A preamble reference cyclic cross-correlation linear frequency modulation spread spectrum short burst communication method

Abstract

The application discloses a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum short burst communication method. A plurality of up-sweep frequency preambles, down-sweep frame synchronization delimiters and cyclic shift linear frequency modulation load symbols are arranged in a frame; the receiving end estimates integer carrier frequency offset and integer timing offset by using the complementary frequency domain indexes of the preambles and the frame synchronization delimiters, estimates decimal carrier frequency offset, decimal timing offset and sampling frequency offset according to the phase difference between adjacent preambles, the average spectrum main peak neighborhood of the preambles and the cross-symbol frequency domain bin drift, constructs a current frame reference spectrum by using the average spectrum of the preambles, performs cyclic cross-correlation on the load spectrum and the reference spectrum and judges the load symbol by using the maximum correlation position. The model is complete, the design is reasonable, the frequency domain spread and additional peaks caused by complex multipath can be converted into reusable intra-frame reference features, the dependence of the short burst communication on single peak detection under the joint action of strong multipath, time-frequency offset and in-band interference is reduced, and the robustness is improved.

Description

Technical Field

[0001] This invention belongs to the field of reliable transmission technology of the physical layer of wireless communication, and in particular relates to a short burst communication method for preamble reference cyclic cross-correlation linear frequency modulation spread spectrum. When complex near-ground multipath, carrier frequency offset, timing offset, sampling frequency offset and in-band interference coexist, robust synchronization and load detection are achieved by using cyclic cross-correlation between the preamble reference spectrum and the load spectrum. Background Technology

[0002] Ground-based unmanned vehicles, unmanned robotic dogs, and mobile inspection robots, among other near-ground mobile platforms, typically operate in complex environments such as urban roads, industrial parks, factories, and underground passages. Due to ground reflection, wall obstruction, equipment scattering, and non-line-of-sight propagation, near-ground wireless links are prone to issues such as multipath fading, delay spread, carrier frequency offset (CFO), timing offset (TO), sampling frequency offset (SFO), and in-band interference, thus affecting the reliable transmission of short burst control information.

[0003] Existing Direct Sequence Spread Spectrum (DSSS) communication methods can achieve processing gain through spreading codes and can be combined with rake receivers to achieve a certain degree of multipath diversity. However, when bandwidth, processing gain, and short burst frame length are limited, further reducing the bit error rate of DSSS usually requires increasing code length, energy, synchronization overhead, or receiver complexity. Traditional Chirp Spread Spectrum (CSS) receivers utilize linear frequency modulation symbols to spread energy within the frequency band, and LoRa (Long Range) further carries multiple bits of information through cyclic chirp. With its low complexity, low power consumption, and low signal-to-noise ratio demodulation capabilities, it has become a typical physical layer architecture for low-power wide area networks. However, CSS often uses a single-peak decision method that takes the maximum peak value in the frequency domain after dechirp. Under strong multipath and co-channel interference conditions, it is easily affected by peak broadening, additional peaks, and inter-peak competition, leading to symbol decision errors.

[0004] Therefore, existing spread spectrum communication methods still suffer from problems such as separation of synchronization and demodulation, insufficient utilization of multipath frequency domain structure, and poor robustness of single-peak detection in complex near-ground multipath environments, making it difficult to simultaneously meet the requirements of short frame length, low synchronization overhead, and high reliable reception. There is an urgent need for a linear frequency modulation spread spectrum communication method that can utilize intra-frame preamble structures to assist in synchronization and payload decision-making, in order to improve the reliability of short burst communication under complex multipath and in-band interference conditions. Summary of the Invention

[0005] The purpose of this invention is to address the problems of traditional dechirp-DFT single-peak detection being susceptible to peak broadening, additional peaks, inter-peak competition, and in-band interference in complex near-ground multipath environments, and to solve the problem of difficulty in uniformly compensating for CFO, TO, and SFO within short burst frames. This invention proposes a Preamble-Referenced Cyclic Cross-Correlation CSS (PRCC-CSS) communication method, which unifies frame structure, start-of-frame delimiter (SFD) synchronization, reference spectrum construction, and payload demodulation into a single frequency domain structure matching process. The preamble is used for frame detection and time-frequency synchronization, as well as for constructing multipath reference spectra. SFD is used not only for frame boundary determination, but also to form a complementary index with the preamble to recover integer CFO and TO, and further estimate fractional CFO, fractional TO and SFO based on coarse synchronization. The payload symbols no longer depend on a single DFT peak, but are cyclically matched with the preamble reference spectrum. Through cyclic cross-correlation decision, the multipath frequency domain structure is transformed from an unfavorable perturbation into a reusable intra-frame reference feature, and specific implementation steps are given.

[0006] To achieve the objective of this invention, a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum short burst communication method is disclosed, comprising the following steps:

[0007] Step 1: Construct a short burst frame at the transmitting end, which includes a preamble sequence and payload symbols;

[0008] Step 2: At the receiving end, frame detection and coarse synchronization are performed using a preamble sequence, and integer carrier frequency offset (CFO) and integer timing offset (TO) are estimated and compensated.

[0009] Step 3: Based on coarse synchronization, perform fine synchronization to further estimate fractional CFO, fractional TO, and sampling frequency offset SFO;

[0010] Step 4: After completing the synchronization compensation, use the preamble sequence as a reference to perform cyclic cross-correlation detection on the received signal and determine the demodulated payload symbol.

[0011] Furthermore, step 1 specifically includes the following steps:

[0012] The transmitting end constructs a linear frequency modulation spread spectrum short burst frame, which sequentially includes a preamble, a frame synchronization delimiter (SFD), and payload data; based on this, the continuous-time expression of the chirp symbol up-chirp is:

[0013]

[0014] in, The imaginary unit satisfies ; It is a continuous-time variable, representing the time of the up-chirp signal within one symbol period; For signal bandwidth; The chirp symbol period is, and Sampling of the basic up-chirp yields a discrete form.

[0015]

[0016] in , For spreading factor, For the index of discrete-time sampling points, satisfying The continuous-time expression for the chirp notation down-chirp under this foundation is:

[0017]

[0018] The sending end converts the information to be transmitted into a binary bit stream, and then... The data is grouped into sets of 1 bit each, and each set is converted into decimal modulation information. ,in ;

[0019] The modulated up-chirp symbol is represented by a cyclic shift of the basic up-chirp.

[0020]

[0021] in, This represents the modulo operation; to ensure phase continuity between symbols, a phase compensation term is introduced.

[0022]

[0023] Further simplification:

[0024]

[0025] A complete short burst frame consists of a preamble, SFD, and payload data in sequence.

[0026]

[0027] in, The number of basic up-chirps in the leader. This represents the number of basic down-chirps in SFD. The number of modulated up-chirps in the payload data;

[0028] The preamble is used for signal detection, coarse synchronization, and preamble reference spectrum construction; SFD is used for frame synchronization confirmation and joint estimation of carrier frequency offset and symbol timing offset; payload data is used to carry the information to be transmitted.

[0029] Furthermore, step 2 specifically includes the following steps:

[0030] The receiver performs frame detection and coarse synchronization on the received signal to determine the preamble position and SFD position, and makes a preliminary estimate of the carrier frequency offset and symbol timing offset.

[0031] The receiver performs direct noncoherent demodulation on the received signal; first, it performs dechirp processing, then multiplies the received signal by the base down-chirp.

[0032]

[0033] in The signal after dechirp, In order to receive signals, The conjugate of the basic down-chirp; then... Perform Discrete Fourier Transform

[0034]

[0035] in Yes The signal after performing a discrete Fourier transform. For frequency index and The modulus of the DFT output is taken, and the index corresponding to the highest amplitude is selected as the demodulation result.

[0036]

[0037] The receiver uses symbol length Using sampling points as the unit, the received signal is demodulated directly and incoherently using DNC for up-chirp; if continuous If all the demodulation indices of the symbols are the same, it is considered that a preamble has been detected, and the demodulation index is recorded as... ;

[0038] After the preamble detection is completed, the receiver simultaneously performs direct noncoherent demodulation of the received signal for both up-chirp and down-chirp. When the maximum amplitude obtained from down-chirp demodulation is greater than the maximum amplitude obtained from up-chirp demodulation, it is considered that SFD has been detected. For the subsequent... The received signal of one symbol length is demodulated using DNC for down-chirp, and the modulo-divided DFT outputs are summed.

[0039]

[0040] in For traversal A loop variable with _ symbols; select the index corresponding to the largest amplitude value and record it as _. ;

[0041] According to the preamble demodulation index and SFD demodulation index Based on the relationship, a preliminary estimate of CFO and TO is made. CFO has the same influence on up-chirp and down-chirp demodulation, while TO has opposite influences. Therefore, the relationship between the demodulation index of the basic up-chirp in the preceding data and CFO and TO is as follows:

[0042]

[0043] The relationship between the demodulation index of the basic down-chirp in SFD and CFO and TO is as follows:

[0044]

[0045] in CFO is an integer. Let TO be an integer; from the above two equations, we get

[0046]

[0047] in, and The integer CFO and integer TO estimates are used respectively, and then the received signal is initially corrected for CFO and TO.

[0048] Furthermore, step 3 specifically includes the following steps:

[0049] After completing the integer CFO and integer TO corrections in step 2, the receiver performs fine processing on the preamble symbol sequence to estimate the fractional CFO, fractional TO, and sampling frequency offset SFO; the receiver then performs further processing on the second... The dechirp output after integer compensation of the leading symbols is represented as follows:

[0050]

[0051] in The symbol corresponding to the received signal. The output includes the equivalent symbolic structure of fractional CFO, fractional TO, and multipath superposition, as well as noise and interference terms.

[0052] Next, fractional CFO estimation is performed. First, the dechirp outputs of adjacent preamble symbols are phase-differentiated to eliminate the interference with the dechirp outputs. The relevant phase term, the decimal CFO estimate is as follows:

[0053]

[0054] in, This is a decimal CFO estimate. The number of leading up-chirps. Represents complex phase, for The conjugate of the two symbols; to enhance reference stability under multipath conditions, the frequency domain outputs of multiple preamble symbols are averaged.

[0055]

[0056] in, The leading average spectrum, For the first The dechirp-DFT output after leading sign integer and decimal CFO compensation. For frequency domain bin index;

[0057] The fractional TO is obtained by interpolation of the neighborhood of the main peak of the average spectrum.

[0058]

[0059] in, The decimal estimate of TO. for The main peak index; this interpolation is performed only in the neighborhood of the main peak, so the computational complexity is lower than that of the two-dimensional joint search;

[0060] The sampling frequency offset manifests as cross-symbol frequency domain bin drift in the load segment; let the relative deviation of the sampling clock at the receiving end be... The equivalent bin drift is written as

[0061]

[0062] in, This is the actual frequency offset estimate obtained from the CFO estimate. For carrier frequency, The equivalent bin shift caused by SFO between adjacent symbols; the frequency domain index of subsequent payload symbols is... Symbol-by-symbol correction is performed; all the above synchronization parameters are estimated from the same frame preamble, so long-term channel tracking is not required; however, its performance depends on the preamble length, preamble signal-to-noise ratio and intra-frame channel stability.

[0063] Furthermore, step 4 specifically includes the following steps:

[0064] After completing the synchronization compensation, the first The dechirp-DFT output of each load symbol is

[0065]

[0066] in, For the first Frequency domain output of each load symbol For the first time after synchronous compensation Each payload symbol receives a sample. The conjugate of the base up-chirp, For frequency domain bin index;

[0067] When the intra-frame channel is quasi-static and the residual synchronization error is small, its amplitude spectrum can be approximated as a cyclic shift of the multipath equivalent frequency domain structure, i.e.

[0068]

[0069] in, The current frame's multipath equivalent frequency domain structure, For the first The true modulation index of each load symbol This is the disturbance term formed by noise, interference, and residual synchronization error;

[0070] The leading average spectrum is used as the reference spectrum for the current frame, and threshold truncation is applied to suppress noise terms.

[0071]

[0072] in, The truncated reference spectrum. For threshold truncation operators, The threshold is determined by the noise floor or the leading mean spectral quantile. It is an indicator function;

[0073] Therefore, a circular cross-correlation statistic is constructed.

[0074]

[0075] in, For the first Each load symbol in candidate cyclic shift The following matching statistics ;

[0076]

[0077] in, For the first Decision index for each load symbol.

[0078] Compared with the prior art, the significant advancements of this invention are as follows: 1) It provides a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum communication method, which can utilize the complementary frequency domain indexes of the preamble and SFD to achieve joint estimation of integer CFO and TO, and combine adjacent preamble phase difference, main peak neighborhood interpolation and cross-symbol bin drift to complete fractional CFO, fractional TO and SFO compensation, thereby effectively reducing the impact of synchronization error on communication performance under complex time-frequency offset conditions; 2) The proposed preamble reference cyclic cross-correlation linear frequency modulation spread spectrum communication method can utilize the preamble average spectrum to construct the current frame multipath reference structure, and complete the overall frequency domain matching detection through the cyclic cross-correlation between the reference spectrum and the load spectrum, thereby effectively reducing the sensitivity of traditional dechirp-DFT single-peak detection to frequency domain peak broadening, additional peaks and inter-peak competition, and improving the reliability of short burst communication under complex multipath and in-band interference environments.

[0079] To more clearly illustrate the functional characteristics and structural parameters of the present invention, further explanation is provided below in conjunction with the accompanying drawings and specific embodiments. Attached Figure Description

[0080] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0081] Figure 1 This is a schematic diagram of the frame structure of the proposed method;

[0082] Figure 2This is a schematic diagram showing the bit error rate (BER) of the proposed method and the comparative DSSS method as a function of the signal-to-noise ratio per bit (Eb / N0) under the conditions of additive white Gaussian noise (AWGN) channel.

[0083] Figure 3 This is a schematic diagram showing the BER as a function of Eb / N0 for the proposed method and the comparative DSSS method under Extended Typical Urban (ETU) channel conditions.

[0084] Figure 4 This is a schematic diagram showing the BER as a function of Eb / N0 for the proposed method and the comparative DSSS method under ETU superimposed in-band interference conditions.

[0085] Figure 5 This is a schematic diagram showing the BER as a function of signal-to-interference-plus-noise ratio (SINR) for the receivers of the proposed method and the comparative CSS method under ETU superimposed in-band interference conditions.

[0086] Figure 6 This is a schematic diagram of the experimental scenario setup and experimental spectrum analysis results;

[0087] Figure 7 This is a schematic diagram of the verification results of the SDR prototype system. Detailed Implementation

[0088] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0089] This invention discloses a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum short burst communication method, applicable to wireless short burst communication links with complex near-ground multipath interference, carrier frequency offset, timing offset, sampling frequency offset, and in-band interference. First, multiple up-scanning preamble symbols, down-scanning frame synchronization delimiters, and cyclically shifted linear frequency modulation payload symbols are set within a frame. Then, the receiver uses the complementary frequency domain indices of the preamble and frame synchronization delimiters to jointly estimate the integer carrier frequency offset and integer timing offset. Further, based on the phase difference between adjacent preambles, the neighborhood of the main peak of the preamble average spectrum, and cross-symbol frequency domain bin drift, the fractional carrier frequency offset, fractional timing offset, and sampling frequency offset are estimated respectively. Finally, a reference spectrum for the current frame is constructed using the preamble average spectrum, and the payload spectrum is cyclically cross-correlated with the reference spectrum, with the payload symbol determined by the position of maximum correlation. The specific implementation of the preamble reference cyclic cross-correlation linear frequency modulation spread spectrum short burst communication method is as follows:

[0090] Step 1: Construct a short burst frame at the transmitting end, which includes a preamble sequence and payload symbols;

[0091] Step 2: At the receiving end, frame detection and coarse synchronization are performed using a preamble sequence, and integer carrier frequency offset (CFO) and integer timing offset (TO) are estimated and compensated.

[0092] Step 3: Based on coarse synchronization, perform fine synchronization to further estimate fractional CFO, fractional TO, and sampling frequency offset SFO;

[0093] Step 4: After completing the synchronization compensation, use the preamble sequence as a reference to perform cyclic cross-correlation detection on the received signal and determine the demodulated payload symbol.

[0094] Specifically, step 1 includes the following steps:

[0095] The transmitting end constructs a linear frequency modulation spread spectrum short burst frame, which sequentially includes a preamble, a frame synchronization delimiter (SFD), and payload data; based on this, the continuous-time expression of the chirp symbol up-chirp is as follows:

[0096]

[0097] in, The imaginary unit satisfies ; It is a continuous-time variable, representing the time of the up-chirp signal within one symbol period; For signal bandwidth; The chirp symbol period is, and Sampling of the basic up-chirp yields a discrete form.

[0098]

[0099] in , For spreading factor, For the index of discrete-time sampling points, satisfying The continuous-time expression for the chirp notation down-chirp under this foundation is:

[0100]

[0101] The sending end converts the information to be transmitted into a binary bit stream, and then... The data is grouped into sets of 1 bit each, and each set is converted into decimal modulation information. ,in ;

[0102] The modulated up-chirp symbol is represented by a cyclic shift of the basic up-chirp.

[0103]

[0104] in, This represents the modulo operation; to ensure phase continuity between symbols, a phase compensation term is introduced.

[0105]

[0106] Further simplification:

[0107]

[0108] A complete short burst frame consists of a preamble, SFD, and payload data in sequence.

[0109]

[0110] in, The number of basic up-chirps in the leader. This represents the number of basic down-chirps in SFD. The number of modulated up-chirps in the payload data;

[0111] The preamble is used for signal detection, coarse synchronization, and preamble reference spectrum construction; SFD is used for frame synchronization confirmation and joint estimation of carrier frequency offset and symbol timing offset; payload data is used to carry the information to be transmitted.

[0112] Specifically, step 2 includes the following steps:

[0113] The receiver performs frame detection and coarse synchronization on the received signal to determine the preamble position and SFD position, and makes a preliminary estimate of the carrier frequency offset and symbol timing offset.

[0114] The receiver performs direct noncoherent demodulation on the received signal; first, it performs dechirp processing, then multiplies the received signal by the base down-chirp.

[0115]

[0116] in The signal after dechirp, In order to receive signals, The conjugate of the basic down-chirp; then... Perform Discrete Fourier Transform

[0117]

[0118] in Yes The signal after performing a discrete Fourier transform. For frequency index and The modulus of the DFT output is taken, and the index corresponding to the highest amplitude is selected as the demodulation result.

[0119]

[0120] The receiver uses symbol length Using sampling points as the unit, the received signal is demodulated using direct non-coherent DNC ​​(DNC) for up-chirp; if continuous If all the demodulation indices of the symbols are the same, it is considered that a preamble has been detected, and the demodulation index is recorded as... ;

[0121] After the preamble detection is completed, the receiver simultaneously performs direct noncoherent demodulation of the received signal for both up-chirp and down-chirp. When the maximum amplitude obtained from down-chirp demodulation is greater than the maximum amplitude obtained from up-chirp demodulation, it is considered that SFD has been detected. For the subsequent... The received signal of one symbol length is demodulated using DNC for down-chirp, and the modulo-divided DFT outputs are summed.

[0122]

[0123] in For traversal A loop variable with _ symbols; select the index corresponding to the largest amplitude value and record it as _. ;

[0124] According to the preamble demodulation index and SFD demodulation index Based on the relationship, a preliminary estimate of CFO and TO is made. CFO has the same influence on up-chirp and down-chirp demodulation, while TO has opposite influences. Therefore, the relationship between the demodulation index of the basic up-chirp in the preceding data and CFO and TO is as follows:

[0125]

[0126] The relationship between the demodulation index of the basic down-chirp in SFD and CFO and TO is as follows:

[0127]

[0128] in CFO is an integer. Let TO be an integer; from the above two equations, we get

[0129]

[0130] in, and The integer CFO and integer TO estimates are used respectively, and then the received signal is initially corrected for CFO and TO.

[0131] Specifically, step 3 includes the following steps:

[0132] After completing the integer CFO and integer TO corrections in step 2, the receiver performs fine processing on the preamble symbol sequence to estimate the fractional CFO, fractional TO, and sampling frequency offset SFO; the receiver then performs further processing on the second... The dechirp output after integer compensation of the leading symbols is represented as follows:

[0133]

[0134] in The symbol corresponding to the received signal. The output includes the equivalent symbolic structure of fractional CFO, fractional TO, and multipath superposition, as well as noise and interference terms.

[0135] Next, fractional CFO estimation is performed. First, the dechirp outputs of adjacent preamble symbols are phase-differentiated to eliminate the interference with the dechirp outputs. The relevant phase term, the decimal CFO estimate is as follows:

[0136]

[0137] in, This is a decimal CFO estimate. The number of leading up-chirps. Represents complex phase, for The conjugate of the two symbols; to enhance reference stability under multipath conditions, the frequency domain outputs of multiple preamble symbols are averaged.

[0138]

[0139] in, The leading average spectrum, For the first The dechirp-DFT output after leading sign integer and decimal CFO compensation. For frequency domain bin index;

[0140] The fractional TO is obtained by interpolation of the neighborhood of the main peak of the average spectrum.

[0141]

[0142] in, The decimal estimate of TO. for The main peak index; this interpolation is performed only in the neighborhood of the main peak, so the computational complexity is lower than that of the two-dimensional joint search;

[0143] The sampling frequency offset manifests as cross-symbol frequency domain bin drift in the load segment; let the relative deviation of the sampling clock at the receiving end be... The equivalent bin drift is written as

[0144]

[0145] in, This is the actual frequency offset estimate obtained from the CFO estimate. For carrier frequency, The equivalent bin shift caused by SFO between adjacent symbols; the frequency domain index of subsequent payload symbols is... Symbol-by-symbol correction is performed; all the above synchronization parameters are estimated from the same frame preamble, so long-term channel tracking is not required; however, its performance depends on the preamble length, preamble signal-to-noise ratio and intra-frame channel stability.

[0146] Specifically, step 4 includes the following steps:

[0147] After completing the synchronization compensation, the first The dechirp-DFT output of each load symbol is

[0148]

[0149] in, For the first Frequency domain output of each load symbol For the first time after synchronous compensation Each payload symbol receives a sample. The conjugate of the base up-chirp, For frequency domain bin index;

[0150] When the intra-frame channel is quasi-static and the residual synchronization error is small, its amplitude spectrum can be approximated as a cyclic shift of the multipath equivalent frequency domain structure, i.e.

[0151]

[0152] in, The current frame's multipath equivalent frequency domain structure, For the first The true modulation index of each load symbol This is the disturbance term formed by noise, interference, and residual synchronization error;

[0153] The leading average spectrum is used as the reference spectrum for the current frame, and threshold truncation is applied to suppress noise terms.

[0154]

[0155] in, The truncated reference spectrum. For threshold truncation operators, The threshold is determined by the noise floor or the leading mean spectral quantile. It is an indicator function;

[0156] Therefore, a circular cross-correlation statistic is constructed.

[0157]

[0158] in, For the first Each load symbol in candidate cyclic shift The following matching statistics ;

[0159]

[0160] in, For the first Decision index for each load symbol.

[0161] Example

[0162] This invention employs MATLAB for communication link simulation and verifies the prototype system based on a Software-Defined Radio (SDR) platform. The parameter settings provided are for illustrative purposes only and do not constitute a limitation on the scope of protection of this invention.

[0163] The specific embodiments of this invention are as follows. The simulation was performed using MATLAB software, and the parameter settings do not affect the generality. The system bandwidth and sampling rate were both set to 10MHz, and the carrier frequency was 2GHz. The frame structure consists of a preamble up-chirp, an SFD down-chirp, and cyclically shifted chirp payload symbols. The preamble is used for synchronization estimation and reference spectrum construction, the SFD is used for joint estimation of integer CFO and TO, and the payload segment completes symbol decision through cyclic cross-correlation. The simulated channels include three scenarios: AWGN channel, ETU multipath channel, and ETU superimposed in-band interference. Among them, the in-band interference adopts a complex Gaussian suppression interference model, and unless otherwise specified, the jamming-to-signal ratio (JSR) is set to 5dB.

[0164] To verify the performance of this invention, two types of comparison baselines were set up. The first type is the DSSS baseline, which includes three modulation schemes: BPSK, QPSK, and 16QAM. The receiver adopts a 9-finger RAKE / Maximum Ratio Combining (MRC) structure, taking the spreading code length. PRCC-CSS , Both have processing gain. The first category is approximately 27.1 dB, and the relationship between BER and Eb / N0 is compared and analyzed. The second category is the traditional LoRa-type dechirp detection baseline, including DNC and coherent peak detection methods. Both traditional LoRa and PRCC-CSS are taken as follows. and A comparative analysis was conducted on the relationship between BER and SINR.

[0165] Figure 1 This is a schematic diagram of the frame structure of the PRCC-CSS method proposed in this invention. Figure 1 This indicates that the frame structure proposed in this invention consists of a preamble up-chirp segment, an SFD down-chirp synchronization segment, and a cyclically shifted chirp data payload segment. The preamble segment is used for frame detection, fractional CFO estimation, and preamble reference spectrum construction. The SFD synchronization segment is used to form a complementary frequency domain index with the preamble to complete the joint estimation of integer CFO and TO. The data payload segment completes symbol decision through cyclic cross-correlation between the preamble reference spectrum and the payload spectrum. Figure 1 This invention demonstrates that it can unify synchronization estimation, reference spectrum construction, and multipath robust detection into the same frame structure, thereby improving short burst reliable communication capabilities under complex multipath and in-band interference environments.

[0166] Figure 2These are curves showing the BER as a function of Eb / N0 for the receivers of the PRCC-CSS method and the comparative DSSS method proposed in this invention under AWGN channel conditions. The horizontal axis represents Eb / N0, and the vertical axis represents the bit error rate (BER). The curves correspond to PRCC-CSS, DSSS-BPSK, DSSS-QPSK, and DSSS-16QAM, respectively. Figure 2 This indicates that, under AWGN channel conditions, the bit error rate (BER) curve of the proposed PRCC-CSS method is generally located to the left of each DSSS baseline, exhibiting a lower Eb / N0 threshold under the same BER condition. When the BER is... At that time, PRCC-CSS requires approximately 5dB Eb / N0, while the best-performing DSSS baseline requires approximately 8.5-9dB, representing a performance improvement of approximately 3.5-4dB; when BER is At that time, PRCC-CSS requires approximately 5.8-6dB, while the optimal DSSS baseline requires approximately 9.8-10dB, representing a performance improvement of approximately 4dB. Figure 2 This indicates that the leading reference cyclic cross-correlation detection method proposed in this invention can effectively improve the system energy utilization efficiency under AWGN conditions.

[0167] Figure 3 These are the curves showing the BER as a function of Eb / N0 for the receivers of the PRCC-CSS method and the comparative DSSS method proposed in this invention under ETU channel conditions. The horizontal and vertical axes correspond to the curves. Figure 2 same. Figure 3 This indicates that under ETU frequency-selective multipath conditions, the bit error rate (BER) curves of all methods shift to the right compared to the AWGN scenario, but the PRCC-CSS method proposed in this invention still maintains the best BER performance. When the BER is... At that time, PRCC-CSS requires approximately 6.5 dB Eb / N0, while the optimal DSSS baseline requires approximately 10 dB, resulting in a performance improvement of approximately 3.5 dB; when BER is At that time, PRCC-CSS requires about 7.3-7.5dB, while the optimal DSSS baseline requires about 11-12dB, resulting in a performance improvement of about 4dB. Figure 3 This indicates that the method proposed in this invention can use the preamble reference spectrum to match the multipath frequency domain structure of the current frame, thereby effectively improving the robust detection capability in complex multipath environments.

[0168] Figure 4 These are the BER (BER) curves as a function of Eb / N0 for the receivers using the PRCC-CSS method proposed in this invention and the comparative DSSS method under ETU channel superposition in-band interference conditions. (ETU channel superposition) In-band suppression interference, the horizontal and vertical axes and the curves correspond to Figure 2 same. Figure 4This demonstrates that, under the combined effects of ETU multipath and in-band interference, the PRCC-CSS method proposed in this invention still maintains a significantly better bit error rate (BER) performance than any DSSS baseline. When the BER is... At that time, PRCC-CSS requires an Eb / N0 of approximately 5.6 dB, while the optimal DSSS baseline requires approximately 10.8-11.0 dB, representing a performance improvement of approximately 5 dB; when BER is At that time, PRCC-CSS requires approximately 6.4-6.6 dB, while the optimal DSSS baseline requires approximately 12.0-12.3 dB, resulting in a performance improvement of approximately 5.5 dB. Figure 4 This indicates that the leading reference cyclic cross-correlation detection method proposed in this invention can effectively improve the anti-interference capability and reliable communication capability of the system under complex multipath and in-band interference environments.

[0169] Figure 5 This diagram shows the bit error rate (BER) versus signal-to-interference-plus-noise ratio (SINR) of the PRCC-CSS method proposed in this invention and its comparison with traditional CSS receiving methods under ETU channel superimposed in-band interference conditions. In the simulation, the system bandwidth and sampling rate were both set to 10MHz, and the ETU channel superimposed... In-band interference; the comparison methods include traditional DNC and coherent peak detection methods, respectively in and Tests were conducted under the specified conditions. Figure 5 The horizontal axis represents SINR, and the vertical axis represents BER. The curves correspond to PRCC-CSS, DNC, and coherent peak detection methods, respectively. Figure 5 This indicates that the traditional DNC method exhibits significant performance degradation under conditions of strong multipath interference and in-band disturbances. It is difficult to achieve within the test SINR range under the given conditions. Bit error rate Under the conditions to reach It requires approximately 4-5 dB; in contrast, the PRCC-CSS method proposed in this invention achieves [a certain result]. Under the conditions to reach Approximately -5dB is required, in Under these conditions, approximately -11 dB is required, representing a 10-15 dB improvement in SINR threshold compared to traditional DNC. Furthermore, the method proposed in this invention maintains a significant performance advantage over traditional coherent peak detection. Figure 5 This indicates that the cyclic cross-correlation detection method proposed in this invention can effectively reduce the impact of frequency domain peak broadening, additional peaks, and inter-peak competition on decision performance, thereby improving robust detection capability under complex environments.

[0170] Figure 6This section describes the experimental scenario setup and spectrum analysis results. The prototype experiment uses an SDR platform for verification. The experimental system consists of an SDR transmitter, a channel simulator, an in-band interference source, a spectrum analyzer, and a receiver processing unit. The experimental conditions are set as follows: ETU channel and... . Figure 6 (a) An experimental platform consisting of an SDR, a channel simulator, and a spectrum analysis device is shown; Figure 6 (b) gives the actual received spectrum under the conditions of AWGN and ETU superimposed interference. Figure 6 This indicates that under complex multipath and in-band interference conditions, the received spectrum exhibits significant noise floor rise and frequency domain fluctuations, but the PRCC-CSS method proposed in this invention can still achieve stable synchronization and reliable reception. Figure 6 This demonstrates that the method proposed in this invention is feasible in complex environments.

[0171] Figure 7 This is the verification result of the SDR prototype system. The experimental conditions were set as follows: ETU channel and... The receiving end completes synchronization compensation, preamble reference spectrum construction, and cyclic cross-correlation detection. Figure 7 (a) The results of the correlation peak trajectory are given. It can be observed that the position of the correlation peak is consistent with the transmitted symbol index, indicating that a stable cyclic alignment relationship can be formed between the reference spectrum and the payload spectrum after synchronization compensation. Figure 7 (b) The statistics of the minimum decision margin are given, where the 5th percentile is about 1.31 dB and the median is about 2.41 dB, indicating that most reliable frames have obvious separation between the main peak and the competing peak. Figure 7 (c) provides the statistical results of reliable frames. Among the 332 received frames, 300 frames passed the 1dB margin threshold screening, and the reliable frame retention rate reached 90.4%. No symbol errors or bit errors were observed in the screened reliable frames. Figure 7 This demonstrates that the leading reference cyclic cross-correlation detection method proposed in this invention has good engineering robustness and short burst reliable communication capability under complex multipath and in-band interference conditions.

[0172] In summary, the preamble reference cyclic cross-correlation linear frequency modulation spread spectrum communication method proposed in this invention achieves reliable short-burst communication under complex multipath and in-band interference environments by jointly designing the frame structure, synchronization estimation, and cyclic cross-correlation detection. Simulation results show that the proposed method has a lower Eb / N0 threshold than the DSSS method under AWGN, ETU multipath, and ETU superimposed in-band interference conditions. Furthermore, compared to traditional dechirp incoherent peak detection and coherent peak detection methods, the proposed method has a lower SINR threshold and stronger robust detection capability under complex multipath and interference environments. Therefore, this invention can effectively improve the multipath resistance, interference resistance, and engineering reliability of short-burst communication systems in complex near-ground environments.

[0173] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0174] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for short burst communication using a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum, characterized in that: Includes the following steps: Step 1: Construct a short burst frame at the transmitting end, which includes a preamble sequence and payload symbols; Step 2: At the receiving end, frame detection and coarse synchronization are performed using a preamble sequence, and integer carrier frequency offset (CFO) and integer timing offset (TO) are estimated and compensated. Step 3: Based on coarse synchronization, perform fine synchronization to further estimate fractional CFO, fractional TO, and sampling frequency offset SFO; Step 4: After completing the synchronization compensation, use the preamble sequence as a reference to perform cyclic cross-correlation detection on the received signal and determine the demodulated payload symbol.

2. The method for short burst communication with a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum according to claim 1, characterized in that, Step 1 specifically includes the following steps: The transmitting end constructs a linear frequency modulation spread spectrum short burst frame, which sequentially includes a preamble, a frame synchronization delimiter (SFD), and payload data; based on this, the continuous-time expression of the chirp symbol up-chirp is: in, The imaginary unit satisfies ; It is a continuous-time variable, representing the time of the up-chirp signal within one symbol period; For signal bandwidth; The chirp symbol period is, and Sampling of the basic up-chirp yields a discrete form. in , For spreading factor, For the index of discrete-time sampling points, satisfying The continuous-time expression for the chirp notation down-chirp under this foundation is: The sending end converts the information to be transmitted into a binary bit stream, and then... The data is grouped into sets of 1 bit each, and each set is converted into decimal modulation information. ,in ; The modulated up-chirp symbol is represented by a cyclic shift of the basic up-chirp. in, This represents the modulo operation; to ensure phase continuity between symbols, a phase compensation term is introduced. Further simplification: A complete short burst frame consists of a preamble, SFD, and payload data in sequence. in, The number of basic up-chirps in the leader. This represents the number of basic down-chirps in SFD. The number of modulated up-chirps in the payload data; The preamble is used for signal detection, coarse synchronization, and preamble reference spectrum construction; SFD is used for frame synchronization confirmation and joint estimation of carrier frequency offset and symbol timing offset; payload data is used to carry the information to be transmitted.

3. The method for short burst communication with a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum according to claim 1, characterized in that, Step 2 specifically includes the following steps: The receiver performs frame detection and coarse synchronization on the received signal to determine the preamble position and SFD position, and makes a preliminary estimate of the carrier frequency offset and symbol timing offset. The receiver performs direct noncoherent demodulation on the received signal; first, it performs dechirp processing, then multiplies the received signal by the base down-chirp. in The signal after dechirp, In order to receive signals, The conjugate of the basic down-chirp; then... Perform Discrete Fourier Transform in Yes The signal after performing a discrete Fourier transform. For frequency index and The modulus of the DFT output is taken, and the index corresponding to the highest amplitude is selected as the demodulation result. The receiver uses symbol length Using sampling points as the unit, the received signal is demodulated directly and incoherently using DNC for up-chirp; if continuous If all the demodulation indices of the symbols are the same, it is considered that a preamble has been detected, and the demodulation index is recorded as... ; After the preamble detection is completed, the receiver simultaneously performs direct noncoherent demodulation of the received signal for both up-chirp and down-chirp. When the maximum amplitude obtained from down-chirp demodulation is greater than the maximum amplitude obtained from up-chirp demodulation, it is considered that SFD has been detected. For the subsequent... The received signal of one symbol length is demodulated using DNC for down-chirp, and the modulo-divided DFT outputs are summed. in For traversal A loop variable with _ symbols; select the index corresponding to the largest amplitude value and record it as _. ; According to the preamble demodulation index and SFD demodulation index Based on the relationship, a preliminary estimate of CFO and TO is made. CFO has the same influence on up-chirp and down-chirp demodulation, while TO has opposite influences. Therefore, the relationship between the demodulation index of the basic up-chirp in the preceding data and CFO and TO is as follows: The relationship between the demodulation index of the basic down-chirp in SFD and CFO and TO is as follows: in CFO is an integer. Let TO be an integer; from the above two equations, we get in, and The integer CFO and integer TO estimates are used respectively, and then the received signal is initially corrected for CFO and TO.

4. The method for short burst communication with a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum according to claim 1, characterized in that, Step 3 specifically includes the following steps: After completing the integer CFO and integer TO corrections in step 2, the receiver performs fine processing on the preamble symbol sequence to estimate the fractional CFO, fractional TO, and sampling frequency offset SFO; the receiver then performs further processing on the second... The dechirp output after integer compensation of the leading symbols is represented as follows: in The symbol corresponding to the received signal. The output includes the equivalent symbolic structure of fractional CFO, fractional TO, and multipath superposition, as well as noise and interference terms. Next, fractional CFO estimation is performed. First, the dechirp outputs of adjacent preamble symbols are phase-differentiated to eliminate the interference with the dechirp outputs. The relevant phase term, the decimal CFO estimate is as follows: in, This is a decimal CFO estimate. The number of leading up-chirps. Represents complex phase, for The conjugate of the two symbols; to enhance reference stability under multipath conditions, the frequency domain outputs of multiple preamble symbols are averaged. in, The leading average spectrum, For the first The dechirp-DFT output after leading sign integer and decimal CFO compensation. For frequency domain bin index; The fractional TO is obtained by interpolation of the neighborhood of the main peak of the average spectrum. in, This is a decimal estimate of TO. for The main peak index; this interpolation is performed only in the neighborhood of the main peak, so the computational complexity is lower than that of the two-dimensional joint search; The sampling frequency offset manifests as cross-symbol frequency domain bin drift in the load segment; let the relative deviation of the sampling clock at the receiving end be... The equivalent bin drift is written as in, This is the actual frequency offset estimate obtained from the CFO estimate. For carrier frequency, The equivalent bin shift caused by SFO between adjacent symbols; the frequency domain index of subsequent payload symbols is... Symbol-by-symbol correction is performed; all the above synchronization parameters are estimated from the same frame preamble, so long-term channel tracking is not required; however, its performance depends on the preamble length, preamble signal-to-noise ratio and intra-frame channel stability.

5. The method for short burst communication with a preamble reference cyclic cross-correlation linear frequency modulation spread spectrum according to claim 1, characterized in that, Step 4 specifically includes the following steps: After completing the synchronization compensation, the first The dechirp-DFT output of each load symbol is in, For the first Frequency domain output of each load symbol For the first time after synchronous compensation Each payload symbol receives a sample. The conjugate of the base up-chirp, For frequency domain bin index; When the intra-frame channel is quasi-static and the residual synchronization error is small, its amplitude spectrum can be approximated as a cyclic shift of the multipath equivalent frequency domain structure, i.e. in, The current frame's multipath equivalent frequency domain structure, For the first The true modulation index of each load symbol This is the disturbance term formed by noise, interference, and residual synchronization error; The leading average spectrum is used as the reference spectrum for the current frame, and threshold truncation is applied to suppress noise terms. in, The truncated reference spectrum. For threshold truncation operators, The threshold is determined by the noise floor or the leading mean spectral quantile. It is an indicator function; Therefore, a circular cross-correlation statistic is constructed. in, For the first Each load symbol in the candidate cyclic shift Matching statistics below ; in, For the first Decision index for each load symbol.

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