CN107612858B - Multi-carrier baseband and FSK hybrid modulation method based on inductive coupling temperature and salt deep chain - Google Patents
Multi-carrier baseband and FSK hybrid modulation method based on inductive coupling temperature and salt deep chain Download PDFInfo
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Abstract
The invention provides a multi-carrier baseband and FSK hybrid modulation method applied to a marine communication system by taking a transmission channel of an inductive coupling temperature-salt deep chain as an application prototype, designs a corresponding receiving demodulation part of time-domain filtering aiming at the communication protocol of the invention so as to form a complete transceiving marine communication system, verifies the feasibility of the modulation method by using matlab, and performs actual test by using LABVIEW software, an actual marine coupling channel and a matlab demodulation program algorithm. The lowest signal-to-noise ratio which can be borne theoretically by software testing and actual channel system testing is 10db, the error rate is controlled within two thousandths of a meter and is far lower than the current channel communication environment, the method provides a simple and feasible data communication method for the inductive coupling temperature-salinity deep transmission channel, the complexity of an underwater data node circuit can be simplified by the implementation of the method, and a new thought is provided for reducing the power consumption of a communication system and prolonging the service life of the system.
Description
Technical Field
The invention provides a multi-carrier baseband and FSK mixed modulation method applied to an ocean communication system by taking a transmission channel of an inductive coupling temperature-salt deep chain as an application prototype, and provides a simple and feasible data communication method for the inductive coupling temperature-salt deep transmission channel.
Background
The data transmission technology based on the inductive coupling channel is one of important communication technologies of ocean measurement, is a non-contact underwater signal transmission channel system realized by adopting an electromagnetic induction principle, has the characteristics of simple structure, low cost and long transmission distance of a transmission mode, and can perform three-dimensional networking on sensor nodes to realize better ocean monitoring effect. The inductive coupling ocean data communication system mainly comprises an underwater data node, a data transmission channel and an above-water receiving modulation system, wherein the underwater data node comprises a sensor and a data transmitting modulation system; the transmission channel consists of a coupling magnetic ring (comprising an above-water magnetic ring and an under-water magnetic ring), a transmission cable and a water body. In the actual measurement work of the inductive coupling ocean, a sensor in an underwater data node acquires information such as seawater temperature, salinity and depth of different nodes, the data is transmitted to an underwater magnetic ring through a data transmitting and modulating system for modulation and packaging, then the data is transmitted to a single-turn coil through inductive coupling and then transmitted to an overwater magnetic ring, and finally the data is transmitted to an overwater receiving and modulating system for demodulation.
The transmission mode of the digital signal is divided into baseband transmission and band-pass transmission, the digital baseband signal is a digital baseband signal which is directly transmitted without carrier modulation, and the communication technology has the advantages of simplicity and feasibility. Frequency Shift Keying (FSK) utilizes frequency variation of a carrier wave to transmit digital information, has the advantages of simple realization, better anti-noise and anti-attenuation performances and the like, and is widely applied to medium and low speed data transmission. At present, the inductive coupling transmission system developed in china uses the marine environment, a ferrite magnetic ring and a high-strength plastic-coated steel cable as transmission channels, and applies ASK or DPSK modulation and demodulation technology to realize data information transmission, and the transmission rate reaches 1200 bps. Compared with china, other countries have various mature products based on the inductive coupling principle. At present, two companies are mainly involved in mastering the inductive coupling transmission technology and actually applying the technology to the ocean monitoring system, namely SBE-BIRD in the united states and RBR in canada. The inductive coupling transmission system of SBE-BIRD company has standard serial interfaces with devices such as current meter, Doppler profiler and the like, can be integrated with a telemetering inductive transmission system, adopts DPSK modulation technology, and has a transmission rate of 9.6 Kbps. The inductive coupling data transmission system of RBR company integrates an underwater inductive coupling transmitter and an underwater instrument together, adopts the DPSK modulation technology, and has the transmission rate of 4.8 Kbps. The method adopts a baseband and FSK hybrid modulation technology, has better anti-interference capability compared with an ASK modulation technology, and has simpler structure compared with a DPSK technology.
Disclosure of Invention
The invention aims to design a signal modulation method of multi-carrier baseband and FSK mixed modulation through in-depth research on baseband modulation and FSK modulation technologies, so as to improve the data transmission rate of an ocean communication system based on an inductive coupling temperature-salt deep chain, reduce the power consumption of nodes at the bottom of a sea of the communication system, prolong the service life of electric quantity, prolong the service life of the whole system and obtain higher ocean monitoring capacity.
The invention carries out deep theoretical analysis according to a baseband modulation technology and an FSK modulation technology, designs a modulation method of mixing a multi-carrier baseband and the FSK according to the actual characteristics of an inductive coupling thermohaline deep chain and the power consumption requirement of a marine communication system, and specifically specifies that: firstly, the whole modulation adopts baseband square wave modulation without adding carrier waves so as to simplify the circuit structure of the whole modulation part; secondly, the whole signal square wave consists of multiple frequencies, the square wave of the first frequency forms the whole set of guided waves for sending signals, and the periodicity is fixed; the latter different frequencies respectively represent different types of parameters, and the period number of each square wave respectively represents the value of the parameter; and finally, forming a signal packet by the guided wave and other parameter waveforms, and packaging and sending the signal packet. The guided wave has the function of providing identification and synchronization for the receiving part, and the following numerical value can be effectively received only after the receiving part successfully identifies the guided wave, and meanwhile, the guided wave has the function of calibrating the frequency of the underwater node circuit on the water. The number of the parameters is set according to the requirement of the system, the system is based on an inductive coupling temperature-salt deep chain and has three signals of temperature, salinity and depth, so that three square waves with different frequencies are set behind the system, the square wave with each frequency represents one parameter, and the periodicity of the square waves is the sending value of the parameter.
The invention relates to a multi-carrier baseband and FSK mixed modulation method based on an inductive coupling temperature-salt deep-chain marine communication system and combining the advantages of baseband modulation and FSK modulation, and a receiving and demodulating system based on a time domain filter is designed on the basis to form a complete marine communication transceiving system. Firstly, simulation test is carried out on MATLAB software, and the feasibility of the hybrid modulation method is verified. In addition, the actual laboratory-level test is carried out on the whole marine communication transceiving system by utilizing LABVIEW software and an actual coupling channel so as to verify the use condition in the actual environment. The invention provides a new method for marine data transmission research, has important practical significance for improving the transmission rate of a marine communication system and reducing power consumption, and provides a solution for a complex marine communication monitoring system.
The technical scheme of the invention is as follows:
the invention is based on the transmission channel of the inductive coupling temperature-salt deep chain, combines the respective advantages of baseband modulation and FSK modulation, invents a multi-carrier baseband and FSK mixed modulation method, designs a corresponding receiving demodulation part of time-domain filtering aiming at the invented communication protocol, thereby forming a complete transceiving marine communication system, verifies the feasibility of the modulation method by using matlab, and carries out actual test by using LABVIEW software, an actual marine coupling channel and a matlab demodulation program algorithm. The data transmission method can be expressed as that a data modulation algorithm program is programmed and designed by LABVIEW software to modulate and send data, and a NI USB-6259 data acquisition card collects and receives modulated data passing through a marine coupling channel, further stores the received data, and restores and sends the data by a receiving and demodulation algorithm program.
The invention provides a multicarrier baseband and FSK hybrid modulation method based on inductive coupling temperature-salt deep chain, which comprises the following specific steps:
Firstly, designing a multi-carrier baseband and FSK mixed modulation method based on the channel characteristics of an inductive coupling temperature-salt deep-chain marine communication system, and carrying out baseband square wave modulation without adding a carrier; the square wave frequency part adopts a frequency change mode similar to FSK, and the signal only transmits four parameters of temperature, salinity and depth, so that four different frequencies are serially transmitted to a channel, the first frequency section is a guided wave, the periodicity is fixed, and the guided wave plays a role in guiding and identifying; the last three frequencies are parameters of temperature, salinity and depth in the ocean respectively, and the value of the period number represents the parameter value; the four frequencies are transmitted together for a group of data.
Respectively passing the modulated signal through four filters with different frequency parameters to extract baseband signals of each frequency, then respectively shaping signal waveforms filtered out by the filters to form square waves, counting by utilizing rising edges, and storing; if the number of cycles of the first frequency is the same as the number of cycles of the transmitted first frequency waveform, storing the data received later; if not, discarding the following data;
step 3, noise test of communication modulation-demodulation system
The data transmitting system and the data receiving system are integrated to form a complete communication transceiving system, MATLAB is used for test simulation, Gaussian white noise is added to the system, 3 types of temperature, salt and depth data are input, corresponding frequency and periodicity are modulated through a modulation system, the signal-to-noise ratio of the system is set, the demodulation system is used for demodulating and receiving, and corresponding parameter values are demodulated and transmitted. Test results show that the multi-carrier baseband and FSK hybrid modulation method based on the inductive coupling temperature-salt deep chain has feasibility, can realize the functions of a marine communication system, and can ensure a very low bit error rate under the condition of a very low signal-to-noise ratio.
Step 4, adding an actual inductive coupling channel to carry out verification experiment
A transmission modulation system is designed by utilizing LABVIEW software, namely, numerical values of three parameters of temperature, salinity and depth are input, square wave signals formed by combining four different frequencies of guided wave, temperature, salinity and depth are modulated, Gaussian white noise is added to simulate an actual environment, signals of mixed noise are transmitted to an actual marine communication inductive coupling channel, and signals passing through the channel are collected by utilizing an NI USB-6259 data collection card. The received digital signal is demodulated by a receiving system program to obtain the specific numerical values of the three parameters. According to experimental results, the multi-carrier baseband and FSK hybrid modulation method based on the inductive coupling temperature-salt deep chain can be used in an actual marine coupling channel, has a certain use value, is consistent with simulation test results of a system, and proves the accuracy of simulation test.
The invention has the advantages and beneficial effects that:
the invention provides a multi-carrier baseband and FSK hybrid modulation method aiming at high requirements of an inductive coupling temperature-salt deep chain and a marine communication system on power consumption, compared with other data communication methods, the method absorbs the advantages of baseband modulation and FSK modulation modes, adopts the characteristics of baseband square wave modulation and FSK frequency change, is simpler to realize, considers practical factors encountered in various marine communications, and meets the requirements of a practical marine communication system. The multi-carrier baseband and FSK mixed modulation method adopts baseband square wave transmission without other carrier modulation, which greatly simplifies the hardware circuit of the transmission part, greatly reduces the power consumption of the transmission module, prolongs the service time of a battery and greatly prolongs the life cycle of the transmission node of the data transmission system. In addition, the frequency change similar to FSK is adopted, the multi-frequency combined square wave is adopted, the data transmission quantity can be greatly increased, three kinds of data of temperature, salt and depth can be simultaneously transmitted, or a monitoring system is expanded according to requirements, the quantity of parameter values is increased, and the complexity of the whole communication system can be conveniently improved. The demodulation part adopts parallel data processing, four filters are arranged in parallel to respectively filter data, fundamental waves of data waveforms are extracted, and then shaping counting is carried out.
Fig. 1 is a general design diagram of marine communication based on multi-carrier baseband and FSK hybrid modulation of an inductive coupling temperature-salt deep chain, mainly comprising: (a) the device comprises an overwater magnetic ring part, (b) a transmission steel cable, (c) an underwater magnetic ring, (d) a modulation part and (e) a demodulation part;
FIG. 2 is a flow chart of algorithm implementation, where (a) is the modulation part and its specific protocol, (b) is the demodulation part and its structure, and (c) is the time-domain filter;
FIG. 3 is a waveform reduction of each node of the marine communication system, wherein (a) is a transmitted original square wave, (b) a noise-added square wave, (c) a filtered square wave, and (d) a shaped square wave;
fig. 4 is a graph of the calculation of the bit error rate, where (a) is a graph of the bit error rate as a function of the signal-to-noise ratio and (b) is a graph of the bit error rate as a function of the transmission frequency;
the following further describes embodiments of the present invention by way of example with reference to the accompanying drawings.
Detailed Description
Example one
The first step is as follows: designing a transmit modulation section
Firstly, selecting a lead code as a square wave of 30KHZ, and setting the periodicity as 5000; the temperature information adopts 100KHZ square waves, and the periodicity is set to be 8000; the salinity information adopts 50KHZ square waves, and the periodicity is set to 10000; the depth information is an 80KHZ square wave with a cycle number set to 12000. And (3) according to the sequence of the serial mode of group package sending, firstly sending a lead code, secondly sending temperature information, thirdly salinity information and finally depth information, and sending out the four square wave group signals with fixed frequency and determined periodicity.
The second step is that: designing a receive demodulation system
The demodulation system consists of four band-pass filters, a shaper and a counter. The filter has 100 orders and is used for filtering out signals of 30KHz, 100KHz, 50KHz and 80KHz respectively. Since the signal passing through the filter is sinusoidal, it is shaped into a square wave using a shaper. The principle of the shaper is that if the voltage value of the input signal is larger than a certain threshold, the output signal is high, and if equal to or lower than the threshold, the output signal is low. In principle, the threshold is a voltage value greater than zero, so that the final output square wave duty cycle is less than 50%. And finally, counting the number of rising edges by adopting a counter, so that the purpose of counting the number of technical square waves can be achieved, and the information contained in the signal can be acquired.
The third step: communications modem system plus noise test
The transmission modulation section was designed as described in the first step, with a guided wave frequency of 30khz and a period of 5000; the temperature frequency is 100KHz, and the cycle number is 8000; salinity frequency is 50KHz, and periodicity is 10000; the depth frequency is 80KHz, and the periodicity is 12000; the modulated signal is output serially, white gaussian noise is added, the signal-to-noise ratio is set to 8db, an output signal interfered by noise is formed, the signal is input into the receiving and demodulating system as described in the second part, corresponding parameter values are demodulated, the demodulated values are compared with the transmitted values, and corresponding error codes are calculated. The feasibility of the multi-carrier baseband and FSK hybrid modulation method based on the inductive coupling temperature-salt deep chain is verified through simulation tests.
The fourth step: verification experiment by adding actual inductive coupling channel
Designing a sending part by utilizing LABVIEW software, inputting temperature, salinity and depth parameter values, and further modulating a square wave of guided wave 30KHz, wherein the periodicity is set to be 5000; the temperature parameter adopts square waves with the frequency of 100KHz, and the periodicity is set to 8000; the salinity parameter adopts a square wave with the frequency of 50KHz, and the periodicity is set to 10000; the depth parameter was a square wave with a frequency of 80KHz and the number of cycles was set to 12000. The square waves with four frequencies are converted into analog electric signals by an analog-to-digital converter, the analog electric signals are input into an inductive coupling channel, and the signals passing through the channel are collected by an NI USB-6259 data collection card. And demodulating the received digital signal by using the receiving system program described in the third step to obtain specific numerical values of the three parameters, and comparing the obtained numerical values with the sending numerical values to calculate the error rate. The test verifies the feasibility of the multi-carrier baseband and FSK mixed modulation method based on the inductive coupling temperature-salt deep chain in practice, and the feasibility is compared with a simulation test, and the result is consistent with a simulation test result of a system, thereby proving the accuracy of the simulation test.
Simulation and analysis results
(1) As can be seen from fig. 3, the multi-carrier baseband and FSK hybrid modulation method based on the deep chain of inductively coupled thermohaline combines the advantages of baseband modulation and FSK modulation, and uses baseband modulation in combination with different frequencies in FSK modulation, each frequency represents a parameter value, and the number of cycles represents the parameter value. The modulation carrier is not added, only the baseband modulation is carried out, the circuit for sending modulation is simplified, the power consumption of the sending modulation circuit is reduced, and the service time is prolonged; by adopting the multi-frequency carrier, various parameter data can be sent, and the data transmission quantity is improved.
(2) It can be seen from fig. 4 that the error rate of the signal tends to increase gradually with the decrease of the signal-to-noise ratio, and when the noise of the signal is too large, the useful signal is drowned out, causing signal interference and the useful signal cannot be extracted, in order to make the error rate within the range of two thousandths, the theoretical minimum signal-to-noise ratio is 4db, and the signal-to-noise ratio in the actual test is increased to 8 db.
The following conclusions can also be drawn from this experiment: the multi-carrier baseband and FSK hybrid modulation method can simplify circuits and reduce power consumption, the transmission system packs temperature, salt and deep multiple data parameters at one time, the transmission information amount is large, the transmitted parameters can be increased according to actual use conditions, the transmission parameter amount is increased, the monitoring range is enlarged, the service life of the whole system can be prolonged, and a feasible scheme is provided for constructing a complex marine monitoring system.
Claims (3)
1. A multi-carrier baseband and FSK mixed modulation method based on an inductive coupling temperature-salt deep chain is characterized in that:
step 1, designing a transmission modulation system
Firstly, designing a multi-carrier baseband and FSK mixed modulation method based on the channel characteristics of an inductive coupling temperature-salt deep-chain marine communication system, and carrying out baseband square wave modulation without adding a carrier; the square wave frequency part adopts a frequency variation mode of FSK, and three parameters of temperature, salinity and depth are required to be transmitted in a signal subjected to baseband modulation except pilot frequency, so that serial data of four different frequencies are transmitted to a channel, the first frequency section is guided wave, the periodicity is fixed, and the guided wave plays roles of guiding, identifying and frequency calibrating; the last three frequencies are parameters of temperature, salinity and depth in the ocean respectively, and the value of the periodicity represents the parameter values of the temperature, the salinity and the depth; the four frequencies are transmitted together as a group of data;
step 2, designing a receiving demodulation system
The demodulation system is composed of four band-pass filters, a shaper and a counter, the modulated signal passes through four filters with different frequency parameters respectively to extract baseband signals of each frequency, then signal waveforms filtered by the filters are respectively shaped to form square waves, and the square waves are counted and stored by utilizing rising edges; if the number of cycles of the first frequency is the same as the number of cycles of the transmitted first frequency waveform, storing the data received later; if not, discarding the following data;
step 3, noise test of communication modulation-demodulation system
Integrating a data sending system and a data receiving system together to form a complete communication receiving and sending system, utilizing MATLAB to carry out test simulation, adding Gaussian white noise to the system, inputting 3 data quantities of temperature, salinity and depth, modulating corresponding frequency and periodicity through a modulation system, setting the signal-to-noise ratio of the system, demodulating and receiving through the demodulation system, and demodulating corresponding sent parameter values;
step 4, adding an actual inductive coupling channel to carry out verification experiment
Designing a transmission modulation system by utilizing LABVIEW software, namely inputting numerical values of three parameters of temperature, salinity and depth, modulating a square wave signal formed by combining four different frequencies of guided wave, temperature, salinity and depth, adding Gaussian white noise to simulate an actual environment, transmitting a signal of mixed noise to an actual marine communication inductive coupling channel, and acquiring the signal passing through the channel by utilizing an NI USB-6259 data acquisition card; the received digital signal is demodulated by a receiving system program to obtain the specific numerical values of the three parameters.
2. The method according to claim 1, wherein the multi-carrier baseband and FSK hybrid modulation method transmission protocol is guided wave, parameter 1, parameter 2, and parameter 3 combined serial transmission, the guided wave frequency and the cycle number are fixed, each parameter frequency is different in the front part of the whole transmission parameter, and the number of the parameters can be expanded arbitrarily according to requirements.
3. The method according to claim 1, wherein the multi-carrier baseband and FSK hybrid modulation method is invented based on an inductively coupled channel thermohaline deep chain, and is suitable for parameter expansion in an inductively coupled thermohaline deep chain based marine communication system.
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