A method for determining the optimal threshold value based on energy difference detection algorithm

Abstract

The disclosed embodiment is about a method for determining an optimal threshold value based on an energy difference detection algorithm. The method includes: using a radio frequency source, a tag, and a reader to construct an IQ-unbalanced environmental backscatter communication system; using a radio frequency source to transmit a source radio frequency signal to the surrounding environment, the tag receives the source radio frequency signal and reflects the radio frequency signal to the surrounding environment, and the reader demodulates the received radio frequency signal; according to the modulated radio frequency signal, the average power of each backscatter signal sample is calculated, according to the differential coding model, the difference in the average power of the time interval between two adjacent backscatter signal sample symbols is calculated, the decision criteria of the detector is designed, and the optimal decision threshold is formulated; according to the radio frequency signal, the first parameter and the second parameter are obtained, and the optimal threshold value is obtained in combination with the optimal decision threshold. The disclosed embodiment adopts a direct detection method, performs detection and judgment based on energy difference, and uses the received signal samples of the reader to estimate a detection threshold value close to the optimal value.

Description

Technical Field

[0001] The embodiments of the present disclosure relate to the technical field of wireless network radio frequency identification, and in particular to a method for determining an optimal threshold value based on an energy difference detection algorithm. Background Art

[0002] Backscatter Communications is one of the key technologies for building a green, energy-saving, low-cost, and flexibly deployable future Internet of Things, and is an important means to achieve "intelligent connection of all things". Backscatter communication technology also provides an effective solution for the communication of massive low-power nodes in the passive Internet of Things, and has received positive attention and attention from the world. The Internet of Things (IoT) is the third wave of development of the world's information industry after computers and the Internet. The Internet of Things connects various objects together with the idea of ​​"interconnecting all things", getting rid of the limitation of traditional communications that require specific devices to access the network, making people's work and life more convenient and improving the production efficiency of various industries.

[0003] In the related technologies, the research on backscatter communication mainly focuses on the research on fading characteristics of scattering channels, path loss model research, coding detection technology, multi-antenna technology and physical layer security technology. Among them, in terms of signal detection, since the tag modulates the signal in the environment, channel information is difficult to obtain and the process of sending pilot symbols is relatively complicated and often accompanied by IQ (in-phase, in-phase component; quadrature, orthogonal component) imbalance, which increases the difficulty of detection. In the related technologies, maximum likelihood detection is proposed for signal detection. Although this method can realize signal detection, its accuracy and complexity still need to be improved.

[0004] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.

[0005] It should be noted that this section is intended to provide background or context for the technical solutions of the present disclosure stated in the claims. The description herein is not admitted to be prior art by virtue of being included in this section. Summary of the invention

[0006] The purpose of the embodiments of the present disclosure is to provide a method for determining an optimal threshold value based on an energy difference detection algorithm, thereby overcoming one or more problems caused by limitations and defects of related technologies at least to a certain extent.

[0007] According to an embodiment of the present disclosure, a method for determining an optimal threshold value based on an energy difference detection algorithm is provided, comprising:

[0008] Use RF source, tag and reader to build IQ imbalance environment backscatter communication system;

[0009] The radio frequency source is used to transmit a source radio frequency signal to the surrounding environment, the tag receives the source radio frequency signal and reflects the radio frequency signal to the surrounding environment, and the reader / writer demodulates the received radio frequency signal; wherein the radio frequency signal includes the source radio frequency signal, the reflected radio frequency signal and a noise signal in the environment;

[0010] Calculate the average power of each backscatter signal sample according to the modulated radio frequency signal, and calculate the difference between the average power of two adjacent backscatter signal sample symbol time intervals according to the differential coding model;

[0011] Designing a decision criterion of the detector according to the difference in average power of sample symbol time intervals of the backscattered signal;

[0012] formulating an optimal decision threshold according to the decision criteria of the detector;

[0013] A first parameter and a second parameter are obtained according to the radio frequency signal received by the reader / writer, and an optimal threshold value is obtained by combining the optimal decision threshold.

[0014] In one embodiment of the present disclosure, the process of calculating the average power of each backscattered signal sample includes:

[0015] Establishing a receiving signal model according to the channel between the radio frequency source and the reader / writer, the channel between the radio frequency source and the tag, and the channel between the reader / writer and the tag;

[0016] Obtaining an equivalent channel according to the received signal model and the IQ imbalance parameter;

[0017] The average power of each backscatter signal sample is calculated according to the equivalent channel.

[0018] In one embodiment of the present disclosure, the received signal model is expressed as:

[0019] y ideal (n)=μ(k)s(n)+w(n),n=1,2,...,N (1)

[0020] μ(k)=h+fgB(k) (2)

[0021] Wherein, k is the RF signal reflected by the kth tag, μ(k) is the channel information, s(n) is the source RF signal, w(n) is the additive white Gaussian noise, h is the channel between the RF source and the reader, f is the channel between the RF source and the tag, g is the channel between the reader and the tag, and B(k) is the backscattered signal.

[0022] In one embodiment of the present disclosure, the backscatter signal is expressed as:

[0023]

[0024] Where A(k) is the kth information bit input to the differential encoder, It is modulo 2 addition.

[0025] In one embodiment of the present disclosure, the expression of the equivalent channel is:

[0026]

[0027] Among them, z1 and z2 are coefficients, and

[0028] In the formula, (·) * represents the conjugate operation, represents the relative phase deviation of the quadrature phase shift, and ρ represents the relative amplitude imbalance between the I and Q branches.

[0029] In one embodiment of the present disclosure, the expression of the average power of each backscattered signal sample is:

[0030]

[0031] Then the expression of the difference between the average power of two adjacent backscatter signal sample symbol time intervals is:

[0032]

[0033] In the formula, is the average power of each backscattered signal sample, The difference between the average power of two adjacent backscatter signal sample symbol time intervals, K is the total number of RF signals reflected by the tag.

[0034] In one embodiment of the present disclosure, the average power of each backscattered signal sample obeys a Gaussian distribution, and the expression of its mean is:

[0035]

[0036] The expression of its variance is:

[0037]

[0038] In the formula, κ is the third parameter, a is the fourth parameter, and Ps is the average power of the source RF signal, E[·] represents the mathematical expectation, and var(·) represents the variance.

[0039] In one embodiment of the present disclosure, the decision criterion of the detector is expressed as:

[0040]

[0041] In the formula, is the detection threshold under IQ imbalance, is the estimated value of A(k).

[0042] In one embodiment of the present disclosure, in the IQ-unbalanced backscatter communication system, the bit error rate is expressed as:

[0043]

[0044] The expression of the optimal decision threshold is:

[0045]

[0046] In the formula, |δ iq | is the first parameter, is the second parameter, is the fifth parameter, is the sixth parameter; where δ iq =κPs(|h+fg| 2 -|h| 2 ),

[0047] In one embodiment of the present disclosure, the expression of the first parameter is:

[0048] and,

[0049] Wherein, the first parameter and the second parameter are obtained according to the radio frequency signal received by the reader and in combination with formula (12) and formula (13). The technical solution provided by the embodiment of the present disclosure may include the following beneficial effects:

[0050] In the embodiment of the present disclosure, through the above-mentioned method for determining the optimal threshold value based on the energy difference detection algorithm, on the one hand, the decision criterion of the detector is used to design the detection threshold value of the detector, relying on the idea of ​​determining the optimal detection threshold value by only using the signal samples received by the reader, that is, the optimal detection threshold value can be blindly measured only based on the received signal samples. On the other hand, it is not necessary to clearly define the channel state information of the environmental RF source in the system, the IQ imbalance parameter ρ and As well as the noise power and signal transmission power values ​​in the environment; it improves the detection performance of environmental backscattering, reduces complexity, and improves the reliability, rigor, practicality and scalability of the environmental backscattering system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0052] Figure 1 A step diagram showing a method for determining an optimal threshold value based on an energy difference detection algorithm in an exemplary embodiment of the present disclosure;

[0053] Figure 2 A schematic diagram showing the structure of an IQ-unbalanced environment backscatter communication system in an exemplary embodiment of the present disclosure;

[0054] Figure 3 Show Figure 2 Model diagram of differential encoding of labels in ;

[0055] Figure 4 The approximate analytical distribution and the real empirical distribution diagram derived from the system receiving signal model when the system IQ imbalance parameter in the exemplary embodiment of the present disclosure is shown;

[0056] Figure 5 A diagram showing the relationship between the bit error rate and the detection threshold under different IQ imbalance parameters in an exemplary embodiment of the present disclosure;

[0057] Figure 6 A relationship diagram is shown between the empirical PDF (Probability Density Function) in the exemplary embodiment of the present disclosure, the PDF derived in the present patent, and the PDF derived in the literature [1] (G. Wang, F. Gao, R. Fan, and C. Tellambura, "Ambient backscatter communication systems: Detection and performance analysis," IEEE Trans. Commun., vol. 64, no. 11, pp. 4836-4846, 2016.);

[0058] Figure 7 It shows that the perfect IQ balance in the exemplary embodiment of the present disclosure is ρ=1, The relationship between bit error rate and signal-to-noise ratio under

[0059] Figure 8 A diagram showing the impact of IQ imbalance on the bit error rate of a detector based on energy difference in an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0060] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the disclosure will be more comprehensive and complete and to fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0061] In addition, the accompanying drawings are only schematic illustrations of the embodiments of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and their repeated descriptions will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0062] This example implementation first provides a method for determining an optimal threshold value based on an energy difference detection algorithm. Figure 1 As shown in , the method for determining the optimal threshold value based on the energy difference detection algorithm may include: steps S101 to S106.

[0063] Step S101: constructing an IQ-unbalanced environment backscatter communication system using a radio frequency source, a tag, and a reader;

[0064] Step S102: using the radio frequency source to transmit a source radio frequency signal to the surrounding environment, the tag receives the source radio frequency signal and reflects the radio frequency signal to the surrounding environment, and the reader / writer demodulates the received radio frequency signal; wherein the radio frequency signal includes the source radio frequency signal, the reflected radio frequency signal and a noise signal in the environment;

[0065] Step S103: calculating the average power of each backscatter signal sample according to the modulated RF signal, and calculating the difference between the average power of two adjacent backscatter signal sample symbol time intervals according to the differential coding model;

[0066] Step S104: designing a decision criterion of the detector according to the difference in average power of the backscatter signal sample symbol time interval;

[0067] Step S105: formulating an optimal decision threshold according to the decision criteria of the detector;

[0068] Step S106: obtaining a first parameter and a second parameter according to the radio frequency signal received by the reader, and combining them with the optimal decision threshold to obtain an optimal threshold value.

[0069] Specifically, in step S101, a single-channel environmental backscatter communication system with IQ imbalance is established, including a tag adopting a differential encoding scheme, a reader based on energy difference detection, and a radio frequency source. The tag is a data transmitter, and the reader is a data receiver. The data transmitter and the data receiver communicate with each other using radio frequency signals in the environment.

[0070] In step S102, a radio frequency source is used to transmit a source radio frequency signal to its surrounding environment; the tag receives the source radio frequency signal from the radio frequency source and continuously reflects the radio frequency signal to its surrounding environment, and the tag converts the communication data into a binary sequence code. In the environmental backscatter communication system, the bits "0" and "1" are represented by the two states of the tag reflecting or not reflecting the radio frequency signal of the surrounding environment. The reader receives the source radio frequency signal from the radio frequency source, the radio frequency signal reflected by the tag, and the noise signal in the environment; the reader demodulates and decodes the radio frequency signal received from the antenna. The demodulated radio frequency signal is obtained.

[0071] In step S103, in a single-channel environmental backscatter communication system with IQ imbalance, the channel between the RF source and the reader is represented by h, the channel between the RF source and the tag is represented by f, and the channel between the reader and the tag is represented by g; the above channels are all set as slow fading channels, that is, the channel does not change within the time interval of at least two consecutive tags sending symbols, the signal sent by the RF source is recorded as s(n), and the tag decides whether to reflect the RF signal by adjusting the internal impedance. The reflection state of the tag B(k) = 1 represents that the tag reflects the RF signal, and B(k) = 0 represents that the tag does not reflect the RF signal. For the RF signals actually received by N consecutive tags, the value of B(k) remains unchanged. It represents the relative phase deviation of the orthogonal (90 degree) phase shift when the system IQ is unbalanced, and ρ represents the relative amplitude imbalance between the I and Q branches when the system IQ is unbalanced.

[0072] The RF source is used to transmit the source RF signal s(n) to the surrounding environment. E(s(n))=0,E(|s(n)| 2 )=Ps, E[·] represents the mathematical expectation, and Ps is the average power of the source RF signal. The noise signal in the environment is set to additive Gaussian white noise, represented by w(n), satisfying

[0073] The tags in the system adopt differential encoding, which is achieved by adding a differential encoder before the modulator. The relationship between the input A(k) and output B(k) of the differential encoder can be expressed as:

[0074]

[0075] Where A(k) represents the kth information bit input to the differential encoder, Indicates modulo 2 addition, B(k) represents the kth output bit of the differential encoder. In environmental backscatter technology, the tag has two reflective states. When the tag is in a non-reflective state, it represents the transmission of bit "0", that is, B(k) = 0; when it is in a reflective state, it represents the transmission of bit "1", at this time B(k) = 1.

[0076] When the tag sends K backscatter signals B(k), the reader will receive KN receiving signals y iq (n), n = 1, 2, ..., KN, in this system, the signal y received by the reader iq (n) can be expressed as:

[0077]

[0078] Among them, z1 and z2 are coefficients, and

[0079] In the formula, (·) * represents the conjugate operation, represents the relative phase deviation of the orthogonal phase shift, and ρ represents the relative amplitude imbalance between the I and Q branches.

[0080] y ideal (n)=μ(k)s(n)+w(n),n=1,2,...,N (1)

[0081] μ(k)=h+fgB(k) (2)

[0082] Formula (1) and Formula (2) represent the received signal of the reader / writer of the environmental backscatter communication system under the ideal scenario of perfect IQ balance.

[0083] From the above, we can see that when When the IQ imbalance communication system is built, it becomes an ideal scenario with perfect IQ balance.

[0084] The calculation formula for the average power of the RF signal demodulated by N consecutive readers is:

[0085]

[0086] It approximately obeys Gaussian distribution, K is the total number of RF signals reflected by the tags, k is the RF signal reflected by the kth tag, and 1≤k≤K.

[0087] Then the expression of the difference between the average power of two adjacent backscatter signal sample symbol time intervals is:

[0088]

[0089] In the formula, is the average power of each backscattered signal sample, The difference between the average power of two adjacent backscatter signal sample symbol time intervals.

[0090] In step S104, the reader receives KN demodulated RF signals in total. Each N consecutive RF signals demodulated by the reader correspond to the reflective state or non-reflective state of the tag. The tag reflects K states to the reader in total. and ρ, The Gaussian distribution it obeys, its mean and variance can be expressed as:

[0091]

[0092]

[0093] In the formula, κ is the third parameter, a is the fourth parameter, and Ps is the average power of the source RF signal, E[·] represents the mathematical expectation, and var(·) represents the variance.

[0094] In step S105, the RF signals demodulated by each N consecutive readers correspond to the tag's reflective state B(k)=1 or non-reflective state B(k)=0. The difference in average power between two adjacent B(k) symbol time intervals is for: because Then A(k) is determined by B(k) and B(k-1) and A(k) reflects the change of B(k). In the signal detection process at the reader, the detection of B(k) can be converted into the detection of A(k). is an estimate of A(k). In the case of IQ imbalance, use y iq (n) Estimation A(k) is a detector based on energy difference, and the final decision criterion is:

[0095]

[0096] in, is the decision threshold in the detector's test decision criteria, is the estimate of A(k). Get the optimal decision threshold Make system signal Infinitely close to A(k), a smaller system bit error rate is obtained, so that the system has better detection performance.

[0097] In order to make the system have better detection performance, the detection threshold value is the optimal threshold value when the bit error rate is the lowest. In the constructed IQ unbalanced backscatter communication system, the bit error rate and the expression close to the optimal detection threshold value are as follows:

[0098]

[0099]

[0100] In the formula, |δ iq | is the first parameter, is the second parameter, is the fifth parameter, is the sixth parameter; where δ iq =κPs(|h+fg| 2 -|h| 2 ),

[0101] In step S106, the optimal threshold value is solved by using the received signal samples of the reader in the IQ-unbalanced environmental backscattering system.

[0102] The optimal threshold value for signal detection is obtained according to the decision criteria of the detector. The specific process is: From the expression of |δ iq | and Substituting into In the IQ-unbalanced backscatter communication system, |δ iq | and It is expressed as:

[0103]

[0104]

[0105] Among them, when When K is large enough, we can get and

[0106] The received signal samples of the reader in the IQ unbalanced backscattering system are used to estimate and calculate the detection threshold value close to the optimal value. According to the above known formula, it can be known that: but It can be expressed as υ1(Δ + )=υ2(Δ + ). According to the function properties, υ1(Δ + ) and υ2(Δ + ) are all about Δ + An increasing function of . If In There exists a satisfying υ1(Δ + )=υ2(Δ + ). This Δ + The value can be found by bisection, and then |δ iq | will also be calculated and substituted into Then, a near-optimal detection threshold value under IQ imbalance can be obtained.

[0107] Through the above-mentioned method for determining the optimal threshold value based on the energy difference detection algorithm, on the one hand, the detection threshold value of the detector is formulated by using the decision criteria of the design detector and relying on the idea of ​​determining the optimal detection threshold value by only using the signal samples received by the reader, that is, the optimal detection threshold value can be blindly measured only based on the received signal samples. On the other hand, there is no need to clearly define the channel state information of the environmental RF source in the system, the IQ imbalance parameter ρ and As well as the noise power and signal transmission power values ​​in the environment; it improves the detection performance of environmental backscattering, reduces complexity, and improves the reliability, rigor, practicality and scalability of the environmental backscattering system.

[0108] Next, we will refer to Figures 1 to 8 Each step of the above-mentioned method for determining the optimal threshold value based on the energy difference detection algorithm in this example implementation is described in more detail.

[0109] In one embodiment, Figure 2 As shown, there are three main devices in the system: RF source, tag and reader. Among them, the tag and reader can be regarded as a transmitter and a receiver with only one antenna respectively. The channel between the RF source and the reader is set to h, and the channel between the RF source and the tag is set to f. The above channels are all set to slow fading channels, that is, the channel does not change within the time interval of at least two consecutive tags sending symbols. The signal sent by the RF source is recorded as s(n), and the tag decides whether to reflect the RF signal by adjusting the internal impedance. The reflection state of the tag B(k) = 1 represents that the tag reflects the RF signal, and B(k) = 0 represents that the tag does not reflect the RF signal. For the RF signals actually received by N consecutive tags, the value of B(k) remains unchanged.

[0110] In one embodiment, Figure 3As shown in the figure, a model of differential encoding at the tag is given. The input of the differential encoder is recorded as A(k), and the output is B(k), which is the final transmission signal of the tag. The relationship between the two can be expressed as follows: if A(k) = 0, it means that B(k) has not changed between the previous and next moments; conversely, if A(k) = 1, it means that B(k) has changed between the previous and next moments. According to this model, A(k) can be used to represent the change of B(k) and B(k-1). Correspondingly, in the signal detection process at the receiver, the detection of B(k) can be converted into the detection of A(k).

[0111] In one embodiment, step S103 specifically includes: establishing a received signal model according to the channel between the RF source and the reader, the channel between the RF source and the tag, and the channel between the reader and the tag; obtaining an equivalent channel according to the received signal model and an IQ imbalance parameter; and calculating the average power of each backscattered signal sample according to the equivalent channel.

[0112] The expression of the received signal model is:

[0113] y ideal (n)=μ(k)s(n)+w(n),n=1,2,...,N (1)

[0114] μ(k)=h+fgB(k) (2)

[0115] Wherein, k is the RF signal reflected by the kth tag, μ(k) is the channel information, s(n) is the source RF signal, w(n) is the additive white Gaussian noise, h is the channel between the RF source and the reader, f is the channel between the RF source and the tag, g is the channel between the reader and the tag, and B(k) is the backscattered signal.

[0116] The expression of the backscattered signal is:

[0117]

[0118] Where A(k) is the kth information bit input to the differential encoder, It is modulo 2 addition.

[0119] In one embodiment, Figure 4 As shown in FIG. 1 , the approximate analytical distribution derived from the image in this embodiment and the true empirical distribution. The normal distribution of the parameters shown matches well with the empirical distribution under the two assumptions of actual IQ imbalance: B(k) = 0 and B(k) = 1. This proves the accuracy of the analysis.

[0120] In one embodiment, Figure 5As shown in FIG. 1 , the relationship between the bit error rate and the detection threshold value under different IQ imbalance parameters is shown. Figure 4 The embodiments are the same and refer to Figure 5 As shown, it can be seen that there is an optimal threshold value that minimizes the bit error rate, and the optimal threshold value decreases as the degree of IQ imbalance increases.

[0121] In one embodiment, Figure 6 As shown in the figure, the established signal model is based on the premise of IQ imbalance. When ρ = 1, the constructed IQ imbalance system becomes an ideal scenario of perfect IQ balance. At this time, the present application is compared with the ideal model constructed by the environmental backscatter communication system in the literature [1]. When ρ = 1, the received signal is blindly measured. and pass The estimated threshold is calculated to be 19.2424. The estimated thresholds obtained by the ideal model established in the literature [1] are 11.0101. Figure 5 , Figure 5 It is an exhaustive search method applied. As shown in the figure, the optimal threshold value in the actual test is closer to 19.2424. In summary, it can be obtained that the optimal threshold value obtained by this patent application is more accurate and reliable. Therefore, this application is more accurate and reliable. The main reason is that this application is in solving In, taking into account It is directly ignored in the threshold solution in reference [1].

[0122] In one embodiment, Figure 7 As shown, the relationship between the bit error rate and the signal-to-noise ratio in an ideal scenario with perfect IQ balance is depicted. It can be seen that the bit error rate derived in this embodiment matches the simulation result well.

[0123] In one embodiment, Figure 8 As shown in FIG. 1 , this embodiment evaluates the impact of IQ imbalance on the bit error rate of the detector based on energy difference. In which, the SNR is assumed to be 0 dB. The percentage of amplitude and phase imbalance is calculated as (1-ρ)×100% and Depend on Figure 8 It is known that the bit error rate increases with the percentage of IQ imbalance, which indicates that IQ imbalance degrades the performance. It can also be seen that the performance degradation for phase imbalance is higher than that for amplitude imbalance. This indicates that the energy difference based detector is more sensitive to phase imbalance than amplitude imbalance.

[0124] In one embodiment, The calculation of |δ iq | and However |δiq | and It also depends on the channel state information of the ambient RF source, the IQ imbalance parameter ρ and As well as the noise power and signal transmission power in the environment, which are all unknown to the reader in the system. In order to solve this problem, the present application designs a simple and practical method, which is to use the received signal samples of the reader in the IQ unbalanced environment backscattering system to estimate the near-optimal detection threshold value.

[0125] Further analysis of the IQ imbalance backscatter communication system shows:

[0126]

[0127]

[0128] From the above formula, we can get: When K is large enough,

[0129] Will The third term on the right side of the equal sign in the formula is moved to the left side of the equal sign. We get υ1(Δ + )=υ2(Δ + ). According to the function properties, υ1(Δ + ) and υ2(Δ + ) are all about Δ + An increasing function of . If In There exists a satisfying υ1(Δ + )=υ2(Δ + ). This Δ + The value can be found by bisection, and then |δ iq | will also be calculated and substituted into Then, a near-optimal detection threshold value under IQ imbalance can be obtained.

[0130] Through the above-mentioned method for determining the optimal threshold value based on the energy difference detection algorithm, on the one hand, the detection threshold value of the detector is formulated by using the decision criteria of the design detector and relying on the idea of ​​determining the optimal detection threshold value by only using the signal samples received by the reader, that is, the optimal detection threshold value can be blindly measured only based on the received signal samples. On the other hand, there is no need to clearly define the channel state information of the environmental RF source in the system, the IQ imbalance parameter ρ and As well as the noise power and signal transmission power values ​​in the environment; it improves the detection performance of environmental backscattering, reduces complexity, and improves the reliability, rigor, practicality and scalability of the environmental backscattering system.

[0131] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0132] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any modification, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. A method for determining an optimal threshold value based on an energy difference detection algorithm, characterized in that: The method includes: Use RF source, tag and reader to build IQ imbalance environment backscatter communication system; The radio frequency source is used to transmit a source radio frequency signal to the surrounding environment, the tag receives the source radio frequency signal and reflects the radio frequency signal to the surrounding environment, and the reader / writer demodulates the received radio frequency signal; wherein the radio frequency signal includes the source radio frequency signal, the reflected radio frequency signal and a noise signal in the environment; Calculate the average power of each backscatter signal sample according to the modulated radio frequency signal, and calculate the difference between the average power of two adjacent backscatter signal sample symbol time intervals according to the differential coding model; Designing a decision criterion of the detector according to the difference in average power of sample symbol time intervals of the backscattered signal; Formulate an optimal decision threshold according to the decision criteria of the detector, wherein the detector is a detector at the reader; Obtaining a first parameter and a second parameter according to the radio frequency signal received by the reader, and obtaining an optimal threshold value in combination with the optimal decision threshold; Wherein, in a single-channel environment backscatter communication system with IQ imbalance, the channel between the RF source and the reader is represented by h, the channel between the RF source and the tag is represented by f, and the channel between the reader and the tag is represented by g; the channels are all set to slow fading channels, that is, the channels do not change within the time interval of at least two consecutive tags sending symbols, the signal sent by the RF source is recorded as s(n), and the tag determines whether to reflect the RF signal by adjusting the internal impedance; the backscatter signal B(k)=1 of the tag represents that the tag reflects the RF signal, and B(k)=0 represents that the tag does not reflect the RF signal; for the RF signals actually received by N consecutive tags, the value of B(k) remains unchanged; The radio frequency source is used to transmit a source radio frequency signal s(n) to the surrounding environment; E(s(n))=0, E(s(n) 2 )=Ps, E[·] represents the mathematical expectation, and Ps is the average power of the source RF signal; The tag in the environmental backscatter communication system adopts a differential coding model, wherein the differential coding model includes a differential encoder and a modulator, and the output of the differential encoder is connected to the input of the modulator; When the tag sends K backscatter signals B(k), the reader will receive KN receiving signals; The process of calculating the average power of each backscattered signal sample includes: Establishing a receiving signal model according to the channel between the radio frequency source and the reader / writer, the channel between the radio frequency source and the tag, and the channel between the reader / writer and the tag; Obtaining an equivalent channel according to the received signal model and the IQ imbalance parameter; Calculating the average power of each backscatter signal sample according to the equivalent channel; The expression of the received signal model under IQ balance is: y ideal (n)=μ(k)s(n)+w(n),n=1,2,...,N (1) μ(k)=h+fgB(k) (2) Where k is the RF signal reflected by the kth tag, μ(k) is the channel information, s(n) is the source RF signal, and w(n) is the additive Gaussian white noise; The expression of the backscattered signal is: Where A(k) is the kth information bit input to the differential encoder, is modulo 2 addition; The expression of the equivalent channel under IQ imbalance is: Among them, z1 and z2 are coefficients, and In the formula, (·) * represents the conjugate operation, represents the relative phase deviation of the quadrature phase shift, and ρ represents the relative amplitude imbalance between the I and Q branches; The expression for the average power of each backscattered signal sample is: Then the expression of the difference between the average power of two adjacent backscatter signal sample symbol time intervals is: In the formula, is the average power of each backscattered signal sample, is the difference in average power between two adjacent backscatter signal sample symbol time intervals, K is the total number of RF signals reflected by the tag, and N is the corresponding received signal y in each backscatter signal B(k). ideal (n) Total number of sampling points; The average power of each backscattered signal sample obeys Gaussian distribution, and the expression of its mean is: The expression of its variance is: In the formula, κ is the third parameter, a is the fourth parameter, and Ps is the average power of the source RF signal, E[·] represents the mathematical expectation, var(·) represents the variance, and N is the corresponding received signal y in each backscattered signal B(k). ideal (n) The total number of sampling points, is the variance of zero-mean additive Gaussian white noise; The expression of the decision criterion of the detector is: In the formula, is the detection threshold under IQ imbalance, is the estimated value of A(k); In the IQ-unbalanced environmental backscatter communication system, the expression of the bit error rate is: The expression of the optimal decision threshold is: In the formula, |δ iq | is the first parameter, is the second parameter, is the fifth parameter, is the sixth parameter; where δ iq =κPs(h+fg 2 -|h 2 ), 2. The method for determining the optimal threshold value based on the energy difference detection algorithm according to claim 1, characterized in that: The expression of the first parameter is: and, Wherein, the first parameter and the second parameter are obtained according to the radio frequency signal received by the reader and in combination with formula (12) and formula (13).

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