A high-speed PPM modulation and demodulation method and device

Abstract

The present invention discloses a high-speed PPM modulation and demodulation method and device. The modulation end inserts a frame header and a silent time slot with good autocorrelation characteristics according to system characteristics, channel characteristics and demodulation end characteristics, which are highly distinguished from data content, so that the PPM modulation signal has stronger channel interference resistance and is more conducive to demodulation end processing. The demodulation end is simple to implement, and the time slot is initially mapped before the frame header matching is performed. For the situation where the maximum value is at the time slot endpoint position, the signal is moved back as a whole by using a rolling processing method to avoid the extreme position, which greatly increases the risk of PPM modulation and demodulation bit errors, which is especially important for signals with extremely low signal-to-noise ratios and improves communication accuracy.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to a high-speed PPM modulation and demodulation method, device and computer-readable storage medium. Background Art

[0002] In the field of communications, modulation and demodulation technologies are the most critical and directly affect the reliability and efficiency of the communication system.

[0003] PPM (Pulse Position Modulation), or pulse position modulation, is a modulation technology in which the pulse position changes according to the changes in the modulated signal. This technology has the advantages of simple coding, high power utilization, and high frequency band utilization, and is widely used in underwater communications, indoor wireless communications, optical communications, ultra-wideband mobile communications, and other fields. PPM modulation is to output a high pulse at the corresponding time slot position of the signal to be modulated at the transmitter, and no pulse is output at other positions; PPM demodulation is the inverse process of PPM modulation, that is, to restore the signal to be demodulated at the receiving end to the pre-modulation information according to the pulse position.

[0004] The PPM modulation method should be designed according to the characteristics of the communication system and the channel, in order to minimize the adverse factors introduced by the system and the channel, and facilitate demodulation and restoration. Due to the characteristics of different sources at the transmitter and receiver of the communication system, PPM demodulation requires very critical clock synchronization technology. If the clock synchronization is wrong, the information after demodulation at the receiver will be seriously wrong.

[0005] In high-speed communication systems, adverse factors such as channel noise, external interference, sudden factors, hardware limitations, etc. have a serious impact on PPM signals, which will cause the demodulated signal to be distorted, deformed, and have uncertainties such as fluctuating noise floors, making PPM clock synchronization and PPM demodulation more difficult. Reliable high-speed PPM modulation and demodulation technology needs to be broken through. Figure 1 The figure shows a schematic diagram of a high-speed PPM signal after transmission through a channel. The characteristics are large fluctuations in signal amplitude and noise floor. The noise floor is even higher than some signals, which makes it difficult to find a unified boundary between signal and noise. This often occurs during the transition period when the ambient noise is large or the hardware device suddenly changes state. This phenomenon of large fluctuations in the signal-to-noise ratio is inevitable in high-speed communications, but traditional demodulation methods are difficult to demodulate, and even cause a large amount of data to be lost due to unsuccessful demodulation.

[0006] In the prior art, most of the clock synchronization methods introduce thresholds or levels to distinguish the coding logic bits. This method is reliable in low-speed communication, but in high-speed communication, it often causes misjudgment of logic bits due to improper threshold introduction. The patent document with application number 200919217164.9 mentions using level jump edges to judge coding logic bits. Improper level selection can easily cause misjudgment and cannot be applied to Figure 1The signal and noise shown are difficult to distinguish; the patent document with application number 202110205676.4 mentions the use of signal-to-noise ratio monitoring and adaptive threshold method to complete the judgment of the coding logic bit, but the real-time performance of signal-to-noise ratio monitoring will affect the real-time performance of the adaptive threshold. Secondly, the selection of threshold prediction interval is relatively complex, and demodulation errors may be caused by improper threshold selection. Summary of the invention

[0007] Technical purpose: In view of the shortcomings of the existing PPM signal demodulation method that the signal amplitude fluctuates greatly and the noise floor fluctuates greatly, and it is impossible to perform accurate and reliable demodulation, the present invention discloses a high-speed PPM modulation and demodulation method and device that can improve the fault tolerance and anti-interference ability of PPM demodulation, and is suitable for harsh conditions such as no obvious boundary between signal and noise and low signal-to-noise ratio.

[0008] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] A high-speed PPM modulation and demodulation method comprises the steps of:

[0010] S01, adding an error correction code to the modulated signal;

[0011] S02, inserting a frame header into the signal for demodulation end clock synchronization; the content of the frame header is different from the PPM modulation format,

[0012] S03, inserting a silent time slot after the frame header;

[0013] S04, generate a PPM modulated signal and transmit it to the receiving end for demodulation

[0014] Preferably, in step S02 of the present invention, the frame header uses N high pulses with a fixed interval of M1 time slots, M1≠L, and L represents the number of time slots of the PPM modulation signal.

[0015] Preferably, each time slot of the PPM modulation signal of the present invention includes Ns sampling periods, where Ns≥3.

[0016] Preferably, in step S04 of the present invention, the demodulation process of the signal includes:

[0017] S041, preprocessing the L-PPM signal to be demodulated, the preprocessing including filtering and waveform shaping;

[0018] S042, perform initial time slot mapping on the pre-processed signal, calibrate the maximum position of each time slot, and when the maximum value is at the start or end position of the time slot, perform rolling processing and readjust the mapping between data and time slots until the maximum value is not at the end position of the time slot;

[0019] S043, performing frame header matching based on pulse interval;

[0020] S044, the data with successful frame header matching is demodulated using the maximum mapping method;

[0021] S045. Perform error correction code decoding on the PPM signal to correct signal errors.

[0022] Preferably, in step S041 of the present invention, the pre-processing uses sliding window filtering to perform signal processing, and performs Ns point sliding window accumulation on the PPM modulated signal, where Ns represents the number of sampling cycles contained in a time slot.

[0023] Preferably, in step S042 of the present invention, the process of rolling processing includes: generating a time slot counter with a counting period of M1×Ns, calibrating the maximum value position for each M1×Ns point, and when the maximum value is at 0 or M1×Ns-1 of the time slot counter and the signal maximum value is at the time slot endpoint position, the data to be demodulated is moved backward by one time slot as a whole, i.e., Ns point, and then remapped, and when the maximum value is not at the time slot endpoint position, entering step S043 for frame header matching.

[0024] Preferably, the frame header matching process performed in step S043 of the present invention includes: according to the final time slot mapping result of step S042, calculating the adjacent maximum value interval, the interval and the set frame header interval are within the error range, the frame header match is successful, and the frame header number is increased by one, otherwise the frame header matching number remains unchanged; comparing the final frame header matching number with the set frame header target number, if it is greater than or equal to the frame header target number, the frame header match is successful, and data demodulation is performed; if the frame header matching number is less than the frame header target number, it means that the current signal is noise, then the frame header matching is re-performed to capture the signal, and the frame header matching is re-performed.

[0025] The present invention also discloses a high-speed PPM modulation and demodulation device, comprising a modulation module and a demodulation module, wherein the modulation module modulates digital signals according to the above-mentioned PPM modulation method, and the demodulation module demodulates signals according to the above-mentioned PPM demodulation method.

[0026] Beneficial effects: The high-speed PPM modulation and demodulation method and device provided by the present invention have the following beneficial effects:

[0027] 1. The modulation end of the present invention inserts a frame header and a silent time slot with good autocorrelation characteristics according to system characteristics, channel characteristics and demodulation end characteristics, which are highly distinguishable from data content, making the PPM modulated signal more resistant to channel interference, more conducive to demodulation end processing, and simple to implement.

[0028] 2. The present invention includes greater than or equal to three sampling periods for each time slot of the modulated signal, leaving an error interval for time slot mapping during PPM demodulation, thereby improving the fault tolerance and anti-interference capability of PPM demodulation, and can effectively resist deformation, notches, and other problems of PPM signals occurring during channel transmission.

[0029] 3. The present invention uses a sliding window accumulation method to pre-process the signal to be demodulated, which can improve the signal-to-noise ratio, weaken high-intensity narrow pulse interference, and optimize the distorted waveform.

[0030] 4. The present invention performs initial time slot mapping before frame header matching. When the maximum value is at the end point of the time slot, the signal is shifted backward as a whole using a rolling process to avoid the risk of extreme position introduction and greatly improve the risk of PPM modulation and demodulation bit errors, which is of great significance especially for signals with extremely low signal-to-noise ratio.

[0031] 5. The present invention uses pulse interval and limit rolling processing to perform clock synchronization, abandons the idea of ​​introducing thresholds to distinguish coding logic bits, can avoid demodulation errors caused by errors in distinguishing coding logic bits, and is particularly suitable for harsh conditions such as no obvious boundary between signal and noise and low signal-to-noise ratio. It also has the advantages of simple implementation and no complex operations. Due to the introduction of the limit rolling method, the limit conditions are rolled to a position that is conducive to algorithm judgment, making the modulation and demodulation method highly robust.

[0032] 6. The present invention uses a maximum position mapping demodulation method and does not use a threshold in the data segment, thereby avoiding demodulation errors caused by improper threshold selection; it is not affected by inter-code crosstalk and waveform broadening, and does not require a PPM signal to design a protection interval, so the communication rate is higher; it is not affected by signal parasitic interference and can demodulate weak signals that are higher than noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0034] Figure 1 This is a schematic diagram of a high-speed PPM signal after passing through a channel;

[0035] Figure 2 The overall flow chart of the high-speed PPM modulation method of the present invention;

[0036] Figure 3 The modulation process flow chart of the high-speed PPM modulation method of the present invention is

[0037] Figure 4 The overall flow chart of the high-speed PPM demodulation method of the present invention;

[0038] Figure 5 It is a demodulation process flow chart of the high-speed PPM demodulation method of the present invention;

[0039] Figure 6 Schematic diagram of 16-PPM modulation signal in an embodiment of the present invention;

[0040] Figure 7 This is a schematic diagram of 16-PPM demodulation in an embodiment of the present invention;. DETAILED DESCRIPTION

[0041] The present invention will be described more clearly and completely below by way of a preferred embodiment in conjunction with the accompanying drawings, but the present invention is not limited to the scope of the embodiment.

[0042] like Figure 2-Figure 5 The figure shows a high-speed PPM modulation and demodulation method disclosed in the present invention, comprising the steps of:

[0043] S01. Add error correction code to the modulated signal; RS coding, LDPC coding and other coding methods can be used to effectively correct channel errors.

[0044] S02. Insert a frame header into the signal for demodulation end clock synchronization; the content of the frame header is different from the PPM modulation format, and the frame header content can be a synchronization code element with good autocorrelation characteristics, such as a Barker code, or a fixed sequence; preferably, the modulation end frame header uses N high pulses with a fixed interval of M1 time slots, M1≠L, L represents the number of time slots of the PPM modulation signal, and one time slot contains Ns sampling periods. In order to make the PPM modulation signal have a strong anti-interference ability, each time slot needs to contain at least 3 sampling periods, that is, Ns≥3. When demodulating, there is a redundant error period on the left and right of the timing interval mapped to the maximum value, which greatly improves the demodulation success rate.

[0045] S03, insert a silent time slot after the frame header; the silent time slot separates the frame header from the modulated data, and is used by the demodulator to complete the determination of the frame header matching number and the frame header target number.

[0046] S04, generate a PPM modulated signal and transmit it to the receiving end for demodulation. Figure 3 As shown, the process of generating a PPM modulation signal includes: converting the data to be modulated into a bit width of The symbol sequence Mi, L indicates that the PPM modulated signal contains L time slots in total, and generates a timing counter cnt with a counting period of L×Ns. The converted symbol sequence is compared with the time slot counter. If Mi is equal to cnt, the PPM modulated signal is set to 1, and if they are not equal, the PPM modulated signal is set to 0, and the PPM modulated signal is output to the receiving end.

[0047] In step S04, the signal demodulation process includes:

[0048] S041. Preprocessing the demodulated L-PPM signal, including filtering and waveform shaping; preferably using a sliding window accumulation method, performing Ns point sliding window accumulation on the PPM modulated signal, where Ns represents the number of sampling cycles contained in a time slot, and the weight of the sliding window accumulation can be flexibly changed according to the signal situation, which can improve the signal-to-noise ratio, weaken high-intensity narrow pulse interference, and optimize the distorted waveform;

[0049] S042, perform initial time slot mapping on the pre-processed signal, calibrate the maximum position of each time slot, and when the maximum value is at the start or end position of the time slot, perform rolling processing and readjust the mapping between data and time slots until the maximum value is not at the end position of the time slot;

[0050] like Figure 5 As shown, the process of rolling processing includes: generating a time slot counter with a counting period of M1×Ns, calibrating the maximum value position for each M1×Ns point, when the maximum value is at 0 or M1×Ns-1 of the time slot counter, and the signal maximum value is at the time slot endpoint position, the data to be demodulated is moved backward by one time slot as a whole, that is, Ns point, and then remapped. When the maximum value is not at the time slot endpoint position, enter step S043 to perform frame header matching.

[0051] S043, then perform frame header matching based on the pulse interval; according to the final time slot mapping result of step S042, calculate the adjacent maximum value interval, the interval and the set frame header interval are within the error range, the frame header matching is successful, and the frame header number is increased by one, otherwise the frame header matching number remains unchanged; compare the final frame header matching number with the set frame header target number, if it is greater than or equal to the frame header target number, the frame header matching is successful, and data demodulation is performed; the frame header matching number is less than the frame header target number, and the current frame header matching is unsuccessful, indicating that the current received signal is channel noise rather than signal, and the frame header matching is performed again to capture the signal. In order to improve the success rate of frame header matching, the frame header target number can be consistent with the actual number of frame headers added by the transmitter, or it can be slightly less than the actual number of frame headers added, which represents the tolerance rate that the frame header matching can bear, and increases the probability of successful demodulation.

[0052] S044. For data with successful frame header matching, use the maximum mapping method for demodulation; find the position of the signal maximum value within L time slot units, and map the maximum value position to the time slot to complete demodulation. This demodulation method can effectively resist the situation of large waveform amplitude fluctuations and large interference; since inter-symbol crosstalk and waveform broadening do not change the core position of the code element, this demodulation method can still complete effective demodulation under the phenomenon of pulse broadening and inter-symbol crosstalk.

[0053] S045. Decode the PPM signal using an error correction code to correct signal errors. This can correct some continuous byte errors and reduce the communication error rate.

[0054] The present invention also provides a high-speed PPM modulation and demodulation device based on the above modulation and demodulation method, including a modulation module and a demodulation module, wherein the modulation module modulates the digital signal according to the PPM modulation method, and the demodulation module demodulates the signal according to the PPM demodulation method. The modulation and demodulation method of the present invention is preferably implemented using FPGA, which has a powerful parallel data processing capability. By using FPGA, the received data can be demodulated in real time, and the real-time performance is strong; a computer-readable storage medium can also be provided in the modulation and demodulation device, storing computer executable instructions, which are used to implement the above PPM modulation and demodulation method when executed by the processing unit, and implemented on a device with data processing capability such as a computer and a DSP chip.

[0055] In this embodiment, a 16-PPM signal is taken as an example, and a time slot is set to contain Ns=3 sampling periods, each sampling period is 8ns. The frame header uses a fixed sequence of 111111, the frame header sequence is spaced 12 time slots apart, and the silent interval is 4 time slots. The 16-PPM modulation format is as follows: Figure 6 As shown in FIG. 1 , after the PPM modulated signal is transmitted through the channel, it is preprocessed by 3-point sliding window accumulation. Figure 7 shown.

[0056] During demodulation, the demodulation end generates a 12*3=36-decimal time slot counter, and calculates the maximum value once every 36 time slot counter intervals. If the maximum value is located at time slot counter 0 or 35, it means that the demodulated signal pulse occurs at the start or end of the time slot. In this case, it cannot be determined whether the maximum value is at the end of the previous time slot or the beginning of the next time slot. This extreme situation is not conducive to demodulation, and a rolling processing method is required to shift the pre-processed data back by 3 sampling points and re-judge. If the maximum value is not located at time slot counter 0 or 35, it means that the demodulated signal is not at the extreme position, and the frame header matching is entered.

[0057] The maximum value is calculated once every 36 time slot counter intervals, and the maximum value interval is calculated. If the maximum value interval is 35, 36, or 37, it means that the interval between the two pulses is consistent with the preset frame header interval 36 or is within the error tolerance range, then the frame header matching number is increased by 1, otherwise the frame header matching number remains unchanged. Since the frame header number at the modulation end in this example is 111111, which means 6 frame headers, the demodulation end considers the fault tolerance range of the system, and the frame header target number can be set to 4. When the frame header matching number is greater than or equal to 4, it is considered that the frame header matching is successful, otherwise the frame header matching is unsuccessful (probably noise), and the time slot initial mapping is performed again. After the frame header matching is successful, the 48-bit time slot counter is regenerated, and the maximum value of the high pulse of the demodulated signal corresponds to the interval of the time slot counter, which is the demodulation result, and the error correction code is decoded according to the error correction code at the modulation end.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high-speed PPM modulation and demodulation method, characterized in that: Includes steps: S01, adding an error correction code to the modulated signal; S02, inserting a frame header into the signal for demodulation end clock synchronization; the content of the frame header is different from the PPM modulation format, S03, inserting a silent time slot after the frame header; S04, generating a PPM modulated signal and transmitting it to a receiving end for demodulation; In step S02, the frame header uses N high pulses with a fixed interval of M1 time slots, M1≠L, and L represents the number of time slots of the PPM modulation signal; Each time slot of the PPM modulated signal contains Ns sampling periods, Ns ≥ 3; In step S04, the signal demodulation process includes: S041, preprocessing the L-PPM signal to be demodulated, the preprocessing including filtering and waveform shaping; S042, perform initial time slot mapping on the pre-processed signal, calibrate the maximum position of each time slot, and when the maximum value is at the start or end position of the time slot, perform rolling processing and readjust the mapping between data and time slots until the maximum value is not at the end position of the time slot; S043, performing frame header matching based on pulse interval; S044, the data with successful frame header matching is demodulated using the maximum mapping method; S045. Perform error correction code decoding on the PPM signal to correct signal errors.

2. A high-speed PPM modulation and demodulation method according to claim 1, characterized in that: In step S041, the pre-processing uses sliding window filtering to perform signal processing, and performs Ns point sliding window accumulation on the PPM modulated signal, where Ns represents the number of sampling cycles contained in a time slot.

3. A high-speed PPM modulation and demodulation method according to claim 1, characterized in that: In step S042, the rolling processing process includes: generating a time slot counter with a counting period of M1×Ns, calibrating the maximum value position for each M1×Ns point, and when the maximum value is at 0 or M1×Ns-1 of the time slot counter and the signal maximum value is at the time slot endpoint position, the data to be demodulated is moved backward by one time slot as a whole, that is, Ns point, and then remapped. When the maximum value is not at the time slot endpoint position, enter step S043 for frame header matching.

4. A high-speed PPM modulation and demodulation method according to claim 1, characterized in that: The frame header matching process in step S043 includes: according to the final time slot mapping result of step S042, the adjacent maximum value interval is calculated, and if the interval and the set frame header interval are within the error range, the frame header match is successful, and the frame header number is increased by one, otherwise the frame header matching number remains unchanged; the final frame header matching number is compared with the set frame header target number, if it is greater than or equal to the frame header target number, the frame header match is successful, and data demodulation is performed; if the frame header matching number is less than the frame header target number, the frame header matching is performed again.

5. A high-speed PPM modulation and demodulation device, characterized in that: It comprises a modulation module and a demodulation module, wherein the modulation module modulates a digital signal according to a high-speed PPM modulation method described in any one of claims 1-4, and the demodulation module demodulates a signal according to a high-speed PPM demodulation method described in any one of claims 1-4.

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