JP3597602B2 - Wireless communication device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a radio communication apparatus capable of easily selecting and receiving a specific subcarrier of an orthogonal frequency division multiplex signal.
[0002]
[Prior art]
2. Description of the Related Art In recent years, multimedia has attracted attention, and its utilization has been studied in various fields.
[0003]
Multimedia can handle image information, audio information, data such as characters and personal information, and the like. The amount of such information varies greatly depending on the type, and conditions also differ in terms of necessity of immediacy. That is, in consideration of the transmission of such information, if the image information is a moving image, it is necessary to send the information in real time to ensure smooth image movement, and if it is audio information, the capacity is smaller than the image information. However, this also requires immediacy. However, in the case of character data or the like, the sentness can be used once it is sent, so that the degree of immediacy is low. When image information is affected by noise and the image is degraded, the image information cannot be watched. In the case of character data, etc., when the influence of noise causes garbled characters, a problem arises. The conditions required in terms of noise resistance are different, for example, the contents can be transmitted though it is hard to hear.
[0004]
As described above, information such as images and sounds, and information such as personal information data have different requirements such as immediacy and noise resistance, but multimedia that transmits such information signals having different requirements in a mixed manner. In communication, a layered modulation / demodulation technique of how to layer different information signals in the same manner, how to generate a radio signal, and how to demodulate the radio signal is important.
[0005]
Also, in the hierarchical modulation scheme in which the layers are divided according to the difference in the amount of information to be received, the configuration of a receiver that receives a small amount of information must be simple. In other words, in multimedia communication, when there is a channel that sends the same image with high definition and a channel that sends a much coarser image, the user can select the image quality according to the purpose and receive it. The receiver can be configured to receive even coarse images depending on the purpose or application, such as a receiver that receives only coarse images. Variations are possible.
[0006]
That is, if the concept that the quality of a receivable image is high is a high-quality product and that the quality of a receivable image is low is a popular product or a simple type, a high-quality image, that is, a high-definition image ( The configuration of a receiver for receiving (a large amount of information) needs to be simpler than the configuration of a receiver for receiving a low image quality, that is, a coarse image (a small amount of information).
[0007]
By the way, in multimedia communication, it is important to be able to simultaneously transmit a plurality of types of different information signals, and an orthogonal frequency division multiplexing signal is one of transmission systems suitable for this. The hierarchization of the orthogonal frequency division multiplexed signal can be achieved by changing the modulation method and power of the subcarriers constituting the orthogonal frequency division multiplexed signal.
[0008]
As an example of the layered orthogonal frequency division multiplexed signal, there is "Digital Terrestrial Broadcasting with OFDM-Study of Layering Method Considering Mobile Reception-" of IEICE General Conference B-918, 1995.
[0009]
FIG. 15 shows the frequency allocation of such a conventional hierarchical orthogonal frequency division multiplexing signal. In an orthogonal frequency division multiplexed signal, a number of subcarriers are arranged orthogonally, and an independent modulation method, a multilevel number, and a carrier power can be set for each carrier.
[0010]
Now, as an example of such an orthogonal frequency division multiplexed signal transmission / reception system, there is a technique disclosed in “Nikkei Electronics 1994.6.20 (pp.81)”. FIG. 16 shows a transmission / reception circuit block according to the disclosed technology.
[0011]
In the configuration shown in FIG. 16, a signal to be transmitted (input symbol sequence) is subjected to serial-to-parallel conversion in a serial-to-parallel conversion section, assigned to each carrier, and mapped in the frequency domain. The mapping data is subjected to inverse FFT in an inverse FFT (inverse Fourier transform) part, and is converted from a frequency domain to a time domain. In order to perform the inverse FFT, the number of samples in the time domain is at least equal to the number of carriers (including null carriers) constituting the orthogonal frequency division multiplexed signal.
[0012]
The time domain data obtained by the inverse FFT is converted into serial data by passing through a parallel / serial conversion and a DA conversion part, and a D / A signal is added after a guard interval is added here for multipath measures. It is converted into an analog signal.
[0013]
Unnecessary components are removed from this analog signal by a low-pass filter (LPF), superimposed on a carrier, and then output to a transmission path through a band-pass filter (BPF). That is, since the orthogonal frequency division multiplexed signal is generated by signal processing in the baseband, it is output to the transmission path after being frequency-converted to a desired transmission frequency band. The band-pass filter at the stage prior to the transmission path blocks an image generated by frequency conversion. The above is the processing on the transmission side.
[0014]
On the other hand, on the receiving side, the orthogonal frequency division multiplexed signal received from the transmission line is filtered through a band-pass filter to remove unnecessary components, and then mixed with the output of an oscillator to perform signal processing in the baseband. I do. Further, the data is sampled by an A / D converter to perform FFT (or DFT). That is, the received signal that has been frequency-converted by being mixed with the output of the oscillator is first subjected to A / D conversion (sampling and quantization) in the A / D conversion and serial / parallel conversion section, and further subjected to serial / parallel conversion to obtain the original signal. After being subjected to FFT, each of them is converted into serial data in a parallel / serial conversion part and output as a received symbol sequence.
[0015]
Note that the signal after the frequency conversion includes a harmonic. In order to satisfy the sampling theorem, it is necessary to remove frequency components equal to or more than １ ／ of the sampling rate of the A / D converter.
[0016]
Therefore, in general, an LPF (low-pass filter) is inserted before the A / D converter in the receiving system. When the data sampled in the time domain is transmitted with a guard interval added on the transmitting side, the guard interval is removed. Since the number of samples in the time domain is converted from the time domain to the frequency domain by FFT, it is necessary to make the number of carriers at least equal to the number of carriers (constituting the orthogonal frequency division multiplexed signal).
[0017]
[Problems to be solved by the invention]
As described above, in the conventional radio communication system using the orthogonal frequency division multiplex signal, when the orthogonal frequency division multiplex signal is received, the orthogonal frequency division multiplex signal is sampled by the A / D converter and sampled. Demodulation is performed by performing FFT processing on the orthogonal frequency division multiplexed signal.
[0018]
Therefore, oversampling is necessary for the total number of carriers (including null carriers for which no information exists) constituting the orthogonal frequency division multiplexed signal. For example, in the case of an orthogonal frequency division multiplex signal composed of 16 carriers, sampling data of 16 times or more is required, and in the case of 256 carriers, sampling data of 256 times or more is required in one effective symbol symbol period.
[0019]
For this reason, even when it is desired to receive only a part of the subcarriers constituting the orthogonal frequency division multiplexed signal, it is necessary to receive all signals (all subcarriers) transmitted by the transmitting side.
[0020]
However, in the hierarchical modulation scheme in which the layers are divided according to the difference in the amount of information to be received, in the case of a receiver in which only information with a small amount of information is to be received, the configuration should be simple.
[0021]
In other words, when sending information with different amounts of information for different purposes or purposes even for the same image, such as high-definition image information and low-definition image information, each channel is a separate channel and a different channel is used. It will be sent by subcarrier. If the receiver only needs to receive low-definition image information, the receiver need only be configured to receive subcarriers for transmitting low-definition image information. Is a configuration in which reception processing is performed including unnecessary subcarriers, which is wasteful and extremely uneconomical. Similarly, there are naturally applications for receiving only the subcarriers of the channel for data transmission and applications for receiving only the subcarriers of the channel for voice transmission. Therefore, consider a receiver for such a specific application. In addition, it is extremely uneconomical to adopt a configuration in which all subcarriers other than the objective are received.
[0022]
However, the conventional orthogonal frequency division multiplexed signal receiver must receive and process all transmission signals (all subcarriers) transmitted by the transmission side as described above, which hinders simplification of the circuit configuration. This hindered miniaturization and low power consumption of the receiver. Particularly, in the process of receiving an orthogonal frequency division multiplexed signal, sampling of the received signal must be performed at high speed in order to separate a large number of subcarriers such as 16 carriers and 256 carriers, which is an expensive A / D converter. In addition, the FFT processing is performed on the sampled data, and the circuit for this FFT processing performs an advanced Fourier transform operation, has a complicated configuration, and the occupied volume of the circuit increases. . Such an A / D converter and an FFT processing circuit require high-speed processing and thus consume large power, which hinders simplification of the circuit configuration and miniaturization and low power consumption of the receiver. .
[0023]
Multimedia communication often requires all subcarriers.However, it is necessary to receive and monitor only low-definition images, to receive only subcarriers of a data transmission channel, or to transmit audio. Of course, there are applications that want to receive only subcarriers of the trusted channel. Considering such a receiver for a specific application, such a receiver is configured to receive all subcarriers that are not intended. It is too expensive to hire.
[0024]
Therefore, an object of the present invention is to solve such a problem and to realize a reception system having a simple configuration for selectively receiving only a part of a plurality of subcarriers constituting the orthogonal frequency division multiplexed signal. In particular, it is an object of the present invention to provide a wireless communication apparatus capable of realizing miniaturization, low power consumption, and low cost as a receiver by suppressing a sampling frequency of an A / D converter necessary for a reception system. is there.
[0025]
[Means for Solving the Problems]
To achieve the above object, the present invention is configured as follows. That is, first, in a communication apparatus using an orthogonal frequency division multiplexing signal in which information is transmitted by a plurality of subcarriers, a receiving system is set to a desired subcarrier among a plurality of subcarriers in the orthogonal frequency division multiplexing signal. It comprises filter means for extracting only the carrier signal component and demodulation means for demodulating information from the extracted signal component.
[0026]
Second, among a plurality of subcarriers in an orthogonal frequency division multiplexed signal, when demodulating desired plural types of subcarriers, a mixer that mixes with a received signal to obtain a baseband signal, A local oscillator that generates a signal to be given as a signal for mixing is of a variable frequency type, and a plurality of filters are provided to mix the received signal while sequentially changing the oscillation frequency of the local oscillator to a predetermined frequency, and Is switched, whereby signal components in the frequency domain of a plurality of desired subcarriers of the received signal are sequentially extracted.
[0027]
Third, when extracting a plurality of specific subcarriers, a band limiting filter is used, and FFT is performed on the orthogonal frequency division multiplexed signal extracted by the band limiting filter.
[0028]
[Action]
In the case of the first configuration, filter means for extracting a signal component in the frequency domain of the desired subcarrier from the received signal is provided, and the signal component of the desired subcarrier is obtained by passing through the filter means. Since the received data is obtained by demodulating the signal components in the demodulation unit, the FFT processing for extracting all the subcarriers as in the related art is unnecessary, and the reception is performed in the demodulation unit targeting the filter and the single carrier. Since the system can be configured, the configuration is simplified, and the effect of reducing the power consumption and the size of the apparatus can be obtained because the FFT processing is not required.
[0029]
Specifically, in order to receive only a part of the subcarriers from the orthogonal frequency division multiplexed signal composed of a plurality of subcarriers generated on the transmission side (modulation system), on the reception side (demodulation system), By changing the frequency of the local oscillator, the frequency is converted so that the center frequency of the subcarrier to be received becomes 0 Hz (DC). Frequency conversion can be performed by mixing the received signal with a reference frequency signal generated from a reference oscillator. The frequency-converted orthogonal frequency division multiplexed signal is band-limited by filter means, specifically, a low-pass filter (LPF) to remove unnecessary subcarriers and extract subcarriers to be extracted. Ingredients only. Since the orthogonal frequency division multiplexed signal after passing through the LPF becomes an NRZ (Non Return to Zero) signal in which adjacent subcarriers are superimposed as interference, the transmission information sequence is demodulated if demodulated by a demodulation method applied to a single carrier. You.
for that reason,
(1) Orthogonal frequency division multiplexing signal modulation means for orthogonally arranging a plurality of subcarriers modulated by a transmission information sequence in the frequency domain to generate an orthogonal frequency division multiplexing signal, and a transmission information sequence from the orthogonal frequency division multiplexing signal. A demodulation system for demodulating the orthogonal frequency division multiplexed signal, the demodulation means includes means for extracting one or more of subcarriers constituting the orthogonal frequency division multiplexed signal, The demodulated subcarrier signal is demodulated.
[0030]
(2) Further, in the wireless communication apparatus of the present invention, the modulation means for generating the orthogonal frequency division multiplexed signal includes a means for adding a guard interval so that the receiving side operates well.
[0031]
(3) In the present invention, in order to demodulate an arbitrary subcarrier from a plurality of subcarriers constituting the orthogonal frequency division multiplexed signal, the demodulation means sets the center frequency of the subcarrier to direct current (DC, zero frequency). Is provided.
[0032]
(4) Further, the demodulation means applied to the wireless communication apparatus of the present invention is a means for sampling a time waveform signal corresponding to any extracted subcarrier, and performs a Fourier transform on the sampled time waveform signal. Means.
[0033]
(5) Further, in the wireless communication apparatus according to the present invention, the demodulation means for demodulating a transmission information sequence from the orthogonal frequency division multiplexed signal may include: The apparatus includes means for extracting one or a plurality of subcarriers constituting the orthogonal frequency division multiplexed signal, and means for demodulating a transmission information sequence from the extracted subcarrier signal.
[0034]
(6) Further, in the wireless communication apparatus of the present invention, different single subcarriers or different subcarriers are extracted within a plurality of time-divided time frames, and a transmission information sequence is demodulated from each extracted subcarrier. .
[0035]
Further, in the case of the second configuration, when demodulating a plurality of desired subcarriers among a plurality of subcarriers in an orthogonal frequency division multiplexed signal, a mixer for mixing with a received signal to obtain a baseband signal In addition, a local oscillator that generates a signal to be given as a signal for mixing is of a variable frequency type, and a plurality of filters are provided to mix the received signal while sequentially changing the oscillation frequency of the local oscillator to a predetermined frequency. , By switching the filter, thereby extracting the signal components in the frequency domain of a plurality of desired sub-carriers of the received signal sequentially, thereby extracting all the sub-carriers as in the related art. Can FFT processing be unnecessary, and a receiving system composed of a filter and a demodulator for single carrier? , The configuration is simplified, also, minutes to eliminate the FFT process, in which apparatus is such that the effect of such power consumption can be lowered by small obtained.
[0036]
In the case of the third configuration, when extracting a plurality of specific subcarriers, a band-limiting filter is used, and FFT is performed on the orthogonal frequency division multiplexed signal extracted by the band-limiting filter.
[0037]
By performing the FFT on the orthogonal frequency division multiplexed signal extracted by the band limiting filter, the total number of samples of the FFT can be reduced, so that the calculation time required for the FFT or the FFT The circuit scale can be shortened or reduced, and the effect that the device is small and the power consumption can be reduced can be obtained accordingly.
[0038]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0039]
(First embodiment)
FIG. 1 shows a frequency spectrum of an orthogonal frequency division multiplexed signal of a wireless communication system according to a first embodiment of the present invention. In FIG. 1, 10 is a frequency domain, 11-1 to 11-n are subcarriers, 12 is a carrier interval Δf, 11-m Is a desired subcarrier to be extracted among the plurality of subcarriers 11-1 to 11-n, and 14 is a characteristic of a low-pass filter.
[0040]
As shown in FIG. 1, orthogonal frequency division multiplexed signals are arranged while maintaining orthogonality among a plurality of subcarriers 11-1 to 11 -n in a frequency domain 10, and a carrier interval Δf indicated by reference numeral 12 is set. I'm narrowing. That is, the subcarriers 11-1 to 11-n of the orthogonal frequency division multiplexed signal are modulated independently of each other and are orthogonally arranged in the transmission band.
[0041]
Of the many subcarriers 11-1 to 11-n, a desired subcarrier to be extracted is set to 11-m, and if attention is paid only to the desired subcarrier 11-m to be extracted, it is regarded as a single carrier modulated wave. Can be. Therefore, in the present invention, the subsequent processing is simplified by extracting the desired extraction target subcarrier 11-m with the low-pass filter 14 having the characteristic according to the frequency band of the subcarrier 11-m. That is the basic idea.
[0042]
FIG. 2 shows a specific configuration example.
[0043]
FIG. 2 is a block diagram showing a system configuration of a communication apparatus of a selective reception system according to the present invention in a wireless communication system using an orthogonal frequency division multiplex signal. In FIG. Here, 20 is an orthogonal frequency division multiplexing signal transmitter main body (hereinafter, referred to as a transmitter main body), 21 is a transmission information sequence, 22 is a frequency axis signal point arrangement processing unit, 23 is a modulation subcarrier, and 24 is an inverse subcarrier. Fourier transform unit, 25 is an orthogonal frequency division multiplex signal time sample, 26 is a guard interval adding unit, 27 is a time waveform signal sample after adding a guard interval, 28 is a D / A converter, 29 is an orthogonal frequency division multiplex signal analog wave, 210 is a transmission RF unit, 211 is a transmission signal, and 212 is a transmission antenna.
[0044]
The frequency axis signal point arrangement processing unit 22 is a device that maps the input transmission information sequence 21 in the frequency domain (f-axis mapping) and outputs the result. The inverse Fourier transform unit 24 performs the frequency axis signal point arrangement processing. The output from the section 22 is subjected to an inverse Fourier transform (inverse FFT) process and is output. The guard interval adding section 26 is provided with a time gap for preventing interference between signals with respect to the output of the inverse Fourier transform section 24. Is added and output.
[0045]
The D / A converter 28 is a device that converts the output of the guard interval addition unit 26 into an analog signal. The transmission RF unit 210 converts this analog signal into a signal of a desired frequency band, and The antenna 212 transmits the signal from the transmission RF unit 210 as a wireless signal.
[0046]
The output signal of the frequency axis signal point arrangement processing unit 22 is a modulation subcarrier of 23, the output of the inverse Fourier transform unit 24 is an orthogonal frequency division multiplexed signal time sample 25, and the output of the guard interval adding unit 26 is 27 is a time waveform signal sample after adding a 27 guard interval. Further, the output of the D / A converter 28 is an orthogonal frequency division multiplexed signal analog wave of 29, and the output of the transmission RF unit 210 is a transmission signal of 211.
[0047]
Figure To two 213 is a receiver body, 214 is an antenna, 215 is a received signal, 216 is an RF unit, 217 is an output signal, 218 is a local oscillator, 219 is a reference signal, 220 is a mixer, 221 is a mixer. A low-frequency signal of a desired frequency, 222 is an LPF (low-pass filter), 223 is a time waveform signal, 224 is an A / D converter (ADC), 225 is a digital signal, and 226 is a single carrier demodulation circuit.
[0048]
The RF unit 216 amplifies the reception signal 215 received by the antenna 214, converts the frequency to an intermediate frequency (IF), and outputs the intermediate frequency (IF). The local oscillator 218 oscillates a reference signal 219 of a required frequency. The mixer 220 mixes the output of the RF section 216 and the reference signal 219 output from the local oscillator 218, converts the frequency into a low-frequency signal 221 having a desired frequency, and outputs the low-frequency signal 221.
[0049]
The frequency of the reference signal 219 oscillated and output by the local oscillator 218 is the frequency at which the center frequency of the desired subcarrier or the desired subcarrier group is converted to 0 (DC (direct current component)), or the highest or highest of the desired subcarrier group. This is a frequency corresponding to the center frequency of the lower subcarrier.
[0050]
The LPF 222 filters the low-pass signal 221 from the mixer 220 with a filter having a predetermined low-pass characteristic to remove unnecessary sub-carriers among the components of the plurality of sub-carriers. A subcarrier component is obtained. The single carrier demodulation circuit 226 is a device for demodulating the extracted subcarrier signal and outputting the demodulated signal as received data.
[0051]
The frequency-converted low-band signal 221 removes adjacent unnecessary subcarriers by the LPF 222, and the obtained time waveform signal 223 corresponding to the desired subcarrier is finally converted to the desired channel by the single carrier demodulation circuit 226. When the single carrier demodulation circuit 226 is constituted by a digital circuit, the LPF output signal 223 is sampled by an A / D converter (ADC) 224 and converted into a digital signal 225. Later, the signal is demodulated by a single carrier demodulation circuit 226 and demodulated to a desired transmission information sequence 227.
[0052]
Further, when the single carrier demodulation circuit 226 is realized by an analog circuit such as a sample hold circuit, an LPF, and an integration circuit, the A / D converter 224 in the figure becomes unnecessary, and the output signal 223 of the LPF 222 is directly converted to a single carrier. It is configured to be input to the demodulation circuit 226 and demodulated to a desired transmission information sequence 227.
[0053]
In particular, in the present invention, the LPF 222 is realized as a circuit for removing unnecessary subcarriers, and the LPF 222 is configured by applying an analog filter which is easy to configure, so that the cost can be reduced and the filter can be reduced. By passing the signal through a single carrier, the sampling frequency of the A / D converter 224 at the subsequent stage can be set low.
[0054]
Next, the operation of the present apparatus having the above configuration will be described.
[0055]
On the transmitter body 20 side, the input transmission data 21 is mapped (f-axis mapping) by the frequency axis signal point arrangement processing unit 22 in the frequency domain. The data (mapping data 23) mapped on the f-axis by the frequency axis signal point arrangement processing unit 22 is converted into a time domain waveform 25 output by performing an inverse FFT process in an inverse FFT unit 24. The data subjected to the inverse FFT processing from the inverse FFT unit 24 is input to the guard interval addition processing unit 26, where the guard interval is added. As a result, a time waveform signal 27 having a signal form in which a guard interval is added to the time waveform signal 25 subjected to the inverse FFT is obtained.
[0056]
The time waveform signal 27 to which the guard interval is added is input to a D / A converter (DAC) 28, where it is converted into an analog time waveform signal 29. Then, the analog signal 29 is converted into a signal of a desired frequency band in the RF unit 210 and output from the antenna 212 as a radio signal 211 amplified to a desired transmission power.
[0057]
The above is the operation of the transmission system. Next, the operation of the reception system will be described.
[0058]
In the receiver main body 213, the received signal 215 received by the antenna 214 is amplified by the RF unit 216 and frequency-converted to an intermediate frequency (IF), and becomes an output signal 217. The output signal 217 that has been frequency-converted to an intermediate frequency by the RF unit 216 and output is mixed (mixed) by the mixer 220 with the reference signal 219 from the local oscillator 218 and frequency-converted to the desired frequency signal 221.
[0059]
The frequency of the reference signal 219 output from the local oscillator 218 is the frequency at which the center frequency of the desired subcarrier or desired subcarrier group is converted to 0 (DC), or the highest or lowest subcarrier of the desired subcarrier group. Is the center frequency.
[0060]
The low-frequency signal 221 that has been frequency-converted and output passes through the LPF 222, so that adjacent unnecessary subcarriers are removed. The time waveform signal 223 corresponding to the desired subcarrier after the unnecessary subcarrier has been removed is converted from the LPF output signal 223 by the A / D converter 224 when the single carrier demodulation circuit 226 is constituted by a digital circuit. After being sampled and converted into a digital signal 225, it is demodulated and demodulated into a desired transmission information sequence 227. When the single-carrier demodulation circuit 226 is realized by an analog circuit, the A / D converter 224 in the figure becomes unnecessary, and the output signal 223 of the LPF 222 is directly input to the single-carrier demodulation circuit 226, and Is demodulated to a transmission information sequence 227 of
[0061]
As described above, in the present invention, in order to obtain a specific subcarrier among a plurality of subcarriers, the received signal 221 that has been converted to a low-band signal through the mixer 220 is passed through the LPF. Thereby, the processing at the subsequent stage is the same as handling a single carrier signal, and the circuit configuration is simplified.
[0062]
In addition, an analog filter that can be easily realized is applied as a filter (LPF 222) for removing unnecessary subcarriers, and cost reduction is achieved. Sampling frequency can be set low, which enables cost reduction and low power consumption of the A / D converter, and eliminates the need for FFT, thereby significantly reducing cost and power consumption. In addition, the circuit occupied volume can be reduced, and downsizing and simplification of the configuration can be realized.
[0063]
Generally, in order to sample data with an A / D converter, it is necessary to remove a frequency component equal to or more than 1/2 of the sampling rate of the A / D converter (sampling theorem).
[0064]
Therefore, when sampling the frequency-converted low-frequency signal 221, an LPF for satisfying the sampling theorem is inserted before the A / D converter 224, but the receiver shown in FIG. The LPF 222 in the configuration of the main body does not refer to the LPF inserted for such a purpose, but is provided for extracting only desired subcarriers and removing unnecessary subcarriers.
[0065]
Therefore, the LPF 222 according to the present embodiment requires a steeper characteristic than the LPF for satisfying the sampling theorem. The characteristics of the LPF 222 of this embodiment affect the reception characteristics of a receiver that selectively demodulates a specific subcarrier of an orthogonal frequency division multiplexed signal. This is because the characteristics of the LPF contribute to the occurrence of intersymbol interference that degrades the reception characteristics of the selected receiver. Hereinafter, the cause of the occurrence of the intersymbol interference will be described.
[0066]
The frequency characteristic of the output signal of the LPF is represented by the product of the frequency characteristic of the LPF and the frequency characteristic of the band-limited signal. Since the product in the frequency domain can be expressed by a convolution in the time domain, the time response of the output signal of the LPF can be expressed by the convolution of the impulse response of the LPF and the time response of the band limit. That is, the time waveform signal 223 obtained by band-limiting the low-frequency signal 221 (corresponding to the band-limited signal described above) by the LPF 222 is represented by the sum of the impulse response of the LPF 222 and the convolution of the low-frequency signal 221. Can be.
[0067]
Intersymbol interference occurs because unnecessary amplitudes from adjacent symbols are mixed into a desired wave. Therefore, the intersymbol interference power is affected by the impulse response of LPF 222.
[0068]
That is, if the impulse response of the filter is zero within one symbol time of the orthogonal frequency division multiplexed signal, there is no influence from adjacent symbols, so that no intersymbol interference occurs. Examples of such a filter are shown in FIGS.
[0069]
FIG. 3 is a diagram showing a frequency characteristic of an LPF applied to a receiver using a selective reception method in a wireless communication system according to the present invention. FIG. 4 is a diagram showing an LPF applied to a receiver using a selective reception method in a wireless communication method according to the present invention. FIG. 4 is a diagram showing time characteristics.
[0070]
3 and 4, reference numeral 501 denotes a frequency domain, 502 denotes a time domain having a time width of T, f denotes frequency, and t denotes time. In the frequency domain 501, a null exists at each subcarrier interval (Δf), and in the time domain 502, the impulse response is zero within one symbol time. However, it is not easy to realize such a filter. Therefore, it is important to select an LPF having a small influence.
[0071]
FIG. 5 shows the relationship between the order of the filter and the intersymbol interference power. The filter is of Bessel type in consideration of simple realization by an analog circuit, and the guard interval length is set to 1/4 of the effective symbol. Determining the order of the filter involves a trade-off between interference power from adjacent subcarriers and intersymbol interference due to the impulse response length.
[0072]
In other words, by setting the filter to a higher order, the cutoff characteristics become steep and interference from adjacent subcarriers is suppressed, but the impulse response length of the LPF becomes longer, and the effect of improving the intersymbol interference power is diminished. Would. In the example of FIG. 5 in which the filter is a Bessel type, adoption of the fifth order makes it possible to reduce the cost due to the interference suppression effect and to reduce the order, thereby improving the reception characteristics.
[0073]
The above is a configuration in which only a desired subcarrier out of a plurality of subcarriers in an orthogonal frequency division multiplexed signal is applied to a purpose of selectively receiving, and a received signal is converted into a signal component in the frequency domain of the desired subcarrier. Is provided, and a signal component of the desired subcarrier is obtained by passing through the filter, and the signal component is demodulated by a demodulation unit to obtain received data. Since the FFT processing for extracting the subcarriers is not required, and the receiving system can be configured by the filter and the demodulation unit for the single carrier, the configuration is simplified and the FFT processing is not required. It is possible to obtain the effect that the device is small and the power consumption can be reduced.
[0074]
In the first embodiment described above, only a specific subcarrier is extracted by a filter and transmission data is received by that subcarrier. However, the target to be demodulated is transmission data by all subcarriers, or all subcarriers are demodulated. Even if it does not reach the transmission data due to the above, it is necessary for the receiving apparatus to demodulate the transmission data by a plurality of subcarriers to have a configuration accompanied by the conversion processing by FFT, and the FFT processing circuit etc. Thus, the problem of power consumption remains. Therefore, if the first embodiment is applied to such an apparatus, and the configuration of the first embodiment is configured to control the power supply on the receiving side, the power consumption can be significantly reduced during standby for reception. Will be possible.
[0075]
Such an embodiment will be described below as a second embodiment.
[0076]
(Second embodiment)
FIG. 6 is a block diagram illustrating a second embodiment of the present invention. The realization of low power consumption of the receiver by using the communication system according to the present invention will be described below.
[0077]
In the figure, 701 is an antenna, 702 is a selector, 703 is a specific subcarrier selection receiver, 704 is an orthogonal frequency division multiplexed signal receiver, 705 is a control circuit, 706 is an assign signal, and 707 is an ON signal.
[0078]
Among them, the antenna 701 is for receiving the orthogonal frequency division multiplexed signal, and the selector 702 is configured to convert the signal received by the antenna 701 into the specific subcarrier selection receiver 703 and the orthogonal frequency division multiplexed signal receiver 704. This is a switch for switching a circuit given to one of them. The control circuit 705 receives a signal (assignment signal 706) from the specific subcarrier selection receiver 703, and controls switching of the selector 702.
[0079]
The specific subcarrier selection receiver 703 is a receiver for extracting a specific subcarrier from among the received subcarriers. As the specific subcarrier selection receiver 703, for example, FIG. 2 (the configuration of the present invention) Is applicable. The orthogonal frequency division multiplexed signal receiver 704 is a receiver that receives all subcarriers, extracts each subcarrier, and demodulates information transmitted on each subcarrier. A configuration as shown in FIG. 16 (a demodulation method according to a conventional method) can be applied.
[0080]
In this system, on the transmission side, assignment information is transmitted using a specific subcarrier, and on the receiver side, the specific subcarrier is monitored to control the power on / off of the orthogonal frequency division multiplexed signal receiver 704. By doing so, power consumption is reduced.
[0081]
Therefore, the specific subcarrier selection receiver 703 targets the subcarrier of the control channel signal as the specific subcarrier, monitors the subcarrier, and when receiving the assignment information by the control channel signal, indicates that the receiver has been assigned. The control circuit 705 is configured to be notified by an assignment signal 706, and the control circuit 705 sends an ON signal 707 to the orthogonal frequency division multiplexed signal receiver 704 by the assignment signal 706 to operate it. Configuration. Since the power consumption of the specific subcarrier selection receiver 703 is significantly smaller than that of the orthogonal frequency division multiplexed signal receiver 704, a configuration capable of realizing low power consumption is realized.
[0082]
The operation of the present device having such a configuration will be described. In this embodiment, a specific carrier (one or more) among a plurality of subcarriers of an orthogonal frequency division multiplex signal transmitted from a transmitter is allocated as a control channel 601 as shown in FIG. The other carrier is the data channel 692. Then, when the receiver is assigned, the assignment information is transmitted using the control channel 601.
[0083]
On the receiver side, the orthogonal frequency division multiplex signal received by the antenna 701 is input to the selector 702, and the output of the selector 702 is input to the specific subcarrier selection receiver 703 or the orthogonal frequency division multiplex signal receiver 704. In the standby state, the control circuit 705 is configured to switch the selector 702 to the specific subcarrier selection receiver 703 side, and the orthogonal frequency division multiplexed signal receiver 704 is configured to control the power supply to be off. is there. In addition, since the specific subcarrier selection receiver 703 is a device that extracts only the subcarrier transmitting the control channel signal and obtains the assignment information, the specific subcarrier selection receiver 703 monitors the control channel signal. become.
[0084]
Thus, in the standby state, the specific subcarrier selection receiver 703 monitors the control channel signal. When receiving the assignment information by the control channel signal, the control circuit 705 is notified by the assignment signal 706 that the receiver has been assigned.
[0085]
The control circuit 705 switches the selector 702 to the orthogonal frequency division multiplexed signal receiver 704 in accordance with the assignment signal 706 from the specific subcarrier selection receiver 703 and an ON signal 707 which is a command signal for power-on operation. Is output to the orthogonal frequency division multiplexing signal receiver 704.
[0086]
The orthogonal frequency division multiplexed signal receiver 704 receives the ON signal 707, turns on the power, and is ready for receiving processing. The power consumption of the specific subcarrier selection receiver 703 employing the configuration of FIG. 2 is significantly smaller than that of the orthogonal frequency division multiplex signal receiver 704 that demodulates all subcarriers. Also in configuring a division multiplexed signal receiver, if the configuration of the present embodiment is adopted, it is possible to realize a great reduction in power consumption of the receiver.
[0087]
Here, as shown in FIG. 8, when a control channel is assigned to only one wave, it may be lost due to the influence of multipath 801 (see control channel (1) 802).
[0088]
In such a case, if the control channels are assigned to a plurality of carriers, for example, the control channel (1) and the control channel (2), and the optimum control channel is selected by measuring the received electric field strength in the receiver, there is no problem. Disappears.
[0089]
Next, a third embodiment will be described.
[0090]
(Third embodiment)
Each of the above embodiments has a configuration in which a desired one of a plurality of subcarriers is extracted and demodulated. If this idea is advanced one step and applied to a configuration for extracting and demodulating desired ones of a plurality of subcarriers, an FFT is required, but compared to a case where all subcarriers are processed, Can be simplified, and the A / D converter can be operated at a low sampling rate, so that power consumption and simplification can be achieved. Such an application is most suitable for a receiving apparatus that does not need all data of all subcarriers and only needs to be able to use data of specific subcarriers.
[0091]
FIG. 9 is a block diagram illustrating a configuration of a receiver of a selective reception scheme of a wireless communication scheme according to a third embodiment of the present invention for such a use. The configuration of the transmitter that generates the orthogonal frequency division multiplexed signal is the same as the example in FIG.
[0092]
In FIG. 9, reference numeral 30 denotes a receiver main body, 31 denotes a receiving antenna, 32 denotes a received signal, 33 denotes an RF unit, and 34 denotes an output signal of the RF unit 33, which is a low-frequency signal. 35 is a mixer, 36 is a local oscillator, 37 is 38, 39 is a band limiting filter (BPF), 310 is a plurality of subcarriers, 311 is an A / D converter, 312 is a discrete signal, 313 is A guard interval removal processing section, 314 a signal from which a guard interval has been removed, 315 a Fourier transform (FFT) section, 316 a Fourier transform (FFT) output, 317 a demapping processing section,
318 is desired reception data.
[0093]
In this embodiment, a received signal 32 received by a receiving antenna 31 is amplified by an RF unit 33, mixed with a reference signal 37 output from a local oscillator 36 by a mixer 35, and frequency-converted. A desired plurality of continuous subcarriers 310 are taken out by passing through. The A / D converter 311 samples the plurality of desired continuous sub-carriers 310 and converts them into digital data. The guard interval removal processing unit 313 outputs the data from the A / D converter 311. The signal (discrete signal) 312 is subjected to a process of removing a guard interval component from the signal 312.
[0094]
A Fourier transform (FFT) unit 315 performs a Fourier transform (FFT) process on the output signal 314 of the guard interval elimination process unit 313, and a demapping process unit 317 performs a demapping process on the data after the FFT process (transmission side). To restore the f-axis mapped data) to obtain desired received data 318.
[0095]
In such a configuration, in the receiver main body 30, the received signal 32 received by the receiving antenna 31 is given to the RF unit 33, and the RF unit 33 amplifies the received signal 32 and sends the amplified signal 34 to the mixer 35. give. In the mixer 35, in addition to the amplified signal 34, a reference signal 37 output from a local oscillator 36 is input, and these are mixed (mixed) to perform frequency conversion. This frequency-converted signal is the 38 signal.
[0096]
Although only one stage of the frequency conversion operation is shown here, a general multistage heterodyne system (such as superheterodyne or double superheterodyne) is included.
[0097]
The signal 38 that has been frequency-converted in the mixer 35 is passed through a band-limiting filter 39, so that a plurality of desired continuous subcarriers 310 are extracted. FIG. 10 shows the frequency spectrum of the signal 310 extracted by the band limiting filter 39. In the figure, 41 is a subcarrier, 42 is a subcarrier interval Δf43 is a desired subcarrier group (a plurality of subcarriers) to be extracted, and 44 is a bandpass filter characteristic of the bandpass filter (BPF) 39. There are a plurality of subcarriers constituting the orthogonal frequency division multiplex signal as indicated by 41 in FIG. If the subcarrier denoted by reference numeral 43 is the target subcarrier to be extracted, a band-limiting filter having a band-pass filter characteristic indicated by 44 as shown in FIG. The band-limited filter output 310 extracted by passing through 39 becomes only subcarriers indicated by reference numeral 43.
[0098]
This band limiting filter output 310 is a part of a subcarrier constituting an orthogonal frequency division multiplexed signal, is sampled by an A / D converter 311 to become a discrete signal 312, and a guard interval removal processing unit 313 removes a guard interval. By performing the FFT processing on the signal 314 after the execution by the Fourier transform unit 315, only the Fourier transform (FFT) output 316 of the desired subcarrier is extracted.
[0099]
Then, the FFT output 316 of the desired subcarrier component is subjected to demapping processing by the demapping processing unit 317, thereby obtaining desired reception data 318.
[0100]
In the present invention, since only a part of the subcarriers is extracted by the band limiting filter 39 and the data transmitted by the part of the subcarriers is demodulated, compared to a configuration in which all the subcarriers are processed, The sampling frequency of the demodulation A / D converter can be reduced. That is, unnecessary carriers are removed by the band limiting filter 39 as in the second embodiment, so that only the extracted subcarriers need to be sampled. Therefore, the sampling frequency of the A / D converter 311 is set low. It is possible to do.
[0101]
However, in this embodiment, since the Fourier transform (FFT) unit 315 performs the FFT processing, the number of samples (the number of samples) in a unit symbol time is equal to or more than the number of the plurality of subcarriers 310 extracted by the band limiting filter 39. I need.
[0102]
When a desired carrier is extracted by the band limiting filter 39, the orthogonality between subcarriers is destroyed due to the effect of the band limitation. This is an effect of the time response of the band limiting filter, and as a result, intersymbol interference occurs. Under the influence of the intersymbol interference, unnecessary interference components become equivalent noises and are mixed into the received signal, and the noise resistance is deteriorated.
[0103]
Therefore, it is necessary to improve noise immunity. To this end, the band of the band-limiting filter 39 is set wider than the bandwidth of the desired subcarrier to be extracted, and the sampling frequency of the A / D converter 311 is adjusted. Should be set high.
[0104]
FIG. 11 shows a frequency spectrum when the band of the band limiting filter 39 is set wider than the bandwidth of the desired subcarrier and the sampling frequency of the A / D converter 311 is set higher.
[0105]
Since the band of the band-limiting filter 39 is widened, intersymbol interference from adjacent symbols can be reduced. In addition, since the sampling frequency is set high, interference from adjacent subcarriers can be suppressed. Be improved.
[0106]
In the above third embodiment, when extracting and demodulating a desired number of subcarriers, an FFT is required. However, compared to a case where all subcarriers are to be processed, the FFT is used. The simplification can be achieved, and the A / D converter can be operated at a low sampling rate, so that power consumption and simplification can be achieved.
[0107]
Here, in the system of the present invention, the transmission system is configured to add a guard interval, but the effectiveness of the addition of the guard interval will be briefly described.
[0108]
FIG. 12 is a diagram illustrating the effectiveness of adding a guard interval. Generally, in the generation of orthogonal frequency division multiplexed signal waves, a guard interval is added to prevent multipath propagation distortion of radio waves. However, in a wireless communication receiver that selectively receives only arbitrary subcarriers as in the present invention, it is very difficult to add a guard interval also for removing intersymbol interference from adjacent symbols. It is valid.
[0109]
FIG. 12 illustrates this. This figure shows an intersymbol interference power 61 with respect to a guard interval length 60 for determining a cutoff characteristic of the LPF 222 when the LPF (low-pass filter) 222 shown in the first embodiment is assumed to be an analog Bessel type. Things.
[0110]
According to this, when the order of the LPF 222 is fixed and evaluated with the guard interval length 60, the intersymbol interference power 62 gradually decreases. As a result, noise power equivalently generated is reduced, and the quality (code error rate characteristic) of the transmission information sequence is greatly improved.
[0111]
(Fourth embodiment)
Next, an example of demodulating a plurality of subcarriers without performing FFT will be described as a fourth embodiment. In the receiving side, as a demodulation system for demodulating a transmission information sequence from an orthogonal frequency division multiplexed signal, the orthogonal frequency division multiplexed signal is configured within a time obtained by time-dividing an effective symbol time determined by adjacent subcarrier intervals into a plurality of times. One or more subcarriers to be extracted are extracted, and a transmission information sequence is demodulated from the extracted subcarrier signals.
[0112]
Details will be described. In this system, in order to transmit different information, information is transmitted by a plurality of subcarriers using different subcarriers for each piece of information to be transmitted. In the transmission system, as shown in FIG. 13, a plurality of subcarriers 71 arranged on the frequency axis 70 have a subcarrier interval Δf denoted by reference numeral 72 set so as to satisfy an orthogonal condition. By inverse Fourier transforming the group, an orthogonal frequency division multiplexed signal time waveform 74 on the time axis 73 is obtained, which is modulated and transmitted from the antenna.
[0113]
Here, the effective symbol length of the information to be transmitted is determined by the reciprocal of the subcarrier interval Δf indicated by reference numeral 72 (T indicated by reference numeral 75) and the guard interval time ΔT (denoted by reference numeral 76). ΔT) is given by a relational expression of T + ΔT.
[0114]
In FIG. 13, the time T is indicated by reference numeral 75, and an example is shown in which the time T is divided into four slots in a time-division manner (see the time slot indicated by reference numeral 77). Here, it is tentatively assumed that T obtained by time-dividing T into four are T1, T2, T3, and T4.
[0115]
T1 is a portion of the time slot 77 with reference numeral 78, T2 is a portion of the time slot 77 with reference numeral 79, T3 is a portion of the time slot 77 with reference numeral 710, and T4 is a portion of the time slot 77. It is assumed that this is the part denoted by reference numeral 711.
[0116]
Here, for example, assuming that the local oscillator 218 of FIG. 2 uses a configuration that can arbitrarily switch the frequency of the oscillation reference signal 219, in each of the slots 78 to 711, the respective timing periods For example, the frequency of the oscillation reference signal 219 of the local oscillator 218 in FIG. In the example of FIG. 13, the frequency is switched to f1 to f4 indicated by reference numerals 712 to 715, and the frequency of the oscillation reference signal 219 is f1 during the slot T1 indicated by reference numeral 78 and the period of the slot T2 is indicated by reference numeral 79. In this case, the frequency of the oscillation reference signal 219 is f2, the frequency of the oscillation reference signal 219 is f3 during the slot T3 indicated by reference numeral 710, and the frequency of the oscillation reference signal 219 is f4 during the slot T4 indicated by reference numeral 711.
[0117]
As described above, the frequency of the oscillation reference signal 219 of the local oscillator 218 is changed in accordance with the timing period of each slot. As a result, the oscillation reference signal 219 having a different frequency is generated in each slot. This makes it possible to obtain received signals of different intermediate frequencies for each frequency of the oscillation reference signal 219. These signals are filtered by LPFs corresponding to the respective intermediate frequencies and extracted to obtain one symbol. It is possible to demodulate a plurality of independent subcarriers in time, thereby eliminating the need for a conventional Fourier transformer for demodulating a plurality of subcarriers as shown in FIG.
[0118]
FIG. 14 shows an example of a receiving-side configuration that embodies the fourth embodiment. In the figure, 80 is a received signal r (n), 81 is a mixer, 82 is a local oscillator, 83 is a reference signal, 84 is a timing generator, 85 is a period T determined by the reciprocal of the subcarrier interval, 86 is a control signal, 87 is a baseband signal, 88 is an LPF, 89 is a delay element, 810 is a sample and hold circuit, 811 is a control signal, 812 is a sample and hold circuit, and 817 is a switching circuit.
[0119]
Among these, the local oscillator 82 generates the reference signal 83, and the frequency of the reference signal 83 can be changed. In order to change the frequency, the local oscillator 82 may be constituted by, for example, a voltage controlled oscillator (VCO).
[0120]
The mixer 81 is a circuit that mixes the received signal r (n) indicated by the reference numeral 80 and the reference signal 83 of the local oscillator 82 to generate a baseband signal 87 having an intermediate frequency, and outputs the baseband signal 87. The timing generator 84 is a circuit for time-divisionally controlling the information 85 of the cycle T determined by the reciprocal of the subcarrier interval, and for each time shorter than the information 85 of the cycle T (T / 4 time in the figure). A control signal 86 for generating the frequencies f1 to f4 is supplied to the local oscillator 82, and a control signal 86 for sequentially controlling the switching of the switching circuit 817 in accordance with each time slot T1 to T4 of the period T indicated by reference numeral 85 is output. Is what you do.
[0121]
Further, the timing generator 84 outputs a control signal 86 for controlling the delay element 89 in order to provide a delay of a predetermined time according to each of the time slots T1 to T4 of the cycle T indicated by the reference numeral 85.
[0122]
The LPF 88 is a low-pass filter having different frequency characteristics, and is composed of four types of filters having filter characteristics adapted to the frequency characteristics of the output obtained from the mixer 81 by changing the oscillation frequency of the local oscillator 82. The switching circuit 817 is a circuit for switching the four types of filters, and is for sequentially switching and controlling the output from the mixer 81 by the control signal 86 and inputting the output to the selected filter.
[0123]
The sample and hold circuit 812 is a circuit for sampling and holding the output of the LPF 88, and the delay element 89 is for delaying a control signal for the sampling and holding.
[0124]
In the receiver having such a configuration, a reception signal r (n), which is received by a reception antenna, subjected to predetermined signal processing in an RF unit, and is provided with a code 80 frequency-converted to an intermediate frequency, is It is input to a mixer 81 for frequency conversion to a band.
[0125]
A reference signal 83 having a predetermined frequency fi is also input from the local oscillator 82 to the mixer 81, and an arbitrary subcarrier among a plurality of subcarriers constituting the orthogonal frequency division multiplexed signal is frequency-converted to a baseband band. . The timing generator 84 is a control circuit for time-divisionally controlling a period T (a period denoted by reference numeral 85 in the figure) determined by the reciprocal of the subcarrier interval. A control signal 86 for generating a frequency of f1 to f4 is sent to the local oscillator 82 every short time (T / 4 in the figure). Further, it also has a role of a switching signal for inputting a plurality of baseband signals 87 frequency-converted by the mixer 81 to predetermined LPFs 88 that exist.
[0126]
Further, the control signal 86 is input to the delay element 89 and becomes a control signal 811 for sampling and holding output signals 810 of a plurality of LPFs indicated by reference numeral 88 after a delay of a predetermined time, and becomes a sample hold circuit. 812.
[0127]
813 to 816 in the figure are conceptual diagrams showing the output time waveform signals 810 of the plurality of LPFs 88. The oscillation frequency of the local oscillator 82 is changed at each timing of the slots T1 to T4, and the filter of the LPF 88 is adjusted accordingly. By changing the characteristics, the information of f1 at the timing of slot T1, the information of f2 at the timing of slot T2, the information of f3 at the timing of slot T3, and the information of f4 at the timing of slot T4, respectively The output information is transmitted, and in each slot, transmission information carried on an independent subcarrier can be demodulated.
[0128]
In this embodiment, the time T uniquely determined by the subcarrier interval (T indicated by reference numeral 85) is divided into four parts, but the number of divisions is not limited to four. . The division of each of the slots T1 to T4 does not have to be an equal division. It is desirable that the LPFs have the same tendency in the filter characteristic curves, but the present invention is not limited thereto.
[0129]
Although various embodiments have been described above, in brief, the present invention extracts only a desired subcarrier from a plurality of subcarriers in an orthogonal frequency division multiplexed signal with a filter, demodulates the subcarrier, and transmits the demodulated signal through the subcarrier. It is configured to receive data.
[0130]
Then, a filter for extracting the signal component of the frequency domain of the desired subcarrier from the received signal is provided, and the signal component of the desired subcarrier is obtained by passing the filter, and the signal component is demodulated by the demodulation unit. As a result, FFT processing for extracting all subcarriers as in the related art is not required, and a reception system can be configured with a filter and a demodulation unit for a single carrier. Therefore, since the configuration is simplified and the FFT processing is not required, effects such as a reduction in the size of the device and a reduction in power consumption can be obtained.
[0131]
When demodulating a plurality of desired subcarriers among a plurality of subcarriers in an orthogonal frequency division multiplexed signal, the demodulated signal is supplied to a mixer for mixing with a received signal to obtain a baseband signal as a signal for mixing. The local oscillator that generates the signal is of a variable frequency type, and a plurality of filters are provided to mix the received signal while sequentially changing the oscillation frequency of the local oscillator to a predetermined frequency, and to switch the filter. By sequentially extracting the signal components in the frequency domain of a plurality of desired sub-carriers of the received signal, the FFT processing for extracting all the sub-carriers as in the related art is unnecessary, and the filter and Since the receiving system can be configured with a demodulation unit targeting a single carrier, the configuration is simplified. Also, minutes to eliminate the FFT process, in which apparatus is such that the effect of such power consumption can be lowered by small obtained.
[0132]
Further, when extracting a plurality of specific subcarriers, a band-limiting filter is used, and FFT is performed on the orthogonal frequency division multiplexed signal extracted by the band-limiting filter. By performing the FFT on the orthogonal frequency division multiplexed signal extracted by the band limiting filter, the total number of samples of the FFT can be reduced, so that the calculation time required for the FFT or the FFT The circuit scale can be shortened or reduced, and the effect that the device is small and the power consumption can be reduced can be obtained accordingly.
[0133]
【The invention's effect】
As described above in detail, the present invention has a configuration in which, on the receiving side, a part or a plurality of carriers constituting an orthogonal frequency division multiplexed signal is extracted by a band limiting filter, and demodulation equivalent to a single carrier demodulation method is performed. As a result, it is possible to selectively receive any subcarrier without receiving all the signals transmitted from the transmission side. Therefore, the wireless communication has a simple configuration and saves space and power. Equipment can be provided. In addition, since the FFT is performed on the orthogonal frequency division multiplexed signal extracted by the band limiting filter, the total number of samples of the FFT can be reduced, so that the calculation time required for the FFT or the circuit scale of the FFT is reduced or reduced. It is possible to do.
[0134]
Further, in the present invention, since the unnecessary carrier is suppressed by the LPF, the sampling rate of the A / D converter of the receiving system can be set low, and the circuit configuration of the receiving system can be simplified.
[0135]
Also, by adding a guard interval in the transmission system, the influence of interference from adjacent symbols of the orthogonal frequency division multiplex signal generated due to the band limitation in the LPF is reduced, so that the discrimination margin of the demodulated signal is reduced. Is increased, and the bit error rate characteristics can be improved.
[0136]
Further, in the receiving system, the center frequency of the subcarriers constituting the orthogonal frequency division multiplexed signal is frequency-converted to zero, and the adjacent carrier is suppressed by the LPF, thereby eliminating the need for a circuit for removing the guard interval. The circuit configuration of the system can be simplified.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an embodiment of the present invention, and is a diagram as an example illustrating a frequency spectrum of an orthogonal frequency division multiplexed signal satisfying an orthogonal condition.
FIG. 2 is a diagram for explaining the embodiment of the present invention, and is a block diagram of a transmission / reception system for explaining the configuration of the radio communication apparatus of the selective reception system according to the first embodiment of the present invention.
FIG. 3 is a diagram for explaining the embodiment of the present invention, and is a diagram showing a frequency characteristic of an LPF applied to a receiver in a wireless communication device according to the selective reception system of the present invention.
FIG. 4 is a diagram for explaining the embodiment of the present invention, and is a diagram showing a time characteristic of an LPF applied to a receiver in a wireless communication device according to the selective reception system of the present invention.
FIG. 5 is a diagram for explaining an embodiment of the present invention, and is a diagram showing a relationship between an order of an LPF applied to a receiver in a wireless communication apparatus according to a selective reception method of the present invention and interference power.
FIG. 6 is a diagram for explaining an embodiment of the present invention, and is a block diagram showing a configuration of a receiver in a wireless communication apparatus using a selective reception system as a second embodiment of the present invention.
FIG. 7 is a diagram for explaining an embodiment of the present invention, and is a diagram showing an example of arrangement of control channels in a second embodiment of the present invention.
FIG. 8 is a diagram for explaining the embodiment of the present invention, showing an example in which a control channel is lost due to multipath.
FIG. 9 is a diagram for explaining an embodiment of the present invention, and is a block diagram for explaining an example of a receiver applied to a selective reception wireless communication apparatus according to a third embodiment of the present invention.
FIG. 10 is a diagram for explaining an embodiment of the present invention, and is a diagram showing an example of a frequency spectrum explaining a concept when a plurality of subcarriers are selected and received simultaneously in the wireless communication system of the present invention.
FIG. 11 is a diagram for explaining the embodiment of the present invention, and is a diagram showing an example of a frequency spectrum for explaining a concept when a plurality of subcarriers are simultaneously selected and received in the wireless communication system of the present invention.
FIG. 12 is a diagram for explaining an embodiment of the present invention, and is a diagram showing a relationship between a guard interval configuring a receiver in the wireless communication system of the present invention and an equivalent noise power included in a demodulated signal.
FIG. 13 is a diagram for explaining an embodiment of the present invention, and is a diagram for explaining a concept of demodulating a plurality of subcarriers in a time division manner in a wireless communication system receiver of the present invention.
FIG. 14 is a diagram for explaining an embodiment of the present invention, and is a block diagram showing a configuration example of a method of demodulating a plurality of subcarriers in a time division manner in a receiver of a wireless communication device of the present invention.
FIG. 15 is a diagram illustrating an example of frequency allocation in a hierarchical orthogonal frequency division multiplexed signal.
FIG. 16 is a diagram for explaining a conventional example, and is a circuit block diagram of a conventional transmission / reception system using an orthogonal frequency division multiplexed signal.
[Explanation of symbols]
10. Frequency axis (frequency domain)
11-1 to 11-n ... subcarriers
11-m desired subcarrier to be extracted
12 ... Subcarrier interval
14, 44, 54, 222 ... Low-pass filter (LPF)
20: orthogonal frequency division multiplexed signal transmitter
21 ... Transmission information sequence
22: frequency axis signal point arrangement processing unit
23 ... Modulation subcarrier
24: inverse Fourier transform (inverse FFT) unit
25: Orthogonal frequency division multiplex signal time sample
26 ... Guard interval addition unit
27 ... Time waveform signal sample after guard interval addition
28 ... D / A converter
29: Orthogonal frequency division multiplex signal analog wave
30 ... Receiver body
31 ... receiving antenna
32 ... Reception signal
33 RF part
34 ... Intermediate frequency
35, 81, 220 ... Mixer
36 Local oscillator
37 ... Reference signal
38 ... Low frequency signal
39 ... Band limiting filter (BPF)
40 ... frequency axis (frequency domain)
41 ... Subcarrier
42 ... Subcarrier interval
43... Desired subcarrier group (plural subcarriers)
50: Frequency axis (frequency domain)
51, 71 ... subcarrier
52, 72 ... Subcarrier interval
53 ... desired subcarrier group (plural subcarriers)
60 ... Guard interval length
61 ... Intersymbol interference power
62 ... Characteristic curve
70 ... frequency axis
73 ... Time axis
74: Orthogonal frequency division multiplex signal time waveform
75 ... Symbol time T
76… Guard interval time
77 ... Slot configuration
78-711 ... slots
80: Intermediate frequency reception signal
82 Local oscillator
83 ... Reference signal
84 timing generator
85 ... Symbol time T
86 ... control signal
87 ... Baseband signal
88 ... LPF group
89 ... Delay element
210: RF transmission section
211 ... transmission signal
212 ... Transmission antenna
213: orthogonal frequency division multiplexed signal receiver
214 ... receiving antenna
215 ... Reception signal
216 ... Reception RF unit
217: Intermediate frequency signal
218 ... Local oscillator
219 ... Reference signal
221 ... low frequency signal
223 ... desired subcarrier signal (band-limited signal)
224, 311 ... A / D converter (ADC)
225 desired subcarrier signal
226 ... Single carrier demodulator
227 demodulated transmission information sequence
310: Multiple subcarriers
312 ... discrete signal
313… guard interval remover
314… time waveform without guard interval
315… Fourier transform (FFT) part
316… Fourier transform unit output
317: Demapping processing unit
318 ... desired transmission information sequence
712 to 715 ... selection switching frequency
810: LPF output signal
811 ... Control signal
812 ... Sample hold circuit
813 to 816 ... Example of LPF output signal time waveform
817: Switch for circuit switching.

Claims (3)

Receiving means for receiving an orthogonal frequency division multiplexed signal on a plurality of subcarriers orthogonal to each other,
Oscillating frequency variable oscillating means for generating a reference signal,
A mixer that obtains a baseband signal by mixing the received orthogonal frequency division multiplexed signal with a reference signal output by the oscillation unit;
A plurality of filters having as input the output of the mixer;
Selecting means for selecting the filter,
Means for sequentially and variably controlling the oscillating frequency of the oscillating means corresponding to a desired subcarrier component to be extracted, and means for controlling the selecting means to select the filter corresponding to a baseband signal output from the mixer; ,
And a demodulating means for demodulating a signal component extracted by the selected filter. Receiving means for receiving an orthogonal frequency division multiplexed signal on a plurality of subcarriers orthogonal to each other,
A filter for extracting a single or a plurality of desired subcarrier components in a received orthogonal frequency division multiplexed signal within a time obtained by time-sharing a plurality of effective symbol times determined by adjacent subcarrier intervals,
A wireless communication device comprising: a demodulation unit configured to demodulate a desired subcarrier component extracted by the filter. 3. The wireless communication apparatus according to claim 2 , wherein the filter extracts a different single subcarrier or a plurality of subcarriers within a plurality of time-divided time frames.

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