CN113328808A - Underwater wireless optical communication system based on partial response shaping technology and TCM (TCM) technology - Google Patents
Underwater wireless optical communication system based on partial response shaping technology and TCM (TCM) technology Download PDFInfo
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- CN113328808A CN113328808A CN202110085488.2A CN202110085488A CN113328808A CN 113328808 A CN113328808 A CN 113328808A CN 202110085488 A CN202110085488 A CN 202110085488A CN 113328808 A CN113328808 A CN 113328808A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/80—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0071—Use of interleaving
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0224—Channel estimation using sounding signals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/024—Channel estimation channel estimation algorithms
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Abstract
本发明涉及水下无线光通信领域，公开了基于部分响应整形技术和TCM技术的水下无线光通信系统，包括：光发射模块、光接收模块、发射端信号处理模块、接收端信号处理模块。光发射模块将数字信号转换为光信号后发送至光接收模块，光接收模块将光信号转换为数字信号。发射端信号处理模块将原始数据进行TCM编码、随机交织、预编码、上采样和根升余弦滤波，接收端信号处理模块对数字信号进行重采样、根升余弦滤波、同步、信道估计、信道均衡、部分响应整形、解交织、最大似然序列估计后得到原始数据。相比于传统方法，在全响应信道均衡后添加部分响应滤波器，能够有效抑制高频部分的噪声放大，提高信噪比，降低误码率，并通过仿真和实验验证了其性能提升。
The invention relates to the field of underwater wireless optical communication, and discloses an underwater wireless optical communication system based on partial response shaping technology and TCM technology, comprising: an optical transmitter module, an optical receiver module, a transmitter signal processing module and a receiver signal processing module. The optical transmitting module converts the digital signal into an optical signal and sends it to the optical receiving module, and the optical receiving module converts the optical signal into a digital signal. The signal processing module at the transmitting end performs TCM coding, random interleaving, precoding, upsampling and root raised cosine filtering on the original data, and the signal processing module at the receiving end performs resampling, root raised cosine filtering, synchronization, channel estimation, and channel equalization on the digital signal. , Partial response shaping, deinterleaving, and maximum likelihood sequence estimation to obtain the original data. Compared with the traditional method, adding a partial response filter after the full response channel equalization can effectively suppress the noise amplification in the high frequency part, improve the signal-to-noise ratio, and reduce the bit error rate, and its performance improvement is verified by simulation and experiments.
Description
Technical Field
The invention relates to the field of underwater wireless optical communication, in particular to an underwater wireless optical communication system combining a partial response shaping technology and a TCM (TCM) technology.
Background
With the gradual shortage of land resources, the development and utilization of abundant marine resources have become important development directions of various countries. The establishment of a complete set of underwater communication network is of great significance to underwater exploration, wherein data and video transmission among underwater vehicles, underwater robots and underwater sensor nodes is an important difficult problem to solve urgently.
The reliability of wired communication is strong and the communication rate is high, but because the research and development of the domestic wet-plug connector is not mature at present, the cost of equipment can be greatly improved by adopting wired communication. Traditional underwater wireless communication generally adopts underwater acoustic communication and radio frequency communication, wherein the underwater acoustic communication has large time delay and limited bandwidth, and because electromagnetic waves are seriously attenuated in water, only a low-frequency band can be used, and the speed of the underwater acoustic communication can not meet the requirement of underwater data transmission. The underwater wireless optical communication has the advantages of high bandwidth, short time delay, good confidentiality and the like, the transmission distance of the underwater wireless optical communication system is increased while the high speed is maintained, the underwater application range of the underwater wireless optical communication system can be greatly expanded, and how to realize the underwater wireless optical transmission with high speed and long distance becomes a research hotspot in the field of the underwater wireless optical communication. In order to increase the transmission distance in an underwater wireless optical communication system, a high-power laser is generally used as a light source, and a photodetector with high detection sensitivity, such as a photomultiplier tube (PMT), a Single Photon Avalanche Diode (SPAD), a multi-pixel photon counter (MPPC), and the like, is used as a detector. The low bandwidth limitation brought by a high-power laser and a high-sensitivity detector introduces serious intersymbol interference (ISI), a full-response equalizer used in the existing channel equalization technology such as Least Square (LS), Least Mean Square (LMS) algorithm, Frequency Domain Equalization (FDE) algorithm and the like can amplify noise while performing signal compensation in a frequency band with serious fading, and brings reduction of signal to noise ratio (SNR), a partial-response equalizer is added after the full-response equalizer to shape a signal frequency spectrum, so that noise amplification can be effectively inhibited, and a Viterbi decoder is adopted to decode a signal subjected to partial-response shaping. The TCM technology combines a channel coding technology with a modulation technology, can bring coding gain without increasing signal bandwidth, can also adopt a Viterbi decoder for decoding, and can improve system performance without increasing excessive hardware overhead when being applied to a partial response shaping system. In addition, colored noise caused by low-frequency cut-off existing in electronic devices such as a power amplifier, a T-shaped biaser and the like can cause performance degradation of the TCM technology, and the scheme also proposes that a random interleaver and precoding are adopted for noise whitening so as to improve the system performance.
Disclosure of Invention
The invention aims to provide a digital signal processing technology combining a partial shaping technology and a TCM (TCM) technology aiming at the low bandwidth characteristic of the existing long-distance underwater wireless optical communication system, which can effectively increase the communication speed of the system, improve the transmission performance and reduce the error rate.
In order to achieve the above purpose, the invention adopts the following technical scheme:
an underwater wireless optical communication system based on partial response shaping technology and TCM technology, comprising: the device comprises a light emitting module, a light receiving module, a transmitting end signal processing module and a receiving end signal processing module;
the optical transmitting module converts the digital signal into an optical signal; the optical transmitting module transmits an optical signal to the optical receiving module; the optical receiving module converts the received optical signal into a digital signal; the transmitting terminal signal processing module sends a digital signal obtained by processing the original data to the light emitting module; the receiving end signal processing module processes the received digital signal and then restores the original data; the transmitting terminal signal processing module is connected with the light emitting module; the optical receiving module is connected with the receiving end signal processing module;
further, the optical transmitting module comprises a signal generator, a power amplifier, an adjustable electrical attenuator, a T-shaped biaser, a direct current power supply module, a laser and a collimating lens; the signal generator, the power amplifier, the adjustable electric attenuator, the T-shaped biaser and the laser are sequentially connected, the T-shaped biaser is provided with bias current by the direct-current power supply module, and the emitting end of the laser is arranged opposite to the collimating lens.
The laser and the collimating lens are arranged in the watertight cabin at the transmitting end;
the signal generator converts the digital signal obtained by the processing of the transmitting end signal processing module into an electric signal;
the collimating lens is a convex lens and is used for collimating an optical signal emitted by the laser;
further, the light receiving module comprises a photomultiplier tube and a mixed signal oscilloscope, wherein the photomultiplier tube is connected with the mixed signal oscilloscope;
the photomultiplier is arranged in a receiving end watertight cabin;
furthermore, the transmitting end signal processing module comprises a TCM coding module, a random interleaver module, a pre-coding module, an up-sampling module and a root-raised cosine filter module which are connected in sequence;
the TCM coding module comprises 2/3 convolutional code encoder and PAM-8 modulation module, as shown in FIG. 3. The original data is processed by a TCM coding module to obtain a sequence { ak}；
The random interleaver module will sequence akGet the sequence b after random arrangementk}；
The precoding module will pair the sequence bkObtaining a sequence { c after precodingkAnd the precoding formula is as follows:
ck＝mod(bk-αck-1+8，16)-8
＝bk-αck-1+16×m，m＝0 or±1
where α is a cut-off coefficient, α is greater than or equal to 0 and less than or equal to 1, and the optimal α needs to be selected according to the spectrum shape of the received signal.
The training sequence and synchronization sequence insertion module respectively inserts a training sequence and a synchronization sequence into the signal, wherein the training sequence is used for receiving end channel estimation, and the synchronization sequence is used for receiving end code element synchronization;
furthermore, the receiving end signal processing module comprises a resampling module, a root raised cosine filter module, a synchronization module, a channel estimation module, a channel equalization module, a partial response shaping module, a de-interleaver module and a Maximum Likelihood Sequence Estimation (MLSE) module which are connected in sequence;
the resampling module resamples the digital signal according to the sampling rate of the signal generator and the mixed signal oscilloscope;
the root raised cosine filter module performs matched filtering on the signal;
the synchronization module carries out code element synchronization according to the synchronization sequence;
the channel estimation module adopts an LS (least squares) criterion to carry out channel estimation according to a training sequence;
the channel equalization module equalizes a received signal according to the estimated value of the channel;
the partial response shaping module performs partial response shaping on the equalized signal, and the z-transform function of the partial response filter is as follows:
H(z)＝1+αz-1
obtaining a sequence d after partial response shapingk}：
dk＝ck+αck-1＝bk+16×m，m＝0 or±1
The maximum likelihood sequence estimation module adopts a Viterbi decoder based on a 4-state grid diagram shown in FIG. 4 to decode to obtain original data;
according to the invention, a partial response filter is added after the traditional full response channel is equalized, so that the noise amplification of a high-frequency part can be effectively inhibited, the signal-to-noise ratio of a signal is improved, and the system error rate is reduced; the TCM technology adopted in the invention can bring coding gain without increasing signal bandwidth, and the coding gain is combined with a partial response shaping technology to share the same Viterbi decoder, thereby increasing the system performance while increasing a small amount of hardware overhead; the random interleaver adopted in the invention can whiten the noise to ensure that the TCM obtains stable coding gain; the precoding technique adopted in the invention enables the signal after the partial response shaping to still be decoded by a Viterbi decoder. The invention has better application prospect in the long-distance underwater wireless optical communication system.
Drawings
FIG. 1 is a schematic diagram of an underwater wireless optical communication system based on a partial response shaping technology and a TCM technology;
FIG. 2 is a flow chart of an algorithm of a transceiver end of an underwater wireless optical communication system based on a partial response shaping technology and a TCM technology;
FIG. 3 is a block diagram of a TCM coding module;
FIG. 4 is a 4-state trellis diagram with dashed circles representing X1With 1, the solid circles indicate X 10, and the dotted line represents Z 31, the solid line denotes Z3＝0；
FIG. 5 is a simulation result of the digital signal processing technique proposed in the present invention;
FIG. 6 is a communication rate and bit error rate relationship when 150 meters are transmitted in a swimming pool by an underwater wireless optical communication system based on a partial response shaping technology and a TCM technology;
Detailed Description
The invention is described in detail below with reference to the accompanying drawings;
first, it should be noted that all electronic components (parts) used in the present invention are well-established technologies and have corresponding commercially available products. The invention can be fully reproduced by those skilled in the art based on the knowledge of software radio and various digital signal processing skills mastered by the software radio upon reading and understanding the application documents;
as shown in fig. 1, the underwater wireless optical communication system based on the partial response shaping technology and the TCM technology includes a signal generator, a power amplifier, an adjustable electrical attenuator, a T-type biaser, a dc power supply module, a laser, a collimating lens, a transmitting end watertight compartment, a reflector, a photomultiplier, a mixed signal oscilloscope, a receiving end watertight compartment, a transmitting end signal processing module, and a receiving end signal processing module;
the method comprises the steps that original data are sent to a transmitting end signal processing module through a cable, digital signals generated by the transmitting end signal processing module are loaded into a signal generator through a USB data line, electric signals generated by the signal generator are amplified through a power amplifier and then the signal power is adjusted through an adjustable electric attenuator, a direct current power supply module provides direct current bias to enable a laser to work in a linear range, a T-shaped bias device is used for enabling the signals to be superposed with the direct current bias, output signals of the T-shaped bias device are transmitted through the cable and then used for driving the laser, and a collimating lens is a convex lens. The laser and the collimating lens are arranged in the watertight cabin at the transmitting end;
the optical signal is incident into water and reflected twice by the reflector and then reaches the receiving end (the reflector can be removed because the reflector is not limited by the field when the optical signal is transmitted in the actual sea area), the photomultiplier converts the optical signal into an electric signal and transmits the electric signal to the mixed signal oscilloscope, the mixed signal oscilloscope converts the electric signal into a digital signal and then inputs the digital signal into the receiving end signal processing module, and the receiving end signal processing module processes the digital signal to restore the original data. The photomultiplier is arranged in a receiving end watertight cabin;
the wavelength of the laser is 450 nm; the peak-to-peak value of the output signal of the signal generator is 0.5V, and the sampling rate is 400/450/500MSamples/s (the corresponding communication rate is 400/450/500 Mbps); the response frequency band of the power amplifier is 100kHz-75MHz, and the gain is 37 dB; the attenuation value of the adjustable electric attenuator is 6 dB; the DC bias provided by the DC power supply is 0.4A; the detection wavelength of the photomultiplier is 230nm-700nm, and the effective detection area diameter is 9 mm; the sampling rate of the mixed signal oscilloscope is 625 MSamples/s;
as shown in fig. 2, the transmitting end signal processing module and the receiving end signal processing module are inverse mapping of the interleaver. The up-sampling multiple of the signal is 2, the length of the training sequence is 2000, the number of taps of the root-raised cosine filter is 101, the roll-off coefficient is 0.01, the length of the random interleaver is 5000, the length of the synchronization sequence is 1000, the number of taps of the full-response equalizer is 81, the backtracking length of the MLSE is 20, and the corresponding cut-off coefficients alpha are 0.1/0.4/0.7 respectively when the communication rate is 400/450/500 Mbps;
FIG. 3 is a TCM coding module, which is composed of 2/3 convolutional code coding and PAM-8 modulation, and the output signal R has 8 levels, R belongs to { -7, -5, -3, -1, +1, +3, +5, +7 };
FIG. 4 is a 4-state trellis diagram in which the dashed circles indicate X1With 1, the solid circles indicate X 10, and the dotted line represents Z 31, the solid line denotes Z 30, path up/downThe number of (a) indicates the possible output value of the state transition path. The receiving end uses a Viterbi decoder to decode according to the grid diagram shown in FIG. 4;
fig. 5(a) shows a simulation result, where a signal generated by the transmitting end signal processing module passes through a channel and is added with noise, and then the signal is input into the receiving end signal processing module, so that the noise is white gaussian noise. The w/L representation adopts least square equalization, the w/PR representation adopts partial response equalization, the w/T representation adopts TCM technology, the w/PRPT representation adopts partial response equalization, precoding and TCM technology, and the w/PRIPT representation adopts partial response equalization, interleaving, precoding and TCM technology. The simulation result shows that compared with the traditional least square equalization, the system performance can be effectively improved by using the partial response equalization, because of the existence of low frequency cut-off, the performance improvement is not obviously brought by adding the precoding and TCM technologies on the basis of the partial response equalization, and the problem can be effectively solved by processing the noise whitening through the interleaving technology. Fig. 5(b) is a noise spectrum after least square equalization, which has peaks in a low frequency part and a high frequency part, and after partial response equalization, as shown in fig. 5(c), noise in the high frequency part is suppressed, and the signal-to-noise ratio is improved, but a peak still exists in the low frequency part, which suppresses the performance of the TCM technique, and after the interleaving technique is introduced, as shown in fig. 5(d), a flat noise spectrum is obtained, which further improves the system performance;
fig. 6 shows the error rates corresponding to signals with different rates after transmitting 150 meters in the swimming pool, and it can be seen from the figure that the method proposed in the present invention can achieve a communication rate of 500Mbps, which can bring about 14.2%, 9.2% and 8.0% communication rate improvement compared with the conventional least square equalization, TCM technique and partial response equalization, respectively;
finally, it should be noted that the above-mentioned list is only a specific embodiment of the present invention. It is obvious that the present invention is not limited to the above embodiments, but many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.
Claims (6)
1. An underwater wireless optical communication system based on partial response shaping technology and TCM technology, comprising: the device comprises a light emitting module, a light receiving module, a transmitting end signal processing module and a receiving end signal processing module;
the light emitting module converts the digital signal into an optical signal and sends the optical signal to the light receiving module; the optical receiving module converts the received optical signal into a digital signal; the transmitting terminal signal processing module sends a digital signal obtained by processing the original data to the light emitting module; the receiving end signal processing module processes the received digital signal and then restores the original data; the transmitting terminal signal processing module is connected with the light emitting module; and the light receiving module is connected with the receiving end signal processing module.
2. The underwater wireless optical communication system based on the partial response shaping technology and the TCM technology as claimed in claim 1, wherein the optical transmission module comprises a signal generator, a power amplifier, an adjustable electrical attenuator, a T-shaped bias device, a DC power supply module, a laser and a collimating lens; the signal generator, the power amplifier, the adjustable electric attenuator, the T-shaped biaser and the laser are sequentially connected, the T-shaped biaser provides a direct current bias signal through the direct current power supply module, and the emitting end of the laser is arranged opposite to the collimating lens.
3. The underwater wireless optical communication system based on the partial response shaping technology and the TCM technology as claimed in claim 1, wherein the light receiving module comprises a photomultiplier tube and a mixed signal oscilloscope.
4. The underwater wireless optical communication system based on the partial response shaping technology and the TCM technology as recited in claim 1, wherein the transmitting end signal processing module comprises a TCM coding module, a random interleaver module, a precoding module, an upsampling module and a root-raised cosine filter module.
5. The underwater wireless optical communication system based on the partial response shaping technology and the TCM technology as claimed in claim 1, wherein the transmitting end signal processing module comprises a TCM coding module, a random interleaver module, a precoding module, an upsampling module and a root-raised cosine filter module;
the TCM coding module consists of an 2/3 convolutional code encoder and a PAM-8 modulation module, and the original signal passes through the TCM coding module to obtain a sequence { ak}；
The TCM coded signal is processed by a random code coder to obtain a sequence { bk}；
The precoding module will pair the sequence bkObtaining a sequence { c after precodingkAnd the precoding formula is as follows:
ck＝mod(bk-αck-1+8，16)-8
＝bk-αck-1+16×m，m＝0 or±1
alpha in the precoding module is a cutoff coefficient, alpha is more than or equal to 0 and less than or equal to 1, and the optimal alpha needs to be selected according to the spectrum shape of the received signal.
6. The underwater wireless optical communication system based on the partial response shaping technology and the TCM technology as claimed in claim 1, wherein the receiving end signal processing module comprises a resampling module, a root-raised cosine filter module, a synchronization module, a channel estimation module, a channel equalization module, a partial response shaping module, a deinterleaver module, a Maximum Likelihood Sequence Estimation (MLSE) module;
the z-transform function of the partial response shaping filter corresponding to the partial response shaping module is as follows:
H(z)＝1+αz-1
the partial response shaping module outputs a sequence dk}：
dk＝ck+αck-1＝bk+16×m，m＝0 or±1
The mapping relation of the de-interleaving module is the inverse mapping of the interleaving module;
the MLSE block decodes the output sequence of the deinterleaving block using a Viterbi decoder to recover the original data.
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| CN116366168A (en) * | 2023-04-03 | 2023-06-30 | 浙江大学 | Underwater wireless optical communication system based on index modulation technology and multi-band CAP technology |
| CN116366168B (en) * | 2023-04-03 | 2025-11-04 | 浙江大学 | Underwater wireless optical communication system based on index modulation technology and multi-band CAP technology |
| CN118740266A (en) * | 2024-07-25 | 2024-10-01 | 武汉邮电科学研究院有限公司 | Signal transmission method, device, equipment and storage medium based on spectrum compression |
| CN118740266B (en) * | 2024-07-25 | 2025-10-28 | 武汉邮电科学研究院有限公司 | Signal transmission method, device, equipment and storage medium based on spectrum compression |
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