Backscatter communication method, device and system based on multicarrier differential modulation

Abstract

The invention belongs to the related technical field of wireless communication, and discloses a backscatter communication method, device and system based on multicarrier differential modulation, and the method comprises the steps: modulating binary bit data to generate a transmission vector ut when a backscatter signal is transmitted; a transmission vector at the t-1 moment is expanded into a symmetrical and full-rank subcarrier block transmission matrix, a transmission vector ut is subjected to rectangular differential modulation to obtain a transmission vector at the t moment, and the transmission vector at the t moment is converted into a time domain data frame and then mapped into a reflection coefficient; the excitation source signal is modulated by means of an impedance network to generate a backscattering signal. Since the differential modulation transmits information based on the difference between adjacent symbols, the channel state information is counteracted in the data detection process of the receiving end, the receiving end can recover the original sending data by performing incoherent detection on the received signal, a complex cascade channel estimation process is not needed, and the data transmission efficiency is improved. And the complexity of the multi-carrier backscatter communication system is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field related to wireless communication, and more specifically, relates to a backscatter communication method, device, and system based on multi-carrier differential modulation. Background Art

[0002] In a wireless communication network, communicating using active radio frequency components requires obtaining sufficient radio frequency energy to transmit data. This will result in a relatively high cost of the device and the complexity of the circuit, and cannot meet the requirements of large-scale and low-cost wireless communication networks. Ambient backscatter communication uses existing radio frequency signals in the environment (such as Wi-Fi signals, Bluetooth signals, etc.) as excitation sources. By using load modulation technology to modulate the ambient radio frequency signals, they are reflected with different reflection coefficients. The reflection coefficient represents the data to be transmitted by the backscatter communication. In this way, the data to be transmitted can be embedded in the ambient radio frequency signal for transmission. The receiving end decodes the information transmitted by the transmitting end by analyzing the reflection coefficient. Ambient backscatter communication transmits by embedding its transmitted signal in the ambient radio frequency signal, achieving low-power and low-cost information transmission. This technology does not require a high-power active radio frequency link and can achieve information transmission only by controlling its own reflection coefficient, greatly reducing the system power consumption and cost. Therefore, backscatter communication is widely regarded as one of the key technologies for realizing the Internet of Everything in the future.

[0003] Orthogonal Frequency Division Multiplexing (OFDM) has shown superior performance in fields such as cellular networks and Wi-Fi, greatly improving the throughput and transmission reliability of communication systems. Inspired by this, researchers have tried to introduce OFDM technology into backscatter communication. Backscatter communication that modulates multiple carriers through an impedance network has become a research hotspot, enabling backscatter communication to have a higher data transmission rate and more stable signal transmission quality.

[0004] However, in the current method for realizing backscatter communication through multi-carrier modulation, its receiver usually needs to perform complex channel state estimation to perform multi-carrier decoding. This not only increases the design complexity of the multi-carrier receiver but also makes the decoding cost higher. Summary of the Invention

[0005] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a backscatter communication method, device, and system based on multi-carrier differential modulation, aiming to reduce the decoding difficulty of the multi-carrier receiver.

[0006] To achieve the above object, the present invention provides a method for transmitting a backscatter signal based on multi-carrier differential modulation, which includes:

[0007] Divide the L sub - carriers in the channel into Q sub - carrier blocks, and each sub - carrier block is used to transmit the allocated binary bit data; for each sub - carrier block, modulate the corresponding binary bit data into the transmission vector of the corresponding sub - carrier block t is the time index, N is the number of sub - carriers in the sub - carrier block, and the transmission vector u t has only one non - zero element;

[0008] For each sub - carrier block, expand the transmission vector S at time t - 1 t-1 into a symmetric and full - rank sub - carrier block transmission matrix U t-1 , and use the matrix U t-1 to perform rectangular differential modulation on the transmission vector u t to obtain the transmission vector S of this sub - carrier block t ;

[0009] Concatenate the transmission vectors of the Q sub - carrier 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 a reflection coefficient;

[0010] Regulate the impedance network so that it modulates and reflects the excitation source signal in the environment with the mapped reflection coefficient to generate a backscattering signal corresponding to the time - domain data frame.

[0011] Optionally, for any sub - carrier block transmission vector the symmetric and full - rank sub - carrier block transmission matrix it expands is G(x) = [x E 1 x E 2 x...E N-1 x], where E n is the n - th power of E, is a right - shift matrix, each row of which has only one 1 element and the rest are 0 elements, and the elements of the latter row are obtained by cyclically shifting the elements of the previous row one bit to the right.

[0012] Optionally, for each sub - carrier block, modulate the corresponding binary bit data into the transmission vector u t , including:

[0013] Divide the corresponding binary bit data B t into data and data Based on 's value, select a transmission sub - carrier from this sub - carrier block and construct the dispersion vector a of this sub - carrier block t , the dispersion vector a tIt has N elements corresponding one by one to N subcarriers. If a subcarrier is selected, the corresponding element is taken as 1, otherwise it is taken as 0. For MPSK modulation is performed to obtain a complex constellation symbol s t , and a transmission vector u of this subcarrier block is constructed t = a t s t .

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

[0015] Optionally, the impedance network includes a first sub-network, a second sub-network and a power splitter / combiner; varactor diodes D1, D2, capacitors C1, C2, resistors R1, R2, inductors L1, L2 and a power splitter / combiner, where:

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

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

[0018] The power splitter / combiner is used to take 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, and combine the two to make the reflection coefficient at the antenna be a + bj.

[0019] The present invention also provides a backscatter 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] A transmission vector construction unit, which is used to divide L subcarriers in a channel into Q subcarrier blocks, and 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 only one element in the transmission vector u t is a non-zero element;

[0021] A transmission vector construction unit, which is used to expand the transmission vector S at time t-1 for each subcarrier block into a symmetric and full-rank subcarrier block transmission matrix U t-1 and use the matrix U t-1 to perform rectangular differential modulation on the transmit vector u t-1 to obtain the transmission vector S of this subcarrier block t ; t ;

[0022] A reflection coefficient construction unit, which is used to splice 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 a reflection coefficient;

[0023] A regulation unit, which is used to regulate the impedance network so that it modulates and reflects the excitation source signal in the environment with the mapped reflection coefficient to generate 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 splitter / combiner; varactor diode D1, varactor diode D2, capacitor C1, capacitor C2, resistor R1, resistor R2, inductor L1, inductor L2 and a power splitter / combiner, where:

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

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

[0027] The power splitter / combiner is used to use 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, and combine the two so that the reflection coefficient at the antenna is a+bj.

[0028] The present invention also provides a method for receiving a backscattered signal based on multi-carrier differential modulation, which includes:

[0029] Obtain the received signal at time t and parse the time-domain data frame after passing through the channel. Perform Fourier transform on the parsed time-domain data frame to parse the corresponding frequency-domain data frame. Split the parsed frequency-domain data frame to parse the transmission vector S’ of each subcarrier block after passing through the channel t , where t is the time index;

[0030] For each subcarrier block, expand the transmission vector S’ of this subcarrier block at time t-1 t-1 into a symmetric and full-rank subcarrier block transmission matrix U’ t-1 , and based on S’ t and U’ t-1 obtain the estimated value of the transmission vector of this subcarrier

[0031] Parse the of each subcarrier block to obtain the binary bit data carried by this subcarrier; Concatenate the binary bit data of Q subcarrier blocks to obtain the complete data carried by the backscatter signal.

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

[0033] A transmission vector parsing unit, configured to obtain the received signal at time t, first parse the reflection coefficient and parse the time-domain data frame corresponding to the reflection coefficient based on the mapping relationship, then perform Fourier transform on the time-domain data frame to parse the frequency-domain data frame, and split the frequency-domain data frame to parse the transmission vector S' of each subcarrier block t , where t is the time index;

[0034] An emission vector parsing unit, configured to, for each subcarrier block, expand the transmission vector S’ of this subcarrier block at time t-1 t-1 into a symmetric and full-rank subcarrier block transmission matrix U’ t-1 , and based on S’ t and U’ t-1 obtain the estimated value of the transmission vector of this subcarrier Parse the to obtain the binary bit data carried by this subcarrier;

[0035] A raw data parsing unit, configured to parse the of each subcarrier block to obtain the binary bit data carried by this subcarrier; Concatenate the binary bit data of Q subcarrier blocks to obtain the complete data carried by the backscatter signal.

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

[0037] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the present invention mainly has the following beneficial effects:

[0038] 1. In the present invention, when realizing the transmission of scattered signals, binary bit data is modulated into a transmission vector of a corresponding subcarrier block and only one element in the vector is a non-zero element. Then, rectangular differential modulation is adopted to realize the transmission of carrier index differential modulation information. Since differential modulation transmits information based on the difference between adjacent symbols, and the influence of the channel on adjacent symbols is the same, the channel state information is cancelled during the data detection process at the receiving end. The receiving end can recover the original transmitted data by performing non-coherent detection on the received signal without a complex cascaded channel estimation process, effectively reducing the complexity of the multi-carrier backscatter communication system.

[0039] 2. In an alternative embodiment, a subcarrier block transmission matrix expansion function G(x) = [x E 1 x E 2 x...E N-1 x] is provided. 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 alternative embodiment, a specific construction method of the transmission vector is provided. The binary bit data B t is divided into data and data The binary bit data B t is mapped to the indices of the selected subcarriers. Only the data needs to be modulated and calculated. Thus, the resources in the communication system can be fully utilized to realize data transmission, reducing the complexity of modulation.

[0041] 4. In an alternative embodiment, a design method of the impedance network is provided. Based on this impedance network, as long as the modulation voltage connected to the impedance network is continuously adjusted, continuous regulation of the reflection coefficient can be achieved, and a continuously variable reflection coefficient is realized to represent continuous time-domain data frames, thereby improving the modulation accuracy and solving the problem of limited modulation. Brief Description of the Drawings

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

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

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

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

[0046] Figure 5 is a flowchart of steps of a backscattered signal receiving method in an embodiment of the present invention. Detailed implementation manners

[0047] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present 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 only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] As Figure 1 shown is a schematic diagram of the architecture of a multi-carrier differential modulation backscatter communication system. The backscatter communication system has a backscattered signal transmitting device (backscatter tag) and a receiver. The backscattered signal transmitting device receives the existing excitation source signal in the environment, modulates it by using the load modulation technology and reflects it with different reflection coefficients. The reflection coefficient represents the data to be transmitted by the backscatter communication. In this way, the data to be transmitted can be embedded in the environmental excitation source signal for transmission, and the receiving end decodes the information transmitted by the transmitting end by analyzing the reflection coefficient. Since there is a problem of relatively high complexity in multi-carrier decoding by the receiver in the traditional method. Therefore, the present invention proposes the following improvement solutions to solve this problem.

[0049] Embodiment 1

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

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

[0052] Among them, Q is a set positive integer. If the value is 1, it means that the signal transmission is achieved by only one sub - carrier block. If the value is greater than 1, it means that the data to be transmitted needs to be divided into several parts, and each sub - carrier block is responsible for transmitting a part of the data.

[0053] Specifically, divide L sub - carriers into Q sub - carrier blocks, and each block contains N = L / Q sub - carriers. The purpose of this step is to construct the transmit vector of each sub - carrier block.

[0054] Specifically, for a certain sub - carrier block: at time t, only the p - th sub - carrier is activated (P < N). Therefore, only one element in the constructed transmit vector is non - zero, which represents the modulated data to be transmitted by the activated sub - carrier.

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

[0056] Divide the corresponding binary bit data B t into data and data Based on the value of, select a transmit sub - carrier from this sub - carrier block and construct the dispersion vector a t , the dispersion vector a t has N elements corresponding one - to - one with N sub - carriers. If the sub - carrier is selected, the corresponding element takes 1, otherwise it takes 0. Then perform MPSK modulation on it to obtain the complex constellation symbol s t , and construct the transmit vector u t = a t s t .

[0057] The sub - carrier activation situation forms the dispersion vector which has exactly one non - zero element Segment the original binary bit data B responsible for transmission by this sub - carrier block t , the data segment B t is divided into and two groups, that is Select the activated sub - carrier in this sub - carrier block through the data segment , determine the dispersion vector a t , for example, N = 4. If the data segment is binary 00, then a t = [1 0 0 0] T , if the data segment is binary 01, then a t = [0 1 0 0] T , if the data segment is binary 10, then a t =[0 01 0] T , if the data segment is binary 11, then a t =[0 0 0 1] T ; For data segment Perform MPSK modulation to obtain complex constellation symbol s t , the combination of the two obtains the subcarrier block transmit vector u t =a t s t Therefore, the subcarrier block transmits the vector has only one non-zero element Where p is the activated subcarrier index of the current subcarrier block (given by the data segment Decision), t The complex constellation symbol contained in the current transmission vector (by the data segment Decide).

[0058] The above method is used to construct the transmission vector. Since the binary bit data B t Divide into data With data Binary bit data B t Mapped to the index of the selected subcarrier, only the data By performing modulation calculations, the information in the communication system can be fully utilized to realize data transmission and reduce the complexity of modulation.

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

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

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

[0062] Plural constellation symbol: s t is a complex constellation point, s t The value of the data segment Perform MPSK modulation (M-ary phase modulation) determination.

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

[0064] The following uses a specific example to illustrate this process.

[0065] Example: Suppose where a and s can be determined according to the following mapping relationship tables 1 and 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, expand its transmission vector S at time t - 1 t-1 into a symmetric and full-rank subcarrier block transmission matrix U t-1 , and use the matrix U t-1 to perform rectangular differential modulation on the transmit vector u t to obtain the transmission vector S of this subcarrier block t .

[0072] In one embodiment, for any subcarrier block transmission vector the symmetric and full-rank subcarrier block transmission matrix it expands is G(x) = [x E 1 x E 2 x... E N-1 x], where E n is the nth power of E, is a right shift matrix, each row of which 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 bit to the right.

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

[0074]

[0075] For example, suppose the dimension N = 4. At this time then:

[0076]

[0077] At this time:

[0078]

[0079] Specifically, the rectangular difference operation on the subcarrier block transmission vector u t can be expressed as S t = U t-1 u t = G(S t-1 )u t , where U t-1 is the transmission matrix at time t - 1. When t = 1, the U 0 at the previous moment can be the identity matrix.

[0080] For example, let where m, n, and k are all 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, perform an inverse Fourier transform on the frequency-domain data frame to convert it into a time-domain data frame, and then linearly map the time-domain data frame to be transmitted to the reflection coefficient of the tag according to the reflection coefficient range that the backscatter tag impedance network can achieve. This mapping relationship is stored in the tag.

[0085] For example, combine the Q subcarrier block transmission vectors corresponding to L subcarriers after segmentation: The dimension of the single subcarrier block transmission vector is Concatenate the Q subcarrier block transmission vectors head to tail to obtain a frequency-domain data frame (when segmenting, L = N × Q) Perform an inverse Fourier transform on the frequency-domain data frame to obtain a time-domain data frame D , whose dimension is the same as D time , and scale it through a set scaling ratio to obtain a reflection coefficient for backscattering. freq

[0086] Step S14: Regulate the impedance network so that it modulates and reflects the excitation source signal in the environment with the mapped reflection coefficient to generate a backscattered signal corresponding to the time-domain data frame.

[0087] ​Specifically, after determining the reflection coefficient, the impedance network can be adjusted to make the impedance network reflect the excitation source signal in the environment with the obtained reflection coefficient through 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 network is adjusted to generate a reflection coefficient Γ corresponding to the time-domain data frame D time (t), so as to generate a multi-carrier differential backscattered signal and realize the transmission of the time-domain data frame. t

[0089] Generally speaking, at the backscattered signal transmitter, the L sub-carriers are divided into Q sub-carrier blocks, and there are N = L / Q sub-carriers in each sub-carrier block. For each sub-carrier block, the tag selects and activates the sub-carriers through indexing and loads constellation symbols on them to obtain the sub-carrier block transmission vector u t ; the transmission vector S at time t - 1 t-1 is expanded into a sub-carrier block transmission matrix U t-1 , and U t-1 is used to perform rectangular differential modulation on the transmission vector u at time t t to obtain the sub-carrier block transmission vector S t . The transmission vectors of each sub-block after the differential operation are combined and multi-carrier modulated to obtain a frame of data to be transmitted; the frame of data to be transmitted is preprocessed to obtain a time-domain data frame, and then according to the range of reflection coefficients that the backscattered tag impedance network can achieve, the time-domain data frame to be transmitted is mapped to the reflection coefficient, and the impedance network is controlled according to this mapping relationship to generate a reflection coefficient corresponding to the time-domain data frame, so as to generate a backscattered signal corresponding to the time-domain data frame and realize the transmission of the time-domain data. In the present invention, backscattered communication modulation is realized through the above method. When realizing the emission of the scattered signal, due to the adoption of a specific differential modulation, carrier index differential modulation information transmission is realized, and the receiving end can recover the original transmitted data by performing non-coherent detection on the received signal. Since the differential modulation transmits information based on the difference between adjacent symbols, and the channel has the same influence on adjacent symbols, the channel state information is cancelled during the data detection process at the receiving end, and there is no need for a complex cascaded channel estimation process, effectively reducing the complexity of the multi-carrier backscattered communication system.

[0090] Considering that in currently commonly used impedance networks, the values of the adjustable reflection coefficients are fixed, so only the adjustment of several fixed reflection coefficients can be realized, and continuous adjustment of the reflection coefficient cannot be realized, which affects the modulation accuracy.

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

[0092] The anti-reflection network includes a first sub-network, a second sub-network, and a power splitter / combiner; varactor diodes D1, D2, capacitors C1, C2, resistors R1, R2, inductors L1, L2, and a power splitter / combiner, where:

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

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

[0095] The power splitter / combiner is used to use 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, and combine the two so that the reflection coefficient at the antenna is a + bj.

[0096] Further, the impedance network is regulated, including driving the first DAC module to generate a first modulation voltage, driving the second DAC module to generate a second modulation voltage, and regulating the impedance network by adjusting the modulation voltage to make it generate a reflection coefficient corresponding to the time-domain data frame.

[0097] In the above impedance network provided in this embodiment, as the voltages applied to inductors L1 and L2 change, the capacitances of varactor diodes D1 and D2 also change accordingly, resulting in a change in the reflection coefficient of the power splitter / combiner for the excitation source signal. Therefore, as long as the modulation voltage applied to the impedance network is continuously adjusted, continuous regulation of the reflection coefficient can be achieved, and a continuously variable reflection coefficient can be realized to represent a continuous time-domain data frame, thereby improving the modulation accuracy and solving the problem of limited modulation.

[0098] Embodiment 2

[0099] The present invention also provides a backscatter signal transmitting device based on multi-carrier differential modulation, also called a backscatter tag device, which includes a radio frequency module and a control module. The radio frequency module includes an impedance network, and the control module is used to execute the method of Embodiment 1 to regulate the impedance network in the radio frequency module so that it reflects the excitation source signal in the environment with the mapped reflection coefficient, generates a backscatter signal corresponding to the time-domain data frame, and realizes data transmission.

[0100] Specifically, the control module includes:

[0101] A transmission vector construction unit, configured to divide L subcarriers in a channel into Q subcarrier blocks, where each subcarrier block is used to transmit the allocated binary bit data; for each subcarrier block, modulate the corresponding binary bit data into a transmission vector of the corresponding subcarrier block N is the number of subcarriers in a subcarrier block, and only one element in the transmission vector u t is non-zero;

[0102] A transmission vector expansion unit, configured to, for each subcarrier block, expand the transmission vector S at its t-1 moment t-1 into a symmetric and full-rank subcarrier block transmission matrix U t-1 , and use the matrix U t-1 to perform rectangular differential modulation on the transmission vector u t to obtain the transmission vector S of this subcarrier block t ;

[0103] A reflection coefficient construction unit, configured to splice 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 a reflection coefficient;

[0104] A regulation unit, configured to regulate the impedance network so that it modulates and reflects the excitation source signal in the environment with the mapped reflection coefficient to generate a backscattering signal corresponding to the time-domain data frame.

[0105] The working principle of this transmitting device is as follows: activate subcarriers through index modulation for the original binary bit data and load constellation symbols on the activated subcarriers; the subcarrier block transmission vector u t of each subcarrier block forms a subcarrier block transmission vector S through differential operations in the front and back time slots t ; the to-be-transmitted vector of each sub-block combines the frequency-domain data frame, and then after preprocessing, it is converted into a tag time-domain data frame; the control module outputs different voltages at different time slots to regulate the impedance network in the RF module to realize the transmission of the frequency-domain data frame.

[0106] More specifically, the control module can adopt an STM32 chip, which is used to construct a transmission vector through index modulation and constellation mapping, perform differential operations on the transmission vector to combine it into a frame of transmitted data, and perform preprocessing on 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 frame at different time slots.

[0107] Further, the impedance network is composed 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] Embodiment 3

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

[0110] As Figure 5 shown in the flowchart of the steps of the backscatter signal receiving method in an embodiment of the present invention, the receiving method includes:

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

[0112] Step S22: For each subcarrier block, expand the transmission vector S’ of the subcarrier block at time t-1 t-1 into a symmetric and full-rank subcarrier block transmission matrix U’ t-1 , and obtain the estimated value of the transmission vector of the subcarrier based on S’ t and U’ t-1 ;

[0113] Step S23: Parse the of each subcarrier block to obtain the binary bit data carried by the subcarrier; splice the binary bit data of Q subcarrier blocks to obtain the complete data carried by the backscatter signal.

[0114] Specifically, in the backscatter communication system, the backscatter signal transmitter modulates the amplitude and phase of the excitation source signal by regulating the reflection coefficient, so as to carry the time-domain data frame to be transmitted. Therefore, after receiving the backscatter signal, only the amplitude and phase of the received signal need to be parsed to parse the time-domain data frame after passing through the channel transmission. In the traditional method, channel estimation is required to parse the original time-domain data frame, and then the data carried by the backscatter signal is parsed based on the original time-domain data frame. In the present invention, due to the improvement of the signal transmission process of the transmitting device, complex channel estimation is not required at the receiving end, and the data carried by the backscatter signal can be directly parsed based on the time-domain data frame after passing through the channel transmission. The principle is described below.

[0115] Since rectangular differential modulation is used to obtain the transmission vector S during signal modulation in the transmitting device t = U t- 1 u t = G(S t-1 )u t , it can be transformed to get Denote the form after channel transmission 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 the channel remains unchanged and the channel coefficients are the same for adjacent time slots, it can be considered that H t ≈ H t-1 . Therefore, it can be obtained that

[0116]

[0117] is 's estimated value

[0118] Therefore, only based on can the estimated value of the transmission vector be obtained

[0119] Illustrate with a specific example

[0120] Continue with as an 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 expanded transmission matrix is as follows

[0125]

[0126]

[0127] Substitute into for channel estimation to get

[0128]

[0129] It can be seen therefrom that the accurate estimation of the transmission vector can be achieved through After obtaining the estimated value of the transmission vector

[0130] After that, according to the construction method of the transmission vector at the transmitting end, the binary values carried by each subcarrier can be inversely analyzed, and finally all the binary values are concatenated to obtain the complete data, completing the data reception at the receiving end. After that, it is possible to, according to the construction method of the transmission vector at the transmitting end, inversely analyze the binary values carried by each subcarrier, and finally concatenate all the binary values to obtain the complete data, completing the data reception at the receiving end.

[0131] Embodiment 4

[0132] The present invention further relates to a backscatter signal receiving device, including:

[0133] A transmission vector analysis unit, configured to obtain the received signal at time t, first analyze the reflection coefficient and inversely analyze the time-domain data frame corresponding to the reflection coefficient based on the mapping relationship, then perform a Fourier transform on the time-domain data frame to analyze the frequency-domain data frame, and split the frequency-domain data frame to analyze the transmission vector S' of each subcarrier block t , where t is a time index;

[0134] A transmission vector analysis unit, configured to, for each subcarrier block, expand the transmission vector S' of the subcarrier block at time t-1 t-1 into a symmetric and full-rank subcarrier block transmission matrix U' t-1 , and based on S' t and U' t-1 obtain the estimated value of the transmission vector of this subcarrier Analyze to obtain the binary bit data carried by this subcarrier;

[0135] An original data analysis unit, configured to analyze for each subcarrier block to obtain the binary bit data carried by this subcarrier; concatenate the binary bit data of Q subcarrier blocks to obtain the complete data carried by the backscatter signal.

[0136] Embodiment 5

[0137] The present invention further 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 in cooperation, a complete backscatter communication can be achieved.

[0138] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification. It should be noted that the "in one embodiment", "for example", "for another example", etc. of the present invention are intended to illustrate the present invention, rather than to limit the present invention.

[0139] The above embodiments only express several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they cannot be construed as a limitation to the scope of the patent application. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A backscatter signal transmission method based on multi-carrier differential modulation, characterized in that: include: 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, 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 transmission vector u t Only one element in is non-zero; For each subcarrier block, the transmission vector S at time t-1 is t-1 Expanded to a symmetric and full-rank subcarrier block transmission matrix U t-1 , using the matrix U t-1 For the emission vector u t Perform rectangular differential modulation to obtain the transmission vector S of the subcarrier block t ; Splicing the transmission vectors of the Q subcarrier blocks to form a frequency domain data frame, performing an inverse Fourier transform on the frequency domain data frame to obtain a time domain data frame, and mapping the time domain data frame to a reflection coefficient; The impedance network is regulated 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 backscatter signal transmitting method according to claim 1, characterized in that: For any subcarrier block transmission vector The 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 is E raised to the power of n, It is a right shift matrix, each row of which has only one 1 element and the rest are 0 elements, and the elements of the next row are the elements of the previous row shifted right by one position.

3. The backscatter signal transmitting method according to claim 1, characterized in that: For each subcarrier block, the corresponding binary bit data is modulated into the transmission vector u of the corresponding subcarrier block t ,include: The corresponding binary bit data B t Divide into data With data based on The value of selects a transmit subcarrier from the subcarrier block and constructs the dispersion vector a of the subcarrier block. t , dispersion vector a t It has N elements corresponding to N subcarriers one by one. If a subcarrier is selected, the corresponding element takes 1, otherwise it takes 0. Perform MPSK modulation to obtain complex constellation symbol s t , construct the transmit vector u of the subcarrier block t =a t s t .

4. The backscatter communication method according to claim 1, wherein: Map the time domain data frame into reflection coefficients, Including mapping the time domain data frame into reflection coefficients by scaling.

5. The backscatter signal transmitting method according to claim 1, characterized in that: The impedance network includes a first sub-network, a second sub-network and a power splitter / combiner; a varactor diode D1, a varactor diode D2, a capacitor C1, a capacitor C2, a resistor R1, a resistor R2, an inductor L1, an inductor L2 and a power splitter / combiner, wherein: The first sub-network includes an inductor L1, a resistor R1, a varactor diode D1 and a capacitor C1, wherein a first end of the inductor L1 is used to receive a first modulation voltage, and a second end of the inductor L1 is connected to an input end of the power splitter / combiner through the resistor R1 and the varactor diode D1 in sequence, and a branch formed by the resistor R1 and the varactor diode D1 connected in series 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, wherein a first end of the inductor L2 is used to receive a second modulation voltage, and a second end is connected to an input end of the power splitter / combiner through the resistor R2 and the varactor diode D2 in sequence, and a branch formed by the resistor R2 and the varactor diode D2 connected in series is connected in parallel with the capacitor C2; The power splitter / combiner is used to use 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, and combine the two so that the reflection coefficient at the antenna is a+bj.

6. A backscatter signal transmitting device, characterized in that: It includes a radio frequency module and a control module; the radio frequency module includes an impedance network; the control module includes: The transmission vector construction unit is used to 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, the corresponding binary bit data is modulated into the transmission vector of the corresponding subcarrier block N is the number of subcarriers in the subcarrier block, and the transmission vector u t Only one element in is non-zero; The transmission vector construction unit is used to construct the transmission vector S at time t-1 for each subcarrier block. t-1 Expanded to a symmetric and full-rank subcarrier block transmission matrix U t-1 , using the matrix U t-1 For the emission vector u t Perform rectangular differential modulation to obtain the transmission vector S of the subcarrier block t ; A reflection coefficient construction unit, used for splicing the transmission vectors of the Q subcarrier blocks to form a frequency domain data frame, performing an inverse Fourier transform on the frequency domain data frame to obtain a time domain data frame, and mapping the time domain data frame to a reflection coefficient; 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, and generates a backscattering signal corresponding to the time domain data frame.

7. The backscatter signal transmitting device according to claim 6, characterized in that: The impedance network includes a first sub-network, a second sub-network and a power splitter / combiner; a varactor diode D1, a varactor diode D2, a capacitor C1, a capacitor C2, a resistor R1, a resistor R2, an inductor L1, an inductor L2 and a power splitter / combiner, wherein: The first sub-network includes an inductor L1, a resistor R1, a varactor diode D1 and a capacitor C1, wherein a first end of the inductor L1 is used to receive a first modulation voltage, and a second end of the inductor L1 is connected to an input end of the power splitter / combiner through the resistor R1 and the varactor diode D1 in sequence, and a branch formed by the resistor R1 and the varactor diode D1 connected in series 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, wherein a first end of the inductor L2 is used to receive a second modulation voltage, and a second end is connected to an input end of the power splitter / combiner through the resistor R2 and the varactor diode D2 in sequence, and a branch formed by the resistor R2 and the varactor diode D2 connected in series is connected in parallel with the capacitor C2; The power splitter / combiner is used to use 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, and combine the two so that the reflection coefficient at the antenna is a+bj.

8. A backscatter signal receiving method based on multi-carrier differential modulation, characterized in that: include: The received signal at time t is obtained and the time domain data frame after the channel is parsed is obtained. The parsed time domain data frame is Fourier transformed to obtain the corresponding frequency domain data frame. The parsed frequency domain data frame is split to parse the transmission vector S' of each subcarrier block after the channel is passed. t , t is the time index; For each subcarrier block, the transmission vector S' of the subcarrier block at time t-1 is t-1 Expanded to a symmetric and full-rank subcarrier block transmission matrix U' t-1 , based on S' t and U' t-1 Get the estimated value of the transmit vector of the subcarrier For each subcarrier block The binary bit data carried by the subcarrier is obtained by analysis; 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: The transmission vector parsing unit is used to obtain the received signal at time t, first parse the reflection coefficient and parse the time domain data frame corresponding to the reflection coefficient based on the mapping relationship, then perform Fourier transform on the time domain data frame to parse the frequency domain data frame, split the frequency domain data frame, and parse the transmission vector S' of each subcarrier block. t , t is the time index; The transmission vector analysis unit is used to analyze the transmission vector S' of each subcarrier block at time t-1 t-1 Expanded to a symmetric and full-rank subcarrier block transmission matrix U' t-1 , based on S' t and U' t-1 Get the estimated value of the transmit vector of the subcarrier right Analyze and obtain the binary bit data carried by the subcarrier; The original data parsing unit is used to analyze the The binary bit data carried by the subcarrier is obtained by analysis; 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: A backscatter signal transmitting device as claimed in claim 6 or 7 and a backscatter signal receiving device as claimed in claim 9.

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