JP2982723B2 - Filter switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter switching device to which a baseband signal is input, and more particularly to a filter switching device for switching a reception baseband filter.

[0002]

2. Description of the Related Art As a conventional filter switching system, for example, as disclosed in Japanese Patent Application Laid-Open No. 59-225620, a digital modulation / demodulation apparatus which divides and uses an audio frequency band for data and audio is called a transmitting side. Then, when not transmitting voice, the data bit rate is changed and the frequency of the carrier of the modulator is also changed so that only data is transmitted using the entire voice frequency band. By detecting the frequency change of the carrier,
When switching from the mode of receiving voice and data to the mode of receiving only data, a method of switching a baseband filter in accordance with the band of data has been proposed.

FIG. 3 is a block diagram on the receiving side of the above-mentioned conventional modem. Here, the carrier in the mode for transmitting data and voice is fc1, and the carrier in the mode for transmitting only data is fc2. Switches SW1, S in FIG.
W2 connects to the solid line when fc1 is detected, and connects to the dotted line when fc2 is detected. A signal received from the transmission path is applied to a band-pass filter 31 (hereinafter, BPF 31) and a band-pass filter 32 (hereinafter, BPF 32), to take out the transmitted carrier waves fc1, fc2, and rectified by rectifier circuits 33, 34. . The determiner 35 determines which carrier wave is transmitted from each of the rectified outputs. If it is determined that the data has been transmitted at fc2, the switches SW1 and SW2 are connected to the dotted lines, and the carrier reproducing circuit 28 and the timing reproducing circuit 29 are notified that only the data has been transmitted.

When the switches SW1 and SW2 are connected to the dotted lines, the waveform of the transmitted signal is automatically equalized by the automatic equalizer 23, and then the carrier wave reproduced from the carrier reproducing circuit 28 in the demodulator 24. The signal modulated using fc2 is demodulated and applied to the baseband digital filter 25. At this time, the characteristics of the baseband digital filter 25 are switched by the clock from the timing recovery circuit 29 to filter characteristics that cover the occupied frequency when only data is transmitted. Next, unnecessary waves are removed by the baseband digital filter 25 and the output is applied to the code conversion circuit 26. The code conversion circuit 26 converts the multi-level signal into binary data and reproduces the transmitted data.

When it is determined that the signal is transmitted at fc1, the switches SW1 and SW2 are connected to the solid line side, and the carrier reproduction circuit 28 and the timing reproduction circuit 2 are connected.
9 is notified of the judgment result. At this time, the characteristic of the baseband digital filter 25 is switched to a filter characteristic that covers the occupied frequency when data and voice are transmitted. When the switches SW1 and SW2 are connected to the solid line side, the transmitted signal including voice and data is branched by the branch circuit 20, and one of the signals is removed by the rejector 27 to obtain a voice signal. The other signal is demodulated by a demodulator 22 through a carrier band filter 21 and is applied to an automatic equalizer 23. The binary data is code-converted by performing the same processing as described above. Is played.

[0006]

As described above, according to the conventional filter switching method, in a digital processing modem that divides and uses an audio frequency band between data and audio, the transmitting side is used when the audio is not transmitted. In order to transmit data using the entire audio frequency band, the data bit rate is changed and the frequency of the carrier of the modulator is changed at the same time, and on the receiving side, the change in the frequency of the carrier is detected. When switching from the mode for receiving voice and data to the mode for receiving only data, the filter characteristics of the baseband are switched according to the band of data.

However, in such a system, the removal of the interference wave by the filter in the baseband section is not actively considered, and therefore, the transmission in which the band of the modulated wave is close to the frequency of the channel interval is not considered. In the system, there is a problem that the filter always passes through such a trade-off that the quality degradation of the desired wave and the degree of suppression of the adjacent channel due to the band limitation are in a trade-off.

Accordingly, the present invention provides a filter switching apparatus capable of sufficiently suppressing adjacent channel interference waves and not deteriorating the reception quality of a desired wave, and improving the characteristics under any conditions. The purpose is to get.

[0009]

According to the present invention, in order to achieve the above object, a first filter having a narrower pass band compared to an interval between adjacent channels of an input baseband signal; A second filter having a passband wider than the interval, and a digital filter by A / D conversion.
Fourier transforms the baseband signal
By doing so, the neighbors included in the baseband signal are
A detection method that determines and detects the power level of interference
Output means and the first and second detection means in response to detection by the detection means.
And selecting means for selecting one of the filters and applying the baseband signal to the selected filter.

A first filter having a pass band narrower than an interval between adjacent channels of the input baseband signal; a second filter having a pass band wider than the interval; From the above baseband signal
A filter for extracting the signal of the interference wave of the adjacent channel
And measuring the power of the extracted signal.
The power level of the adjacent channel interference wave
There is provided a detecting means for detecting, and a selecting means for selecting one of the first and second filters in accordance with the detection of the detecting means and supplying the baseband signal to the selected filter.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment, and shows a case where a filter switching device according to the present invention is applied to baseband processing in a receiving unit of a mobile phone. In the figure, an input signal from a signal input terminal 1 is a demodulated baseband signal. This is input to the analog baseband filter 2 and filtering is performed gently compared to the channel interval to remove unnecessary waves. Next, baseband amplifier 3
After the amplification, digital conversion is performed by the A / D converter 4.

The digitally converted baseband signal is supplied to a filter selection unit 5 and an adjacent channel power measurement unit 8.
Passed to The filter selection unit 5 stores the input digital baseband signal in an internal memory until the measured value is passed from the adjacent channel power measurement unit 8. When the measured value of the adjacent channel power is input, the result is compared with a reference threshold Pref stored therein. If the measured value is larger than Pref, the digital baseband stored in the memory is compared. The signal is output to the narrowband digital baseband filter 7. Also, if the measured value is smaller than Pref,
The digital baseband signal is output to the wideband digital baseband filter 6.

As described above, when the level of the adjacent channel interference wave is high, it is possible to sufficiently suppress the noise with the narrow band filter 7, and when the level of the adjacent channel interference wave is low, the signal is passed through the wide band filter 6. Thus, it is possible to prevent the desired wave from being unnecessarily suppressed, reduce the amount of intersymbol interference, and prevent deterioration of the reception characteristics.

Next, a process of measuring power in the adjacent channel power measuring section 8 will be described. When the digital baseband signal is input from the A / D converter 4, the adjacent channel power measurement unit 8 stores data in the internal data memory 9. Then, when the stored number becomes equal to the Fourier transform length L set by the fast Fourier transform operation unit 10, this is output to the fast Fourier transform unit 10.
The Fourier transform length L can be any value as long as it is a power of 2 from the characteristics of the fast Fourier transform.
Since the continuity between frames is not guaranteed in the communication method, it is appropriate to consider this length for one frame.

The fast Fourier transform unit 10 obtains and outputs a power distribution in the frequency domain of the digital baseband signal by performing a Fourier transform operation. The adjacent channel power extracting unit 11 extracts data corresponding to the frequency of the adjacent channel from the input data indicating the calculation result, and outputs the data to the filter selecting unit 5 as an adjacent channel power measurement value.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 shows a case where the filter switching device according to the present invention is applied to baseband processing in a receiving section of a mobile phone. In the figure, an input signal from a signal input terminal 1 is a demodulated baseband signal. This is input to the analog baseband filter 2 and the bandpass filter 12.
The analog baseband filter 2 performs filtering that is gradual compared to the channel interval, and removes unnecessary waves.
Next, after amplification by the baseband amplifier 3, digital conversion is performed by the A / D converter 4.

The digitally converted baseband signal is passed to a filter selection unit 5. Filter selection unit 5
Stores the input digital baseband signal in the internal memory until the adjacent channel power measurement value is passed from the power calculation unit 14. When the measured value of the adjacent channel power is input, the result is compared with a reference threshold Pref stored therein. If the measured value is larger than Pref, the digital baseband stored in the memory is compared. The signal is output to the narrowband digital baseband filter 7. If the measured value is smaller than Pref, the signal is output to the wideband digital baseband filter 6.

As described above, when the level of the adjacent channel interference wave is high, it is possible to sufficiently suppress the interference by the narrow band filter 7. On the other hand, when the level of the adjacent channel interference wave is low, the signal is passed through the wide band filter 6. ,
It is possible to prevent the desired wave from being unnecessarily suppressed, reduce the amount of intersymbol interference, and prevent deterioration of the reception characteristics.

Next, a process of power measurement in the second embodiment will be described. The demodulated baseband signal from signal input terminal 1 is input to bandpass filter 12. The bandpass filter 12 is a filter for extracting a signal of an adjacent channel interference wave. In the baseband signal, the adjacent channel interference wave is a signal having a frequency corresponding to the channel interval, and can be extracted by using the bandpass filter 12 that passes this frequency.

Therefore, the output of the band-pass filter 12 is a signal of an adjacent channel interference wave. This signal is A
The signal is converted into a digital signal by the / D converter 13. Then, the digital signal data for one frame is stored in a memory inside the power calculation unit 14, the average power for one frame is calculated by numerical calculation, and this is output to the filter selection unit 5 as a measured value of the adjacent channel power. .

[0021]

As described above, according to the present invention,
As a result, it is possible to sufficiently suppress adjacent channel interference waves and not to deteriorate the reception quality of a desired wave. The reason is that a filter having characteristics capable of sufficiently suppressing adjacent channel interference waves and a filter having characteristics not deteriorating the reception quality of a desired signal are provided, and the power level of adjacent channel interference waves included in the received signal is detected. This is because the two filters are switched according to the detection result.

Further, in order to measure the power level of the adjacent channel interference wave, the baseband signal is subjected to A / D conversion and then measured by performing Fourier transform.
Measurement can be performed accurately. Furthermore, adjacent channel interference is directly extracted from the baseband signal,
By measuring the power level, the measurement can be performed with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional filter switching method.

[Explanation of symbols]

 Reference Signs List 1 signal input terminal 2 analog baseband filter 3 baseband amplifier 4 A / D converter 5 filter selection unit 6 wideband digital baseband filter 7 narrowband digital baseband filter 8 adjacent channel power measurement unit 9 data memory 10 fast Fourier transform operation unit Reference Signs List 11 adjacent channel power extraction unit 12 bandpass filter 13 A / D converter 14 power calculation unit

Claims (1)

(57) [Claims] 1. A first baseband signal having a narrower passband than an interval between adjacent channels of an input baseband signal.
, A second filter having a passband wider than the interval, and a Fourier transform of the baseband signal digitized by A / D conversion, so that the baseband signal is included in the baseband signal. Detecting means for obtaining and detecting the power level of the interference wave of the adjacent channel; and selecting one of the first and second filters according to the detection of the detecting means, and applying the baseband signal to the selected filter. A filter switching device comprising a selection unit.