Backscatter communication baseband interference suppression system and method

Abstract

The present invention discloses a backscatter communication baseband interference suppression system and method. The first device's transmitting unit sends a carrier signal to a second device and sends an interference signal to the first device's receiving unit. The second device modulates the data to be transmitted onto the carrier signal to obtain a first signal, and then backscatters the first signal to the first device. The first device's receiving unit transmits the received signal, including the first signal and the interference signal, to the first device's receiving processing unit. The first device's receiving processing unit samples the received signal and restores the interference signal by smoothing it through interpolation and reconstruction. The first device's receiving processing unit deletes the interpolated and reconstructed interference signal to achieve interference signal suppression. The first device reconstructs the interference signal through simple processing and calculation, which is simple to implement, highly versatile, and flexible, and is of great significance for improving backscatter communication performance.

Description

Technical Field

[0001] The present invention relates to the field of Internet of Things and backscatter communication technology, and in particular to a backscatter communication baseband interference suppression system and method. Background Art

[0002] Backscatter communication technology, which modulates and reflects incident signals to transmit information, is a key technology in the Internet of Things. Backscatter technology was initially used by the military to identify its own aircraft by attaching tags to them. The tags' backscattered radar signals were then used to verify the aircraft's identity. Subsequently, a large number of applications based on backscatter technology emerged, primarily in RFID systems. Currently, backscatter technology is widely used in automated production, anti-counterfeiting measures, logistics tracking, and warehouse inventory.

[0003] In the backscatter system, the backscatter device (also referred to as the second device in the present invention) does not generate a radio frequency signal itself, but transmits information by modulating and reflecting the amplitude and phase of the radio frequency signal from the transmitter (also referred to as the first device in the present invention). Traditional backscatter systems need to be equipped with a dedicated transmitter to provide a continuous wireless excitation signal, so the system flexibility is low and the power consumption is high. The environmental backscatter communication system uses radio frequency signals (such as WiFi, broadcast, and cellular signals) from the environment to communicate, which can effectively reduce communication energy consumption and improve the flexibility of the system. Applying backscatter communication technology in the Internet of Things scenario can effectively reduce the energy consumption of Internet of Things nodes, extend the life of Internet of Things nodes, and expand their usage scenarios.

[0004] In practical communication systems, RF signals from the transmitter enter the receiving path through various paths, becoming interference signals and impacting the demodulation and decoding of the backscattered signal. For single-antenna backscatter systems, the main interference paths include: the transmitted signal returning to the receiving path due to impedance mismatch at the transmitter antenna, and leakage from the circulator due to limited isolation. For multi-antenna backscatter systems, the main interference path is leakage from the transmitted signal due to antenna coupling. The interference signal power is much greater than the backscattered signal, and due to the combined influence of various nonlinear devices in the transmit and receive paths, it exhibits nonlinear characteristics, which hinders backscattered signal recovery. Due to the precision limitations of the receiver's digital-to-analog converter, excessive interference signal power can drown out the backscattered signal. Furthermore, the nonlinearity of the interference signal can distort the received signal. Therefore, interference suppression is a key function of the receiver in communication systems.

[0005] Existing backscatter communication systems (particularly RFID systems) simply model the interfering carrier as a sinusoidal signal. At the baseband receiver, since the sinusoidal signal is down-converted to a DC component, the receiver simply takes the average of the carrier signal as an estimate of the interference signal. After subtracting the estimate, the backscatter signal is recovered and decoded. This solution only works well when the interference signal power and nonlinear fluctuations are weak, and requires the backscatter device to cooperate with anti-interference coding. However, backscatter devices are constrained by cost and power consumption, and their processing performance is limited. When backscatter devices use high-order modulation (such as multi-element amplitude keying), they cannot perform complex coding, and the interference at the receiver cannot be effectively suppressed. The backscatter signal is superimposed on the nonlinear interference, significantly increasing the decoding bit error rate.

[0006] In traditional digital communication systems, self-interference suppression relies on adaptive filters. These filters use the known transmitter baseband signal as input and the received interference signal as the desired signal to train filter parameters. The trained parameters are then used to suppress interference. This method dynamically tracks the interference signal and adjusts the filter tap coefficients to minimize the interference signal power. However, the receiver requires the transmitter baseband signal to be known, and it is generally used in conjunction with an RF interference suppression module. Therefore, its performance is limited when used alone.

[0007] Furthermore, when applying this method to backscatter communication systems, it is typically necessary to first train parameters using interference signals when the backscatter device is not transmitting. After receiving the backscatter signal, the trained parameters are then used to suppress interference. However, when the backscatter data is long, this method cannot effectively suppress the changing interference signal due to channel variations. Real-time tracking and reconstruction of the interference signal requires hardware modifications at the transceiver to introduce the interference signal into the adaptive filter, increasing the cost and complexity of the system.

[0008] Therefore, it is necessary to design an efficient and flexible interference signal reconstruction algorithm based on the characteristics of the backscatter system to dynamically suppress the interference at the receiving end and restore the backscatter device signal. Summary of the Invention

[0009] In view of the defects in the prior art, the present invention aims to provide a

[0010] To achieve the above objectives, the technical solution adopted by the present invention is: a backscatter communication baseband interference suppression method, comprising the following steps: a first device transmitting unit sends a carrier signal to a second device, and sends an interference signal to a first device receiving unit; the second device modulates the data to be sent onto the carrier signal to obtain a first signal, and then backscatters the first signal to the first device; the first device receiving unit transmits the received signal r(t) including the first signal and the interference signal to the first device receiving processing unit; the first device receiving processing unit samples the received signal r(t) and restores the interference signal by smoothing processing according to interpolation reconstruction; the first device receiving processing unit deletes the interference signal after interpolation and reconstruction to achieve interference signal suppression.

[0011] Preferably, the first device receives the processing unit at a sampling rate f ADC The received signal r(t) is sampled to obtain a signal r[n], where t is time, n∈[1,2,…,N], and n is a sampling point.

[0012] Preferably, the first device receiving and processing unit interpolates and reconstructs the interference signal according to the following steps: based on the signal r[n], the maximum value pk(i) among Q points is obtained at intervals of P points, and the position point loc(i) of the maximum value is obtained; the maximum value pk(i) is stored in the maximum value set pks, and the position point loc(i) is stored in the maximum value position set locs, and the size of the maximum value set pks and the maximum value position set locs is L; the first device receiving and processing unit checks the points in the maximum value set pks, and if pk(i) < Th1 or pk(i) < Th2, pk(i) is removed from the maximum value set pks, and the corresponding position point loc(i) is removed from the maximum value position set locs; all points in the maximum value set pks are traversed to obtain the processed maximum value set pks * and the maximum position set locs * .

[0013] Preferably, in, is the mean of the sampling points in the sliding window w1, e is the amplitude coefficient, u is the reference amplitude of the backscattering device signal, w2 is the opening length of the sliding window 2, and f is the amplitude coefficient of the threshold Th2. The reference amplitude of the backscattering device signal can be obtained by the formula express.

[0014] Preferably, the first device receiving and processing unit further performs interpolation reconstruction on the interference signal according to the following steps:

[0015] The first device receives and processes the maximum value set pks* and the maximum value position set locs * Perform cubic spline interpolation fitting to obtain the first reconstructed signal of the interference signal Among them, s i (x) = a i (x-loc(i)) 3 +b i (x-loc(i)) 2 +c i (x-loc(i))+d i , 1≤i<L-1,s i (x) is the cubic spline function on the i-th sampling interval; x is the independent variable of the spline function; a i ,b i ,c i ,d i are the coefficients of the cubic term, quadratic term, linear term and constant term of the spline function in the i-th sampling interval; loc(i) is the maximum position set locs * The i-th value in .

[0016] Preferably, d i =pk(i), where h i =loc(i+1)-loc(i), M i =s” i (x) = 6a i (x-loc(i))+2b i .

[0017] Preferably, the first device receiving processing unit further performs interpolation reconstruction on the interference signal according to the following steps: inverting the signal r[n] to obtain a signal -r[n], interpolating the signal -r[n] to obtain a second reconstructed signal S2(x), and acquiring a signal S(x) based on the first reconstructed signal and the second reconstructed signal, wherein S(x)=(S2(x)-S1(x)) / 2,

[0018] The signal S(x) is sampled one by one to obtain the discrete signal S[n], and the discrete signal S[n] is subjected to g-point sliding average to obtain the reconstructed interference signal

[0019] Preferably, the interference-suppressed signal y[n] obtained after the first device receiving processing unit deletes the interference signal after interpolation and reconstruction can be expressed as y[n]=r[n]-c[n].

[0020] The present invention also provides a backscatter communication baseband interference suppression system, comprising a first device and a second device, configured as follows: the first device transmitting unit is capable of sending a carrier signal to the second device, and sending an interference signal to the first device receiving unit; the second device modulates the data to be sent onto the carrier signal to obtain a first signal, and then backscatters the first signal to the first device; the first device receiving unit transmits the received signal r(t) including the first signal and the interference signal to the first device receiving processing unit; the first device receiving processing unit samples the received signal r(t) and restores the interference signal by smoothing processing according to interpolation reconstruction; the first device receiving processing unit deletes the interference signal after interpolation and reconstruction to achieve interference signal suppression.

[0021] The present invention also provides a computer-readable storage medium comprising computer-executable instructions, which, when executed by one or more processors, cause the one or more processors to perform the method of one of the preceding claims.

[0022] The present invention has the following advantages: using the backscatter communication baseband interference suppression method provided by the present invention, the first device reconstructs the interference signal through simple processing and calculation, which is simple to implement, highly versatile, and highly flexible, and is of great significance to improving the backscatter communication performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention has the following accompanying drawings:

[0024] The accompanying drawings are provided for a better understanding of the present invention and are not intended to limit the present invention.

[0025] Figure 1 Structural block diagram of the backscatter communication system of the present invention.

[0026] Figure 2 Simulation comparison diagram of the first device receiving signal and reconstructed signal.

[0027] Figure 3 Simulation diagram of received signal-to-noise ratio and symbol error probability curve.

[0028] Figure 4 Flow chart of the backscatter communication baseband interference suppression method. DETAILED DESCRIPTION

[0029] The present invention will be described in further detail below with reference to the accompanying drawings. The detailed description, which is provided for illustrative purposes only and includes various details to aid understanding of the embodiments of the present invention, should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions and structures are omitted from the following description.

[0030] In a backscatter communication system, considering the differences in interference signals generated by the first device, the present invention designs a universal baseband interference suppression system and interference suppression method:

[0031] First, the first device receives the interference signal and the backscattered signal to the first device receiving unit.

[0032] Next, the first device selects peak points of the received signal and the corresponding locations of the peak points at intervals. The obtained points are filtered to obtain a set of peak points and a set of location points. Cubic spline interpolation is performed on the obtained set to obtain a reconstructed signal of the interference signal, which is then smoothed.

[0033] Finally, the first device processor subtracts the reconstructed interference signal to achieve interference signal suppression for subsequent decoding processing.

[0034] A backscatter communication baseband interference suppression system is as follows Figure 1 Shown, including:

[0035] A first device and a second device consisting of a transmission processing unit, a transmission unit, a receiving unit, and a reception processing unit;

[0036] The first device is used to generate a specific carrier signal; the transmission processing unit is used to generate a baseband signal for transmission of the first device, and the transmission unit is used to transmit an interference signal and a second device excitation signal; the receiving unit is used to receive the interference signal and the second device signal and demodulate them into a digital baseband signal; the receiving processing unit is used to generate and process the digital baseband signal, including estimating, reconstructing and suppressing the interference signal; the second device is used to receive the carrier signal and generate a data signal to be sent to realize backscatter communication;

[0037] Working principle of backscatter communication system:

[0038] The first device implements the reader / writer function, generating an RF excitation signal and transmitting it into space. The second device generates a data signal to be transmitted and modulates it onto the carrier signal transmitted by the first device via backscattering, generating a backscattered signal. The RF excitation signal generated by the first device undergoes a nonlinear transformation and is then sent to the receiving end of the first device, generating an interference signal. The first device's receiving unit receives the backscattered signal and the interference signal and sends them to the receiving processing unit.

[0039] The backscatter communication baseband interference suppression method using the above scheme includes the following steps:

[0040] Step 1: The transmitting unit of the first device sends a carrier signal to the second device and simultaneously sends an interference signal to the receiving unit of the first device;

[0041] Step 2: The second device modulates the data to be sent onto the carrier signal to obtain a first signal, and then backscatters the first signal to the first device;

[0042] Step 3: The receiving unit of the first device receives the backscattered signal of the second device and the interference signal of the first device, and sends the received signal to the receiving processing unit.

[0043] Step 4: The receiving processing unit of the first device samples the received signal, reconstructs the interference signal through interpolation, and performs smoothing on the reconstruction.

[0044] Step 5: The receiving processing unit of the first device subtracts the reconstructed interference signal to achieve interference signal suppression.

[0045] Step 3: The received signal is composed of two superpositions: one is the interference signal generated by device 1, and the other is the data signal generated by device 2. The received signal is sampled and sent to the receiving processing unit.

[0046] Below, the reverse link frequency rate is 1Mbps, the first device sampling rate is 10MHz, and the received interference signal includes third-order intermodulation residual interference, which includes 1kHz and 0.5KHz cosine signal components and a DC component. The DC component amplitude is 1 and the cosine signal amplitude is 0.03; the second device signal baseband signal uses bipolar non-return-to-zero coding; the power ratio of the interference signal to the second device signal is 20dB; the received signal contains 1000 second device symbols each time for baseband interference suppression.

[0047] In step 4, after the first device sends the sampled signal r[n] to the processor, it first calculates the maximum value pk(i) among the Q points at intervals P, and records the location of the maximum value loc(i). Then, pk(i) is stored in the maximum value set pks, and loc(i) is stored in the maximum value location set locs. The size of the sets pks and locs is L. Next, the first device's receiving processing unit checks the points in set pks. If pk(i) < Th1 or pk(i) < Th2, pk(i) is removed from the set pks, and the corresponding loc(i) is removed from the set locs.

[0048] The definition of threshold Th1 is shown in formula (1):

[0049]

[0050] in, is the mean of the sampling points in the sliding window w1, e is the amplitude coefficient, and u is the reference amplitude of the backscatter device signal, which is defined as the mean of the sampling points minus the mean of the received signal. The expression is shown in formula (2):

[0051]

[0052] The threshold Th2 is defined as the mean value of the received signal in the sliding window w2, and the expression is shown in formula (3):

[0053]

[0054] Where f is the amplitude coefficient of threshold 2. After traversing all the points of pks, the processed maximum value set pks is obtained * and the maximum position set locs * .

[0055] Next, the first device receives the maximum value set pks * Sum and maximum position set locs * Perform cubic spline interpolation fitting, the cubic spline interpolation function expression is shown in formula (4)

[0056]

[0057] where s i (x) = a i (x-loc(i)) 3 +bi(x-loc(i)) 2 +ci(x-loc(i))+d i The function S1(x) passes through all sampling points, and each segment of the function s i (x) is continuous, and its first and second derivatives are also continuous. Define h i =loc(i+1)-loc(i), M i =s” i (x) = 6a i (x-loc(i))+2b i , according to the cubic spline interpolation function, d i =pk(i).

[0058] Written in matrix form as shown in formula (5):

[0059]

[0060] Add boundary conditions to solve the above equations. The boundary conditions can be natural boundaries: M1 = M L-1=0, Not-a-Knot boundary condition: s"'1(x i )=s”'2(x i );s”' L-2 (x i )=s L-1 ”'(x i ) etc. Obtain M i After that, we can deduce a i ,b i ,c i ,d i , and obtain the final reconstructed signal S1(x) of the interference signal.

[0061] Obtain the signal upper envelope S i (x), the received sampling signal r[n] is inverted to obtain -r[n], and the above operation is performed on -r[n] to obtain the reconstructed signal S2(x) of the wavy interference signal.

[0062] Next, subtract the signals S1(x) and S2(x) and divide by 2 to get the signal S(x). Sampling S(x) one by one will get the discrete signal S[n].

[0063] Finally, the g-point sliding average of the discrete signal S[n] is performed to reconstruct the interference signal c[n], and the sliding average is shown in formula (6).

[0064]

[0065] Based on the above solution, in step 5, the first device subtracts the reconstructed interference signal to obtain the interference suppressed signal as shown in formula (6):

[0066] y[n]=r[n]-c[n]#(7)

[0067] The specific process of step 4 can be: sample the received signal r[n], take the maximum value of 30 points every 150 points, and obtain the maximum point set pks and the maximum point location set locs. Set e = f = 0.8, w1 = 10, w2 = 50, traverse the maximum point set, calculate the thresholds Th1 and Th2 according to formula (1) and formula (3), filter out the maximum points and corresponding location points that do not meet the threshold conditions, and obtain the processed maximum value set pks * and the maximum position set locs * . For the set pks * and locs *Perform cubic spline interpolation and use the Not-a-Knot boundary condition to obtain the first reconstructed signal S1(x). Invert the received signal to obtain -r[n], perform interval sampling on -r[n], and take the maximum value of 30 points every 150 points to obtain the maximum point set pks2 and the maximum point location set locs2. Traverse the sampling point set, filter out points less than the threshold and their corresponding location points, and obtain the processed maximum value set and the maximum position set Pair Collection and Perform cubic spline interpolation with the Not-a-Knot boundary condition to obtain the second reconstructed signal S2(x). Next, subtract the first reconstructed signal S1(x) from the second reconstructed signal S2(x) and divide by 2 to obtain signal S(x). Sample S(x) point by point to obtain the discrete signal S[n]. Finally, perform a 100-point sliding average of the discrete signal S[n] to obtain the reconstructed interference signal c[n].

[0068] The simulation comparison diagram of the received signal and the interference reconstruction signal in step 4 is shown in the attached figure. Figure 2 As shown:

[0069] In the simulation, the signal to noise power ratio of the second device is set to 20dB. Figure 2 The dark curve in the middle is the received signal, and the light curve is the reconstructed interference signal. As can be seen from the figure, the reconstructed signal can fit the fluctuations of the interference signal.

[0070] In step 5, the first device subtracts the reconstructed interference signal from the received signal r[n] to obtain a processed signal y[n].

[0071] The simulation diagram of the received signal-to-noise ratio and symbol error probability curve of the symbol timing synchronization signal obtained by the present invention is shown in the attached figure. Figure 3 As shown:

[0072] In the simulation, the signal power to noise power ratio of the second device is set to 0-20dB, and the signal to noise ratio points are taken at equal intervals with a step size of 1dB. The curve is the average value of 1000 results. Figure 3 The curve marked with a solid hollow circle represents the bit error rate of decoding the signal without interference suppression. The curve marked with a dotted circle represents the bit error rate of decoding the signal after interference suppression.

[0073] From the attached Figure 3 It can be seen from the figure that: 1) the bit error rate curves all decrease significantly with the increase of the received signal-to-noise ratio; 2) the bit error rate with interference suppression is lower than the bit error rate without interference suppression; based on the above two points, it can be considered that this method effectively suppresses interference signals and improves signal detection performance in interference scenarios.

[0074] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0075] Obviously, the above examples of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the embodiments of the present invention. A person skilled in the art can make other changes or modifications based on the above description. It is impossible to enumerate all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A backscatter communication baseband interference suppression method, characterized in that: The steps include: The transmitting unit of the first device sends a carrier signal to the second device and sends an interference signal to the receiving unit of the first device; The second device modulates the data to be sent onto the carrier signal to obtain a first signal, and then backscatters the first signal toward the first device; The first device receiving unit receives a received signal including the first signal and the interference signal Transmitting to a receiving and processing unit of the first device; The first device receiving processing unit processes the received signal Sampling is performed, and the interference signal is restored by smoothing processing by interpolation reconstruction; The first device receiving processing unit deletes the interpolation-reconstructed interference signal to achieve interference signal suppression; The first device receives the processing unit at a sampling rate To receive the signal Sampling to get the signal ,in, For time, is the sampling point; The first device receiving and processing unit performs interpolation reconstruction on the interference signal according to the following steps: Based on the signal , every interval Point request The maximum value among the points , and obtain the location of the maximum value ; The maximum value Store in the maximum value collection , the location point Store to the maximum value position set , the maximum value set and the maximum position set The size is ; The first device receives a processing unit pair of the maximum value set Check the points in or , then From the maximum value set Remove it and set the corresponding position points From the maximum position set Eliminate Traverse the maximum value set All points in the set have been processed to obtain the maximum value and the maximum position set ; ; ; in, For sliding window The mean of the sampling points, is the amplitude coefficient, is the reference amplitude of the backscatter device signal, is the length of sliding window 2, is the threshold The amplitude coefficient of the backscatter device signal reference amplitude can be obtained by the formula ; express; The first device receiving and processing unit further performs interpolation reconstruction on the interference signal according to the following steps: The first device receives the maximum value set from the processing unit and the maximum position set Perform cubic spline interpolation fitting to obtain the first reconstructed signal of the interference signal ; The signal Invert to get the signal , for the signal Interpolation processing has been performed to obtain the second reconstructed signal , acquiring a signal based on the first reconstructed signal and the second reconstructed signal ,in, , Signal Sampling points one by one to obtain discrete signals , for discrete signals conduct Point sliding average to obtain the reconstructed interference signal .

2. The backscatter communication baseband interference suppression method according to claim 1, characterized in that: The first device receiving and processing unit further performs interpolation reconstruction on the interference signal according to the following steps: The first device receives the maximum value set from the processing unit and the maximum position set Perform cubic spline interpolation fitting to obtain the first reconstructed signal of the interference signal ; in, , For the Cubic spline function on the sampling interval; is the independent variable of the spline function; The spline functions are The coefficients of the cubic term, quadratic term, linear term and constant term over the sampling interval; is the maximum position set Middle values.

3. The backscatter communication baseband interference suppression method according to claim 2, characterized in that: , in, .

4. The backscatter communication baseband interference suppression method according to claim 1, characterized in that: The first device receiving processing unit deletes the interference signal reconstructed by interpolation to obtain the interference suppressed signal Can be expressed as 。 5. A backscatter communication baseband interference suppression system, using the backscatter communication baseband interference suppression method according to any one of claims 1 to 4, characterized in that: The first device and the second device are configured as follows: The first device transmitting unit is capable of transmitting a carrier signal to the second device and transmitting an interference signal to the first device receiving unit; The second device modulates the data to be sent onto the carrier signal to obtain a first signal, and then backscatters the first signal toward the first device; The first device receiving unit receives a received signal including the first signal and the interference signal Transmitting to a receiving and processing unit of the first device; The first device receiving processing unit processes the received signal Sampling, and performing interpolation and reconstruction on the interference signal in a manner of smoothing the interpolation and reconstruction process; The first device receiving processing unit deletes the interference signal after interpolation and reconstruction to achieve interference signal suppression.

6. A computer-readable storage medium comprising computer-executable instructions, which, when executed by one or more processors, cause the one or more processors to perform the method according to any one of claims 1 to 4.

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