A backscattering communication method, device and system based on multi-carrier differential modulation

Abstract

The application belongs to the technical field of wireless communication, and discloses a backscattering communication method, device and system based on multi-carrier differential modulation t The transmission vector at t-1 time is expanded into a symmetric and full-rank subcarrier block transmission matrix, the transmission vector u t is subjected to rectangular differential modulation to obtain the transmission vector at t time, and then is converted into a time-domain data frame and mapped into a reflection coefficient; and the excitation source signal is modulated by means of an impedance network to generate a backscattering signal. Since differential modulation transmits information based on the difference between adjacent symbols, the channel state information is cancelled in the process of data detection at the receiving end, and the original sending data can be recovered by non-coherent detection of the receiving signal at the receiving end, without a complex cascaded channel estimation process, so that the complexity of the multi-carrier backscattering communication system is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, and more specifically, relates to a backscatter communication method, apparatus and system based on multi-carrier differential modulation. Background Technology

[0002] In wireless communication networks, using active radio frequency (RF) components requires sufficient RF energy to transmit data, leading to high equipment costs and circuit complexity, which cannot meet the demands of large-scale and low-cost wireless communication networks. Ambient backscatter communication (APR), however, uses existing environmental RF signals (such as Wi-Fi signals and Bluetooth indicator lights) as an excitation source. By using load modulation techniques to modulate the ambient RF signal, it reflects data with different reflection coefficients. These reflection coefficients represent the data to be transmitted, allowing the data to be embedded within the ambient RF signal. The receiving end decodes the information transmitted by analyzing the reflection coefficients. APR achieves low-power, low-cost information transmission by embedding its transmitted signal within the ambient RF signal. This technology eliminates the need for high-power active RF links, achieving information transmission simply by controlling its own reflection coefficient, significantly reducing system power consumption and cost. Therefore, APR is widely considered one of the key technologies for realizing the Internet of Things (IoT).

[0003] Orthogonal Frequency Division Multiplexing (OFDM) has demonstrated superior performance in cellular networks and Wi-Fi, significantly improving the throughput and transmission reliability of communication systems. Inspired by this, researchers have attempted to introduce OFDM technology into backscatter communication. Backscatter communication, which modulates multiple carriers through impedance networks, has become a research hotspot, enabling it to achieve higher data transmission rates and more stable signal transmission quality.

[0004] However, current methods for achieving backscatter communication through multi-carrier modulation typically require receivers to perform complex channel state estimation before multi-carrier decoding. This not only increases the design complexity of multi-carrier receivers but also raises decoding costs. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a backscatter communication method, device and system based on multi-carrier differential modulation, the purpose of which is to reduce the decoding difficulty of multi-carrier receivers.

[0006] To achieve the above objectives, the present invention provides a backscatter signal transmission method based on multi-carrier differential modulation, comprising:

[0007] The L subcarriers in the channel are divided into Q subcarrier blocks, each subcarrier block is used to transmit the allocated binary bit data; for each subcarrier block, the corresponding binary bit data is modulated into the transmission vector of the corresponding subcarrier block. t is the time index, N is the number of subcarriers in the subcarrier block, and the transmit vector u t Only one element in the array is non-zero;

[0008] For each subcarrier block, its transmission vector S at time t-1 is... t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U t-1 Using matrix U t-1 For the emission vector u t Rectangular differential modulation is performed to obtain the transmission vector S of the subcarrier block. t ;

[0009] The transmission vectors of Q subcarrier blocks are concatenated to form a frequency domain data frame. An inverse Fourier transform is performed on the frequency domain data frame to obtain a time domain data frame. The time domain data frame is then mapped to a reflection coefficient.

[0010] The impedance network is modulated to modulate and reflect the excitation source signal in the environment with the reflection coefficient obtained by mapping, thereby generating a backscattered signal corresponding to the time-domain data frame.

[0011] Optionally, for any subcarrier block transmission vector Its extended symmetric and full-rank subcarrier block transmission matrix is ​​G(x)=[x E 1 x E 2 x ...E N-1 x], where E n E raised to the power of n It is a right-shifted matrix, in which each row has only one 1 element and the rest are 0 elements, and the elements of the next row are obtained by cyclically shifting the elements of the previous row one position to the right.

[0012] Optionally, for each subcarrier block, its corresponding binary bit data is modulated into the corresponding subcarrier block's transmit vector u. t ,include:

[0013] Its corresponding binary bit data B t Divided into data With data based on The value is used to select a transmit subcarrier from the subcarrier block, and the dispersion vector a of the subcarrier block is constructed. t Dispersion vector a tIt has N elements that correspond one-to-one with N subcarriers. If a subcarrier is selected, the corresponding element is set to 1; otherwise, it is set to 0. MPSK modulation yields complex constellation symbols s t Construct the transmit vector u of this subcarrier block t =a t s t .

[0014] Optionally, mapping a time-domain data frame to a reflection coefficient includes mapping the time-domain data frame to a reflection coefficient by scaling.

[0015] Optionally, the impedance network includes a first sub-network, a second sub-network, and a power divider / combiner; varactor diode D1, varactor diode D2, capacitor C1, capacitor C2, resistor R1, resistor R2, inductor L1, inductor L2, and the power divider / combiner, wherein:

[0016] The first sub-network includes an inductor L1, a resistor R1, a varactor diode D1, and a capacitor C1. The first end of the inductor L1 is used to receive the first modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R1 and the varactor diode D1. The branch formed by the series connection of the resistor R1 and the varactor diode D1 is connected in parallel with the capacitor C1.

[0017] The second sub-network includes an inductor L2, a resistor R2, a varactor diode D2, and a capacitor C2. The first end of the inductor L2 is used to receive the second modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R2 and the varactor diode D2. The branch formed by the series connection of the resistor R2 and the varactor diode D2 is connected in parallel with the capacitor C2.

[0018] The power divider and combiner is used to combine the reflection coefficients at the antenna with the reflection coefficient a of the first sub-network as the real part of the reflection coefficient and the reflection coefficient b of the second sub-network as the imaginary part of the reflection coefficient, so that the reflection coefficient at the antenna is a+bj.

[0019] The present invention also provides a backscattered signal transmitting device, which includes a radio frequency module and a control module; the radio frequency module includes an impedance network; the control module includes:

[0020] The transmit vector construction unit divides the L subcarriers in the channel into Q subcarrier blocks, each subcarrier block being used to transmit the allocated binary bit data; for each subcarrier block, the corresponding binary bit data is modulated into the transmit vector of the corresponding subcarrier block. N is the number of subcarriers in the subcarrier block, and the transmit vector u t Only one element in the array is non-zero;

[0021] Transmission vector construction unit, used for each subcarrier block, to construct its transmission vector S at time t-1. t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U t-1 Using matrix U t-1 For the emission vector u t Rectangular differential modulation is performed to obtain the transmission vector S of the subcarrier block. t ;

[0022] The reflection coefficient construction unit is used to concatenate the transmission vectors of Q subcarrier blocks to form a frequency domain data frame, perform an inverse Fourier transform on the frequency domain data frame to obtain a time domain data frame, and map the time domain data frame to reflection coefficients.

[0023] The control unit is used to control the impedance network so that it modulates and reflects the excitation source signal in the environment with the reflection coefficient obtained by mapping, thereby generating a backscattered signal corresponding to the time domain data frame.

[0024] Optionally, the impedance network includes a first sub-network, a second sub-network, and a power divider / combiner; varactor diode D1, varactor diode D2, capacitor C1, capacitor C2, resistor R1, resistor R2, inductor L1, inductor L2, and the power divider / combiner, wherein:

[0025] The first sub-network includes an inductor L1, a resistor R1, a varactor diode D1, and a capacitor C1. The first end of the inductor L1 is used to receive the first modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R1 and the varactor diode D1. The branch formed by the series connection of the resistor R1 and the varactor diode D1 is connected in parallel with the capacitor C1.

[0026] The second sub-network includes an inductor L2, a resistor R2, a varactor diode D2, and a capacitor C2. The first end of the inductor L2 is used to receive the second modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R2 and the varactor diode D2. The branch formed by the series connection of the resistor R2 and the varactor diode D2 is connected in parallel with the capacitor C2.

[0027] The power divider and combiner is used to combine the reflection coefficients at the antenna with the reflection coefficient a of the first sub-network as the real part of the reflection coefficient and the reflection coefficient b of the second sub-network as the imaginary part of the reflection coefficient, so that the reflection coefficient at the antenna is a+bj.

[0028] The present invention also provides a backscatter signal receiving method based on multi-carrier differential modulation, comprising:

[0029] The received signal at time t is acquired and the time-domain data frame after passing through the channel is parsed out. A Fourier transform is performed on the parsed time-domain data frame to extract the corresponding frequency-domain data frame. The parsed frequency-domain data frame is then split, and the transmission vector S' of each subcarrier block after passing through the channel is extracted. t t is the time index;

[0030] For each subcarrier block, the transmission vector S' of that subcarrier block at time t-1 is... t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U' t-1 Based on S' t and U' t-1 Obtain the transmit vector estimate of this subcarrier.

[0031] For each subcarrier block The binary bit data carried by the subcarrier is obtained by parsing; the binary bit data of the Q subcarrier blocks are concatenated to obtain the complete data carried by the backscattered signal.

[0032] The present invention also provides a backscatter signal receiving device, comprising:

[0033] The transmission vector resolution unit is used to acquire the received signal at time t. It first resolves the reflection coefficients and, based on the mapping relationship, resolves the time-domain data frame corresponding to the reflection coefficients. Then, it performs a Fourier transform on the time-domain data frame to resolve the frequency-domain data frame. Finally, it splits the frequency-domain data frame and resolves the transmission vector S' of each subcarrier block. t t is the time index;

[0034] The transmit vector resolution unit is used to resolve the transmission vector S' of each subcarrier block at time t-1. t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U' t-1 Based on S' t and U' t-1 Obtain the transmit vector estimate of this subcarrier. right The binary bit data carried by the subcarrier is obtained by parsing.

[0035] The raw data parsing unit is used to analyze each subcarrier block. The binary bit data carried by the subcarrier is obtained by parsing; the binary bit data of the Q subcarrier blocks are concatenated to obtain the complete data carried by the backscattered signal.

[0036] The present invention also provides a backscatter communication system, comprising: a backscatter signal transmitting device as described above and a backscatter signal receiving device as described above.

[0037] In summary, compared with the prior art, the technical solutions conceived in this invention have the following main advantages:

[0038] 1. In this invention, when transmitting the scattered signal, binary bit data is modulated into the transmission vector of the corresponding subcarrier block. Furthermore, only one element in the vector is non-zero. Rectangular differential modulation is then used to achieve carrier index differential modulation information transmission. Since differential modulation transmits information based on the differences between adjacent symbols, and the channel has the same effect on adjacent symbols, the channel state information is canceled out during the data detection process at the receiving end. The receiving end can recover the original transmitted data by performing noncoherent detection on the received signal, without the need for a complex cascaded channel estimation process, effectively reducing the complexity of multi-carrier backscatter communication systems.

[0039] 2. In an optional embodiment, a subcarrier block transmission matrix extension function G(x) = [x E 1 x E 2 x ...E N-1 Based on this function, the transmission vector can be quickly expanded into a symmetric and full-rank subcarrier block transmission matrix.

[0040] 3. In an optional embodiment, a specific method for constructing the emission vector is provided, which transmits the binary bit data B t Divided into data With data Binary bit data B t Mapping to the index of the selected subcarrier only requires data... Modulation calculations are performed, which allows for full utilization of resources in the communication system to achieve data transmission and reduces the complexity of modulation.

[0041] 4. In an optional embodiment, an impedance network design is provided. Based on this impedance network, the reflection coefficient can be continuously adjusted by continuously adjusting the modulation voltage connected to the impedance network. This enables a continuously variable reflection coefficient to characterize continuous time-domain data frames, thereby improving the modulation accuracy and solving the modulation limitation problem. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a multi-carrier differential modulation backscatter communication system architecture;

[0043] Figure 2 This is a flowchart of the steps of a backscattered signal transmission method provided in an embodiment of the present invention;

[0044] Figure 3 This is a simplified flowchart of a backscattered signal transmission method provided in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the impedance network in one embodiment of the present invention;

[0046] Figure 5 This is a flowchart of the steps of a backscatter signal receiving method according to an embodiment of the present invention. Detailed Implementation

[0047] 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.

[0048] like Figure 1 The diagram illustrates the architecture of a multi-carrier differential modulation backscatter communication system. The backscatter communication system includes a backscatter signal transmitter (backscatter tag) and a receiver. The backscatter signal transmitter receives existing excitation source signals from the environment, modulates them using load modulation technology, and reflects them with different reflection coefficients. These reflection coefficients represent the data to be transmitted in the backscatter communication. This allows the data to be embedded into the environmental excitation source signal for transmission. The receiver decodes the information transmitted by analyzing the reflection coefficients. However, traditional methods suffer from high complexity in multi-carrier decoding by the receiver. Therefore, this invention proposes the following improvement to address this problem.

[0049] Example 1

[0050] like Figure 2 The diagram shown is a flowchart of the backscattered signal transmission method provided in an embodiment of the present invention. Figure 3 The diagram shown is a simplified flowchart of a backscattered signal transmission method according to an embodiment of the present invention. The order of the steps can be adjusted according to actual circumstances and is not limited thereto. The steps are described in detail below.

[0051] Step S11: Divide the L subcarriers in the channel into Q subcarrier blocks, each subcarrier block is used to transmit the allocated binary bit data; for each subcarrier block, modulate the corresponding binary bit data into the transmission vector of the corresponding subcarrier block. N is the number of subcarriers in the subcarrier block, and the transmit vector u t Only one element in the array is non-zero.

[0052] Where Q is a set positive integer. If the value is 1, it means that only one subcarrier block is used to transmit the signal. If the value is greater than 1, it means that the data to be transmitted needs to be divided into several parts, and each subcarrier block is responsible for transmitting a part of the data.

[0053] Specifically, the L subcarriers are divided into Q subcarrier blocks, each containing N = L / Q subcarriers. The purpose of this step is to construct the transmission vector for each subcarrier block.

[0054] Specifically, for a given subcarrier block: at time t, only the p-th subcarrier is activated (P < N). Therefore, the constructed transmit vector contains only one non-zero element, representing the modulation data that the activated subcarrier needs to transmit.

[0055] Specifically, the process of constructing the transmit vector for each subcarrier block is as follows:

[0056] Its corresponding binary bit data B t Divided into data With data based on The value is used to select a transmit subcarrier from the subcarrier block, and the dispersion vector a of the subcarrier block is constructed. t Dispersion vector a t It has N elements that correspond one-to-one with N subcarriers. If a subcarrier is selected, the corresponding element is set to 1; otherwise, it is set to 0. MPSK modulation yields complex constellation symbols s t Construct the transmit vector u of this subcarrier block t =a t s t .

[0057] The subcarrier activation state forms the dispersion vector There is one and only one non-zero element The raw binary bit data B responsible for transmitting this subcarrier block t Segmentation is performed, data segment B t Divided into and Two groups, namely Through data segment Select the activated subcarriers in this subcarrier block and determine the dispersion vector a. t For example, if N=4, if the data segment If it is binary 00, then a t =[1 0 0 0] T If data segment If it is binary 01, then a t =[0 1 0 0] T If data segment If it is binary 10, then a t =[0 01 0] T If data segment If it is binary 11, then a t =[0 0 0 1] T For data segments MPSK modulation yields complex constellation symbols s t The two are combined to obtain the transmit vector u of the subcarrier block. t =a t s t Therefore, the subcarrier block transmit vector There is a unique non-zero element Where p is the index of the active subcarrier in the current subcarrier block (from the data segment). Decision), s t The complex constellation symbols contained in the current emission vector (from the data segment) Decide).

[0058] Using the above method to construct the emission vector, since the binary bit data B... t Divided into data With data Binary bit data B t Mapping to the index of the selected subcarrier only requires data... Modulation calculations are performed, which allows for full utilization of information in the communication system to achieve data transmission and reduces the complexity of modulation.

[0059] The concepts involved in the above process are summarized as follows:

[0060] Data blocks: The binary data transmitted by a single subcarrier block at time t is divided into... and Two groups, which respectively determine the active subcarrier sequence number and the complex constellation symbols transmitted by the active subcarrier.

[0061] Subcarrier block dispersion vector (dispersion vector): At time t, only the p-th subcarrier is activated. And there is only one non-zero element. The value of p (i.e., the sequence number of the active subcarrier) is determined by the data segment. Decide.

[0062] Plural constellation symbol: s t For a plural constellation point, s t The value is determined by the data segment The decision to perform MPSK modulation (M-ary phase modulation) is made.

[0063] Subcarrier block transmit vector: ut =a t s t .

[0064] The process will be illustrated with specific examples below.

[0065] Example: Let in a can be determined according to the following mapping relationships Table 1 and Table 2. t s t :

[0066] Table 1

[0067]

[0068] Table 2

[0069]

[0070] at this time, s t =-1+j,

[0071] Step S12: For each subcarrier block, calculate its transmission vector S at time t-1. t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U t-1 Using matrix U t-1 For the emission vector u t Rectangular differential modulation is performed to obtain the transmission vector S of the subcarrier block. t .

[0072] In one embodiment, the arbitrary subcarrier block transmission vector is... Its extended symmetric and full-rank subcarrier block transmission matrix is ​​G(x)=[x E 1 x E 2 x...E N-1 x], where E n E raised to the power of n It is a right-shifted matrix, in which each row has only one 1 element and the rest are 0 elements, and the elements of the next row are obtained by cyclically shifting the elements of the previous row one position to the right.

[0073] Specifically, matrix E can be designed according to the actual situation; for example, it can be set in the following form:

[0074]

[0075] For example, let When dimension N = 4, at this time but:

[0076]

[0077] at this time:

[0078]

[0079] Specifically, for the subcarrier block transmit vector u t The rectangular difference operation can be represented as S t =U t-1 u t =G(S t-1 )u t U t-1 Let U0 be the transfer matrix at time t-1. When t=1, U0 at the previous time can be the identity matrix.

[0080] For example, let Where m, n, and k are constellation symbols (complex values), then:

[0081]

[0082]

[0083] Step S13: Concatenate the transmission vectors of Q subcarrier blocks to form a frequency domain data frame, perform an inverse Fourier transform on the frequency domain data frame to obtain a time domain data frame, and map the time domain data frame to the reflection coefficient of the tag.

[0084] Specifically, the frequency domain data frame is converted into a time domain data frame through an inverse Fourier transform. Then, based on the range of reflection coefficients achievable by the backscattering tag impedance network, the time domain data frame to be transmitted is linearly mapped to the tag's reflection coefficients. This mapping relationship is stored in the tag.

[0085] For example, the transmission vector of the Q subcarrier blocks corresponding to the L subcarrier blocks. Combining: The dimension of the transmission vector of a single subcarrier block is By concatenating the transmission vectors of the Q subcarrier blocks end to end, a frequency domain data frame is obtained. (When dividing the data into blocks, L = N × Q) Perform an inverse Fourier transform on the frequency domain data frame to obtain the time domain data frame D. time Its dimension is the same as D freq Similarly, by scaling it according to a set scaling ratio, a reflection coefficient for backscattering can be obtained.

[0086] Step S14: Adjust the impedance network so that it modulates and reflects the excitation source signal in the environment with the reflection coefficient obtained by mapping, thereby generating a backscattered signal corresponding to the time domain data frame.

[0087] Specifically, after determining the reflection coefficient, the impedance network can be adjusted so that the impedance network reflects the excitation source signal in the environment with the reflection coefficient obtained by mapping. The reflected signal is the backscattered signal, and its amplitude and phase are determined by the reflection coefficient.

[0088] For example, at time t, the impedance-controlled network generates a time-domain data frame D. time The reflection coefficient Γ corresponding to (t) t This generates a multi-carrier differential backscatter signal, enabling the transmission of time-domain data frames.

[0089] In general, at the backscatter signal transmitter, L subcarriers are divided into Q subcarrier blocks, with N = L / Q subcarriers in each block. For each subcarrier block, a tag selects and activates a subcarrier using an index and loads constellation symbols onto it, thus obtaining the subcarrier block transmission vector u. t ; the transfer vector S at time t-1 t-1 Expanded into subcarrier block transmission matrix U t-1 , borrow U t-1 The emission vector u at time t t Rectangular differential modulation is performed to obtain the subcarrier block transmission vector S. t The transmit vectors of each sub-block that has undergone differential operation are combined and multi-carrier modulated to obtain a frame of data to be transmitted. This frame of data is preprocessed to obtain a time-domain data frame. Then, based on the range of reflection coefficients achievable by the backscatter tag impedance network, the time-domain data frame to be transmitted is mapped to a reflection coefficient. The impedance network is controlled according to this mapping relationship to generate a reflection coefficient corresponding to the time-domain data frame, thereby generating a backscatter signal corresponding to the time-domain data frame, thus realizing the transmission of time-domain data. In this invention, backscatter communication modulation is achieved through the above method. When transmitting the scattered signal, due to the use of specific differential modulation, carrier index differential modulation information is transmitted. The receiving end can recover the original transmitted data by performing incoherent detection on the received signal. Since differential modulation transmits information based on the differences between adjacent symbols, and the channel has the same effect on adjacent symbols, the channel state information is canceled out during the data detection process at the receiving end, eliminating the need for a complex cascaded channel estimation process and effectively reducing the complexity of the multi-carrier backscatter communication system.

[0090] Considering that the adjustable reflection coefficient in commonly used impedance networks is fixed, only a few fixed reflection coefficients can be adjusted, and continuous adjustment of the reflection coefficient cannot be achieved, which affects the modulation accuracy.

[0091] Based on this, this embodiment also provides a design for an impedance network, such as... Figure 4 The diagram shown is a schematic diagram of the impedance network in one embodiment of the present invention.

[0092] The anti-interference network includes a first sub-network, a second sub-network, and a power divider / combiner; varactor diode D1, varactor diode D2, capacitor C1, capacitor C2, resistor R1, resistor R2, inductor L1, inductor L2, and the power divider / combiner, wherein:

[0093] The first sub-network includes an inductor L1, a resistor R1, a varactor diode D1, and a capacitor C1. The first end of the inductor L1 is used to receive the first modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R1 and the varactor diode D1. The branch formed by the series connection of the resistor R1 and the varactor diode D1 is connected in parallel with the capacitor C1.

[0094] The second sub-network includes an inductor L2, a resistor R2, a varactor diode D2, and a capacitor C2. The first end of the inductor L2 is used to receive the second modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R2 and the varactor diode D2. The branch formed by the series connection of the resistor R2 and the varactor diode D2 is connected in parallel with the capacitor C2.

[0095] The power divider and combiner is used to combine the reflection coefficients at the antenna with the reflection coefficient a of the first sub-network as the real part of the reflection coefficient and the reflection coefficient b of the second sub-network as the imaginary part of the reflection coefficient, so that the reflection coefficient at the antenna is a+bj.

[0096] Furthermore, the impedance network is modulated by driving the first DAC module to generate a first modulation voltage and driving the second DAC module to generate a second modulation voltage. The impedance network is modulated by adjusting the modulation voltage so that it generates a reflection coefficient corresponding to the time-domain data frame.

[0097] In the impedance network provided in this embodiment, as the voltage connected to inductors L1 and L2 changes, the capacitance of varactor diodes D1 and D2 also changes, causing the reflection coefficient of the power divider / combiner to change the excitation source signal. Therefore, by continuously adjusting the modulation voltage connected to the impedance network, the reflection coefficient can be continuously controlled, and a continuously variable reflection coefficient can be used to characterize continuous time-domain data frames, thereby improving the modulation accuracy and solving the modulation limitation problem.

[0098] Example 2

[0099] The present invention also provides a backscatter signal transmitting device based on multi-carrier differential modulation, also known as a backscatter tag device, which includes an radio frequency module and a control module. The radio frequency module includes an impedance network. The control module is used to execute the method of embodiment 1 to adjust the impedance network in the radio frequency module so that it reflects the excitation source signal in the environment with the reflection coefficient obtained by mapping, thereby generating a backscatter signal corresponding to the time domain data frame and realizing data transmission.

[0100] Specifically, the control module includes:

[0101] The transmit vector construction unit divides the L subcarriers in the channel into Q subcarrier blocks, each subcarrier block being used to transmit the allocated binary bit data; for each subcarrier block, the corresponding binary bit data is modulated into the transmit vector of the corresponding subcarrier block. N is the number of subcarriers in the subcarrier block, and the transmit vector u t Only one element in the array is non-zero;

[0102] Transmission vector construction unit, used for each subcarrier block, to construct its transmission vector S at time t-1. t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U t-1 Using matrix U t-1 For the emission vector u t Rectangular differential modulation is performed to obtain the transmission vector S of the subcarrier block. t ;

[0103] The reflection coefficient construction unit is used to concatenate the transmission vectors of Q subcarrier blocks to form a frequency domain data frame, perform an inverse Fourier transform on the frequency domain data frame to obtain a time domain data frame, and map the time domain data frame to reflection coefficients.

[0104] The control unit is used to control the impedance network so that it modulates and reflects the excitation source signal in the environment with the reflection coefficient obtained by mapping, thereby generating a backscattered signal corresponding to the time domain data frame.

[0105] The transmitting device works by: activating subcarriers through index modulation of the original binary bit data and loading constellation symbols onto the activated subcarriers; the subcarrier block transmission vector u for each subcarrier block... t The subcarrier block transmission vector S is formed through differential operations on the preceding and following time slots. t The vectors to be transmitted in each sub-block are combined into frequency domain data frames, which are then preprocessed and converted into tag time domain data frames. The control module outputs different voltages in different time slots to adjust the impedance network in the RF module, thereby realizing the transmission of frequency domain data frames.

[0106] More specifically, the control module can use an STM32 chip to construct the transmit vector through index modulation and constellation mapping, perform differential operations on the transmit vector to combine it into a frame of transmit data, and preprocess the frame data to obtain a time-domain data frame; call the DAC module to control the DAC module to output analog voltages corresponding to the time-domain data frames in different time slots.

[0107] Furthermore, the impedance network consists of two varactor diodes, capacitors, inductors, and other components. The varactor diodes are connected to the DAC output of the control module and can generate different reflection coefficients according to different voltages output by the DAC.

[0108] Example 3

[0109] The present invention also provides a backscatter signal receiving method based on multi-carrier differential modulation, which is used to demodulate the backscatter signal emitted by the backscatter signal transmitting device mentioned in Embodiment 2 to obtain the original binary data.

[0110] like Figure 5 The diagram shows a flowchart of a backscattered signal receiving method according to an embodiment of the present invention. The receiving method includes:

[0111] Step S21: Obtain the received signal at time t and parse out the time-domain data frame after passing through the channel. Perform a Fourier transform on the parsed time-domain data frame to parse out the corresponding frequency-domain data frame. Decompose the parsed frequency-domain data frame and parse out the transmission vector S' of each subcarrier block after passing through the channel. t t is the time index;

[0112] Step S22: For each subcarrier block, calculate the transmission vector S' of that subcarrier block at time t-1. t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U' t-1 Based on S' t and U' t-1 Obtain the transmit vector estimate of this subcarrier.

[0113] Step S23: For each subcarrier block The binary bit data carried by the subcarrier is obtained by parsing; the binary bit data of the Q subcarrier blocks are concatenated to obtain the complete data carried by the backscattered signal.

[0114] Specifically, in a backscatter communication system, the backscatter signal transmitter modulates the amplitude and phase of the excitation source signal by adjusting the reflection coefficient, thereby enabling it to carry the desired time-domain data frame. Therefore, upon receiving the backscatter signal, only the amplitude and phase of the received signal need to be analyzed to extract the time-domain data frame transmitted through the channel. In traditional methods, channel estimation is required, the original time-domain data frame needs to be analyzed, and then the data carried by the backscatter signal needs to be extracted from the original time-domain data frame. However, in this invention, due to improvements in the signal transmission process of the transmitting device, complex channel estimation is unnecessary at the receiving end; the data carried by the backscatter signal can be directly extracted from the time-domain data frame transmitted through the channel. The principle is explained below.

[0115] Because rectangular differential modulation is used to obtain the transmission vector, i.e., S, during signal modulation in the transmitting device. t =U t- 1u t =G(S t-1 )u t The result can be obtained by deformation: Let the form after transmission through the channel be denoted as S' t =H t S t S' t-1 =H t-1 S t-1 ,U' t-1 =H t-1 U t-1 Since adjacent time slot channels remain unchanged and have the same channel coefficients, H can be considered... t ≈H t-1 Therefore, we can obtain:

[0116]

[0117] for The estimated value.

[0118] Therefore, it is only necessary to base it on This allows us to obtain an estimate of the emission vector.

[0119] Let's illustrate with specific examples.

[0120] Continue with For example;

[0121] The parameters at the transmitting end are as follows:

[0122]

[0123] After the above parameters pass through the channel, S' t =H t S t ,at this time:

[0124] The extended transmission matrix is ​​as follows:

[0125]

[0126]

[0127] Substitution Channel estimation is performed, and the following is obtained:

[0128]

[0129] Therefore, it can be seen that... Achieve accurate estimation of the emission vector.

[0130] After obtaining the emission vector estimate Then, based on the method of constructing the transmitter's transmission vector, it can be used to... By reverse-engineering the binary values ​​carried by each subcarrier, and finally concatenating all the binary values, the complete data can be obtained, thus completing the data reception at the receiving end.

[0131] Example 4

[0132] The present invention also relates to a backscatter signal receiving device, comprising:

[0133] The transmission vector resolution unit is used to obtain the received signal at time t. It first resolves the reflection coefficients and, based on the mapping relationship, resolves the time-domain data frame corresponding to the reflection coefficients. Then, it performs a Fourier transform on the time-domain data frame to resolve the frequency-domain data frame. Finally, it splits the frequency-domain data frame and resolves the transmission vector S' of each subcarrier block. t t is the time index;

[0134] The transmit vector resolution unit is used to resolve the transmission vector S' of each subcarrier block at time t-1. t-1 Expanded into a symmetric, full-rank subcarrier block transmission matrix U' t-1 Based on S' t and U' t-1 Obtain the transmit vector estimate of this subcarrier. right The binary bit data carried by the subcarrier is obtained by parsing.

[0135] The raw data parsing unit is used to analyze each subcarrier block. The binary bit data carried by the subcarrier is obtained by parsing; the binary bit data of the Q subcarrier blocks are concatenated to obtain the complete data carried by the backscattered signal.

[0136] Example 5

[0137] The present invention also relates to a backscatter communication system, which includes the backscatter signal transmitting device in Embodiment 2 and the backscatter signal receiving device in Embodiment 4. When used together, the two can realize complete backscatter communication.

[0138] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. It should be noted that the terms "in one embodiment," "for example," and "again" are intended to illustrate the present invention and are not intended to limit the present invention.

[0139] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for transmitting backscattered signals based on multi-carrier differential modulation, characterized in that, include: In the channel Each subcarrier is divided into There are several subcarrier blocks, each used to transmit the allocated binary bit data; for each subcarrier block, its corresponding binary bit data is modulated into the corresponding subcarrier block's transmit vector. t is the time index, N is the number of subcarriers in the subcarrier block, and the transmit vector Only one element in the array is non-zero; For each subcarrier block, its transmission vector at time t-1 is... Expanded into a symmetric, full-rank subcarrier block transmission matrix Using matrices For the emission vector Rectangular differential modulation is performed to obtain the transmission vector of the subcarrier block. ; The transmission vectors of Q subcarrier blocks are concatenated to form a frequency domain data frame. An inverse Fourier transform is performed on the frequency domain data frame to obtain a time domain data frame. The time domain data frame is then mapped to a reflection coefficient. The impedance network is modulated to modulate and reflect the excitation source signal in the environment with the reflection coefficient obtained by mapping, thereby generating a backscattered signal corresponding to the time-domain data frame.

2. The backscattered signal transmission method as described in claim 1, characterized in that, For any subcarrier block transmission vector Its extended symmetric and full-rank subcarrier block transmission matrix is ,in, for power of n It is a right-shifted matrix, in which each row has only one 1 element and the rest are 0 elements, and the elements of the next row are obtained by cyclically shifting the elements of the previous row one position to the right.

3. The backscattered signal transmission method as described in claim 1, characterized in that, For each subcarrier block, its corresponding binary bit data is modulated into the transmission vector of that subcarrier block. ,include: its corresponding binary bit data Divided into data With data ,based on The value is used to select a transmit subcarrier from the subcarrier block, and the dispersion vector of the subcarrier block is constructed. Dispersion vector It has N elements that correspond one-to-one with N subcarriers. If a subcarrier is selected, the corresponding element is set to 1; otherwise, it is set to 0. conduct Modulation yields complex constellation symbols Construct the transmit vector of this subcarrier block. .

4. The backscattered signal transmission method as described in claim 1, characterized in that, Map time-domain data frames to reflection coefficients This includes mapping time-domain data frames to reflection coefficients through scaling.

5. The backscattered signal transmission method as described in claim 1, characterized in that, The impedance network includes a first sub-network, a second sub-network, and a power divider / combiner; wherein: The first sub-network includes an inductor L1, a resistor R1, a varactor diode D1, and a capacitor C1. The first end of the inductor L1 is used to receive the first modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R1 and the varactor diode D1. The branch formed by the series connection of the resistor R1 and the varactor diode D1 is connected in parallel with the capacitor C1. The second sub-network includes an inductor L2, a resistor R2, a varactor diode D2, and a capacitor C2. The first end of the inductor L2 is used to receive the second modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R2 and the varactor diode D2. The branch formed by the series connection of the resistor R2 and the varactor diode D2 is connected in parallel with the capacitor C2. The power splitter and combiner is used to measure the reflection coefficient of the first subnetwork. The real part of the reflection coefficient, and the reflection coefficient of the second subnetwork. As the imaginary part of the reflection coefficient, combining the two makes the reflection coefficient at the antenna equal to... .

6. A backscattering signal transmitting device, characterized in that, It includes a radio frequency (RF) module and a control module; the RF module includes an impedance network; the control module includes: Transmit vector construction unit, used to transmit vectors in the channel Each subcarrier is divided into There are several subcarrier blocks, each used to transmit the allocated binary bit data; for each subcarrier block, its corresponding binary bit data is modulated into the corresponding subcarrier block's transmit vector. N is the number of subcarriers in the subcarrier block, and the transmission vector Only one element in the array is non-zero; Transmission vector construction unit, used to construct the transmission vector at time t-1 for each subcarrier block. Expanded into a symmetric, full-rank subcarrier block transmission matrix Using matrices For the emission vector Rectangular differential modulation is performed to obtain the transmission vector of the subcarrier block. ; The reflection coefficient construction unit is used to concatenate the transmission vectors of Q subcarrier blocks to form a frequency domain data frame, perform an inverse Fourier transform on the frequency domain data frame to obtain a time domain data frame, and map the time domain data frame to reflection coefficients. The control unit is used to control the impedance network so that it modulates and reflects the excitation source signal in the environment with the reflection coefficient obtained by mapping, thereby generating a backscattered signal corresponding to the time domain data frame.

7. The backscatter signal transmitting device as described in claim 6, characterized in that, The impedance network includes a first sub-network, a second sub-network, and a power divider / combiner; wherein: The first sub-network includes an inductor L1, a resistor R1, a varactor diode D1, and a capacitor C1. The first end of the inductor L1 is used to receive the first modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R1 and the varactor diode D1. The branch formed by the series connection of the resistor R1 and the varactor diode D1 is connected in parallel with the capacitor C1. The second sub-network includes an inductor L2, a resistor R2, a varactor diode D2, and a capacitor C2. The first end of the inductor L2 is used to receive the second modulation voltage, and the second end is connected to the input end of the power divider and combiner in sequence through the resistor R2 and the varactor diode D2. The branch formed by the series connection of the resistor R2 and the varactor diode D2 is connected in parallel with the capacitor C2. The power splitter and combiner is used to measure the reflection coefficient of the first subnetwork. The real part of the reflection coefficient, and the reflection coefficient of the second subnetwork. As the imaginary part of the reflection coefficient, combining the two makes the reflection coefficient at the antenna equal to... .

8. A method for receiving backscattered signals based on multi-carrier differential modulation, characterized in that, include: Get The system receives signals at specific times and parses out time-domain data frames after they have passed through the channel. It then performs a Fourier transform on the parsed time-domain data frames to extract the corresponding frequency-domain data frames. Finally, it decomposes the frequency-domain data frames and extracts the transmission vectors of each subcarrier block after they have passed through the channel. t is the time index; For each subcarrier block, the transmission vector of that subcarrier block at time t-1 is... Expanded into a symmetric, full-rank subcarrier block transmission matrix ,based on and Obtain the transmit vector estimate for this subcarrier block. ; For each subcarrier block The binary bit data carried by the subcarrier block is obtained by parsing; the binary bit data of the Q subcarrier blocks are concatenated to obtain the complete data carried by the backscatter signal.

9. A backscatter signal receiving device, characterized in that, include: Transmission vector resolution unit, used to obtain For the received signal at a given time, first, the reflection coefficients are analyzed, and the corresponding time-domain data frames are derived based on the mapping relationship. Then, a Fourier transform is performed on the time-domain data frames to derive the frequency-domain data frames. Finally, the frequency-domain data frames are split, and the transmission vectors of each subcarrier block are derived. t is the time index; The transmit vector resolution unit is used to resolve the transmission vector of each subcarrier block at time t-1. Expanded into a symmetric, full-rank subcarrier block transmission matrix ,based on and Obtain the transmit vector estimate for this subcarrier block. ,right The binary bit data carried by the subcarrier block is obtained by parsing. The raw data parsing unit is used to analyze each subcarrier block. The binary bit data carried by the subcarrier block is obtained by parsing; the binary bit data of the Q subcarrier blocks are concatenated to obtain the complete data carried by the backscatter signal.

10. A backscatter communication system, characterized in that, include: The backscatter signal transmitting device as described in claim 6 or 7 and the backscatter signal receiving device as described in claim 9.

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