A method for backscattering communication based on MIMO characteristics of LTE signals

Abstract

The application discloses a method for backscattering communication based on MIMO characteristics of LTE signals, comprising the following steps: capturing the LTE signals in the environment by using a backscattering tag, and performing space-time coding on the tag data and modulating the LTE signals; after capturing the backscattering LTE signals by using a receiver, demodulating and decoding the backscattering LTE signals, and obtaining the tag data. The application can capture the LTE signals reflected by the backscattering tag based on the characteristics of the LTE signals, and decode the tag data from the tag-modulated LTE signals, and simultaneously solves the tag synchronization problem. By eliminating the channel influence before the tag reflection and the channel influence after the tag reflection, the receiver can be correctly demodulated, the space-time coding is adopted by the double-antenna tag, and the universality and throughput of the system are improved.

Description

Technical Field

[0001] This invention relates to the field of backscatter communication technology based on LTE signals, and more particularly to a backscatter communication method based on the MIMO characteristics of LTE signals. Background Technology

[0002] Backscattering is a passive communication system that offers a promising low-power wireless communication method for the Internet of Things. For backscattering communication systems to be widely deployed, they need to meet certain conditions: first, the presence of an environmental excitation signal; second, a continuous excitation signal; and third, a ubiquitous excitation signal.

[0003] Current backscatter communication systems mostly use dedicated transmitters to emit a single radio frequency signal as the system excitation source. However, this type of radio frequency signal is not suitable for low-power IoT applications. Currently, more backscatter communication systems use WiFi and LoRa signals as excitation sources. However, the limited coverage area of ​​WiFi and LoRa signals, as well as the intermittent nature of WiFi signals, are factors that cause instability in WiFi backscatter. LTE signals are continuous in the time domain and ubiquitous in coverage area. Therefore, tag data can be carried on continuous LTE signals. The maximum data rate of LTE signals is mainly achieved by combining MIMO and OFDM technologies. It can be seen as a combination of MIMO multi-antenna configuration and OFDM multi-carrier transmission scheme.

[0004] Patent document CN117294398B discloses an efficient environmental LTE signal backscatter communication system and method. In this system, an LTE signal transceiver communicates with the backscatter tag via the backscatter signal. It can demodulate the RS symbols in the received backscatter signal to obtain tag data by restoring the original predefined RS values, and demodulate the non-RS symbols in the received backscatter signal using a checksum-based codeword conversion method to obtain tag data. This system and method can achieve efficient backscatter tag data transmission. However, it also has the drawback of not effectively utilizing the MIMO and OFDM characteristics of LTE signals, making it difficult to guarantee the system performance and reliability of the reflection communication. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a backscatter communication method based on the MIMO characteristics of LTE signals, utilizing the MIMO and OFDM characteristics of LTE signals to improve the data transmission rate of tags.

[0006] The objective of this invention can be achieved through the following technical solution: a backscatter communication method based on the MIMO characteristics of LTE signals, comprising the following steps:

[0007] S1. The backscatter tag captures LTE signals in the environment and performs backscattering;

[0008] S2. While backscattering, the tag data is spatiotemporally encoded and LTE signal modulated.

[0009] S3. After the receiver captures the backscattered LTE signal, it demodulates and decodes the backscattered LTE signal to obtain tag data.

[0010] Furthermore, when the backscatter tag captures LTE signals in the environment, the backscatter tag synchronizes with the LTE signals and determines the starting position of the backscatter tag data.

[0011] Furthermore, the backscatter tag is synchronized with the LTE signal, and the starting position of the backscatter tag data is determined, including the following steps:

[0012] S11. The backscatter tag maximizes the input LTE signal through impedance matching;

[0013] S12. Filter the LTE signal through a filter and output the envelope of the high-frequency signal;

[0014] S13. Detect whether the LTE signal synchronization signal PSS appears using a voltage comparator;

[0015] S14. After detecting the PSS signal, the tag preamble sends a continuous sequence of "0"s.

[0016] S15. Determine the starting position of the backscatter tag data based on the continuous "0" sequence.

[0017] Furthermore, the backscatter tag includes two antennas, and the backscatter tag performs spatiotemporal encoding of tag data based on antenna switching.

[0018] Furthermore, the backscatter tag performs spatiotemporal encoding of tag data based on the antenna switch, including:

[0019] In spatiotemporal coding, two bits are grouped together and represented as symbols S0 and S1 respectively. At time t, the two antennas transmit two tag data symbols S0 and S1; at time t+1, the two antennas transmit tag data symbols -S1 and S0.

[0020] Further, in S2, LTE signal modulation is performed, including:

[0021] The LTE signal is represented as a combination of timing signals of different basic timing units. Backscattered spatiotemporal coded tag data is embedded into different basic timing units. The duration of the backscattered modulation unit is set to be the same as the duration of the basic timing unit. The LTE signal is phase-modulated and timing modulation is performed on each basic timing unit.

[0022] Furthermore, the formula for constructing the basic timing unit in the LTE signal time domain is as follows:

[0023]

[0024] Where, x n This is a baseband signal, generated by the OFDM module, X k is the value for each subcarrier, and K is the size of the FFT.

[0025] Furthermore, the demodulation and decoding of the backscattered LTE signal in S3 includes the following steps:

[0026] S31. After detecting the backscattered LTE signal, the receiver performs channel estimation. The channel estimation consists of two parts: one is the channel estimation from the LTE signal to the tag, and the other is the channel estimation from the tag to the receiver. The receiver signal model is represented as follows:

[0027] S = H t θH r X+N

[0028] in, It is the channel coefficient between the LTE signal and the tag. It is the channel coefficient between the tag and the receiver, and S is the received signal symbol. The tag data symbols transmitted by the tag, where N is noise;

[0029] S32. Utilize backscattered tag data packets to eliminate the channel interference before and after backscattered LTE signals;

[0030] S33. Using the tag and receiver-specific reference signals, perform correlation calculations on the received backscattered LTE signal to determine the starting position of the backscattered bit in the tag data packet.

[0031] S34. The receiving end demodulates and decodes the received reflected LTE signal and calculates the value of the tag data bits.

[0032] Furthermore, the tag data packet in S32 includes a preamble portion and a backscattered tag data portion, wherein the preamble portion includes a sequence of "0"s and a reference sequence:

[0033] The channel estimator uses the "0" sequence portion for parsing, and then performs equalization to eliminate the channel effects before the backscattered LTE signal; the reference sequence is used to eliminate the channel effects from the tag to the receiver.

[0034] Furthermore, the demodulation and decoding processing of the received reflected LTE signal by the receiving end in S34 also includes:

[0035] The maximum likelihood estimation module is used to estimate the signal transmitted by the tag, and then the spatiotemporally encoded backscattered tag data is decoded to calculate the value of the tag data bits.

[0036] The beneficial effects of this invention are:

[0037] This invention employs a backscatter communication method based on the MIMO characteristics of LTE signals. When a tag needs to transmit information, the backscattered data is carried on the ambient LTE signal. Utilizing the MIMO characteristics of LTE, the dual-antenna tag spatially encodes the transmitted information under low power consumption. The tag uses a modulation method with a duration shorter than symbol-level modulation to improve throughput. The tag modulates its data while backscattering the LTE signal. Based on the characteristics of LTE signals, the receiver can capture the LTE signal reflected by the backscattered tag and decode the tag data from the LTE signal modulated by the tag. This also solves the tag synchronization problem. By eliminating the channel interference before and after tag reflection, the receiver can perform correct demodulation. The dual-antenna tag uses spatiotemporal coding, improving the system's versatility and throughput. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating a backscatter communication method based on the MIMO characteristics of LTE signals according to the present invention.

[0039] Figure 2 This is a schematic diagram of the scattering communication system of the present invention;

[0040] Figure 3 This is a schematic diagram of the data frame structure of the tag of the present invention;

[0041] Figure 4 This is a flowchart of the backscatter communication data processing of the present invention. Detailed Implementation

[0042] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0043] like Figure 1 As shown, this invention discloses a backscatter communication method based on the MIMO characteristics of LTE signals, comprising the following steps:

[0044] S1. The backscatter tag captures LTE signals in the environment and performs backscattering;

[0045] S2. While backscattering, the tag data is spatiotemporally encoded and LTE signal modulated.

[0046] S3. After the receiver captures the backscattered LTE signal, it demodulates the backscattered LTE signal to obtain tag data.

[0047] The LTE signal backscatter communication system utilized in this invention, such as Figure 2 As shown, the system mainly includes LTE signal base stations, dual-antenna tags, and receivers.

[0048] like Figure 4 As shown, the tag captures LTE signals in the environment. LTE signals are continuous in the time domain. When the tag captures LTE signals, it needs to be synchronized. The main synchronization signal (PSS) in the LTE signal can be used to synchronize the tag with the LTE signal. The LTE signal PSS is embedded into one frame of the LTE signal every 5ms.

[0049] After the LTE signal is captured by the tag antenna, impedance matching is performed, the input signal is maximized, and then it passes through a filter to output the envelope of the high-frequency signal. A voltage comparator is used to determine whether PSS occurs.

[0050] After detecting the PSS signal, the tag sends a continuous sequence of "0"s in the preamble. The tag will not modify the phase of the LTE signal, thus ensuring that the PSS signal is not modified. When the receiver receives the signal, it also uses this characteristic to detect the arrival of the backscattered signal.

[0051] After detecting an LTE signal, the backscatter tag needs to load the tag data onto the LTE signal. The backscatter tag includes two antennas, and the backscatter tag performs spatiotemporal encoding of the tag data based on the antenna switching.

[0052] In spatiotemporal coding, two bits are grouped together, represented as symbols S0 and S1 respectively. After spatiotemporal coding, the two antennas of the tag transmit symbols simultaneously. At time t, the two antennas transmit two tag data symbols S0 and S1; at time t+1, the tag data symbols transmitted by the two antennas are... and After spatiotemporal coding, at time t+1, the conjugate of another tag data will be reflected. Since the tag data reflected by the tag is a real number, and the conjugate of the reflected tag data is itself, the tag data symbols transmitted by the two antennas at time t+1 can be represented as -S1 and S0.

[0053] The tag carries tag data on the LTE signal. After the tag data is spatiotemporally encoded, it is modulated. An LTE signal frame consists of 20 time slots of equal size. Each time slot consists of several OFDM symbols. Tag data can be embedded by phase changes of different basic timing units.

[0054] The modulation time of the basic timing unit is less than the modulation time on one OFDM symbol. The formula for the basic timing unit in the time domain of the LTE signal is as follows:

[0055]

[0056] Where, x n This is a baseband signal, generated by the OFDM module, X k K is the value for each subcarrier, and K is the size of the FFT. A useful symbol consists of K units. The basic modulation unit time is 66.7 μs / K. The basic timing unit is a basic unit in the time domain of the LTE signal, with a duration of 66.7 μs / K. 66.7 μs is the duration of a useful symbol.

[0057] The LTE signal is represented as a combination of timing signals of different basic timing units. Backscatter tag data is embedded into different basic timing units. The duration of the backscatter modulation unit is set to be the same as the duration of the basic timing unit. The LTE signal is phase-modulated and timing modulation is performed on each basic timing unit.

[0058] If the tag transmits tag data 1, the basic timing unit of the LTE signal is phase-shifted. If the tag transmits tag data 0, the basic timing unit of the LTE signal is not phase-shifted. The antenna on the tag uses an RF switch to backscatter the LTE signal. The RF switch is controlled by a square wave, and the switching action is a series of square waves used to modulate the phase of the LTE signal.

[0059] After detecting the backscattered LTE signal, the receiver decodes the tag data and needs to perform channel estimation. Channel estimation mainly consists of two parts: the channel estimation effect from the LTE signal to the tag and the channel estimation effect from the tag to the receiver. The receiver signal model can be represented as follows:

[0060] S = H t θH r X+N

[0061] in, It is the channel coefficient between the LTE signal and the tag. It is the channel coefficient between the tag and the receiver, and S is the received signal symbol. The tag data symbols transmitted by the tag, where N is noise;

[0062] To address the channel interference caused by backscattered LTE signals, a special multi-antenna backscattered tag data packet was designed. For example... Figure 3 As shown, the tag data packet includes a preamble part and a backscatter tag data part. The preamble part includes a "0" sequence and a reference sequence. The "0" sequence indicates that the tag modulation does not change the phase, does not change the phase of the LTE signal, and does not embed backscatter tag data in the LTE signal.

[0063] The tag data packets in this part, by sending a continuous sequence of "0", are represented by the signal received by the receiver as follows:

[0064] Y0 = H t θH r X+N

[0065] Y0 is the signal of a continuous sequence of "0"s sent by the dual-antenna tag received by the receiver. The channel estimator uses this part of the tag data packet to parse it and then performs equalization to eliminate the channel influence before the backscattered LTE signal.

[0066] Another part of the preamble is the reference sequence, which is a sequence known to the receiver and is used to eliminate the channel effect from the tag to the receiver.

[0067] Another part of the tag data packet is the backscattered tag data. After addressing the channel influence from the tag to the receiver, and before acquiring the tag data θ, the starting position of the tag data is calculated. This can be done by using specific reference signals from the tag and the receiver to perform correlation calculations on the received backscattered LTE signal. By using the preamble pattern and the expected pattern to perform correlation calculations, the starting position with the smallest error is obtained. Then, based on the correlation calculation results, the modulation offset that maximizes the matching degree between the received signal and the expected signal is found, thus confirming the starting position of the backscattered bits in the tag data packet.

[0068] After resolving the channel interference before and after the backscattered LTE signal and confirming the starting position of the reflected tag data, the receiver demodulates and decodes the received reflected LTE signal. It can first perform equalization processing, use the maximum likelihood estimation module to estimate the signal transmitted by the tag, and then decode the spatiotemporally encoded backscattered tag data to calculate the value of the tag data bits.

[0069] This invention presents a backscatter communication method based on the MIMO characteristics of LTE signals. When a tag needs to transmit information, the backscattered tag data is carried on the ambient LTE signal. Utilizing the MIMO characteristics of LTE, the dual-antenna tag performs spatial-temporal coding of the transmitted information under low power consumption. The tag employs a modulation method with a duration shorter than symbol-level modulation to improve throughput. The tag modulates its data while backscattering the LTE signal. Based on the characteristics of the LTE signal, the receiver can capture the LTE signal reflected by the backscattered tag and decode the tag data from the LTE signal modulated by the tag. This also solves the tag synchronization problem. By eliminating channel interference before and after tag reflection, the receiver can perform correct demodulation. This system features sample-to-tag data modulation, and the dual-antenna tag uses spatiotemporal coding, improving the system's versatility and throughput.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A backscatter communication method based on the MIMO characteristics of LTE signals, characterized in that, Including the following steps: S1. The backscatter tag captures LTE signals in the environment and performs backscattering; S2. While backscattering, the tag data is spatiotemporally encoded and LTE signal modulated. S3. After the receiver captures the backscattered LTE signal, it demodulates and decodes the backscattered LTE signal to obtain tag data; When the backscatter tag captures LTE signals in the environment, the backscatter tag synchronizes with the LTE signals and determines the starting position of the backscatter tag data. The demodulation and decoding of the backscattered LTE signal in S3 includes the following steps: S31. After detecting the backscattered LTE signal, the receiver performs channel estimation. The channel estimation consists of two parts: one is the channel estimation from the LTE signal to the tag, and the other is the channel estimation from the tag to the receiver. The receiver signal model is represented as follows: ； in, It is the channel coefficient between the LTE signal and the tag. It is the channel coefficient between the tag and the receiver, and S is the received signal symbol. The tag data symbols transmitted by the tag, where N is noise; S32. Utilize backscattered tag data packets to eliminate the channel interference before and after backscattered LTE signals; S33. Using the tag and receiver-specific reference signals, perform correlation calculations on the received backscattered LTE signal to determine the starting position of the backscattered bit in the tag data packet. S34. The receiving end demodulates and decodes the received reflected LTE signal and calculates the value of the tag data bits. The tag data packet in S32 includes a preamble portion and a backscattered tag data portion, wherein the preamble portion includes a "0" sequence and a reference sequence: The channel estimator uses the "0" sequence portion for parsing, and then performs equalization to eliminate the channel effects before the backscattered LTE signal; the reference sequence is used to eliminate the channel effects from the tag to the receiver. The receiving end in S34 performs demodulation and decoding processing on the received reflected LTE signal, and also includes: The maximum likelihood estimation module is used to estimate the signal transmitted by the tag, and then the spatiotemporally encoded backscattered tag data is decoded to calculate the value of the tag data bits.

2. The backscatter communication method based on the MIMO characteristics of LTE signals according to claim 1, characterized in that, The backscatter tag is synchronized with the LTE signal, and the starting position of the backscatter tag data is determined, including the following steps: S11. The backscatter tag maximizes the input LTE signal through impedance matching; S12. Filter the LTE signal through a filter and output the envelope of the high-frequency signal; S13. Detect whether the LTE signal synchronization signal PSS appears using a voltage comparator; S14. After detecting the PSS signal, the tag preamble sends a continuous sequence of "0"s. S15. Determine the starting position of the backscatter tag data based on the continuous "0" sequence.

3. The backscatter communication method based on the MIMO characteristics of LTE signals according to claim 1, characterized in that, The backscatter tag includes two antennas, and the backscatter tag performs spatiotemporal encoding of tag data based on antenna switching.

4. The backscatter communication method based on the MIMO characteristics of LTE signals according to claim 3, characterized in that, The backscatter tag performs spatiotemporal encoding of tag data based on the antenna switch, including: In spatiotemporal coding, two bits are grouped together and represented as symbols. and At time t, the two antennas transmit two tag data symbols. and The tag data symbols transmitted by the two antennas at time t+1 and .

5. The backscatter communication method based on the MIMO characteristics of LTE signals according to claim 1, characterized in that, The S2 step involves LTE signal modulation, including: The LTE signal is represented as a combination of timing signals of different basic timing units. Backscattered spatiotemporal coded tag data is embedded into different basic timing units. The duration of the backscattered modulation unit is set to be the same as the duration of the basic timing unit. The LTE signal is phase-modulated and timing modulation is performed on each basic timing unit.

6. The backscatter communication method based on the MIMO characteristics of LTE signals according to claim 5, characterized in that, The formula for constructing the basic timing unit in the LTE signal time domain is as follows: ； in, This is a baseband signal, generated by the OFDM module. is the value for each subcarrier, and K is the size of the FFT.

Images