A LoRa concurrent communication demodulation method and system based on frequency domain interference iterative cancellation

Abstract

The present invention discloses a LoRa concurrent communication demodulation method and system based on frequency-domain interference iterative cancellation, including signal transmission; taking chirp signals as processing units, the node end transmits signals in the standard LoRa data packet frame format; signal reception; the gateway end receives LoRa signals in a conflict state based on the frequency-domain characteristics of the pilot part, and the conflict state means that multiple data packets are transmitted in the same time period; signal preprocessing; performing low-pass filtering and signal synchronization on the LoRa signals in the conflict state, dividing them into multiple chirp symbols with the chirp length as the step size, and performing carrier frequency offset correction on the chirp symbols; conflict signal demodulation; performing frequency-domain interference estimation and cancellation on the chirp symbols preprocessed in step three to complete symbol demodulation. The demodulation method provided by the present invention has stronger robustness under low signal-to-noise ratios and can complete the demodulation of conflict signals when the signal strength is much lower than the noise strength.

Description

Technical Field

[0001] The present invention belongs to the field of communications, and particularly relates to a LoRa concurrent communication demodulation method and system based on frequency-domain interference iterative cancellation. Background Art

[0002] LoRa is based on linear spread-spectrum modulation technology. Each modulated signal, i.e., chirp, is a sin wave with linearly increasing (upchirp) or decreasing (downchirp) frequency. In the frequency band range (-BW / 2, BW / 2), the frequency of the chirp linearly increases from the initial frequency f0 until bw / 2, and then returns to the lower frequency band boundary -bw / 2, thus sweeping across the entire bandwidth. Different chirps correspond to different starting frequencies, with a total of 2^SF kinds. As Figure 1 (a) and Figure 1 (b) show, they respectively represent the time-frequency diagrams of two up-chirps with different starting frequencies. It can be seen from the figure that the frequency of the signal is in a gradually increasing state within a certain interval. As Figure 1 (c) shows, it is the time-frequency diagram of a standard down-chirp. It can be seen from the figure that the frequency of the signal gradually decreases with time. During demodulation, pulse compression is performed on the original chirp to obtain the starting frequency. Since there is a conjugate relationship between upchirp and downchirp, here, the upchirp can be directly multiplied by the standard downchirp and Fourier transform is performed to obtain the frequency energy peak in this interval. The frequency corresponding to the energy peak is its initial frequency for demodulation.

[0003] However, with the large-scale deployment of LoRa nodes, thousands of LoRa nodes are connected to a LoRa gateway. The serious packet conflicts brought about by the aggregated network structure result in a large number of packet losses and a decrease in throughput. In wireless transmission technology, the handling methods for conflict problems are divided into conflict avoidance and conflict resolution.

[0004] In terms of collision avoidance, LoRa uses multiple PHY technologies to transmit multiple LoRa nodes in parallel. LoRa nodes can be configured with different radio parameters (e.g., channels, spreading factors, etc.) to mitigate collisions, but this requires cooperation between different operators and service providers, and a LoRa gateway can support at most 8 LoRa nodes transmitting simultaneously. However, since LoRa signals are mostly transmitted in an environment below the noise floor, it is difficult to complete signal-based channel monitoring, resulting in the failure of collision avoidance. At the same time, channel monitoring requires nodes to consume a large amount of computing power and energy, thus shortening the working life of LoRa nodes. Limited by hardware capabilities and power supply, LoRa nodes usually adopt a simple Aloha-based MAC to avoid collisions. According to the protocol specifications, LoRa nodes can transmit data packets without performing channel detection. When a LoRa gateway cannot decode a data packet sent from a node due to a collision, the data packet will be retransmitted after a random backoff time, and the backoff retransmission further exacerbates the collision problem in the LoRa network. At the same time, it also causes unnecessary energy waste due to multiple transmissions by nodes. Therefore, our more ideal state is that nodes can send data packets whenever they want to, and the gateway decodes the colliding signal packets.

[0005] There has also been some related work in terms of collision decoding. For example, Choir classifies colliding frames according to the different fractional-bit hardware frequency offsets of each LoRa node. However, in practical applications, due to the influence of interference and noise, it is difficult to accurately extract the carrier frequency offset caused by hardware. At the same time, as the number of nodes increases, the fractional-bit hardware frequency offsets will inevitably repeat, resulting in the failure of classification. Another work, mLoRa, derives the time offset between two colliding packets according to the designed preamble detection strategy, and then obtains chirp-level collision-free samples and corresponding frequencies. Based on these collision-free frequencies and samples, using the chirp amplitude of the preamble part and the linear spread spectrum modulation method of the chirp, the time-domain samples of the colliding signal are estimated and reconstructed. Subtracting the estimated and reconstructed time-domain samples of the colliding signal from the time-domain of the colliding signal, and through repeated estimation and subtraction operations, the colliding data packets in a sample are decoded. However, since LoRa signals are mostly transmitted at a low signal-to-noise ratio, and in this method, when the SNR decreases, the decoding accuracy will be greatly reduced, limiting the communication performance of LoRa. CoLaRa uses packet time offset to eliminate collisions. The received signal is cut into a series of receiving windows, and the length of each window is equal to the chirp. The symbols are segmented using misaligned windows. Then, for the signal in each window, collision decoding is performed according to the fact that the height of the frequency-domain peak is proportional to the length of the segment. However, in the process of the SNR decreasing from 0 dB to -15 dB, the system throughput is reduced to half of the original, and the performance is greatly reduced. Summary of the Invention

[0006] The present invention provides a LoRa concurrent communication demodulation method and system based on iterative elimination of frequency-domain interference, which can demodulate conflicting LoRa signals when SNR < 0; this method combines sliding window detection and uses the frequency-domain correlation analysis of the received signal after pulse compression and the prior signal to ensure accurate packet detection even when the intensity of the LoRa signal is much lower than the noise intensity.

[0007] To achieve the above tasks, the present invention adopts the following technical solutions, including:

[0008] A LoRa concurrent communication demodulation method based on iterative elimination of frequency-domain interference is executed according to the following steps:

[0009] Step 1: Signal transmission;

[0010] Taking the chirp signal as the processing unit, the node sends the signal in the standard LoRa data packet frame format.

[0011] Step 2: Signal reception;

[0012] The gateway receives the LoRa signal in the conflict state based on the frequency-domain characteristics of the pilot part, and the conflict state means that multiple data packets are transmitted in the same time period.

[0013] Step 3: Signal preprocessing;

[0014] Perform low-pass filtering and signal synchronization on the LoRa signal in the conflict state, divide it into multiple chirp symbols with the chirp length as the step size, and correct the carrier frequency offset of the chirp symbols.

[0015] Step 4: Demodulation of conflicting signals;

[0016] Estimate and eliminate the frequency-domain interference of the chirp symbols preprocessed in Step 3 to complete symbol demodulation.

[0017] Optionally, in the above Step 4, the estimation of the frequency-domain interference includes obtaining the frequency-domain peak frequency point and the frequency-domain peak height;

[0018] Among them, the obtaining of the frequency-domain peak frequency point includes:

[0019]

[0020] Among them, f′ A1-1 , f′ A1-2 is the frequency-domain peak frequency point of the interference generated by chirp symbol A1 on chirp symbol B1, Hz; f A1-1 , f A1-2is the peak frequency point of the chirp symbol A1 in the frequency domain, Hz; BW is the bandwidth, Hz; t 1_2 is the time window offset, s; T is the complete time length of the chirp symbol, s;

[0021] The acquisition of the peak height in the frequency domain includes:

[0022] When :

[0023]

[0024] When :

[0025]

[0026] where h′ A1-1 , h′ A1-2 is the peak height in the frequency domain of the interference generated by the chirp symbol A1 on the chirp symbol B1; h A1-1 , h A1-2 is the peak height in the frequency domain of the chirp symbol A1, Hz; h is the complete peak energy height in the frequency domain of the chirp symbol, Hz.

[0027] Optionally, in the fourth step, after the frequency domain interference is estimated, the symbol demodulation process includes:

[0028] In the frequency domain, eliminate the estimated frequency domain interference (f′ A1-1 , h′ A1-1 ), (f′ A1-2 , h′ A1-2 );

[0029] In the frequency domain after eliminating the interference position, find the frequency point f where the peak in the frequency domain is the highest,

[0030] When :

[0031]

[0032] When :

[0033]

[0034] where: f is the frequency point where the peak is the highest in the frequency domain of the chirp symbol B1 after eliminating the interference, Hz; BW is the bandwidth, Hz; f 0-B is the starting frequency of the chirp symbol B1, Hz; finding the starting frequency of the chirp symbol B1 completes the demodulation of the chirp symbol.

[0035] Optionally, in step three, the specific process of correcting the carrier frequency offset is shown as follows;

[0036]

[0037] where: S′ is the chirp symbol after carrier frequency offset correction, S chirp is the original chirp symbol, f0 is the starting frequency of the original chirp symbol, in Hz, f cfo is the carrier frequency offset frequency, in Hz; k is the frequency change rate, in Hz / s; t is the time, in s; j is the imaginary part signal.

[0038] Optionally, in step three, the low-pass filtering is performed using an IIR low-pass filter.

[0039] Optionally, in step three, the frequency-domain energy of the LoRa signal after low-pass filtering is pulse-compressed, and the position of the maximum energy after pulse compression is found using a sliding window, which is the starting position of the payload of the chirp signal, to achieve signal synchronization; a sliding window is used with the size of 10 downchirps;

[0040] The sliding window is used to perform signal synchronization on the LoRa signal after low-pass filtering, and the Payload signal in the LoRa signal after low-pass filtering is segmented according to the time unit.

[0041] A LoRa concurrent communication demodulation system based on frequency-domain interference iterative cancellation includes:

[0042] A signal sending module, which takes the chirp signal as the processing unit, and the node end sends signals in the standard LoRa data packet frame format;

[0043] A signal receiving module, which is based on the frequency-domain characteristics of the pilot part at the gateway end to receive the LoRa signal in the collision state, and the collision state means that multiple data packets are transmitted in the same time period;

[0044] A signal preprocessing module, which performs low-pass filtering and signal synchronization on the LoRa signal in the collision state, divides it into multiple chirp symbols with the chirp length as the step size, and corrects the carrier frequency offset of the chirp symbols;

[0045] A collision signal demodulation module, which estimates and eliminates the frequency-domain interference of the chirp symbols preprocessed in step three to complete symbol demodulation.

[0046] Optionally, in the collision signal demodulation module, the estimation of the frequency-domain interference includes obtaining the frequency-domain peak frequency point and the frequency-domain peak height;

[0047] Among them, the obtaining of the frequency-domain peak frequency point includes:

[0048]

[0049] Among them, f′ A1-1 , f′ A1-2 is the peak frequency point in the frequency domain of the interference generated by chirp symbol A1 on chirp symbol B1, Hz; f A1-1 , f A1-2 is the peak frequency point in the frequency domain of chirp symbol A1, Hz; BW is the bandwidth, Hz; t 1_2 is the time window offset, s; T is the complete time length of the chirp symbol, s;

[0050] The acquisition of the peak height in the frequency domain includes:

[0051] When :

[0052]

[0053] When :

[0054]

[0055] Among them, h′ A1-1 , h′ A1-2 is the peak height in the frequency domain of the interference generated by chirp symbol A1 on chirp symbol B1; h A1-1 , h A1-2 is the peak height in the frequency domain of chirp symbol A1, Hz; h is the complete peak energy height in the frequency domain of the chirp symbol, Hz.

[0056] Optionally, after estimating the interference in the frequency domain, the symbol demodulation process includes:

[0057] In the frequency domain, eliminate the estimated frequency domain interference (f′ A1-1 , h′ A1-1 ), (f′ A1-2 , h′ A1-2 );

[0058] In the frequency domain after eliminating the interference position, find the frequency point f where the peak in the frequency domain is the highest,

[0059] When :

[0060]

[0061] When :

[0062]

[0063] where: f is the frequency point at the highest peak in the frequency domain of the chirp symbol B1 after interference elimination, in Hz; BW is the bandwidth, in Hz; f 0-B is the starting frequency of the chirp symbol B1, in Hz; finding the starting frequency of the chirp symbol B1 completes the demodulation of the chirp symbol.

[0064] Optionally, in the signal preprocessing module, the specific process of correcting the carrier frequency offset is shown in the following formula;

[0065]

[0066] where: S′ is the chirp symbol after carrier frequency offset correction, S chirp is the original chirp symbol, f0 is the starting frequency of the original chirp symbol, in Hz, f cfo is the carrier frequency offset frequency, in Hz; k is the frequency change rate, in Hz / s; t is the time, in s; j is the imaginary part signal.

[0067] The present invention has the following characteristics compared with the prior art:

[0068] The present invention will propose a method and system for demodulating LoRa signal conflicts during concurrent communication based on the original LoRa communication mechanism. By iteratively predicting and eliminating the frequency domain interference when LoRa signals conflict, the demodulation of LoRa signals in the conflict state is completed. This conflict demodulation method does not require an additional hardware module. At the same time, the method for demodulating LoRa signal conflicts can also be used together with channel parameter optimization and other solutions to further improve the network performance. The idea of realizing conflict signal demodulation by iteratively predicting and eliminating frequency domain interference has never been considered in previous work. Compared with other methods for demodulating conflict signals based on signal time domain characteristics or signal energy characteristics, this method has stronger robustness at low signal-to-noise ratios and can complete the demodulation of conflict signals when the signal strength is much lower than the noise strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification, and are used together with the following specific embodiments to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the accompanying drawings:

[0070] Figure 1 are the time-frequency diagrams of three different chirps, (a) up-chirp with a starting frequency of -250 kHz; (b) up-chirp with a starting frequency of -125 kHz; (c) standard down-chirp;

[0071] Figure 2It is the time-frequency diagram of LoRa data packets in the normal state;

[0072] Figure 3 It is the time-frequency diagram of LoRa data packets in the conflict state;

[0073] Figure 4 It is the demodulation accuracy rate of conflict signals at different signal-to-noise ratios when SF = 8. Specific implementation manner

[0074] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the following described embodiments are only a part of the embodiments of the present invention, not all embodiments, and no formal restrictions are imposed on the present invention. Any use of the technical solutions of this embodiment, including simple changes to this embodiment, falls within the scope of protection of the present invention.

[0075] The standard LoRa signal data packet includes the following parts: the pilot for signal detection, i.e., Preamble, the start frame delimiter Start Frame Delimiter (SFD) for signal synchronization, and the payload data part Payload for recording the original transmission information.

[0076] The payload data part Payload is composed of each chirp signal. Multiple chirp signals are obtained by dividing the Payload signal according to the time unit; in the signal sending stage, the sending signal is not changed, and it is carried out according to the standard frame format specified by LoRaWAN, so that it retains the original sending settings and communication protocols, does not conflict with the original communication protocols, and ensures that this system can be compatible with the original LoRa communication system;

[0077] With the large-scale deployment of LoRa nodes, thousands of LoRa nodes are connected to a LoRa gateway. The serious packet conflicts brought by the aggregated network structure lead to a large number of packet losses and throughput degradation. Based on this problem, a demodulation system for conflict packets in concurrent communication is proposed. In order to further complete the demodulation of LoRa concurrent transmission conflict signals at low signal-to-noise ratios, the present invention proposes a method for iteratively estimating and eliminating the frequency-domain interference of conflict signals. The present invention can demodulate conflict LoRa signals when SNR < 0; this method combines sliding window detection and uses the frequency-domain correlation analysis of the received signal after pulse compression and the prior signal, which can ensure accurate packet detection even when the intensity of the LoRa signal is much lower than the noise intensity. It includes:

[0078] Step 1: The node (signal sender) sends a data packet in the standard LoRaWAN frame format to the gateway (signal receiver). Specifically, for example, the sender selects an appropriate spreading factor SF, bandwidth BW, and number of pilot chirps according to the communication environment in accordance with the LoRaWAN protocol, without making any changes or restrictions to the signal transmission at the node side;

[0079] Step 2: Signal reception.

[0080] Based on the frequency-domain characteristics of the pilot part, the gateway receives LoRa signals in a collision state as shown in Figure 3 where the collision state means that multiple data packets are transmitted in the same time period. As shown in Figure 2 is the time-frequency diagram of LoRa data packets in the normal transmission state, and as shown in Figure 3 is the time-frequency diagram of LoRa data packets in the collision state; perform correlation analysis on the frequency-domain characteristics after pulse compression of the pilot signal and the frequency-domain characteristics of the prior signal. If the degree of correlation is higher than the degree of correlation between the noise and the frequency-domain characteristics of the prior signal, it is determined as a LoRa signal, and the data packet is received.

[0081] Step 3: Perform data preprocessing on the received signal.

[0082] Perform high-frequency noise filtering, signal segmentation (i.e., segment each chirp signal according to the time length), and carrier frequency offset correction on the LoRa signal;

[0083] In the signal preprocessing stage, use an IIR low-pass filter to filter the signal to remove high-frequency noise outside the signal bandwidth. Use a sliding window for signal synchronization and segmentation. The carrier frequency offset is caused by the mismatch between the local crystal oscillators of the transceiver and the Doppler frequency shift during signal transmission. And this frequency offset will cause the frequency point value after pulse compression of the LoRa signal to shift, thus affecting the decoding result. It is necessary to correct the carrier frequency offset in the signal preprocessing stage to obtain the accurate original frequency-domain characteristics of the signal.

[0084] In Step 3, it is necessary to perform data preprocessing operations. The first thing to do well in this step is the signal synchronization and accurate interception problems. Here, use a sliding window to multiply the signal with the Down chirp within the window to compress the frequency-domain energy. Use the sliding window to find the position of the maximum energy after pulse compression, which is the starting position of the chirp signal payload, that is, to achieve accurate signal synchronization. Then, according to the time length of the chirp signal, segment each chirp signal. Finally, calculate the carrier frequency offset frequency f cfo to complete the frequency offset correction.

[0085] In Step 3, the carrier frequency offset is estimated using the pilot part of the LoRa data packet and frequency correction is performed to obtain an accurate frequency point value.

[0086]

[0087] Where: S′ is the chirp symbol after carrier frequency offset correction, S chirp is the original chirp symbol, f0 is the starting frequency of the original chirp symbol, in Hz, f cfo is the carrier frequency offset frequency, in Hz; k is the frequency change rate, in Hz / s; t is the time, in s; j is the imaginary part signal.

[0088] Step 4: Perform frequency domain interference prediction and cancellation to complete demodulation.

[0089] For the chirp signal preprocessed in Step 3, according to the starting position between its signal synchronizations, calculate the time window offset t generated by the time difference of signal arrival at the chirp symbol level 1_2 .

[0090] t 1_2 = p2 - p1 - N × T;

[0091] Where, the value range of the time window offset t 1_2 is between 0 and T, in s; p2 is the arrival time of the second packet, in s; p1 is the arrival time of the first packet, in s; N is a positive integer, and T is the duration of the chirp symbol, in s.

[0092] Then demodulate the clean segment of the first chirp symbol A1 where the previous data packet A conflicts with the subsequent data packet B. The process is as follows: The clean segment signal is first multiplied by the corresponding length of down chirp. The specific process is shown in the following formula;

[0093]

[0094] Where: Cu is upchirp, Cd is downchirp, f o is the starting frequency of Cu, in Hz; k is the frequency change rate, in Hz / s; BW is the frequency band width, in Hz; t is the time, with a value range from 0 to t 1_2 , in s; fBw / 2 is the starting frequency of Cd, in Hz; j is the imaginary part signal.

[0095] Then perform Fourier transform on the multiplied signal to obtain the starting frequency f0.

[0096] Then, based on the obtained starting frequency f0 of the first chirp symbol A1 where the previous data packet A conflicts with the subsequent data packet B, estimate the frequency domain peak frequency point and frequency domain peak height of symbol A1.

[0097]

[0098]

[0099] Among them, f A1-1 , f A1-2 is the peak frequency point in the frequency domain of symbol A1, in Hz; h A1-1 , h A1-2 is the corresponding peak height; f0 is the starting frequency of symbol A1, in Hz; BW is the bandwidth, in Hz; h is the peak energy height of the complete chirp in the frequency domain.

[0100] Based on the peak frequency point and peak height in the frequency domain estimated for symbol A1, calculate the peak frequency point and peak height in the frequency domain where the interference generated by it on the chirp symbol B1 that conflicts with the subsequent data packet B and A1 is located.

[0101] Specifically, the calculation process of the peak frequency point in the frequency domain where the interference is located is as follows:

[0102]

[0103] Among them, f′ A1-1 , f′ A1-2 is the peak frequency point in the frequency domain of the interference generated by symbol A1 on B1, in Hz; f A1-1 , f A1-2 is the peak frequency point in the frequency domain of symbol A1, in Hz; BW is the bandwidth, in Hz; t 1_2 is the time window offset, in s; T is the complete time length of the chirp symbol, in s.

[0104] Specifically, the calculation process of the peak frequency height in the frequency domain where the interference is located is as follows:

[0105] When :

[0106]

[0107] When :

[0108]

[0109] Among them, h′ A1-1 , h′ A1-2 is the peak frequency height in the frequency domain of the interference generated by symbol A1 on B1; h A1-1 , h A1-2 is the peak frequency height of symbol A1, in Hz; h is the peak energy height of the complete chirp in the frequency domain, in Hz; t 1_2is the time window offset, s; T is the complete time length of the chirp symbol, s.

[0110] Next, first demodulate the chirp symbol B1 where the subsequent data packet B conflicts with A1, and then perform a Fourier transform on the multiplied signal to obtain its frequency domain characteristics. In the frequency domain, eliminate the estimated frequency domain interferences (f′ A1-1 , h′ A1-1 ), (f′ A1-2 , h′ A1-2 ).

[0111] In the frequency domain after eliminating the interference positions, find the frequency point f where the highest peak in the frequency domain is located.

[0112] When :

[0113]

[0114] When :

[0115]

[0116] Where: f is the frequency point where the highest peak is located in the frequency domain of the chirp symbol B1 after eliminating the interference, Hz; BW is the bandwidth, Hz; f 0-B is the starting frequency of the chirp symbol B1, Hz; finding the starting frequency of the chirp symbol B1 completes the demodulation of the chirp symbol.

[0117] Finding the starting frequency of symbol B1 completes the demodulation of the conflicting symbol. Similarly, use the starting frequency of symbol B1 to repeat steps 4.4 and 4.5 to complete the demodulation of symbol A2.

[0118] And so on, perform iterative estimation and elimination of frequency domain interference on the conflicting signals.

[0119] Example 1:

[0120] This example proposes a LoRa splicing communication method based on segmented neural network decoding, including the following steps:

[0121] Step 1: The standard LoRa signal data packet consists of the following parts: the preamble for signal detection, i.e., the Preamble, the start frame delimiter for signal synchronization, Start Frame Delimiter (SFD), and the payload data part for recording the original transmission information, Payload. During the signal transmission phase, this method does not modify the transmitted signal and follows the standard frame format specified by LoRaWAN, enabling it to maintain its original transmission settings and communication protocol without conflicting with the original communication protocol, ensuring that this system can be compatible with the original LoRa communication system.

[0122] Step 2: Use the gateway to receive the conflicting signals. The gateway receives the conflicting signals based on the frequency domain characteristics of the preamble part. Perform a correlation analysis on the frequency domain characteristics of the compressed pilot signal pulse and the frequency domain characteristics of the prior signal. If the degree of correlation is higher than that of the correlation analysis between the noise and the frequency domain characteristics of the prior signal, it is determined to be a LoRa signal, and the data packet is received.

[0123] Step 3: Perform data preprocessing on the received signal. Filter out high-frequency noise from the LoRa signal to reduce the impact of out-of-band noise, segment the signal, i.e., segment to obtain each chirp signal according to the time length, and correct the carrier frequency offset of the received signal.

[0124] Step 3.1: First, use an IIR low-pass filter to filter the signal to remove high-frequency noise.

[0125] Step 3.2: Signal synchronization and payload segmentation. Since the splicing mechanism retains the preamble of the original LoRa signal, LoRa standard packet detection can be used to ensure signal synchronization. That is, use a window size of 10 downchirps to implement a sliding window to monitor the channel. Then, multiply the sliding window of the channel by 2.25 upchirps and perform a Fourier transform to synchronize the signal. When the peak intensity of the fast Fourier transform of the signal exceeds the preset threshold, the signal synchronization is completed, and this moment is the accurate starting position p of the payload part of the signal i , and this peak frequency point position is the carrier frequency offset frequency f cfo . According to the length of the signal, starting from the accurate starting position p of the payload part i , segment the signal in the payload to obtain the payload, and at the same time obtain the frequency domain peak height h of the chirp symbol according to the preamble part for subsequent step calculations.

[0126] Step 3.3: Use the pilot part of the LoRa data packet to estimate the carrier frequency offset and perform frequency correction, so as to remove the frequency offset caused by the mismatch between the local crystal oscillators of the transceiver and the Doppler frequency shift during signal transmission.

[0127]

[0128] Where: S′ is the chirp symbol after carrier frequency offset correction, S chirp is the original chirp symbol, f0 is the starting frequency of the original chirp symbol, Hz, f cfo is the carrier frequency offset frequency, Hz; k is the frequency change rate, Hz / s; t is the time, s; j is the imaginary part signal.

[0129] Step Four: Iteratively estimate the frequency domain interference and eliminate the interference to achieve accurate demodulation of the conflicting signals.

[0130] Step 4.1: For the chirp signal preprocessed in Step Three, calculate the time window offset t generated at the chirp symbol level due to the time difference of signal arrival according to the starting position between its signal synchronizations 1_2 .

[0131] t 1_2 = p2 - p1 - N × T

[0132] Where, the value range of the time window offset t 1_2 is between 0 and T, s; p2 is the arrival time of the second packet, s; p1 is the arrival time of the first packet, s; N is a positive integer, and T is the duration of the chirp symbol, s.

[0133] Step 4.3: Demodulate the clean segment of the first chirp symbol A1 where the previous data packet A conflicts with the subsequent data packet B. The process is as follows: The clean segment signal is first multiplied by the corresponding length of the down chirp. The specific process is shown in the following formula;

[0134]

[0135] Where: Cu is the upchirp, Cd is the downchirp, f o is the starting frequency of Cu, Hz; k is the frequency change rate, Hz / s; BW is the bandwidth, Hz; t is the time, and the value range is from 0 to t i_2 , s; fBw / 2 is the starting frequency of Cd, Hz; j is the imaginary part signal.

[0136] Then, perform Fourier transform on the multiplied signal to obtain the starting frequency f0.

[0137] Step 4.4: Based on the starting frequency f0 of the first chirp symbol A1 where the previous data packet A and the subsequent data packet B conflict obtained in Step 4.3, estimate the frequency-domain peak frequency point and frequency-domain peak height of symbol A1.

[0138]

[0139]

[0140] Among them, f A1-1 , f A1-2 is the frequency-domain peak frequency point of chirp symbol A1, Hz; h A1-1 , h A1-2 is its corresponding peak height; f0 is the starting frequency of chirp symbol A1, Hz; BW is the bandwidth, Hz; h is the peak energy height of the complete chirp in the frequency domain.

[0141] Step 4.5: Calculate the frequency-domain peak frequency point and frequency-domain peak height where the interference generated by symbol A1 is located on the chirp symbol B1 where the subsequent data packet B conflicts with A1 according to the estimated frequency-domain peak frequency point and frequency-domain peak height of symbol A1.

[0142] Specifically, the calculation process of the frequency-domain peak frequency point where the interference is located is as follows:

[0143]

[0144] Among them, f′ A1-1 , f′ A1-2 is the frequency-domain peak frequency point of the interference generated by symbol A1 on B1, Hz; f A1-1 , f A1-2 is the frequency-domain peak frequency point of symbol A1, Hz; BW is the bandwidth, Hz; t 1_2 is the time window offset, s; T is the complete time length of the chirp symbol, s.

[0145] Specifically, the calculation process of the frequency-domain peak height where the interference is located is as follows:

[0146] When :

[0147]

[0148] When :

[0149]

[0150] Among them, h′ A1-1 , h′ A1-2 is the frequency-domain peak height of the interference generated by symbol A1 on B1; h A1-1, h A1-2 is the peak height in the frequency domain of symbol A1, Hz; h is the peak energy height of the complete chirp in the frequency domain, Hz; t 1_2 is the time window offset, s; T is the complete time length of the chirp symbol, s.

[0151] Step 4.5: Iteratively eliminate frequency domain interference

[0152] First, demodulate the chirp symbol B1 where the subsequent data packet B conflicts with A1. The process is as follows: The B1 signal is first multiplied by the corresponding length of down chirp. The specific process is shown in the following formula;

[0153]

[0154] where: Cu is upchirp, Cd is downchirp, f o is the starting frequency of Cu, Hz; k is the frequency change rate, Hz / s; BW is the frequency band width, Hz; t is time, with a value range from 0 to T, s; f BW / 2 is the starting frequency of Cd, Hz; j is the imaginary part signal.

[0155] Then, perform a Fourier transform on the multiplied signal to obtain its frequency domain characteristics. In the frequency domain, eliminate the frequency domain interference (f′ A1-1 , h′ A1-1 ), (f′ A1-2 , h′ A1-2 ) estimated in Step 4.4.

[0156] In the frequency domain after eliminating the interference position, find the frequency point f where the highest frequency domain peak is located.

[0157] When :

[0158]

[0159] When :

[0160]

[0161] where: f is the frequency point where the highest peak is located in the frequency domain of the chirp symbol B1 after eliminating the interference, Hz; BW is the frequency band width, Hz; f 0-B is the starting frequency of the chirp symbol B1, Hz; Finding the starting frequency of the chirp symbol B1 completes the demodulation of the chirp symbol.

[0162] Finding the starting frequency of the chirp symbol B1 completes the demodulation of the conflicting symbol.

[0163] Similarly, repeat steps 4.4 and 4.5 using the starting frequency of chirp symbol B1 to complete the demodulation of symbol A2.

[0164] And so on, estimate and eliminate the iterative frequency-domain interference of the conflicting signals.

[0165] The LoRa conflicting signal demodulation was carried out using this method in different parameter environments. The same transceiver equipment was used in the verification experiments in this section. The Arduino module equipped with the sx1276 chip was used at the transmitting end to transmit LoRa signals, and the USRP-2954 manufactured by the US company National Instruments was used at the receiving end to receive LoRa signals. The frequency band selected for signal transmission was 915.9 MHz, and the signal bandwidth was 500 KHz. The demodulation part of the conflicting data packets was implemented on MATLAB. The signal-to-noise ratio of the signal was adjusted by adjusting the transmission power of the transmitting end node, changing the transmission distance between the transmitting end and the receiving end, and adding an attenuator at the receiving end and changing the attenuation power.

[0166] When SF = 8 and the SNR is between -5 dB and -10 dB, the demodulation accuracy of the conflicting signals of this method can reach 89.06%. When SF = 10 and the SNR is between -15 dB and -20 dB, the demodulation accuracy of the conflicting signals of this method can reach 92.94%. As Figure 4 shown is the demodulation accuracy of the conflicting signals at different signal-to-noise ratios when SF = 8.

[0167] The preferred embodiments of the present disclosure have been described in detail above. However, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept scope of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0168] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination methods.

[0169] Furthermore, any combination can be made between the various different embodiments of the present disclosure, as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A LoRa concurrent communication demodulation method based on frequency-domain interference iterative cancellation, characterized in that Execute according to the following steps: Step 1: Signal transmission; Taking the chirp signal as the processing unit, the node end sends the signal in the standard LoRa data packet frame format; Step 2: Signal reception; Based on the frequency domain characteristics of the pilot part, the gateway end receives the LoRa signal in the conflict state, and the conflict state means that multiple data packets are transmitted in the same time period; Step 3: Signal preprocessing; Perform low-pass filtering and signal synchronization on the LoRa signal in the conflict state, segment it with the chirp length as the step size to obtain multiple chirp symbols, and correct the carrier frequency offset of the chirp symbols; Step 4: Conflict signal demodulation; Estimate and eliminate the frequency domain interference of the chirp symbols preprocessed in Step 3 to complete symbol demodulation; In the said Step 4, the estimation of the frequency domain interference includes obtaining the frequency domain peak frequency point and the frequency domain peak height; Among them, the obtaining of the frequency domain peak frequency point includes: where f′ A1-1 , f′ A1-2 is the peak frequency point in the frequency domain of the interference generated by chirp symbol A1 on chirp symbol B1, Hz; f A1-1 , f A1-2 is the peak frequency point in the frequency domain of chirp symbol A1, Hz; BW is the bandwidth, Hz; t 1_2 is the time window offset, s; T is the complete time length of the chirp symbol, s; The obtaining of the frequency domain peak height includes: When : When : where h′ A1-1 and h′ A1-2 is the peak height in the frequency domain of the interference generated by chirp symbol A1 on chirp symbol B1; h A1-1 and h A1-2 is the peak height in the frequency domain of chirp symbol A1, in Hz; h is the complete peak energy height in the frequency domain of the chirp symbol, in Hz.

2. The LoRa concurrent communication demodulation method based on frequency domain interference iterative cancellation according to claim 1, wherein In the said Step 4, after the frequency domain interference is estimated, the symbol demodulation process includes: In the frequency domain, eliminate the estimated frequency-domain interference (f′ A1-1 , h′ A1-1 ), (f′ A1-2 , h′ A1-2 ). In the frequency domain after eliminating the interference position, find the frequency point f where the frequency domain peak is the highest; When : When : where: f is the frequency point at the highest peak in the frequency domain of chirp symbol B1 after interference elimination, in Hz; BW is the bandwidth, in Hz; f 0-B is the starting frequency of chirp symbol B1, in Hz; finding the starting frequency of chirp symbol B1 completes the demodulation of the chirp symbol.

3. The LoRa concurrent communication demodulation method based on iterative elimination of frequency-domain interference according to claim 1 or 2, characterized in that In the said Step 3, the specific process of correcting the carrier frequency offset is shown in the following formula; Where: S′ is the chirp symbol after carrier frequency offset correction, S chirp is the original chirp symbol, f0 is the starting frequency of the original chirp symbol, Hz, f cfo is the carrier frequency offset, Hz; k is the frequency change rate, Hz / s; t is time, s; j is the imaginary part signal.

4. The LoRa concurrent communication demodulation method based on frequency domain interference iterative cancellation according to claim 1 or 2, characterized in that In Step 3, the said low-pass filtering is performed using an IIR low-pass filter.

5. The LoRa concurrent communication demodulation method based on frequency-domain interference iterative cancellation according to claim 1 or 2, characterized in that In Step 3, perform pulse compression on the frequency domain energy of the low-pass filtered LoRa signal, and use a sliding window to find the position of the maximum energy after pulse compression, which is the starting position of the payload of the chirp signal, to achieve signal synchronization; use the size of 10 downchirps for the sliding window; Use a sliding window to perform signal synchronization on the low-pass filtered LoRa signal, and segment the Payload signal in the low-pass filtered LoRa signal according to the time unit.

6. A LoRa concurrent communication demodulation system based on frequency domain interference iterative cancellation, characterized in that, Include: A signal transmission module, taking the chirp signal as the processing unit, and the node end sends the signal in the standard LoRa data packet frame format; A signal reception module, based on the frequency domain characteristics of the pilot part, the gateway end receives the LoRa signal in the conflict state, and the conflict state means that multiple data packets are transmitted in the same time period; A signal preprocessing module, performing low-pass filtering and signal synchronization on the LoRa signal in the conflict state, segmenting it with the chirp length as the step size to obtain multiple chirp symbols, and correcting the carrier frequency offset of the chirp symbols; A conflict signal demodulation module, estimating and eliminating the frequency domain interference of the chirp symbols preprocessed in Step 3 to complete symbol demodulation; In the said conflict signal demodulation module, the estimation of the frequency domain interference includes obtaining the frequency domain peak frequency point and the frequency domain peak height; Among them, the obtaining of the frequency domain peak frequency point includes: where f′ A1-1 , f′ A1-2 is the peak frequency point in the frequency domain of the interference generated by chirp symbol A1 on chirp symbol B1, Hz; f A1-1 , f A1-2 is the peak frequency point in the frequency domain of chirp symbol A1, Hz; BW is the bandwidth, Hz; t 1_2 is the time window offset, s; T is the complete time length of the chirp symbol, s; The obtaining of the frequency domain peak height includes: When : When : where h' A1-1 and h' A1-2 is the peak height in the frequency domain of the interference generated by chirp symbol A1 on chirp symbol B1; h A1-1 and h A1-2 is the peak height in the frequency domain of chirp symbol A1, in Hz; h is the peak energy height of the complete chirp symbol in the frequency domain, in Hz.

7. The LoRa concurrent communication demodulation system based on frequency domain interference iterative cancellation according to claim 6, wherein After the frequency domain interference is estimated, the symbol demodulation process includes: In the frequency domain, eliminate the estimated frequency-domain interference (f′ A1-1 , h′ A1-1 0, (f′ A1-2 , h′ A1-2 ). In the frequency domain after eliminating the interference position, find the frequency point f where the frequency domain peak is the highest; When : When : where: f is the frequency point at the highest peak in the frequency domain of the chirp symbol B1 after interference elimination, in Hz; BW is the bandwidth, in Hz; f 0-B is the starting frequency of the chirp symbol B1, in Hz; finding the starting frequency of the chirp symbol B1 completes the demodulation of the chirp symbol.

8. The LoRa concurrent communication demodulation system based on frequency domain interference iterative cancellation according to claim 6 or 7, characterized in that In the said signal preprocessing module, the specific process of correcting the carrier frequency offset is shown in the following formula; Where: S′ is the chirp symbol after carrier frequency offset correction, S chirp is the original chirp symbol, f0 is the starting frequency of the original chirp symbol, Hz, f cfo is the carrier frequency offset, Hz; k is the frequency change rate, Hz / s; t is the time, s; j is the imaginary part signal.

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