CN104113501A - Modulator, demodulator, modulation method and demodulation method for low-frequency magnetic induction communication - Google Patents
Modulator, demodulator, modulation method and demodulation method for low-frequency magnetic induction communication Download PDFInfo
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Abstract
The invention provides a modulator, demodulator, modulation method and demodulation method for low-frequency magnetic induction communication. Therefore, problems of mutual restriction of a bandwidth and a Q value of the existing low-frequency magnetic induction communication transmitting terminal, low low-frequency communication rate, low integration degree and flexibility of the hardwire demodulation mode of the receiving terminal, and large calculation amount of the software demodulation mode in the prior art can be solved. According to the modulator, use data are successively processed by channel coding, BPSK digital modulation, D/A conversion and power amplification and then are inputted into a first series connection resonance loop; voltage physical reversing of the two ends of a first capacitor in the resonance loop is carried out at the time of phase changing of the loop current signal of the first series connection resonance loop, thereby avoiding the loop current signal attenuation. Therefore, the modulation signal bandwidth can be substantially improved on the premise that the Q value is maintained to be high; and the communication rate is improved.
Description
Technical field
The invention belongs to the modulation-demodulation technique of the communications field, relate in particular to a kind of modulator, demodulator and modulator approach and demodulation method of low-frequency magnetic inductive communication.
Background technology
At present, low frequency magnetic strength is communicated by letter because its antenna size is little, is not subject to multipath effect in communication process, the impact of propagation delay and decline and being widely used in subsurface communication and underground communication.But the channel under low frequency frequency range is a low-rate channel, how the most effectively utilizing communication channel is the difficult point in current LF communication technology.
In prior art, low-frequency resonant circuit common in the transmitting terminal of low frequency magnetic strength communication generally need to be accepted or rejected between bandwidth and Q value, wanting to increase resonant bandwidth must be taking the Q value of reduction circuit as cost, vice versa, therefore be all generally after balance, choose suitable bandwidth with Q value to meet the condition of communicating by letter, bandwidth and Q value cannot be got maximum simultaneously.In addition, when the receiving terminal of low frequency magnetic strength communication carries out signal capture, local replica has also reduced the real-time of communicating by letter with the related operation of lead code, and existing hardware demodulation mode hardware integration degree is low, demodulation flexibility is not high, for addressing this problem, the scheme of software demodulation has been proposed in prior art, replace complicated demodulator circuit with monolithic system, the integrated level that has so not only improved hardware system has more increased the flexibility of demodulation, but than traditional circuit type hardware demodulation, the shortcoming of existing software demodulation is that amount of calculation is larger, processing time that need to be longer.
In sum, the bandwidth of existing low frequency magnetic strength communications transmit end and the value of Q value mutually limit and cause LF communication speed low, and the hardware demodulation mode integrated level of receiving terminal is low, flexibility is not high, and software demodulation mode exists the problem that amount of calculation is large.
Summary of the invention
The invention provides a kind of modulator, demodulator and modulator approach and demodulation method of low-frequency magnetic inductive communication, mutually limit and cause LF communication speed low for solving the bandwidth of existing low frequency magnetic strength communications transmit end and the value of Q value, the hardware demodulation mode integrated level of receiving terminal is low, flexibility is not high, and software demodulation mode exists the problem that amount of calculation is large.
For addressing the above problem, first the present invention provides a kind of modulator of low-frequency magnetic inductive communication, comprising: the first arm processor, phase-shifting full-bridge BPSK modulation circuit and low-frequency magnetic induced emission antenna; The input of described phase-shifting full-bridge BPSK modulation circuit is connected with described the first arm processor by FSMC bus, and output connects described low-frequency magnetic induced emission antenna; Described the first arm processor carries out chnnel coding to user data, obtains sequence of symhols to be sent and described sequence of symhols is sent to described phase-shifting full-bridge BPSK modulation circuit through FSMC bus; Described phase-shifting full-bridge BPSK modulation circuit added preamble sequence 01010101 and the sequence of symhols of receiving is modified before the sequence of symhols of receiving: whenever 0101010 just after insert one 0, and amended sequence of symhols is carried out obtaining the first modulated-analog signal after BPSK Digital Modulation, D/A conversion and power amplification successively; The port of exporting described the first modulated-analog signal forms the first series resonant tank by first electric capacity and described low-frequency magnetic induced emission antenna successively, and described in described phase-shifting full-bridge BPSK modulation circuit real-time judge, whether the phase place of the loop current signals of the first series resonant tank will there is the change of 180 degree, if so, in moment of the phase change of the loop current signals of described the first series resonant tank by described the first electric capacity both end voltage physical property reversion; Described low-frequency magnetic induced emission antenna is converted to low frequency magnetic field signal by the current signal that flows through self and sends.
Preferably, described phase-shifting full-bridge BPSK modulation circuit comprises: BPSK digital modulation module, D/A modular converter, power amplifier, the first switch, second switch, the 3rd switch, the 4th switch, switching circuit control module, not gate logical device and described the first electric capacity; The input of described BPSK digital modulation module is connected with described the first arm processor by FSMC bus, and output is connected with the input of described D/A modular converter; Described BPSK digital modulation module added preamble sequence 01010101 and the sequence of symhols of receiving is modified before the sequence of symhols of receiving: whenever 0101010 just after insert one 0; And amended sequence of symhols is carried out to BPSK Digital Modulation; The output of described D/A modular converter is connected with the input of described power amplifier; The output of described power amplifier is connected with one end of described the first switch, the 3rd switch simultaneously, and the other end of the other end of described the first switch and the 3rd switch is connected by described the first electric capacity; The link of described the first switch and the first electric capacity is also connected with one end of described second switch, and the other end of described second switch is connected with coil one end of described low-frequency magnetic induced emission antenna, the coil other end ground connection of described low-frequency magnetic induced emission antenna; The link of described the 3rd switch and the first electric capacity is also connected with one end of described the 4th switch, and the other end of described the 4th switch connects the coil connecting terminal of described second switch and described low-frequency magnetic induced emission antenna; Described switching circuit control module is connected with described BPSK digital modulation module, and its control output end is connected with the input of described not gate logical device, the control end of the first switch, the input of the 4th switch simultaneously, the output of described not gate logical device is connected with the control end of described second switch and the control end of the 3rd switch simultaneously; Described switching circuit control module is the modulation case to sent sequence of symhols according to described BPSK digital modulation module, the moment of spending at the phase change 180 of the loop current signals of described the first series resonant tank, the digital signal of exporting to described not gate logical device is carried out to 0-1/1-0 switching, to control described the first switch, second switch, the 3rd switch, the 4th switch changes current on off state.
Preferably, described BPSK digital modulation module and switching circuit control module adopt FPGA mode to realize.
Preferably, described phase-shifting full-bridge BPSK modulation circuit also comprises the first resistance, isolating amplifier circuit, an A/D modular converter and current zero detection module; The coil other end not being connected with described second switch of described low-frequency magnetic induced emission antenna is by described the first grounding through resistance, described isolating amplifier circuit input connects the coil of described low-frequency magnetic induced emission antenna and the link of the first resistance, and output connects the input of a described A/D modular converter; The output of a described A/D modular converter connects the input of described current zero detection module, and the output of described current zero detection module is connected with described switching circuit control module; Described current zero detection module detects the direction of the loop current of described the first series resonant tank by an A/D modular converter, isolating amplifier circuit, the first resistance and low-frequency magnetic induced emission antenna institute connection circuit, and notifies described switching circuit control module in the loop current of described the first series resonant tank by the zero passage moment; The loop current of the first series resonant tank that described switching circuit control module is sent according to described current zero detection module is notified by zero passage, judge that whether current signal element to be sent is identical with the upper code element just having sent, if not, in the loop current zero passage moment of described the first series resonant tank, the digital signal of exporting to described not gate logical device is carried out to 0-1/1-0 switching.
The present invention also provides a kind of modulator of low-frequency magnetic inductive communication of the modulator corresponding to above-mentioned low-frequency magnetic inductive communication, comprising: low-frequency magnetic induction reception antenna, the second electric capacity, impedance matching transformer, active filter, programmable amplifying circuit, the 2nd A/D modular converter, BPSK demodulation module and the second arm processor; The alternating magnetic field of the low frequency magnetic field signal formation that described low-frequency magnetic induction reception antenna sends according to the modulator of low-frequency magnetic inductive communication induces the second analog current modulation signal; The primary coil of described low-frequency magnetic induction reception antenna, the second electric capacity and impedance matching transformer is composed in series the second series resonant tank, it is pure resistive and equate with the internal resistance of described low-frequency magnetic induction reception antenna that the equiva lent impedance of described impedance matching transformer in described the second series resonant tank is, and described the second series resonant tank is carried out frequency-selecting for the second analog current modulation signal that described low-frequency magnetic induction reception antenna is exported; The 3rd analog current modulation signal of the secondary coil output of described impedance matching transformer is successively through described active filter filtering, carry out signal amplification through described programmable amplifying circuit, be converted to digital modulation signals through described the 2nd A/D modular converter, after described BPSK demodulation module is demodulated into digital demodulation signal, send to described the second arm processor to carry out error detection, described the second arm processor offers user using correct digital demodulation signal as user data; Wherein, the signal that described BPSK demodulation module is 01010101 for demodulation lead code, described BPSK demodulation module adopts FPGA mode to realize.
Preferably, the described BPSK demodulation module in described demodulator comprises: carrier recovery unit, correlation demodulation unit, lead code recognition unit, clock sampling unit and thresholding judging unit; Described carrier recovery unit adopts costa ring computational methods, the phase difference of the signal carrier of the digital modulation signals of exporting by local carrier and described the 2nd A/D modular converter is revised in real time to carrier phase, and revised carrier wave is sent to described correlation demodulation unit; Described correlation demodulation unit comprises multiplier and FIR low pass filter, described multiplier is connected with the output of the output of described the 2nd A/D modular converter, described carrier recovery unit and the input of described FIR low pass filter respectively, the digital modulation signals of the carrier signal that described multiplier is exported described carrier recovery unit and the output of the 2nd A/D modular converter carries out sending to described FIR low pass filter after multiplication, and described FIR low pass filter carries out filtering to input signal and obtains baseband signal and export described lead code recognition unit to; The lead code of the baseband signal of described lead code recognition unit to the output of FIR low pass filter is identified, and draws the phase place of sampling clock and offers described clock sampling unit and thresholding judging unit with this; Described clock sampling unit is connected with described carrier recovery unit, be used for the phase place of the sampling clock of sending according to described lead code recognition unit, carrier signal to described carrier recovery unit output is carried out clock sampling, obtains the frequency of sampling clock and provides it to described thresholding judging unit; The phase place of sampling clock that the utilization of described thresholding judging unit is received and the frequency of sampling clock, obtain sampling clock and with this clock, described baseband signal carried out to threshold judgement, demodulates digital demodulation signal.
Corresponding to the modulator of low-frequency magnetic inductive communication provided by the invention, the present invention also provides a kind of modulator approach of low-frequency magnetic inductive communication, and the method comprising the steps of:
S11: user data is carried out to chnnel coding, obtain sequence of symhols to be sent;
S12: described sequence of symhols to be sent is carried out to BPSK Digital Modulation, and in modulated process, the lead code of the digital signal after modulation is set as to 01010101, and the sequence of symhols of receiving is modified: whenever 0101010 just after insert one 0, obtain BPSK digital modulation signals;
S13: described BPSK digital modulation signals is carried out to D/A conversion, obtain BPSK modulated-analog signal;
S14: described BPSK modulated-analog signal is carried out to power amplification and obtain the first modulated-analog signal;
S15: in the first series resonant tank that described the first modulated-analog signal input one is made up of port, the first electric capacity and the low-frequency magnetic induced emission antenna of described the first modulated-analog signal of output, and described in real-time judge, whether the phase place of the loop current signals of the first series resonant tank will there is the change of 180 degree, if so, in moment of the phase change of described loop current signals by described the first electric capacity both end voltage physical property reversion;
S16: described low-frequency magnetic induced emission antenna is converted to low frequency magnetic field signal by the current signal that flows through self and sends.
Preferably, in the modulator approach of described low-frequency magnetic inductive communication, whether the phase place that judges the loop current signals of described the first series resonant tank described in S15 by the method for the changes that 180 degree occur is: judge that whether current signal element to be sent is identical with the upper code element just having sent, if not, near the current zero-crossing point generation phase shift of the loop current signals of described the first series resonant tank code element changes the moment.
Corresponding to the demodulator of low-frequency magnetic inductive communication provided by the invention, the present invention also provides a kind of demodulation method of low-frequency magnetic inductive communication, comprises step:
S21: the alternating magnetic field of the low frequency magnetic field signal formation that low-frequency magnetic induction reception antenna sends according to the modulator of low-frequency magnetic inductive communication induces the second analog current modulation signal;
S22: described the second analog current modulation signal is carried out to the 3rd analog current modulation signal that frequency-selecting obtains;
S23: described the 3rd analog current modulation signal is carried out successively to active power filtering, signal amplify, A/D conversion, obtain lead code and be 01010101 digital modulation signals;
S24: the described digital modulation signals that is 01010101 to lead code carries out BPSK demodulation, and the sequence of symhols that demodulation is obtained is modified: often run into 01010100 and just remove finally 0, obtain digital demodulation signal;
S25: described digital demodulation signal is carried out to error detection, and correct digital demodulation signal is offered to user as user data.
Preferably, in above-mentioned demodulation method, the method that the described digital modulation signals that is 01010101 to lead code described in S24 carries out BPSK demodulation is:
S241: adopt costa ring computational methods, the phase difference of the signal carrier by local carrier and described digital modulation signals is revised in real time to carrier phase;
S242: carry out multiplying by the carrier signal that described digital modulation signals and S241 are obtained, and multiplication result is carried out to FIR low-pass filtering, recover baseband signal;
S243: the lead code 01010101 to described baseband signal is identified, and just remove finally 0 running into 01010100 at every turn, finally draws the phase place of sampling clock, and the carrier signal that S241 is obtained is carried out clock sampling and obtain the frequency of sampling clock;
S244: utilize the phase place of described sampling clock and the frequency of sampling clock to obtain sampling clock, and with the sampling clock obtaining, described baseband signal is carried out to threshold judgement, and revise code element, demodulate digital demodulation signal.
Preferably, utilize finite automaton state machine to identify the lead code 01010101 of described baseband signal in described S243, concrete recognition methods is:
S31: set condition machine initial condition value is 0, represents that lead code is to be identified, gets the hang of 1 if recognize the rising edge of baseband signal in this state;
S32: under the prerequisite of state 1, if recognize the next hopping edge of baseband signal and be trailing edge and and time interval of previous rising edge for (1-m) T is between (1+m) T, get the hang of 2, if exceed (1+m) T and occur return state 0 without trailing edge with the time interval of previous rising edge; Wherein m is fixed value and 0<m<1/2, and T is a code-element period;
S33: under the prerequisite of state 2, if recognize the next hopping edge of baseband signal and be rising edge and and time interval of previous trailing edge between (1+m) T, get the hang of 3 for (1-m) T, if with time interval of previous trailing edge for exceeding (1+m) T and occurring return state 0 without rising edge; Wherein m is fixed value and 0<m<1/2, and T is a code-element period;
S34: the process of repeating step S32-S33, each detection by state value increasing 1, otherwise state value returns to 0, until get the hang of 7, the lead code of described baseband signal is identified successfully.
Preferably, the method of identifying the hopping edge of baseband signal in described S31-S34 process is: be n point by the data point markers of the current baseband signal that needs identification, Ruo Dang (n-N/2) o'clock is negative and lower than the negative threshold value of setting to the point between (n-k) point, and the point between (n+k) o'clock to (n+N/2) point is just and higher than in the positive threshold value of setting, think that rising edge appears in the current data point place of baseband signal that needs identification, and within 1/2 code-element period time next, suspend the hopping edge of identification baseband signal; Wherein, k is constant and 0<k<N/4, and N is a sampling number that code-element period is corresponding.
The beneficial effect of technique scheme of the present invention is as follows:
In the modulator and modulator approach of low-frequency magnetic inductive communication provided by the invention, by low-frequency magnetic induced emission antenna, the first electric capacity and loop resistance form series resonant circuit, resonant capacitance (i.e. the first electric capacity) is arranged in " H " bridge switch circuit, changing in transmission of symbols is the signal phase shift moment, can control the first electric capacity by " H " bridge switch circuit reverses in circuit, allow the course of discharge of signal voltage direction and the first electric capacity be consistent, thereby avoid the decay of current signal, make modulation signal in resonant tank, maintain maximum resonance state always, can under the prerequisite that keeps higher Q value, greatly improve the bandwidth of modulation signal, effectively raise the speed of LF communication, the bandwidth of existing low frequency magnetic strength communications transmit end and the problem that value limits mutually and traffic rate is low of Q value are solved.In addition, the demodulator of corresponding low-frequency magnetic inductive communication provided by the invention and demodulation method adopt digital demodulation mode to carry out demodulation, can catch fast and accurately lead code, ensure the real-time of demodulation, increase the flexibility of demodulation and improved the integrated level of hardware, in demodulation, adopt pattern recognition to carry out lead code and catch, amount of calculation, far below traditional correlation capturing, is conducive to the low power dissipation design of whole system.
Brief description of the drawings
The modulator structure schematic diagram of a kind of low-frequency magnetic inductive communication that Fig. 1 provides for the embodiment of the present invention;
Wherein a kind of preferably structural representation in real time of the modulator of the low-frequency magnetic inductive communication that Fig. 2 provides for the embodiment of the present invention
Fig. 3 is the phase-shifting full-bridge BPSK modulated process schematic diagram in circuit shown in Fig. 2;
Fig. 4 is that the another kind of the modulator of low-frequency magnetic inductive communication is preferably implemented structural representation;
Fig. 5 is the modulator approach flow chart of low-frequency magnetic inductive communication provided by the invention;
Fig. 6 is the demodulator structure schematic diagram of a kind of low-frequency magnetic inductive communication provided by the invention;
Fig. 7 is the preferably real-time structural representation of the one of the demodulator of low-frequency magnetic inductive communication shown in Fig. 6;
Fig. 8 is the demodulation method flow chart of low-frequency magnetic inductive communication provided by the invention.
[accompanying drawing main components description of symbols]
1, the first arm processor;
2, phase-shifting full-bridge BPSK modulation circuit;
3, low-frequency magnetic induced emission antenna;
4, BPSK digital modulation module;
5, D/A modular converter;
6, power amplifier;
7, switching circuit control module;
8, not gate logical device;
9, isolating amplifier circuit;
10, an A/D modular converter;
11, current zero detection module;
12, low-frequency magnetic induction reception antenna;
13, impedance matching transformer;
14, active filter;
15, programmable amplifying circuit;
16, the 2nd A/D modular converter;
17, BPSK demodulation module;
18, the second arm processor;
19, carrier recovery unit;
20, correlation demodulation unit;
21, lead code recognition unit;
22, clock sampling unit;
23, thresholding judging unit;
24, multiplier;
25, FIR low pass filter;
K1, the first switch;
K2, second switch;
K3, the 3rd switch;
K4, the 4th switch;
C1, the first electric capacity;
R1, the first resistance;
C2, the second electric capacity.
Embodiment
For making the technical problem to be solved in the present invention, technical scheme and advantage clearer, be described in detail below in conjunction with the accompanying drawings and the specific embodiments.
The modulator structure schematic diagram that Figure 1 shows that a kind of low-frequency magnetic inductive communication that the embodiment of the present invention provides, as shown in fig. 1, this modulator comprises: the first arm processor 1, phase-shifting full-bridge BPSK modulation circuit 2 and low-frequency magnetic induced emission antenna 3.Wherein, the input of phase-shifting full-bridge BPSK modulation circuit 2 is connected with the first arm processor 1 by FSMC bus, and output connects low-frequency magnetic induced emission antenna 3.The first arm processor 1 carries out chnnel coding to user data, obtains sequence of symhols to be sent and sequence of symhols is sent to phase-shifting full-bridge BPSK modulation circuit 2 through FSMC bus, and be responsible for the interface protocol of this modulator and other equipment.Phase-shifting full-bridge BPSK modulation circuit 2 added preamble sequence 01010101 and the sequence of symhols of receiving is modified before the sequence of symhols of receiving: whenever 0101010 just after insert one 0 to avoid occurring the sequence identical with lead code, and amended sequence of symhols is carried out to BPSK Digital Modulation, D/A are changed successively and power amplification after obtain the first modulated-analog signal; The port of exporting the first modulated-analog signal forms the first series resonant tank by first electric capacity and low-frequency magnetic induced emission antenna 3 successively, and whether the phase place of the loop current signals of phase-shifting full-bridge BPSK modulation circuit 2 real-time judge the first series resonant tank will there is the change of 180 degree, if so, in the moment of the phase change of the loop current signals of the first series resonant tank, the first electric capacity both end voltage physical property is reversed.Low-frequency magnetic induced emission antenna 3 is converted to low frequency magnetic field signal by the current signal that flows through self and sends.
In traditional BPSK modulation, because transmitting terminal resonant tank has limited bandwidth, electric current in resonant tank can be decayed 180 ° of phase shift point, in the series resonant circuit course of work, energy transmits back and forth in electric capacity and inductance, in the loop current zero passage moment, energy is all stored in resonant tank electric capacity, and next moment electric capacity will discharge, discharging current direction is contrary with before zero passage, and under BPSK modulation system, can there are 180 ° of phase shifts in the current over-zero moment in signal, cause the signal voltage of power amplifier output contrary with the voltage direction of electric capacity, the two can make loop current signals decay after cancelling out each other.In the present invention, pass through in the signal phase shift moment, the first electric capacity both end voltage physical property to be reversed, allow voltage and the signal voltage direction of the first electric capacity be consistent, thereby realize signal phase place unattenuated in the situation that and be able to quick change, this mode of modulating by physics mode can greatly improve the bandwidth of modulation signal under the prerequisite that keeps higher Q value.
Figure 2 shows that wherein a kind of preferably structural representation in real time of the modulator of the low-frequency magnetic inductive communication that the embodiment of the present invention provides, as shown in Figure 2, in the modulator of this low-frequency magnetic inductive communication, phase-shifting full-bridge BPSK modulation circuit comprises: BPSK digital modulation module 4, D/A modular converter 5, power amplifier 6, the first K switch 1, second switch K2, the 3rd K switch 3, the 4th K switch 4, switching circuit control module 7, not gate logical device 8 and the first capacitor C 1.
Wherein, the input of BPSK digital modulation module 4 is connected with the first arm processor 1 by FSMC bus, and output is connected with the input of D/A modular converter 5; BPSK digital modulation module 4 added preamble sequence 01010101 and the sequence of symhols of receiving is modified before the sequence of symhols of receiving: whenever 0101010 just after insert one 0 to avoid occurring the sequence identical with lead code, and amended sequence of symhols is carried out to BPSK Digital Modulation, and the digital signal after modulation is sent to D/A modular converter 5.The output of D/A modular converter 5 is connected with the input of power amplifier 6; The output of power amplifier 6 is connected with one end of the first K switch 1, the 3rd K switch 3 simultaneously, and the other end of the other end of the first K switch 1 and the 3rd K switch 3 is connected by the first capacitor C 1; The link of the first K switch 1 and the first capacitor C 1 is also connected with one end of second switch K2, and the other end of second switch K2 is connected with coil one end of low-frequency magnetic induced emission antenna 3, the coil other end ground connection of low-frequency magnetic induced emission antenna 3; The link of the 3rd K switch 3 and the first capacitor C 1 is also connected with one end of the 4th K switch 4, and the other end of the 4th K switch 4 connects the coil connecting terminal of second switch K2 and low-frequency magnetic induced emission antenna 3.Switching circuit control module 7 is connected with BPSK digital modulation module 4, and the input of its control output end while NAND gate logical device 8, the control end of the first K switch 1, the input of the 4th K switch 4 connect, and the output of not gate logical device 8 is connected with the control end of second switch K2 and the control end of the 3rd K switch 3 simultaneously.Switching circuit control module 7 is connected with BPSK digital modulation module 4, and according to BPSK digital modulation module 4 modulation case to sent sequence of symhols, the moment of spending at the phase change 180 of the loop current signals of the first series resonant tank, the digital signal of exporting to not gate logical device 8 is carried out to 0-1/1-0 switching, to control the first K switch 1, second switch K2, the 3rd K switch 3, the four K switch 4 change current on off state.Wherein, power amplifier 6 is a kind of low noise LF power amplifier, carries out power amplification to drive transmitting antenna loop in order to the BPSK modulation signal that D/A modular converter 5 is exported.
And can obviously be found out by Fig. 2, because the first K switch 1 is connected the input of not gate logical device 8 with the control end of the 4th K switch 4, and second switch K2 is connected the output of not gate logical device 8 with the 3rd K switch 3, therefore the on off state of the first K switch 1 and the 4th K switch 4 is forever consistent, and the on off state of second switch K2 and the 3rd K switch 3 is forever consistent and contrary with the on off state of the first K switch 1 and the 4th K switch 4.Different from conventional resonant circuit is, the first electric capacity in Fig. 2 is arranged in " H " bridge switch circuit, therefore, can control " H " bridge switch circuit being formed by first, second, third, fourth switch by switching circuit control module 7 and not gate logical device 8, thereby realizing allows the first capacitor C 1 reverse fast in the series resonant tank current over-zero moment, allow the first capacitor C 1 back discharge, realize 180 degree phase shifts of loop current.
Fig. 3 is the phase-shifting full-bridge BPSK modulated process schematic diagram in circuit shown in Fig. 2.Normal humorous center of percussion resonant capacitance can experience positive charge, back discharge, reverse charging, forward electric discharge four-stage successively as can see from Figure 2, shown in Fig. 2 in circuit, the initial condition of 4 electronic switches is K1, K4 conducting, and K2, K3 disconnect, now the first capacitor C 1 forward place in circuit.Because code element variation for the first time occurs in the current over-zero moment after the first electric capacity reverse charging finishes, there are 180 ° of phase shifts in power amplifier 6 output voltages now, now control " H " bridge switch circuit and be switched to K1, K4 disconnection, K2, K3 conducting, so that the reverse place in circuit of the first capacitor C 1, make 180 ° of loop current phase shifts by this reverse turn operation physically, thereby allow artificially resonance normally go on.
Preferably, as shown in Figure 2, BPSK digital modulation module 4 and switching circuit control module 7 adopt FPGA mode to realize, and can realize in same FPGA coprocessor.For example, FPGA coprocessor can adopt the cyclone IV family chip of altera corp.
Preferably, can control more accurately the switching over action in " H " bridge switch circuit in order to make switching circuit control module 7, can adopt the direction of the loop current to series resonant tank to detect to assist control, specifically, as the another kind of the modulator of the low-frequency magnetic inductive communication of Fig. 4 is preferably implemented as shown in structural representation, phase-shifting full-bridge BPSK modulation circuit also comprises the first resistance R 1, isolating amplifier circuit 9, an A/D modular converter 10 and current zero detection module 11.Wherein, the coil other end not being connected with second switch K2 of low-frequency magnetic induced emission antenna 3 is by the first resistance R 1 ground connection, isolating amplifier circuit 9 inputs connect the coil of low-frequency magnetic induced emission antenna 3 and the link of the first resistance R 1, and output connects the input of an A/D modular converter 10; The output of the one A/D modular converter 10 connects the input of current zero detection module 11, and the output of current zero detection module 11 is connected with switching circuit control module 7.In Fig. 4, current zero detection module 11 detects the direction of the loop current of the first series resonant tank by an A/D modular converter 10, isolating amplifier circuit 9, the first resistance R 1 and 3 connection circuits of low-frequency magnetic induced emission antenna, and notifies switching circuit control module 7 in the loop current of the first series resonant tank by the zero passage moment.The loop current of the first series resonant tank that switching circuit control module 7 is sent according to current zero detection module 11 is notified by zero passage, judge that whether current signal element to be sent is identical with the upper code element just having sent, if not, in the loop current zero passage moment of the first series resonant tank, the digital signal of exporting to not gate logical device 8 is carried out to 0-1/1-0 switching.
Corresponding to the modulated terminal of low-frequency magnetic inductive communication provided by the invention, the present invention also provides a kind of modulator approach of low-frequency magnetic inductive communication, and as shown in Figure 5, the modulator approach of low-frequency magnetic inductive communication provided by the invention comprises step:
S11: user data is carried out to chnnel coding, obtain sequence of symhols to be sent;
S12: carry out BPSK Digital Modulation to sent sequence of symhols, and in modulated process, the lead code of the digital signal after modulation is set as to 01010101, and the sequence of symhols of receiving is modified: whenever 0101010 just after insert one 0, obtain BPSK digital modulation signals;
S13: BPSK digital modulation signals is carried out to D/A conversion, obtain BPSK modulated-analog signal;
S14: BPSK modulated-analog signal is carried out to power amplification and obtain the first modulated-analog signal;
S15: in the first series resonant tank that the first modulated-analog signal input one is made up of port, the first electric capacity and the low-frequency magnetic induced emission antenna of output the first modulated-analog signal, and whether the phase place of the loop current signals of real-time judge the first series resonant tank will there is the change of 180 degree, if so, in the moment of the phase change of loop current signals, the first electric capacity both end voltage physical property is reversed;
S16: low-frequency magnetic induced emission antenna is converted to low frequency magnetic field signal by the current signal that flows through self and sends.
Preferably, in the modulator approach of above-mentioned low-frequency magnetic inductive communication, whether the phase place that judges the loop current signals of the first series resonant tank in step S15 by the method for the changes that 180 degree occur is: judge that whether current signal element to be sent is identical with the upper code element just having sent, if not, near the current zero-crossing point generation phase shift of the loop current signals of the first series resonant tank code element changes the moment.
The modulator of the low-frequency magnetic inductive communication providing corresponding to the embodiment of the present invention, the embodiment of the present invention also provides a kind of demodulator of low-frequency magnetic inductive communication as shown in Figure 6, and this demodulator comprises: low-frequency magnetic induction reception antenna 12, the second capacitor C 2, impedance matching transformer 13, active filter 14, programmable amplifying circuit 15, the 2nd A/D modular converter 16, BPSK demodulation module 17 and the second arm processor 18.
In the demodulator of the inductive communication of low-frequency magnetic shown in Fig. 6, the alternating magnetic field of the low frequency magnetic field signal formation that low-frequency magnetic induction reception antenna 12 sends according to the modulator of low-frequency magnetic inductive communication induces the second analog current modulation signal.The primary coil of low-frequency magnetic induction reception antenna 12, the second capacitor C 2 and impedance matching transformer 13 is composed in series the second series resonant tank.The second series resonant tank is carried out frequency-selecting for the second analog current modulation signal that low-frequency magnetic induction reception antenna 12 is exported, to suppress a part of noise, it is pure resistive and equate with 12 internal resistances of low-frequency magnetic induction reception antenna that the equiva lent impedance of impedance matching transformer 13 in the second series resonant tank is, thereby reach the impedance matching between amplifying circuit and resonant circuit, thereby the signal of reception is coupled to late-class circuit with maximum power.The 3rd analog current modulation signal of the secondary coil output of impedance matching transformer 13, successively through active filter 14 filtering, sends to the 2nd A/D modular converter 16 to carry out A/D conversion after programmable amplifying circuit 15 carries out signal amplification.This is due in practical communication, along with the change of transmitting power and communication distance, the signal power receiving also can change, if directly carry out A/D conversion, the impact bringing when the fainter quantization error of signal is larger, in order to ignore quantization error, should before A/D conversion, signal be amplified to certain stable amplitude, therefore this is between active filter 14 and the 2nd A/D modular converter 16 programmable amplifying circuit 15 is set.Subsequently, the analog signal of input is converted to digital modulation signals by the 2nd A/D modular converter 16, after BPSK demodulation module 17 is demodulated into digital demodulation signal, send to the second arm processor 18 to carry out error detection, final the second arm processor 18 offers user using correct digital demodulation signal as user data again.Wherein, the signal that BPSK demodulation module 17 is 01010101 for demodulation lead code, preferably, BPSK demodulation module 17 adopts FPGA coprocessor mode to realize, and FPGA coprocessor also can regulate according to current demand signal amplitude the signal amplification factor of programmable amplifying circuit 15 in real time, so that signal amplitude is stabilized in certain scope.
Fig. 7 is the preferably real-time structural representation of the one of the demodulator of low-frequency magnetic inductive communication shown in Fig. 6, wherein, BPSK demodulation module 17 comprises: carrier recovery unit 19, correlation demodulation unit 20, lead code recognition unit 21, clock sampling unit 22 and thresholding judging unit 23.Wherein,
Carrier recovery unit 19 adopts costa ring computational methods, the phase difference of the signal carrier of the digital modulation signals of exporting by local carrier and the 2nd A/D modular converter 16 is revised in real time to carrier phase, and revised carrier wave is sent to correlation demodulation unit 20.
Correlation demodulation unit 20 comprises multiplier 24 and FIR low pass filter 25, the input of the output of multiplier 24 the respectively with two A/D modular converter 16, the output of carrier recovery unit 19 and FIR low pass filter 25 is connected, the digital modulation signals that the carrier signal that multiplier 24 is exported carrier recovery unit 19 and the 2nd A/D modular converter 16 are exported carries out sending to FIR low pass filter 25 after multiplication, and FIR low pass filter 25 carries out filtering to input signal and obtains baseband signal and export lead code recognition unit 21 to.
The lead code of the baseband signal that lead code recognition unit 21 is exported FIR low pass filter 25 is identified, and draws the phase place of sampling clock and offers clock sampling unit 22 and thresholding judging unit 23 with this.
Clock sampling unit 22 is connected with carrier recovery unit 19, be used for the phase place of the sampling clock of sending according to lead code recognition unit 21, the carrier signal that carrier recovery unit 19 is exported is carried out clock sampling, obtains the frequency of sampling clock and provides it to thresholding judging unit 23.
Thresholding judging unit 23 utilizes the phase place of sampling clock and the frequency of sampling clock received, obtains sampling clock and with this clock, baseband signal is carried out to threshold judgement, demodulates digital demodulation signal.
Corresponding to the demodulator of low-frequency magnetic inductive communication provided by the invention, the embodiment of the present invention also provides a kind of demodulation method of low-frequency magnetic inductive communication, is illustrated in figure 8 the demodulation method flow chart of this low-frequency magnetic inductive communication, comprises step:
S21: the alternating magnetic field of the low frequency magnetic field signal formation that low-frequency magnetic induction reception antenna sends according to the modulator of low-frequency magnetic inductive communication induces the second analog current modulation signal;
S22: the second analog current modulation signal is carried out to the 3rd analog current modulation signal that frequency-selecting obtains;
S23: the 3rd analog current modulation signal is carried out successively to active power filtering, signal amplify, A/D conversion, obtain lead code and be 01010101 digital modulation signals;
S24: the digital modulation signals that is 01010101 to lead code carries out BPSK demodulation, and the sequence of symhols that demodulation is obtained is modified: often run into 01010100 and just remove finally 0, obtain digital demodulation signal;
S25: digital restituted signal is carried out to error detection, and correct digital demodulation signal is offered to user as user data.
Preferably, shown in Fig. 8, in method, the method that the digital modulation signals that is 01010101 to lead code in step S24 carries out BPSK demodulation is:
S241: adopt costa ring computational methods, the phase difference of the signal carrier by local carrier and digital modulation signals is revised in real time to carrier phase;
S242: carry out multiplying by the carrier signal that digital modulation signals and S241 are obtained, and multiplication result is carried out to FIR low-pass filtering, recover baseband signal;
S243: the lead code 01010101 to baseband signal is identified, and just remove finally 0 running into 01010100 at every turn, finally draws the phase place of sampling clock, and the carrier signal that S241 is obtained is carried out clock sampling and obtain the frequency of sampling clock;
S244: utilize the phase place of sampling clock and the frequency of sampling clock to obtain sampling clock, and with the sampling clock obtaining, baseband signal is carried out to threshold judgement, demodulate digital demodulation signal.
Preferably, utilize finite automaton state machine to identify the lead code 01010101 of baseband signal in step S243, concrete recognition methods comprises the following steps:
S31: set condition machine initial condition value is 0, represents that lead code is to be identified, gets the hang of 1 if recognize the rising edge of baseband signal in this state;
S32: under the prerequisite of state 1, if recognize the next hopping edge of baseband signal and be trailing edge and and time interval of previous rising edge for (1-m) T is between (1+m) T, get the hang of 2, if exceed (1+m) T and occur return state 0 without trailing edge with the time interval of previous rising edge; Wherein m is fixed value and 0<m<1/2, and T is a code-element period;
S33: under the prerequisite of state 2, if recognize the next hopping edge of baseband signal and be rising edge and and time interval of previous trailing edge between (1+m) T, get the hang of 3 for (1-m) T, if with time interval of previous trailing edge for exceeding (1+m) T and occurring return state 0 without rising edge; Wherein m is fixed value and 0<m<1/2, and T is a code-element period;
S34: the process of repeating step S32-S33, each detection by state value increasing 1, otherwise state value returns to 0, until get the hang of 7, the lead code of baseband signal is identified successfully.
Preferably, the method of identifying the hopping edge of baseband signal in S31-S34 process is: be n point by the data point markers of the current baseband signal that needs identification, Ruo Dang (n-N/2) o'clock is negative and lower than the negative threshold value of setting to the point between (n-k) point, and the point between (n+k) o'clock to (n+N/2) point is just and higher than in the positive threshold value of setting, think that rising edge appears in the current data point place of baseband signal that needs identification, and within 1/2 code-element period time next, suspend the hopping edge of identification baseband signal; Wherein, k is constant and 0<k<N/4, and N is a sampling number that code-element period is corresponding.
In the modulator and modulator approach of low-frequency magnetic inductive communication provided by the invention, by low-frequency magnetic induced emission antenna, the first electric capacity and loop resistance form series resonant circuit, resonant capacitance (i.e. the first electric capacity) is arranged in " H " bridge switch circuit, changing in transmission of symbols is the signal phase shift moment, can control the first electric capacity by " H " bridge switch circuit reverses in circuit, allow the course of discharge of signal voltage direction and the first electric capacity be consistent, thereby avoid the decay of current signal, make modulation signal in resonant tank, maintain maximum resonance state always, can under the prerequisite that keeps higher Q value, greatly improve the bandwidth of modulation signal, effectively raise the speed of LF communication, the bandwidth of existing low frequency magnetic strength communications transmit end and the problem that value limits mutually and traffic rate is low of Q value are solved.In addition, the demodulator of corresponding low-frequency magnetic inductive communication provided by the invention and demodulation method adopt digital demodulation mode to carry out demodulation, can catch fast and accurately lead code, ensure the real-time of demodulation, increase the flexibility of demodulation and improved the integrated level of hardware, in demodulation, adopt pattern recognition to carry out lead code and catch, amount of calculation, far below traditional correlation capturing, is conducive to the low power dissipation design of whole system.
The above is the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, do not departing under the prerequisite of principle of the present invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (12)
1. a modulator for low-frequency magnetic inductive communication, is characterized in that, comprising: the first arm processor, phase-shifting full-bridge BPSK modulation circuit and low-frequency magnetic induced emission antenna; The input of described phase-shifting full-bridge BPSK modulation circuit is connected with described the first arm processor by FSMC bus, and output connects described low-frequency magnetic induced emission antenna;
Described the first arm processor carries out chnnel coding to user data, obtains sequence of symhols to be sent and described sequence of symhols is sent to described phase-shifting full-bridge BPSK modulation circuit through FSMC bus;
Described phase-shifting full-bridge BPSK modulation circuit added preamble sequence 01010101 and the sequence of symhols of receiving is modified before the sequence of symhols of receiving: whenever 0101010 just after insert one 0, and amended sequence of symhols is carried out obtaining the first modulated-analog signal after BPSK Digital Modulation, D/A conversion and power amplification successively; The port of exporting described the first modulated-analog signal forms the first series resonant tank by first electric capacity and described low-frequency magnetic induced emission antenna successively, and described in described phase-shifting full-bridge BPSK modulation circuit real-time judge, whether the phase place of the loop current signals of the first series resonant tank will there is the change of 180 degree, if so, in moment of the phase change of the loop current signals of described the first series resonant tank by described the first electric capacity both end voltage physical property reversion;
Described low-frequency magnetic induced emission antenna is converted to low frequency magnetic field signal by the current signal that flows through self and sends.
2. the modulator of low-frequency magnetic inductive communication as claimed in claim 1, it is characterized in that, described phase-shifting full-bridge BPSK modulation circuit comprises: BPSK digital modulation module, D/A modular converter, power amplifier, the first switch, second switch, the 3rd switch, the 4th switch, switching circuit control module, not gate logical device and described the first electric capacity;
The input of described BPSK digital modulation module is connected with described the first arm processor by FSMC bus, and output is connected with the input of described D/A modular converter; Described BPSK digital modulation module added preamble sequence 01010101 and the sequence of symhols of receiving is modified before the sequence of symhols of receiving: whenever 0101010 just after insert one 0; And amended sequence of symhols is carried out to BPSK Digital Modulation;
The output of described D/A modular converter is connected with the input of described power amplifier; The output of described power amplifier is connected with one end of described the first switch, the 3rd switch simultaneously, and the other end of the other end of described the first switch and the 3rd switch is connected by described the first electric capacity; The link of described the first switch and the first electric capacity is also connected with one end of described second switch, and the other end of described second switch is connected with coil one end of described low-frequency magnetic induced emission antenna, the coil other end ground connection of described low-frequency magnetic induced emission antenna; The link of described the 3rd switch and the first electric capacity is also connected with one end of described the 4th switch, and the other end of described the 4th switch connects the coil connecting terminal of described second switch and described low-frequency magnetic induced emission antenna;
Described switching circuit control module is connected with described BPSK digital modulation module, and its control output end is connected with the input of described not gate logical device, the control end of the first switch, the input of the 4th switch simultaneously, the output of described not gate logical device is connected with the control end of described second switch and the control end of the 3rd switch simultaneously;
Described switching circuit control module is the modulation case to sent sequence of symhols according to described BPSK digital modulation module, the moment of spending at the phase change 180 of the loop current signals of described the first series resonant tank, the digital signal of exporting to described not gate logical device is carried out to 0-1/1-0 switching, to control described the first switch, second switch, the 3rd switch, the 4th switch changes current on off state.
3. the modulator of low-frequency magnetic inductive communication as claimed in claim 2, is characterized in that, described BPSK digital modulation module and switching circuit control module adopt FPGA mode to realize.
4. the modulator of low-frequency magnetic inductive communication as claimed in claim 3, is characterized in that, described phase-shifting full-bridge BPSK modulation circuit also comprises the first resistance, isolating amplifier circuit, an A/D modular converter and current zero detection module; The coil other end not being connected with described second switch of described low-frequency magnetic induced emission antenna is by described the first grounding through resistance, described isolating amplifier circuit input connects the coil of described low-frequency magnetic induced emission antenna and the link of the first resistance, and output connects the input of a described A/D modular converter; The output of a described A/D modular converter connects the input of described current zero detection module, and the output of described current zero detection module is connected with described switching circuit control module;
Described current zero detection module detects the direction of the loop current of described the first series resonant tank by an A/D modular converter, isolating amplifier circuit, the first resistance and low-frequency magnetic induced emission antenna institute connection circuit, and notifies described switching circuit control module in the loop current of described the first series resonant tank by the zero passage moment;
The loop current of the first series resonant tank that described switching circuit control module is sent according to described current zero detection module is notified by zero passage, judge that whether current signal element to be sent is identical with the upper code element just having sent, if not, in the loop current zero passage moment of described the first series resonant tank, the digital signal of exporting to described not gate logical device is carried out to 0-1/1-0 switching.
5. the demodulator of a low-frequency magnetic inductive communication, it is characterized in that, comprising: low-frequency magnetic induction reception antenna, the second electric capacity, impedance matching transformer, active filter, programmable amplifying circuit, the 2nd A/D modular converter, BPSK demodulation module and the second arm processor;
The alternating magnetic field of the low frequency magnetic field signal formation that described low-frequency magnetic induction reception antenna sends according to the modulator of low-frequency magnetic inductive communication induces the second analog current modulation signal;
The primary coil of described low-frequency magnetic induction reception antenna, the second electric capacity and impedance matching transformer is composed in series the second series resonant tank, it is pure resistive and equate with the internal resistance of described low-frequency magnetic induction reception antenna that the equiva lent impedance of described impedance matching transformer in described the second series resonant tank is, and described the second series resonant tank is carried out frequency-selecting for the second analog current modulation signal that described low-frequency magnetic induction reception antenna is exported;
The 3rd analog current modulation signal of the secondary coil output of described impedance matching transformer is successively through described active filter filtering, carry out signal amplification through described programmable amplifying circuit, be converted to digital modulation signals through described the 2nd A/D modular converter, after described BPSK demodulation module is demodulated into digital demodulation signal, send to described the second arm processor to carry out error detection, described the second arm processor offers user using correct digital demodulation signal as user data;
Wherein, the signal that described BPSK demodulation module is 01010101 for demodulation lead code, described BPSK demodulation module adopts FPGA mode to realize.
6. the demodulator of low-frequency magnetic inductive communication as claimed in claim 5, is characterized in that, described BPSK demodulation module comprises: carrier recovery unit, correlation demodulation unit, lead code recognition unit, clock sampling unit and thresholding judging unit;
Described carrier recovery unit adopts costa ring computational methods, the phase difference of the signal carrier of the digital modulation signals of exporting by local carrier and described the 2nd A/D modular converter is revised in real time to carrier phase, and revised carrier wave is sent to described correlation demodulation unit;
Described correlation demodulation unit comprises multiplier and FIR low pass filter, described multiplier is connected with the output of the output of described the 2nd A/D modular converter, described carrier recovery unit and the input of described FIR low pass filter respectively, the digital modulation signals of the carrier signal that described multiplier is exported described carrier recovery unit and the output of the 2nd A/D modular converter carries out sending to described FIR low pass filter after multiplication, and described FIR low pass filter carries out filtering to input signal and obtains baseband signal and export described lead code recognition unit to;
The lead code of the baseband signal of described lead code recognition unit to the output of FIR low pass filter is identified, and draws the phase place of sampling clock and offers described clock sampling unit and thresholding judging unit with this;
Described clock sampling unit is connected with described carrier recovery unit, be used for the phase place of the sampling clock of sending according to described lead code recognition unit, carrier signal to described carrier recovery unit output is carried out clock sampling, obtains the frequency of sampling clock and provides it to described thresholding judging unit;
The phase place of sampling clock that the utilization of described thresholding judging unit is received and the frequency of sampling clock, obtain sampling clock and with this clock, described baseband signal carried out to threshold judgement, demodulates digital demodulation signal.
7. a modulator approach for low-frequency magnetic inductive communication, is characterized in that, comprises step:
S11: user data is carried out to chnnel coding, obtain sequence of symhols to be sent;
S12: described sequence of symhols to be sent is carried out to BPSK Digital Modulation, and in modulated process, the lead code of the digital signal after modulation is set as to 01010101, and the sequence of symhols of receiving is modified: whenever 0101010 just after insert one 0, obtain BPSK digital modulation signals;
S13: described BPSK digital modulation signals is carried out to D/A conversion, obtain BPSK modulated-analog signal;
S14: described BPSK modulated-analog signal is carried out to power amplification and obtain the first modulated-analog signal;
S15: in the first series resonant tank that described the first modulated-analog signal input one is made up of port, the first electric capacity and the low-frequency magnetic induced emission antenna of described the first modulated-analog signal of output, and described in real-time judge, whether the phase place of the loop current signals of the first series resonant tank will there is the change of 180 degree, if so, in moment of the phase change of described loop current signals by described the first electric capacity both end voltage physical property reversion;
S16: described low-frequency magnetic induced emission antenna is converted to low frequency magnetic field signal by the current signal that flows through self and sends.
8. the modulator approach of low-frequency magnetic inductive communication as claimed in claim 7, it is characterized in that, whether the phase place that judges the loop current signals of described the first series resonant tank described in S15 by the method for the changes that 180 degree occur is: judge that whether current signal element to be sent is identical with the upper code element just having sent, if not, near the current zero-crossing point generation phase shift of the loop current signals of described the first series resonant tank code element changes the moment.
9. a demodulation method for low-frequency magnetic inductive communication, is characterized in that, comprises step:
S21: the alternating magnetic field of the low frequency magnetic field signal formation that low-frequency magnetic induction reception antenna sends according to the modulator of low-frequency magnetic inductive communication induces the second analog current modulation signal;
S22: described the second analog current modulation signal is carried out to the 3rd analog current modulation signal that frequency-selecting obtains;
S23: described the 3rd analog current modulation signal is carried out successively to active power filtering, signal amplify, A/D conversion, obtain lead code and be 01010101 digital modulation signals;
S24: the described digital modulation signals that is 01010101 to lead code carries out BPSK demodulation, and the sequence of symhols that demodulation is obtained is modified: often run into 01010100 and just remove finally 0, obtain digital demodulation signal;
S25: described digital demodulation signal is carried out to error detection, and correct digital demodulation signal is offered to user as user data.
10. the demodulation method of low-frequency magnetic inductive communication as claimed in claim 9, is characterized in that, the method that the described digital modulation signals that is 01010101 to lead code described in S24 carries out BPSK demodulation is:
S241: adopt costa ring computational methods, the phase difference of the signal carrier by local carrier and described digital modulation signals is revised in real time to carrier phase;
S242: carry out multiplying by the carrier signal that described digital modulation signals and S241 are obtained, and multiplication result is carried out to FIR low-pass filtering, recover baseband signal;
S243: the lead code 01010101 to described baseband signal is identified, and just remove finally 0 running into 01010100 at every turn, finally draws the phase place of sampling clock, and the carrier signal that S241 is obtained is carried out clock sampling and obtain the frequency of sampling clock;
S244: utilize the phase place of described sampling clock and the frequency of sampling clock to obtain sampling clock, and with the sampling clock obtaining, described baseband signal is carried out to threshold judgement, and revise code element, demodulate digital demodulation signal.
The demodulation method of 11. low-frequency magnetic inductive communications as claimed in claim 10, is characterized in that, utilizes finite automaton state machine to identify the lead code 01010101 of described baseband signal in described S243, and concrete recognition methods is:
S31: set condition machine initial condition value is 0, represents that lead code is to be identified, gets the hang of 1 if recognize the rising edge of baseband signal in this state;
S32: under the prerequisite of state 1, if recognize the next hopping edge of baseband signal and be trailing edge and and time interval of previous rising edge for (1-m) T is between (1+m) T, get the hang of 2, if exceed (1+m) T and occur return state 0 without trailing edge with the time interval of previous rising edge; Wherein m is fixed value and 0<m<1/2, and T is a code-element period;
S33: under the prerequisite of state 2, if recognize the next hopping edge of baseband signal and be rising edge and and time interval of previous trailing edge between (1+m) T, get the hang of 3 for (1-m) T, if with time interval of previous trailing edge for exceeding (1+m) T and occurring return state 0 without rising edge; Wherein m is fixed value and 0<m<1/2, and T is a code-element period;
S34: the process of repeating step S32-S33, each detection by state value increasing 1, otherwise state value returns to 0, until get the hang of 7, the lead code of described baseband signal is identified successfully.
The demodulation method of 12. low-frequency magnetic inductive communications as claimed in claim 11, it is characterized in that, the method of identifying the hopping edge of baseband signal in described S31-S34 process is: be n point by the data point markers of the current baseband signal that needs identification, Ruo Dang (n-N/2) o'clock is negative and lower than the negative threshold value of setting to the point between (n-k) point, and the point between (n+k) o'clock to (n+N/2) point is just and higher than in the positive threshold value of setting, think that rising edge appears in the data point place of the current baseband signal that needs identification, and within 1/2 code-element period time next, suspend the hopping edge of identification baseband signal, wherein, k is constant and 0<k<N/4, and N is a sampling number that code-element period is corresponding.
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