A backscattering communication method, device and system without channel estimation

Abstract

The application discloses a backscattering communication method, device and system without channel estimation, and belongs to the wireless communication field, which comprises the following steps: constructing an antenna matrix to map information in multiple dimensions, forming an information space-time block, performing differential encoding in the time dimension, and generating an information space-time block to be transmitted by a tag; setting different reflection coefficients, summing and averaging receiver signal components under the reflection coefficients to obtain a component of a direct link, and the receiver needs to subtract the component before detecting tag information; removing the direct link signal according to a received signal, and separating a differential signal of a cascaded backscattering link by the receiver, so that the antenna index sequence and constellation symbols and other multi-dimensional information can be directly detected without estimating the cascaded backscattering channel, and the detection result is corrected through a correction mechanism. The application can avoid complex backscattering link channel estimation of the receiver, directly decode multi-dimensional information transmitted by the tag, and save the tag pilot overhead.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication, and more specifically, relates to a backscatter communication method, apparatus and system without channel estimation. Background Technology

[0002] Passive backscatter communication does not require the active generation of radio frequency (RF) signals. Instead, it loads tag information by modulating the RF signals in the environment through tags placed in the RF environment, making it a green communication method. Passive backscatter tags abandon traditional high-power devices and mostly use passive components, offering advantages such as ultra-low power consumption, small size, and easy deployment, making it one of the important technologies for the future Internet of Things (IoT).

[0003] Initially, backscatter communication relied on a single antenna for signal modulation, depending solely on the impedance of that single antenna connection, resulting in low transmission rates and system throughput. With the advent of Multi-Input Multi-Output (MIMO) technology, industry and academia began researching multi-antenna backscatter communication. Utilizing multi-antenna tags for backscatter communication improved the system's transmission rate and throughput. Currently, research on backscatter communication using multi-antenna spatial modulation transmission schemes and multi-antenna space-time coding backscatter communication has been conducted, both of which have improved the transmission reliability and speed of backscatter communication systems to varying degrees.

[0004] However, current multi-antenna backscatter communication receivers all employ coherent detection. The receiver needs to estimate the cascaded backscatter channel information, and the multiple antenna tags also need to transmit the necessary pilot symbols for cascaded channel estimation. This results in high decoding costs for multi-antenna backscatter communication, and the pilot overhead becomes enormous with the increase in the number of antennas. Furthermore, errors in channel estimation are also introduced into information detection, degrading the overall communication performance of the backscatter communication system.

[0005] In summary, the proposed multi-antenna passive backscatter communication method and system that does not require cascaded backscatter channel estimation has significant application value. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a channel estimation-free backscatter communication method and system. Its purpose is to realize differential coding for multi-antenna tag communication and solve the problems of complex cascaded channel estimation and large tag pilot overhead in multi-antenna backscatter communication.

[0007] To achieve the above objectives, according to one aspect of the present invention, a backscatter communication method without channel estimation is provided, applied to backscatter tags, comprising: constructing an antenna matrix to map information in multiple dimensions to form information space-time blocks, performing differential encoding in the time dimension, and generating information space-time blocks to be transmitted by the tag.

[0008] Furthermore, regarding the index space dimension, the multi-antenna tag divides the transmitted bits into two parts, used respectively to construct the antenna index matrix and generate the constellation symbols carried under the antenna index matrix. The first part of the bits is used to determine the antenna index matrix, and its bit length is... There are Q possible antenna index matrices. in, This indicates a floor operation; it selects one from the set of Q-antenna index matrices as the index sequence of the antennas activated in each time slot within the current space-time block. Since only one antenna is activated in each time slot, each column of the antenna index matrix contains only one element. The tag activates different antennas in different time slots based on the antenna index sequence of the space-time block to be transmitted, by configuring the impedance network. The number of tag antennas is N. t N t Each time slot is used to activate all antennas. The resulting antenna index matrix is ​​of full rank. Each antenna index matrix corresponds to an antenna index sequence. When the number of tag antennas is N t At that time, the total number of antenna index matrices formed is N. t ! Types of sorting results.

[0009] Furthermore, the length of the second part of the bits is N t This indicates the number of tag antennas, and M represents the modulation order; the second part of the bits is modulated into N. t Each constellation symbol is placed at its corresponding position in the antenna index matrix, forming a multi-antenna backscattered tag information space-time block to be differentially processed. The antenna index matrix is ​​represented by P. q This means that the information spacetime block X(i) can be represented as: Here, `diag()` represents forming a diagonalized matrix from a vector. After mapping bits into information space-time blocks, a difference operation is performed between the preceding and following space-time blocks, setting the identity matrix of the first information space-time block. The differential spatial backscattering information matrix after differential operation can be expressed as: S(i)=S(i-1)X(i). The multi-antenna tag controls the RF switch and impedance network to generate the corresponding reflection coefficient to generate the differential spatial backscattering information matrix.

[0010] Furthermore, diversity gain can be introduced on top of the index space dimension before differential coding. In this case, the dimension of the constructed antenna index matrix is ​​N. t / 2×Nt / 2, the first bit length of the tag is then... The antenna index matrix has a total of One possibility, among which This indicates a floor operation. The length of the second part of the bits is... First, modulate it to N t Each constellation symbol is then orthogonally space-time encoded to form N. t / 2 orthogonal space-time code matrices, selecting a column of the antenna index matrix and N t One of the two orthogonal space-time code matrices is sequentially subjected to the Kronecker product to form the information space-time block to be differentially processed. The preceding and following information space-time blocks are then differentially processed, which can be represented as: S(i) = S(i-1)X(i). S(i) is the information block to be transmitted by the current tag. The tag configures the impedance network according to the antenna index of the differentially processed space-time block. Within one orthogonal space-time code matrix time, the impedance network is used to select and activate one antenna combination for transmitting the orthogonal space-time code matrix.

[0011] This invention also provides a channel-estimate-free backscatter communication method applied to a receiver, comprising: setting different reflection coefficients for tags; summing and averaging the receiver signal components under these reflection coefficients as the direct link component; the receiver needs to subtract this component before detecting tag information; removing the direct link signal from the received signal; separating the differential signal of the cascaded backscattered link from the receiver; directly detecting multi-dimensional information such as antenna index sequence and constellation symbol without estimating the cascaded backscattered channel; and correcting the detection results through a correction mechanism.

[0012] Furthermore, each RF switch of the tag has two reflection coefficients available for operation. When the tag operates with reflection coefficient α1, the receiver signal component is represented as (h d +h b α1)·s(n), where h d For direct-link channels, h b This represents the cascaded backscattering link channel; when the tag operates with a reflection coefficient α2, the signal components of the receiver signal are represented as (h d +h b α2)·s(n); The receiver signal components when the two reflection coefficients are working are added together and the average value is taken as the direct link component when the tag transmits the differential signal. When the tag is working with reflection coefficient α1, the backscatter signal component is obtained by subtracting the direct link component. at this time As the reflection coefficient;

[0013] The backscattered signal component is obtained by subtracting the direct link component from the reflection coefficient α2 of the tag. at this time As the reflection coefficient.

[0014] Furthermore, the receiver subtracts the direct link signal component to obtain the backscattered differential signal. Without needing to estimate the channel information of the cascaded backscattered links, the receiver estimates the antenna index matrix and constellation symbols respectively, and designs a correction mechanism to determine whether the estimated antenna index matrix is ​​reliable.

[0015] Furthermore, the correction mechanism determines whether the estimated antenna index matrix is ​​reliable. Assuming the antenna index matrix set has Q matrices, it calculates the similarity between the estimated antenna index sequence and each candidate vector in the set of index sequences corresponding to the Q antenna matrices, and calculates the same number of ξ as a similarity representation. The number of identical elements between the estimated index sequence and each candidate vector can be expressed as ξ = [ξ1, ..., ξ2]. Q ], obtained by sorting in descending order The corresponding antenna index sequence set is also obtained through corresponding operations. if This indicates that the index sequence is reliable; otherwise, the index sequence is unreliable.

[0016] According to a third aspect of the present invention, a backscatter tag is provided, comprising a backscatter modulation module, an radio frequency (RF) module, and a control module. The RF module consists of a microcontroller connected to an RF switch, which is connected to different loads. The control module controls the RF switch to select different loads to achieve differential index spatial dimension and differential index spatiotemporal dimension modulation of the tag signal. The control module comprises a microcontroller, such as an FPGA chip, to control the RF switch. The backscatter modulation module is used to construct an antenna index matrix to perform multi-dimensional mapping of the excitation source signal and differential encoding in the time dimension.

[0017] According to a fourth aspect of the present invention, a receiver is provided, including a receiving module, a backscatter demodulation module, a detection module, and a correction module;

[0018] The receiving module is used to receive signals;

[0019] The backscatter demodulation module is used to sum the received signal components under different reflection coefficients and take the average value as the direct link component; the direct link component is subtracted from the received signal components under different reflection coefficients to separate the differential signal of the cascaded backscatter link.

[0020] The detection module is used to detect the antenna index sequence and the corresponding bits of the constellation symbol in the differential signal;

[0021] The correction module is used to correct the antenna index sequence through a correction mechanism to obtain bit information.

[0022] The present invention also provides a backscatter communication system without channel estimation, including the backscatter tag and receiver described above.

[0023] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0024] (1) A differential antenna index matrix was designed for backscattering in the index space dimension. The antenna index matrix was proposed to improve the tag transmission rate. Differential coding was performed while maintaining the superior performance of the index space dimension. This avoided complex cascaded channel estimation, saved the tag pilot overhead, and achieved low-cost decoding at the receiver.

[0025] (2) For the index space-time dimension, a differential coding backscatter communication scheme for the index space-time dimension was designed, so that the backscatter communication system can maintain multiplexing gain and diversity gain, while the receiver can achieve incoherent detection without cascading backscatter channels.

[0026] (3) A corresponding low-complexity detector was designed for the proposed differential indexed multi-dimensional backscatter transmission scheme. The receiver eliminates the interference of the direct link signal based on the working characteristics of the different reflection coefficients of the tags, detects the antenna index matrix and constellation symbols respectively, and designs a correction mechanism to correct the detected antenna index matrix. By separating the antenna index matrix and constellation symbols, the search range of the detector is reduced, and the detection of backscattered multi-dimensional signals is realized without the need to estimate the cascaded channel. Attached Figure Description

[0027] Figure 1 A flowchart of a backscatter communication method for channel-free estimation provided in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of index space dimension backscatter communication for channel-free estimation provided in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of indexed spatiotemporal backscatter communication for channel-free estimation provided in an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram illustrating a low-complexity detection method for a channel-free backscatter communication method provided in an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of a backscatter communication system architecture for channel-free estimation provided in an embodiment of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0034] Example 1:

[0035] This embodiment provides a channel estimation-free backscatter communication method for use with backscatter tags. (See also...) Figure 1 and Figure 2 The method includes: the tag divides the transmitted bits into two parts, see [link to relevant documentation]. Figure 2 These are used to construct the antenna index matrix and generate the constellation symbols carried under the antenna index matrix, respectively. The first part of the bits is used to determine the antenna index matrix, and the bit length is [bit length missing]. There are Q possible antenna index matrices. in, This represents the floor operation; it selects one from the set of Q-antenna index matrices as the index sequence of the active antennas in each time slot within the current space-time block. Since only one antenna is activated in each time slot, each column of the antenna index matrix contains only one element. The resulting antenna index matrix is ​​of full rank. Each antenna index matrix corresponds to one antenna index sequence. When the number of tag antennas is N t At that time, the total number of antenna index matrices formed is N. t The sorting results are as follows. Taking a tag with 3 antennas as an example, the mapping relationship between the transmission index bits, the active antenna index sequence, and the antenna matrix is ​​illustrated below:

[0036]

[0037] The length of the second part of bits is N t This indicates the number of tag antennas, and M represents the modulation order; the second part of the bits is modulated into N. t Each constellation symbol is placed at its corresponding position in the antenna index matrix, forming a space-time block of backscattered tag information to be differentially processed. The antenna index matrix is ​​represented by P. q This means that the information spacetime block X(i) can be represented as: Here, `diag(·)` denotes forming a diagonalized matrix from a vector. After mapping bits into information space-time blocks, a difference operation is performed between the preceding and following space-time blocks, setting the identity matrix of the first information space-time block. The differential index space dimension backscattering information matrix after differential operation can be represented as: S(i)=S(i-1)X(i). The tag controls the RF switch and impedance network to generate the corresponding reflection coefficient to generate the differential space backscattering information matrix.

[0038] Example 2:

[0039] This embodiment provides a channel-estimate-free backscatter communication method for backscattered tag terminals. The method includes introducing diversity gain based on the differential index space dimension, see [link to documentation]. Figure 1 and Figure 3 Then differential encoding is performed. At this point, the dimension of the constructed antenna index matrix is ​​N. t / 2×N t / 2, the first bit length of the tag is then... The antenna index matrix has a total of One possibility, among which This indicates a floor operation. The length of the second part of the bits is... First, modulate it to N t Each constellation symbol is then orthogonally space-time encoded to form N. t / 2 orthogonal space-time code matrices, select one column from the antenna index matrix and N t One of the two orthogonal space-time code matrices is sequentially subjected to the Kronecker product to form the information space-time block to be differentially processed. Here, we take an example with 4 tag antennas: An antenna index matrix A is obtained. The constellation symbols are modulated into two orthogonal spacetime codes. and The information spacetime block is formed by sequentially performing the Kronecker product operation on a column of the antenna index matrix and one of the two orthogonal spacetime code matrices. Then, by performing a difference operation on the preceding and following space-time blocks, it can be represented as: S(i) = S(i-1)X(i). S(i) is the space-time block of information to be transmitted by the current tag.

[0040] Example 3:

[0041] This embodiment provides a channel-estimate-free backscatter communication method for a receiver. The method includes: the receiver detecting the backscattered signal in the differential index space dimension, see reference. Figure 4 Within the spacetime block time i, which is N t In each time slot, the receiver signal Y(i) can be expressed as: Where p represents the emission power of the environmental excitation source, Hd H represents direct link channel information. b H represents backscatter link channel information. f This represents the forward scattering link channel information, where s(i) represents the excitation source signal. Let S(i) represent the Hadamard product, S(i) be the backscattered differential signal, and W represent the noise component; correspondingly, within the space-time block time i-1, the receiver signal can be expressed as: Each RF switch of the tag has two reflection coefficients available for operation. When the tag operates using reflection coefficient α1, the receiver signal component is represented as (h d +h b α1)·s(n), where h d For direct-link channels, h b This represents the cascaded backscattering link channel; when the tag operates with a reflection coefficient α2, the signal components of the receiver signal are represented as (h d +h b α2)·s(n); The receiver signal components when the two reflection coefficients are working are added together and the average value is taken as the direct link component when the tag transmits the differential signal. When the tag is working with reflection coefficient α1, the backscatter signal component is obtained by subtracting the direct link component. at this time As the reflection coefficient; when the tag is reflected using the reflection coefficient α2, the direct link component is subtracted to obtain the backscattered signal component. at this time As the reflection coefficient, the receiver eliminates the direct link h through this process. d ·s(n) separated the cascaded backscattered link signal.

[0042] After denoising and removing the excitation source signal component from the backscattered signal of each time slot in the space-time block, the equivalent backscattered signal of space-time block i can be expressed as: Y c (i)=[y c (1),y c (2),...,y c (N t Furthermore, for differential backscattering in the index space dimension, a low-complexity detection scheme is designed. First, the non-zero elements in each time slot of the antenna matrix are calculated to estimate the antenna index sequence and the corresponding constellation symbol. The backscattered signal received in each time slot is represented as: in, x i (t), n i (t) represent Y respectively c The t-th column of (i), X(i), N(t). The receiver uses the maximum likelihood criterion to detect the antenna index sequence and constellation symbols respectively. For the space-time block N tAfter detecting the antenna index and constellation symbol of each time slot, the antenna index sequence is obtained. And constellation symbol vector The receiver determines the reliability of the antenna index sequence by calculating the similarity between the estimated antenna index sequence and each candidate vector in the set of index sequences corresponding to the Q antenna matrices, and calculating the same number ξ as a similarity characterization. The number of identical elements between the estimated index sequence and each candidate vector can be represented as ξ = [ξ1,…,ξ]. Q ], obtained by sorting in descending order The corresponding antenna index sequence set is also obtained through corresponding operations. if A positive result indicates a reliable index sequence; otherwise, the index sequence is unreliable. If the detection result is deemed valid, the antenna index sequence is output. and symbol vector Conversely, define Q ξ To find the number of maximum values ​​in ξ, choose... Middle front M≥Q ξ The antenna matrix corresponding to each element is used as a new candidate set for further detection, denoted as: Among them, A q Represents the antenna index matrix. It can be by Calculated, and then combined This is the final detection result. This detection mechanism achieves separate detection of the antenna index matrix and constellation symbols, with a low antenna matrix search range, enabling low-complexity detection of the differential index space dimension. The detection method for backscattered signals in the differential index space-time dimension is similar and will not be elaborated here.

[0043] Example 4:

[0044] This embodiment illustrates a backscatter communication device without channel estimation. It includes a backscatter modulation module, a radio frequency module, and a control module.

[0045] Specifically, the backscatter modulation module is used to construct an antenna index matrix to map the excitation source signal in multiple dimensions and perform differential coding in the time dimension; the control module is mainly composed of an FPGA chip and a microcontroller connected to several RF switches to realize the mapping of differential coding space-time blocks; the RF module is composed of a microcontroller connected to RF switches, and the RF switches are connected to different loads. The control module controls the RF switches to select different loads to realize differential coding modulation of the tag signal in the index spatial dimension and index space-time dimension.

[0046] Example 5:

[0047] This embodiment provides a backscatter communication system without channel estimation, including an environmental excitation source, a tag, and a receiver. (See attached document.) Figure 5 An environmental excitation source generates an excitation source signal; the tag can perform the actions shown in Embodiments 1 and 2; the receiver can perform the actions shown in Embodiment 3. For details not covered in this embodiment, please refer to the descriptions in Embodiments 1 to 4 above, which will not be repeated here.

[0048] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A backscatter communication method without channel estimation, characterized in that, This method is applied to backscattered tags, including: Constructing an antenna index matrix maps the excitation source signal in multiple dimensions and performs differential encoding in the time dimension; Regarding the index space dimension, with One time slot is one period, in bits. Construct an antenna index matrix, where, This indicates a round-down operation. The number of tag antennas is used to assign a modulation order to the corresponding time slot in the corresponding space based on the antenna index sequence. The constellation symbols form a dimension of The information space-time block is multiplied by the information space-time block transmitted in the previous cycle to form the information space-time block transmitted in the current cycle. The impedance network of each antenna is adjusted according to the information space-time block transmitted in the current cycle to achieve backscattering of the excitation source signal. For the index space-time dimension, with One time slot is one period, in bits. Construct an antenna index matrix, with a bit length of... Bits mapped to A constellation symbol, Indicates the modulation order, Each constellation symbol is grouped into pairs and orthogonally space-time encoded to form... A set of orthogonal space-time code matrices, selecting a column of the antenna index matrix and... One of the orthogonal space-time code matrices is sequentially subjected to Kronecker product operations to form an information space-time block to be differentially processed. The product of this information space-time block and the information space-time block transmitted in the previous cycle is used as the information space-time block transmitted in the current cycle. The impedance network of each antenna is adjusted according to the information space-time block transmitted in the current cycle to achieve backscattering of the excitation source signal.

2. A backscatter communication method without channel estimation, characterized in that, This method is applied to a receiver and includes: The received signal components are summed and averaged under different reflection coefficients to obtain the direct link component; the reflection coefficient is used as the reference value. During operation, the receiver signal components are represented as follows: Using the reflection coefficient During operation, the signal components of the receiver signal are represented as follows: ;in, For direct-link channels, This indicates a cascaded backscattering link channel. s ( n () is the excitation source signal; The receiver signal components at the operation of the two reflection coefficients are summed and the average value is taken as the direct link component when the tag transmits the differential signal. ; Reflectance coefficient During operation, subtracting the direct link component yields the backscattered signal component. ,at this time As a new reflection coefficient; Reflectance coefficient During operation, the backscattered signal component is obtained by subtracting the direct link component. ,at this time As a new reflection coefficient; The direct-link component is subtracted from the received signal components under different reflection coefficients to separate the differential signal of the cascaded backscattering link. The antenna index sequence and constellation symbol corresponding bits in the differential signal are detected, and the antenna index sequence is corrected through a correction mechanism to obtain the bit information.

3. The backscatter communication method without channel estimation according to claim 2, characterized in that, The correction mechanism: Assume the set of antenna index matrices has Given a matrix, calculate the estimated antenna index sequence and... The similarity of each candidate vector in the set of index sequences corresponding to each antenna matrix is ​​calculated, and the same number of similar vectors are calculated. As a similarity indicator; The estimated index sequence and the number of identical elements in each candidate vector are represented as follows: After sorting in descending order, we get The corresponding antenna index sequence set is also obtained through corresponding operations. ; if , The value represents the number of tag antennas, indicating that the index sequence is reliable. The output is the antenna index sequence and constellation symbol; otherwise, if the index sequence is unreliable, then... for The number of maximum values ​​in the range, and select The front of the middle The antenna matrix corresponding to each element is used as a new candidate set for further detection.

4. A backscattering tag for performing the backscattering communication method of claim 1, characterized in that, Includes a backscatter modulation module, an RF module, and a control module; The backscatter modulation module is used to construct an antenna index matrix to map the excitation source signal in multiple dimensions and perform differential encoding in the time dimension. The radio frequency module is connected to a radio frequency switch via a microcontroller. The radio frequency switch is connected to different loads. The control module controls the radio frequency switch to select different loads to achieve differential coding modulation of the index spatial dimension and index space-time dimension of the tag signal. The control module is a microcontroller composed of an FPGA chip, which can flexibly control the radio frequency switch.

5. A receiver, characterized in that, The method for performing the backscatter communication method according to claim 2 or 3 includes a receiving module, a backscatter demodulation module, a detection module, and a correction module; The receiving module is used to receive signals; The backscatter demodulation module is used to sum the received signal components under different reflection coefficients and take the average value as the direct link component; the direct link component is subtracted from the received signal components under different reflection coefficients to separate the differential signal of the cascaded backscatter link. The detection module is used to detect the antenna index sequence and the corresponding bits of the constellation symbol in the differential signal; The correction module is used to correct the antenna index sequence through a correction mechanism to obtain bit information.

6. A backscatter communication system without channel estimation, characterized in that, It includes the backscatter tag as described in claim 4 and the receiver as described in claim 5.

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