CN109818635B - Signal transmission method based on zero intermediate frequency receiver - Google Patents
Signal transmission method based on zero intermediate frequency receiver Download PDFInfo
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Abstract
The invention discloses a signal transmission method based on a zero intermediate frequency receiver, which comprises the following steps: the transmitter modulates binary data by taking a first signal as a modulation fundamental wave, wherein the first signal is a linear frequency modulation signal which jumps to fc + fm at the moment of frequency fc-fn, fc is the central frequency of a carrier wave, fn is the frequency difference value between the first signal and fc before jumping, fm is the frequency difference value between the second signal and fc after jumping, and fm is more than or equal to fn; the transmitter transmits the modulated radio frequency signal; the zero intermediate frequency receiver receives the radio frequency signal and performs frequency mixing processing on the radio frequency signal to reduce the frequency of the radio frequency signal into a zero frequency signal; filtering out the noise signal of the zero-frequency signal through a high-pass filter; and demodulating the signal after passing through the high-pass filter to obtain an original signal. The signal transmission method based on the zero intermediate frequency receiver can reduce the requirement of the system on the performance of phase noise and improve the sensitivity of the system.
Description
Technical Field
The present invention relates to wireless communications, and more particularly, to a signal transmission method based on a zero intermediate frequency receiver.
Background
The Chirp signal is a spread spectrum signal, which exhibits a Chirp modulation (LFM) characteristic in which the frequency of the signal varies linearly with time, and is also called a linear frequency sweep signal. Have found a great deal of application in radar detection, underwater acoustic communications, laser communications, ultra-wideband communications, and LORA communications. In a communication system, a frequency sweep characteristic of a Chirp signal, such as a frequency sweep speed, a frequency sweep direction, and the like, is used to represent data symbols for communication, thereby achieving a spread spectrum effect. The Chirp spread spectrum communication system has the advantages of large processing gain, strong anti-fading capability, strong anti-interception capability and the like of the traditional spread spectrum communication system, and has the characteristics of low power spectral density, strong anti-frequency deviation capability, low system power consumption and the like.
At present, a narrow-band Chirp modulated receiver, such as LORA of Semtech, has a maximum bandwidth of 500kHz, and adopts a low-intermediate frequency receiver, which has the advantages of low requirement on phase noise of a carrier and phase noise resistance, but has high requirement on image suppression, the larger the bandwidth, the higher the complexity of a receiving system and the higher cost.
In the prior art, in order to reduce the cost of the receiver, a receiver with a zero intermediate frequency is generally adopted. The zero intermediate frequency receiver directly changes signals from radio frequency signals to baseband signals without modulation and demodulation of intermediate frequency. Its advantages are low requirement to image suppression and low complexity. But can produce local oscillator leakage and dc offset. The local oscillation leakage is that the local oscillation passes through a circuit or in the air and enters an outlet of the frequency mixer from an inlet of the frequency mixer, so that a single-frequency point output with the local oscillation is contained in an output signal. The dc offset is a zero adjustment error of the mixer input, so that the input signal has a dc component, resulting in a local oscillation signal of the signal output by the mixer. The phase noise causes the local oscillation signal to shake, the formed whole signal is in the bandwidth of the useful signal, and the receiver cannot remove the signal, so that the system performance is influenced.
However, based on this, the inventors of the present application have found that since noise signals generated by local oscillation leakage, dc offset, and phase noise cannot be filtered within an operating frequency band, the accuracy of a circuit is strictly controlled to prevent performance deterioration due to excessive noise.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Disclosure of Invention
The invention aims to provide a signal transmission method based on a zero intermediate frequency receiver, which can reduce the requirement of a system on the performance of phase noise and improve the sensitivity of the system.
In order to achieve the above object, the present invention provides a signal transmission method based on a zero intermediate frequency receiver, including: the transmitter modulates binary data by taking a first signal as a modulation fundamental wave, wherein the first signal is a linear frequency modulation chirp signal which jumps to fc + fm at the moment of frequency fc-fn, fc is the central frequency of a carrier wave, fn is the frequency difference value between the first signal and fc before jumping, fm is the frequency difference value between the second signal and fc after jumping, and fm is more than or equal to fn; the transmitter transmits the modulated radio frequency signal; the zero intermediate frequency receiver receives the radio frequency signal and performs frequency mixing processing on the radio frequency signal to reduce the frequency of the radio frequency signal into a zero frequency signal; filtering out the noise signal of the zero-frequency signal through a high-pass filter; and demodulating the signal after passing through the high-pass filter to obtain an original signal.
In a preferred embodiment, the cut-off frequency of the high-pass filter is between fc-fn and fc + fm.
In a preferred embodiment, the transmitter uses the first signal as a modulation fundamental wave, and the modulating the binary data includes: the transmitter processes the first signal to enable the first signal to carry binary information; the transmitter modulates the processed first signal by a carrier signal.
In a preferred embodiment, the initial frequency of the first signal is fc-2/B.
In a preferred embodiment, the initial frequency of the first signal is non fc-2/B.
Compared with the prior art, according to the signal transmission method based on the zero intermediate frequency receiver, provided by the invention, binary data are modulated by using a first signal as a modulation fundamental wave, wherein the first signal is a chirp signal of which the frequency jumps to fc + fm at the moment of frequency fc-fn, fc is the central frequency of a carrier wave, fn is the frequency difference value between fc before jumping and fm after jumping, fm is the frequency difference value between fc after jumping, and fm is larger than or equal to fn; transmitting the modulated radio frequency signal; receiving the radio frequency signal, performing frequency mixing processing on the radio frequency signal, and reducing the frequency of the radio frequency signal into a zero frequency signal; filtering out a noise signal of the signal by a high-pass filter; and demodulating the signal passing through the high-pass filter to obtain an original signal. The influence of phase noise can be avoided under the condition of not losing performance, and the sensitivity of the system is improved; the requirement of the system on the phase noise performance is reduced, the cost of the receiver is further reduced, and the application requirement of broadband communication is met.
Drawings
Fig. 1 is a time-frequency diagram of a chirp signal according to an embodiment of the present invention.
Fig. 2 is a spectral diagram of a chirp signal in accordance with an embodiment of the present invention.
Fig. 3 is a diagram of a baseband signal spectrum of a zero intermediate frequency receiver according to an embodiment of the present invention.
Fig. 4 is a flowchart of a signal transmission method based on a zero intermediate frequency receiver according to an embodiment of the present invention.
FIG. 5 is a time-frequency diagram of a first signal with an initial frequency fc-2/B according to an embodiment of the present invention.
Fig. 6 is a time-frequency diagram of a first signal with an initial frequency of an arbitrary frequency according to an embodiment of the present invention.
Fig. 7 is a spectral diagram of a zero if receiver with a K-0.95 time-base band signal superimposed with a noise signal according to an embodiment of the present invention.
Fig. 8 is a spectral diagram of a high pass filter according to an embodiment of the present invention.
Detailed Description
The following detailed description of the present invention is provided in conjunction with the accompanying drawings, but it should be understood that the scope of the present invention is not limited to the specific embodiments.
Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.
When the sweep frequency bandwidth is B and the sweep frequency time is T, the basic linear sweep frequency signal expression is as follows:
wherein:
t∈[0,T)
fcis the carrier frequency.
As shown in fig. 1, which is a time-frequency diagram of a chirp signal according to a preferred embodiment of the present invention, the frequency is fc-B/2 at time 0, and as time increases, the frequency changes linearly, and when it reaches time T, the frequency becomes fc + B/2, the whole sweep range is B, and the sweep speed is B/T.
As shown in fig. 2, which is a spectral diagram of a chirp signal in accordance with a preferred embodiment of the present invention.
Aiming at the linear frequency modulation signal, when the zero intermediate frequency receiver with a simple structure is adopted, the noise signal is converted into 0 frequency after down-conversion, and a narrow-band noise near the 0 frequency is formed. However, noise is superimposed in a useful frequency band, is difficult to eliminate, interferes with a useful signal, and reduces the sensitivity of the system.
As shown in fig. 3, which is a spectrum diagram of a baseband signal of a zero intermediate frequency receiver according to a preferred embodiment of the present invention. The energy of the phase noise in the figure is-30 dBc. At the receiver end, the signal-to-interference ratio due to phase noise is 30 dB.
As shown in fig. 4, which is a flowchart of a signal transmission method based on a zero intermediate frequency receiver according to a preferred embodiment of the present invention, includes steps S1-S5.
In step S1, the transmitter modulates the binary data by using a first signal as a modulation fundamental wave, where the first signal is a chirp signal that jumps to fc + fm at a time point having a frequency fc-fn, fc is a center frequency of a carrier, fn is a frequency difference value between fc before the jump and fm after the jump, and fm is equal to or greater than fn.
Note that the first signal skips bandwidth fm + fn, and can be set to any bandwidth including fc. The values of fm and fn are related to the crystal oscillator performance of the transmitter, and can be set according to requirements.
Specifically, step S1 may include step S11 and step S12.
In step S11, the transmitter processes the first signal so that the first signal carries binary information. In particular, the first signal and the binary data may be passed through a multiplier.
In step S12, the transmitter modulates the processed first signal by a carrier signal to obtain a radio frequency signal to be transmitted. In particular, the mixing may be implemented by mixing a sine wave signal with the processed first signal.
In this embodiment, the slope of the first signal generated by the transmitter is:
the first signal expression is:
when the initial frequency is fc-2/B, as shown in fig. 5, it is a time-frequency diagram of the first signal with the initial frequency of fc-2/B according to the preferred embodiment of the present invention. When the initial frequency is an arbitrary frequency other than fc-2/B, as shown in fig. 6, it is a time-frequency diagram of the first signal whose initial frequency is an arbitrary frequency according to the preferred embodiment of the present invention. In the figure, at time t0 when the first signal has a frequency fc-fn, the frequency jumps to fc + fm, and the slope is unchanged before and after the jump.
In step S2, the transmitter transmits the modulated radio frequency signal.
In step S3, the zero intermediate frequency receiver receives the radio frequency signal and performs frequency mixing processing on the radio frequency signal, so that the radio frequency signal is down-converted to a zero frequency signal.
Specifically, in this embodiment, a zero intermediate frequency receiver is used to process the radio frequency signal. Received radio frequency signals are directly converted into zero-frequency signals through frequency mixing, noise signals are also converted into 0 frequency through frequency conversion, and narrow-band noise close to the 0 frequency is formed.
Fig. 7 is a spectrum diagram of a zero intermediate frequency receiver according to the preferred embodiment of the present invention, in which a noise signal is superimposed on a 0.95 time-base band signal. The noise signal in fig. 7 is not within the useful band.
In step S4, filtering out the noise signal of the zero-frequency signal by a high-pass filter; as shown in fig. 8, which is a spectral diagram of a high pass filter according to a preferred embodiment of the present invention.
In step S5, the signal passed through the high-pass filter is demodulated to obtain an original signal. Thus, since the phase noise of the receiver is not within the effective bandwidth of the signal, the phase noise can be completely filtered out by the filter without affecting the demodulation performance.
Wherein the cut-off frequency of the high-pass filter is between fc-fn and fc + fm.
Therefore, in the signal transmission method based on the zero intermediate frequency receiver provided by this embodiment, a first signal is used as a modulation fundamental wave to modulate binary data, where the first signal is a chirp signal whose frequency jumps to fc + fm at a time instant whose frequency is fc-fn, fc is a center frequency of a carrier wave, fn is a frequency difference value between fc before the jump and fm, fm is a frequency difference value between fc after the jump, and fm is greater than or equal to fn; transmitting the modulated radio frequency signal; receiving the radio frequency signal, performing frequency mixing processing on the radio frequency signal, and reducing the frequency of the radio frequency signal into a zero frequency signal; filtering out a noise signal of the signal by a high-pass filter; and demodulating the signal passing through the high-pass filter to obtain an original signal. The influence of phase noise can be avoided under the condition of not losing performance, and the sensitivity of the system is improved; the requirement of the system on the phase noise performance is reduced, the cost of the receiver is further reduced, and the application requirement of broadband communication is met.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.
Claims (5)
1. A signal transmission method based on a zero intermediate frequency receiver is characterized by comprising the following steps:
the transmitter modulates binary data by taking a first signal as a modulation fundamental wave, wherein the first signal is a linear frequency modulation chirp signal which jumps to fc + fm at the moment of frequency fc-fn, fc is the central frequency of a carrier wave, fn is the frequency difference value between the first signal and fc before jumping, fm is the frequency difference value between the second signal and fc after jumping, and fm is more than or equal to fn;
the transmitter transmits the modulated radio frequency signal;
the zero intermediate frequency receiver receives the radio frequency signal and performs frequency mixing processing on the radio frequency signal to reduce the frequency of the radio frequency signal into a zero frequency signal;
filtering out the noise signal of the zero-frequency signal through a high-pass filter;
and demodulating the signal after passing through the high-pass filter to obtain an original signal.
2. Method for signal transmission according to claim 1, characterized in that the cut-off frequency of the high-pass filter is between fc-fn and fc + fm.
3. The signal transmission method of claim 1, wherein the transmitter modulates the binary data with the first signal as a modulation fundamental wave, comprising:
the transmitter processes the first signal to enable the first signal to carry binary information;
the transmitter modulates the processed first signal by a carrier signal.
4. The signal transmission method according to claim 1, wherein the initial frequency of the first signal is fc-2/B, where B is a swept bandwidth.
5. The signal transmission method according to claim 1, wherein the initial frequency of the first signal is non-fc-2/B, where B is a swept bandwidth.
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