WO2006097033A1

WO2006097033A1 - A base-band signal demodulation preprocess system and method

Info

Publication number: WO2006097033A1
Application number: PCT/CN2006/000348
Authority: WO
Inventors: Ling Yue
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2005-03-14
Filing date: 2006-03-08
Publication date: 2006-09-21
Also published as: CN1835488A; CN1835488B

Abstract

A base-band signal demodulation preprocessing system and method. Said preprocess system includes an amplifier, a mixer and a limiter circuit; said amplifier preamplifies the received radio frequency (RF) analog signal; said mixer mixes the amplified RF analog signal and local oscillation signal by non-linear transformation to obtain intermediate frequency (IF) analog signal; said limiter circuit is connected to said amplifier and said mixer in series, and limits the amplitude of the interference signal level which is higher than the useful signal level. The base-band signal demodulation preprocessing system according to present invention can provide anti-interference preprocess for analog demodulation system or digital demodulation system, or provide anti-interference preprocess by combining with digital filtering technique. In virtue of the use of limiter circuit the dynamic range of system is increased.

Description

Baseband signal demodulation preprocessing system method

Technical field

The present invention relates to a baseband signal processing technique in a communication system, and more particularly to a demodulation preprocessing system and method for a baseband intermediate frequency signal.

BACKGROUND OF THE INVENTION The so-called baseband intermediate frequency signal demodulation preprocessing includes: converting a radio frequency signal into an intermediate frequency signal for providing to a demodulation unit, and performing anti-interference processing before demodulation. In the pre-processing system, how to improve the anti-interference performance, and thus improve the signal quality sent to the demodulation unit is a key point.

In the field of communications, interference is an important factor affecting the normal operation of a base station. One of the factors that cause interference is: Due to limited frequency resources, the frequencies used by different communication systems are close to each other, resulting in interference, such as: PHS forward channel and Wideband Code Division Multiple Access (WCDMA) and Interference between the reverse channels of the CDMA (1900 MHz band) due to the closeness of the frequency; mutual interference between the forward channel of the CDMA (800 MHz band) and the reverse channel of the GSM (Global System for Mobile Communications) due to the close frequency, and Other similar situations. In order to solve the above problem of mutual interference between systems, the commonly used methods include frequency planning and filtering to remove interference at the transmitting output of the system. Frequency planning refers to the reasonable allocation of frequency resources occupied by a system in space and time, so that the frequency used by the system and the frequency of other communication systems are as little as possible to generate mutual interference. In some cases, this method cannot reduce interference between systems. For example, CDMA450 uses a frequency band of 450 MHz, and there are also interference sources such as trunking communication systems and broadcasting stations in the frequency range. Among them, the frequency band used by the trunking communication system is 450MHz; the frequency used by the broadcasting station is concentrated in the 90MHz range. Due to the large transmission power, the 5th harmonic of the broadcast signal (the frequency range is 450MHz) will cause significant interference to the CDMA450 system. Another method of the prior art is to add a filter in the baseband signal demodulation preprocessing system, but the above problem cannot be solved by using a general analog filter, because the interference source frequency is the same as the communication system frequency, and is in-band. In the case of interference, a typical analog bandpass filter cannot filter out noise in the same frequency band. Based on the above reasons, the more common methods are: The system obtains the digital intermediate frequency signal, and adopts the adaptive filtering technology (digital filter) to filter out the in-band interference. The principle is shown in the figure. minus 2-

1 is shown.

As can be seen from FIG. 1, the input signal (which is an analog signal) is amplified by the low noise amplifier 11 and input to the mixer 12 for mixing to obtain an intermediate frequency signal, and an analog/digital converter (A/D) 13 is used for mixing. The IF analog signal is converted into a digital signal and sent to the adaptive filter 14 to filter out the noise. The denoised signal can be further processed, such as being sent to the demodulator for demodulation.

The disadvantages of the prior art system and method are: The adaptive filter is a digital filter, and the essence is that the digital domain is filtered by a certain software algorithm. Therefore, the adaptive filter cannot be applied to the filtering of the intermediate frequency noise of the analog system. In addition, electronic components need to work in a certain level range (that is, have a certain dynamic range). When the level of the interference signal is strong, in the digital filtering system, the simulation cannot be performed due to the dynamic limitation of the analog-to-digital converter. The interference signal is converted into a digital signal without distortion, and then filtered by an adaptive filter; the filtering principle of the adaptive filter is to dynamically find the interference frequency and filter out the signal of the interference frequency. Therefore, the adaptive filter also filters out the wanted signal at that frequency. As shown in Figure 1, the input signal clip carries the interference signal. After the adaptive filter is output, although the interference signal is filtered out, the useful signal also has a spectral loss in the interference frequency range.

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to provide a baseband signal demodulation preprocessing system and method, which can perform anti-interference processing in an analog domain or a digital domain; moreover, when the system itself performs anti-interference processing, It does not cause a loss of spectrum in the useful signal. Based on this, the technical problem further solved by the present invention is to provide a baseband signal demodulation preprocessing system and method, which can meet the requirements of the dynamic range of the system when anti-jamming. In order to solve the above technical problem, the object of the present invention is achieved by the following technical solutions: The baseband signal demodulation preprocessing system of the present invention includes an amplifier, a mixer and a limiting circuit; the amplifier will receive the radio frequency simulation The signal is preamplified; the mixer obtains an intermediate frequency analog signal by nonlinearly transforming the RF analog signal amplified by the amplifier and the local oscillator signal; the limiting circuit is connected in series with the amplifier and the mixer, and is high The amplitude is limited by the level of the interfering signal at the useful signal level. In the above-mentioned baseband signal demodulation preprocessing system, an analog/digital converter and an adaptive filter are also included. The wave unit, the analog/digital converter is configured to convert the clipped intermediate frequency analog signal into an intermediate frequency digital signal; the adaptive filter receives the intermediate frequency digital signal output by the analog/digital converter, and performs digital filtering processing. In the baseband signal demodulation preprocessing system, the limiting circuit can be connected in series with the amplifier to receive the radio frequency analog signal, and after the limiting process, send the radio frequency analog signal to the amplifier; or, the limiting The circuit is connected between the amplifier and the mixer, receives the RF analog signal amplified by the amplifier, and sends the RF analog signal to the mixer after limiting processing; or, the limiting circuit is serially connected to the mixer After the frequency converter, the intermediate frequency analog signal output by the mixer is received and subjected to limiting processing. In the baseband signal demodulation preprocessing system of the present invention, the limiting circuit is implemented by an antistatic diode, or the limiting circuit is implemented by a PIN limiting diode. The baseband signal demodulation preprocessing method of the present invention comprises: preamplifying a received radio frequency analog signal; and obtaining an intermediate frequency analog signal by nonlinearly transforming the radio frequency analog signal and the local oscillator signal amplified by the amplifier; It also includes: Amplitude limiting of the level of the interfering signal above the useful signal level. In the method, the amplitude limitation is performed by a radio frequency analog signal before the preamplification; or the amplitude limitation is performed on the preamplified radio frequency analog signal; or the amplitude limitation is a needle intermediate frequency simulation. Signal implementation.

The method further includes: converting the clipped-processed intermediate frequency analog signal into an intermediate frequency digital signal; and performing digital filtering processing on the intermediate frequency digital signal. As can be seen from the above technical solution, the limiter circuit is used in the present invention to limit the interference level and reduce the energy of the noise in the signal. Therefore, the purpose of anti-interference is achieved, and the signal-to-noise ratio of the signal in the system is improved. Also, since the limiter circuit only limits the level of in-band interference, rather than filtering out all signals (including useful signals) in the corresponding frequency range. Therefore, no loss of the useful signal in the spectrum is generated. Meanwhile, since the limiter circuit operates in the analog domain instead of the digital domain, it implements anti-interference processing at the intermediate frequency stage of the system analog signal, and thus the present invention can be applied to the analog system. Baseband signal demodulation preprocessing. Similarly, the analog signal after the interference suppression circuit is processed by the analog-to-digital conversion can also be provided to the digital system. In summary, the system of the present invention can be An analog demodulation system or digital demodulation system provides anti-interference pre-processing. On the other hand, if an adaptive filtering technique is added to the system of the present invention (i.e., after the system is subjected to clipping processing, the signal is converted into a digital signal, and then filtered by an adaptive filter), the The anti-interference performance of the pre-processing system; and, because the strong interference signal is first subjected to clipping processing (in the analog domain), the interference signal level satisfies the dynamic range of the analog-to-digital converter, and thus can be converted by analog-to-digital conversion. The converter transforms into a digital signal and is filtered out in the adaptive filter. In fact, due to the presence of the limiter circuit, the anti-interference dynamics of the adaptive filter are improved. As described above, the system can be used for the baseband signal demodulation preprocessing of the analog system. Similarly, since the limiter circuit suppresses the level of the level, the level of the demodulated signal satisfies the dynamic range of the quadrature demodulation circuit, so that the circuit is not saturated, that is, the demodulation dynamics of the quadrature demodulation circuit is improved.

In the present invention, an antistatic diode or a PIN limiting diode is used to implement the limiting circuit required in the preprocessing system. Since the limiting circuit implemented by the diode is low in cost, the system cost of the preprocessing system of the present invention is reduced.

DRAWINGS

1 is a prior art pre-processing system including an adaptive filtering technique; FIG. 2 is a schematic diagram of a limiting characteristic of a diode; FIG. 3 is a diagram of a limiting circuit; FIG. 4 is a diagram of a pre-processing system for demodulating a baseband signal according to the present invention. FIG. 5 is a block diagram of a second embodiment of a baseband signal demodulation preprocessing system according to the present invention; FIG. 6 is a block diagram of a third embodiment of a baseband signal demodulation preprocessing system according to the present invention; 7 is a block diagram of a fourth embodiment of a baseband signal demodulation preprocessing system according to the present invention; FIG. 8 is a block diagram of a fifth embodiment of a baseband signal demodulation preprocessing system according to the present invention; A block diagram of a sixth embodiment of a baseband signal demodulation pre-processing system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The core idea of the present invention is: use a limiting technique to solve the interference problem in communication, and suppress the interference higher than the useful signal to achieve the purpose of anti-interference; at the same time, ensure that the demodulation circuit does not Saturated, that is: In the digital intermediate frequency circuit, the analog-to-digital converter is guaranteed to be unsaturated. In the analog circuit, the quadrature demodulation circuit is guaranteed to be unsaturated. The baseband signal demodulation preprocessing system of the present invention mainly comprises a low noise amplifier, a limiting circuit and a mixer. Low Noise Amplifier (LNA), in the circuit is mainly to amplify the RF signal received by the antenna to meet the amplitude requirements of the mixer in the preprocessing system. The low noise amplifier is the first stage amplification circuit of the receiver, located behind the antenna unit. A low noise amplifier can be used to improve the overall noise figure of the receiver. A limiter circuit (limiter), as known to those skilled in the art, the function of the limiter circuit is to limit the amplitude of the output signal within a certain range, that is, when the input voltage exceeds a certain threshold voltage value, the output voltage will be It is limited to a certain level (called the clipping level) and does not change with the input voltage. The limiting circuit in the present invention can be divided into an upper limit amplitude circuit, a lower limit amplitude circuit and a bidirectional limiter circuit according to the limiting characteristics, and the specific implementation manner is as follows. In the present invention, a diode limiting circuit is recommended. The diode used in the limiting circuit is recommended to use an antistatic diode (such as BAV99, etc.) and a PI limiting diode. The limiting characteristics are shown in Fig. 2. Since the diode has better switching characteristics and lower cost, the system cost is reduced while ensuring the beneficial effects of the present invention. As shown in the limiter circuit of Fig. 3, when there is no signal input at the input terminal, since the diode 31 is connected in reverse, the output voltage is zero. When the signal is input, if the input signal voltage is greater than the voltage E of the power supply 32, the diode is turned on, so that the maximum value of the output pulse of the circuit is the power supply voltage E and the forward voltage drop of the diode (such as 0.6V), that is, E+0.6. Is the threshold voltage of this limiter circuit. The limiting circuit is an upper limit circuit. If the diodes are connected in reverse, the lower limit circuit is formed. Similarly, the diode can be connected in series with the input and output terminals, and the limiting circuit can also be realized. The upper limit amplitude circuit or the lower limit amplitude circuit can also be realized by using the characteristics of the diode forward conduction reverse cutoff. By combining the upper limit amplitude circuit and the lower limit amplitude circuit, a bidirectional limiter circuit can be formed.

In addition to the diode limiting circuit described above, the limiting circuit can also be formed by the cut-off and saturation characteristics of the triode. This type of circuit also has the function of amplification. If it is required to meet higher technical requirements, it can also be constructed with an integrated operational amplifier. Limiting circuit. According to the amplification and limiting function of the triode, it can be One 6—

The low noise amplifier referred to in the present invention is combined with a limiter circuit to simultaneously achieve low noise amplification and amplitude limiting of the level of the interference signal above the useful signal level by the triode circuit. a mixer (or a mixer circuit) (MIXER) that combines a radio frequency signal with a local frequency of a local oscillator signal to obtain a difference frequency or a sum frequency (the difference frequency or the sum frequency is fixed), Obtaining an IF signal, this change is also known as spectrum shifting. After mixing, the system can get the desired IF signal, but the mixing also produces components of other frequencies that are detrimental to the system. Therefore, a bandpass filter can be used in the circuit after the mixer. The method filters out these frequency components. In practical applications, mixers are implemented in many ways, such as: double balanced ring switch mixers and 6FET ring mixers. In the present invention, the baseband signal demodulation preprocessing system is constructed by connecting the low noise amplifier, the mixer and the limiter circuit in series. Since the output signal of the system is an analog signal, the output signal of the system can be directly input into the analog demodulation system. Since the limiting circuit limits the level of the interference signal and reduces the energy of the interference signal, the anti-interference effect is achieved. , the system is implemented to pre-process the anti-interference processing before the analog demodulation system. Similarly, the analog signal output by this system can be input to a digital demodulation system through an analog-to-digital converter. For the above reasons, the present invention also achieves pre-processing including anti-interference processing in the digital demodulation system. In summary, the pre-processing system implements anti-interference processing before the analog demodulation system and the digital demodulation system; from another perspective, the system can replace the adaptation in the prior art before digital demodulation. The filtering system implements anti-interference processing.

In the preprocessing system of the present invention, the mixer is connected in series with the low noise amplifier to receive a high frequency signal amplified by the low noise amplifier. The limiter circuit can be connected in series between the low noise amplifier front end, the low noise amplifier and the mixer, or after the mixer. The position where the limiter circuit is connected in series is determined by the slice level of the limiter circuit and the interference level in the actual signal; if the analog demodulation system is connected after the preprocessing system, the specific position of the limiter circuit in the system It is also necessary to determine the maximum linear input level of the analog quadrature demodulator. If the pre-processing system is connected to a digital demodulation system, the analog signal output by the system needs to be converted into a digital signal by an analog-to-digital converter. At this time, the specific position of the limiter circuit in the system needs to be determined in conjunction with the maximum linear input level of the analog-to-digital converter. In general, combined with the above factors for comprehensive consideration, limiting The lower the clipping level of the circuit, the closer the limiting circuit should be to the input of the preprocessing system. FIG. 4 shows an embodiment of the present invention. In this embodiment, the mixer 42 is serially connected to the low noise amplifier 41, and the limiting circuit 43 is connected in series with the mixer 42 to limit the anti-interference processing. The resulting output signal can be sent directly to the quadrature demodulation system 44 for analog demodulation, or after passing through the analog to digital converter 45, the resulting digital signal is sent to a digital demodulation system 46 for digital demodulation. As shown, the amplitude of the noise signal is reduced by the output signal of the limiter circuit compared to the input signal of the preprocessing system. 5 and FIG. 6 are two other embodiments of the present invention. In the two embodiments, as shown in FIG. 5, the limiting circuit is connected in series between the low chirp amplifier and the mixer; The limiter circuit is connected in series before the low noise amplifier. On the basis of the above preprocessing system, digital filtering technology can be added, that is, the analog/digital converter receives the analog intermediate frequency signal subjected to the limiting anti-interference processing, and after analog-to-digital conversion, the obtained digital intermediate frequency signal is sent to the adaptive filtering. In the device, the adaptive filter filters out signals in the frequency range of the interference signal to filter out the interference signal. The signal subjected to the limiting anti-interference processing and the adaptive filtering process is finally sent to the digital demodulation system through the output of the system for digital demodulation processing. FIG. 7, FIG. 8 and FIG. 9 are respectively schematic diagrams showing an embodiment of adding an adaptive filtering technique to a preprocessing system. As shown in the figure, the general system structure is as follows: The preprocessing system first performs limiting and anti-interference processing on the input signal, and the obtained intermediate frequency analog signal is converted into a digital intermediate frequency signal by an analog/digital converter, and sent to the adaptive filter. Digital filtering is performed.

Referring to the above general system structure, the low noise amplifier in the system is connected in series before the mixer; meanwhile, as shown in FIG. 7, the limiting circuit is connected in series after the mixer; as shown in FIG. 8, the limiting circuit is serially connected to Between the low noise amplifier and the mixer; as shown in Figure 9, the limiter circuit is connected in series with the low noise amplifier. The position where the limiter circuit is connected in series is determined by the slice level of the limiter circuit and the interference level in the actual signal, and since the analog intermediate frequency signal is also converted into a digital intermediate frequency signal for digital filtering processing in the system, The specific position of the limiter circuit in the system also needs to be determined in conjunction with the maximum linear input level of the analog-to-digital converter before the adaptive filter. In general, combined with the above factors, the lower the limiting level of the limiting circuit, the closer the limiting circuit should be to the input of the preprocessing system. The six specific implementation methods of the present invention are provided herein, which correspond to FIG. 4 to FIG. 9 respectively, and the implementation methods of the six pre-processing systems may be used alone or in combination with each other.

The baseband signal demodulation preprocessing system provided by the present invention has been described in detail above. The description is only for helping to understand the method and core idea of the present invention. Meanwhile, for those skilled in the art, according to the idea of the present invention, There will be changes in the specific implementation and application scope. In summary, the content of the specification should not be construed as limiting the invention.

Claims

Rights request

1. A baseband signal demodulation preprocessing system, the system comprising an amplifier and a mixer;

The amplifier preamplifies the received radio frequency analog signal;

The mixer obtains an intermediate frequency analog signal by using a preamplified RF analog signal and a local oscillator signal through a non-linear transformation;

The method further includes: a limiting circuit connected in series with the amplifier and the mixer to perform amplitude limiting on an interference signal level higher than a useful signal level.

2. The baseband signal demodulation preprocessing system according to claim 1, further comprising: an analog/digital converter and an adaptive filtering unit;

The analog/digital converter is configured to convert the limited-processed intermediate frequency analog signal into an intermediate frequency digital signal;

The adaptive filter receives the intermediate frequency digital signal output by the analog to digital converter and performs digital filtering processing.

The baseband signal demodulation preprocessing system according to claim 1 or 2, wherein: the limiting circuit is connected in series with the amplifier to receive a radio frequency analog signal, and the radio frequency is processed after limiting processing. The analog signal is sent to the amplifier.

The baseband signal demodulation preprocessing system according to claim 1 or 2, wherein: the limiting circuit is serially connected between the amplifier and the mixer, and receives a radio frequency simulation of the amplifier preamplifier. After the signal is processed, the radio frequency analog signal is sent to the mixer.

The baseband signal demodulation preprocessing system according to claim 1 or 2, wherein: the limiting circuit is serially connected to the mixer, and receives an intermediate frequency analog signal output by the mixer and limits the frequency. Processing.

6. The baseband signal demodulation preprocessing system according to claim 1, wherein: said limiting circuit comprises an antistatic diode, a PIN limiting diode and/or a triode circuit.

7. The baseband signal demodulation preprocessing system according to claim 1, wherein: said limiting circuit and the amplifier are integrated by a triode circuit.

8. A baseband signal demodulation preprocessing method, comprising: preamplifying a received radio frequency analog signal;

The RF analog signal preamplified by the amplifier and the local oscillator signal are nonlinearly transformed to obtain an intermediate frequency analog signal; the amplitude of the interference signal level above the useful signal level is limited.

9. The baseband signal demodulation preprocessing method according to claim 8, wherein: the amplitude limitation is performed by a radio frequency analog signal before pin preamplification; or the amplitude limitation is for preamplification. The RF analog signal is implemented; or, the amplitude limit is an implementation of a pin IF analog signal.

The baseband signal demodulation preprocessing method according to claim 8 or 9, further comprising: converting the amplitude-modulated intermediate frequency analog signal into an intermediate frequency digital signal; performing digital filtering on the intermediate frequency digital signal deal with.