CN101741788A - Method for modulating and demodulating minimum frequency shift keying signal and special method for designing complex analytic band-pass filter - Google Patents

Abstract

The invention relates to a method for modulating and demodulating a minimum frequency shift keying signal and a special method for designing a complex analytic band-pass filter. A complex analytic band-pass filtering method is adopted to realize the modulation and demodulation of the minimum frequency shift keying signal; the minimum frequency shift keying signals of different central frequencies do not need various band-pass filters, the minimum frequency shift keying signals of the same transmission bandwidth only need one band-pass filter, and then a processor calculates the complex analytic band-pass filter having the central frequency serving as a carrier frequency, so the complexity of a signal processing algorithm is greatly lowered and sharing among wave filters having the same transmission rate is realized.

Description

The modulation-demo-demodulation method of minimum frequency shift keying signal and special-purpose complex analytic band-pass filter method for designing

Technical field

The present invention relates to a kind of minimum frequency shift keying signal modulation-demo-demodulation method and special-purpose complex analytic band-pass filter method for designing.

Background technology

(1) modulation and demodulation of traditional minimum shift keying (MSK) signal is used real signal usually and is handled and realize, because minimum frequency shift keying signal is a bandpass signal, for identical message transmission rate, though the minimum frequency shift keying signal transmission bandwidth is identical, but because the centre frequency difference of minimum frequency shift keying signal, need the different band pass filter (BPF) of design, can't realize sharing of filter, thereby implement more loaded down with trivial details.

(2) because minimum frequency shift keying signal has following characteristics:

1. the amplitude of modulated signal is constant; 2. the frequency shift strictness of signal equals ± r _b/ 4 (r _bBe message transmission rate); 3. with the carrier phase be the signal phase of benchmark in a code-element period exactly linear change be ± pi/2; 4. in a code-element period, signal should comprise the integral multiple of 1/4th carrier cycles; 5. in the code element conversion constantly, the phase place of signal is continuous.

Satisfy above 5 characteristics, general Minimum Shift Keying Modulation signal is finished by differential coding, serial/parallel conversion, orthogonal function weighting, quadrature carrier modulation, stack and 6 processing procedures of bandpass filtering.

(3) digital demodulation of traditional minimum frequency shift keying signal can be used coherent demodulation, non-coherent demodulation and differential ference spiral.The interference free performance of coherent demodulation slightly is better than other forms of demodulation, but since coherent demodulation need receiving terminal carry out carrier extract and synchronously, differential decoding, parallel serial conversion, implement more complicated.The non-coherent demodulation mode realizes simply, need not to recover synchronous carrier wave, its demodulation mode has envelope detected method, frequency-discrimination method, zero passage detection method and differential ference spiral method, but these demodulation methods are when adopting DSP (Digital Signal Processing) to realize, its algorithm is very complicated, implementation procedure is very loaded down with trivial details, can't satisfy the requirement of the various host-host protocols of minimum frequency shift keying signal.

Summary of the invention

At the problems referred to above, task of the present invention provides a kind of modulation and demodulation that adopts the method realization minimum frequency shift keying signal of multiple parsing bandpass filtering treatment, reduce the complexity of signal processing algorithm, to improve the flexibility of system, can satisfy the requirement of the various host-host protocols of minimum frequency shift keying signal.

For realizing above-mentioned task, technical scheme of the present invention is to have adopted a kind of modulation that the bandpass filtering method realizes minimum frequency shift keying signal of resolving again, and it is as follows that the method comprising the steps of:

1. sampling rate f _sSelection:

Message transmission rate is generally 300bit/s, 600bit/s, 1200bit/s, 2400bit/s, 4800bit/s, 9600bit/s, 19200bit/s etc.For the ease of signal processing, get the integral multiple that sampling rate is a message transmission rate, therefore in minimum frequency shift keying signal modulation and demodulation system, if message transmission rate is no more than 1200bit/s, choosing sampling rate is 9.600kHz, and promptly sampling rate is respectively transmission rate 300bit/s, 600bit/s, 1200bit/s 32 times, 16 times, 8 times.When transmission rate during, consider the operational capability of digital signal processor, generally get sampling rate and be transmission rate 8 times greater than 1200bit/s.

2. modulator approach:

The initial phase of minimum frequency shift keying signal is set at 0, data to transmission are sampled, the pass of the data of the step-length of phase change and transmission is during each the sampling, if the data of transmission are " 0 ", the step-length of phase change is that the carrier frequency of minimum frequency shift keying signal and 1/4th sums of transmission rate multiply by 2 π again divided by sampling rate; If the data of transmission are " 1 ", the step-length of phase change is that 1/4th difference of the carrier frequency of minimum frequency shift keying signal and transmission rate multiply by 2 π again divided by sampling rate.The present phase value of minimum frequency shift keying signal of transmission equals the original phase value and the step-length sum of phase change, produces the range value of multiple sinusoidal signal then according to present phase value, can obtain the multiple bandpass signal of minimum shift keying.Real coefficient FIR low pass filter be multiply by the complex carrier signal signal obtain the complex analytic band-pass filter that centre frequency is a carrier frequency, the complex analytic band-pass filter that by centre frequency is carrier frequency carries out multiple parsing bandpass filtering to the multiple bandpass signal of minimum shift keying, inhibition zone external spectrum composition, get the real part of multiple bandpass signal, the minimum shift keying that conversion can obtain transmitting through D/A is simulated real bandpass signal, finishes whole modulation treatment process.

Corresponding with the modulator approach of above-mentioned minimum frequency shift keying signal, the demodulation method of minimum frequency shift keying signal of the present invention is as follows:

The Binary Frequency Shift Keying that receives is simulated real bandpass signal and is become digital real signal through A/D, the complex analytic band-pass filter that by centre frequency is carrier frequency carries out multiple parsing bandpass filtering to the digital real signal that receives, the outer unwanted signal frequency content of filtering band, signal becomes multiple bandpass signal by original real bandpass signal; This multiple bandpass signal is postponed, the sampling that postpones is counted and is the twice of sampling rate divided by transmission rate, the conjugation of the multiple bandpass signal after postponing, the multiple bandpass signal before the delay, the phase shift factor relevant with carrier frequency are carried out complex multiplication, get the resulting long-pending imaginary part that multiplies each other, if the value of imaginary part is greater than zero, dateout " 0 " then is if the value of imaginary part is less than zero, dateout " 1 " then, thus whole differential ference spiral process finished.

For minimum shift keying is realized resolving again bandpass filtering, must design complex analytic band-pass filter, the invention provides the design of complex analytic band-pass filter, this method for designing is as follows:

At first for different transmission rates, design and the irrelevant real coefficient FIR low pass filter of minimum frequency shift keying signal carrier frequency, with the coefficient storage of filter in the program storage of processor; Carry out at processor before the modulation handling procedure of minimum frequency shift keying signal, processor is according to corresponding low pass filter in the different transmission rate option program memories, product by processor compute low pass filtered device and complex carrier signal signal, obtain the complex analytic band-pass filter that centre frequency is a carrier frequency, with the coefficient storage of complex analytic band-pass filter in the program storage of processor, so just finish the design of complex analytic band-pass filter, realized the sharing of filter of identical traffic speed.The processor that adopts in this method is a digital signal processor.

Adopt the method for resolving bandpass filtering again to realize the modulation and demodulation of minimum shift keying (MSK) signal, do not need to design miscellaneous band pass filter for the different minimum frequency shift keying signal of centre frequency, the minimum frequency shift keying signal identical for transmission bandwidth only need design a kind of low pass filter, calculate the complex analytic band-pass filter that centre frequency is a carrier frequency by processor then, reduce the complexity of signal processing algorithm so greatly, realized the sharing of filter of identical traffic speed.

Description of drawings

The complex signal handling principle block diagram of Fig. 1 minimum shift keying of the present invention (MSK) modulation;

The complex signal handling principle block diagram of Fig. 2 minimum shift keying of the present invention (MSK) differential ference spiral;

Fig. 3 minimum shift keying of the present invention (2FSK) modulation and demodulation hardware block diagram;

Fig. 4 f _s=9.6kHz, r _b=600b/s, f _cThe msk signal oscillogram of=1200Hz.

Embodiment

1. adopt DSP and complex signal to handle the method that realizes minimum shift keying (MSK) signal

1.1 minimum shift keying (MSK) signal

The expression formula of minimum shift keying (MSK) signal can be write as

s(t)＝cos[2πf _ct+θ(t)] (1)

Wherein:

kT _b≤t≤(k+1)T _b(2)

In the formula: f _cBe carrier frequency; T _bBe symbol width; a _kRelevant with k input symbols, its value ± 1;

Be k the phase constant in the input symbols, at time kT _bThe T of≤t≤(k+1) _bIn remain unchanged.If establishing the transmission rate of binary system minimum shift keying (MSK) signal is r _b, frequency deviation is f _Δ, signal frequency is f when sending data " 0 " sign indicating number ₂, a _k=1; Signal frequency is f when sending data " 1 " sign indicating number ₁, a _k=-1; Then

r _b＝1/T _b (3)

${\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="H2009101727811E0000011.png,H2009101727811E0000021.png"\; state="\{\{state\}\}">f</figure-callout>}}_1=f_c-\frac{1}{4}{r}_b---\left(4\right)$

$f_2=f_c+\frac{1}{4}{r}_b---\left(5\right)$

$f_{\mathrm{\&Delta;}}=\frac{1}{4}{r}_b---\left(6\right)$

The coefficient correlation of two signal waveforms of Binary Frequency Shift Keying is

$\mathrm{\&rho;}=\frac{\sin 2\mathrm{\&pi;}(f_2-f_1)T_b}{2\mathrm{\&pi;}(f_2-f_1)T_b}+\frac{\sin 4\mathrm{\&pi;}{f}_c{T}_b}{4\mathrm{\&pi;}{f}_c{T}_b}---\left(7\right)$

Because minimum shift keying is a kind of quadrature modulation, its signal waveform coefficient correlation is 0, and first of equal sign back equals 0, and therefore second also must equal 0, that is:

$f_c=\frac{k}{{4T}_b}=\frac{k}{4}{r}_b$ k＝1，2，3，…(8)

Phase constant Selection should guarantee that signal phase is that phase place is continuous in code element conversion constantly.

From above discussion as can be known, msk signal must have following characteristics:

1. the amplitude of modulated signal is constant; 2. the frequency shift strictness of signal equals ± r _b/ 4; 3. with the carrier phase be the signal phase of benchmark in a code-element period exactly linear change be ± pi/2; 4. in a code-element period, signal should comprise the integral multiple of 1/4th carrier cycles; 5. in the code element conversion constantly, the phase place of signal is continuous.

General MSK modulation signal is finished by differential coding, serial/parallel conversion, orthogonal function weighting, quadrature carrier modulation, stack and bandpass filtering, and wherein different carrier frequencies need design different band pass filters.Adopt DSP and complex signal to handle and realize the MSK modulation, only need phase place stack, multiple bandpass signal to produce and resolve bandpass filtering again and can finish, wherein complex analytic band-pass filter is by obtaining with irrelevant real coefficient low pass filter and the complex carrier signal signal multiplication of carrier frequency.

1.2MSK the complex signal of modulation is handled implementation method

Because message transmission rate is generally 300bit/s, 600bit/s, 1200bit/s, 2400bit/s, 4800bit/s, 9600bit/s, 19200bit/s etc., for the ease of signal processing, gets sampling rate f _sBe r _bIntegral multiple, therefore in MSK modulation and demodulation system, choose

f _s＝9600·n(Hz) (9)

In the formula: n=1,2,4,8 ..., when message transmission rate≤1200bit/s, n=1.

Can obtain the multiple bandpass signal expression formula of minimum shift keying (MSK) numeral by formula (1) is:

$c\left(n\right)=e^{j[2\mathrm{\&pi;}{f}_{c}n/\mathrm{fs}+\mathrm{\&theta;}\left(n\right)]}---\left(10\right)$

If the initial phase of minimum frequency shift keying signal

$\mathrm{\&theta;}\left(n\right)=\mathrm{\&theta;}(n-1)+\frac{\mathrm{\&pi;}{a}_k{r}_b}{{2f}_s}---\left(11\right)$

When input data d (n)=0, a _k=1,

When input data d (n)=1, a _k=-1,

Therefore formula (10) can be put in order and is

$c\left(n\right)=e^{j[2\mathrm{\&pi;}{f}_{c}n/\mathrm{fs}+\mathrm{\&theta;}\left(n\right)]}=e^{j2\mathrm{\&pi;}[f_c+a_k{r}_b/4]n/\mathrm{fs}}---\left(12\right)$

Order $\mathrm{\&alpha;}\left(n\right)=2\mathrm{\&pi;}(f_c+\frac{a_k{r}_b}{4})\frac{n}{f_s}$

Then $\mathrm{\&alpha;}\left(n\right)=\mathrm{\&alpha;}(n-1)+2\mathrm{\&pi;}(f_c+\frac{a_k{r}_b}{4})\frac{1}{f_s}---\left(13\right)$

In order to suppress the out of band spectrum composition of msk signal, must carry out filtering to multiple bandpass signal c (n).If directly adopt band pass filter to carry out filtering, for identical message transmission rate, though the bandwidth of filter is identical, but because the band pass filter of the different needs of carrier frequency design different center frequency, implement more loaded down with trivial details like this, and to take a large amount of memory resource of DSP, this paper adopts the method for resolving bandpass filtering again to simplify the implementation method of MSK modulation with innovating.

As shown in Figure 1, at first for design of different message transmission rate and the irrelevant real coefficient FIR low pass filter h (n) of carrier frequency, with the coefficient storage of filter in the program storage of DSP; Before the operation of DSP main program, DSP is according to corresponding low pass filter in the different transmission rate selection memories, by DSP compute low pass filtered device h (n) and complex carrier signal signal then

Product, obtain the complex analytic band-pass filter that centre frequency is a carrier frequency

, promptly

$\tilde{h}\left(n\right)=h\left(n\right)\&CenterDot;e^{j2\mathrm{\&pi;}{f}_{c}n/f_s}---\left(14\right)$

Will

Coefficient storage in the program storage of DSP, so just finished the design of complex analytic band-pass filter.

Multiple bandpass signal c (n) is carried out multiple parsing bandpass filtering, inhibition zone external spectrum composition:

$y\left(n\right)=c\left(n\right)*\tilde{h}\left(n\right)---\left(15\right)$

* in the formula--represent convolution

Get the real part of y (n), obtain minimum shift keying (MSK) real signal:

y _r(n)＝Re{y(n)} (16)

With digital signal y _r(n) carry out digital-to-analogue conversion (D/A) output MSK analog signal:

s(t)＝cos[2πf _ct+θ(t)] (17)

From whole complex signal processing procedure as can be seen, the modulation signal that obtains thus satisfies 5 features of minimum frequency shift keying signal fully.

1.2.MSK the complex signal of differential ference spiral is handled implementation method

The data of recovering transmission from minimum frequency shift keying signal can be used coherent demodulation, non-coherent demodulation and differential ference spiral, and the antijamming capability of coherent demodulation slightly is better than other forms of demodulation.But because coherent demodulation need be carried out carrier extract and synchronous at receiving terminal, implement more complicated, other forms of demodulation need not to recover synchronous carrier wave, implements fairly simplely, so this paper introduces the differential ference spiral that the method that adopts complex signal to handle realizes minimum frequency shift keying signal.

The input signal s (t) of receiving terminal becomes digital signal s (n) through analog-to-digital conversion (A/D), and the multiple low-pass signal of establishing after the demodulation is x (n), and according to the complex demodulation principle of Binary Frequency Shift Keying, the demodulating process of received signal is represented with following equation:

$x\left(n\right)=[s\left(n\right)\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{c}n/f_s}]*h\left(n\right)---\left(18\right)$

Utilize the character of Fourier transform to obtain:

$x\left(n\right)=\left\{\right[s\left(n\right)*[h\left(n\right)\&CenterDot;e^{j2\mathrm{\&pi;}{f}_{c}n/f_s}]\}\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{c}n/f_s}=[s\left(n\right)*\tilde{h}\left(n\right)]\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{c}n/f_s}---\left(19\right)$

Complex analytic band-pass filter

Filter out the outer interference of useful signal band, order

$m\left(n\right)=s\left(n\right)*\tilde{h}\left(n\right)---\left(20\right)$

In the formula: m (n) is multiple bandpass signal, then

$x\left(n\right)=m\left(n\right)\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{c}n/f_s}---\left(21\right)$

X (n) is after postponing the sampling period of M integral multiple and get conjugation and obtain signal x ^*(n-M), carry out differential ference spiral, can obtain:

$w\left(n\right)=x\left(n\right)\&CenterDot;x^{*}(n-M)$

$=m\left(n\right)\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{c}n/f_s}\&CenterDot;m^{*}(n-M)\&CenterDot;e^{j2\mathrm{\&pi;}{f}_c(n-M)/f_s}$

$=m\left(n\right)\&CenterDot;m^{*}(n-M)\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{c}M/f_s}---\left(22\right)$

Wherein $M=\frac{f_s}{{2r}_b},$ $e^{-j2\mathrm{\&pi;}{f}_{c}M/f_s}$ Be complex constant

Get the imaginary part of w (n):

V＝Im{w(n)} (23)

Order: $m\left(n\right)=c\left(n\right)=e^{-j2\mathrm{\&pi;}[f_c+a_k{r}_b/4]n/\mathrm{fs}},$ Then:

$V=\sin \left(\mathrm{\&pi;}{a}_k{\mathrm{<figure-callout\; id="1"\; label="r\; b\; M"\; filenames="H2009101727811E0000011.png,H2009101727811E0000021.png"\; state="\{\{state\}\}">r</figure-callout>}}_{b}M\frac{1}{2f_s}\right)=\sin \left(a_k\frac{\mathrm{\&pi;}}{4}\right)---\left(24\right)$

Therefore, work as a _k=1 o'clock, V＞0, dateout d ₁(n)=0;

Work as a _k=-1 o'clock, V＜0, dateout d ₁(n)=1.

The theory diagram that the complex signal that can obtain binary system minimum shift keying (MSK) differential ference spiral by above-mentioned analysis is handled implementation method as shown in Figure 2.As can be seen, introduce complex analytic band-pass filter, input signal is carried out multiple parsing bandpass filtering after, needn't carry out demodulation to multiple bandpass signal, directly will answer the conjugated signal m after bandpass signal m (n) and its delay ^*(n-M), phase shift factor

Carry out complex multiplication, resulting long-pending imaginary part is adjudicated to recover initial data.

2. the digital multiple modulation and the complex demodulation implementation of binary system minimum shift keying (MSK) signal

As shown in Figure 3, utilize high-speed dsp (Digital Signal Processing), dual-channel audio codec (CODEC), RS232 interface convertor, microcontroller composition function powerful hardware platform such as (MCU).Data-signal carries out delivering to DSP after the level conversion through the RS232 interface convertor, DSP carries out the multiple bandpass signal of phase-accumulated and direct generation according to the data of input, by corresponding complex analytic band-pass filter multiple bandpass signal is carried out filtering, inhibition zone external spectrum composition, get the real part of multiple bandpass signal, lead to analog signal by being with in fact of D/A output MSK of dual-channel audio codec (CODEC) then.The logical analog signal of the real band of the MSK that receives converts digital signal to and delivers to DSP and carry out differential ference spiral and handle through the A/D of dual-channel audio codec (CODEC), carry out filtering to the received signal by complex analytic band-pass filter and obtain multiple bandpass signal, will answer bandpass signal and directly carry out differential ference spiral and recover primary signal.Adopt the C++Builder programming technique to realize the man-machine dialog interface of perfect in shape and function, PC by microcontroller (MCU) to the centre frequency of msk signal, transmission rate, be provided with modulation and demodulation parameters such as anti-phase, similarities and differences step and transmission levels, to satisfy the requirement of various host-host protocols.This hardware platform can be realized the transmission of the msk signal of two channels simultaneously, perhaps utilizes frequency division multiplexing mode transmitting two paths msk signal simultaneously on a channel.Fig. 4 is with sampling frequency f _s=9.6kHz, data rate r _b=600Bd, f _c=1200Hz is the minimum frequency shift keying signal modulation and demodulation signal waveforms of example.

Claims (8)

1. the modulator approach of a minimum frequency shift keying signal is characterized in that, it is as follows that the method comprising the steps of:

(1) message transmission rate is not more than above 1200bit/s, and getting sampling rate is 9.600kHz; Transmission rate is during greater than 1200bit/s, get sampling rate and be transmission rate 8 times;

(2) initial phase with minimum frequency shift keying signal is set at 0, data to transmission are sampled, the relation of the data of the step-length of phase change and transmission is as follows during each the sampling: if the data of transmission are " 0 ", the step-length of phase change is that the carrier frequency of minimum frequency shift keying signal and 1/4th sums of transmission rate multiply by 2 π again divided by sampling rate; If the data of transmission are " 1 ", the step-length of phase change is that 1/4th difference of the carrier frequency of minimum frequency shift keying signal and transmission rate multiply by 2 π again divided by sampling rate;

(3) the present phase value of Chuan Shu minimum frequency shift keying signal equals the original phase value and the step-length sum of phase change;

(4) obtain the range value of multiple sinusoidal signal then according to present phase value, and then obtain the multiple bandpass signal of minimum shift keying;

(5) real coefficient FIR low pass filter be multiply by the complex carrier signal signal and obtain the complex analytic band-pass filter that centre frequency is a carrier frequency, the complex analytic band-pass filter that by centre frequency is carrier frequency carries out multiple parsing bandpass filtering, inhibition zone external spectrum composition to the multiple bandpass signal of minimum shift keying;

(6) get the real part of multiple bandpass signal, the minimum shift keying that conversion can obtain transmitting through D/A is simulated real bandpass signal, finishes whole modulation treatment process.

2. the modulator approach of minimum frequency shift keying signal as claimed in claim 1 is characterized in that, the described centre frequency of step (5) is that the method for designing of complex analytic band-pass filter of carrier frequency is as follows:

(1) at first for different transmission rates, design and the irrelevant real coefficient FIR low pass filter of minimum frequency shift keying signal carrier frequency, with the coefficient storage of filter in the program storage of processor;

(2) before processor is carried out the modulation handling procedure of minimum frequency shift keying signal, processor is according to corresponding low pass filter in the different transmission rate option program memories, by the product of processor compute low pass filtered device and complex carrier signal signal, obtain the complex analytic band-pass filter that centre frequency is a carrier frequency;

(3) with the coefficient storage of complex analytic band-pass filter in the program storage of processor, so just finished the design of complex analytic band-pass filter.

3. the modulator approach of minimum frequency shift keying signal as claimed in claim 2 is characterized in that, the processor that adopts in this method is a digital signal processor.

4. the demodulation method of a minimum frequency shift keying signal is characterized in that, it is as follows that the method comprising the steps of:

(1) Binary Frequency Shift Keying that receives is simulated real bandpass signal and is become digital real signal through A/D, the complex analytic band-pass filter that by centre frequency is carrier frequency carries out multiple parsing bandpass filtering to the digital real signal that receives, the outer unwanted signal frequency content of filtering band, signal becomes multiple bandpass signal by original real bandpass signal;

(2) this multiple bandpass signal is postponed, the sampling of delay is counted and is the twice of sampling rate divided by transmission rate;

(3) conjugation of the multiple bandpass signal after will postponing, the multiple bandpass signal before postponing, the phase shift factor relevant with carrier frequency are carried out complex multiplication, get the resulting long-pending imaginary part that multiplies each other, if the value of imaginary part is greater than zero, dateout " 0 " then, if the value of imaginary part is less than zero, dateout " 1 " then, thus whole differential ference spiral process finished.

5. the demodulation method of minimum frequency shift keying signal as claimed in claim 4 is characterized in that, the described centre frequency of step (1) is that the method for designing of complex analytic band-pass filter of carrier frequency is as follows:

(1) at first for different transmission rates, design and the irrelevant real coefficient FIR low pass filter of minimum frequency shift keying signal carrier frequency, with the coefficient storage of filter in the program storage of processor;

(2) before processor is carried out the modulation handling procedure of minimum frequency shift keying signal, processor is according to corresponding low pass filter in the different transmission rate option program memories, by the product of processor compute low pass filtered device and complex carrier signal signal, obtain the complex analytic band-pass filter that centre frequency is a carrier frequency;

(3) with the coefficient storage of complex analytic band-pass filter in the program storage of processor, so just finished the design of complex analytic band-pass filter.

6. the demodulation method of minimum frequency shift keying signal as claimed in claim 5 is characterized in that, the processor that adopts in this method is a digital signal processor.

7. a complex analytic band-pass filter method for designing is characterized in that, it is as follows that the method comprising the steps of:

(1) at first for different transmission rates, design and the irrelevant real coefficient FIR low pass filter of minimum frequency shift keying signal carrier frequency, with the coefficient storage of filter in the program storage of processor;

(2) before processor is carried out the modulation handling procedure of minimum frequency shift keying signal, processor is according to corresponding low pass filter in the different transmission rate option program memories, by the product of processor compute low pass filtered device and complex carrier signal signal, obtain the complex analytic band-pass filter that centre frequency is a carrier frequency;

(3) with the coefficient storage of complex analytic band-pass filter in the program storage of processor, so just finished the design of complex analytic band-pass filter.

8. complex analytic band-pass filter method for designing as claimed in claim 7 is characterized in that, the processor that adopts in this method is a digital signal processor.

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