CN103441803B - A kind of underground low frequency wireless communication system based on low-power small electric antenna - Google Patents
A kind of underground low frequency wireless communication system based on low-power small electric antenna Download PDFInfo
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- CN103441803B CN103441803B CN201310409920.4A CN201310409920A CN103441803B CN 103441803 B CN103441803 B CN 103441803B CN 201310409920 A CN201310409920 A CN 201310409920A CN 103441803 B CN103441803 B CN 103441803B
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Abstract
The present invention proposes a kind of underground low frequency wireless communication system based on low-power small electric antenna, this communication system comprises the transmitting terminal FPGA digital control module be linked in sequence, power amplification and impedance matching module, small size VLF transmit antennas, small size vlf receiving antenna, receiving terminal filter and amplification module, receiving terminal FPGA digital control module, host computer, this system replaces electromagnetic communication mode by adopting magnetic induction way, solve traditional VLF antenna large scale, the shortcoming of large transmitting power, available and underground---underground and underground---directional radio communication between ground, also can be used as the short-distance and medium-distance wireless transmission that standalone module completes in-ground sensor data receiving device earthward.
Description
Technical field
The present invention relates to a kind of underground low frequency wireless communication system based on low-power small electric antenna, belong to the technical field of low frequency communication system integrated circuit (IC) design under earth's surface, in particular to a kind of design realizing the electronically small antenna (ESA, electrically small antenna) being embedded in LF communication between the node in soil.
Background technology
Wirelessly lower sensor network (WUSN) can realize the monitoring of underground environment, the water in such as soil and the content of mineral matter, the Oil spills of oil reservoir, plate motion, the monitoring of landslide and earthquake, is quite to enliven at present and promising research field.But, because transmission medium is no longer air, but soil, rock and water, radio communication has certain challenge for underground environment.For ground lower channel, in order to walk around the barriers such as rock, technical staff must use LF communication, and this makes antenna size very large, is not suitable for being embedded in underground.Thus the radio signal propagation technology that result in use electromagnetic wave (EM) perfect can not well work in underground environment.Therefore, under the condition ensureing LF communication, how reducing the Focal point and difficult point that antenna size becomes the research realizing underground communication at present, is also one of study hotspot of current low frequency underground communication.
Replacing traditional electromagnetic wave radio communication, utilize induced field to communicate, is one of key technology that can solve underground communication large-size antennae.Magnetic strength communication can make antenna size much smaller than wavelength, and its communication distance is far away in addition, decays little, so it is more suitable for the low wirelessly lower sensor network system of frequency.
At present, the research of underground communication mainly concentrates on mine district, tunnel, the environment of the underground spaciousnesses such as underground garage, and still utilizes frequency electromagnetic waves to communicate, and due to the problem of technical difficulty, the research utilizing magnetic strength to carry out communicating is few.That carries out this research mainly contains following Liang Ge unit: 1) SunZhi of Georgia Tech to be communicated with magnetic strength the path loss of (MI) and bandwidth by contrast electromagnetic wave (EM), proposes a kind of method increasing propagation distance.They test in mine district, and to channel model, channel capacity etc. are studied.But its propagation medium remains air, be not that node is embedded in soil.2) R.R.A.Syms of the Imperial College bandwidth of structuring the formation to linear and cross topological structure, energy density, theoretical research is carried out in the transmitting refraction etc. of different medium.In addition, its student summarizes to its work, emulates, but all stop at theory analysis from other angles, does not carry out actual experiment.
The antenna size size of communication is relevant to specific implementation, current communication system employing electromagnetic communication mode, due to antenna length and communication wavelengths comparable, make when very low frequency (VLF) communication, antenna size reaches a few km, is not easy to burying underground of node; And support the system of electromagnetic communication, be applied to when communicating in soil, its transmitting power also requires very large, and this needs us again to plan underground communication issue.
Summary of the invention
Be directed to above-mentioned technological deficiency, the present invention is based on magnetic induction principle and design a kind of small size very low frequency magnetic strength electronically small antenna, make only the Coupled Signal Power of receiving terminal antenna just can be made to reach distinguishable rank by less transmitting power, and design analog filtering and the multistage amplifier circuit of a solution Hz noise for receiving terminal, realize the digital modulation in this communication system, demodulation based on field programmable gate array FPGA simultaneously.Native system can with and underground---underground and underground---directional radio communication between ground, can be used as the short-distance and medium-distance wireless transmission that standalone module completes in-ground sensor data receiving device earthward.
This communication system comprise be linked in sequence transmitting terminal FPGA digital control module, power amplification and impedance matching module, small size VLF transmit antennas, small size vlf receiving antenna, receiving terminal filter and amplification module, receiving terminal FPGA digital control module, host computer.Transmitting terminal FPGA numerical control system and receiving terminal FPGA digital control module, it comprise cyclone II chip, flash chip, A D conversion chip, D A conversion chip, channel selecting chip.Wherein cyclone II chip is the low and middle-end FPGA of altera corp, be used for realizing modulation logic, D A interface driver logic, A D interface drive logic, demodulation logic; Flash chip is that the flash of external 64M is used for storing reception data; A D conversion chip be 8 A D conversion chip be used for produce modulation after analog signal; D A conversion chip be 8 D A conversion chips be used for receiving terminal amplify after signal sample; Channel selecting chip be used for control D A gather the signal of different amplification.
Described power amplification and impedance matching module are the transmitting terminal analog circuits be made up of power amplification circuit and impedance matching circuit, wherein, power amplification circuit carries out prime amplification by operational amplifier, accurate complementary output level circuit is formed to improve current output capability by pliotron, impedance matching circuit comprises the transformer that the output impedance of circuit and the input impedance of load circuit are matched, thus makes load obtain maximum power.
Described small size VLF transmit antennas and small size vlf receiving antenna are self be perceptual square coil, make transmitting and receiving loop be purely resistive by connecting with resonant capacitance.So-called small size very low frequency refers to and size is far smaller than the wavelength that transmits, respective value scope well known in the art, and such as can arrange the square coil that transmitting antenna is length of side 0.8m, very low frequency also has corresponding common art-recognized meanings in this area.Modulation signal is through power amplification and be loaded into loop, magnetic strength antenna place after carrying out impedance matching, and in coil, the current signal of alternation can make the magnetic field occurred in transmitting coil near field range with the change of signal rule; The structure of reception antenna is identical with transmitting antenna, is in the receiving coil in transmitting antenna near field range and goes out electromotive force by the magnetic field induction of alternation, just can obtain modulation signal after this small-signal being carried out pre-amplification, active bandpass filiter, multistage amplification.Because current-carrying coil normal direction magnetic field intensity decays with the cube rule of distance in theory, as long as control transmitting terminal power and communication distance well, the signal that receiving coil is coupled to just can identify completely after filter and amplification.
Described receiving terminal filter and amplification module comprises the pre-amplification circuit, bivalent high-pass filter, eight rank active band-pass filters, the multistage amplifier circuit that connect in turn.General site of deployment Hz noise is serious, and power frequency and most of odd harmonic thereof all belong to very low frequency category, and the antenna that accepts based on magnetic strength principle is easy to be coupled into power frequency component, the letter of signal and Hz noise/disturb than being sometimes even less than-30dB.Need large technological difficulties of solution so solution power frequency and the interference of odd harmonic to signal thereof are the present invention, and this key problem in technology point is the design of analog filtering amplifying circuit.In order to reach good filter effect, in the present invention, first series resonance mode can be adopted by magnetic strength antenna, resonance frequency is signal center frequency, then by induced signal by exporting after the cascade filtering of second order passive high three-way filter and eight rank active band-pass filters, thus under the prerequisite that effectively inhibit Hz noise, extract useful signal.In order to improve the response time to received signal, amplifier section adopts multistage amplification, the signal of the different gains that FPGA control AD multichannel cycle detection is not at the same level, selects suitable passage automatically by amplitude detection algorithm, thus effectively reduces the gain-adjusted time of tradition from gain amplifier.
Described host computer is used for monitoring each channel signal waveform and relevant parameter, and as peak-to-peak value, signal amplification factor etc. are gone forward side by side, line frequency is composed, Digital Filter Analysis.This host computer designs based on LabView graphical programming software, receive the data of FPGA transmission by UART interface, and the waveform showing each passage can be refreshed in real time, have and calculate received power for a certain passage waveform, carry out Fourier transform in real time, and draw out the functions such as spectrogram.This host computer is not only exchanged examination and is brought great convenience, also can as host computer data processing terminal.
Accompanying drawing explanation
Fig. 1 is underground of the present invention wireless LF communication system general diagram;
Fig. 2 is underground of the present invention wireless LF communication systems radiate terminal circuit figure;
Fig. 3 is underground of the present invention wireless LF communication system receiving terminal filtering, amplification circuit diagram;
Fig. 4 is underground of the present invention wireless LF communication system multistage amplifier circuit operation principle and digital processing schematic diagram;
Fig. 5 is the wireless LF communication system FPGA in underground of the present invention and host computer communication scheme;
Fig. 6 is underground of the present invention---underground communication schematic diagram;
Fig. 7 is underground of the present invention---ground communication schematic diagram.
Embodiment
Below in conjunction with accompanying drawing and embodiment, the present invention is described in further detail.
Fig. 1 is underground of the present invention wireless LF communication system general diagram.As shown in the figure, communication system adopts coil magnetic strength mode to carry out radio communication, solves the bottleneck of traditional VLF antenna large scale and large transmitting power.This communication system comprise be linked in sequence transmitting terminal FPGA digital control module, power amplification and impedance matching module, small size VLF transmit antennas, small size vlf receiving antenna, receiving terminal filter and amplification module, receiving terminal FPGA digital control module, host computer.Digital signal modulated is converted to analog signal by transmitting terminal FPGA digital control module, this analog signal is loaded into small size VLF transmit antennas through power amplification and impedance matching module, the alternating current produced in transmitting antenna makes the magnetic field of surrounding with the change of signal regularity, small size vlf receiving antenna goes out signal by the magnetic field induction of change, the signal induced carries out frequency-selecting amplification through receiving terminal filter and amplification module, signal after amplification is converted to digital signal again, after the process of receiving terminal FPGA digital control module, be sent to host computer.
Fig. 2 is underground of the present invention wireless LF communication systems radiate terminal circuit figure.After signal is carried out digital modulation by FPGA by D A be converted to analog signal, by low pass filter decay D A conversion in produce high-frequency signal, then filtered signal is sent to power amplification circuit.The signal be coupled to make receiving terminal reaches and can detect rank, needs suitably to increase the electric current in transmitting coil thus the magnetic field intensity strengthened around it.In order to reach this object, transmitting coil and electric capacity being formed series resonant circuit, making radiating circuit input impedance close to purely resistive, thus make power amplifier can produce larger resonance current with less output voltage, reduce the burden of power amplifier.
Fig. 3 is underground of the present invention wireless LF communication system receiving terminal filtering, amplification circuit diagram.Can see from figure, and transmitting coil is similar, the same and resonant capacitance of receiving coil forms series resonant circuit, unlike, the effect of resonant circuit be herein to coil-induced to signal carry out preliminary frequency-selecting, suppress a part of noise; First the upper voltage signal of resonant capacitance carries out elementary amplification to strengthen signal power through high input impedance amplifying circuit, in order to suppress the interference of power frequency and its industrial frequency harmonic, then the passive high-pass filtering of second order is carried out to signal, then by active eight rank band pass filters, signal is selected further, finally multistage amplification is carried out to the signal after filtering frequency-selecting.
Fig. 4 is underground of the present invention wireless LF communication system multistage amplifier circuit operation principle and digital processing schematic diagram.Conventional variable gain amplifier needs certain regulating time to make the signal amplitude after amplification stable within the specific limits, in order to improve the response time to received signal, amplifier section of the present invention adopts multistage amplification mode, FPGA is by the signal of channel to channel adapter cycle detection different amplification, analyzed by AD sampling, once find that the signal of effective breadth appears in certain passage, just this passage selected immediately, carries out further digital filtering to the data from this channel acquisition, demodulation obtains digital signal.Thus effectively reduce the gain-adjusted time of tradition from gain amplifier.
Fig. 5 is the wireless LF communication system FPGA in underground of the present invention and host computer communication scheme.Host computer plays an important role in can not only debugging at the scene, simultaneously also can in actual applications as the in-ground sensor data that data center process FPGA sends.The major function of host computer has: the Received signal strength waveform of display receiver in real time, the power of Received signal strength is calculated according to time domain waveform effective value and multiplication factor, Fourier transform carried out to time-domain signal and demonstrates frequency-domain waveform, by variable element digital filter, further Filtering Analysis being carried out to waveform.
Fig. 6 is underground of the present invention---underground communication schematic diagram.This communication system lower poweredly can realize signal and propagate in soil, and when small sized antenna is the square coil of length of side 0.8m, propagation distance all can reach 30m, thus carries out the monitoring of underground environment.
Fig. 7 is underground of the present invention---ground communication schematic diagram.This communication system can be applied to the short-distance and medium-distance wireless transmission of in-ground sensor data receiving device earthward as standalone module.By adjustment aerial angle, the collection signal of underground still can be reached 30m to the distance transmitted on the ground as standalone module by native system, thus completes being converged to ground server by underground monitoring information of task.
The wireless LF communication system in underground of a kind of low-power small electric antenna based on magnetic strength proposed by the invention replaces electromagnetic communication mode by adopting magnetic induction way, solves the shortcoming of traditional VLF antenna large scale, large transmitting power.According to antenna general principle, if adopt traditional electromagnetic communication mode, the size of VLF antenna need reach a few km and signal Net long wave radiation could be gone out, and existing very low frequency (VLF) communication signal loading to the antenna of a few km will realize the transmitting of signal with relatively high power.And the magnetic strength antenna in the present invention is far smaller than the wavelength that transmits first dimensionally, be easy to carry installation, and pass through resonance, the electric field alternately conversion of the magnetic field that transmitting coil produces and series capacitance, make the active loss of energy less, this resonance manner also reduces the driving power of transmitting terminal power amplifier.
Disclosedly above be only preferred embodiment of the present invention, can not limit interest field of the present invention with this, the equal change done according to the present patent application the scope of the claims, still belongs to the scope that the present invention is contained.
Claims (4)
1. the underground low frequency wireless communication system based on low-power small electric antenna, it is characterized in that, this communication system comprise be linked in sequence transmitting terminal FPGA digital control module, power amplification and impedance matching module, small size VLF transmit antennas, small size vlf receiving antenna, receiving terminal filter and amplification module, receiving terminal FPGA digital control module, host computer, wherein, digital signal modulated is converted to analog signal by transmitting terminal FPGA digital control module, this analog signal is loaded into small size VLF transmit antennas through power amplification and impedance matching module, the alternating current produced in transmitting antenna makes the magnetic field of surrounding with the change of signal regularity, small size vlf receiving antenna goes out signal by the magnetic field induction of change, the signal induced carries out frequency-selecting amplification through receiving terminal filter and amplification module, signal after amplification is converted to digital signal again, host computer is sent to after the process of receiving terminal FPGA digital control module, wherein, described power amplification and impedance matching module are the transmitting terminal analog circuits be made up of power amplification circuit and impedance matching circuit, wherein, power amplification circuit carries out prime amplification by operational amplifier, accurate complementary output level circuit is formed by pliotron, impedance matching circuit comprises the transformer that the output impedance of circuit and the input impedance of load circuit are matched, described receiving terminal filter and amplification module comprises the pre-amplification circuit, bivalent high-pass filter, eight rank active band-pass filters, the multistage amplifier circuit that connect in turn.
2. communication system according to claim 1, it is characterized in that, described transmitting terminal FPGA digital control module and receiving terminal FPGA digital control module be comprise cyclone II chip, flash chip, A D conversion chip, D A conversion chip, channel selecting chip.
3. communication system according to claim 1, is characterized in that, described small size VLF transmit antennas and small size vlf receiving antenna are self be perceptual square coil, make transmitting and receiving loop be purely resistive by connecting with resonant capacitance.
4. communication system according to claim 1, is characterized in that, described host computer is used for monitoring each channel signal waveform and relevant parameter and goes forward side by side line frequency spectrum, Digital Filter Analysis.
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