CN101316252A - Demodulation method for unifying binary modulation signal - Google Patents

Abstract

The invention provides a method for demodulating uniform binary modulation signals, which includes a narrowband digital band pass filter and a threshold detector; the narrowband digital band pass filter is composed of one or more IIR digit filter basic links that are concatenated together, each basic link utilizes a pair of zero point and an extreme point that have very approximate resonant frequency to generate a zero group delay point on a phase-frequency characteristic curve, which can indicate the modulation characteristics of the signal while removing the noise; the threshold detector adjudicates the amplitude jump corresponding to the signal modulation characteristics at the output end of the narrowband digital band pass filter directly by a given or self-adjusted level value so as to demodulate the binary modulation information of the uniform binary modulation signals.

Description

A kind of demodulation method that is used for unified binary modulating signal

Technical field

The present invention is a kind of digital demodulation method that is used for unified binary modulating signal, belongs to the technical field of digital information transmission.

Background technology

Be subject to concrete application background or field target for the efficient communication Study on Technology both at home and abroad more, lay particular emphasis on certain real system (as 3G (Third Generation) Moblie) or specific targets (as code check), to have generally acknowledged theoretical foundation and obtain practice test thus new industrial research such as new technology that risk is very low such as OFDM (OFDM) modulation, ultra broadband (UWB) transmission, many antennas (MIMO) space-time/space time frequency coding awfully hot, achievement is rich.But for new ideas that do not obtain common recognition as yet or the higher potential technology of risk, then rare make inquiries or nobody goes into seriously.For example, for super arrowband (UNB:Ultra Narrow Bandwidth) the modulating/demodulating patented technology that waits a series of high spectrum utilization that propose by U.S. Harold doctor R.Walker, many according to " general knowledge " or only just negate easily with " experience ", rare people (comprising Walker) its whether feasible theoretical foundation that can get across.And, find to realize the key of UNB communication that can practicability according to our concentrating on studies for many years, be how to realize the rectangular window that adapts with various low-angle modulation waveforms.

Walker is based on the thought of zero group delay filter, obtained far above the spectrum efficiency of binary phase shift keying (BPSK) modulation and be not inferior to the power efficiency of BPSK, analog band-pass filter (Fig. 1 of the high quality factor of being invented (Q value), see H.R.Walker:Ultra Narrow Band Modulation Textbook, 2006, http://www.vmsk.org/) though effect has obtained the confirmation of U.S.'s Bell Laboratory recently, but because it adopts quartz crystal to realize, and the centre frequency of crystal filter is in case set just non-adjustable, very flexible not only, influenced by temperature and vibrations etc., and it is integrated to be difficult to digitlization, particularly theoretical the and deficient of his what is called " zero group delay "; Simultaneously, for a long time, people's (comprising Walker) think traditional digital filter, no matter are finite impulse response (FIR) filter or infinite impulse response (IIR) filter construction, all can't be used for the super narrow bandpass letter.

Summary of the invention

Technical problem: the demodulation method that the objective of the invention is to design a kind of unified binary modulating signal, it comprises a kind of digital filter and threshold detector of realizing unified binary modulation demodulates information that can approach the quartz-crystal filter of simulation in the function performance.Binary phase modulation (the EBPSK of the low-angle modulation expansion that particularly we proposed that this filter and UNB are commonly used, see " unified binary phase modulating and demodulating method ", application for a patent for invention number: 200610040767.2, publication number: CN1889550A) with unified binary quadrature shift keying (UBSK, see " unified binary quadrature shift keying modulation and demodulation method ", application for a patent for invention number: 200710025203.6, publication number: 101094209A) the modulation signal waveform matches, so that inhibit signal feature and filtering noise as much as possible to greatest extent, and simplified receiver structure.

Technical scheme: no matter which kind of concrete method is super narrowband modulation use realize that its common issue with that faces will allow the SPA sudden phase anomalies signal can pass through narrow band filter exactly.Observe 3 kinds of Walker shown in Figure 1, zero group delay filter, be not difficult to find that quartz crystal is most important therein.But, when Walker when the transmission of its UNB system and receiving terminal adopt what is called " zero group delay " (Zero Group Delay) filter based on quartz crystal simultaneously, then be subject to precision, stability and the drift of quartz crystal self parameter, the transmitting-receiving frequency difference is inevitable, this is for the performance of the UNB system of bandwidth " super narrow ", and the skew of carrier frequency or centre frequency is catastrophic often.Quartz crystal is in case determine in addition, and the adjustable extent of its filter center frequency is just minimum and difficultly maybe should not be controlled by electric tuning, thereby reliability, stability and flexibility are all very poor.But, for a long time, it is believed that some special nature that quartz crystal has is necessary in the super narrow bandpass letter just, thereby the digital filter of traditional FIR or IIR structure can not be finished super narrow-band filtering.

Yet, we notice when the series connection of quartz crystal and parallel resonant point very near the time, its amplitude-frequency and phase frequency resultant curve just and Walker the filter amplitude-frequency and the phase frequency curve that provide match.If consider with the crystal filter Digital Realization, then this series and parallel resonance point just corresponds respectively to zero, the limit of filter, by design the iir filter of N to very close conjugation zero, limit arranged, can finish the Digital Realization of Walker crystal filter.

A kind of demodulation method that is used for unified binary modulating signal of the present invention is used to remove narrow-band digital band pass filter and threshold detector of realizing unified binary modulation demodulates information that noise is also given prominence to the signal modulation signature simultaneously based on one; Described narrow-band digital band pass filter is made of the basic link cascade of one or more iir digital filters, each basic link is utilized the zero group delay point on very close zero point of a pair of resonance frequency and the limit generation phase-frequency characteristic curve, but the centre frequency of this basic link and signal carrier frequency are inconsistent, and its side-play amount is matched by the phase-frequency characteristic of the modulation angle of unified binary modulating signal and the basic link of this filter and incompatiblely determines, makes can change the modulation angle of input signal to give prominence in filtering noise to be the amplitude saltus step of output signal; The threshold detector of described unified binary modulation demodulates information directly by set or self-adjusting thresholding the high-low level judgement is carried out in this amplitude saltus step, demodulate the binary modulated information of unified binary modulating signal.

Beneficial effect: advantage of the present invention is as follows:

1. can in the inhibit signal feature, remove noise well.

Digital filtering mechanism proposed by the invention is the ability strong (because narrow bandwidth) of filtering noise not only, and inhibit signal feature (because have special phase-frequency characteristic) well, this character is for particular importance all such as radar, sonar, image processing, but is the deadly defect of conventional filter.Simultaneously, this understands from frequency domain, with regard to meaning this filter the bandwidth that modulation signal presented is greater than (even being far longer than) its bandwidth that is presented for noise and interference, thereby provides actual illustration for expanding the shannon capacity expansion.

2. be suitable for face width.Digital filter zero point, limit number that present patent application is invented are not limit, and carrier frequency can be set according to different system requirements with the deviation of filter center frequency, can under the very big degree of freedom, control filtering performance, to adapt to different channel circumstances.

3. simplified receiver structure.

The rectangular window that the present invention proposes matches with low-angle modulation signals such as EBPSK, UBSK, produce overshoot at section start corresponding to the modulation waveform of " 1 ", its amplitude is apparently higher than the non-saltus step place waveform of original phase place, thereby can directly adjudicate by amplitude detection, (publication number: what propose CN1889550A) is the receiver demodulation structure of core with the phase-locked loop to have simplified " unified binary phase modulating and demodulating method " patent application greatly.Because phase-locked loop is not participated in the demodulation of EBPSK signal, the phase-locked loop chip (being Fig. 7 frame of broken lines content) that can directly select for use (or integrated) widely to use, thereby whole EBPSK transmission system can realize that total digitalization handles, and it is integrated and simplify to be particularly conducive to the integrated circuit (IC) chip of receiver.

Description of drawings

Fig. 1 is the circuit diagram of 3 kinds zero group delay filters of Walker invention.

Fig. 2 is the typical amplitude-frequency characteristic and the phase-frequency characteristic curve of the zero group delay filter of Walker invention.

Fig. 3 and Fig. 4 be respectively quartz crystal also, amplitude-frequency and phase-frequency characteristic profile during series resonance.

Fig. 5 is a Filter Structures block diagram proposed by the invention.

Fig. 6 is the amplitude-frequency characteristic and the phase-frequency characteristic curve of filter proposed by the invention.

Fig. 7 is the EBPSK signal by the time domain waveform before and after this filter: (a) be original EBPSK signal, (b), (c) and (d) be respectively left side, right side and the strict conformance (being " accurately tuning " that common people understand and adopt) that carrier frequency is positioned at the filter center frequency.

Fig. 8 is the super narrow-band receiver structure chart of simplifying.

Fig. 9 is a filter proposed by the invention performance boost experimental result to the efficient modulating system of EBPSK, verifies with ber curve.

Embodiment

The amplitude-frequency and the phase frequency curve of the zero group delay filter that Fig. 2 provides for Walker, amplitude-frequency, phase-frequency characteristic curve synoptic diagram when Fig. 3 and Fig. 4 are respectively quartz crystal generation parallel connection and series resonance, obviously when the series and parallel resonance point very close to the time, the amplitude-frequency of crystal and phase frequency resultant curve just and the amplitude-frequency and the phase frequency curve of the filter that provides of Walker identical.If consider with this crystal filter Digital Realization, then this series and parallel resonance point just corresponds respectively to zero, the limit of digital filter, we have the very close zero point and the iir filter of conjugate pole by design, can finish the Digital Realization of Walker crystal filter.

As embodiment, its transfer function is with the iir filter of a pair of conjugation zero, limit in the present invention:

$H\left(z\right)=\frac{b_0+{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="A20081012447500082.png,A20081012447500102.png"\; state="\{\{state\}\}">b</figure-callout>}}_1\&CenterDot;z^{-1}+b_2\&CenterDot;z^{-2}}{1-a_1\&CenterDot;z^{-1}-a_2\&CenterDot;z^{-2}}---\left(1\right)$

B wherein ₀=1, b ₁=-1.630, b ₂=1, a ₁=1.608 and a ₂=-0.996, corresponding structure of block diagram as shown in Figure 5, amplitude-frequency and phase-frequency characteristic curve are as shown in Figure 6.Filtering result under various situations when Fig. 7 has provided filter center frequency and EBPSK signal carrier frequency respectively deviation is arranged, wherein, Fig. 7 (a) is original EBPSK signal, filtering result when Fig. 7 (b) is positioned at filter center frequency left side for carrier frequency, result when the filtering result when Fig. 7 (c) is positioned at filter center frequency right side for carrier frequency, Fig. 7 (d) then match for carrier frequency and filter center frequency, obvious, the phase hit of this moment is erased fully, and 0,1 signal can't be distinguished at all.

This EBPSK transmission system is utilized the result shown in Fig. 7 (b), be at phase hit point place generation overshoot phenomenon after the filtering, adopt receiver structure as shown in Figure 8, detect " 0 ", " 1 " signal are adjudicated by wave-shape amplitude, simplified the realization of EBPSK receiver greatly each initial moment of code element.Fig. 9 has provided the error rate that receiving terminal adds filter and do not add filter relatively, and obviously, after using this receiving filter, the bit error rate performance of system has clear improvement.

The carrier frequency that the present invention proposes the centre frequency of digital filter and EBPSK signal is deviation slightly, when carrier frequency is positioned at filter center frequency left side (low side), signal phase trip point place produces the parasitic amplitude modulation that increases, and promptly the amplitude of phase hit part obviously raises; When carrier frequency was positioned at filter center frequency right side (high-end), the wave-shape amplitude of phase hit part then obviously reduced, for non-saltus step part then amplitude remain unchanged; And if inhibit signal carrier frequency and digital filter centre frequency be when in full accord, then the phase hit of EBPSK signal will be erased fully, and " 0 " and " 1 " modulation signal can't be distinguished at all.This it is believed that the basic reason that the quartz-crystal filter of Walker can't Digital Realization just usually.

And the side-play amount of carrier frequency and filter center frequency is not at will to set, but will make the modulation angle of EBPSK signal match with the phase-frequency characteristic of digital filter.Carrier frequency should be located at the falling edge of phase frequency curve just, utilizes its transient response to make the EBPSK signal produce overshoot phenomenon at the phase hit place by the output of filter.

The EBPSK signal is by behind this rectangular window proposed by the invention, there is being the cycle of saltus step to locate the waveform generation overshoot corresponding to " 1 " modulation waveform is initial, amplitude is 0 sinusoidal wave part apparently higher than initial phase, thereby under the situation of precise synchronization, we can directly adjudicate " 0 ", " 1 " signal by amplitude detection, thereby make receiver structure simplify greatly.Simultaneously, owing to utilized the transient response of this filter, studies show that its inhibit signal feature and filtering noise as much as possible to greatest extent, present bigger signal bandwidth and less noise bandwidth, make the expansion of channel capacity become possibility, and enlightened new approach for the lifting of the development of filtering theory and communication performance.

Claims (1)

1, a kind of demodulation method that is used for unified binary modulating signal, it is characterized in that this demodulation method is used to remove narrow-band digital band pass filter and threshold detector of realizing unified binary modulation demodulates information that noise is also given prominence to the signal modulation signature simultaneously based on one; Described narrow-band digital band pass filter is made of the basic link cascade of one or more iir digital filters, each basic link is utilized the zero group delay point on very close zero point of a pair of resonance frequency and the limit generation phase-frequency characteristic curve, but the centre frequency of this basic link and signal carrier frequency are inconsistent, and its side-play amount is matched by the phase-frequency characteristic of the modulation angle of unified binary modulating signal and the basic link of this filter and incompatiblely determines, makes can change the modulation angle of input signal to give prominence in filtering noise to be the amplitude saltus step of output signal; The threshold detector of described unified binary modulation demodulates information directly by set or self-adjusting thresholding the high-low level judgement is carried out in this amplitude saltus step, demodulate the binary modulated information of unified binary modulating signal.

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