Joint synchronization and frequency offset estimation method and system for FSCM signal

Abstract

The invention provides an FSCM signal joint synchronization and frequency offset estimation method and system, and the method comprises the steps: carrying out the preprocessing of an FSCM signal at a receiving end, and sequentially carrying out the signal detection, block synchronization and decimal frequency offset estimation; compensating the signal based on the estimated decimal frequency offset, and completing block synchronization correction and fine synchronization through iterative correction to obtain an initial position of a first data block and a position of a first optimal sampling point; carrying out time delay compensation by taking the position of the sampling point as a reference, and carrying out secondary correction on the position of the data block; and finally, integral frequency offset and time delay are jointly estimated based on a corrected result, final compensation and correction are carried out, and a first data sampling point is accurately positioned. The invention provides a joint frequency offset estimation, time delay estimation and synchronous correction method for the FSCM signal, which eliminates potential mutual influence among different estimators and can realize high-performance synchronization and frequency offset estimation under an extremely low signal-to-noise ratio.

Description

Technical Field

[0001] This invention relates to the field of wireless communication, and more specifically, to a method and system for joint synchronization and frequency offset estimation of FSCM signals. Background Technology

[0002] FSCM (Frequency Shift Chirp Modulation) is a modulated signal based on chirp signals. It inherits the advantages of chirp signals, such as low power consumption, strong anti-interference capabilities, and long-distance communication, while significantly improving the communication capacity of chirp signals by shifting the spectrum to carry information. Currently, FSCM applications are concentrated in the Internet of Things (IoT) field, primarily using the ISM (Industrial, Scientific, and Medical) band. Due to its characteristics similar to frequency hopping and spread spectrum, FSCM also possesses strong stealth and anti-interception capabilities, providing a new solution for low-speed, long-range military communications.

[0003] FSCM information is represented by spectral shifting of chirps, making it particularly sensitive to time delay and frequency offset. Frequency offset directly causes a spectral shift in the signal, leading to errors in demodulated symbols; while time delay is indirectly reflected in the spectral shift, significantly impacting demodulation performance. Therefore, the effects of time delay and frequency offset on FSCM signal demodulation are coupled, and neither can be accurately estimated independently. Furthermore, FSCM signals are frequently used in scenarios with extremely low signal-to-noise ratios, posing new challenges to the estimation of their time delay and frequency offset.

[0004] Due to the unique form of FSCM signals, demodulation can be cleverly achieved through block division, conjugate multiplication, DFT (Discrete Fourier Transform), and peak value calculation. This specific demodulation method can also be applied to the synchronization and frequency offset estimation of FSCM signals. Compared to traditional methods based on correlation sequences, this method significantly reduces computational complexity through FFT calculation and also mitigates the effects of multipath propagation.

[0005] Current research on FSCM signals mostly focuses on modulation and demodulation, as well as different waveform designs, with relatively little research on synchronization and frequency offset estimation, and even that research is incomplete. These studies often make idealized assumptions about certain steps of the receiving system and then demonstrate the validity of specific steps, lacking a holistic consideration of the synchronization and frequency offset estimation system. At the same time, research on signal detection, the primary step in synchronization methods, is relatively scarce, and specific implementation methods are lacking.

[0006] Patent document CN113194053A discloses a high-speed transmission multi-channel LoRa modulation and demodulation method based on fractional Fourier transform, but it mainly provides a multiple access method for LoRa that effectively reduces collisions, solving the problem of limited transmission rate of current LoRa technology.

[0007] The present invention aims to design a relatively complete synchronization and frequency offset estimation method, covering the entire process from the arrival detection of the baseband received signal to the demodulation of the received signal, so as to achieve the overall optimal performance of synchronization and frequency offset estimation. Summary of the Invention

[0008] In view of the deficiencies in the prior art, the purpose of this invention is to provide a method and system for joint synchronization and frequency offset estimation of FSCM signals.

[0009] A joint synchronization and frequency offset estimation method for FSCM signals provided by the present invention includes: Step S1: At the transmitting end, the transmitted signal is modulated by FSCM to obtain an FSCM signal, which is then sent to the receiving end; Step S2: Enable the receiver to receive the FSCM signal and verify it; Step S3: Perform block synchronization on the received FSCM signal and obtain the fractional frequency offset based on the preamble signal; Step S4: Based on the fractional frequency offset, perform frequency offset compensation on the FSCM signal, and perform block synchronization correction and fine synchronization on it to obtain the initial position of the first data block; Step S5: Based on the results of fine synchronization, perform time delay compensation on the FSCM signal and perform secondary block synchronization correction to locate the precise position of the first data block; Step S6: Based on the result of the block synchronization secondary correction, jointly estimate the integer multiple frequency offset and time delay, perform final frequency offset compensation and fine synchronization correction on the FSCM signal, locate and output the final position of the first data sampling point.

[0010] Preferably, step S1 includes the following sub-steps: Step S1.1: Express the unmodulated chirp signal and its normalized frequency as follows:

[0011]

[0012] Where n is the discrete time. SF is the spreading factor, indicating that each symbol can carry SF bits of information, including... One sampling point; The modulated FSCM signal and its normalized frequency are represented as follows:

[0013]

[0014] Where m is the information to be modulated. ; Step S1.2: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require the full context.] The up-chirp symbols of s0[n], A down-chirp symbol and A frame is composed of s[n] data symbols, which are then upsampled four times, modulated to radio frequency for transmission, received by the receiver, and downconverted to baseband.

[0015] Preferably, step S2 includes the following sub-steps: Step S2.1: Divide the received signal into 4 channels according to each sampling point, and each channel is divided into... For blocks of length, multiply each block by the conjugate of up-chirp, and denote the result as... , represented as:

[0016] Where s * 0[n] is the conjugate of s0[n]; perform a DFT on the result of the multiplication, and denote the result as... :

[0017] but

[0018] Take the modulo of the result, and denote the calculated value of the i-th block as... ; Step S2.2: Calculate the mean

[0019] in Calculate the average number of blocks for block synchronization; Step S2.3: Denote the peak value of each mean as , represented as:

[0020] When there is When the value is greater than a certain threshold, that is:

[0021] An FSCM signal has been detected; among which For scaling parameters, For noise parameters, take as .

[0022] Preferably, step S3 includes the following sub-steps: Step S3.1: Starting from the arrival of the FSCM signal, calculate the block with the highest peak value, and denote its index as k, represented as:

[0023] The k-th block is identified as the first block in the received signal containing the FSCM preamble, and the j-th sampling point with the highest peak value is recorded. Step S3.2: Starting from the k-th block of the j-th channel, record the received signal of each block as follows: The corresponding transmitting signal is , decimal frequency deviation The effect on the received signal is expressed as follows:

[0024] Estimate of decimal octave frequency deviation It can be obtained from the following formula:

[0025] Where * represents the conjugate of the corresponding signal.

[0026] Preferably, step S4 includes the following sub-steps: Step S4.1: Using the values ​​obtained in step S3.2 Perform frequency offset compensation on the received signal, and repeat step S3.1 to update k and j; Step S4.2: Record the peak position of the k-th block as p, i.e.

[0027] Let q be the point of precise synchronization, and q be represented as:

[0028] The precise synchronization point is the position of the q-th point of the k-th block of the j-th channel of the received signal; this position is the first point of the preamble of the received signal.

[0029] Preferably, step S5 includes the following sub-steps: Step S5.1: Synchronize the received signal according to j, k, q in step S4.2; Step S5.2: Repeat steps S2.2 and S3.1 to update k; Step S5.3: Synchronize the received signal based on the updated k.

[0030] Preferably, step S6 includes the following sub-steps: Step S6.1: Take a block of one symbol length from the down-chirp portion, multiply it by the conjugate of the standard down-chirp, calculate the DFT, find the peak, and record the peak position as . ; Step S6.2: Let Integer multiple frequency offset estimation and secondary synchronization point Represented as

[0031]

[0032] Step S6.3: Use Frequency offset compensation is performed on the received signal, using Perform precise synchronization correction to obtain the starting position of the data symbols.

[0033] A joint synchronization and frequency offset estimation system for FSCM signals provided by the present invention includes: Module M1: At the transmitting end, the transmitted signal is modulated by FSCM to obtain an FSCM signal, which is then sent to the receiving end; Module M2: Enables the receiver to receive and verify the FSCM signal; Module M3: Performs block synchronization on the received FSCM signal and obtains the fractional frequency offset based on the preamble signal; Module M4: Based on the fractional frequency offset, the FSCM signal is compensated for frequency offset, and block synchronization correction and fine synchronization are performed on it to obtain the initial position of the first data block; Module M5: Based on the results of fine synchronization, it performs time delay compensation on the FSCM signal and performs secondary block synchronization correction to locate the precise position of the first data block; Module M6: Based on the results of the block synchronization secondary correction, it jointly estimates the integer multiple frequency offset and time delay, performs final frequency offset compensation and fine synchronization correction on the FSCM signal, and locates and outputs the final position of the first data sampling point.

[0034] Preferably, module M1 includes the following sub-modules: Module M1.1: Represents the unmodulated chirp signal and its normalized frequency as follows:

[0035]

[0036] Where n is the discrete time. SF is the spreading factor, indicating that each symbol can carry SF bits of information, including... One sampling point; The modulated FSCM signal and its normalized frequency are represented as follows:

[0037]

[0038] Where m is the information to be modulated. ; Module M1.2: will The up-chirp symbols of s0[n], A down-chirp symbol and A frame is composed of s[n] data symbols, which are then upsampled four times, modulated to radio frequency for transmission, received by the receiver, and downconverted to baseband.

[0039] Preferably, module M2 includes the following sub-modules: Module M2.1: Divides the received signal into 4 channels based on each sampling point, with each channel divided into... For blocks of length, multiply each block by the conjugate of up-chirp, and denote the result as... , represented as:

[0040] Where s * 0[n] is the conjugate of s0[n]; perform a DFT on the result of the multiplication, and denote the result as... :

[0041] but

[0042] Take the modulo of the result, and denote the calculated value of the i-th block as... ; Module M2.2: Calculate the mean

[0043] in Calculate the average number of blocks for block synchronization; Module M2.3: Let the peak value of each mean be denoted as . , represented as:

[0044] When there is When the value is greater than a certain threshold, that is:

[0045] An FSCM signal has been detected; among which For scaling parameters, For noise parameters, take as .

[0046] Preferably, module M3 includes the following sub-modules: Module M3.1: Starting from the arrival of the FSCM signal, calculate the block with the highest peak value, denoted by index k, and represented as:

[0047] The k-th block is identified as the first block in the received signal containing the FSCM preamble, and the j-th sampling point with the highest peak value is recorded. Module M3.2: Starting from the k-th block of the j-th channel, record the received signal of each block as follows: The corresponding transmitting signal is , decimal frequency deviation The effect on the received signal is expressed as follows:

[0048] Estimate of decimal octave frequency deviation It can be obtained from the following formula:

[0049] Where * represents the conjugate of the corresponding signal.

[0050] Preferably, module M4 includes the following sub-modules: Module M4.1: Obtained using module M3.2 The received signal is frequency offset compensated, and module M3.1 is executed again to update k and j; Module M4.2: Records the peak position of the k-th block as p, i.e.

[0051] Let q be the point of precise synchronization, and q be represented as:

[0052] The precise synchronization point is the position of the q-th point of the k-th block of the j-th channel of the received signal; this position is the first point of the preamble of the received signal.

[0053] Preferably, module M5 includes the following sub-modules: Module M5.1: Synchronizes the received signal according to j, k, q of module M4.2; Module M5.2: Re-execute modules M2.2 and M3.1, and update k; Module M5.3: Synchronizes received signals based on the updated k.

[0054] Preferably, module M6 includes the following sub-modules: Module M6.1: Take a block of one symbol length from the down-chirp region, multiply it by the conjugate of the standard down-chirp, calculate the DFT, find the peak, and record the peak position as . ; Module M6.2: Command Integer multiple frequency offset estimation and secondary synchronization point Represented as

[0055]

[0056] Module M6.3: Use Frequency offset compensation is performed on the received signal, using Perform precise synchronization correction to obtain the starting position of the data symbols.

[0057] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention proposes a complete method for FSCM signal synchronization and frequency offset estimation, which can provide design guidance for the entire process from received signal detection to signal demodulation.

[0058] 2. This invention proposes a joint frequency offset estimation, time delay estimation and synchronization correction method for FSCM signals, which eliminates the potential mutual influence between different estimators and can achieve high-performance synchronization and frequency offset estimation under extremely low signal-to-noise ratio.

[0059] 3. This invention proposes using the average of multiple peak values ​​as the decision statistic for signal detection and designs an adaptive threshold based on noise averaging, which can achieve a high detection probability while ensuring a low false alarm rate. Attached Figure Description

[0060] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart of the joint synchronization and frequency offset estimation method for FSCM signals.

[0061] Figure 2 The spectrum of the FSCM signal when it is modulated into a frame.

[0062] Figure 3 Spectrum diagram for receiving up-chirp blocks.

[0063] Figure 4 This is a schematic diagram of the secondary correction for block synchronization.

[0064] Figure 5 This is a schematic diagram illustrating the effects of time delay and frequency offset on the FSCM signal.

[0065] Figure 6 This diagram illustrates the performance comparison of FSCM signals under different spreading factors.

[0066] Figure 7 This diagram illustrates the performance comparison of FSCM signals using different methods. Detailed Implementation

[0067] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0068] A method for joint synchronization and frequency offset estimation of FSCM signals, comprising: Step S1: At the transmitting end, the transmitted signal is modulated by FSCM to obtain an FSCM signal, which is then sent to the receiving end; Step S2: Enable the receiver to receive the FSCM signal and verify it; Step S3: Perform block synchronization on the received FSCM signal and obtain the fractional frequency offset based on the preamble signal; Step S4: Based on the fractional frequency offset, perform frequency offset compensation on the FSCM signal, and perform block synchronization correction and fine synchronization on it to obtain the initial position of the first data block; Step S5: Based on the results of fine synchronization, perform time delay compensation on the FSCM signal and perform secondary block synchronization correction to locate the precise position of the first data block; Step S6: Based on the result of the block synchronization secondary correction, jointly estimate the integer multiple frequency offset and time delay, perform final frequency offset compensation and fine synchronization correction on the FSCM signal, locate and output the final position of the first data sampling point.

[0069] like Figure 1 As shown, in one embodiment, the above steps specifically include: Step 1: At the transmitting end, the transmitted signal is modulated using FSCM and sent to the receiving end.

[0070] Step 2: Detect whether an FSCM signal has arrived.

[0071] Step 3: After determining that an FSCM signal has arrived, perform block synchronization, and then estimate the fractional frequency offset based on the preamble signal.

[0072] Step 4: After frequency offset compensation of the received signal, block synchronization correction and fine synchronization are performed on the received signal to determine the position of the first block containing data and the position of the first optimal sampling point of the received signal.

[0073] Step 5: Based on the results of fine synchronization, perform time delay compensation on the received signal, perform secondary block synchronization correction, and locate the position of the first data block.

[0074] Step 6: Perform joint estimation of integer multiple frequency offset and time delay, perform frequency offset compensation and fine synchronization correction, and accurately locate the position of the first data sampling point.

[0075] Step 7: Perform subsequent demodulation steps, etc. Step 1 includes the following steps: Step 1.1: The unmodulated chirp signal and its normalized frequency can be expressed as: (1) (2) Where n is the discrete time. SF stands for spreading factor, indicating that each symbol can carry SF bits of information, including... There are 10 sampling points. The modulated FSCM signal and its normalized frequency can be expressed as: (3) (4) Where m is the information to be modulated. .

[0076] Step 1.2: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require the full context.] The up-chirp symbol as shown in (1), A down-chirp symbol (the conjugate of an up-chirp) and Data symbols as shown in (3) form a frame, which is then upsampled four times, modulated to radio frequency for transmission, received by the receiver, and downconverted to baseband.

[0077] Step 2 includes the following steps: Step 2.1: Divide the received signal into 4 channels according to each sampling point, and each channel is divided into... For blocks of length, multiply each block by the conjugate of up-chirp, and denote the result as... , represented as (5) Where s * 0[n] is the conjugate of s0[n]. The DFT of the multiplication result is taken, and the result is denoted as...

[0078] (6) It is evident that (7) Formulas (5) and (6) ignore noise terms. Calculate the modulus of the result, and record the calculated value of the i-th block as... .

[0079] Step 2.2: Calculate the mean (8) in Calculate the average number of blocks for block synchronization.

[0080] Step 2.3: Denote the peak value of each mean as , represented as (9) When there is When the value is greater than a certain threshold, that is (10) An FSCM signal has been detected. For scaling parameters, For noise parameters, take as (11) Step 3 includes the following steps: Step 3.1: Starting from the arrival of the FSCM signal, calculate the block with the highest peak value, and denote its index as k, represented as... (12) The k-th block is considered to be the first block in the received signal containing the FSCM preamble, and the j-th sampling point with the highest peak value is recorded.

[0081] Step 3.2: Starting from the k-th block of the j-th channel, record the received signal of each block as follows: The corresponding transmitting signal is , decimal frequency deviation The effect on the received signal can be expressed as (13) Estimate of decimal octave frequency deviation It can be obtained from the following formula (14) Where * represents the conjugate of the corresponding signal.

[0082] Step 4 includes the following steps: Step 4.1: Using the values ​​obtained in Step 3.2 Perform frequency offset compensation on the received signal, and repeat step 3.1 to update k and j.

[0083] Step 4.2: Record the peak position of the k-th block as p, i.e. (15) The definition is as described in step S2.2. Let q be the point of precise synchronization, and q is represented as... (16) The precise synchronization point is the position of the q-th point in the k-th block of the j-th channel of the received signal. This position is the first point of the preamble of the received signal.

[0084] Step 5 includes the following steps: Step 5.1: Synchronize the received signal according to j, k, q as shown in step 4.2.

[0085] Step 5.2: To eliminate the possible influence of q on k, execute steps 2.2 and 3.1 again to update k.

[0086] Step 5.3: Synchronize the received signal according to the new k.

[0087] Step 6 includes the following steps: Step 6.1: Take a block of one symbol length from the down-chirp portion, multiply it by the conjugate of the standard down-chirp, calculate the DFT, find the peak, and record the peak position as . .

[0088] Step 6.2: Let Integer multiple frequency offset estimation and secondary synchronization point It can be represented as (17) (18) Step 6.3: Use Frequency offset compensation is performed on the received signal, using Perform precise synchronization correction to obtain the starting position of the data symbols.

[0089] Example 1 This invention specifically divides the proposed method into four parts: signal detection, detecting the arrival of a target signal; block synchronization, locating the first block of the FSCM received signal; fine synchronization, i.e., delay estimation, locating the first sampling point of the data; and frequency offset estimation, estimating the frequency offset of the received signal relative to the transmitted signal. These four parts overlap, forming a complete process from the detection of the baseband received signal to the accurate location of the data signal. The flowchart of the proposed FSCM signal joint synchronization frequency offset estimation method is shown below. Figure 1 As shown, the main body of the method is within the dashed box. The spreading factor selected in this embodiment... ,bandwidth Signed rate bit rate .

[0090] The technical solution of the present invention is as follows: Step 1: At the transmitting end, the transmitted signal is modulated using FSCM and sent to the receiving end.

[0091] Step 2: Detect whether an FSCM signal has arrived.

[0092] Step 3: After determining that an FSCM signal has arrived, perform block synchronization and estimate the fractional frequency offset based on the preamble signal.

[0093] Step 4: After frequency offset compensation of the received signal, block synchronization correction and fine synchronization are performed on the received signal to determine the position of the first block containing data and the position of the first optimal sampling point of the received signal.

[0094] Step 5: Based on the results of fine synchronization, perform time delay compensation on the received signal, perform secondary block synchronization correction, and locate the position of the first data block.

[0095] Step 6: Perform joint estimation of integer multiple frequency offset and time delay, perform frequency offset compensation and fine synchronization correction, and accurately locate the position of the first data sampling point.

[0096] Step 7: Perform subsequent demodulation steps, etc. Step 1 includes the following steps: Step 1.1: The unmodulated chirp signal and its normalized frequency can be expressed as: (19) (20) Where n is the discrete time. SF stands for spreading factor, indicating that each symbol can carry SF bits of information, including... There are 10 sampling points. The modulated FSCM signal and its normalized frequency can be expressed as: (twenty one) (twenty two) Where m is the information to be modulated. .

[0097] Step 1.2: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require the full context.] The up-chirp symbol as shown in (1), A down-chirp symbol (the conjugate of an up-chirp) and A frame is composed of data symbols as shown in (3). The time spectrum of a frame is shown in Figure 1. Figure 2As shown. 1 and 5 represent the guard interval, 2 is the up-chirp symbol, 3 is the down-chirp symbol, and 4 is the data symbol. Symbols 2 and 3 together form the preamble, used in the joint synchronization and frequency offset calculation in this example. In this example... , , , The larger the value, the better the synchronization performance. The larger the value, the better the frequency offset estimation performance.

[0098] Then, after being upsampled four times, it is modulated to the radio frequency for transmission, received by the receiver, and downconverted to the baseband.

[0099] Step 2 includes the following steps: Step 2.1: Divide the received signal into 4 channels according to each sampling point, and each channel is divided into... For blocks of length, multiply each block by the conjugate of up-chirp, and denote the result as... , represented as (twenty three) Where s * 0[n] is the conjugate of s0[n]. The DFT of the multiplication result is taken, and the result is denoted as... , represented as (twenty four) It is evident that (25) Formulas (23) and (24) ignore noise terms. The modulus of the result is calculated, and the calculated value of the i-th block is recorded as... .

[0100] Since the preamble consists of 6 identical up-chirps and 2.25 identical down-chirps, when the received signal is segmented, the segments are not aligned by sign, resulting in FSCM signal segments with the following issues in the up-chirp portion: Figure 3 The form shown is the same as Consistent. The presence or absence of peak values ​​can be used as a standard for detecting the arrival of FSCM signals. Peak position can be used as a standard for fine synchronization calculation.

[0101] Step 2.2: Calculate the mean (26) in Calculate the average number of blocks for block synchronization. In this example, we take... That is, the length of the up-chirp portion.

[0102] Step 2.3: Denote the peak value of each mean as , represented as (27) When there is When the value is greater than a certain threshold, that is (28) An FSCM signal has been detected. The scaling parameter can be adjusted to balance the detection probability and the false alarm probability; in this example, it is selected as 3.5. For noise parameters, take as (29) Step 3 includes the following steps: Step 3.1: Starting from the arrival of the FSCM signal, calculate the block with the highest peak value, and denote its index as k, represented as... (30) The k-th block is considered to be the first block in the received signal containing the FSCM preamble, and the j-th sampling point with the highest peak value is recorded.

[0103] Step 3.2: Starting from the k-th block of the j-th channel, record the received signal of each block as follows: The corresponding transmitting signal is , decimal frequency deviation The effect on the received signal can be expressed as (31) Estimate of decimal octave frequency deviation It can be obtained from the following formula (32) Where * represents the conjugate of the corresponding signal.

[0104] Since the fractional frequency offset has a significant impact on the peak value and peak position calculated in step 2, the k and j calculated in step 3.1 block synchronization are inaccurate and require block synchronization correction. Because the fractional frequency offset will cause an offset of at most one block to k, and as mentioned in step 5, it may cause an offset of at most one block to k, the block synchronization correction in step 4 below will start from the (k-2)th block.

[0105] Step 4 includes the following steps: Step 4.1: Using the values ​​obtained in Step 3.2 Frequency offset compensation is performed on the received signal. At this point, the influence of fractional frequency offset on the DFT peak and peak position is eliminated. Step 3.1 is executed again to update k and j, and the block synchronization result of step 3.1 is corrected. The j obtained at this time is accurate, and the sampling points of other paths can be discarded to reduce overhead; however, the accuracy of the k value is still affected by the fine synchronization result and needs to be corrected a second time, as described in step 5.

[0106] Step 4.2: Record the peak position of the k-th block as p, i.e. (33) The definition is as described in step S2.2. Let q be the point of precise synchronization, and q is represented as... (34) The precise synchronization point is the position of the q-th point in the k-th block of the j-th channel of the received signal. This position is the first point of the preamble of the received signal.

[0107] Step 5 includes the following steps: Step 5.1: Synchronize the received signal according to j, k, q as shown in Step 4.2. However, the position of fine synchronization will affect the accuracy of k, such as... Figure 4 As shown, since an up-chirp is typically allocated across two blocks, during reception... Each up-chirp will most likely have actual coverage. There are several blocks. During block synchronization, due to noise, k may be located in block i+1 or i+2. Especially when p is very small, the block synchronization in step 4.1 will most likely locate block i+2, causing a block location error. Therefore, the block synchronization result needs to be corrected a second time to correctly locate block i+1.

[0108] Therefore, when synchronizing the signal, the received signal is synchronized according to the j-th channel, the (k-1)-th block, and the q-th sampling point.

[0109] Step 5.2: To eliminate the potential influence of q on k, execute steps 2.2 and 3.1 again to update k. After executing step 2.2, the value of q becomes 0. One up-chirp just covers it. By performing block synchronization again in step 3.2, the accurate value of k can be obtained.

[0110] Step 5.3: Perform synchronization compensation on the received signal according to the new k.

[0111] Step 6 includes the following steps: Step 6.1: Take a block of one symbol length from the down-chirp portion, multiply it by the conjugate of the standard down-chirp, calculate the DFT, find the peak, and record the peak position as . In FSCM signals, frequency offset and time delay have similar effects, both manifesting as frequency spectrum shifts. For example... Figure 5 As shown, where Figure 5 'a' represents the ideal received signal and the signal after time delay and frequency offset. Figure 5 b is Figure 5 a. The sampled signal. It can be seen that after sampling, the q value estimated in step 4.2 for fine synchronization is actually the part where the real delay and the real frequency offset cancel each other out. This cancellation effect becomes superposition in the down-chirp part. Therefore, the real frequency offset and the delay canceled out during the first fine synchronization can be estimated by the peak value of the down-chirp part.

[0112] Step 6.2: Let the integer multiple frequency offset estimate be... The second precision synchronization point is So there are (35) remember The estimation of frequency offset and time delay can be expressed as: (36) (37) Step 6.3: Use Frequency offset compensation is performed on the received signal, using By performing precise synchronization correction, the starting position of the data symbols can be obtained.

[0113] The effects of this invention can be illustrated using MATLAB simulation. Specifically, the MATLAB simulation conditions are MATLAB R2014a simulation software, with the following settings: spreading factor of 7, bandwidth of 125kHz, and normalized delay of... Random values ​​between, normalized frequency offset is Random values ​​between; the number of iterations is 100,000. The simulation content and results are as follows: 1) Performance comparison of the FSCM signal joint synchronization and frequency offset estimation method described in this paper under different spreading factors. Figure 6 As shown, when SF=7, this method can achieve a bit error rate of approximately 1% at -7dB. This proves that this method can achieve high-performance synchronization and frequency offset estimation at extremely low signal-to-noise ratios. When SF increases by 2, the SNR can be reduced by about 5dB at the same bit error rate, but the communication rate decreases exponentially at the same bandwidth.

[0114] 2) Comparison of the bit error rate performance of the FSCM signal joint frequency offset estimation method described in this invention with other methods, as follows: Figure 7 As shown in the diagram, the red line represents the method described in this invention; the blue line represents the control group, i.e., the performance without delay and frequency offset; and the green line represents the uncorrected simple synchronization and frequency offset estimation method. Since the simulation was performed 100,000 times, the performance difference around 10^-7 is negligible. It can be seen that the traditional synchronization and frequency offset estimation method, due to the interaction of various parameters, causes the bit error rate to converge to around 10^-2; the method proposed in this invention can limit the impact of delay and frequency offset to about 2dB.

[0115] The present invention also provides a joint synchronization and frequency offset estimation system for FSCM signals. The joint synchronization and frequency offset estimation system for FSCM signals can be implemented by executing the process steps of the joint synchronization and frequency offset estimation method for FSCM signals. That is, those skilled in the art can understand the joint synchronization and frequency offset estimation method for FSCM signals as a preferred embodiment of the joint synchronization and frequency offset estimation system for FSCM signals.

[0116] Specifically, a joint synchronization and frequency offset estimation system for FSCM signals includes: Module M1: At the transmitting end, the transmitted signal is modulated by FSCM to obtain an FSCM signal, which is then sent to the receiving end; Module M2: Enables the receiver to receive and verify the FSCM signal; Module M3: Performs block synchronization on the received FSCM signal and obtains the fractional frequency offset based on the preamble signal; Module M4: Based on the fractional frequency offset, the FSCM signal is compensated for frequency offset, and block synchronization correction and fine synchronization are performed on it to obtain the initial position of the first data block; Module M5: Based on the results of fine synchronization, it performs time delay compensation on the FSCM signal and performs secondary block synchronization correction to locate the precise position of the first data block; Module M6: Based on the results of the block synchronization secondary correction, it jointly estimates the integer multiple frequency offset and time delay, performs final frequency offset compensation and fine synchronization correction on the FSCM signal, and locates and outputs the final position of the first data sampling point.

[0117] The module M1 includes the following sub-modules: Module M1.1: Represents the unmodulated chirp signal and its normalized frequency as follows:

[0118]

[0119] Where n is the discrete time. SF is the spreading factor, indicating that each symbol can carry SF bits of information, including... One sampling point; The modulated FSCM signal and its normalized frequency are represented as follows:

[0120]

[0121] Where m is the information to be modulated. ; Module M1.2: will The up-chirp symbols of s0[n], A down-chirp symbol and A frame is composed of s[n] data symbols, which are then upsampled four times, modulated to radio frequency for transmission, received by the receiver, and downconverted to baseband.

[0122] Module M2 includes the following sub-modules: Module M2.1: Divides the received signal into 4 channels based on each sampling point, with each channel divided into... For blocks of length, multiply each block by the conjugate of up-chirp, and denote the result as... , represented as:

[0123] Where s * 0[n] is the conjugate of s0[n]; perform a DFT on the result of the multiplication, and denote the result as... :

[0124] but

[0125] Take the modulo of the result, and denote the calculated value of the i-th block as... ; Module M2.2: Calculate the mean

[0126] in Calculate the average number of blocks for block synchronization; Module M2.3: Let the peak value of each mean be denoted as . , represented as:

[0127] When there is When the value is greater than a certain threshold, that is:

[0128] An FSCM signal has been detected; among which For scaling parameters, For noise parameters, take as .

[0129] The module M3 includes the following sub-modules: Module M3.1: Starting from the arrival of the FSCM signal, calculate the block with the highest peak value, denoted by index k, and represented as:

[0130] The k-th block is identified as the first block in the received signal containing the FSCM preamble, and the j-th sampling point with the highest peak value is recorded. Module M3.2: Starting from the k-th block of the j-th channel, record the received signal of each block as follows: The corresponding transmitting signal is , decimal frequency deviation The effect on the received signal is expressed as follows:

[0131] Estimate of decimal octave frequency deviation It can be obtained from the following formula:

[0132] Where * represents the conjugate of the corresponding signal.

[0133] The module M4 includes the following sub-modules: Module M4.1: Obtained using module M3.2 The received signal is frequency offset compensated, and module M3.1 is executed again to update k and j; Module M4.2: Records the peak position of the k-th block as p, i.e.

[0134] Let q be the point of precise synchronization, and q be represented as:

[0135] The precise synchronization point is the position of the q-th point of the k-th block of the j-th channel of the received signal; this position is the first point of the preamble of the received signal.

[0136] The module M5 includes the following sub-modules: Module M5.1: Synchronizes the received signal according to j, k, q of module M4.2; Module M5.2: Re-execute modules M2.2 and M3.1, and update k; Module M5.3: Synchronizes received signals based on the updated k.

[0137] Preferably, module M6 includes the following sub-modules: Module M6.1: Take a block of one symbol length from the down-chirp region, multiply it by the conjugate of the standard down-chirp, calculate the DFT, find the peak, and record the peak position as . ; Module M6.2: Command Integer multiple frequency offset estimation and secondary synchronization point Represented as

[0138]

[0139] Module M6.3: Use Frequency offset compensation is performed on the received signal, using Perform precise synchronization correction to obtain the starting position of the data symbols.

[0140] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0141] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for joint synchronization and frequency offset estimation of FSCM signals, characterized in that, include: Step S1: At the transmitting end, the transmitted signal is modulated by FSCM to obtain an FSCM signal, which is then sent to the receiving end; Step S2: Enable the receiver to receive the FSCM signal and verify it; Step S3: Perform block synchronization on the received FSCM signal and obtain the fractional frequency offset based on the preamble signal; Step S4: Based on the fractional frequency offset, perform frequency offset compensation on the FSCM signal, and perform block synchronization correction and fine synchronization on it to obtain the initial position of the first data block; Step S5: Based on the results of fine synchronization, perform time delay compensation on the FSCM signal and perform secondary block synchronization correction to locate the precise position of the first data block; Step S6: Based on the result of the block synchronization secondary correction, jointly estimate the integer multiple frequency offset and time delay, perform final frequency offset compensation and fine synchronization correction on the FSCM signal, locate and output the final position of the first data sampling point.

2. The joint synchronization and frequency offset estimation method for FSCM signals according to claim 1, characterized in that, Step S1 includes the following sub-steps: Step S1.1: Express the unmodulated chirp signal and its normalized frequency as follows: Where n is the discrete time. SF is the spreading factor, indicating that each symbol can carry SF bits of information, including... One sampling point; The modulated FSCM signal and its normalized frequency are represented as follows: Where m is the information to be modulated. ; Step S1.2: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require the full context.] The up-chirp symbols of s0[n], A down-chirp symbol and A frame is composed of s[n] data symbols, which are then upsampled four times, modulated to radio frequency for transmission, received by the receiver, and downconverted to baseband.

3. The joint synchronization and frequency offset estimation method for FSCM signals according to claim 2, characterized in that, Step S2 includes the following sub-steps: Step S2.1: Divide the received signal into 4 paths according to each sampling point, and each path is divided into... For blocks of length, multiply each block by the conjugate of up-chirp, and denote the result as... , represented as: Where s * 0[n] is the conjugate of s0[n]; perform a DFT on the result of the multiplication, and denote the result as... : but Take the modulo of the result, and denote the calculated value of the i-th block as... ; Step S2.2: Calculate the mean in Calculate the average number of blocks for block synchronization; Step S2.3: Denote the peak value of each mean as , represented as: When there is When the value is greater than a certain threshold, that is: An FSCM signal has been detected; among which For scaling parameters, For noise parameters, take as 。 4. The joint synchronization and frequency offset estimation method for FSCM signals according to claim 3, characterized in that, Step S3 includes the following sub-steps: Step S3.1: Starting from the arrival of the FSCM signal, calculate the block with the highest peak value, and denote its index as k, represented as: The k-th block is identified as the first block in the received signal containing the FSCM preamble, and the j-th sampling point with the highest peak value is recorded. Step S3.2: Starting from the k-th block of the j-th channel, record the received signal of each block as follows: The corresponding transmitting signal is , decimal frequency deviation The effect on the received signal is expressed as follows: Estimate of decimal octave frequency deviation It can be obtained from the following formula: Where * represents the conjugate of the corresponding signal.

5. The joint synchronization and frequency offset estimation method for FSCM signals according to claim 4, characterized in that, Step S4 includes the following sub-steps: Step S4.1: Using the values ​​obtained in step S3.2 Perform frequency offset compensation on the received signal, and repeat step S3.1 to update k and j; Step S4.2: Record the peak position of the k-th block as p, i.e. Let q be the point of precise synchronization, and q be represented as: The precise synchronization point is the position of the q-th point of the k-th block of the j-th channel of the received signal; this position is the first point of the preamble of the received signal.

6. The joint synchronization and frequency offset estimation method for FSCM signals according to claim 5, characterized in that, Step S5 includes the following sub-steps: Step S5.1: Synchronize the received signal according to j, k, q in step S4.2; Step S5.2: Repeat steps S2.2 and S3.1 to update k; Step S5.3: Synchronize the received signal based on the updated k.

7. The joint synchronization and frequency offset estimation method for FSCM signals according to claim 6, characterized in that, Step S6 includes the following sub-steps: Step S6.1: Take a block of one symbol length from the down-chirp portion, multiply it by the conjugate of the standard down-chirp, calculate the DFT, find the peak, and record the peak position as . ; Step S6.2: Let Integer multiple frequency offset estimation and secondary synchronization point Represented as Step S6.3: Use Frequency offset compensation is performed on the received signal, using Perform precise synchronization correction to obtain the starting position of the data symbols.

8. A joint synchronization and frequency offset estimation system for FSCM signals, characterized in that, include: Module M1: At the transmitting end, the transmitted signal is modulated by FSCM to obtain an FSCM signal, which is then sent to the receiving end; Module M2: Enables the receiver to receive and verify the FSCM signal; Module M3: Performs block synchronization on the received FSCM signal and obtains the fractional frequency offset based on the preamble signal; Module M4: Based on the fractional frequency offset, the FSCM signal is compensated for frequency offset, and block synchronization correction and fine synchronization are performed on it to obtain the initial position of the first data block; Module M5: Based on the results of fine synchronization, it performs time delay compensation on the FSCM signal and performs secondary block synchronization correction to locate the precise position of the first data block; Module M6: Based on the results of the block synchronization secondary correction, it jointly estimates the integer multiple frequency offset and time delay, performs final frequency offset compensation and fine synchronization correction on the FSCM signal, and locates and outputs the final position of the first data sampling point.

9. The joint synchronization and frequency offset estimation system for FSCM signals according to claim 8, characterized in that, The module M1 includes the following sub-modules: Module M1.1: Represents the unmodulated chirp signal and its normalized frequency as follows: Where n is the discrete time. SF is the spreading factor, indicating that each symbol can carry SF bits of information, including... One sampling point; The modulated FSCM signal and its normalized frequency are represented as follows: Where m is the information to be modulated. ; Module M1.2: will The up-chirp symbols of s0[n], A down-chirp symbol and A frame is composed of s[n] data symbols, which are then upsampled four times, modulated to radio frequency for transmission, received by the receiver, and downconverted to baseband.

10. The joint synchronization and frequency offset estimation system for FSCM signals according to claim 9, characterized in that, Module M2 includes the following sub-modules: Module M2.1: Divides the received signal into 4 channels based on each sampling point, with each channel divided into... For blocks of length, multiply each block by the conjugate of up-chirp, and denote the result as... , represented as: Where s * 0[n] is the conjugate of s0[n]; perform a DFT on the result of the multiplication, and denote the result as... : but Take the modulo of the result, and denote the calculated value of the i-th block as... ; Module M2.2: Calculate the mean in Calculate the average number of blocks for block synchronization; Module M2.3: Let the peak value of each mean be denoted as . , represented as: When there is When the value is greater than a certain threshold, that is: An FSCM signal has been detected; among which For scaling parameters, For noise parameters, take as 。

Images