The present invention relates to a signal processing circuit, a wireless communication device, and a signal processing method, and more particularly, to a signal processing circuit, a wireless communication device, and a signal processing method which receive a plurality of radio signals transmitted with different frequency bands.
In general, radio signals received via a wireless communication line include a desired signal in which data to be processed by a receiver is set and an adjacent interfering signal. The adjacent interfering signal has a frequency set to be adjacent to the frequency that is set to the desired signal. Accordingly, a study has been made on a method for controlling a signal processing circuit according to the power intensity of a received adjacent interfering signal in order to avoid crosstalk between the desired signal and the adjacent interfering signal and reduce a loss of desired signal components.
Patent Literature 1 discloses a receiver that adjusts the bandwidth of a filter according to the power intensity of a detected adjacent interfering signal. The configuration of the receiver disclosed in Patent Literature 1 is described with reference to
Next, operation of the receiver disclosed in Patent Literature 1 will be described. First, the desired signal and the adjacent interfering signal are converted into digital signals by the AD converter 230 via the antenna 210 and the analog processing unit 220. These digital signals are output to the energy detection unit 250 via the digital processing unit 240 to calculate the power intensity of the adjacent interfering signal. When this power intensity is high, the bandwidth of a digital filter within the digital processing unit 220 is decreased to thereby avoid crosstalk between the desired signal and the adjacent interfering signal. When this power intensity is low, the bandwidth of the digital filter is increased to thereby reduce a loss of the desired signal components. The use of such a configuration enables the receiver to perform stable communication, independently of the power intensity of the interfering signal.
Patent Literature 2 discloses a method for controlling a sampling frequency in an AD converter according to the power intensity of a detected interfering signal. When the power intensity of the detected interfering signal is high, the receiver increases the sampling frequency. When the power intensity of the interfering signal is low, the receiver reduces the sampling frequency. When the power intensity of the interfering signal is low, the sampling frequency is reduced, thereby making it possible to reduce the power consumption in the AD converter.
Patent Literature 3 discloses a receiving device that switches optimum filter characteristics according to the power intensity of a detected interfering signal, and carries out AFC (automatic frequency control). The switching of the optimum filter characteristics is executed by controlling the passband width and damping property of a filter.
In the receiving devices disclosed in Patent Literatures 1 to 3, however, the desired signal is greatly influenced by the adjacent interfering signal when the power intensity of the adjacent interfering signal is large. As a result, crosstalk occurs between the adjacent interfering signal and the desired signal. Thus, there is a problem that as the power intensity of the adjacent interfering signal increases, it may become more difficult to eliminate the influence of the crosstalk due to the interfering signal, by using the filter or the like within the receiving device.
The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a signal processing circuit, a wireless communication device, and a signal processing method which reduce crosstalk of an adjacent interfering signal in a desired signal.
A signal processing circuit according to a first aspect of the present invention includes: a power acquisition unit that receives a plurality of radio signals transmitted with different frequency bands and acquires a power intensity of each of the radio signals received; and a frequency selection unit that selects, from among frequency bands used for radio signals having the power intensity lower than a predetermined power intensity, a frequency band having a relatively low power intensity in a frequency band near the frequency bands as each frequency band in which communication is executed.
A wireless communication device according to a second aspect of the present invention includes: a power acquisition unit that receives a plurality of radio signals transmitted with different frequency bands and acquires a power intensity of each of the radio signals received; a frequency selection unit that selects, from among frequency bands used for radio signals having the power intensity lower than a predetermined power intensity, a frequency band having a relatively low power intensity in a frequency band near the frequency bands as each frequency band in which communication is executed; and a communication unit that notifies a counterpart communication device of the selected frequency band.
A signal processing method according to a third aspect of the present invention includes the steps of receiving a plurality of radio signals transmitted with different frequency bands and acquiring a power intensity of each of the radio signals received; and selecting, from among frequency bands used for radio signals having the power intensity lower than a predetermined power intensity, a frequency band having a relatively low power intensity in a frequency band near the frequency bands as each frequency band in which communication is executed.
According to the present invention, it is possible to provide a signal processing circuit, a wireless communication device, and a signal processing method which reduce crosstalk of an adjacent interfering signal in a desired signal.
Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. A configuration example of a wireless communication device 1 according to a first exemplary embodiment of the present invention will be described with reference to
The communication unit 2 acquires radio signals transmitted from a device that executes communication with the wireless communication device 1. Examples of the device that executes communication include a mobile phone terminal. The communication unit 2 outputs the acquired radio signal to the power acquisition unit 4.
The power acquisition unit 4 acquires a plurality of radio signals from the communication unit 2. The radio signals are transmitted from a mobile phone terminal or the like by using different frequency bands. The power acquisition unit 4 acquires the power intensity of each of the received radio signals. Examples of the power intensity include transmitted power set by the mobile phone terminal or the like, and received power detected when the wireless communication device 1 receives a radio signal. The power acquisition unit 4 may be notified of a transmitted power value from the mobile phone terminal or the like, or may measure the received power of each radio signal acquired by the communication unit 2 to thereby detect the received power. The power acquisition unit 4 outputs the acquired power intensity to the frequency selection unit 5.
The frequency selection unit 5 extracts the radio signal, the received power intensity of which is lower than a predetermined power intensity. This enables extraction of a frequency band used for the radio signal having a power intensity lower than the predetermined power intensity (hereinafter, “threshold power”). For example, “0” is set as the threshold power. As a result, data transmission is not executed in the frequency band in which the power intensity is “0”, that is, no power intensity is detected, so it is possible to determine the frequency band as a free space.
The frequency selection unit 5 selects, from among frequency bands used for the extracted radio signal, a frequency band having a relatively low power intensity in a frequency band near the frequency bands as each frequency band in which communication is executed. The nearby frequency bands include a plurality of frequency bands such as adjacent frequency bands and frequency bands adjacent to the adjacent frequency bands. The frequency selection unit 5 outputs information on the selected frequency bands to the communication unit 2. The communication unit 2 notifies the mobile phone terminal or the like of the acquired information on the frequency bands, and executes communication using the selected frequency bands.
As described above, the use of the signal processing circuit according to the first exemplary embodiment of the present invention enables acquisition of the power intensity in each frequency band. Furthermore, the use of the acquired frequency bands enables selection of frequency bands, which are less affected by the radio signals set to the nearby frequency bands, as the frequency bands in which communication is executed. The notification of the selected frequency bands to the mobile phone terminal or the like enables execution of wireless communication which is less affected by the radio signals set to the nearby frequency bands.
Subsequently, a detailed configuration example of the signal processing circuit 3 according to the first exemplary embodiment of the present invention will be described with reference to
The analog processing unit 20 executes amplification of the amplitude of each radio signal acquired via the antenna 10, and filter control to extract a desired signal for executing communication, for example. Further, the analog processing unit 20 adjusts the amplification of the amplitude and the filter control, for example, according to the control signal notified from the energy detection unit 30. Furthermore, the analog processing unit 20 outputs the radio signal subjected to an analog signal processing to the AD converter 40. Further, the analog processing unit 20 outputs the radio signals acquired via the antenna 10 to the energy detection unit 30.
The energy detection unit 30 detects a plurality of radio signals output from the analog processing unit 20, and selects a frequency band to be used for the desired signal.
The AD converter 40 converts the signal received from the analog processing unit 20 into a digital signal, and outputs the digital signal to the digital processing unit 50. The digital processing unit 50 executes filtering control or the like with a digital filter by using the received digital signal, and performs digital signal processing.
Subsequently, a detailed configuration example of the signal processing circuit 3 according to the first exemplary embodiment of the present invention will be described with reference to
Subsequently, a configuration example of the energy detection unit 30 according to the first exemplary embodiment of the present invention will be described with reference to
The square-law detection unit 32 detects energy by an analog operation using an integrator, for example. The energy is used as the same meaning as a signal intensity. The analog output signal of the square-law detection unit 32 is converted into a digital signal by the AD converter 33. In the digital processing unit 34, digital signal processing for generating a control signal for controlling the analog processing unit 20 according to the signal intensity can be performed. The digital processing unit 34 writes the results of the digital signal processing into the memory 35 and stores the results, thereby making is possible to compile a database for a plurality of trial results of the energy detection. Accordingly, it is possible to generate the control signal depending on the plurality of energy detection results by referring to this database. Note that the reason for using such digital signal processing is that when the recent fine CMOS process is employed, this fine CMOS process is highly compatible with digital circuits.
Subsequently, another configuration example of the energy detection unit 30 according to the first exemplary embodiment of the present invention will be described with reference to
Subsequently, a configuration example of the oscillator 23 according to the first exemplary embodiment of the present invention will be described with reference to
The phase comparator/charge pump 72 converts a phase difference between a reference frequency signal output from the crystal oscillator 71 and an output signal output from the frequency divider 74 into voltage, and outputs the voltage to the voltage control oscillator 73. The voltage control oscillator 73 outputs frequency signals having different values according to the voltage value received from the phase comparator/charge pump 72. The frequency divider 74 divides the frequency of each frequency signal output from the voltage control oscillator 73 at a frequency division ratio that can be switched. Thus, the output frequency can be switched by switching the frequency division ratio of the frequency divider 74. Note that the output frequency can be switched in the same manner as in the oscillator shown in
Subsequently, a configuration example of the variable filter 24 according to the first exemplary embodiment of the present invention will be described with reference to
Subsequently, relations between frequency bands and power intensities of radio signals acquired in the energy detection unit 30 according to the first exemplary embodiment of the present invention will be described with reference to
In
The cognitive radio is required to determine whether the frequencies are used or not by micro-power detection called spectrum sensing. For example, the detection accuracy is equal to or lower than −116 dBm in a band of 6 MHz per channel in IEEE802.22. A two-step sensing method is proposed to perform spectrum sensing of such micro power over a wide band. Specifically, at a first step, energy detection (or blind detection) that allows high-speed detection is carried out, while the detection sensitivity is slightly low. Next, in a second step, feature detection that allows detection with high accuracy is carried out. Note that the feature detection in the latter step is generally achieved by large-scale digital processing requiring a long period of time.
Subsequently, a flow of processing for determining the desired signal frequency according to the first exemplary embodiment of the present invention will be described with reference to
First, a frequency fLO of the oscillator 23 is set to the minimum frequency f1 (S11), and power P1 is detected by the energy detection unit 30 (S12). Next, the frequency of the oscillator 23 is increased by Δf according to the control signal from the energy detection unit 30, and is set to f2 (S13). Thus, power P2 is detected in the energy detection unit 30 (S14). The power detection as described above is repeated until completion of the power detection for the frequency f9 (S15). Though the power detection is sequentially carried out from the minimum frequency to the maximum frequency in this case, the order of frequencies can be arbitrarily set, and the frequency step Δf can be finely set.
Next, the frequency band of the desired signal and the control signal of the analog processing unit are determined depending on the detected power intensity (S16). The processing for determining the frequency band of the desired signal and the control signal of the analog processing unit is periodically carried out. Thus, the frequency band of the desired signal and the control signal of the analog processing unit can be determined depending on a change in power intensity. Specifically, the processing for determining the desired frequency signal in the case of the example shown in
When the frequency f3 is selected as the frequency of the desired signal (
On the other hand, in the case of selecting the frequency f8 as the desired signal frequency (
Note that in the selection of the desired signal frequency described above, the power intensities of the frequencies f1 to f9 are not remeasured after the extraction of the frequencies f3 and f8 at which no power is detected, and the power intensity values used to extract the frequencies f3 and f8 are used. Thus, it is only necessary to measure the power intensities once. This contributes to a reduction in time for selecting the desired signal frequency as compared with the case of measuring the power intensities multiple times.
With this configuration, the cognitive radio system for reducing power consumption can be achieved by reflecting the detection results of the power intensities in the nearby frequencies including the adjacent channel frequency and the channel frequency subsequent to the adjacent channel frequency, upon determination of the desired signal frequency. Furthermore, the same energy detection unit can detect the presence or absence of vacant frequencies and the intensity of the interfering signal, thereby reducing the overheads of circuits and operation time.
Subsequently, a configuration example of a signal processing circuit according to a second exemplary embodiment of the present invention will be described with reference to
The oscillator shown in
As described above, the use of the oscillator 123 according to the second exemplary embodiment of the present invention enables switching of the phase noise according to the power intensity of the interfering signal. Consequently, when the power intensity of the interfering signal is relatively low, the current consumption in the oscillator 123 can be suppressed.
Subsequently, a configuration example of a signal processing circuit according to a third exemplary embodiment of the present invention will be described with reference to
Alternatively, as shown in
Subsequently, operation of the signal processing circuit shown in
As described above, the use of the AD converter according to the third exemplary embodiment of the present invention enables change of the number of conversion bits according to the power intensity of the interfering signal. Consequently, when the power intensity of the interfering signal is relatively low, the current consumption in the AD converter 40 can be suppressed.
The whole or part of the exemplary embodiments disclosed above can be described as, but not limited to, the following supplementary notes.
(Supplementary note 1) A signal processing circuit comprising: a power acquisition unit that receives a plurality of radio signals transmitted with different frequency bands and acquires a power intensity of each of the radio signals received; and a frequency selection unit that selects, from among frequency bands used for radio signals having the power intensity lower than a predetermined power intensity, a frequency band having a relatively low power intensity in a frequency band near the frequency bands as each frequency band in which communication is executed.
(Supplementary note 2) The signal processing circuit according to Supplementary note 1, wherein the frequency selection unit extracts a frequency band used for the radio signals having the power intensity lower than the predetermined intensity, based on the power intensity acquired by the power acquisition unit, and selects, as each frequency band in which the communication is executed, a frequency band having a relatively low power intensity in a frequency band near the extracted frequency band, by using a power intensity used to extract the frequency band, without remeasuring the power intensity of each radio signal using frequency bands other than the extracted frequency band.
(Supplementary note 3) The signal processing circuit according to Supplementary note 1 or 2, wherein the power acquisition unit controls frequency bands used for a filter for the received radio signals according to the acquired power intensity.
(Supplementary note 4) The signal processing circuit according to Supplementary note 3, wherein the power acquisition unit controls a filter provided in an analog signal processing unit that processes the radio signals into analog signals.
(Supplementary note 5) The signal processing circuit according to Supplementary note 3 or 4, wherein the power acquisition unit relatively decreases a frequency bandwidth of output data output from the filter when the power intensity in the frequency band near the frequency band in which the communication is executed is larger than a predetermined value, and relatively increases the frequency bandwidth of the output data when the power intensity in the frequency band near the frequency band in which the communication is executed is smaller than the predetermined value.
(Supplementary note 6) The signal processing circuit according to any one of Supplementary notes 3 to 5, wherein the filter includes a plurality of sub-filters having different damping properties, and the signal processing control unit controls the number of the sub-filters to be activated according to the power intensity in the frequency band near the frequency band in which the communication is executed, and adjusts an amount of removed interfering signals using frequencies interfering with the frequency band in which the communication is executed.
(Supplementary note 7) The signal processing circuit according to any one of Supplementary notes 3 to 6, further comprising an amplification unit that amplifies an amplitude of each of the radio signals, wherein the power acquisition unit amplifies the amplitude of each of the radio signals to be relatively large when the power intensity in the frequency band near the frequency band in which the communication is executed is larger than the predetermined value, and amplifies the amplitude of each of the radio signals to be relatively small when the power intensity in the frequency band near the frequency band in which the communication is executed is smaller than the predetermined value.
(Supplementary note 8) The signal processing circuit according to any one of Supplementary notes 3 to 7, further comprising a digital signal conversion unit that converts a signal output from the analog signal processing unit into a digital signal, wherein the signal processing control unit relatively increases the number of quantized bits of the digital signal in the digital signal conversion unit when the power intensity in the frequency band near the frequency band used for the desired signal is larger than the predetermined value, and relatively decreases the number of quantized bits of the digital signal in the digital signal conversion unit when the power intensity in the frequency band near the frequency band used for the desired signal is smaller than the predetermined value.
(Supplementary note 9) The signal processing circuit according to any one of Supplementary notes 3 to 8, wherein the power acquisition unit decreases phase noise in an oscillation unit that oscillates a plurality of local signals to be activated with different frequencies when the power intensity in the frequency band near the frequency band in which the communication is executed is larger than the predetermined value, and increases the phase noise in the oscillation unit when the power intensity in the frequency band near the frequency band in which the communication is executed is smaller than the predetermined value.
(Supplementary note 10) A wireless communication device comprising: a power acquisition unit that receives a plurality of radio signals transmitted with different frequency bands and acquires a power intensity of each of the radio signals received; a frequency selection unit that selects, from among frequency bands used for radio signals having the power intensity lower than a predetermined power intensity, a frequency band having a relatively low power intensity in a frequency band near the frequency bands as each frequency band in which communication is executed; and a communication unit that notifies a counterpart communication device of the selected frequency band.
(Supplementary note 11) A signal processing method comprising the steps of: receiving a plurality of radio signals transmitted with different frequency bands and acquiring a power intensity of each of the radio signals received; and selecting, from among frequency bands used for radio signals having the power intensity lower than a predetermined power intensity, a frequency band having a relatively low power intensity in a frequency band near the frequency bands as each frequency band in which communication is executed.
Note that the present invention is not limited to the above exemplary embodiments, but can be modified as appropriate without departing from the scope of the invention.
The present invention has been described above with reference to exemplary embodiments, but the present invention is not limited to the above embodiments. The configuration and details of the present invention can be changed in various manners which can be understood by those skilled in the art within the scope of the invention.
This application is based upon and claims the benefit of priority from Japanese patent application No. 2010-039903, filed on Feb. 25, 2010, the disclosure of which is incorporated herein in its entirety by reference.
Number | Date | Country | Kind |
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2010-039903 | Feb 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2010/007366 | 12/20/2010 | WO | 00 | 8/9/2012 |