives, meanwhile reduce eavesdropping user Intercept probability.

With reference to Fig. 1, the system model figure of the present invention is described in detail below:

Consider a wireless transmitting system comprising three nodes, one of them source node Alice, a destination node Bob and listener-in Eve.Private data file is issued Bob by Alice attempt, and meanwhile Eve can eavesdrop sent literary composition Part information.Before wireless data transmission, first secret file to be sent is divided into and is associated with each other the k wrapping a length of L by Alice Individual packet, then Alice uses fountain codes coded method to encode k information bag.Bob and Eve attempts to obtain foot Enough purpose fountain codes packets are to recover original secret data file.K information is completed when Bob end receives enough fountain bags The decoding of bag, then need to send feedback information to Alice end and inform that it terminates coding and sends.Like this, stop sending out when Alice end When sending fountain bag, if Eve end is not fully complete the decoding of k information bag, then the transmission of this private data file security is ensured.

In Fig. 1, Alice → Bob link is legitimate channel and Alice → Eve link is tapping channel, these two wireless communication Road is all modeled as block flat Rayleigh fading channel, and in the sending time slots of the most each bag, channel coefficients keeps constant, different time-gap Between independent change.Channel coefficients h between node i and node j_ijIt is that a zero-mean, variance areCirculation Symmetric complex stochastic variable, wherein d_ijRepresenting the distance between node i and node j, α is path loss coefficient.The additivity of receiving terminal The variance of white Gaussian noise n is N₀.If the power that Alice end sends verification bag isThen the reception SNR of receiving terminal j can be with table It is shown as γ_Aj=ρ | h_Aj|², andExpression system SNR.

With reference to Fig. 2, the realization mechanism figure (operational flowchart) of the present invention specifically comprises the following steps that

It should be understood that before wireless data transmission, first secret file to be sent is divided into each other by transmitting terminal K the information bag (s being associated₁,s₂,...,s_k), and a length of L of bag of each fountain codes, the transmission of following each time slot comprises Following steps:

1) each time slot transmitting terminal uses novel fountain code encoding method to complete the cataloged procedure of a fountain bag, and according to Maximum speed R that instantaneous signal-to-noise ratio γ obtains obtaining under different transmit powers μ (μ | γ)；

2) transmitting terminal calculates under power-limited condition each according to the maximum rate R (μ | γ) under different signal to noise ratios Transmission number ω maximum in the optimal varied rate λ * of speed and each time slot when unit power increases in time slot；

3) system is according to the instantaneous signal-to-noise ratio γ of user feedback, calculates and sends different number when current instantaneous signal-to-noise ratio γ During mesh fountain codes packet, the subgradient of correspondence power is interval, and judges iptimum speed rate of change λ * is belonging to send which number The subgradient of mesh fountain codes power is interval, and transmitting terminal sends the number of fountain codes packet according to the interval judgement belonging to λ *, with And distribute corresponding power.

Step 1) in obtain specifically comprising the following steps that of maximum rate under different transmit power

Bandwidth B that 1-1) first transmitting terminal is allocated according to user and the long L of bag of fountain codes, specifying instantaneous signal-to-noise ratio γ Under transmitting terminal needs when obtaining sending different number of fountain codes j power:

${\mathrm{\&mu;}}^{\left(j\right)}=\frac{1}{\mathrm{\&gamma;}}(2^{\frac{jL}{BT}}-1),j=0,1,2,...$

What now j represented is the number of the fountain codes packet sent, and the span of j is whole natural number.

1-2) under specifying instantaneous signal-to-noise ratio γ, the speed obtained of different transmit powersIt is (iL, μ^(j)) Convex combination.In order to maximize transmit power, it is taken at speed R maximum in the case of identical transmit power (μ | γ), obtains:

$R\left(\mathrm{\&mu;}\right|\mathrm{\&gamma;})=\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}\mathrm{\&mu;},{\mathrm{\&mu;}}^{\left(j\right)}\&le;\mathrm{\&mu;}<{\mathrm{\&mu;}}^{(j+1)},j=0,1,2,...$

In the most each time slot send fountain bag maximum number be do not have conditional.

Step 2) in iptimum speed rate of change λ^*The concrete step determined with maximum fountain codes number i sent in each time slot Rapid as follows:

2-1) the Lagrangian formula of foundation maximization user's average speed:

$L(\mathrm{\&mu;},\mathrm{\&lambda;})={\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}R\left(\mathrm{\&mu;}\right|\mathrm{\&gamma;})p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}-\mathrm{\&lambda;}{\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}\mathrm{\&mu;}\left(\mathrm{\&gamma;}\right)p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}$

Maximizing transfer rate and when setting up, power needs to meet restrictive condition:

$E\&lsqb;\mathrm{\&mu;}\&rsqb;={\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}\mathrm{\&mu;}\left(\mathrm{\&gamma;}\right)p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}\&le;1$

The most normalized power is less than equal to mean power.

2-2) carry out numerical computations according to Lagrangian to solve and obtain, when increasing unit power, optimal speed change Rate λ^*。

2-3) according to maximum rate rate of change λ^*, when transmitting terminal transmission fountain codes packet reaches maximum channel capacity, often Minima ω of the number of the maximum fountain code data bag sent in individual time slot.

Step 2) in the core of fountain codes coded method be: the bandwidth B being allocated according to user and the long L of fountain bag bag Obtain rate gain λ optimal under unit power^*With upper limit ω that fountain codes packet in each time slot sends number.

Step 3) determine that transmitting terminal sends specifically comprising the following steps that of fountain codes packet number operation

3-1) obtain the subgradient when different power according to rate equation interval:

$\&part;R\left(\mathrm{\&mu;}\right)=\left\{\begin{array}{cc}\{\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\}& {\mathrm{\&mu;}}^{\left(j\right)}<\mathrm{\&mu;}<{\mathrm{\&mu;}}^{(j+1)}\\ \&lsqb;\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;},\frac{L\mathrm{\&gamma;}}{2^{\frac{(j-1)L}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\&rsqb;& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(j\right)},j=1,2,\mathrm{...}\mathrm{\&omega;}-1\\ (-\mathrm{\&infin;},\frac{L\mathrm{\&gamma;}}{2^{\frac{(j-1)L}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\&rsqb;& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(\mathrm{\&omega;}\right)}\\ \&lsqb;\frac{L\mathrm{\&gamma;}}{2^{\frac{L}{BT}}-1}-\mathrm{\&lambda;},+\mathrm{\&infin;})& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(0\right)}\end{array}\right.$

Here the fountain bag that may send under not carrying out signal to noise ratio γ specified before power control that j represents Number, the bag of what L represented is fountain bag is long, and bandwidth that user is allocated that what B represented is, T is that the time slot of flat fading channel is long Degree, ω represents that maximum sends the minima of fountain bag number when reaching maximum channel capacity when specifying and wrapping long L, and transmitting terminal is being sent out The when of sending the number of different fountain bags, transmitting terminal can distribute corresponding power μ, and under different power, speed R (μ) has Corresponding subgradient is interval

3-2) judge λ^*Belong in the number j differential interval of the fountain codes sending how many numbers.According to affiliated subgradient Interval, transmitting terminal determines to send number i of fountain codes packet, simultaneously to the transmitting terminal corresponding power of distribution:

${\mathrm{\&mu;}}^{\left(i\right)}=\frac{1}{\mathrm{\&gamma;}}(2^{\frac{iL}{BT}}-1)$

If 3-3) transmitting terminal receives Bob data and decoded feedback, then return to step 1；Otherwise file not by Bob has decoded, and returns to 3-2).

Step 3) in different signal to noise ratios under send fountain codes counting method core be: according to the instantaneous noise of user Determine that transmitting terminal sends number i of fountain codes in current time slots and distributes corresponding power μ than γ⁽ⁱ⁾, at validated user Bob ratio is under listener-in's Eve channel condition, and transmitting terminal uses Poewr control method of the present invention, as long as appointing in sending the period of file The number of the fountain bag that the middle Bob that anticipates receives is more than Eve, then just than Eve first by file decoding more out, Eve end is or not Bob By secret file decoding out can so make to have fully ensured that the safety of file while maximizing speed.

In sum, the main realization mechanism of the present invention is that Alice uses fountain codes to compile in wireless data transmission Code method k information bag is encoded, and using Bob feedback the bag sequence number set of decoded information as encode power, if In respect of being beneficial to promote the verification packet encoder scheme of Bob end decoding rate, thus ensure that Bob end is prior to Eve end successfully decoded.This volume The core of code scheme is will to decode in set D all elements and do not decode some element in set and carry out XOR, according to stealing As long as the fading characteristic Eve end listening channel has a unsuccessful decoding of element in D, then Eve must solve remaining information bag, The most now Eve end is eavesdropped unsuccessfully.

In Fig. 3 emulation, along with K value constantly increases, the data volume that validated user receives in time slot T the most constantly increases Greatly.Meanwhile, the data volume of the reception of Bob end does not ad infinitum increase along with the increase of K, but levels off to one surely Definite value.In simulations, under the long L of each bag, there is minima ω of a K reaching maximum rate, the most each time slot sends spray The maximum of spring code packet there is no need to exceed this value, exceedes this value to speed when Bob time slot maximum sends number Improve and there is no effect.And can be definite value Γ at the product of the long L of ω value and bag, the value of ω is greater than product divided by bag The smallest positive integral of long L.

In the emulation of Fig. 4, Alice uses the different long L of bag to send fountain codes packet, and along with the increase of L, Bob is at list The data volume received in digit time slot reduces constantly.When the value wrapping long L is more than Γ, the value of K is 1 the most always, now single The data volume that in individual time slot, Bob can receive is declining, because could send data when Bob instantaneous channel capacity is greater than L Bag, this causes the outage probability that Bob is the biggest.

In emulation in Fig. 5, the intercept probability of Eve when Alice uses difference bag length to be transmitted.In emulation, file quilt The fountain codes packet being divided into k is to wrap long L the longest, and intercept probability is the lowest.Simultaneously in the long L of identical bag, a file is divided into The number of fountain codes packet the most, intercept probability is the least.

Being divided into the increase of fountain bag number along with a file in Fig. 6, scheme proposed by the invention is cut listener-in Obtain probability aspect and be much better than traditional benchmark scheme；Intercept probability reduces with the increase of fountain bag number.

In Fig. 7, along with the increase of Eve end position, the intercept probability of power control scheme of the present invention is significantly lower than tradition side The intercept probability of case.When the position of Eve is to during close to 1.7, and the scheme that power of the present invention controls makes the intercept probability of Eve end connect It is bordering on 0；When the when of being closely located to 1.0 of Eve end, the solution of the present invention is much better than traditional scheme, can keep good safety Property.

In sum, the inventive method is decoded into power, Alice end efficiency of transmission three at listener-in's intercept probability, Eve end Individual aspect is superior to traditional benchmark scheme.

Claims (4)

1. a safe transmission discrete power control method based on fountain codes, it is characterised in that carry out nothing using fountain codes Before the transmission of line data, transmitting terminal first has to secret file to be passed is divided into k the fountain codes packet s being associated₁, s₂,...,s_k, and a length of L of bag of each fountain codes, the method comprises the following steps:

1) each time slot transmitting terminal uses fountain codes coded method to complete the cataloged procedure of a fountain bag, and according to instantaneous noise Maximum speed R under different transmit powers μ (μ | γ) is obtained than γ；

2) unit in each time slot when transmitting terminal calculates power limited according to the maximum rate R (μ | γ) under different signal to noise ratios Speed optimal varied rate λ when power increases^*And transmission number ω that in each time slot, fountain codes is maximum；

3) system is according to the instantaneous signal-to-noise ratio γ of user feedback, calculates and sends different number spray when current instantaneous signal-to-noise ratio γ The subgradient of power corresponding to spring code packet is interval, and judges iptimum speed rate of change λ^*Which it is belonging to send number spray The subgradient of spring code power is interval, and transmitting terminal is according to λ^*Affiliated interval judgement sends number i of fountain codes packet, calculates and sends out I fountain bag is sent to need the power μ of distribution⁽ⁱ⁾。

Safe transmission discrete power control method based on fountain codes the most according to claim 1, it is characterised in that step 1) specifically comprising the following steps that of maximum rate R under different transmit power μ (μ | γ) is obtained in

Bandwidth B that 1-1) first transmitting terminal is allocated according to user and the long L of bag of fountain codes, obtain specifying instantaneous signal-to-noise ratio γ The power that during lower transmission different number of fountain codes j, transmitting terminal needs:

${\mathrm{\&mu;}}^{\left(j\right)}=\frac{1}{\mathrm{\&gamma;}}(2^{\frac{jL}{BT}}-1)$

What now j represented is the number of the fountain codes packet sent, and the span of j is whole natural number；

1-2) under specifying instantaneous signal-to-noise ratio γ, the speed obtained of different transmit powersIt is (iL, μ^(j)) convex group Close, in order to maximize transmit power, be taken at speed R maximum in the case of identical transmit power (μ | γ), obtain:

$R\left(\mathrm{\&mu;}\right|\mathrm{\&gamma;})=\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}\mathrm{\&mu;},{\mathrm{\&mu;}}^{\left(j\right)}\&le;\mathrm{\&mu;}<{\mathrm{\&mu;}}^{(j+1)}$

The maximum number sending fountain bag in the most each time slot is not have conditional, and scope is whole natural number.

Safe transmission discrete power control method based on fountain codes the most according to claim 1, it is characterised in that step 2) iptimum speed rate of change λ in^*With specifically comprising the following steps that maximum fountain codes number ω sent in each time slot determines

2-1) the Lagrangian formula of foundation maximization user's average speed:

$L(\mathrm{\&mu;},\mathrm{\&lambda;})={\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}R\left(\mathrm{\&mu;}\right|\mathrm{\&gamma;})p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}-\mathrm{\&lambda;}{\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}\mathrm{\&mu;}\left(\mathrm{\&gamma;}\right)p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}$

Maximize transfer rate and set up Lagrangian optimize formula time, power meets restrictive condition:

$E\&lsqb;\mathrm{\&mu;}\&rsqb;={\&Integral;}_{-\mathrm{\&infin;}}^{+\mathrm{\&infin;}}\mathrm{\&mu;}\left(\mathrm{\&gamma;}\right)p\left(\mathrm{\&gamma;}\right)d\mathrm{\&gamma;}\&le;1$

The most normalized power is less than equal to mean power；

2-2) carry out numerical computations according to Lagrangian to solve and obtain, when increasing unit power, optimal speed rate of change λ^*；

2-3) according to maximum rate rate of change λ^*, obtain transmitting terminal and send fountain codes packet when reaching maximum channel capacity, each Transmission number ω that in time slot, fountain codes is maximum.

Safe transmission discrete power control method based on fountain codes the most according to claim 1, it is characterised in that step 3) determine that transmitting terminal sends specifically comprising the following steps that of fountain codes packet number operation

3-1) obtain the subgradient when different power μ according to rate equation R (μ) interval:

$\&part;R\left(\mathrm{\&mu;}\right)=\left\{\begin{array}{cc}\{\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\}& {\mathrm{\&mu;}}^{\left(j\right)}<\mathrm{\&mu;}<{\mathrm{\&mu;}}^{(j+1)}\\ \&lsqb;\frac{L\mathrm{\&gamma;}}{2^{\frac{jL}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;},\frac{L\mathrm{\&gamma;}}{2^{\frac{(j-1)L}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\&rsqb;& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(j\right)},j=1,2,\mathrm{...}\mathrm{\&omega;}-1\\ (-\mathrm{\&infin;},\frac{L\mathrm{\&gamma;}}{2^{\frac{(j-1)L}{BT}}(2^{\frac{L}{BT}}-1)}-\mathrm{\&lambda;}\&rsqb;& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(\mathrm{\&omega;}\right)}\\ \&lsqb;\frac{L\mathrm{\&gamma;}}{2^{\frac{L}{BT}}-1}-\mathrm{\&lambda;},+\mathrm{\&infin;})& \mathrm{\&mu;}={\mathrm{\&mu;}}^{\left(0\right)}\end{array}\right.$

Wherein, j represents the number of the fountain bag that may send under not carrying out signal to noise ratio γ specified before power control, L Represent is that the bag of fountain bag is long, and bandwidth that user is allocated that what B represented is, T is the slot length of flat fading channel, ω table Showing that when reaching maximum channel capacity when specifying and wrapping long L, maximum sends the minima of fountain bag number, transmitting terminal is sending difference The number of fountain bag when transmitting terminal can distribute corresponding power μ, under different power, speed R (μ) has accordingly Subgradient is interval

3-2) judge λ^*Belong in the number j subgradient interval of the fountain codes sending how many numbers, according to λ^*Affiliated subgradient district Between, transmitting terminal determines to send number i of fountain codes packet, and what wherein i represented is that transmitting terminal determines after overpower control The number of the fountain bag sent, simultaneously to the transmitting terminal corresponding power of distribution:

${\mathrm{\&mu;}}^{\left(i\right)}=\frac{1}{\mathrm{\&gamma;}}(2^{\frac{iL}{BT}}-1)$

If 3-3) transmitting terminal receives Bob data and decoded feedback, then return to step 1)；Otherwise file is not by Bob Decoding completes, and returns to 3-2).