CN111556222B - Fountain code-based image data variable-rate safe transmission method - Google Patents

Abstract

The invention provides a fountain code-based image data variable-rate safe transmission method, which adjusts the number of code packets sent by each time slot according to the channel condition of a legal link so as to fully utilize channel resources and reduce decoding delay. And simultaneously, the channel quality advantage of a legal link is expanded, the safe transmission of information is ensured, and source data packets participating in the encoding process are selected according to the importance of the source data packets, the time delay constraint of a system and the channel quality. The method of the invention can enable a legal receiver to accumulate important data as soon as possible, simultaneously prevent an eavesdropper from intercepting the data, ensure the communication safety of the legal user and simultaneously give consideration to the requirements of the user on time delay and service quality.

Description

Fountain code-based image data variable-rate safe transmission method

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a fountain code-based image data variable-rate safe transmission method.

Background

In fountain code based transmission, a source file is divided into N equal length packets of source data. The sending end carries out bitwise XOR operation on different source data packets to construct an unlimited number of fountain packets, and then the fountain packets are transmitted to the receiving end until the receiving end successfully accumulates N mutually independent coding packets to recover the whole file. This feature of fountain codes means that legitimate users will not leak information as long as enough encoded packets are accumulated before an eavesdropper. The fountain code based anti-eavesdropping technique can significantly improve the transmission rate between legitimate transceivers compared to traditional physical layer security strategies designed primarily to maximize the privacy rate or minimize the privacy disruption probability, since the rate is limited only by shannon capacity.

Most of today's efforts to enhance transmission security by fountain coding deliver coded packets at a constant rate, i.e. the transmitter sends only one coded packet per time slot, regardless of how the fountain packet is constructed. However, due to the randomness of the wireless channel, when the channel condition is good, only one code packet is transmitted, which easily causes waste of resources. In addition, most existing fountain code based transmission schemes mainly focus on the interception probability of the system, that is, they only concern the transmission security of the bit stream. However, these methods are not applicable to image services that require adequate consideration of the mutual coupling and constraint relationship between security constraints and diversified quality of service requirements.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a fountain code-based image data variable-rate safe transmission method, which can fully consider the mutual coupling and restriction relation between security restriction and diversified service quality requirements, simultaneously considers the multidimensional requirements of reliability, safety, time delay and the like, and provides comprehensive service quality guarantee for users.

The purpose of the invention is realized by the following technical scheme:

a fountain code-based image data variable-rate safe transmission method comprises the following steps:

(1) before transmission occurs, a legal transmitter firstly divides a source file into N source data packets, each source data packet comprises K bits, and carries out importance ordering on each source data packet to obtain an ordered data packet set pi ═ pi₁,π₂,…,π_NA source packet with a smaller index sequence number is more important;

(2) in the transmission process, at the end of each time slot, the legal transmitter obtains the index of the source data packet recovered by the legal receiver through a feedback channel; then, the constructed decoded set D is updated_πAnd un-decoded set U_πWherein D is_πContains all source packets Bob has recovered, and U_πContaining all Bob unrecovered source packets; in the updated U_πIn the method, source packets are reordered according to the importance of each source packet, and the indexes of the packets start from 1, and the updated U is sent_πIs marked as U_π＝{π₁,π₂,…}；

(3) At the beginning of the next time slot, the legal transmitter first obtains the channel quality gamma of the legal link according to the channel feedback_ABThen with an interrupt threshold gamma_vBy comparison, the process of the first and second steps,

when gamma is_AB<γ_vThen, no coded packet is transmitted in the current time slot, where γ_vIs the transmission interruption threshold;

when gamma is_AB≥γ_vIn time, the number of the code packets which can be correctly received by Bob at most under the current legal link channel condition is calculated

Then entering the next step;

(4) alice will have last since D_πSource data packet pi recovered from middle_recAnd the slave U_πThe selected L source packets { pi_ind,…,π_ind+L-1Fountain coding is carried out to obtain L coding packets { t }₁,…,t_LThe construction method of the coding packet is as follows:

wherein ind is from U_πAn index of a source packet;

(5) and (4) feeding the decoded source data packet index back to Alice by Bob, and repeating the steps (2) to (4) until the whole source file is solved by Bob or the delay requirement limit is reached.

Further, assuming that B and T are the system bandwidth and the duration of the transmission slot, i and j represent two nodes in the system, respectively, the channel coefficient of link i → j is modeled as a mean value of zero and a variance of zero

The circularly symmetric complex Gaussian random variable is recorded as

Wherein

Alpha and d_ijRespectively representing the path loss exponent and the distance between nodes i and j, and the SNR is the average transmit power of the transmitter

And receiving end noise variance N₀The interruption threshold gamma is defined by the ratio between the two thresholds gamma, in the case of a condition that the probability of eavesdropping on the coded packet Eve must be less than eta_vThe determination method of (2) is as follows:

wherein,

and

representing the channel coefficient variances of links a → E and a → B, respectively.

Further, the ind is determined by the following formula:

wherein M represents U up to the current time slot number_πNumber of source packets, T_reqAnd T_comsRespectively representing the delay limit required for transmitting a complete file and the transmission time that has been consumed up to the current time slot, both times being measured in units of the number of time slots, T_expIndicating the number of slots required on average to transfer a complete file.

The invention has the following beneficial effects:

(1) the transmission method provided by the invention can adaptively adjust the number of the coding packets transmitted each time by fully utilizing channel resources, and reduce the decoding time delay of legal users. The requirement of high-speed transmission of image service and strict time delay limitation are met.

(2) The fountain packet construction method utilized by the transmission method provided by the invention can effectively enlarge the channel advantages of the legal link, and still has certain anti-eavesdropping performance when the average channel quality of the legal link is inferior to that of the eavesdropping link.

(3) The transmission method provided by the invention can select the source data packet participating in the encoding process each time according to the importance of the source data packet, the time delay constraint of the system and the channel quality. By using the proposed fountain packet construction method, a legitimate receiver can accumulate important data as soon as possible within a limited time delay, while also preventing eavesdroppers from intercepting the important data.

Drawings

FIG. 1 is a graph of decoding delay required by a legitimate receiver Bob to recover a source file as a function of SNR;

FIG. 2 is a graph of the percentage of source packets recovered by a legitimate receiver Bob and an eavesdropper Eve as a function of a delay threshold;

fig. 3 is an image restored at Bob and Eve by three different fountain packet constructing methods, wherein fig. 3a is an image restored at Bob according to the fountain packet constructing method proposed by the present invention, fig. 3b is an image restored at Eve according to the fountain packet constructing method proposed by the present invention, fig. 3c is an image restored at Bob by randomly selecting a source packet constructing fountain packet, fig. 3d is an image restored at Eve by randomly selecting a source packet constructing fountain packet, fig. 3e is an image restored at Bob by preferentially selecting the most important packet to construct a fountain packet, and fig. 3f is an image restored at Eve by preferentially selecting the most important packet to construct a fountain packet.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the objects and effects of the invention will become more apparent. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Assuming that the system bandwidth is B, the system comprises three nodesAlice, Bob and Eve, representing a legitimate transmitter, a legitimate receiver and an eavesdropper, respectively. The wireless channel is assumed to be a block fading channel model, and the channel coefficient h_ijIs a circularly symmetric complex Gaussian random variable with a mean of zero and a variance of

Namely, it is

Wherein α and d_ijRepresenting the path loss exponent and the distance between nodes i and j, respectively. Average transmission power of transmitter

The variance of the noise at the receiving end is N₀Is defined as SNR of

The invention relates to a fountain code-based image data variable-speed safe transmission method, which comprises the following steps:

(1) before transmission occurs, a legal transmitter firstly divides a source file into N source data packets, each source data packet comprises K bits, and carries out importance ordering on each source data packet to obtain an ordered data packet set pi ═ pi₁,π₂,…,π_N}; the source packets ordered top have higher priority, that is, the source packets with smaller index sequence number are more important to the legal receiver.

(2) In the transmission process, at the end of each time slot, the legal transmitter obtains the index of the source data packet recovered by the legal receiver through a feedback channel; then, the constructed decoded set D is updated_πAnd un-decoded set U_πWherein D is_πContains all source packets Bob has recovered, and U_πContaining all Bob unrecovered source packets; in the updated U_πIn the method, the source packets are reordered according to the importance of the source packets, and the indexes of the packets are from 1 to 1New U_πIs marked as U_π＝{π₁,π₂,…}；

(3) At the beginning of the next time slot, the legal transmitter first obtains the channel quality gamma of the legal link according to the channel feedback_ABThen with an interrupt threshold gamma_vBy comparison, the process of the first and second steps,

when gamma is_AB<γ_vThen, no coded packet is transmitted in the current time slot, where γ_vIs the transmission interruption threshold;

when gamma is_AB≥γ_vIn time, the number of the code packets which can be correctly received by Bob at most under the current legal link channel condition is calculated

Under the current legal link channel condition, Bob can receive the maximum number of code packets correctly, so that the channel resources of the legal link can be fully utilized, the receiving rate of Bob is improved, and the decoding delay is reduced.

In the step, under the constraint condition that the probability of the coded packet intercepted by Eve is smaller than eta, the maximum number of the coded packets which can be received by each time slot by a legal user is the maximum optimization target, and the interruption threshold gamma is obtained_vThe solution of (a) is as follows:

wherein,

and

representing the channel coefficient variances of links a → E and a → B, respectively.

(4) Alice will have last since D_πSource data packet pi recovered from middle_recAnd the slave U_πSelected L source packets { π_ind,…,π_ind+L-1Fountain coding is carried out to obtain L coding packets { t }₁,…,t_LThe construction method of the coding packet is as follows:

wherein ind is from U_πThe index of a source packet.

The coding structure is designed to ensure that each source packet decoded by Bob can only participate in the coding process of two fountain packets at most. This has two benefits, first, assuming Bob receives an encoded packet and decodes it to get the source packet π during time slot t_jHowever, because the condition of eavesdropping the link channel in the time slot is poor, Eve cannot recover the source data packet, and then Eve cannot recover any new undecoded source data packet in all subsequent transmissions, so that the channel advantage of a legal link is expanded; second, as long as Alice delivers a coded packet, Bob can be provided with a new undecoded source packet, so that each transmission slot is not wasted, which further reduces decoding delay.

In the above construction process of the encoded packet, ind may be determined by the following formula:

wherein M represents U up to the current time slot number_πNumber of source packets, T_reqAnd T_comsRespectively representing the delay limit required for transmitting a complete file and the transmission time that has been consumed up to the current time slot, both times being measured in units of the number of time slots, T_expIndicating the number of slots required on average to transfer a complete file.

Suppose that the probability that n coded packets can be transmitted per slot is P_nCan deduce

Wherein,

and

thus, the average number of code packets that can be transmitted per slot is represented as follows:

as can be seen from the coding scheme design of the present invention, Alice can provide Bob with a new undecoded source packet every time Alice transmits one coded packet, so Bob can decode the source packet in the average number of coded packets per time slot equal to the number of coded packets per time slot transmitted by Alice

So T_expCan be prepared from

And (4) approximately determining.

In determining the function of the ind,

representing a mapping of the difference between the instantaneous channel quality of the legitimate link and the average channel quality of the eavesdropped link to the source packet index sequence number, gamma_ABCompared with the average channel quality of the eavesdropping link, the higher the average channel quality of the eavesdropping link is, the smaller the value is, the smaller the source data packet index sequence number should be selected, which indicates that the source data packet with a higher contribution degree to the image quality tends to be sent when the channel quality of the Alice-Bob link is better than the average channel quality of the eavesdropping link, which is more beneficial for a legal receiving end to obtain important data as soon as possible, and therefore, the function of the channel quality and the image content on the fountain code structure is embodied.

And min (1, T)_req/T_exp) Are two important adjustment factors, which represent the role of delay constraints in the construction of fountain codes. In particular, T_comsThe larger the size, the more limited the transmission time remaining available until the current time, and thus important data packets should be transmitted preferentially, so that the time is the longer the transmission time is

The value of (2) is small, and the index sequence number of the selected source data packet needs to be in

On the basis of the adjustment value, multiplying the adjustment value by the adjustment value; due to T_expIndicating the number of slots required to transfer the entire file on average, so T_req/T_expThe smaller the data packet size is, the smaller the probability of transmitting a complete file within the limited time delay constraint is, the more important source data packets should be transmitted preferentially at the moment, so that a legal user can obtain enough important information under the limited time delay condition, and the experience quality of the legal user is improved. Thus taking T_req/T_expThe minimum value of and 1 is used as the adjustment factor and

the multiplication is to further reduce the value of ind under the condition that the delay constraint is tight (full file transmission cannot be completed under the limited delay constraint) so as to select more important source packets to participate in encoding. In conclusion, the fountain code construction method jointly considers multiple factors such as the priority of the source data packet, the channel quality, the time delay constraint and the like, can ensure that a legal receiver accumulates more important information as soon as possible, and simultaneously prevents an eavesdropper from intercepting the data.

After the coding is finished, let pi_recIs equal to pi_ind+L-1For the next encoding.

(5) And (4) feeding back the decoded source data packet index to Alice by Bob, and repeating the steps (2) to (4) until the whole source file is solved by Bob or the delay requirement limit is reached.

The simulation effect of the present invention will be briefly described below.

The invention adjusts the number of the coding packets transmitted each time through the channel quality of the legal link, thereby fully utilizing the channel resources and greatly reducing the decoding time delay of Bob. Meanwhile, through the structural design of the fountain packets, each coding packet is independent, and Alice can provide a new undecoded source data packet for Bob every time Alice sends one coding packet, so that the decoding delay is further reduced. The present invention has great advantages in decoding delay, as shown in fig. 1, where T is_req＝N×(1+Δ)。

The invention can provide better guarantee for information safety while reducing decoding time delay. As can be seen from fig. 2, under a tighter delay constraint, Bob can still recover more information, while the source packet percentage recovered by Eve is kept at a lower level.

Fig. 3 illustrates the present invention applied to a specific image transmission service, comparing images restored by Bob and Eve under a source packet method using three different options to participate in the encoding process. For the sake of comparison, the delay constraint is given more tightly. It can be seen that the construction method provided by the invention not only can enable a legal receiver to accumulate more important data (face area) as soon as possible within limited time delay constraint, but also can prevent an eavesdropper from intercepting the data.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and although the invention has been described in detail with reference to the foregoing examples, it will be apparent to those skilled in the art that various changes in the form and details of the embodiments may be made and equivalents may be substituted for elements thereof. All modifications, equivalents and the like which come within the spirit and principle of the invention are intended to be included within the scope of the invention.

Claims (3)

1. A fountain code-based image data variable-rate secure transmission method is characterized by comprising the following steps:

(1) the legitimate sender first sends the source file before the transmission takes placeDividing the data into N source packets, each source packet containing K bits, and performing importance sorting on each source packet to obtain a sorted data packet set pi ═ pi₁,π₂,…,π_NA source packet with a smaller index sequence number is more important;

(2) in the transmission process, at the end of each time slot, the legal transmitter obtains the index of the source data packet recovered by the legal receiver through a feedback channel; then, the constructed decoded set D is updated_πAnd un-decoded set U_πWherein D is_πContains all source packets Bob has recovered, and U_πContaining all Bob unrecovered source packets; in the updated U_πIn the method, source packets are reordered according to the importance of each source packet, and the indexes of the packets start from 1, and the updated U is sent_πIs marked as U_π＝{π₁,π₂,…}；

(3) At the beginning of the next time slot, the legal transmitter first obtains the channel quality gamma of the legal link according to the channel feedback_ABThen with an interrupt threshold gamma_vBy comparison, the process of the first and second steps,

when gamma is_AB＜γ_vThen, no coded packet is transmitted in the current time slot, where γ_vIs the transmission interruption threshold;

when gamma is_AB≥γ_vIn time, the number of the code packets which can be correctly received by Bob at most under the current legal link channel condition is calculated

Then entering the next step; wherein B and T are the system bandwidth and the duration of the transmission time slot, respectively;

(4) alice will have last since D_πSource data packet pi recovered from middle_recAnd the slave U_πSelected L source packets { π_ind,…,π_ind+L-1Fountain coding is carried out to obtain L coding packets { t }₁,…,t_LThe construction method of the coding packet is as follows:

wherein ind is from U_πAn index of a source packet;

(5) and (4) feeding the decoded source data packet index back to Alice by Bob, and repeating the steps (2) to (4) until the whole source file is solved by Bob or the delay requirement limit is reached.

2. The fountain code-based method for variable-rate secure transmission of image data as defined in claim 1, wherein i and j represent two nodes in the system, respectively, and the channel coefficients of link i → j are modeled as a mean value of zero and a variance of zero

The circularly symmetric complex Gaussian random variable is recorded as

Wherein

Alpha and d_ijRespectively representing the path loss exponent and the distance between nodes i and j, and the SNR is the average transmit power of the transmitter

And receiving end noise variance N₀The interruption threshold gamma is defined by the ratio between the two thresholds gamma, in the case of a condition that the probability of eavesdropping on the coded packet Eve must be less than eta_vThe determination method of (2) is as follows:

wherein,

and

representing the channel coefficient variances of links a → E and a → B, respectively.

3. The fountain code based image data variable rate secure transmission method according to claim 1 or 2, wherein the ind is determined by the following formula:

wherein M represents U up to the current time slot number_πNumber of source packets, T_reqAnd T_comsRespectively representing the delay limit required for transmitting a complete file and the transmission time that has been consumed up to the current time slot, both times being measured in units of the number of time slots, T_expIndicating the number of slots required on average to transfer a complete file.

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