JP2007074351A - Multicarrier wireless communication system, transmitter and receiver, and multicarrier wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multicarrier wireless communication system, a transmitter and a receiver, and a multicarrier wireless communication method capable of reducing deterioration in propagation path estimate accuracy eminently appearing in a subcarrier located at a high frequency region among all subcarriers in a frequency band while suppressing an increase in a circuit scale. <P>SOLUTION: The wireless transmitter includes a dummy carrier attaching means for attaching a dummy carrier to a data carrier used at data transmission in the case of transmission of a propagation path estimate symbol for measuring a frequency response of a propagation path and transmitting the resulting data carrier to the wireless receiver, and the wireless receiver includes: a propagation path estimate means for obtaining the frequency response of the propagation path on the basis of the propagation path estimate symbol; a dummy carrier separation means that separates the frequency response into a frequency response of a part corresponding to the dummy carrier and a frequency response of a part corresponding to the data carrier; and a data demodulation means for demodulating the data by utilizing the frequency response of the part corresponding to the data carrier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multicarrier wireless communication system, a transmitter and a receiver, and a multicarrier wireless communication method represented by OFDM (Orthogonal Frequency Division Multiplexing).

In recent years, the number of users seeking to increase the speed of wireless communication systems has increased, and a multi-carrier transmission system typified by OFDM has attracted attention as one of the systems that can achieve higher speed and higher capacity.
The OFDM system is a system in which tens to thousands of carriers are arranged at a minimum frequency interval where theoretically no interference occurs and information signals are transmitted in parallel by frequency division multiplexing. This OFDM scheme has the advantage that if the number of subcarriers used is increased, the symbol time becomes longer than that of a single carrier scheme having the same transmission rate, so that it is less susceptible to multipath interference.

However, in a multipath environment, each subcarrier is subjected to different amplitude fluctuations and phase fluctuations, and therefore it is necessary to compensate for these fluctuations when demodulating data on the receiving side. In this propagation path compensation method, a signal (pilot signal) having a known amplitude and phase is transmitted using all or part of the subcarrier on the transmission side, and each subcarrier is received from the received pilot signal on the reception side. Estimate propagation path variations and compensate for them.
The configuration of a conventional OFDM demodulator will be described below (Patent Document 1, etc.).

FIG. 7 is a block diagram showing a configuration of a conventional OFDM demodulator. A signal received by the antenna unit 1000 is first frequency-converted by the radio reception unit 1001 to a frequency band where A / D (Analog / Digital) conversion is possible. The data converted into the digital signal by the A / D conversion unit 1002 is OFDM symbol synchronized by the synchronization unit 1003, and the guard interval is removed by the GI (Guard Interval) removal unit 1004.
Thereafter, a Fourier transform is performed in the Fourier transform unit 1005 and separated into signals for each subcarrier. Pilot extraction section 1006 extracts a pilot signal inserted for propagation path estimation from the signal after Fourier transform (here, a scattered pilot scheme is assumed). The extracted received pilot signal is divided by a dividing unit 1007 with a known pilot signal generated by a pilot generating unit 1008. By the division in the division unit 1007, the propagation path fluctuation of the pilot signal in the frequency domain can be obtained as the amplitude value and the phase value of the propagation coefficient.

Next, after inserting zeros into samples other than the pilot signal in the zero insertion unit 1009, inverse Fourier transform is performed in the inverse Fourier transform unit 1010, and the channel variation in the frequency domain is the channel variation (impulse response) in the time domain. Is converted to In this impulse response, the low sample removal unit 1011 performs processing to replace samples whose magnitude is below a certain threshold with 0, and then replaces samples exceeding a predetermined time (number of samples) with 0 in the time window unit 1012. It is done. This process is to remove signals other than the pilot signal and the delayed signal of the pilot signal converted into an impulse response, so that signals below a certain threshold value are treated as noise, and signals exceeding a predetermined time are also treated as noise. Is to be deleted.
The Fourier transform unit 1013 performs Fourier transform on the output of the time window unit 1012 to obtain a frequency domain propagation path variation in which samples other than the pilot signal have values, and the propagation path compensation unit 1014 performs a Fourier transform unit. Propagation path compensation using the output of 1013 is performed. The data compensated in this way is decoded by the error correction decoding unit 1015 to obtain data.

In the example shown in FIG. 7, the low sample removal unit 1011 and the time window unit 1012 remove noise components and interference components to obtain a highly accurate propagation path estimation value.
However, in the configuration shown in this example, since the output bandwidth (number of output samples) of the zero insertion unit 1009 is narrower (smaller) than the input bandwidth (number of input samples) of the inverse Fourier transform unit 1010, the inverse Fourier The output of the conversion unit 1010 becomes an impulse response having a side lobe component.
Also, when the reception timing of the signal arriving at the receiver does not coincide with the time sample timing, the output of the inverse Fourier transform unit 1010 becomes an impulse response having a side lobe component. That is, the impulse response is not simply attenuated, but becomes a response having secondary peaks on several frequency axes.

  When an impulse response having such a side lobe component is input to the low sample removal unit 1011 or the time window unit 1012, the side lobe component is removed, and as a result, obtained as an output of the Fourier transform unit 1013. Distortion occurs in the propagation path fluctuation in the frequency domain. Such distortion of channel fluctuation appears particularly prominently in subcarriers located in a high frequency region among all subcarriers in the band, and causes deterioration in channel estimation accuracy in those subcarriers.

As a solution to this problem, a technique described in Patent Document 2 is known. This point will be described below.
FIG. 8 is a block diagram illustrating a configuration of the propagation path estimation unit 1112 (modification of the propagation path estimation unit 1016 in FIG. 7). The propagation path estimation unit 1112 includes a pilot extraction unit 1101, a division unit 1102, a pilot generation unit 1103, a zero insertion unit 1104, a frequency window multiplication unit 1105, an inverse Fourier transform unit 1106, a low sample removal unit 1107, a time window unit 1108, A Fourier transform unit 1109 and a frequency window division unit 1110 are included.

  The propagation path estimation unit 1112 shown in FIG. 8 has a configuration in which a frequency window multiplication unit 1105 and a frequency window division unit 1110 are added to the propagation path estimation unit 1016 shown in FIG. The functions of other pilot extraction section 1101, division section 1102, pilot generation section 1103, zero insertion section 1104, inverse Fourier transform section 1106, low sample removal section 1107, time window section 1108, and Fourier transform section 1109 are shown in FIG. Since it is the same as the pilot extraction unit 1006, division unit 1007, pilot generation unit 1008, zero insertion unit 1009, inverse Fourier transform unit 1010, low sample removal unit 1011, time window unit 1012, and Fourier transform unit 1013 of the path estimation unit 1016. Those explanations are omitted.

In FIG. 8, the frequency window function multiplier 1105 multiplies the window function (this window function uses a type of function having an effect of suppressing side lobes, such as a Hamming function), and thereby the inverse Fourier transform unit 1106. It is possible to suppress the side lobe component of the impulse response output from, and as a result, the distortion of propagation path fluctuation in the frequency domain output from the Fourier transform unit 1109 is reduced.
Japanese Patent No. 3044899 JP 2005-130485 A

  However, in the configuration of the propagation path estimation unit shown in FIG. 8, a frequency window multiplication unit 1105 and a frequency window division unit 1110 are added to the configuration shown in FIG. That is, there is a problem that the degree of integration increases or the power consumption increases when the circuit is integrated into a semiconductor.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to estimate a propagation path that appears prominently in subcarriers located in a high frequency region among all subcarriers in the band while suppressing an increase in circuit scale. An object of the present invention is to provide a multicarrier radio communication system, a transmitter and a receiver, and a multicarrier radio communication method capable of reducing deterioration in accuracy.

  The present invention has been made to solve the above problems, and is a multi-carrier wireless communication system including a wireless transmitter and a wireless receiver, wherein the wireless transmitter propagates between the wireless receivers. A dummy carrier adding means for adding a dummy carrier to a data carrier used at the time of data transmission and transmitting to the radio receiver when transmitting a propagation path estimation symbol for measuring the frequency response of the path; The wireless receiver is obtained by a propagation path estimation means for obtaining a frequency response of a propagation path with the wireless transmitter based on a propagation path estimation symbol received from the wireless transmitter, and the propagation path estimation means. Dummy carrier separation means for separating a frequency response of a portion corresponding to the dummy carrier and a frequency response of a portion corresponding to the data carrier from a frequency response; It is over carrier separating means and having a data demodulation means for demodulating the utilizing frequency response of the portion corresponding to the separate data carrier data.

  Also, the present invention is characterized in that the dummy carrier adding means adds the dummy carrier at the same frequency interval to frequency bands on both outer sides of the frequency band of the data carrier.

  Further, the present invention is characterized in that the dummy carrier adding means adds the same number of dummy carriers to frequency bands on both outer sides of the frequency band of the data carrier.

  Further, the present invention is characterized in that the dummy carrier adding means adds the dummy carrier so that the peak-to-average power ratio of the propagation path estimation symbol is lower than before adding the dummy carrier.

  In addition, the present invention provides a wireless communication method in which a dummy carrier is added to a data carrier used at the time of data transmission when transmitting a propagation path estimation symbol for measuring a frequency response of a propagation path with a wireless receiver. A dummy carrier adding means for transmitting to the receiver is provided.

  Further, the present invention provides a propagation path estimation means for obtaining a frequency response of a propagation path with the wireless transmitter based on a propagation path estimation symbol received from the wireless transmitter, and the propagation path estimation means. A dummy carrier separating means for separating a frequency response of a portion corresponding to the dummy carrier and a frequency response of a portion corresponding to the data carrier from a frequency response; and a portion corresponding to the data carrier separated by the dummy carrier separating means And a data demodulating means for demodulating data using the frequency response.

  The present invention is also a multi-carrier wireless communication method for performing communication between a wireless transmitter and a wireless receiver, the propagation for measuring a frequency response of a propagation path between the wireless receiver and the wireless receiver. A first step of transmitting a dummy carrier to a data carrier used at the time of data transmission when transmitting a path estimation symbol, and transmitting from the wireless transmitter to the wireless receiver; and a propagation received from the wireless transmitter Corresponding to the dummy carrier from the second step of obtaining the frequency response of the propagation path with the radio transmitter based on the path estimation symbol by the radio receiver and the frequency response obtained in the second step A third step of separating a frequency response of a portion and a frequency response of a portion corresponding to the data carrier by the wireless receiver; and for data separated in the third step Wherein the Yaria using a frequency response of the corresponding portion and a fourth step of demodulating the data by the wireless receiver.

In the present invention, when transmitting the propagation path estimation symbol for measuring the frequency response of the propagation path to the wireless receiver by the dummy carrier adding means of the wireless transmitter, the data carrier used at the time of data transmission is transmitted. Then, a dummy carrier was added and transmitted to the wireless receiver. Further, the propagation path estimation means of the wireless receiver obtains the frequency response of the propagation path to the wireless transmitter based on the propagation path estimation symbol received from the wireless transmitter, and the dummy carrier separation means The frequency response of the corresponding part and the frequency response of the part corresponding to the data carrier are separated, and the data demodulation means performs data demodulation using the frequency response of the part corresponding to the data carrier.
As a result, when transmitting a propagation path estimation symbol for measuring the frequency response of the propagation path, a dummy carrier is added to the area where distortion occurs with respect to the data carrier transmitted from the wireless transmitter by the dummy carrier addition means. Then, by transmitting from the wireless transmitter, it is possible to estimate the propagation path using the propagation path estimation symbol by the propagation path estimation means, and to generate a distortion in the dummy carrier, Distortion can be prevented from occurring. Therefore, it is possible to prevent the estimation accuracy of the propagation path from deteriorating and to receive a data carrier free from distortion by separating the dummy carrier and the data carrier by the dummy carrier separation means. it can. In addition, since it is not necessary to provide a frequency window multiplying circuit or a frequency window dividing circuit, it is possible to prevent the circuit scale from increasing.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The multi-carrier wireless communication method according to the present embodiment reduces the degradation of the propagation path estimation accuracy by reducing the distortion at the band edge that occurs during propagation path estimation by the time window method. As shown in the above-mentioned conventional example, the time window method is converted to the frequency domain after receiving the pilot signal, and after multiplying by the complex conjugate of the code used at the time of transmission (multiplying the complex conjugate of the code used at the time of transmission is The pilot signal is converted to an impulse signal by converting to the time domain (substantially equivalent to dividing by the code used during transmission), and noise components other than the impulse signal are deleted by using the time window. Then, it is a method of obtaining propagation path information by converting to the frequency domain.

  When DFT (Discrete Fourier Transform) / IDFT (Inverse Discrete Fourier Transform) is used for the conversion between the time axis signal and the frequency axis signal, the carrier of the pilot signal is used for all processing points of DFT / IDFT. When is set, the signal converted to the time axis signal becomes one impulse, but when the pilot signal carrier is not set at all DFT / IDFT processing points (non-Nyquist sampling state), time window processing is performed. There is a problem in that distortion occurs at both band ends of the pilot signal when performing. In an actual circuit, from the viewpoint of calculation speed and circuit scale, FFT (Fast Fourier Transform) / IFFT (Inverse) in which the processing point is a number based on 2 is used for the conversion between the time axis signal and the frequency axis signal. Fast Fourier Transform) is often used.

FIG. 1 is a diagram for explaining the principle that distortion occurs in an OFDM received signal.
FIG. 1A shows a signal obtained by multiplying a frequency axis signal of a pilot signal received in an ideal state without multipath by a complex conjugate of a code used at the time of transmission, and FIG. 1B shows a time window. This is converted to the frequency axis. As shown in FIG. 1A, since the pilot signal is not arranged at all the DFT / IDFT processing points, it is expressed to have a finite band.
Time window processing is processing that multiplies the pilot signal multiplied by the complex conjugate to the time axis, and multiplies the time window waveform on the time axis. When this processing is expressed on the frequency axis, the pilot multiplied by the complex conjugate This is a process of convolving the frequency signal of the time window with the frequency signal of the signal. A waveform obtained by convolving the waveform shown in FIG. 1A and the waveform shown in FIG. 1B is the waveform shown in FIG.

As shown in FIG. 1C, when the band of the pilot signal is finite, the band edge of the output signal is distorted when time window processing is performed. Since this distortion is a component not included in the original pilot signal, the propagation path estimation result is also distorted.
The multi-carrier wireless communication method according to the present embodiment pays attention to this point, and is generated when the pilot signal band is increased by adding a dummy carrier to the pilot signal at the time of transmission and noise removal processing is performed by the time window method at the time of reception. By concentrating the distortion to be performed at the position of the dummy carrier and removing the dummy carrier, the distortion is prevented from being added to the propagation path estimation result of the band used for data transmission.

FIG. 2 is a block diagram illustrating a configuration of the multicarrier radio transmitter according to the present embodiment. This multicarrier wireless transmitter includes an error correction coding unit 201, an S / P (Serial / Parallel) conversion unit 202, a mapping unit 203, an IFFT unit 204, a P / S (Parallel / Serial) conversion unit 205, a switch unit 206, A pilot signal generation unit 207, a GI insertion unit 208, a D / A conversion unit 209, a radio unit 210, and an antenna unit 211 are included.
The error correction code unit 201 performs an error correction code encoding process on the communication data. The S / P converter 202 performs serial-parallel conversion on the signal after error correction coding. The mapping unit 203 determines which bit is assigned to which carrier. The IFFT unit 204 performs inverse fast Fourier transform on the mapped data to change it into a time axis signal.

The P / S conversion unit 205 performs parallel-serial conversion on the signals after the inverse fast Fourier transform processing and rearranges them in time series. The switch unit 206 switches between a pilot signal and a signal obtained by modulating data. The pilot signal generation unit 207 is a block that generates a pilot signal. Details will be described later with reference to FIG.
The GI insertion unit 208 adds a guard interval to the OFDM symbol. The D / A conversion unit 209 converts the digital signal into analog. The radio unit 210 converts the baseband signal into a frequency that is actually used, and amplifies it to a predetermined output for transmission from the antenna.
The antenna unit 211 is an antenna unit including a transmission antenna.

  When transmitting data, first, the switch unit 206 switches to the pilot signal generation unit 207 side and sends a pilot signal for one OFDM symbol to the GI insertion unit 208. Next, the switch unit 206 is switched to the OFDM signal side, and the OFDM symbol generated according to the communication data using the path from the error correction code unit 201 to the P / S conversion unit 205 is sent to the GI insertion unit. The GI insertion unit 208 adds a GI to the transmitted signal and sends the signal to the D / A conversion unit 209, and then passes through the radio unit 210 and the antenna unit 211 to add the pilot signal generated by the pilot signal generation unit. A signal is transmitted.

FIG. 3 is a configuration diagram of the pilot signal generation unit 207 (FIG. 2) of the multicarrier radio transmitter according to the present embodiment. In FIG. 3, pilot signal generation section 207 has S / P conversion 301, multiplication section 303, IFFT section 304, and P / S conversion section 305.
The S / P converter 301 parallelizes the input signal in order to process each subcarrier. Multiplier 303 spreads the data of each subcarrier. The IFFT unit 304 performs inverse fast Fourier transform processing that reads data of each subcarrier and converts it into a time axis waveform. The P / S conversion unit 305 converts the parallel signal after the inverse fast Fourier transform processing into serial data.

The S / P converter 301 prepares data for the number of subcarriers used for the pilot signal. The S / P converter 301 always receives a 1 + j0 signal. This 1 + j0 means a signal having a real part size of 1 and an imaginary part size of 0. Therefore, 1 + j0 is supplied to all subcarriers. The number of subcarriers used in the pilot signal is equal to the number of subcarriers N used in data transmission plus the number of dummy carriers added.
In this embodiment, two dummy carriers are added to both sides of the band. Subsequently, the multiplier 303 spreads the data of each carrier using the random number ρ. The multiplier 303 is composed of the same number of complex multipliers as the number of subcarriers to be used, and can multiply the signal of each subcarrier by a value according to the random number ρ. In principle, this random number ρ may be anything, but here it is a random number of length N. As the random number used for the dummy carrier, a value obtained by circulating ρ as shown in FIG. 3 is used.

  The output of the multiplication unit 303 is input to the IFFT unit 304. The IFFT unit 304 uses a minimum power-of-two processing point number M greater than the number of carriers N + 4 including dummy carriers. Zero data is set at the M− (N + 4) point where there is no carrier data input. If the data is set so that it is evenly arranged on both the positive and negative points with the zero point as the center, and the inverse fast Fourier transform process is performed, a pilot signal having the spectrum shown in FIG. 4 can be generated. Region a in FIG. 4 shows carriers used during data transmission, and region b shows dummy carriers arranged. The area between the area a and the area b is an unused carrier area. However, all the areas may be assigned dummy carriers, and in this case, the area b is filled. The signals input to the IFFT unit 204 do not necessarily have to be uniformly arranged around the 0th point. However, in this embodiment, the baseband signal band is not biased, and other designs such as filters are easier. It shall be arranged symmetrically.

By transmitting a pilot signal of such a spectrum and using it with a multicarrier radio receiver having the configuration shown in FIG. 5 described later, distortion can be reduced on the receiving side.
In this embodiment, the random number multiplied by the dummy carrier is used by circulating the original random number ρ, but any random number may be used. Therefore, it is possible to adjust the random number to reduce the peak-to-average power ratio (PAPR) of the pilot signal.
As an example, a case where the number of subcarriers used for data transmission is 24, the number of dummy carriers is 4, and the number of fast Fourier transform points is 32 will be described. [1, -1,1, -1, -1, -1, -1, -1,1, -1, -1,1, -1, -1, -1, -1, -1, -1, -1, The sequence 1,1,1,1,1, -1, −1] is used. Using data including dummy carriers generated by circulating ρ, the IFFT unit 304 [-1, 1, -1, -1, 1, -1, 1, 1, 1, 1, -1, −1,1, −1,0,0,0,0, −1, −1,1, −1,1, −1, −1, −1, −1,1,1, −1,1, −1] is set to a pilot signal PAPR of 4.7173, and the dummy carrier value is adjusted to obtain [−1, −1, −1, −1, 1, −1, 1, 1]. , 1, 1, -1, -1, 1, -1, 0, 0, 0, 0, -1, -1, 1, -1, 1, -1, -1, -1, -1, 1 , 1, -1, 1, -1] has a PAPR of 4.6609, and the PAPR can be lowered by adjusting the dummy carrier value.
Note that the data is set in the IFFT unit 304 in the order of subcarrier 17 starting with two unused carriers (0 is set), two dummy carriers, the first to twelfth random numbers ρ, and subcarrier 1 Returning to No. 13, the random numbers ρ are 13th to 24th, two dummy carriers, and two unused carriers.

  FIG. 5 is a block diagram showing the configuration of the multicarrier radio receiver according to the present embodiment. This multicarrier radio receiver includes an antenna unit 401, a radio reception unit 402, an A / D conversion unit 403, a synchronization unit 404, a GI removal unit 405, an S / P conversion unit 406, an FFT unit 407, a code multiplication unit 408, a code A selection unit 409, an IFFT unit 410, a time window unit 411, an FFT unit 412, a propagation path estimation unit 413, a data demodulation unit 414, and a dummy carrier deletion unit 415 are provided.

The antenna unit 401 converts the received radio wave into an electric signal. The radio reception unit 402 converts a received RF (Radio Frequency) signal into a baseband signal. The A / D conversion unit 403 converts an analog baseband signal into digital.
Synchronizing section 404 performs OFDM symbol synchronization using a pilot signal in the baseband signal. The GI removal unit 405 removes the card interval from the received signal. The S / P converter 406 performs serial-parallel conversion on the input signal.
The FFT unit 407 changes the time axis signal to the frequency axis signal. The code multiplier 408 performs a despreading process for multiplying the signal of each carrier by the code output from the code selector 409. The code selection unit 409 generates a complex conjugate of the code used on the multicarrier radio transmitter side.

The IFFT unit 410 converts a signal on the frequency axis into a signal on the time axis. The time window unit 411 removes unnecessary signals by setting a window on the time axis. The FFT unit 412 performs fast Fourier transform processing for changing the signal subjected to the time window processing into a signal on the frequency axis again.
The propagation path estimation unit 413 estimates a propagation path using the output of the dummy carrier deletion unit 415. Data demodulation section 414 demodulates received data from the output of FFT section 407 and the output of propagation path estimation section 412. The dummy carrier deletion unit 415 deletes the dummy carrier from the output of the FFT unit 412.

  Next, the whole of FIG. 5 will be described. A signal received from the antenna unit 401 is converted into a baseband by the wireless reception unit 402 and converted into a digital signal by the A / D conversion unit 403. The synchronization unit 404 performs synchronization for each OFDM symbol in order to remove the guard interval. Any method is good, and if it can be synchronized, the result will not be affected. As an example, a method of examining a cross-correlation between a known pilot signal and a received signal using a correlator and using a place where the correlation is the highest as a reference can be considered.

Next, the GI removal unit 405 removes the guard interval. The signal after removal of the guard interval is parallelized by the S / P converter 406 so that it can be fast Fourier transformed. This signal is converted into a signal on the frequency axis by the FFT unit 407 and decomposed for each subcarrier. Up to this point, the pilot signal and the data signal are processed in the same way.
The pilot signal is decomposed into signals for each subcarrier, and then sent to the code multiplier 408. The code multiplier 408 performs despreading processing for multiplying the signal of each subcarrier by the complex conjugate of the code used at the time of transmission generated by the code selector 409. The result after despreading is a frequency response including a dummy carrier and noise. Processing for reducing noise is performed in the subsequent processing.

  The IFFT unit 410 performs inverse fast Fourier transform processing to convert it into a time axis signal. The converted signal becomes an impulse response including a dummy carrier and noise. A time window is applied to the impulse response by the time window unit 411, and signals other than the impulse signal are deleted. Although any time width can be applied to the time window, in the present embodiment, the signal passes through the same time as the GI length where most of the delay wave is supposed to be centered around t = 0, and the remaining time is the signal. Set the window width to set to 0. The signal after noise removal is converted again to a signal on the frequency axis by FFT 412. This state is a frequency response in which noise is reduced and distortion is generated in the vicinity of the dummy carrier due to the influence of the time window. Therefore, the dummy carrier deletion unit 415 deletes the dummy carrier before sending it to the propagation path estimation unit 413. In the signal sent to the propagation path estimation unit 413, noise is reduced by the time window, and distortion generated in the time window is also reduced.

  FIG. 6 is a diagram illustrating a waveform of a signal processed by the multicarrier radio receiver according to the present embodiment. FIG. 6A shows the received baseband signal. 6B, symbol synchronization is performed by the synchronization unit 404 (FIG. 5), the pilot signal from which the guard interval is removed by the GI removal unit 405 is converted into a signal on the frequency axis by the FFT unit 407, and the code multiplication unit. This is a signal after despreading at 408. FIG. 6C is an outline of a time window process to be applied to a signal after being converted into a signal on the time axis by the IFFT unit 410. As a result of the inverse fast Fourier transform, the pilot signal including the delayed wave is converted into an impulse-like signal centered at t = 0, whereas the noise component spreads over all the time. Can be deleted.

FIG. 6D shows a signal after performing fast Fourier transform after time window processing. This signal includes a dummy carrier with a distortion component. FIG. 6E shows a signal that is deleted from the dummy carrier and is finally input to the propagation path estimation unit 413. In the signal input to the propagation path estimation unit 413, the noise component is reduced by the time window unit 411, and the distortion at the band edge caused by the time window process is also reduced by deleting the dummy carrier.
The propagation path estimation unit 413 calculates a correction amount for each subcarrier based on the input propagation path information, and sends the correction data to the data demodulation unit 414. The data part sent following the pilot signal is similarly processed up to FFT 407. Thereafter, the data is input to the data demodulator 414, and demodulation and error correction are performed using the correction data from the propagation path estimator 413.
By operating as described above, it is possible to reduce distortion caused by time window processing at the time of propagation path estimation, and to correctly perform propagation path correction in subsequent data transmission.

  In the embodiment described above, the error correction coding unit 201, S / P (conversion unit 202, mapping unit 203, IFFT unit 204, P / S conversion unit 205, switch unit 206, pilot signal generation unit 207 in FIG. , GI insertion unit 208, D / A conversion unit 209, radio unit 210, S / P conversion 301 in FIG. 3, multiplication unit 303, IFFT unit 304, P / S conversion unit 305, radio reception unit 402 in FIG. / D conversion unit 403, synchronization unit 404, GI removal unit 405, S / P conversion unit 406, FFT unit 407, code multiplication unit 408, code selection unit 409, IFFT unit 410, time window unit 411, FFT unit 412, propagation A computer-readable description of a program for realizing the functions of the path estimation unit 413, the data demodulation unit 414, the dummy carrier deletion unit 415, or a part of these functions The multi-carrier radio transmitter and the multi-carrier radio receiver may be controlled by recording on a medium and causing the computer system to read and execute the program recorded on the recording medium. The “computer system” includes an OS and hardware such as peripheral devices.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” dynamically holds a program for a short time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, it is also assumed that a server that holds a program for a certain time, such as a volatile memory inside a computer system that serves as a server or client. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and a design and a general multi-carrier system without departing from the gist of the present invention. Extensions to are also included.

It is a figure for demonstrating the principle which distortion generate | occur | produces in an OFDM received signal. It is a block diagram which shows the structure of the multicarrier radio | wireless transmitter by embodiment of this invention. It is a block diagram of the pilot signal generation part 207 of the multicarrier radio | wireless transmitter by this embodiment. It is a figure which shows an example of the pilot signal produced | generated by the multicarrier radio transmitter of this embodiment. It is a block diagram which shows the structure of the multicarrier radio | wireless receiver by this embodiment. It is a figure which shows the waveform of the signal processed with the multicarrier radio | wireless receiver by this embodiment. It is a block diagram which shows the structure of the demodulator of the conventional multicarrier system. It is a block diagram which shows another structure of the propagation path estimation part in the demodulator of the conventional OFDM system.

Explanation of symbols

301 ... S / P conversion, 303 ... multiplication unit, 304 ... IFFT unit, 305 ... P / S conversion unit, 201 ... error correction code unit, 202 ... S / P conversion , 203... Mapping section, 204... IFFT section, 205... P / S conversion section, 206... Switch section (dummy carrier adding means in claims), 207. 208 ... GI insertion unit, 209 ... D / A conversion unit, 210 ... radio unit, 211 ... antenna unit, 401 ... antenna unit, 402 ... radio reception unit, 403 ..A / D conversion unit, 404... Synchronization unit, 405... GI removal unit, 406... S / P conversion unit, 407... FFT unit (dummy carrier separation means in claims), 408 ... Sign multiplier, 409 ... sign selection , 410 ... IFFT section, 411 ... time window section, 412 ... FFT section, 413 ... propagation path estimation section (propagation path estimation means in claims), 414 ... data demodulation section (billing) 415... Dummy carrier deletion unit, 1000... Antenna unit, 1001... Radio reception unit, 1002... A / D conversion unit, 1003. ..GI removal unit, 1005 ... Fourier transform unit, 1006 ... Pilot extraction unit, 1007 ... Division unit, 1008 ... Pilot generation unit, 1009 ... Zero insertion unit, 1010 ... Reverse Fourier transform unit, 1011 ... low sample removal unit, 1012 ... time window unit, 1013 ... Fourier transform unit, 1014 ... propagation path compensation unit, 1015 ... error correction decoding unit DESCRIPTION OF SYMBOLS 1100 ... Fourier-transform part, 1101 ... Pilot extraction part, 1102 ... Division part, 1103 ... Pilot generation part, 1104 ... Zero insertion part, 1105 ... Frequency window multiplication part, 1106. ..Inverse Fourier transform unit, 1107 ... low sample removal unit, 1108 ... time window unit, 1109 ... Fourier transform unit, 1110 ... frequency window division unit, 1111 ... channel compensation unit

Claims (7)

A multi-carrier wireless communication system comprising a wireless transmitter and a wireless receiver,
The wireless transmitter is
When transmitting a propagation path estimation symbol for measuring the frequency response of the propagation path to and from the wireless receiver, a dummy carrier is added to the data carrier used when transmitting data and transmitted to the wireless receiver. A dummy carrier adding means for
The wireless receiver
Propagation path estimation means for obtaining a frequency response of a propagation path with the wireless transmitter based on the propagation path estimation symbol received from the wireless transmitter;
Dummy carrier separation means for separating the frequency response of the portion corresponding to the dummy carrier and the frequency response of the portion corresponding to the data carrier from the frequency response obtained by the propagation path estimation means;
A multicarrier wireless communication system comprising: data demodulating means for demodulating data using a frequency response of a portion corresponding to the data carrier separated by the dummy carrier separating means. The dummy carrier adding means is
The multi-carrier wireless communication system according to claim 1, wherein the dummy carriers are added to the frequency bands on both outer sides of the data carrier frequency band at the same frequency interval. The dummy carrier adding means is
The multicarrier wireless communication system according to claim 1 or 2, wherein the same number of dummy carriers are added to frequency bands on both outer sides of the frequency band of the data carrier.   The dummy carrier adding means adds the dummy carrier so that a peak-to-average power ratio of a propagation path estimation symbol is lower than that before adding the dummy carrier. A multicarrier wireless communication system according to 1. A dummy that adds a dummy carrier to a data carrier used when transmitting data and transmits it to the wireless receiver when transmitting a propagation path estimation symbol for measuring the frequency response of the propagation path to the wireless receiver. A multicarrier radio transmitter comprising carrier addition means. Propagation path estimation means for obtaining a frequency response of a propagation path with the wireless transmitter based on the propagation path estimation symbol received from the wireless transmitter;
Dummy carrier separation means for separating the frequency response of the portion corresponding to the dummy carrier and the frequency response of the portion corresponding to the data carrier from the frequency response obtained by the propagation path estimation means;
Data demodulating means for demodulating data using the frequency response of the portion corresponding to the data carrier separated by the dummy carrier separating means;
A multi-carrier radio receiver comprising: A multi-carrier wireless communication method for performing communication between a wireless transmitter and a wireless receiver,
When transmitting a propagation path estimation symbol for measuring the frequency response of the propagation path to and from the wireless receiver, a dummy carrier is added to the data carrier used when transmitting the data, and the wireless transmitter A first step of transmitting to the receiver;
A second step of obtaining a frequency response of a propagation path between the wireless transmitter and the wireless transmitter based on the propagation path estimation symbol received from the wireless transmitter;
A third step of separating a frequency response of a portion corresponding to the dummy carrier and a frequency response of a portion corresponding to the data carrier from the frequency response obtained in the second step by the wireless receiver;
A fourth step of demodulating data by the wireless receiver using the frequency response of the portion corresponding to the data carrier separated in the third step;
A multi-carrier wireless communication method comprising:

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