A method and apparatus for processing ultraviolet communication signals

Abstract

The application discloses a kind of ultraviolet communication signal processing method and device, it is related to ultraviolet light wireless communication field.The existing kilometer-level communication, error rate is high, communication algorithm is complex.Spread spectrum processing is carried out to the bit sequence to be transmitted, the spread spectrum code obtained by each bit is evenly divided into multiple chip clusters according to the number of time diversity, and the chip clusters corresponding to all bits are interleaved in each time diversity;Pulse shaping is carried out on the interleaved chip clusters under each time diversity, intensity modulation symbols are obtained, and an ultraviolet emitter is driven to emit an ultraviolet light signal;The ultraviolet receiver collects the ultraviolet light signal sequentially adopts threshold sampling strategy, deinterleaving method and despreading processing, and restores the complete bit sequence.It is used to solve the problem of communication error rate and transmission rate.

Description

Technical Field

[0001] This invention relates to the field of ultraviolet wireless communication. Background Technology

[0002] With the growth of applications such as emergency communication, unmanned / autonomous system collaboration, maritime and port digitalization, and rapid networking in complex terrain, free-space optical communication has demonstrated unique advantages in terms of "plug-and-play, rapid deployment, and resistance to electromagnetic interference." Among these, the solar-blind ultraviolet (UV) band, operating in the 200–280 nm range, has become a strong candidate for low-visibility, obstructed environments, and temporary long-distance links due to its low environmental background and non-line-of-sight (NLOS) propagation capability formed by multiple scattering. At the same time, real-world networks are showing a trend towards "larger scale, more dynamic topologies, and more bursty services": links need to maintain stable throughput and low bit error rate under power-constrained, bandwidth-constrained, mobile disturbances, and rapidly time-varying channels. This places higher demands on physical layer anti-fading and anti-interference algorithms.

[0003] However, kilometer-scale UV NLOS (ultraviolet non-line-of-sight) links suffer from a series of engineering bottlenecks, making it difficult for traditional receiver processing to balance reliability and efficiency: First, strong absorption and multiple scattering lead to superlinear path loss, resulting in tight power budgets at the transmitter; second, fluctuations in the refractive index of the near-Earth / sea boundary layer introduce slow multiplicative fading (scintillation), with coherence times typically on the order of milliseconds to tens of milliseconds, causing strong non-stationarity of bit errors over time; third, at long distances in low light, the receiver tends to operate in a quasi-photon counting region, with strong randomness in pulse amplitude and arrival, and easy threshold drift; fourth, the limited bandwidth and recovery time of the LED / receiver / front-end amplifier cause the pulse wakes broadened by scattering to superimpose, forming ISI-like interference; fifth, low signal-to-noise ratio and platform micro-vibrations lead to unstable synchronization correlation peaks, and slow fluctuations in DC / background drag the decision threshold. These factors combined cause "error bursts" and fluctuations in decision statistics, putting pressure on backend error correction.

[0004] Existing methods each have their limitations: simply slowing down or extending the integration can reduce bit errors, but it significantly sacrifices throughput and exacerbates wake accumulation; using only time-division aggregation (EGC / MRC) has limited gain under strong flicker and extremely low SNR; using only direct sequence spread spectrum (DSSS) has processing gain, but correlator mismatch will offset the de-amplification gain when device bandwidth is limited and multipath widening occurs; relying solely on FEC without robust front-end decision and interleaving is difficult to absorb error bursts caused by deep fading, resulting in a high bit error rate; spatial diversity / multi-receiver schemes are effective, but have high cost, size and orientation requirements, making it difficult to meet rapid deployment, and the control algorithm is complex.

[0005] Furthermore, engineering scenarios present two typical channel-side constraints: one is bandwidth-limited, emphasizing improving robustness and coverage without reducing the given chip rate; the other is bandwidth redundancy with a demand for effective rate, emphasizing improving anti-interference and anti-fading capabilities while maintaining the effective information rate. Addressing the high bit error rate caused by the transmitter and receiver processing methods in the aforementioned kilometer-scale UV NLOS (ultraviolet non-line-of-sight) links, as well as the channel-side constraints, there is an urgent need for a low-complexity, platform-independent time-frequency joint anti-fading scheme that can operate under both "fixed chip rate" and "fixed effective rate" constraints, while maintaining controllable implementation costs and stably reducing bit errors and improving link availability. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of high bit error rate and complex communication algorithms in existing kilometer-level communication methods, and to propose an ultraviolet communication signal processing method and device.

[0007] A method for processing ultraviolet communication signals, the method comprising the following:

[0008] The bit sequence to be transmitted is spread spectrum processed by dividing the spreading code obtained from each bit into multiple chip clusters on an average basis according to the number of time diversity, and interleaving the chip clusters corresponding to all bits in each time diversity.

[0009] Pulse shaping is performed on the interleaved chip clusters under each time diversity to obtain intensity modulation symbols, which drive the ultraviolet transmitter to emit ultraviolet light signals; the ultraviolet receiver collects the ultraviolet light signals and sequentially applies a threshold sampling strategy, a deinterleaving method, and despreading processing to recover the complete bit sequence.

[0010] Preferably, the chip clusters corresponding to all bits are interleaved in each time set, specifically as follows:

[0011] A time-diversity interleaved chip cluster is formed by chip clusters with the same number of bits.

[0012] Preferably, the method further includes:

[0013] A frame header identifier for identifying each interleaved chip cluster is added to the front end of each interleaved chip cluster. A synchronization sequence is added to the front end of each frame header identifier. Each interleaved chip cluster, its front-end frame header identifier, and the synchronization sequence constitute a microframe. The synchronization sequences in multiple microframes are all the same. The transmission time interval between multiple microframes is preset.

[0014] Preferably, synchronous decision processing is included before the threshold sampling strategy;

[0015] The simultaneous judgment process is as follows:

[0016] The ultraviolet receiver converts the acquired ultraviolet light signal into a digital sampling sequence; it uses a normalized cross-correlation operation method, combined with the synchronization sequence and frame header identifier, to determine whether the digital sampling sequence is complete, and restores the missing segments in the digital sampling sequence, thereby obtaining a complete digital sampling sequence.

[0017] Preferably, the threshold sampling strategy is as follows:

[0018] A threshold sampling strategy is used to convert the complete digitized sampling sequence into a binary vector.

[0019] Preferably, the de-intertwining method is as follows:

[0020] The deinterleaving method is used to select the corresponding binarized elements of the same bit from the binarized vector and combine them together to form the deinterleaved vector of each bit.

[0021] Preferably, the despreading process is as follows:

[0022] Binarize the multiple chip clusters corresponding to each bit to obtain the spreading vector of each bit;

[0023] The deinterleaving vector of each bit is despread with the corresponding spreading vector to obtain the statistics of each bit.

[0024] The statistics of all bits are used to make a judgment, thereby recovering the complete bit sequence.

[0025] Preferably, a transmission time interval T is preset between multiple microframes. p ≥5 / ƒ_c, where ƒ_c is the cutoff frequency of the turbulent envelope.

[0026] Preferably, the specific process for obtaining a complete digital sampling sequence is as follows:

[0027] The normalized cross-correlation operation is performed between the digitized sampling sequence and the preset training sequence to obtain the normalized correlation coefficient of each sampling point;

[0028] The normalized correlation coefficients greater than the threshold value are selected from the normalized correlation coefficients of each sampling point as the corresponding values ​​of the synchronization sequence, and the corresponding values ​​of the synchronization sequence are the peak values. By counting the number of corresponding values ​​of the synchronization sequence and combining them with the microframe length, it is determined whether the digital sampling sequence is complete. If there are missing segments in the digital sampling sequence, the missing segments are compensated and restored using the frame header identifier and the peak position, thereby obtaining a complete digital sampling sequence.

[0029] Preferably, the statistics of all bits are used to make a decision, thereby recovering the complete bit sequence, specifically as follows:

[0030] The statistics of each bit are compared with the threshold. If the statistics of the corresponding bit are greater than the threshold, output 0; if the statistics of the corresponding bit are less than or equal to the threshold, output 1. The output results of all bits are obtained, forming a complete bit sequence.

[0031] An ultraviolet communication signal processing apparatus includes a storage device, a processor, and a computer program stored in the storage device and executable on the processor. The processor executes the computer program to implement an ultraviolet communication signal processing method.

[0032] The beneficial effects of this invention are:

[0033] This invention provides a Time-Interleaved Spread Spectrum (TISS) communication method for deep fading ultraviolet (UV) channels. By integrating "spreading + time interleaving / diversity + correlation despreading", it significantly suppresses multiplicative noise and bit errors caused by turbulence scintillation and photon-level random processes in long-distance UV links. Furthermore, the communication algorithm of this invention is simple. Therefore, the ultraviolet light communication of this invention has the advantages of low bit error rate and strong robustness for long-distance transmission. Attached Figure Description

[0034] Figure 1 The microframe structure diagram set according to strategy A shows the first transmission rate;

[0035] Figure 2 The microframe structure diagram set according to strategy B shows the second transmission rate;

[0036] Figure 3 A flowchart of an ultraviolet communication signal processing method;

[0037] Figure 4 This is a flowchart illustrating the communication process between the ultraviolet light emitter and the ultraviolet light receiver.

[0038] Figure 5 A comparison of the BER (bit error probability) of using time-series union technique and TISS algorithm alone under the same effective rate conditions;

[0039] Figure 6 The graph shows a comparison of the performance of each algorithm under different signal-to-noise ratios. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0043] Example 1:

[0044] The channel is analyzed below to illustrate the theoretical basis for setting up this embodiment:

[0045] The damage or noise in various parts of long-distance deep fading wireless ultraviolet light communication channels is decomposed and corrected. The main noise and damage in long-distance ultraviolet light communication channels are divided into the following five categories: narrowband interference from solar scattered background light, band-limited noise caused by inter-symbol interference generated by strong scattering wakes, broadband additive Gaussian white noise, turbulent scintillation of low-frequency multiplicative fading (usually in DC-1KHz), and large fluctuations in intra-symbol light intensity caused by high-frequency photon pulse random processes.

[0046] The latter two are damages specific to long distances or large non-line-of-sight angles, and they have the greatest impact on communication performance.

[0047] A. Long-distance ultraviolet (UV) communication channels, measured in kilometers, have been shown in numerous studies to be affected by turbulence. Furthermore, due to the shorter wavelength of UV light, it is more susceptible to turbulence, leading to intensity scintillation. Intensity scintillation I can be represented by a gamma-gamma distribution:

[0048] (1)

[0049] In the formula, It is the gamma function. It is the second kind of modified Bessel function of order . , and It is the distribution constant, expressed by formula (2).

[0050] (2)

[0051] (3)

[0052] In the formula, The Litov variance can be expressed by formula (3). It is the atmospheric refractive index constant, which can express the intensity of atmospheric turbulent physical processes. Wave number It refers to communication distance.

[0053] Atmospheric turbulence originates from the time-varying non-uniform distribution of refractive index in the signal propagation path, and its variation spectrum typically covers the range from DC to kilohertz (DC–1 kHz). In transmission theory, turbulence manifests as fluctuations in the received signal strength over time, equivalent to a type of multiplicative noise.

[0054] B. In non-line-of-sight scattering scenarios at kilometer or high elevation angles, ultraviolet communication signals suffer deep fading due to atmospheric absorption, scattering, and turbulence, leaving only a weak pulse response at the receiving end on the order of a single photon. This single-photon response process is affected by four random effects: (1) the number of incident photons (signal and background noise); (2) the photon arrival time; (3) photomultiplier tube gain fluctuations; and (4) the superposition of multiple photon pulses.

[0055] The number of signal and noise photons received per unit time in a long-distance ultraviolet channel follows a Poisson distribution, as shown in equation (4):

[0056] (4)

[0057] In the formula, The number of signal photons per unit time. The background photon incident frequency is denoted as . unit of time The probability of having k incident photons.

[0058] The time-domain waveform of the single-photon photocurrent pulse output after multiplication by the PMT exhibits a Gaussian function distribution, as shown below.

[0059] (5)

[0060] In the formula, It is the conversion constant from photoelectrons to pulse amplitude; different PMTs have their own conversion efficiencies. The Gaussian pulse width of a single pulse output by the PMT. The pulse peak position represents the equivalent photon arrival time. This represents the total gain of the PMT. This determines the output pulse amplitude of the PMT.

[0061] However, the total gain of the system It is not fixed; the secondary electron emission processes of all multiplication stages in a PMT follow a Poisson distribution. When each multiplication stage has the same gain, and all are greater than 1, assuming the PMT has r multiplication stages, the total system gain distribution is... It approximately satisfies the Gaussian function:

[0062] (6)

[0063] In the formula, For the r-th doubling level, For the gain of the multiplication stage, where Let V be the variance of the Gaussian function.

[0064] As the above analysis shows, even if the transmitter produces the same transmitted signal, the number of photons, the multiplication gain, the photon arrival time, and the PMT output pulse height will all differ within each time interval. To address this complex stochastic phenomenon of low-power signal detection, a Monte Carlo simulation process was established to model the detection process.

[0065] For each sampling point, a symbol interval is first divided into several time slices, and the observation window is defined as... ,in, This is the sampling time. The output pulse amplitude of the PMT is obtained within this window.

[0066] The Monte Carlo simulation steps are as follows:

[0067] a) Generate within the aforementioned time window A signal photon and There are 10 background noise photons; their arrival times follow a Poisson distribution. and .

[0068] b) According to the Gaussian distribution Each signal photon randomly generates an arrival time stamp; simultaneously, within the interval The interior is uniformly distributed A noise photon is generated and arrives at the timescale.

[0069] c). For each timescale, generate a timescale with a fixed amplitude and variance according to equation (4). Gaussian pulses; summing all photon pulses within the window yields the total output waveform of the PMT.

[0070] d) At the sampling time The amplitude of the PMT output pulse is extracted and a discrimination threshold is applied: if the amplitude exceeds the threshold, it is considered that a photoelectron has been detected at the sampling point; otherwise, it is considered that no photoelectron has been detected.

[0071] e) Repeat steps a)–d) for a predetermined number of simulations to obtain the detection probability of the sampling point; at the same time, perform statistical analysis on the probability density distribution of the PMT output pulse amplitude.

[0072] This embodiment designs an ultraviolet communication signal processing method based on channel analysis. The method includes the following:

[0073] This embodiment is applied in a kilometer-level non-line-of-sight ultraviolet (UV) link, with the transmitting and receiving ends using existing UV transmitters / receivers.

[0074] The bit sequence to be transmitted is spread spectrum processed by dividing the spreading code obtained from each bit into multiple chip clusters on an average basis according to the number of time diversity, and interleaving the chip clusters corresponding to all bits in each time diversity.

[0075] Pulse shaping is performed on the interleaved chip clusters under each time diversity to obtain intensity modulation symbols, which drive the ultraviolet transmitter to emit ultraviolet light signals; the ultraviolet receiver collects the ultraviolet light signals and sequentially applies a threshold sampling strategy, a deinterleaving method, and despreading processing to recover the complete bit sequence.

[0076] The chip clusters corresponding to all bits are interleaved in various time subsets, specifically as follows:

[0077] A time-diversity interleaved chip cluster is formed by chip clusters with the same number of bits.

[0078] Specifically, the spread spectrum processing of the bit sequence to be transmitted is performed by spreading the spectrum using a spreading factor N. N can be selected as 4, 8, 16, or 32, and can also be adjusted according to the real-time situation of the ultraviolet wireless channel. The larger the spreading factor, the better the damage suppression effect. Step 1 obtains robustness through spread spectrum and time diversity. The spread spectrum sequence obtained by spreading the bit sequence can be one of Walsh, complementary, or m-sequences.

[0079] In order for the receiving end to acquire the complete sequence, the method is further specified below as including:

[0080] A frame header identifier for identifying each interleaved chip cluster is added to the front end of each interleaved chip cluster. A synchronization sequence is added to the front end of each frame header identifier. Each interleaved chip cluster, its front-end frame header identifier, and the synchronization sequence constitute a microframe. The synchronization sequences in multiple microframes are all the same. The transmission time interval between multiple microframes is preset.

[0081] Specifically, after forming microframes, pulse shaping is performed on the interleaved chip clusters under each time diversity to obtain intensity modulation symbols, which then drive the ultraviolet transmitter to emit ultraviolet light signals. Specifically, pulse shaping is performed on each microframe to obtain intensity modulation symbols, and the ultraviolet transmitter is then driven to emit ultraviolet light signals. Transmission time interval T p ≥5 / ƒ_c, where ƒ_c is the cutoff frequency of the turbulence envelope. This time interval can also be no less than the atmospheric turbulence coherence time. To enhance diversity near independence, it has been tested and found that it can be set to 0.5ms.

[0082] To further specify, synchronous decision processing is included before the threshold sampling strategy;

[0083] The simultaneous judgment process is as follows:

[0084] The ultraviolet receiver converts the acquired ultraviolet light signal into a digital sampling sequence; it uses a normalized cross-correlation operation method, combined with the synchronization sequence and frame header identifier, to determine whether the digital sampling sequence is complete, and restores the missing segments in the digital sampling sequence, thereby obtaining a complete digital sampling sequence.

[0085] The specific process for obtaining a complete digital sampling sequence is as follows:

[0086] The normalized cross-correlation operation is performed between the digitized sampling sequence and the preset training sequence to obtain the normalized correlation coefficient of each sampling point;

[0087] The normalized correlation coefficients greater than the threshold value are selected from the normalized correlation coefficients of each sampling point as the corresponding values ​​of the synchronization sequence, and the corresponding values ​​of the synchronization sequence are the peak values. By counting the number of corresponding values ​​of the synchronization sequence and combining them with the microframe length, it is determined whether the digital sampling sequence is complete. If there are missing segments in the digital sampling sequence, the missing segments are compensated and restored using the frame header identifier and the peak position, thereby obtaining a complete digital sampling sequence.

[0088] Specifically, normalized cross-correlation plus peak protection is used because turbulence causes significant changes in signal energy over time, which can lead to many spurious peaks during the correlation peak synchronization process. Therefore, the following normalized cross-correlation scheme is adopted for synchronization. Let the upsampled sequence of the synchronization sequence be P, with a length of... Normalized cross-correlation is:

[0089] (7)

[0090] In the formula, The normalized cross-correlation coefficient represents the number of times the received sequence is shifted relative to the preset training sequence. The similarity at each sampling point is dimensionless and ranges from [-1, 1]. It is a delayed (shift) index, with units of sample points, scanned. To find The maximum value. k is the summation index, which iterates through the sampling points of the reference sequence (pilot / training sequence), k=0,1,… . For the discrete sampling sequence at the receiving end, it represents the sequence from... Starting point, length is The sliding window data segment; The upsampled waveform samples are known reference / pilot sequences.

[0091] Threshold A value of 0.3-0.8 can be used, and a "peak protection window" strategy is adopted: when the first peak is detected, the peak is the starting position of the first microframe. Combined with the length of the microframe, the first microframe is collected. When calculating the next peak, the starting position of the next microframe is used, and the frame length of the previous microframe will not be included, thus avoiding the repetition of false peaks.

[0092] Each peak indicates the starting point of a frame; combined with the "interleaving index field" in the frame header, the frame header sequence number and chip boundary within the microframe are recovered. For missing or distorted microframes, a "missing frame flag" is recorded.

[0093] The preset training sequence is the M sequence.

[0094] like Figure 3 As shown, after transmission through a kilometer-scale atmospheric wireless channel, the ultraviolet light signal reaches the receiver at a level of near-single-photon weakness due to atmospheric absorption, scattering, and turbulence. Therefore, it's crucial to use a high-magnification ADC to acquire the signal, ensuring sufficient resolution for single-photon pulse acquisition. Generally, a sampling rate sufficient to guarantee an oversampling rate of 50 times for the chip is adequate. Applying low-pass filtering at the receiver would actually weaken the signal photon pulses, further damaging the single-photon pulse signal. Generally, no processing is needed; signal normalization is sufficient.

[0095] Normalized cross-correlation is performed based on a preset synchronization sequence to complete clock / frame synchronization, and the integrity of the chip sequence is verified according to the frame header identifier; if a frame is missing, a "missing frame flag" is recorded. See the attached diagram "DSP Processing Flow" for the flowchart. Figure 4 As shown.

[0096] The following further defines the processing procedure at the receiving end: The threshold sampling strategy is as follows:

[0097] A threshold sampling strategy is used to convert the complete digitized sampling sequence into a binary vector.

[0098] The uninterruption method is as follows:

[0099] The deinterleaving method is used to select the corresponding binarized elements of the same bit from the binarized vector and combine them together to form the deinterleaved vector of each bit.

[0100] Despreading is performed as follows:

[0101] Binarize the multiple chip clusters corresponding to each bit to obtain the spreading vector of each bit;

[0102] The deinterleaving vector of each bit is despread with the corresponding spreading vector to obtain the statistics of each bit.

[0103] The statistics of all bits are used to make a judgment, thereby recovering the complete bit sequence.

[0104] The complete bit sequence is recovered by making a decision based on the statistics of all bits.

[0105] The statistics of each bit are compared with the threshold. If the statistics of the corresponding bit are greater than the threshold, output 0; if the statistics of the corresponding bit are less than or equal to the threshold, output 1. The output results of all bits are obtained, forming a complete bit sequence.

[0106] Specifically, the threshold is 0.

[0107] In the time dimension, the same bit chips from different microframes are recombined and merged (equal gain merging, EGC) to obtain the final decision statistics; the rationale for EGC comes from the fact that "each chip is in a different time set and is of similar importance".

[0108] Figure 5 By comparing the BER of time diversity spreading with that of the TISS algorithm when using time diversity combining technique alone at the same effective rate, the effectiveness of diversity spreading can be verified. The horizontal axis represents... The values ​​represent the number of incident photons. TISS-SF32 indicates the TISS algorithm used with a spreading factor of 32; TISS-SF16 indicates the TISS algorithm used with a spreading factor of 16; TISS-SF8 indicates the TISS algorithm used with a spreading factor of 8; TISS-SF4 indicates the TISS algorithm used with a spreading factor of 4; EGC-L4 indicates the time-partition merging method used in this application with a spreading factor of 4; EGC-L8 indicates the time-partition merging method used in this application with a spreading factor of 8; EGC-L16 indicates the time-partition merging method used in this application with a spreading factor of 16; and EGC-L32 indicates the time-partition merging method used in this application with a spreading factor of 32. It is evident that TISS technology can significantly reduce the bit error rate (BER), and higher-order spreading factors generally correspond to lower BERs.

[0109] Figure 6 The performance comparison charts of each algorithm under different signal-to-noise ratios are given; among them, The background incident photon count (background noise) is CER1, the bit error rate (BER) is BER; spread spectrum generates the concept of chips (which can be calculated as CER), and a group of spread spectrum chips constitutes a symbol (which can be calculated as BER).

[0110] Further specifying, pulse shaping is performed on the interleaved chip clusters under each time diversity to obtain the transmission rate after intensity modulation of the symbols, including:

[0111] Strategy A: When device / bandwidth becomes the bottleneck, and the transmission rate is not limited (the goal is high performance rather than high communication speed), set the same chip rate for all chips in all chip clusters. For example, for... Figure 1 Each chip S 1,1 S 2,1 …Set the same sending rate Then calculate the effective information rate using the following formula:

[0112] ;

[0113] In the formula, Indicates expenses, Indicates chip rate, Indicates the spread factor. For each symbol, net bits This is the upper limit for the device. Let be the effective information rate of strategy A.

[0114] Strategy A prioritizes increasing LLL and / or NNN to achieve processing and diversity gains without exacerbating ISI. This transmission rate setting avoids severe ISI (inter-symbol interference) by maintaining a constant chip rate when limited by device bandwidth.

[0115] Strategy B: When the sending rate is limited, maintain the effective information rate unchanged; when the service has hard targets for throughput... At that time, the transmission rate of each chip is obtained. :

[0116] (8)

[0117] In the formula, The business has strict performance targets for throughput. The effective information rate for strategy B;

[0118] If limited by device limits The achievable upper limit of the spread spectrum is constrained to be:

[0119] (9)

[0120] In the formula, The achievable upper limit of the spread spectrum;

[0121] Strategy B has hard targets for the effective information rate in the business. In scenarios where throughput remains constant, robustness is enhanced through spread spectrum and time diversity, and parameters such as chip rate, frame overhead, and modulation bit count are linked when necessary. Both strategies share a unified frame structure, synchronization, and statistical decision framework, differing only in the coupling between optimization objectives and parameters.

[0122] If limited by device limits The achievable upper limit of the spread spectrum is shown in formula (9). Due to existing device technology, high-power UV LEDs typically have large junction capacitances, resulting in low modulation bandwidths; a 3dB bandwidth is approximately 3MHz. Under these constraints... ≤ Under the premise of maximizing L and N first to obtain processing gain and diversity gain; otherwise, decrease them sequentially. or improve .

[0123] Figure 2 The diagram shows the transmission rate for strategy B. The transmission rate in this embodiment is faster than that in embodiment 1.

[0124] The following verifies the reliability of recovering the complete bit sequence using statistics:

[0125] Dual-threshold demodulation algorithm, deinterleaving and despreading:

[0126] A. Adopting a dual-threshold demodulation strategy: The highly oversampled photoelectric conversion analog signal is binarized, and its decision threshold is determined by the prior channel estimation result. In this case, "+1" in the symbol vector indicates that a photon has been detected, and vice versa. According to the Poisson channel model, the number of photons received X per unit time follows a Poisson distribution:

[0127] (10)

[0128] In the formula, Factorial indicates that it is a mathematical operation. Indicates that a symbol was detected One photon, This indicates that N photons were detected within the symbol.

[0129] Therefore, for the binarized symbol vector, the number of photons detected in each sampling interval still follows a Poisson distribution, for OOK symbols. and The mean values ​​are respectively and , It is the average number of photons detected per sampling interval of intensity modulation symbol 1. It is the average number of photons detected in each sampling interval of intensity modulation symbol 0. It is the average number of photons detected during the duration of intensity modulation symbol 1. It is the average number of photons detected during the duration of intensity modulation symbol 1. This represents the oversampling rate. Under high sampling conditions, the probability of detecting more than one photon in a sampling interval is infinitesimally small, and the Poisson distribution can be approximated by a Bernoulli distribution. Within the sampling interval... Internally detected photon count The probability is:

[0130] (11)

[0131] (12)

[0132] In the formula, This indicates whether a photon was detected within the sampling interval. This indicates that a photon has been detected. This indicates that no photons were detected. For the duration of the symbol, This is the oversampling rate.

[0133] B. The binarized received signal after deinterleaving and recombination is After recombination according to the spread spectrum sequence, use This indicates that the original spread spectrum sequence was subsequently oversampled. and The relevant solution expansion, i.e., "product + summation", is shown in Formula 11. Wherein... It is the actual number of chips added at one time. , This refers to the actual number of chips added at one time. For oversampling rate, It is the spreading factor.

[0134]

[0135] In the formula, For each bit of the deinterleaved vector, the first... One element, For the first bit of the spreading vector per bit One element;

[0136] Symbolic decision-making Therefore, the key lies in providing the actual symbols. ,random variable The distribution of the photons. The probability of a single chip detecting a photon can be expressed by formulas (11) and (12), denoted here as . and , It is the probability of detecting a photon in each sampling interval of intensity modulation symbol 1. This is the probability of detecting a photon in each sampling interval of intensity modulation symbol 0. At this point, the random variable... The conditional probability is given by formula (12). .

[0137] (13)

[0138] Because all The random variables are independent and identically distributed, therefore we have formula (9), where This represents the number of times +1 appears. After replacing the symbols with equal amounts, the probability of determining the symbol can be obtained.

[0139] (14)

[0140] Ultimately, the conditional probability of a correct decision can be expressed by the following two formulas:

[0141] (15)

[0142] In equation (15), For statistics per bit, , From Select from elements The number of distinct combinations of elements.

[0143] The above is used to verify the accuracy of the judgment using statistics. It can be seen that the error rate of recovering the original data using statistics is low.

[0144] Example 2:

[0145] An ultraviolet communication signal processing apparatus includes a storage device, a processor, and a computer program stored in the storage device and executable on the processor, wherein the processor executes the computer program to implement an ultraviolet communication signal processing method.

[0146] In summary, system performance is mainly constrained by the following four parameters: spreading factor SF, oversampling factor M, average number of incident signal photons, and average number of background photons. Appropriately increasing the spreading factor, oversampling factor, or number of signal photons can significantly improve symbol decision accuracy, allowing the receiver performance to quickly approach the ideal state. Theoretical derivation shows that the time-interleaved spreading algorithm can effectively improve processing gain and diversity gain in weak photon-level turbulent channels, thereby significantly reducing the bit error rate.

[0147] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for processing ultraviolet communication signals, characterized in that, The method includes the following: The bit sequence to be transmitted is spread spectrum processed by dividing the spreading code obtained from each bit into multiple chip clusters on an average basis according to the number of time diversity, and interleaving the chip clusters corresponding to all bits in each time diversity. Pulse shaping is performed on the interleaved chip clusters under each time diversity to obtain intensity modulation symbols, which drive the ultraviolet transmitter to emit ultraviolet light signals; the ultraviolet receiver collects the ultraviolet light signals and sequentially applies a threshold sampling strategy, a deinterleaving method, and despreading processing to recover the complete bit sequence; The chip clusters corresponding to all bits are interleaved in various time subsets, specifically as follows: A chip cluster interleaved under time diversity consists of chip clusters with the same number of bits in sequence. The method further includes: A frame header identifier for identifying each interleaved chip cluster is added to the front end of each interleaved chip cluster. A synchronization sequence is added to the front end of each frame header identifier. Each interleaved chip cluster, its front-end frame header identifier, and the synchronization sequence constitute a microframe. The synchronization sequences in multiple microframes are all the same. The transmission time interval between multiple microframes is preset.

2. The ultraviolet communication signal processing method according to claim 1, characterized in that, Synchronous decision processing is also included before the threshold sampling strategy; The simultaneous judgment process is as follows: The ultraviolet receiver converts the acquired ultraviolet light signal into a digital sampling sequence; it uses a normalized cross-correlation operation method, combined with the synchronization sequence and frame header identifier, to determine whether the digital sampling sequence is complete, and restores the missing segments in the digital sampling sequence, thereby obtaining a complete digital sampling sequence.

3. The ultraviolet communication signal processing method according to claim 2, characterized in that, The threshold sampling strategy is as follows: A threshold sampling strategy is used to convert the complete digitized sampling sequence into a binary vector.

4. The ultraviolet communication signal processing method according to claim 3, characterized in that, The uninterruption method is as follows: The deinterleaving method is used to select the corresponding binarized elements of the same bit from the binarized vector and combine them together to form the deinterleaved vector of each bit.

5. The ultraviolet communication signal processing method according to claim 4, characterized in that, Despreading is performed as follows: Binarize the multiple chip clusters corresponding to each bit to obtain the spreading vector of each bit; The deinterleaving vector of each bit is despread with the corresponding spreading vector to obtain the statistics of each bit. The statistics of all bits are used to make a judgment, thereby recovering the complete bit sequence.

6. The ultraviolet communication signal processing method according to claim 1, characterized in that, Transmission time interval T p ≥5 / ƒ_c, where ƒ_c is the cutoff frequency of the turbulent envelope.

7. A method for processing ultraviolet communication signals according to claim 2 or 5, characterized in that, The specific process for obtaining a complete digital sampling sequence is as follows: The normalized cross-correlation operation is performed between the digitized sampling sequence and the preset training sequence to obtain the normalized correlation coefficient of each sampling point; The normalized correlation coefficients greater than the threshold value are selected from the normalized correlation coefficients of each sampling point as the corresponding values ​​of the synchronization sequence, and the corresponding values ​​of the synchronization sequence are the peak values. By counting the number of corresponding values ​​of the synchronization sequence and combining them with the microframe length, it is determined whether the digital sampling sequence is complete. If there are missing segments in the digital sampling sequence, the missing segments are compensated and restored using the frame header identifier and the peak position, thereby obtaining a complete digital sampling sequence.

8. The ultraviolet communication signal processing method according to claim 5, characterized in that, The complete bit sequence is recovered by making a decision based on the statistics of all bits. The statistics of each bit are compared with the threshold. If the statistics of the corresponding bit are greater than the threshold, output 0; if the statistics of the corresponding bit are less than or equal to the threshold, output 1. The output results of all bits are obtained, forming a complete bit sequence.

9. An ultraviolet communication signal processing apparatus, the apparatus comprising a storage device, a processor, and a computer program stored in the storage device and executable on the processor, characterized in that, The processor executes the computer program to implement the method as described in any one of claims 1 to 8.

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