CN117081704B - Non-orthogonal multiple access transmission method for enabling environment backscatter communication - Google Patents
Non-orthogonal multiple access transmission method for enabling environment backscatter communication Download PDFInfo
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Abstract
The invention relates to a non-orthogonal multiple access transmission method for enabling environment backscatter communication, comprising the following steps: constructing a multi-user non-orthogonal multiple access transmission system based on environment backscatter communication; the base station generates superposition information, and broadcasts the superposition information to the back scattering equipment and all NOMA users through a direct link; distributing power distribution factors and user decoding thresholds for each NOMA user according to the channel distance between the base station and each NOMA user and the back scattering equipment, and distributing BD decoding thresholds for the back scattering equipment; the back scattering equipment transmits the BD self information carried by the back scattering equipment to all NOMA users through a back scattering link; in each NOMA user, acquiring a plurality of signal-to-interference-and-noise ratios for decoding all user information and a signal-to-noise ratio for decoding BD self information; and (3) distinguishing NOMA users to which all user information belongs and identifying BD self information by using a continuous interference elimination technology so as to acquire user information corresponding to each NOMA user and BD self information of the backscatter equipment and complete information transmission on each NOMA user.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a non-orthogonal multiple access transmission method for enabling environment backscatter communication.
Background
In recent years, due to the increase of the number of access devices, the orthogonal multiple access technology faces the problem of resource starvation of the communication device to access the network. The non-orthogonal multiple access technology NOMA (non-orthogona l mu L T I P L E ACCESS) greatly improves the connection capacity of the communication system and relieves the problem of frequency spectrum resource shortage of the communication system. However, the studies on NOMA are focused on the studies on quality of service, security, etc., and there are still places to explore for the combination of NOMA and other technologies.
On the other hand, as a passive technology, environmental backscatter communication AmBC (Amb i ent backscatter commun i cat i on) is considered to be a key technology for low cost, sustainable and promising future internet of things. The BD in AmBC provides power for information transmission and self-equipment by collecting the energy of the television signal, the cellular base station, the wireless access point, etc. However, most of the current research on AmBC is focused on systems based on orthogonal multiple access technology. Recently, some research has tended to combine NOMA and AmBC to increase the number of device connections and energy utilization, further enhancing the spectral efficiency of the system.
While existing studies have made some research into AmBC-enabled NOMA systems, unfortunately, these studies have focused more on BD's application scenario; without focusing on the information transmitted by the BD from the backscatter link. This has led to the existing research of treating BD signals as interference in order to more easily obtain the desired signals; some studies assume that BD information can only be decoded at the user with the best channel conditions; other studies consider the existence of the double fading effect, assuming that other users cannot receive BD backscatter information.
In summary, the existing non-orthogonal multiple access transmission technology may cause waste of spectrum and energy; furthermore, in an actual network, when all users want to know BD information, the existing studies do not give a detailed analysis procedure.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to overcome the problems that the spectrum and energy utilization rate of the AmBC-based NOMA system in the prior art is low, and the BD self information of the backscatter devices cannot be utilized at each user.
In order to solve the technical problem, the invention provides a non-orthogonal multiple access transmission method for enabling environment backscatter communication, comprising the following steps:
Constructing a multi-user non-orthogonal multiple access transmission system based on environment backscatter communication, which comprises a base station, backscatter equipment and a plurality of NOMA users;
the base station superimposes user information of all NOMA users on the same resource block, generates superimposed information, and broadcasts the superimposed information to the backscatter equipment and all NOMA users through a direct link; distributing power distribution factors and user decoding thresholds for each NOMA user according to the channel distance between the base station and each NOMA user and the back scattering equipment, and distributing BD decoding thresholds for the back scattering equipment;
The back scattering equipment transmits BD self information carried by the back scattering equipment to all NOMA users through a back scattering link;
in each NOMA user, based on the received superposition information and BD self information, acquiring a plurality of signal-to-interference-and-noise ratios for decoding all user information in the superposition information and a signal-to-noise ratio for decoding BD self information;
Comparing the signal-to-interference-noise ratio with the user decoding threshold value ordered from large to small in sequence by utilizing a continuous interference elimination technology so as to identify all user information in the superimposed information in sequence, and eliminating the identified user information until one user information is eliminated, so that the NOMA users to which all the user information belongs are distinguished, and the user information corresponding to each NOMA user is acquired;
And comparing the signal-to-interference-and-noise ratio of the information of the remaining decoded user and the signal-to-noise ratio of the information of the BD with a BD decoding threshold value, and distinguishing the BD information so as to acquire the BD information of the backscatter device and complete the information transmission on each NOMA user.
In one embodiment of the present invention, the direct link and the backscatter link are both quasi-static channels, both affected by path loss and independently and uniformly distributed block rayleigh fading;
The direct link coefficient h i satisfies complex gaussian distribution, expressed as:
The backscatter link coefficient g i satisfies a complex gaussian distribution, expressed as:
Wherein Ω is an exponential path loss, denoted Ω=d -υ, d and v respectively represent a distance loss index and a path loss index; i denotes the ith NOMA user M i or the back-scattering device BD, I denotes the total number of NOMA users in the multi-user non-orthogonal multiple access transmission system based on ambient back-scattering communication.
In one embodiment of the present invention, when the channel gain of the direct link satisfies |h 1|2≥|h2|2≥…≥|hI|2, the power allocation factors of the plurality of NOMA users corresponding to the plurality of direct links satisfy: α 1+α2+…+αI =1 and 0 < α 1＜α2＜…＜αI < 1;
Where h i denotes the direct link coefficient between the ith NOMA user M i and the base station, α i denotes the power allocation factor of the ith NOMA user M i, I e {1,2, …, I }, I denotes the total number of NOMA users in the environment backscatter communication-based multi-user non-orthogonal multiple access transmission system.
In one embodiment of the present invention, the allocating a power allocation factor to each NOMA user according to the channel distance between the base station and each NOMA user and the backscatter device includes:
The power R i allocation for multiple NOMA users all satisfies:
Ri(1+γi,i)≥0.5log2(1+ρ|hi|2)，i∈{1,2,…,I}；
the power allocation factor for each NOMA user satisfies:
Calculating the distance D i of each NOMA user M i to the backscatter device, and the sum D of D i of all NOMA users;
Calculating the ratio of the distances D i to D of each NOMA user M i to the backscatter device as the power split factor a i for each NOMA user M i;
Wherein h i represents the direct link coefficient between the ith NOMA user M i and the base station, and the base station transmission signal-to-noise ratio ρ=p s/σ2,Ps represents the base station transmission power.
In one embodiment of the present invention, when the number of NOMA users i=3, the generation of the power allocation factor for each NOMA user includes:
If α 3 is less than 0.5, then the power allocation factor α 3 for NOMA user M 3 is calculated as:
Alpha 3＝α3+0.05·count·(α1+α2), count represents the calculated times of alpha 3 < 0.5 until alpha 3 is more than or equal to 0.5, and current alpha 3 is output as a power distribution factor of NOMA user M 3;
a 1＝0.2·(α1-0.05·count·α1) is assigned to NOMA user M 2, expressed as a power allocation factor a 2:
α2＝α2-0.05·count·α2+Δα1；
The power allocation factor α 1 for NOMA user M 1 is expressed as:
α1＝0.8·(α1-0.05·count·α1)；
Wherein 0.05 represents a preset step size, Δα 1 represents an increment of α 1＜α2.
In one embodiment of the present invention, the superimposition information is represented as:
Wherein x 1(t),x2 (t) and x I (t) represent user information of NOMA user M 1, NOMA user M 2 and NOMA user M I, respectively, on the t-th resource block of the base station; the user signal is a normalized unit power signal, expressed as:
α 1,α2 and α I represent power allocation factors for NOMA users M 1, M 2 and M I, respectively, dividing the base station transmit power.
In one embodiment of the present invention, the superimposition information received at each NOMA user and BD itself information are expressed as:
Wherein h i represents the direct link coefficient between the ith NOMA user M i and the base station, x (t) represents superposition information, h BD represents the coefficient of the direct link between the backscatter device BD and the base station, and g i represents the backscatter link coefficient; the BD self information c (t) of the back scattering device is normalized and then meets Eta is the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta is the percent of backscatter power split, beta e [0,1]; n i (t) represents additive white Gaussian noise at the ith NOMA user M i, subject to n i(t)～CN(0,σ2), I ε {1,2, …, I }.
In one embodiment of the present invention, in each NOMA user, based on the received superposition information and BD self information, a plurality of signal-to-interference-and-noise ratios for decoding all user information in the superposition information are obtained, including:
In the ith NOMA user M i, obtaining the signal-to-interference-and-noise ratio for decoding all the user information in the superimposed information, including: acquiring the signal-to-interference-and-noise ratio of user information of a decoding NOMA user and the signal-to-interference-and-noise ratio of user information of other decoding users, wherein the signal-to-interference-and-noise ratio of the user information of the ith decoding NOMA user M i is expressed as follows:
Wherein, gamma i,i represents the signal-to-interference-and-noise ratio of the i-th NOMA user M i for decoding the information of the NOMA user; α i represents the power allocation factor of the ith NOMA user M i; base station transmit signal to noise ratio ρ=p s/σ2,Ps represents base station transmit power; eta represents the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta represents the percent of backscatter power split, beta e [0,1]; h i represents the direct link coefficient of the i-th NOMA user M i with the base station, h BD represents the coefficient of the direct link of the backscatter device BD with the base station, g i represents the backscatter link coefficient of the i-th NOMA user M i with the backscatter device.
In one embodiment of the present invention, the signal-to-noise ratio of decoding the BD self information is expressed as:
γi,BD＝ηβρ|gi|2|hBD|2；
wherein, gamma i,BD represents the signal-to-noise ratio of the information of the ith NOMA user M i for decoding BD itself; eta represents the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta represents the percent of backscatter power split, beta e [0,1]; base station transmit signal to noise ratio ρ=p s/σ2,Ps represents base station transmit power; g i denotes the backscatter link coefficient of the i-th NOMA user M i with the backscatter device, and h BD denotes the coefficient of the direct link of the backscatter device BD with the base station.
In one embodiment of the invention, the successive interference cancellation technique includes zero-breaking equalized serial interference cancellation and minimum mean square error serial interference cancellation.
Compared with the prior art, the technical scheme of the invention has the following advantages:
According to the non-orthogonal multiple access transmission method for enabling the environment backscatter, a power distribution factor and a user decoding threshold value are distributed to each NOMA user according to the channel distance between a base station and each NOMA user and the backscatter device, and a BD decoding threshold value is distributed to the backscatter device; during decoding, a continuous interference elimination technology is utilized to carry out power distinction on different NOMA users and backscatter devices, BD self information is prevented from being used as interference processing, and decoding of information in the backscatter devices by all NOMA users in a system is realized; based on NOMA technology, the power distribution of a plurality of NOMA users is considered, the spectrum utilization rate of the system is improved, and the number of devices connectable to the system is increased. The multi-user non-orthogonal multiple access transmission method for enabling the environment backscatter communication has higher sum rate and lower interruption probability.
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In order that the invention may be more readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings, in which
Fig. 1 is a flow chart of steps of a method for enabling environmental backscatter non-orthogonal multiple access transmission provided by the present invention;
Fig. 2 is a schematic diagram of a three-purpose non-orthogonal multiple access transmission system based on environmental backscatter communication provided by the present invention;
fig. 3 is a graph of outage probability with base station transmission signal-to-noise ratio for a non-orthogonal multiple access transmission method for enabling environmental backscatter provided by the present invention;
Fig. 4 is a system and rate comparison diagram of the environment backscatter enabled non-orthogonal multiple access transmission method provided by the present invention and the prior art scheme.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
Referring to fig. 1, the step flow chart of the non-orthogonal multiple access transmission method for enabling environmental backscatter provided by the present invention includes the following specific steps:
S101: constructing a multi-user non-orthogonal multiple access transmission system based on environment backscatter communication, which comprises a base station, backscatter equipment and a plurality of NOMA users;
s102: the base station superimposes user information of all NOMA users on the same resource block, generates superimposed information, and broadcasts the superimposed information to the backscatter equipment and all NOMA users through a direct link; distributing power distribution factors and user decoding thresholds for each NOMA user according to the channel distance between the base station and each NOMA user and the back scattering equipment, and distributing BD decoding thresholds for the back scattering equipment;
s102-1: and enabling the channel gain of the direct link to meet the requirement of |h 1|2≥|h2|2≥…≥|hI|2, and enabling the power distribution factors of the plurality of NOMA users corresponding to the plurality of direct links to meet the requirement of: α 1+α2+…+αI =1 and 0 < α 1＜α2＜…＜αI < 1;
s102-2: according to the channel distance between the base station and each NOMA user and the back scattering equipment, distributing power distribution factors to each NOMA user, wherein the power distribution factors comprise:
The power R i allocation for multiple NOMA users all satisfies:
Ri(1+γi,i)≥0.5log2(1+ρ|hi|2)，i∈{1,2,…,I}；
the power allocation factor for each NOMA user satisfies:
S102-3: calculating the distance D i of each NOMA user M i to the backscatter device, and the sum D of D i of all NOMA users;
S102-4: calculating the ratio of the distances D i to D of each NOMA user M i to the backscatter device as the power split factor a i for each NOMA user M i;
Wherein h i represents the direct link coefficient between the ith NOMA user M i and the base station, alpha i represents the power distribution factor of the ith NOMA user M i, I epsilon {1,2, …, I }, I represents the total number of NOMA users in the multi-user non-orthogonal multiple access transmission system based on environment backscatter communication; base station transmit signal to noise ratio ρ=p s/σ2,Ps represents base station transmit power;
s103: the back scattering equipment transmits BD self information carried by the back scattering equipment to all NOMA users through a back scattering link;
S104: in each NOMA user, based on the received superposition information and BD self information, acquiring a plurality of signal-to-interference-and-noise ratios for decoding all user information in the superposition information and a signal-to-noise ratio for decoding BD self information;
S104-1: in the ith NOMA user M i, obtaining the signal-to-interference-and-noise ratio for decoding all the user information in the superimposed information, including: acquiring the signal-to-interference-and-noise ratio of user information of a decoding NOMA user and the signal-to-interference-and-noise ratio of user information of other decoding users, wherein the signal-to-interference-and-noise ratio of the user information of the ith decoding NOMA user M i is expressed as follows:
S104-2: decoding the signal-to-noise ratio of the BD self information, expressed as:
γi,BD＝ηβρ|gi|2|hBD|2；
Wherein, gamma i,i represents the signal-to-interference-and-noise ratio of the i-th NOMA user M i for decoding the information of the NOMA user; gamma i,BD represents the signal-to-noise ratio of the ith NOMA user M i to decode BD self information; α i represents the power allocation factor of the ith NOMA user M i; base station transmit signal to noise ratio ρ=p s/σ2,Ps represents base station transmit power; eta represents the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta represents the percent of backscatter power split, beta e [0,1]; h i represents the direct link coefficient of the i-th NOMA user M i with the base station, h BD represents the coefficient of the direct link of the back-scattering device BD with the base station, g i represents the back-scattering link coefficient of the i-th NOMA user M i with the back-scattering device;
S105: comparing the signal-to-interference-noise ratio with the user decoding threshold value ordered from large to small in sequence by utilizing a continuous interference elimination technology so as to identify all user information in the superimposed information in sequence, and eliminating the identified user information until one user information is eliminated, so that the NOMA users to which all the user information belongs are distinguished, and the user information corresponding to each NOMA user is acquired;
S106: and comparing the signal-to-interference-and-noise ratio of the information of the remaining decoded user and the signal-to-noise ratio of the information of the BD with a BD decoding threshold value, and distinguishing the BD information so as to acquire the BD information of the backscatter device and complete the information transmission on each NOMA user.
Specifically, in the embodiment of the present invention, the direct link and the backscatter link are both quasi-static channels, and are both affected by path loss and independent co-distributed block rayleigh fading;
The direct link coefficient h i satisfies complex gaussian distribution, expressed as:
The backscatter link coefficient g i satisfies a complex gaussian distribution, expressed as:
Wherein Ω is an exponential path loss, denoted Ω=d -υ, d and v respectively represent a distance loss index and a path loss index; i denotes the ith NOMA user M i or the back-scattering device BD, I denotes the total number of NOMA users in the multi-user non-orthogonal multiple access transmission system based on ambient back-scattering communication.
Specifically, the superimposition information is expressed as:
Wherein x 1(t),x2 (t) and x I (t) represent user information of NOMA user M 1, NOMA user M 2 and NOMA user M I, respectively, on the t-th resource block of the base station; the user signal is a normalized unit power signal, expressed as:
α 1,α2 and α I represent power allocation factors for NOMA users M 1, M 2 and M I, respectively, dividing the base station transmit power.
The superimposition information received at each NOMA user and BD own information are expressed as:
Wherein h i represents the direct link coefficient between the ith NOMA user M i and the base station, x (t) represents superposition information, h BD represents the coefficient of the direct link between the backscatter device BD and the base station, and g i represents the backscatter link coefficient; the BD self information c (t) of the back scattering device is normalized and then meets Eta is the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta is the percent of backscatter power split, beta e [0,1]; n i (t) represents additive white Gaussian noise at the ith NOMA user M i, subject to n i(t)～CN(0,σ2), I ε {1,2, …, I }.
Specifically, in the embodiment of the invention, the continuous interference cancellation technique comprises zero-breaking equalization serial interference cancellation and minimum mean square error serial interference cancellation.
According to the non-orthogonal multiple access transmission method for enabling the environment backscatter, a power distribution factor and a user decoding threshold value are distributed to each NOMA user according to the channel distance between a base station and each NOMA user and the backscatter device, and a BD decoding threshold value is distributed to the backscatter device; during decoding, power distinction is carried out on different NOMA users and back scattering equipment, BD self information is prevented from being used as interference processing, and decoding of information in the back scattering equipment by all NOMA users in a system is realized; based on NOMA technology, the power distribution of a plurality of NOMA users is considered, the spectrum utilization rate of the system is improved, and the number of devices connectable to the system is increased.
In this embodiment, referring to fig. 2, a three-purpose non-orthogonal multiple access transmission system based on environmental backscatter communication when the number of users i=3 is shown.
Specifically, the three-user non-orthogonal multiple access transmission system based on environmental backscatter communication includes a base station BS, a backscatter device BD, three legacy users; it is assumed that the BS and all nodes in the system have direct links. Similarly, BD and three user nodes also have backscatter links. All nodes in the system are equipped with a single antenna. The BS superimposes signals of three users on the same resource block and broadcasts the superimposed signals to the users M 1,M2 and M 3, while the BD uses the collected environmental radio frequency signals for self power supply and information transmission;
It is assumed that all channels are quasi-static and are affected by path loss and independently co-distributed block rayleigh fading. In addition, the channel coefficients of the direct link and the backscatter link both meet complex gaussian distribution, and the direct link coefficient h i exists Backscatter link coefficient g i exists/>In the three-user non-orthogonal multiple access transmission system based on the environment backscatter communication of the present embodiment, all channels satisfy an exponential path loss, i.e., Ω=d -υ, d and v represent a distance loss exponent and a path loss exponent, respectively.
It is assumed that the same slot transmission completes all information, including BD decoding all users' information, and backscattering its own information to all users. Thus, following the NOMA principle, the broadcast signal of the BS at the t-th resource block is expressed as:
Where x 1(t),x2 (t) and x 3 (t) represent information of users M 1,M2 and M 3, respectively. These signals are normalized unit power signals, i.e Α 1,α2 and α 3 represent power allocation factors for users M 1,M2 and M 3 to divide BS transmit power, respectively;
it is assumed that perfect channel state information of users in the downlink is available at the BS. Accordingly, |h 1|2≥|h2|2≥|h3|2 is ordered according to channel gain. Furthermore, since the NOMA scheme is adopted, α 1+α2+α3 =1 and 0 < α 1＜α2＜α3 < 1 should be satisfied between the three user power allocation factors.
The received signal expression at the user is:
Wherein, the normalized BD information satisfies the following conditions Eta is the backscattering execution efficiency, and 0< eta is less than or equal to 1, beta is the backscattering power division percentage, and beta epsilon [0,1]. n i (t) represents additive white gaussian noise at D i, subject to n i(t)～CN(0,σ2). Here, i ε {1,2,3}.
In this embodiment, when each user decodes information, the method includes:
the specific signal-to-interference-and-noise ratio steps for M 1 to decode all user information are as follows:
For M 1, the signal-to-interference-and-noise ratio of the M 3 information with the largest decoding power is:
Where ρ=p S/σ2 represents the BS transmit signal-to-noise ratio;
The signal-to-interference-and-noise ratio of the M 2 user information with poor decoding channel conditions of M 1 is as follows:
The signal-to-interference-and-noise ratio of M 1 for decoding the self information is:
the user receives less power about BD information than user information transmitted over the direct link due to the fading characteristics of the backscatter link. M 1 decodes all the direct link user information before decoding BD information. The traversal snr for decoding BD information at M 1 is then as follows
γ1,BD＝ηβρ|g1|2|hBD|2；
The signal-to-interference-and-noise ratio and the signal-to-noise ratio required for decoding the own information and BD information at M 2 are as follows
And gamma 2,BD＝ηβρ|g2|2|hBD|2;
the signal-to-interference-and-noise ratios and signal-to-noise ratios required to decode the own and BD information at M 3 are as follows
And gamma 3,BD＝ηβρ|g3|2|hBD|2;
Specifically, in the embodiment of the present invention, the power allocation factors for all users have the following steps:
The power allocation for the three user NOMA should satisfy:
Ri(1+γi,i)≥0.5log2(1+ρ|hi|2)，i∈{1,2,3}；
Therefore, the three-user power allocation factor should satisfy:
calculating the sum D of the distances M 1,M2 and M 3 from the BS;
Calculating the distances from M 1,M2 and M 3 to BS to be alpha 1、α2、α3 respectively in the proportion of D;
When alpha 3 is less than 0.5, calculating alpha 3＝α3+0.05·count·(α1+α2) until alpha 3 is more than or equal to 0.5, and counting is the number of times;
To more easily distinguish between M 1 and M 2 power allocation factors, Δα 1＝0.2·(α1-0.05·count·α1) is allocated to α 2;
m 1 power division factor α 1＝0.8·(α1-0.05·count·α1);
M 2 power division factor a 2＝α2-0.05·count·α2+Δα1.
Based on the above embodiment, in this embodiment, the outage probability and the sum rate of data transmission by using the non-orthogonal multiple access transmission method for enabling environmental backscatter communication provided by the present invention are compared with the existing schemes 1 and 2; specifically, scheme 1 decodes BD information only at users with better channel conditions, and processes BD information as interference at users with worse channel conditions; scheme 2 is that BD information is only decoded at users with better channel conditions, and BD information is not accepted at users with worse channel conditions.
In the embodiment of the invention, the distance from the first user M 1 to the base station BS is 9M, the distance from the second user M 2 to the base station BS is 11M, and the distance from the third user M 3 to the base station BS is 15M; the distance from the back-scattering device BD to the base station BS is 12m; the distance from the first user M 1 to the back-scattering device BD is 3M, the distance from the second user M 2 to the back-scattering device BD is 3M, and the distance from the third user M 3 to the back-scattering device BD is 4M. Let α=2, r 1＝R2＝R3＝0.01,RBD =0.002, and noise power σ 2 =1.
The outage probability for M 1 to decode its own user information is expressed as:
Here, γ th3,γth2 and γ th1 represent the target signal-to-interference-and-noise ratios of the user decoding x 3(t),x2 (t) and x 1 (t), respectively, and Wherein R i is the user target rate;
the outage probability for M 2 to decode its own user information is expressed as:
The outage probability for M 3 to decode its own user information is expressed as:
the outage probability of M 1 decoding BD information is expressed as:
wherein, Representing the target signal-to-noise ratio of the user decoding c (t). R BD is BD target rate;
the outage probability of M 2 decoding BD information is expressed as:
The outage probability of M 3 decoding BD information is expressed as:
Based on the above description, referring to fig. 3, the outage probability of all user decoding received all user information in the non-orthogonal multiple access transmission method for enabling the environmental backscatter communication provided by the present invention is shown; as can be seen from fig. 3, the present invention achieves a low outage probability of decoded information at the user in case of η=0.5, β=0.6. The invention realizes decoding BD information at the user, and the BD information decoding is carried out at the user by using the non-orthogonal multiple access transmission method for enabling the environment backscatter communication according to the invention, which has lower interruption probability as shown in figure 3.
Referring to fig. 4, a system and a rate comparison diagram of a non-orthogonal multiple access transmission method for enabling environmental backscatter communication according to the present invention, with respect to scheme 1 and scheme 2 during information transmission are shown; as can be seen from the figure, the non-orthogonal multiple access transmission method for enabling the environment backscatter communication provided by the invention has higher system and rate, improves the frequency spectrum efficiency of the system, and increases the connectable number of user equipment in the system.
The invention relates to a non-orthogonal multiple access transmission method for enabling environment backscattering, which is based on NOMA principle, and allocates a power allocation factor and a user decoding threshold value for each NOMA user and allocates a BD decoding threshold value for backscattering equipment according to the channel distance between a base station and each NOMA user and backscattering equipment; based on AmBC principles, the backscatter devices harvest energy from the environment, power their own circuitry, and send BD's own information from each NOMA user over the backscatter link. During decoding, a continuous interference elimination technology is utilized to carry out power distinction on different NOMA users and backscatter devices, BD self information is prevented from being used as interference processing, and decoding of information in the backscatter devices by all NOMA users in a system is realized; based on NOMA technology, the power distribution of a plurality of NOMA users is considered, the spectrum utilization rate of the system is improved, and the number of devices connectable to the system is increased. The multi-user non-orthogonal multiple access transmission method for enabling the environment backscatter communication has higher sum rate and lower interruption probability.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations and modifications of the present invention will be apparent to those of ordinary skill in the art in light of the foregoing description. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
1. A method of non-orthogonal multiple access transmission enabling ambient backscatter communications, comprising:
Constructing a multi-user non-orthogonal multiple access transmission system based on environment backscatter communication, which comprises a base station, a backscatter device BD and a plurality of NOMA users;
the base station superimposes user information of all NOMA users on the same resource block, generates superimposed information, and broadcasts the superimposed information to the backscatter equipment and all NOMA users through a direct link; distributing power distribution factors and user decoding thresholds for each NOMA user according to the channel distance between the base station and each NOMA user and the back scattering equipment, and distributing BD decoding thresholds for the back scattering equipment;
The back scattering equipment transmits BD self information carried by the back scattering equipment to all NOMA users through a back scattering link;
In each NOMA user, based on the received superposition information and BD self information, acquiring a plurality of signal-to-interference-and-noise ratios of all user information in the superposition information after decoding and the signal-to-noise ratio of the BD self information after decoding;
Comparing the signal-to-interference-noise ratio with the user decoding threshold value ordered from large to small in sequence by utilizing a continuous interference elimination technology so as to identify all user information in the superimposed information in sequence, and eliminating the identified user information until one user information is eliminated, so that the NOMA users to which all the user information belongs are distinguished, and the user information corresponding to each NOMA user is acquired;
And comparing the signal-to-interference-and-noise ratio of the decoded residual user information and the signal-to-noise ratio of the decoded BD self information with a BD decoding threshold value, and distinguishing BD self information so as to acquire BD self information of the backscatter device, thereby completing information transmission on each NOMA user.
2. The method for enabling non-orthogonal multiple access transmission of environmental backscatter communications of claim 1 wherein the direct link and the backscatter link are quasi-static channels, both affected by path loss and independently co-distributed block rayleigh fading;
The direct link coefficient h i satisfies complex gaussian distribution, expressed as:
The backscatter link coefficient g i satisfies a complex gaussian distribution, expressed as:
Wherein Ω is an exponential path loss, denoted Ω=d -υ, d and v respectively represent a distance loss index and a path loss index; i denotes the I-th NOMA user M i and the I-th backscatter device BD, I denotes the total number of NOMA users in the multi-user non-orthogonal multiple access transmission system based on ambient backscatter communication.
3. The method for enabling non-orthogonal multiple access transmission of environmental backscatter communications of claim 1, wherein, when the channel gain of the direct link satisfies |h 1|2≥|h2|2≥…≥|hI|2, the power allocation factors of a plurality of NOMA users corresponding to a plurality of direct links satisfy: α 1+α2+…+αI =1 and 0 < α 1＜α2＜…＜αI < 1;
Where h i denotes the direct link coefficient between the ith NOMA user M i and the base station, α i denotes the power allocation factor of the ith NOMA user M i, I e {1,2, …, I }, I denotes the total number of NOMA users in the environment backscatter communication-based multi-user non-orthogonal multiple access transmission system.
4. A method of non-orthogonal multiple access transmission enabling ambient backscatter communications according to claim 3, wherein said assigning a power allocation factor to each NOMA user based on the channel distance of the base station from each NOMA user and the backscatter device comprises:
The power R i allocation for multiple NOMA users all satisfies:
Ri(1+γi,i)≥0.5log2(1+ρ|hi|2)，i∈{1,2,…,I}；
the power allocation factor for each NOMA user satisfies:
Calculating the distance D i of each NOMA user M i to the backscatter device, and the sum D of D i of all NOMA users;
Calculating the ratio of the distances D i to D of each NOMA user M i to the backscatter device as the power split factor a i for each NOMA user M i;
Wherein, gamma i,i represents the signal-to-interference-and-noise ratio of the NOMA user self information decoded by the ith NOMA user M i; h i represents the direct link coefficient between the ith NOMA user M i and the base station, the base station transmission signal-to-noise ratio ρ=p s/σ2,Ps represents the base station transmission power, and σ 2 represents the noise power.
5. The method for non-orthogonal multiple access transmission with environment backscatter communication of claim 4, wherein when the number of NOMA users I = 3, the generation of the power allocation factor for each NOMA user comprises:
If α 3 is less than 0.5, then the power allocation factor α 3 for NOMA user M 3 is calculated as:
Alpha 3＝α3+0.05·count·(α1+α2), count represents the calculated times of alpha 3 < 0.5 until alpha 3 is more than or equal to 0.5, and current alpha 3 is output as a power distribution factor of NOMA user M 3;
a 1＝0.2·(α1-0.05·count·α1) is assigned to NOMA user M 2, expressed as a power allocation factor a 2:
α2＝α2-0.05·count·α2+Δα1；
The power allocation factor α 1 for NOMA user M 1 is expressed as:
α1＝0.8·(α1-0.05·count·α1)；
Wherein 0.05 represents a preset step size, Δα 1 represents an increment of α 1＜α2.
6. The environment-backscatter communication-enabled non-orthogonal multiple access transmission method of claim 4, wherein the superposition information is represented as:
Wherein x 1(t),x2 (t) and x I (t) represent user information of NOMA user M 1, NOMA user M 2 and NOMA user M I, respectively, on the t-th resource block of the base station; the user information is normalized unit power signal, expressed as:
α 1,α2 and α I represent power allocation factors for NOMA users M 1, M 2 and M I, respectively, dividing the base station transmit power.
7. The environment-backscatter communication-enabled non-orthogonal multiple access transmission method of claim 6, wherein the superposition information received at each NOMA user and BD self information are expressed as:
Wherein h i represents the direct link coefficient between the ith NOMA user M i and the base station, x (t) represents superposition information, h BD represents the coefficient of the direct link between the backscatter device BD and the base station, and g i represents the backscatter link coefficient; the BD self information c (t) of the back scattering device is normalized and then meets Eta is the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta is the percent of backscatter power split, beta e [0,1]; n i (t) represents additive white Gaussian noise at the ith NOMA user M i, subject to n i(t)～CN(0,σ2), I ε {1,2, …, I }.
8. The method for enabling non-orthogonal multiple access transmission of environmental backscatter communication of claim 7, wherein said obtaining, in each NOMA user, based on the received superposition information and BD self information, a plurality of signal-to-interference-and-noise ratios of all user information in the superposition information after decoding comprises:
In the ith NOMA user M i, acquiring the signal-to-interference-and-noise ratio of all user information in the decoded superimposed information, including: acquiring the signal-to-interference-and-noise ratio of the user information of the decoded NOMA user and the signal-to-interference-and-noise ratio of the user information of the other decoded user, wherein the signal-to-interference-and-noise ratio of the user information of the decoded i NOMA user M i is expressed as follows:
wherein, gamma i,i represents the signal-to-interference-and-noise ratio of the NOMA user self information decoded by the ith NOMA user M i; α i represents the power allocation factor of the ith NOMA user M i; base station transmit signal to noise ratio ρ=p s/σ2,Ps represents base station transmit power; eta represents the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta represents the percent of backscatter power split, beta e [0,1]; h i represents the direct link coefficient of the i-th NOMA user M i with the base station, h BD represents the coefficient of the direct link of the backscatter device BD with the base station, g i represents the backscatter link coefficient of the i-th NOMA user M i with the backscatter device.
9. The environment-backscatter communication-enabled non-orthogonal multiple access transmission method of claim 8, wherein the signal-to-noise ratio of the decoded BD self information is expressed as:
γi,BD＝ηβρ|gi|2|hBD|2；
Wherein, gamma i,BD represents the signal-to-noise ratio of the BD self information decoded by the ith NOMA user M i; eta represents the backscattering execution efficiency, and eta is more than 0 and less than or equal to 1; beta represents the percent of backscatter power split, beta e [0,1]; base station transmit signal to noise ratio ρ=p s/σ2,Ps represents base station transmit power; g i denotes the backscatter link coefficient of the i-th NOMA user M i with the backscatter device, and h BD denotes the coefficient of the direct link of the backscatter device BD with the base station.
10. The method of environmental backscatter communication enabled non-orthogonal multiple access transmission of claim 1 wherein the successive interference cancellation technique comprises zero-breaking equalized serial interference cancellation and minimum mean square error serial interference cancellation.
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