A synchronization-free backscattering multi-tag transmission method, device and system

Abstract

The application discloses a kind of free synchronization backscattering multi-label transmission method, equipment and system, it is related to wireless communication field, including: base station emits excitation signal;Backscattering label carries out different frequency shift frequency backscattering processing to excitation signal;Receiver receives the backscattering signal transmitted by multiple labels, after pre-processing, it is distinguished in frequency domain, and the asynchronous problem between label and excitation signal is solved by sliding window, so as to demodulate the information transmitted by different labels.The backscattering label in the application does not need to keep synchronization with base station, and multiple labels can be transmitted in the same frequency band, while reducing the synchronization overhead, the spectral efficiency of system is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of wireless communication, and more particularly, relates to a synchronization-free backscatter multi-tag transmission method, device and system. BACKGROUND

[0002] With the rise and large-scale commercial use of the Internet of Things, the backscatter communication technology has become one of the most attractive solutions due to its ultra-low power consumption advantage. The backscatter tag modulates its own information onto the radio frequency signal in the environment by controlling the impedance state of the antenna port, thereby realizing information transmission. Therefore, the tag does not need a high-power radio frequency module, greatly reducing the communication power consumption, but its short distance and low rate characteristics greatly limit the application range.

[0003] The LoRa backscatter technology overcomes the short communication distance defect of the traditional scheme and can realize long-distance communication, and is expected to be widely applied in smart cities, smart medical care, smart agriculture and the like. With the increasingly dense deployment of devices and the increasingly extensive coverage, a large amount of data needs to be transmitted and processed. Due to the limited frequency spectrum resources, the transmission rate of a single tag is low, and the existing scheme is difficult to meet the above communication requirements.

[0004] In order to solve the above problems, the LoRa signal characteristics can be used to realize backscatter multi-tag transmission. Multiple backscatter tags simultaneously transmit information, which can greatly improve the system throughput. However, the receiver needs all the tags to transmit synchronously to realize concurrent decoding. However, it is difficult for multiple tags to achieve precise time synchronization, which is easily affected by various factors, including the propagation delay of the excitation signal, the hardware differences of different tags and the interference of other radio frequency signals in the environment. SUMMARY

[0005] In view of the above defects of the prior art, the present application provides a synchronization-free backscatter multi-tag transmission method, device and system, which does not require the backscatter tag to keep synchronization with the base station, and multiple tags can transmit in the same frequency band, thereby reducing the synchronization overhead and improving the spectrum utilization of the system.

[0006] In a first aspect, the present application provides a synchronization-free backscatter multi-tag transmission method, comprising the following steps:

[0007] The base station transmits an excitation signal;

[0008] The backscatter tag performs backscatter processing on the excitation signal at different frequency shift frequencies;

[0009] The receiver receives the backscatter signals transmitted by the multiple backscatter tags and demodulates the information transmitted by the different backscatter tags.

[0010] The excitation signal is a cyclically transmitted same linear frequency modulation LoRa symbol.

[0011] Further, the backscatter tag performs backscatter processing on the excitation signal at different frequency-shifted frequencies, including:

[0012] The plurality of tags generate modulated signals at different frequencies, which do not need to be synchronized with the excitation signal, and the plurality of modulated signals also do not need to be synchronized with each other;

[0013] The frequency-shifted frequency of the tag is denoted as f s = f0+ nΔf, where f0is a large-scale frequency component, Δf is a small-scale frequency component, n is a tag serial number, n = 0, 1, …, N-1, and N is the total number of tags;

[0014] The tag determines whether to perform frequency-shift modulation on the excitation signal according to the transmitted information bits, for example, performing frequency-shift when transmitting a bit "1", and not performing frequency-shift when transmitting a bit "0";

[0015] The backscatter signal frame includes a preamble symbol, a data symbol, and a stop symbol, the preamble symbol includes a plurality of bits "1", and the stop symbol includes a plurality of bits "0".

[0016] Further, the receiver receives the backscatter signals transmitted by the plurality of tags, demodulates the information transmitted by different tags, including the following steps:

[0017] The receiver pre-processes the backscatter signal, and separates the signals corresponding to different tags in the frequency domain;

[0018] The receiver determines the frame start position of each tag backscatter signal, and starts decoding from the frame start position to obtain the information bits transmitted by all backscatter tags.

[0019] Further, the receiver pre-processes the backscatter signal, including the following steps:

[0020] The receiver determines the start position of a standard LoRa symbol in the received signal;

[0021] The receiver de-chirps the backscatter signal from the start position of the standard LoRa symbol, and converts the linear frequency modulation backscatter signal corresponding to a single tag into a single frequency point pre-processed signal;

[0022] The receiver performs fast Fourier transform on the pre-processed signal, finds the frequency spectrum peak value in the result, and determines the frequency of the pre-processed signal corresponding to different tags.

[0023] Further, the receiver determines the frame start position of each tag backscatter signal, including the following steps:

[0024] The receiver uses a sliding window with a length equal to the length of a LoRa symbol to intercept the preprocessed signal, and performs a fast Fourier transform on the signal intercepted by the window every time the window slides by one sample point.

[0025] The receiver uses two sliding windows to intercept the feature value vector corresponding to a single tag, the first sliding window intercepts the feature value vector corresponding to the backscattered signal received first, and the length of the first sliding window is the length of the stop symbol in the backscattered signal frame minus one LoRa symbol length, and the second sliding window intercepts the feature value vector corresponding to the backscattered signal received later, and the length of the second sliding window is the length of the preamble symbol in the backscattered signal frame minus one LoRa symbol length; the interval between the two sliding windows is one LoRa symbol length.

[0026] The two sliding windows of the receiver slide simultaneously, and every time the window slides by one sample point, the data intercepted by the second window is summed and divided by the sum of the data intercepted by the first window, and the result is recorded as the amplitude ratio. When the amplitude ratio reaches the maximum, the starting position of the corresponding second window is the starting position of the backscattered signal frame of the tag;

[0027] The receiver determines the information bits transmitted by the tag according to the amplitude of each data symbol in the signal frame.

[0028] The receiver repeats the above process until the information demodulation of all tags is completed.

[0029] In a second aspect, the present application provides a backscattered tag, comprising a frequency synthesis module and a backscattered modulation module.

[0030] The frequency synthesis module is used to generate a square wave with a specified frequency.

[0031] The backscattered modulation module uses the square wave as input to frequency-shift modulate the excitation signal.

[0032] In a third aspect, the present application provides a receiver, comprising a preprocessing module, a frame synchronization module, and a multi-tag decoding module.

[0033] The preprocessing module is used to de-modulate the backscattered signal to obtain a preprocessed signal, and determine the frequency points corresponding to different tags in the preprocessed signal.

[0034] The frame synchronization module is used to determine the starting position of the signal frame of different tags.

[0035] The multi-tag decoding module is used to decode the information bits transmitted by all tags.

[0036] In a fourth aspect, the application provides a synchronization-free backscattering multi-tag transmission system, comprising the backscattering tag provided in the second aspect and the receiver provided in the third aspect.

[0037] Compared with the prior art, the application has the following advantages:

[0038] 1. The application provides a synchronization-free backscattering multi-tag transmission method, which uses the characteristics of the excitation signal to solve the asynchronization problem between the tag and the excitation signal through a sliding window, so that the backscattering tag and the base station do not need to keep synchronization, and the time synchronization overhead is reduced.

[0039] 2. In the synchronization-free backscattering multi-tag transmission method, the excitation signal is subjected to different frequency shift processing to generate backscattering signals with different starting frequencies, so that multiple tags can transmit in the same frequency band, and the spectrum utilization of the system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A flowchart of the synchronization-free backscattering multi-tag transmission method provided in the embodiment of the application is shown in the figure.

[0041] Figure 2 A schematic diagram of the backscattering processing of the backscattering tag on the excitation signal with different frequency shift frequencies is shown in the figure.

[0042] Figure 3 A schematic diagram of the preprocessing of the receiver on the backscattering signal is shown in the figure.

[0043] Figure 4 A schematic diagram of the working principle of the receiver using double sliding windows to realize frame synchronization is shown in the figure. DETAILED DESCRIPTION

[0044] In order to explain the purpose, technical scheme and advantages of the application, the following embodiments are described in conjunction with the drawings. It should be understood that the specific embodiments described herein are only used to explain the application, and are not all embodiments. On the contrary, these embodiments are provided to enable a thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0045] To achieve the above-mentioned purpose, the embodiment of the application provides a synchronization-free backscattering multi-tag transmission method, as shown in the figure, comprising the following steps: Figure 1

[0046] The base station:

[0047] ​The LoRa symbol with the same chirp is sent as the excitation signal in a cycle.

[0048] Specifically, the basic unit of the LoRa symbol is a linear chirp, whose frequency changes linearly over time. The chirp with a linearly rising frequency over time is called an up-chirp, and the chirp with a linearly falling frequency over time is called a down-chirp. The LoRa symbol is data-encoded by cyclically shifting the chirp symbol in the frequency domain, and different starting frequencies of the chirp symbol represent different data. The LoRa symbol is multiplied by the down-chirp to perform dechirping, and then a Fast Fourier Transform (FFT) is performed. The frequency of the peak in the FFT spectrum depends on the starting frequency of the LoRa symbol. One LoRa symbol can be determined by two parameters, a bandwidth (BW) and a spreading factor (SF). In the embodiment, the bandwidth is 500 kHz, and the spreading factor is 10. The symbol period can be calculated as T = 2 SF / BW.

[0049] Backscattering tag:

[0050] The backscattering tag performs backscattering processing on the excitation signal with different frequency shift frequencies.

[0051] Specifically, the backscattering tag performs backscattering processing on the excitation signal with different frequency shift frequencies, including the following steps:

[0052] (1) A plurality of tags generate modulated signals with different frequency shift frequencies. The modulated signals do not need to be synchronized with the excitation signal, and the plurality of modulated signals also do not need to be synchronized.

[0053] (2) The tag determines whether to perform frequency shift modulation on the excitation signal according to the transmitted information bits.

[0054] Specifically, Figure 2 The principle diagram of the tag performing frequency shift modulation on the excitation signal is shown. In the diagram, the excitation signal sent by the base station has a center frequency of f c , and the backscattering tag generates modulated signals with different frequencies, and the frequency shift frequencies are f c +f o +Δf, f c +f o +2Δf, f c +f o +3Δf, and the transmitted bits are “100”, “110”, and “001”, respectively. The signals generated by the plurality of tags do not need to be synchronized with the excitation signal, and directly perform frequency shift keying modulation on the excitation signal according to the transmitted information bits. In the embodiment, the center frequency of the excitation signal is f c = 900 MHz, and the tag performs frequency shift modulation on the large-scale frequency component fo = 750 kHz, small scale frequency component Δf = 4 kHz, number of tags N = 128. Where Δf is much smaller than the bandwidth of the excitation signal, so that the backscattered signals corresponding to different tags are partially overlapped in the frequency spectrum, so as to save the spectrum resources. When the tag transmits bit "1", the tag shifts the frequency of the excitation signal, and when it transmits bit "0", it does not shift the frequency. The backscattered signal frame in this embodiment includes 4 preamble symbols, 8 data symbols and 4 stop symbols.

[0055] Receiver:

[0056] The backscattered signal is preprocessed to distinguish the signals corresponding to different tags in the frequency domain.

[0057] Specifically, the step of preprocessing the backscattered signal includes:

[0058] (1) determining the starting position of a standard LoRa symbol in the received signal;

[0059] (2) dechirping the backscattered signal from the starting position of the standard LoRa symbol, converting the linear frequency modulation backscattered signal corresponding to a single tag into a single frequency point preprocessed signal;

[0060] (3) performing FFT on the preprocessed signal to find the spectral peak in the result to determine the frequency of the preprocessed signal corresponding to different tags.

[0061] Specifically, Figure 3 The principle and process of the receiver preprocessing the backscattered signal are shown. The backscattered signal in the figure is a LoRa symbol after frequency shift modulation, which is not synchronized in time. The correlation function of the backscattered signal and the up-chirp is taken, and when the correlation value reaches the maximum, the starting position of a standard LoRa symbol in the received signal can be determined. The center frequency of the backscattered signal in the figure is f c +f o +2Δf symbol is a standard LoRa symbol. The backscattered signal is dechirped from the starting position of the symbol to obtain a preprocessed signal whose frequency does not change with time. After performing FFT, the preprocessed signals at frequencies f c +f o +Δf, f c +f o +2Δf, f c +f o +3Δf correspond to the spectral peaks at FFT frequency domain sampling points F1, F2 and F3 respectively, and the relationship between F1, F2 and F3 is:

[0062] F1 + ΔFFTbin = F2 = F3 - ΔFFTbin

[0063] Wherein The pre-processing signal frequency corresponding to one tag is determined, and the pre-processing signal frequencies corresponding to other tags can also be determined.

[0064] The frame start position of the backscattering signal of each tag is determined.

[0065] Specifically, the step of determining the frame start position of the backscattering signal of each tag comprises:

[0066] (1) A sliding window with a length equal to the length of a LoRa symbol is used to intercept the pre-processing signal; specifically, the length of the sliding window is T; every time the window slides by one sampling point, the signal portion intercepted by the window is subjected to FFT, and the change in the spectral amplitude corresponding to different tags caused by the sliding of the window is recorded as the feature vector corresponding to different tags;

[0067] (2) Two sliding windows are used to intercept the feature value vector corresponding to a single tag; the first sliding window intercepts the feature value vector corresponding to the backscattering signal received first, and the length of the first sliding window is the length of the stop symbol in the backscattering signal frame minus one LoRa symbol length, while the second sliding window intercepts the feature value vector corresponding to the backscattering signal received later, and the length of the second sliding window is the length of the leading symbol in the backscattering signal frame minus one LoRa symbol length; the interval between the two sliding windows is one LoRa symbol length;

[0068] (3) The two sliding windows slide simultaneously, every time the window slides by one sampling point, the data intercepted by the second window is summed and divided by the sum of the data intercepted by the first window, and the result is recorded as the amplitude ratio. When the amplitude ratio reaches the maximum, the start position of the second window at this time is the start position of the backscattering signal frame of the tag.

[0069] Specifically, Figure 4The working principle diagram of the receiver proposed in the application for realizing frame synchronization by using double sliding windows is shown in the figure. The frame of the backscattering signal transmitted by the tag is shown in the figure. From t1 to t1+T, the tag transmits bit "1", and there is a spectral line in the window after performing FFT. From t1+T to t1+3T, the tag transmits bit "0", and there is no spectral line after performing FFT. The spectral amplitude of the preprocessed signal is recorded in sequence. The spectral amplitude in the window is recorded by sampling the spectral amplitude of the preprocessed signal by using a single sliding window. In the figure, the starting end of the window is at t1, and the spectral amplitude in the window is maximum. When the starting end slides from t1 to t1+T, the spectral amplitude in the window gradually decreases. When the starting end is at t1+T, the spectral amplitude in the window decreases to a minimum. When sliding from t1+T to t1+2T, the amplitude in the window remains unchanged. With the continuous sliding of the window, the curve of the spectral line amplitude in the window changing with time is obtained. Finally, the spectral line amplitude in the single sliding window is sampled by using two sliding windows win1 and win2. In the figure, the lengths of win1 and win2 are 3T, and the interval is T. With the sliding of the two windows, the amplitude ratio of the two windows is recorded. When the starting end of win1 is at t1+8T and the starting end of win2 is at t1+4T, the amplitude ratio of win1 and win2 reaches a maximum, and at this time, the starting end of win1 is the frame starting position.

[0070] (4) Decoding starts from the frame starting position to obtain all the information bits of the backscattering tag transmission.

[0071] The receiver judges the information bits of the tag transmission according to the spectral amplitude of the preprocessed signal from the frame starting position.

[0072] The application further provides a backscattering tag, comprising a frequency synthesis module and a backscattering modulation module.

[0073] The frequency synthesis module generates a square wave of a specified frequency.

[0074] The backscattering modulation module performs frequency shift modulation on the excitation signal.

[0075] The application further provides a receiver, comprising a preprocessing module, a frame synchronization module and a multi-tag decoding module.

[0076] The preprocessing module demodulates the backscattering signal to obtain a preprocessed signal and determines the frequency points corresponding to different tags in the preprocessed signal.

[0077] The frame synchronization module determines the starting positions of the signal frames of different tags.

[0078] The multi-tag decoding module decodes all the information bits of the tag transmission.

[0079] The application further provides a synchronization-free backscattering multi-tag transmission system, comprising the above-mentioned base station transmitting LoRa symbols, a backscattering tag and a receiver.

[0080] In summary, the application provides a synchronization-free backscattering multi-tag transmission method, device and system, the backscattering tag transmits data information by frequency shift modulation on the excitation signal, the backscattering tag does not need to keep synchronization with the base station, and multiple tags can transmit in the same frequency band, thereby reducing the synchronization overhead and improving the spectrum utilization of the system.

[0081] Finally, it should be explained that the above embodiments are only used to illustrate the technical solutions of the application, and do not limit the patent scope of the application. Those skilled in the art should understand that any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application should be included in the scope of the claims of the application.

Claims

1. A method of synchronization-free backscattering multi-tag transmission, the method comprising: The method comprises the following steps: The backscattering signal is generated by backscattering the excitation signal transmitted by the base station at different frequency shifts; The method applied to the backscattering tag comprises the following steps: Multiple backscattering tags generate modulation signals at different frequencies, which do not need to be synchronized with the excitation signal, and the multiple modulation signals also do not need to be synchronized; The frequency shift of the tag is represented as wherein is a large scale frequency component, is a small scale frequency component, is a tag number, , and is the total number of tags; wherein is much smaller than the bandwidth of the excitation signal, so that the backscattered signals corresponding to different tags partially overlap in the frequency spectrum; The tag modulates the excitation signal by frequency shift keying according to the transmitted information bits, that is, frequency shift when transmitting bit "1", and no frequency shift when transmitting bit "0"; The generated backscattering signal frame comprises a preamble symbol, a data symbol and a stop symbol, the preamble symbol comprises multiple bits "1", and the stop symbol comprises multiple bits "0"; The receiver simultaneously receives the backscattering signals transmitted by multiple backscattering tags and demodulates the information transmitted by different backscattering tags; the method applied to the receiver comprises the following steps: The receiver pre-processes the backscattering signal and separates the signals corresponding to different backscattering tags in the frequency domain; The starting position of the frame corresponding to each backscattering tag is determined, and the information bits transmitted by all backscattering tags are obtained by decoding from the starting position of the frame.

2. A method of synchronization-free backscattering multi-tag transmission as claimed in claim 1, wherein, The excitation signal is a same linear frequency modulation (LoRa) symbol transmitted in a cycle.

3. A method of synchronization-free backscattering multi-tag transmission as claimed in claim 2, wherein, The pre-processing of the backscattering signal by the receiver comprises: Determining the starting position of a standard LoRa symbol in the received signal; De-modulating the backscattering signal from the starting position of the standard LoRa symbol to convert the linear frequency modulation backscattering signal corresponding to a single tag into a pre-processed signal at a single frequency point; Performing fast Fourier transform on the pre-processed signal to find the frequency spectrum peak in the result and determine the frequency of the pre-processed signal corresponding to different tags.

4. A method of synchronization-free backscattering multi-tag transmission as claimed in claim 2, wherein, The determination of the starting position of the frame corresponding to each backscattering tag comprises: A sliding window with a length equal to the length of a LoRa symbol is used to intercept the pre-processed signal corresponding to a single backscattering tag, the fast Fourier transform is performed on the signal intercepted by the window every time the window slides by one sample point, and the change of the frequency spectrum amplitude of different tags at the corresponding frequency point caused by the window sliding is recorded as a characteristic value vector corresponding to different tags; Two sliding windows are used to intercept the characteristic value vector corresponding to a single tag, the first sliding window intercepts the characteristic value vector corresponding to the backscattering signal received first, and the length of the first sliding window is the length of the stop symbol in the backscattering signal frame minus the length of a LoRa symbol, while the second sliding window intercepts the characteristic value vector corresponding to the backscattering signal received later, and the length of the second sliding window is the length of the preamble symbol in the backscattering signal frame minus the length of a LoRa symbol; the interval between the two sliding windows is the length of a LoRa symbol; The two sliding windows slide simultaneously, the sum of the data intercepted by the second window is divided by the sum of the data intercepted by the first window every time the two windows slide by one sample point, and the amplitude ratio is recorded, when the amplitude ratio reaches the maximum, the starting position of the second window corresponding thereto is the starting position of the backscattering signal frame of the tag; The information bits transmitted by the tag are determined according to the amplitude of each data symbol in the signal frame. Repeat the above process until all the tags' information demodulation is completed.

5. A backscatter tag, characterized by, The frequency synthesis module and the backscatter modulation module are included. The frequency synthesis module generates a square wave of a specified frequency. The backscatter modulation module uses the square wave as input to perform frequency shift keying modulation on the excitation signal, and executes the synchronization-free backscatter multi-tag transmission method of claim 1.

6. A receiver, characterized by The pre-processing module, frame synchronization module, and multi-tag decoding module are included. The pre-processing module is used to de-modulate the backscatter signal of the backscatter tag transmission of claim 5 to obtain a pre-processed signal, and determine the frequency points corresponding to different tags in the pre-processed signal. The frame synchronization module is used to determine the starting positions of the signal frames of different tags. The multi-tag decoding module is used to decode the information bits transmitted by all the tags.

7. An asynchronous backscatter multi-tag transmission system, characterized by, The backscatter tag of claim 5 and the receiver of claim 6 are included.

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