JP5718785B2 - Wireless communication system, wireless receiver and wireless transmitter - Google Patents

Description

  The present invention relates to OFDM radio technology, and more particularly to OFDM radio technology using fractional sampling.

  In recent years, an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme has been widely used. The OFDM modulation scheme is a type of multicarrier digital modulation scheme that uses a plurality of subcarriers (subcarriers) that are orthogonal to each other, and can achieve high frequency utilization efficiency.

  In the OFDM modulation method, fractional sampling (FS) is proposed as a method for implementing the diversity effect relatively easily (Non-Patent Document 1). The FS samples the received signal at a rate higher than the Nyquist frequency and performs DFT processing in parallel, thereby decomposing the multipath. When the signal is upsampled by the transmitter, an imaging component of the desired band signal is generated outside the band on the frequency axis. This signal is filtered by the baseband filter, and only the signal in the desired band is transmitted, but the signal in the adjacent band remains due to the frequency response of the filter. This out-of-band residual signal creates diversity in the FS. That is, the diversity effect due to FS can be regarded as frequency diversity due to the imaging component in the adjacent band.

  By the way, cognitive radio in which another radio communication system uses a frequency (white space) allocated to a radio communication system but not used has been studied. The reason why such a frequency exists is that systems using the frequency are geographically separated (for example, a TV white space frequency), and that a plurality of systems like the ISM band share a frequency. Something is considered.

C. Tepedelenlioglu, R. Challagualla, "Low Complexity Multipath Diversity Through Fractional Sampling in OFDM," IEEE Trans. On Signal Processing, vol.52, no.11, Nov. 2004. B. Jabbari, R. Pickholtz, M. Norton, "Dynamic Spectrum Access and Management," IEEE Wireless Communications, issue 4, vol.17, pp.6-15, Oct. 2010. S. Geirhofer, Lang Tong, B. M. Sadler, "Cognitive Radios for Dynamic Spectrum Access in the Time Domain: Modeling and Exploiting White Space," IEEE Magazine on Communications, issue 5, vol. 45, pp. 66-72, May 2007.

  In order to realize path diversity by the method of Non-Patent Document 1, it is necessary to transmit part or all of the image component of the desired signal to another channel, which causes interference with other systems.

  An object of the present invention is to provide a system that can obtain a diversity effect by fractional sampling while suppressing interference with other systems.

  In the present invention, when transmitting the target OFDM signal (target signal) and the image signal together, the receiver side selects and transmits and receives only the image components that can obtain the diversity effect by the fractional sampling. Thus, the interference effect on other systems is suppressed while realizing the diversity effect by the fractional sampling.

More specifically, a wireless communication system according to one aspect of the present invention is provided.
A wireless transmitter that transmits together a target signal that is a target OFDM signal and an image signal of the target signal;
A filter that removes other than the target signal and the image signal from the received signal, and the received target signal and the image signal are sampled and converted into a digital signal at an oversampling rate of G times (G is an integer of 2 or more). An A / D converter, G Fourier transformers for converting digital modulation symbols into digital signals in the frequency domain at each phase of 1 / G of the symbol period 1 / Fs, and digital signal output of the Fourier transform means A signal synthesizer for demodulating the transmitted OFDM signal based on
Including
Said image signal, a frequency interval between the target signal is the n · Fs, n is n ≠ K · G (K is an arbitrary integer) Ri integer der satisfying,
The wireless receiver
An image signal having a frequency interval with the target signal of m · Fs (where m = K · G) has a frequency interval with the target signal of n · Fs (where n ≠ K · G). A frequency converter for frequency converting the received signal,
A synthesizer that synthesizes the received signal and the received signal frequency-converted by the frequency converter;
Have

  The image signal whose frequency interval with the target signal is (K · G) Fs is coherent with the target signal, and therefore a diversity effect cannot be obtained. By making the image signal a component whose frequency interval with the target signal is n · Fs (n ≠ K · G), a path diversity effect can be obtained. Note that the S / N may be improved by transmitting an image signal having a frequency interval of (K · G) Fs. However, by not transmitting such an image signal, interference with other systems can be suppressed. it can. Further, on the wireless receiver side, by removing the bands that do not contribute to the diversity effect with a filter, it is possible to avoid deterioration of reception performance due to noise or interference in these bands.

  A coherent image signal whose frequency interval with the target signal is m · Fs (m = K · G) does not contribute to the diversity effect. When a coherent image signal is transmitted from the wireless transmitter, a diversity effect can be obtained by performing frequency conversion in the receiver. Therefore, even when the G value of the wireless receiver is unknown to the wireless transmitter, the diversity effect by the fractional sampling can be obtained.

  Note that it is preferable to remove signals other than the converted image signal from the frequency-converted signal by a filter before input to the synthesizer. Moreover, it is preferable to remove signals other than the target signal from the received signal by a filter before input to the combiner. Although it is not essential to remove these signals before input to the combiner, this makes it possible to remove unnecessary signals and improves reception performance.

A wireless communication system according to another aspect of the present invention is
A wireless transmitter for transmitting together a target signal, which is a target OFDM signal, and an image signal of the target signal;
A filter that removes other than the target signal and the image signal from the received signal, and the received target signal and the image signal are sampled and converted into a digital signal at an oversampling rate of G times (G is an integer of 2 or more). An A / D converter, G Fourier transformers that convert digital modulation symbols into digital signals in the frequency domain at each phase of 1 / G of the symbol period 1 / Fs, and digital signal output of the Fourier transformer Based on
A radio receiver comprising: a signal synthesizer that demodulates the received OFDM signal;
A wireless communication system comprising:
The image signal has a frequency interval of n · Fs with the target signal, n is an integer satisfying n ≠ K · G (K is an arbitrary integer),
The wireless transmitter includes an OFDM modulator that generates the target signal and the image signal by an inverse Fourier transformer that is M · G times (M is an integer) times the number of subcarriers of the OFDM signal, and a sampling frequency M · G · Fs. And a D / A converter that performs sampling processing to convert the signal into an analog signal, and a filter that removes signals other than the target signal and the image signal.
With this configuration, it is possible to transmit an image signal in a desired frequency band.
In the present invention,
The wireless receiver has a notification means for notifying the wireless transmitter of the G value,
The radio transmitter sets the frequency at which the image signal is transmitted based on the G value notified from the radio receiver so that the frequency interval between the image signal and the target signal is n · Fs (n ≠ K · G). To decide,
It is also preferable.

  The transmission frequency of the image signal from which the diversity effect is obtained depends on the G value (number of branches) of the wireless receiver. In this way, by notifying the G value from the radio receiver to the radio transmitter, even if the radio transmitter does not know the G value of the radio receiver in advance, the diversity effect by fractional sampling can be obtained. can get. It is also preferable that the wireless transmitter separately notifies the wireless receiver of the frequency for transmitting the image signal.

In the present invention,
The wireless receiver has notification means for notifying a frequency at which the wireless transmitter should transmit an image signal,
The wireless transmitter transmits an image signal at a frequency notified from the wireless receiver.
It is also preferable.

  Since the transmission frequency of the image signal from which the diversity effect is obtained depends on the G value of the wireless receiver, the frequency at which the image signal should be transmitted can also be calculated on the wireless receiver side. Therefore, the diversity effect by the fractional sampling can be obtained also by determining the transmission frequency of the image signal on the wireless receiver side and the wireless transmitter transmitting the image signal according to the determination.

In the present invention,
The wireless receiver configures the Fourier transformer and the A / D converter by a reconfigurable device, and the G value is variable.
It is also preferable that

Here, reconfigurable devices include FPGA (Field Programmable Gate Array) and D
A circuit that can be reconfigured by software (circuit configuration data or a program) such as SP (Digital Signal Processor) is included. By making the G value (number of branches) of the wireless receiver variable, it is possible to adjust the amount of resources allocated to the reception process according to the processing load on the wireless receiver. Also, when the wireless receiver reconfigures and changes the G value, it is preferable to notify the wireless transmitter of the changed G value as described above.

In the present invention,
The image signal has at least G-1 wave,
The frequency of the image signal is selected such that the remainder obtained by dividing the frequency interval n · Fs between the target signal and the image signal by G · Fs takes all of Fs to (G−1) · Fs.
It is also preferable to do so.

  Image signals having the same remainder obtained by dividing the frequency interval with the target signal by G · Fs are coherent with each other. Therefore, by selecting the frequency of the image component so that the remainder obtained by dividing the frequency interval n · Fs of the image signal by G · Fs takes all of Fs to (G−1) · Fs, the diversity effect of the G path can be obtained. can get.

In the present invention, the wireless transmitter includes a radio wave detector that determines whether or not there is a radio wave transmitted from another radio transmitter for the frequency band to be used, and the target signal and the It is also preferable that the image signal is transmitted in a frequency band that is not used by another wireless transmitter.

  By transmitting an image signal using white space, interference with other systems can be suppressed.

  In addition, this invention can also be grasped | ascertained as a radio | wireless communications system which has said each means. The present invention can also be understood as a wireless communication method in a wireless communication system having at least a part of the above means, or a program for realizing this method. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention. The present invention can also be understood as a wireless receiver and a wireless transmitter that constitute the wireless communication system.

In addition, a wireless receiver as one embodiment of the present invention is
A filter for removing signals other than the target signal and the image signal from a received signal;
An A / D converter that samples the received target signal and the image signal at an oversampling rate of G times (G is an integer of 2 or more) and converts the signal into a digital signal;
A Fourier transformer that converts a digital modulation symbol into a frequency domain digital signal at each phase of 1 / G of a symbol period 1 / Fs;
A signal synthesizer that demodulates the transmitted OFDM signal based on the digital signal output of the Fourier transform means;
A wireless receiver comprising:
Said image signal, a frequency interval between the target signal is the n · Fs, n is n ≠ K · G (K is an arbitrary integer) Ri integer der satisfying,
An image signal whose frequency interval to the target signal is m · Fs (where m = K · G)
A frequency converter that converts the frequency of the received signal so that a frequency interval with the target signal is n · Fs (where n ≠ K · G);
A synthesizer that synthesizes the received signal and the received signal frequency-converted by the frequency converter;
It comprises, characterized in that.

That is, the wireless transmitter as one aspect of the present invention is
A wireless transmitter for transmitting both a target signal which is a target OFDM signal and an image signal of the target signal;
Said image signal, a frequency interval between the target signal is the n · Fs, n is n ≠ K · G (K is an arbitrary integer) Ri integer der satisfying,
An OFDM modulator that generates the target signal and the image signal by an inverse Fourier transformer of M · G times (M is an integer) times the number of subcarriers of the OFDM signal;
A D / A converter that performs sampling processing at a sampling frequency M, G, and Fs to convert it into an analog signal;
A filter for removing signals other than the target signal and the image signal;
It comprises, characterized in that.

  According to the present invention, it is possible to obtain a diversity effect by fractional sampling while suppressing interference with other systems.

It is a figure which shows the functional block of the radio | wireless communications system concerning 1st Embodiment. It is a figure explaining the response of the transmission / reception filter and transmission / reception signal spectrum in 1st Embodiment. It is a figure explaining the "Nth separation band" and "the frequency interval of a target signal and an image signal". It is another example of the spectrum of the target signal and image signal in 1st Embodiment. It is a figure which shows the functional block of the radio | wireless communications system concerning 2nd Embodiment. It is a figure explaining the response of the transmission / reception filter and transmission / reception signal spectrum in 2nd Embodiment. It is a figure which shows the functional block of the radio | wireless receiver concerning 3rd Embodiment. It is a figure which shows the flow of the exchange process of the control signal in 4th Embodiment. It is a figure which shows the flow of the exchange process of the control signal in 6th Embodiment.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram of a wireless communication system according to the first embodiment, FIG. 1A is a functional block diagram of a wireless transmitter, and FIG. 1B is a functional block diagram of a wireless receiver. In the present embodiment, the radio transmitter 1 uses the image component after D / A conversion to generate the same signal component for a plurality of channels, and the radio receiver 2 implements a path diversity effect using fractional sampling. To do.

で表されるＯＦＤＭ信号を生成する。ここで、n (n = 0, 1, ..., N-1) は時間インデッ
クスである。ガードインターバルが挿入された後に、サンプリング周波数Ｆｓ＝２０ＭＨｚのＤ／Ａ変換器１２によってデジタル−アナログ変換される。図２Ａに示すように、２０ＭＨｚでＤ／Ａ変換されたＯＦＤＭ変調信号は周波数軸上で２０ＭＨｚごとに繰り返しそのイメージ成分が発生する。このようにイメージ成分が発生するが、送信フィルタ１３によって目的信号と必要なイメージ成分のみを通過させて、アップコンバータ１４によりアップコンバートして送信する。送信フィルタ１３の周波数特性ｐ_Ｔ（ｔ）を図２Ｂに示す。ここでは一例として、目的信号以外に、目的信号から３チャンネル離れたイメージ成分を１つ通過させるフィルタを採用している。どのようなイメージ成分を送信するかについては、後で詳しく説明する。 The wireless transmitter 1 includes an OFDM modulator 11, a D / A converter 12, a transmission filter 13, and an up converter 14. In the OFDM modulator 11, inverse discrete Fourier transform (IDFT) is performed, and information symbols corresponding to the kth subcarrier are set as s [k] (k = 0,..., N-1),

An OFDM signal represented by Here, n (n = 0, 1, ..., N-1) is a time index. After the guard interval is inserted, digital-to-analog conversion is performed by the D / A converter 12 having a sampling frequency Fs = 20 MHz. As shown in FIG. 2A, an OFDM modulated signal that has been D / A converted at 20 MHz repeatedly generates its image component every 20 MHz on the frequency axis. Although the image component is generated in this way, only the target signal and the necessary image component are allowed to pass through the transmission filter 13, and up-converted by the up-converter 14 and transmitted. The frequency characteristic p _T (t) of the transmission filter 13 is shown in FIG. 2B. Here, as an example, a filter that passes one image component separated by three channels from the target signal is adopted in addition to the target signal. What kind of image component is transmitted will be described in detail later.

と表される。ここで、ｈ（ｔ）は送受信フィルタ入出力間のチャネルのインパルス応答であり、ｈ（ｔ）＝ｐ_Ｔ（ｔ）＊ｃ（ｔ）＊ｐ_Ｒ（ｔ）と表される。ｃ（ｔ）は送受信間のマルチパスチャネルのインパルス応答、記号＊は畳み込みを表す。また、Ｔｓはシンボル間隔（Ｔｓ＝１／Ｆｓ）、ｖ（ｔ）はフィルタリングされた加法性白色ガウス雑音である。 The wireless receiver 2 includes a down converter 21, a reception filter 22, an A / D converter 23, G (G is an integer of 2 or more) OFDM demodulator 24, a noise whitening filter 25, and a signal synthesizer 26. A transmission signal from the wireless transmitter 1 is down-converted by the down converter 21 and filtered by the reception filter 22. As shown in FIG. 2C, the frequency characteristic p _R (t) of the reception filter 22 is the same as that of the transmission filter 13 of the wireless transmitter 1 and has a frequency characteristic that captures a target signal and an image signal to be transmitted. The signal spectrum after the reception filter is as shown in FIG. 2D. The filtered received signal is

It is expressed. Here, h (t) is an impulse response of the channel between the transmission / reception filter input and output, and is expressed as h (t) = p _T (t) * c (t) * p _R (t). c (t) represents an impulse response of the multipath channel between transmission and reception, and symbol * represents convolution. Ts is a symbol interval (Ts = 1 / Fs), and v (t) is a filtered additive white Gaussian noise.

  The A / D converter 23 A / D converts the received signal at a rate G times the bandwidth, that is, a sampling frequency of G · Fs. Here, G is an integer of 2 or more, and usually takes 2, 4, 8. The converted digital signal is input to the same OFDM demodulator 24 for each G sample, and is subjected to discrete Fourier transform (DFT) after the guard interval is removed.

  v (t) is obtained by filtering noise. When sampling is performed at the baud rate 1 / Ts, the noise samples are not correlated with each other, so that white noise is generated. However, when sampling at a rate higher than the baud rate, the noise samples have a correlation. Therefore, the noise sample is whitened by the noise whitening filter 25.

  The signal synthesizer 26 synthesizes the received signal using maximum ratio combining (MRC) so that the signal-to-noise ratio (S / N) is maximized from a plurality of received signals obtained by fractional sampling. Thereby, path diversity is realized in the multipath channel.

ここで、ｘ（ｔ）は送受信フィルタを通過したベースバンド信号、Ｌはマルチパスの数、α_ｉ、τ_ｉはそれぞれｉ番目の遅延波の利得および遅延時間、δはディラックのδ関数である。この信号の周波数領域表現は、

となる。ここで、ｆｓ＝１／Ｔｓはサンプリング周波数、Ｘ（ｆ）はｘ（ｔ）の周波数領域表現である。 The oversampling ratio (number of branches) G of the fractional sampling is related to the frequency of the image signal component having the diversity effect. If noise is ignored for the sake of simplicity, the received signal sampled in the g-th branch from the sampling theorem is generally expressed as follows.

Here, x (t) is the baseband signal that has passed through the transmission / reception filter, L is the number of multipaths, α _i and τ _i are the gain and delay time of the i-th delayed wave, and δ is the Dirac δ function. . The frequency domain representation of this signal is

It becomes. Here, fs = 1 / Ts is a sampling frequency, and X (f) is a frequency domain representation of x (t).

となる。ここで、Ｑ＝Ｋ・Ｇ（Ｋは整数）の場合、この受信信号は、

となる。すなわち、Ｋ・Ｇ番目の離隔帯域を使用した場合、それぞれのブランチで同じ各パスの成分量を受信することになるので、ブランチ間でコヒーレントとなりダイバーシチ効果が得られないことが分かる。 Here, it is assumed that the received signal is limited to two bands, a central band (q = 0) and a certain isolated band (q = Q: Q is an integer) by filtering. If the signal generated outside the band is an image component of the center band (Y (f) = Y (f + qfs)), the frequency domain representation of the signal received in the fractional sampling branch is

It becomes. Here, when Q = K · G (K is an integer), this received signal is

It becomes. That is, when the K / G-th separation band is used, the same amount of component of each path is received in each branch, so that it becomes coherent between the branches and the diversity effect cannot be obtained.

  Here, the ± N-th separation band means an image component having a frequency of the target signal as Fs [Hz] and a frequency interval (interval between center frequencies) of the target signal of ± N · Fs [Hz]. . FIG. 3 is a diagram for explaining the relationship between the “Nth separation band” and the “frequency interval between the target signal and the image signal”.

  Based on the above consideration, appropriate frequency characteristics of the transmission filter 13 and the reception filter 22 will be described. In order to obtain the effect of path diversity, it is necessary that N ≠ K · G (G is an oversampling ratio, K is an arbitrary integer) when the image signal is the Nth separation band from the target signal. . In other words, the image signal needs to have a frequency interval of n · Fs (n ≠ K · G integer) with respect to the target signal.

  For example, when G = 2 is adopted as the oversampling ratio (the number of branches), as shown in FIG. 2B, the image component of the -3rd separation band, in other words, the frequency interval with the target signal is -3 × Fs. It is preferable to design the transmission filter so that a certain image component is transmitted together with the target signal. By doing so, the effect of two-pass diversity can be obtained.

Referring to Equation (5), when a plurality of separated bands are used as the image signal, the separated _i- th and n _j- th separated bands satisfying G _i modulo G (n _i ≡n _j mod G). You can see that they are coherent. In the case of the oversampling ratio G, a maximum G-path diversity effect can be obtained. For this purpose, it is necessary not only to make the image component uncorrelated with the target signal but also to use G-1 types of incoherent image components. There is. That is, when the image component uses at least G-1 waves and each image component uses the nth separation band, the image component is such that the remainder obtained by dividing n by G takes all 1 to G-1. If the use frequency is selected, a G-path diversity effect can be obtained. In other words, when the frequency interval between the image component and the target signal is n · Fs, the remainder obtained by dividing n · Fs by G · Fs takes all of Fs to (G−1) · Fs. When the frequency of the image component is selected, a G-path diversity effect can be obtained. However, in the case of G> 2, it is not always necessary to satisfy this condition, and a diversity effect of G ′ (1 <G ′ <G) path may be obtained.

Here, mutually coherent image components may be used. For example, when the oversampling ratio is G = 2, as shown in FIG. 4, two coherent image signals such as the −3rd and 3rd separated bands may be transmitted. When the image component is one wave as shown in FIG. 2B, the diversity gain is maximized when the signal level is equal to the target signal. However, when two waves are used as shown in FIG. 4, the image signal is used as the target signal. 3dB for
Even when the signal level is down, the maximum gain of two-wave path diversity can be obtained. Thus, by using a plurality of image components coherent with each other, the signal level of the image signal can be reduced in inverse proportion to the number to be used. Therefore, when a plurality of image components are used, the signal level of the signal can be reduced to make it difficult to give interference. Similarly, the S / N at the receiver may be increased by using a target signal and a coherent image signal (K · Gth separation band).

  Further, the frequency band for transmitting the image signal may be a frequency band (white space) that is not used by other wireless stations. That is, the wireless transmitter is configured to have a radio wave detector that determines whether or not there is a radio wave transmitted from another radio transmitter for the frequency band to be used, and the other radio transmitter uses It is preferable to transmit the image signal in a frequency band that is not.

  As described above, according to the present embodiment, diversity can be realized by an OFDM receiver using fractional sampling by transmitting an image signal of a target signal using white space or the like. Furthermore, there is an advantage that unnecessary interference can be avoided as a wireless transmitter by not transmitting an image signal that does not provide a diversity effect. Further, the wireless receiver has an advantage that it is possible to avoid a decrease in reception performance due to interference in these frequency bands and environmental noise by removing the frequency bands that do not contribute to the diversity effect with a filter.

  Further, in the present embodiment, it is not necessary to increase the DFT circuit or increase the speed of the D / A converter on the transmitter side, so that the cost and power consumption of the transmitter can be reduced.

(Second Embodiment)
FIG. 5 is a block diagram of a wireless communication system according to the second embodiment. In the present embodiment, in the wireless transmitter 3, the same signal component is used for a plurality of channels by using inverse discrete Fourier transform (IDFT) having a size of M · G (G is an oversampling ratio, M is an integer) times the subcarrier. And a path diversity effect is realized using fractional sampling in the wireless receiver 4.

  The wireless transmitter 3 includes an OFDM modulator 31, a D / A converter 32, a transmission filter 33, and an upconverter 34. As described above, the OFDM modulator 31 uses an IDFT having a size of M · G times the subcarrier, and converts the OFDM modulated signal (target signal) and its image signal on the frequency axis to M · G as shown in FIG. 6A. G-1 channels are placed apart.

  The OFDM modulated signal and its image signal are digital-analog converted by a D / A converter 32 having a sampling frequency M · G · Fs (for example, Fs = 20 MHz) after a guard interval is inserted. The D / A conversion generates the repetitive component of FIG. 6A. As shown in FIG. 6B, the transmission signal 33 having a frequency characteristic that allows only the OFDM modulated signal output from the OFDM modulator 31 and the image signal to pass through Only the image signal separated by the MG-1 channel is filtered. The filtered signal is up-converted by the up-converter 34 and transmitted.

  The wireless receiver 4 includes a down converter 41, a reception filter 42, an A / D converter 43, G OFDM demodulators 44, a noise whitening filter 45, and a signal synthesizer 46. Since the configuration and operation of the wireless receiver 4 are substantially the same as those in the first embodiment, differences will be mainly described. In the present embodiment, the reception filter 42 has a frequency characteristic that captures a target signal and an image signal transmitted from the wireless transmitter 3, as shown in FIG. 6C.

  The frequency selection of the image signal in the wireless transmitter 3 is the same as in the first embodiment. That is, the image signal has an Nth separation band from the target signal (an integer satisfying N ≠ K · G (K is an integer)). In other words, the frequency interval between the image signal and the target signal is n · Fs (n ≠ K · G is an integer).

  More preferably, when the image component uses G-1 waves and each image component uses the nth separated band, the image is such that the remainder obtained by dividing n by G takes all of 1 to G-1. Select the frequency of use of the component. By doing so, a G-path diversity effect can be obtained. In other words, when the frequency interval between the image component and the target signal is n · Fs, the remainder obtained by dividing n · Fs by G · Fs takes all of Fs to (G−1) · Fs. It is preferable to obtain the G-path diversity effect by selecting the frequency of the image component.

(Third embodiment)
In the above description, it is assumed that the wireless transmitter knows in advance the number of branches G of the wireless receiver and knows at what frequency the diversity effect can be obtained by transmitting an image signal. In the present embodiment, the diversity effect can be obtained even when the wireless transmitter does not know in advance at which frequency the image signal should be transmitted. In the present embodiment, the frequency of the image signal is frequency-converted on the wireless receiver side, so that the diversity effect can be obtained even when the image signal is transmitted at a frequency at which the diversity effect cannot be obtained.

  FIG. 7 is a diagram illustrating functional blocks of the wireless receiver according to the present embodiment. Note that any one of the above embodiments may be used as the wireless transmitter, and thus description thereof is omitted here.

  The difference between the radio receiver according to the present embodiment and the radio receiver according to the first and second embodiments is that a frequency converter 27 that converts the frequency of the received signal from the antenna in the previous stage of the down converter 21, and a frequency A filter 28 for the converted signal and a synthesizer 29 for combining the frequency-converted signal and the received signal from the antenna are provided. About the structure after the down converter 21, it is the same as that of 1st and 2nd embodiment.

  As described above, the diversity effect cannot be obtained from an image signal whose frequency interval with the target signal is m · Fs (m = K · G, G is the number of branches, K is an arbitrary integer, and Fs is a sampling frequency). . Therefore, the frequency converter 27 converts the frequency of the image signal whose frequency interval with the target signal is m · Fs so that the frequency interval with the target signal is n · Fs (n ≠ K · G). As long as the frequency conversion satisfies the above conditions, the frequency converter 27 may have any configuration. For example, the frequency of the input signal may be converted by ± Fs, or by ± G / 2 · Fs (when G is an even number) or ± (G ± 1) / 2 · Fs (when G is an odd number). You may do it.

  The filter 28 is a filter that removes the frequency component of the image signal included in the received signal. That is, other than the image signal after frequency conversion is removed. The filter 28 is not essential, but reception performance can be improved by removing unnecessary signal components. It is also preferable to provide a filter that removes signals other than the target signal in the path directly input from the antenna to the combiner 29.

In this way, the diversity effect can be obtained by converting the frequency of the image signal. According to this embodiment, since the wireless transmitter can transmit an image signal at an arbitrary frequency, there is an advantage that it is not necessary to know in advance the number of branches (G value) of the wireless receiver. Further, when performing broadcast to a plurality of wireless receivers, even if the number of branches of each wireless receiver is different, a diversity effect can be obtained because the receiver side takes measures.

(Fourth embodiment)
In the third embodiment, the diversity effect is obtained by performing frequency conversion of the image signal on the wireless receiver side without changing the transmission frequency of the image signal. In the present embodiment, the wireless transmitter adjusts the transmission frequency of the image signal according to the configuration of the wireless receiver (the number of branches G).

  The wireless receiver according to the present embodiment also has a wireless transmission function. That is, in addition to the structure of 1st Embodiment (FIG. 1) or 3rd Embodiment (FIG. 7), a transmission means is provided. This transmission means is used to notify the communication partner of the number of branches (G value) of the wireless receiver. This notification (hereinafter referred to as G value notification message) may be sent through an arbitrary channel.

  The wireless transmitter according to the present embodiment includes receiving means for receiving a G value notification message from the receiver side, and means for determining a frequency for transmitting an image signal based on the received G value. From the G value notified by the G value notification message, the wireless transmitter knows that the frequency for transmitting the image signal should be n · Fs (n ≠ K · G). A frequency that is not used by another wireless station is detected and used from among the frequencies that satisfy this condition.

  Hereinafter, the process of exchanging control signals between transmission and reception will be described with reference to FIG.

  First, the wireless transmitter superimposes an image signal on a predetermined frequency and transmits a target signal to the wireless receiver. On the wireless receiver side, the quality of the received signal is evaluated, and if the signal quality is not good, the number of branches (G value) is notified to the wireless transmitter by a G value notification message.

  The wireless transmitter that has received the G value notification message determines the frequency for transmitting the image signal based on the notified G value. Then, the determined transmission frequency of the image signal is notified to the wireless receiver by an image frequency information message. In the following data transmission, the target signal is transmitted by superimposing the image signal at the determined transmission frequency.

  In this way, since the image signal is transmitted at an appropriate frequency according to the G value of the wireless receiver, a diversity effect by fractional sampling can be realized.

  In the above description, the G value notification message is sent when the received signal quality is not good. However, this is not essential and may be sent at any timing. For example, it is conceivable to transmit a G value notification message when starting communication.

(Fifth embodiment)
In the fourth embodiment, the wireless receiver notifies the G value to the wireless transmitter, and the wireless transmitter determines the transmission frequency of the image signal. In the present embodiment, an appropriate image signal transmission frequency corresponding to the G value is determined on the wireless receiver side and notified to the wireless transmitter.

  When the quality of the signal received from the radio receiver is not good, the radio receiver is based on the number of branches (G value) of the n · Fs (n ≠ K · G) frequency, Determine frequencies that are not used by other radio stations. Then, the determined frequency is notified to the wireless transmitter side. The wireless transmitter side superimposes the image signal on the notified frequency and transmits the target signal.

  According to this embodiment, the same effect as that of the fourth embodiment can be obtained.

(Sixth embodiment)
In the present embodiment, each functional unit is configured by a circuit (reconfigurable circuit) that can reconfigure the radio receiver. As the reconfigurable circuit, a field programmable gate array (FPGA), a digital signal processor (DSP), or the like can be employed. Each functional unit has a processing function realized by an execution module of software (circuit configuration data or a program), and can be reconfigured by changing the execution module of the software.

  For example, in the radio receiver according to the present embodiment, the number (G value) and processing contents of the A / D converters 23 and OFDM demodulators 24 and processing contents shown in the third embodiment (FIG. 7) The processing contents of the noise whitening filter 25, the signal synthesizer 26, the frequency converter 27, the filter 28, etc. can be reconfigured.

  In the wireless receiver according to the present embodiment, the G value can be arbitrarily changed according to the internal processing load. In other words, the radio receiver can be reconfigured so that a larger G value is adopted when the processing load is small, and a smaller G value is obtained when the processing load is large. As a result, the apparatus can be configured by selecting an optimum G value according to the processing load at that time.

  Also in this embodiment, it is preferable to transmit the G value to the wireless transmitter side as in the fourth embodiment. The control signal exchange process in this embodiment will be described with reference to FIG. If the quality of the signal received from the radio receiver is not good, the frequency of n · Fs (n ≠ K · G) is selected by another radio station based on the number of branches (G value). Determine unused frequencies. Then, the determined frequency is notified to the wireless transmitter side. Here, the case where the G value notification message is notified when the quality of the received signal is not good has been described. However, when the G value is changed by reconfiguring the wireless receiver due to a change in processing load or the like. It is also preferable to send a G value notification message.

  The G value notification message determines the frequency at which the image signal is transmitted based on the notified G value. Then, the radio receiver is notified of the frequency at which the image signal is transmitted by the image frequency information message.

  The wireless receiver reconfigures the frequency converter 27, the filter 28, the reception filter 22, and the like so that the image signal can be received at the frequency notified by the image frequency information message.

  According to the present embodiment, an appropriate G value can be adopted according to the processing load of the wireless receiver. For example, it is possible to decrease the G value when it is necessary to allocate a large amount of calculation resources for image signal processing or the like, and conversely increase the G value when there is a surplus of calculation resources.

DESCRIPTION OF SYMBOLS 1,3 Radio transmitter 11,31 OFDM modulator 12,32 D / A converter 13,33 Transmission filter 14,34 Up converter 2,4 Wireless receiver 21,41 Down converter 22,42 Reception filter 23,43 A / D converter 24,44 OFDM demodulator 25,45 Noise whitening filter 26,46 Signal synthesizer 27 Frequency converter 28 Filter 29 Synthesizer

Claims (18)

A wireless transmitter for transmitting together a target signal, which is a target OFDM signal, and an image signal of the target signal;
A filter that removes other than the target signal and the image signal from the received signal, and the received target signal and the image signal are sampled and converted into a digital signal at an oversampling rate of G times (G is an integer of 2 or more). An A / D converter, G Fourier transformers that convert digital modulation symbols into digital signals in the frequency domain at each phase of 1 / G of the symbol period 1 / Fs, and digital signal output of the Fourier transformer A signal synthesizer for demodulating the transmitted OFDM signal based on
A wireless communication system comprising:
Said image signal, a frequency interval between the target signal is the n · Fs, n is n ≠ K · G (K is an arbitrary integer) Ri integer der satisfying,
The wireless receiver
An image signal having a frequency interval with the target signal of m · Fs (where m = K · G) has a frequency interval with the target signal of n · Fs (where n ≠ K · G). A frequency converter for frequency converting the received signal,
A synthesizer that synthesizes the received signal and the received signal frequency-converted by the frequency converter;
A wireless communication system. A wireless transmitter for transmitting together a target signal, which is a target OFDM signal, and an image signal of the target signal;
A filter that removes other than the target signal and the image signal from the received signal, and the received target signal and the image signal are sampled and converted into a digital signal at an oversampling rate of G times (G is an integer of 2 or more). An A / D converter, G Fourier transformers that convert digital modulation symbols into digital signals in the frequency domain at each phase of 1 / G of the symbol period 1 / Fs, and digital signal output of the Fourier transformer A signal synthesizer for demodulating the transmitted OFDM signal based on
A wireless communication system comprising:
The image signal has a frequency interval of n · Fs with the target signal, n is an integer satisfying n ≠ K · G (K is an arbitrary integer),
The wireless transmitter includes an OFDM modulator that generates the target signal and the image signal by an inverse Fourier transformer that is M · G times (M is an integer) times the number of subcarriers of the OFDM signal, and a sampling frequency M · G · Fs. A D / A converter that performs sampling processing and converts the analog signal into an analog signal, and a filter that removes other than the target signal and the image signal,
Wireless communication system. The wireless receiver has a notification means for notifying the wireless transmitter of the G value,
The radio transmitter sets the frequency at which the image signal is transmitted based on the G value notified from the radio receiver so that the frequency interval between the image signal and the target signal is n · Fs (n ≠ K · G). To decide,
The wireless communication system according to claim 1 or 2. The wireless receiver has notification means for notifying a frequency at which the wireless transmitter should transmit an image signal,
The wireless transmitter transmits an image signal at a frequency notified from the wireless receiver.
The wireless communication system according to claim 1 or 2. The wireless receiver configures the Fourier transformer and the A / D converter by a reconfigurable device, and the G value is variable.
The radio | wireless communications system in any one of Claims 1-4. The image signal has at least G-1 wave,
The frequency of the image signal is selected such that the remainder obtained by dividing the frequency interval n · Fs between the target signal and the image signal by G · Fs takes all of Fs to (G−1) · Fs.
The radio | wireless communications system in any one of Claims 1-5. The wireless transmitter includes a radio wave detector that determines whether or not there is a radio wave transmitted from another radio transmitter for a frequency band to be used, and the target signal and the image signal are transmitted from another radio Transmit in a frequency band not used by the transmitter,
The radio | wireless communications system in any one of Claims 1-6. A filter that removes a signal other than the target signal and the image signal, which is the target OFDM signal, from the received signal;
G A / D converters that sample the received target signal and the image signal at an oversampling rate of G times (G is an integer of 2 or more) and convert the signal into a digital signal;
A Fourier transformer that converts a digital modulation symbol into a frequency domain digital signal at each phase of 1 / G of a symbol period 1 / Fs;
A signal synthesizer that demodulates the transmitted OFDM signal based on the digital signal output of the Fourier transform means;
A wireless receiver comprising:
Said image signal, a frequency interval between the target signal is the n · Fs, n is n ≠ K · G (K is an arbitrary integer) Ri integer der satisfying,
An image signal having a frequency interval with the target signal of m · Fs (where m = K · G) has a frequency interval with the target signal of n · Fs (where n ≠ K · G). A frequency converter for frequency converting the received signal,
A synthesizer that synthesizes the received signal and the received signal frequency-converted by the frequency converter;
A wireless receiver. Having a notification means for notifying the communication partner of the G value;
The wireless receiver according to claim 8 . Having a notification means for notifying the frequency at which the communication partner should transmit the image signal;
The wireless receiver according to claim 8 . The Fourier transformer and the A / D converter are configured by a reconfigurable device, and the G value is variable.
The radio receiver according to any one of claims 8 to 10 . The image component is a G-1 wave,
The frequency of the image component is selected such that the remainder obtained by dividing the frequency interval n · Fs between the target signal and the image component by G · Fs takes all of Fs to (G−1) · Fs.
The radio receiver according to any one of claims 8 to 11 . A wireless transmitter for transmitting both a target signal which is a target OFDM signal and an image signal of the target signal;
Said image signal, the frequency interval between the target signal is a n · Fs, n is n ≠ K · G (K is an arbitrary integer, G is an integer of 2 or more) Ri integer der satisfying,
An OFDM modulator that generates the target signal and the image signal by an inverse Fourier transformer of M · G times (M is an integer) times the number of subcarriers of the OFDM signal;
A D / A converter that performs sampling processing at a sampling frequency M, G, and Fs to convert it into an analog signal;
A filter for removing signals other than the target signal and the image signal;
A wireless transmitter. Based on the G value notified from the communication partner, the frequency at which the image signal is transmitted is determined so that the frequency interval between the image signal and the target signal is n · Fs (n ≠ K · G).
The wireless transmitter according to claim 13 . Send the image signal at the transmission frequency of the image signal notified from the communication partner,
The wireless transmitter according to claim 13 or 14 . The image component is a G-1 wave,
The frequency of the image component is selected such that the remainder obtained by dividing the frequency interval n · Fs between the target signal and the image component by G · Fs takes all of Fs to (G−1) · Fs.
The wireless transmitter according to any one of claims 13 to 15 . For the frequency band to be used, it has a radio wave detector that determines whether there is a radio wave transmitted from another wireless transmitter,
The target signal and the image signal are transmitted in a frequency band that is not used by another wireless transmitter.
The wireless transmitter according to any one of claims 13 to 16 . An OFDM modulator that generates the target signal by an inverse Fourier transformer of the number of subcarriers of the OFDM signal;
A D / A converter for sampling the target signal at a sampling frequency Fs and converting it into an analog signal;
A filter for removing signals other than the target signal and the image signal;
Comprising a radio transmitter according to any one of claims 13-17.

Images