CN216873206U - Differential mutual check demodulation device in free space optical communication - Google Patents

Abstract

The utility model discloses a differential mutual check demodulation device in free space optical communication, which comprises a receiving end, a receiving end and a demodulation end, wherein the receiving end comprises an optical wavelength division module; the photoelectric detector is used for converting two paths of optical signals with different wavelengths into corresponding electric signals; the differential mutual check module is used for comparing the light intensity of the two paths of light with two wavelengths; the signal demodulation unit is used for carrying out differential mutual check demodulation according to the light intensity condition obtained by the comparator; a demodulated signal output; the optical wavelength division module, the photoelectric detector, the differential mutual verification module, the signal demodulation unit and the demodulation signal output end are sequentially connected. The utility model does not need to pay attention to the specific content of energy attenuation and emission of a single beam of light any more, only needs to pay attention to the relative size of the energy of two beams of light, eliminates the influence of interference and improves the communication quality; the transmission distance is longer; the light with the required color can be mixed through different chromaticity proportions according to the environment requirement, and the functions of communication and illumination can be achieved.

Description

Differential mutual check demodulation device in free space optical communication

This application is a divisional application for a utility model patent application with an application number of 202120933139.7, an application date of April 30, 2021, and an invention-creation titled "differential inter-check modulation and demodulation device in free space optical communication".

technical field

The utility model relates to the technical field of wireless optical communication, in particular to a differential mutual check demodulation device for free space optical communication.

Background technique

Wireless optical communication is different from wired optical fiber communication. It uses light as a carrier to realize point-to-point, point-to-multipoint and multipoint-to-multipoint data, voice, image and video in free media such as the atmosphere. Two-way transmission. Since the transmission medium of wireless optical communication is free space, there is no need to lay a route, and the communication method is more flexible and convenient, so it can complete tasks that cannot be completed by optical fiber communication, and has great application value for solving the "last mile" communication. In addition, it also has the characteristics of strong confidentiality, large communication capacity, low cost and easy maintenance, etc., and can be used in emergency communication, local area network expansion, optical fiber communication backup and other fields.

At the same time, optical communication in free space is also susceptible to various interferences in the working process due to the randomness of the transmission channel due to the influence of weather conditions, terrain conditions, and foreign objects, and the complexity of its own system composition, which in turn causes system communication quality. The decline of the power supply can even lead to communication interruption in severe cases, making it difficult to achieve all-weather, beyond-line-of-sight communication. In addition, the contradiction between the transmission distance and bandwidth of free-space optical communication and the bit error rate is also very prominent, and the improvement obtained only by increasing the transmit power is limited. Scholars often use means such as selecting a beam wavelength with good transmittance and increasing the receiving aperture to solve this contradiction, but these methods are complicated to operate, and the volume, weight and cost of the system will also increase accordingly. In addition, it is also necessary to select appropriate modulation, coding and demodulation methods to avoid system performance degradation. At present, most free-space optical communication systems use IM-DD (Intensity Modulation, Direct Detection) method, and the most representative encoding method is OOK (On-Off Keying) encoding. In the face of serious external interference, the transmission distance of optical signals is greatly reduced after attenuation. shorten, and the bit error rate increases.

Utility model content

In order to improve the anti-interference ability of the free space optical communication system, so that it can adapt to the changeable environment and enhance the transmission stability and accuracy while exerting its high-speed transmission characteristics, the utility model provides a differential mutual communication system in the free space optical communication. Check the demodulator.

The technical scheme adopted by the utility model to solve its technical problems is as follows:

A differential mutual check modulation method in free space optical communication, comprising a differential mutual check modulation and demodulation device in free space optical communication, the device includes a transmitter, and the modulation method includes the following steps:

The sending end processes the binary bit stream to be sent. If "1" is to be sent, the sending power of the optical signal with wavelength λ ₁ in one modulation time slot is P ₁ , and the amplitude of the corresponding electrical signal is U ₁ , the transmission power of the optical signal with wavelength λ ₂ is P ₂ , the amplitude of the corresponding electrical signal is U ₂ , and P ₁ >P ₂ (U ₁ >U ₂ ); if “0” is to be sent, two The transmit power of each optical signal P ₁ <P ₂ (U ₁ <U ₂ );

Or if "0" is to be sent, then P ₁ >P ₂ (U ₁ >U ₂ ); if "1" is to be sent, then P ₁ <P ₂ (U ₁ <U ₂ ).

A differential mutual check and demodulation method in free space optical communication includes a differential mutual check modulation and demodulation device in free space optical communication, the device includes a receiving end, and the demodulation method includes the following steps:

The receiving end separates the optical signal from the transmitting end to obtain two optical signals of different wavelengths from the transmitting end, and converts the two beams of optical signals into electrical signals through two photodetectors respectively. Differential mutual verification of voltage amplitude: the amplitudes U ₁ and U ₂ of the transmitted signal are U ₁ ´ and U ₂ ´ after channel attenuation, that is, if U ₁ ´>U ₂ ´, the demodulation is "1"; If U ₁ ´<U ₂ ´, the demodulation is "0", or if U ₁ ´>U ₂ ´, the demodulation is "0"; if U ₁ ´<U ₂ ´, the demodulation is "1"".

A differential mutual check modulation and demodulation device in free space optical communication, comprising a transmitting end, the transmitting end includes

an electrical signal input terminal to be modulated, which is used to input the electrical signal to be modulated;

The signal modulation unit is used to perform differential mutual check modulation on the electrical signal to be sent, so that the light source emits an optical signal according to the encoded requirements;

a light source, which is used to generate two optical signals of different wavelengths;

Optical multiplexing module, which is used to combine two optical signals of different wavelengths into one channel and transmit them through the same channel;

The input end of the electrical signal to be modulated, the signal modulation unit, the light source and the optical multiplexing module are connected in sequence.

A differential mutual check modulation and demodulation device in free space optical communication, including a receiving end, the receiving end includes

Optical demultiplexing module, used to separate two wavelengths of light;

Photodetectors are used to convert two optical signals of different wavelengths into corresponding electrical signals;

Differential mutual verification module, used to compare the light intensity of two paths of two wavelengths of light;

The signal demodulation unit is used for differential mutual check demodulation according to the light intensity obtained by the comparator;

The demodulated signal output terminal is used to output the demodulated transmitted signal;

The optical demultiplexing module, the photodetector, the differential mutual verification module, the signal demodulation unit and the demodulation signal output terminal are connected in sequence.

A differential mutual check modulation and demodulation method in free-space optical communication, which is different from the prior art is that n beams of light with different wavelengths and different energies are selected at the transmitting end, and the sizes are compared at the receiving end. can get n! In this case, select 2 ^m cases and demodulate them into 2 ^m kinds of m-bit binary numbers, where 2 ^m < n! .

Advantages or beneficial effects of the present utility model:

(1) The demodulation of the present invention performs differential mutual verification processing on the energy of the two beams of light. Since the attenuation of the two beams of light is basically the same under the same channel, and they do not carry information, it is no longer necessary to pay attention to the single beam. For the specific content of light energy attenuation and emission, we only need to care about the relative size of the two beams of light energy, which eliminates the influence of interference and improves the communication quality;

(2) Another advantage of using differential mutual verification in this utility model is that both beams of light can be sent out with very high energy, and it is only necessary to ensure that the relative sizes of the two exist, which means that the transmitted beams have the ability to penetrate Stronger, longer transmission distance;

(3) The utility model is used as a communication system, if the flicker frequency 1/T _s sent by two beams of light is recorded, T _s is a symbol period, and the flicker frequency F that can be felt by the human eye is usually less than 200Hz, and generally 1 /T _s >> F, therefore, the human eye does not feel flickering, and according to the needs of the environment, the light of the desired color can be mixed with different chromaticity ratios, which can have both communication and lighting functions.

Description of drawings

1 is a block diagram of a differential mutual check modulation and demodulation device in an embodiment;

2 is a schematic diagram of a specific modulation process of a transmitting end in an embodiment;

3a and 3b are schematic diagrams of a specific demodulation process at the receiving end in the embodiment.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to be used to explain the present invention, but should not be construed as a limitation of the present invention.

Example:

A differential mutual check modulation method in free space optical communication, comprising a differential mutual check modulation and demodulation device in free space optical communication, the device includes a transmitter, and the modulation method includes the following steps:

The sending end processes the binary bit stream to be sent. If "1" is to be sent, the sending power of the optical signal with wavelength λ ₁ in one modulation time slot is P ₁ , and the amplitude of the corresponding electrical signal is U ₁ , the transmission power of the optical signal with wavelength λ ₂ is P ₂ , the amplitude of the corresponding electrical signal is U ₂ , and P ₁ >P ₂ (U ₁ >U ₂ ); if “0” is to be sent, two The transmit power of each optical signal P ₁ <P ₂ (U ₁ <U ₂ );

Or if "0" is to be sent, then P ₁ >P ₂ (U ₁ >U ₂ ); if "1" is to be sent, then P ₁ <P ₂ (U ₁ <U ₂ ).

A differential mutual check and demodulation method in free space optical communication includes a differential mutual check modulation and demodulation device in free space optical communication, the device includes a receiving end, and the demodulation method includes the following steps:

The receiving end separates the optical signal from the transmitting end to obtain two optical signals of different wavelengths from the transmitting end, and converts the two beams of optical signals into electrical signals through two photodetectors respectively. Differential mutual verification of voltage amplitude: the amplitudes U ₁ and U ₂ of the transmitted signal are U ₁ ´ and U ₂ ´ after channel attenuation, that is, if U ₁ ´>U ₂ ´, the demodulation is "1"; If U ₁ ´<U ₂ ´, the demodulation is "0", or if U ₁ ´>U ₂ ´, the demodulation is "0"; if U ₁ ´<U ₂ ´, the demodulation is "1"".

As shown in FIG. 1 , the differential mutual check modulation and demodulation device in free space optical communication implementing the above method includes a transmitting end, and the transmitting end includes

an electrical signal input terminal to be modulated, which is used to input the electrical signal to be modulated;

The signal modulation unit is used to perform differential mutual check modulation on the electrical signal to be sent, so that the light source emits an optical signal according to the encoded requirements;

a light source, which is used to generate two optical signals of different wavelengths;

Optical multiplexing module, which is used to combine two optical signals of different wavelengths into one channel and transmit them through the same channel;

The input end of the electrical signal to be modulated, the signal modulation unit, the light source and the optical multiplexing module are connected in sequence.

As shown in FIG. 1 , the differential mutual check modulation and demodulation device in free space optical communication implementing the above method includes a receiving end, and the receiving end includes

Optical demultiplexing module, used to separate two wavelengths of light;

Photodetectors are used to convert two optical signals of different wavelengths into corresponding electrical signals;

Differential mutual verification module, used to compare the light intensity of two paths of two wavelengths of light;

The signal demodulation unit is used for differential mutual check demodulation according to the light intensity obtained by the comparator;

The demodulated signal output terminal is used to output the demodulated transmitted signal;

The optical demultiplexing module, the photodetector, the differential mutual verification module, the signal demodulation unit and the demodulation signal output terminal are connected in sequence.

The basic operation process of the differential mutual check modulation and demodulation system in free space optical communication proposed by the present invention will be described below with reference to the accompanying drawings.

Differential mutual check modulation method:

In order to send binary "0" or "1", the sending end selects two beams of light with different wavelengths and different energies, combines them and sends them. After the receiving end separates the received light, by comparing the magnitude of the two beams of light energy, two situations are obtained, one is demodulated to "0", and the other is demodulated to "1", and then the transmission of the transmitting end is restored. Information.

It is further extended to more than two elements. For example, if three beams of light with different wavelengths and different energies are selected at the transmitting end, the sizes can be compared pairwise at the receiving end, and six cases can be obtained: P ₁ , P ₂ and P ₃ represent three beams respectively. The energy of the beam, in descending order from left to right: P ₁ P ₂ P ₃ ; P ₁ P ₃ P ₂ ; P ₂ P ₁ P ₃ ; P ₂ P ₃ P ₁ ; P ₃ P ₁ P ₂ ; P ₃ P ₂ P ₁ , four cases can be selected, demodulated as "00", "01", "10" and "11", thus n yuan can get n! In this case, 2 ^m cases can be selected and demodulated into 2 ^m kinds of m-bit binary numbers, 2 ^m < n! .

Fig. 1 shows the overall block diagram of the differential mutual check modulation and demodulation system. Specifically, the PC is connected to the minimum system board with the FPGA chip as the core through the serial port to form the transmitting end and the receiving end of the present utility model, wherein,

The light source in the transmitting end is two light-emitting diode modules, LED1 and LED2; the optical multiplexing module is an optical multiplexer of several types such as diffraction grating type, prism type or waveguide type; the signal modulation unit is the smallest system with FPGA as the core The minimum system board includes: a power supply module, which respectively generates 3.3V, 2.5V and 1.2V to supply power for the chip; a crystal oscillator module, which uses a 50MHz active crystal oscillator; a serial port module, which is designed by the RS-232 standard serial port. The power level conversion chip is composed of MAX232; the FLASH module is composed of a 4Mbit serial configuration device EPCS4SI8N; the last is the JTAG and AS download port and the I/O port led out through the pin header; the optical demultiplexing module in the receiving end is a diffraction grating type One of several types of optical demultiplexer, such as prism type or waveguide type; the photodetector is a PIN or APD photodiode; the differential mutual verification module is a comparator or a subtractor circuit, the signal demodulation unit and the signal of the transmitting end The modulation unit is the same.

The process of the differential mutual check modulation and demodulation method in the free space optical communication is as follows:

sender:

The PC sends information to the minimum system board with the FPGA chip as the core through the serial port, and performs the differential mutual check modulation proposed by the utility model. If the transmitted data is "1", LED1 will be lit with an electrical signal with an amplitude of U ₁ =5V in a modulation time slot, and LED2 will be lit with an electrical signal with an amplitude of U ₂ =3V; if the transmitted data is "0", LED1 The corresponding U ₁ =3V, and the corresponding U ₂ =5V of LED2. Figure 2 shows the specific modulation process of the sender. For example, the original binary bit stream sent is 101001. The modulated two IO ports are respectively transmitted to two groups of LEDs with different wavelengths according to the level signals shown in the figure, and finally two beams will be emitted. The light is combined into a beam of optical signals through an optical combiner and sent out.

Receiving end:

First, the transmitted light is separated into the original two wavelengths of optical signals by the optical splitter, and the optical signals are converted into two sets of electrical signals by the two photodiodes PIN1 and PIN2, and the two sets of electrical signals are checked by differential mutual verification. The module and the signal demodulation module perform the differential mutual check processing proposed by the present utility model, assuming that the transmitted data is 101001:

a. The specific process is shown in Figure 3a. After the two sets of electrical signals are connected to the comparator, if the output signal is high level, the demodulation is "1", and the signal is low level, then the demodulation is "0";

b. The specific process is shown in Figure 3b. After the two sets of electrical signals are connected to the subtractor, if the output signal is positive, the demodulation is "1", and if the signal is negative, the demodulation is "0".

Finally, the FPGA system board sends the demodulated data to the PC through the serial port.

The preferred embodiments of the present invention disclosed above are only to help illustrate the present invention, and do not limit the present invention to only the described specific embodiments. Obviously, many modifications and variations are possible in light of the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention.

Claims (1)

1. The differential mutual check demodulation device in free space optical communication is characterized by comprising a receiving end, wherein the receiving end comprises

The optical wavelength division module is used for separating light with two wavelengths;

the photoelectric detector is used for converting the two paths of optical signals with different wavelengths into corresponding electric signals;

the difference mutual check module is used for comparing the light intensity of the two paths of light with two wavelengths;

the signal demodulation unit is used for carrying out differential mutual check demodulation according to the light intensity condition obtained by the comparator;

a demodulated signal output terminal for outputting the demodulated transmission signal;

the optical wavelength division module, the photoelectric detector, the differential mutual verification module, the signal demodulation unit and the demodulation signal output end are sequentially connected.

Images