JP2004241916A - Apparatus and system for interference suppression - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a system for interference suppression that enable guard intervals of an OFDM signal to be set short. <P>SOLUTION: The interference suppression apparatus is used for a receiving device which performs Fourier transformation of the OFDM signal. This device has a timing setting means of setting a first time frame and a second time frame for the Fourier transform, a first Fourier transforming means of performing the Fourier transform with the first time frame, a second Fourier transforming means of performing the Fourier transform with the second time frame set differently from the first time frame, and an adding means of generating an output signal by adding signals outputted from the first and second Fourier transforming means together by subcarriers of the OFDM signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the technical field of mobile communication, and in particular, to an interference suppression device for satisfactorily receiving a signal subjected to orthogonal frequency division multiplexing (OFDM) (hereinafter, referred to as an “OFDM signal”). And an interference suppression system.
[0002]
[Prior art]
In a mobile communication environment, a signal wirelessly transmitted from a transmitter is reflected by the ground, a building, or another obstacle, and reaches a receiver through a plurality of propagation paths. Therefore, it is necessary to construct a system that can receive signals well even in such a multipath propagation environment. The multi-carrier transmission scheme is a technique that meets such a purpose, and the orthogonal frequency division multiplexing (OFDM) scheme is particularly promising in the technical field.
[0003]
A signal transmitted by the OFDM scheme is composed of a series of OFDM symbol sequences, and each OFDM symbol includes a guard interval (GI) and an effective symbol section after that. In principle, the OFDM method enables a received signal to be restored with high quality if the delay amount between a plurality of paths (multipaths) included in the received signal is within a guard interval. I do. However, if there is a path arriving later than the guard interval in the received signal, the quality of the received signal is rapidly deteriorated due to intersymbol interference. Therefore, if the guard interval is set to include the delay amount for all paths, such a disadvantage may not occur. However, an excessively long guard interval is not preferable from the viewpoint of increasing the transmission capacity and effectively using the frequency.
[0004]
In this regard, as disclosed in Non-Patent Documents 1 and 2, there is a technique for reducing interference by a path arriving later than a guard interval using a multipath interference canceller (MPIC). However, such a method tentatively determines a signal of each subcarrier after demodulation, estimates a signal (replica) with little distortion by taking account of a channel estimation result, and uses the result to perform Fourier transform and demodulation again. It is necessary to perform processing and the like. Therefore, there is a problem that a calculation load for reducing interference is large, and a circuit scale, power consumption, and the like are also increased.
[0005]
[Non-patent document 1]
Uesugi, "Basic Performance of Multipath Interference Canceller for OFDM", 2002 General Conference of Electronic Information and Communication, B-5-182
[0006]
[Non-patent document 2]
Suyama, Suzuki, Fukawa, "OFDM Reception Method for Multipath Environment with Delay Profile Exceeding Guard Interval", 2002 General Conference on Electronics, Information and Communication, B-5-169
[0007]
[Problems to be solved by the invention]
An object of the present application is to provide an interference suppression device and an interference suppression system suitable for use in a receiving device compatible with the OFDM method.
[0008]
Another object of the present application is to provide an interference suppression apparatus and an interference suppression system capable of reducing a calculation load for reducing interference in a receiving apparatus that receives an OFDM signal, as compared with the related art.
[0009]
[Means for Solving the Problems]
According to the present invention,
An interference suppression device used in a receiving device that performs a Fourier transform of an OFDM signal,
Timing setting means for setting a first time frame and a second time frame for performing the Fourier transform;
First Fourier transform means for performing a Fourier transform in the first time frame;
A second Fourier transform unit that performs a Fourier transform in the second time frame that is set separately from the first time frame;
Adding means for forming an output signal by adding signals output from the first and second Fourier transform means for each subcarrier of the OFDM signal
Interference suppressing device characterized by having
Is provided.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
[First embodiment]
FIG. 1 shows a block diagram of a receiving apparatus including an interference suppressing apparatus according to the first embodiment of the present invention. The receiving apparatus 100 includes an antenna unit 102 for receiving a radio signal, and a radio unit 104 connected to the antenna unit 102. In the wireless unit 104, processing as a front end such as band limiting processing and frequency conversion is performed. The receiving device 100 has an analog-to-digital conversion unit 106 that converts an analog signal from the wireless unit 104 into a digital signal. The receiving apparatus 100 includes a timing section 108 connected to the output of the analog-to-digital conversion section 106, and performs timing determination on a path included in the OFDM signal. The receiving apparatus 100 has a fast Fourier transform unit 110 connected to an output of the analog-to-digital converter 106, and performs fast Fourier transform using timing information from the timing unit 108. The receiving device 100 includes a demodulation unit 112 connected to the output of the Fourier transform unit 110 and performing further demodulation processing. Mainly, the Fourier transform unit 110 and the timing unit 108 form an interference suppression device 114 according to the first embodiment of the present invention.
[0011]
The timing section 108 has a correlation section 116 that performs a correlation calculation using the output signal of the analog-to-digital conversion section 106. The timing section 108 has a timing determination section 118 connected to the output of the correlation calculation section 116. The timing determination unit 118 determines the timings and delay amounts of a plurality of paths included in the received signal based on the result of the correlation calculation. The timing section 108 has first and second FFT window setting sections 120 and 122 connected to the timing determination section 118. The first and second FFT window setting units 120 and 122 use a time frame for performing Fast Fourier Transform (FFT) by using timings regarding various paths determined by the timing determination unit 118 or Set the window. In the present embodiment, since Fourier transform is performed over two time frames, two FFT window setting units are prepared to set them.
[0012]
The Fourier transform unit 110 has a serial-to-parallel converter 124 connected to the output of the analog-to-digital converter 106, and converts the serial signal sequence from the analog-to-digital converter 196 into a plurality of signals related to the number of subcarriers. Convert to parallel signal series. The Fourier transform unit 110 has a first fast Fourier transform unit 126 connected to the parallel output of the serial-to-parallel transform unit 124, which is set by the first FFT window setting unit 120 for the parallel output. A fast Fourier transform is performed in a first time frame. The Fourier transform unit 110 has a second fast Fourier transform unit 128 connected to the parallel output of the serial-to-parallel transform unit 124, which is set by the second FFT window setting unit 122 for the parallel output. A fast Fourier transform is performed in a second time frame.
[0013]
The Fourier transform unit 110 includes a plurality of adders 130 that add the outputs from the first and second fast Fourier transform units 126 and 128 for each subcarrier. A phase adjuster 132 is provided between the second fast Fourier transform unit 128 and the adder 130 for each adder 130. The phase adjusted by the phase adjustment unit 132 is the time difference T between the first and second time frames.₀Is set based on By adjusting the phase by the phase adjusting unit 132, the signals subjected to the fast Fourier transform in different time frames can be added by the adding unit 130 in the same phase for each component. Note that each phase adjuster 132 uses a phase set for each subcarrier. Phase φ adjusted for i-th subcarrier_iIs
φ_i= 2πf_iT₀
Where f_iIs the frequency of the subcarrier and T₀Indicates the time difference between the first and second time frames. In this embodiment, the phase adjustment unit 132 is connected to the output of the second fast Fourier transform unit 128, but may be provided on the first fast Fourier transform unit 126 side. It is also possible to provide a phase adjustment unit for both outputs to adjust the phase. When the received signal is phase-modulated, the phase shift amount (for example, the phase shift amount corresponding to the length of the guard interval GI) corresponding to the difference between the start times of the first and second FFT processes is set to It is also necessary to compensate for each of the signals corresponding to the frequencies. In any case, it suffices if the outputs from the respective fast Fourier transform units can be added in the same phase by the adding unit 130 for each subcarrier. The Fourier transform unit 110 has a parallel-serial converter 134 connected to the output of each adder 130, which converts a parallel signal sequence into a serial signal sequence and provides it to the subsequent-stage demodulator 112. .
[0014]
Hereinafter, the operation in the present embodiment will be described with reference to FIGS. FIG. 2 is a diagram illustrating a relationship between an OFDM signal and a time frame of Fourier transform. For the sake of simplicity, it is assumed that two paths 202 and 204 exist in the OFDM signal, and the time difference between them falls within the category of the guard interval. Although two paths 202 and 204 are separately illustrated in the drawing, they are actually mixed in the OFDM signal.
[0015]
First, the timing determination unit 118 determines that two paths are included in the received signal by correlation calculation, and finds information on their timing. Based on this information, first FFT window setting section 120 sets first time frame W over a certain period from the end of guard interval Tg for the OFDM symbol of preceding path 202.₁Set. This fixed period is 1 / f which is an effective symbol section of the OFDM symbol.₀, Where f₀Is a frequency representing an interval between subcarriers. In the first fast Fourier transform unit 126, the first time frame W₁Fast Fourier transform is performed at the timing shown in FIG. In the present example, the received signal includes a preceding path 202 and a delayed path 204. For the preceding path 202, the effective symbol section and the first time frame W₁And match. For the delayed path 204, the effective symbol period and the first time frame W₁Does not match. However, the first time frame W₁The guard interval portion of the path 204 included in the above is a copy of the end portion of the succeeding effective symbol section. Therefore, the first time frame W₁, Only signals related to the same symbol exist. Therefore, the first fast Fourier transform unit 126 can perform the calculation without causing the inter-symbol interference and supply the output signal to the adding unit 130.
[0016]
On the other hand, in the second FFT window setting section 122, based on the information from the timing determination section 118, a second time frame W over a certain period from the beginning of the OFDM symbol of the delayed path 204₂Set. Even using such a time frame, it is possible to demodulate the received signal. This fixed period is also 1 / f which is an OFDM effective symbol section.₀Is equal to the period of In the second fast Fourier transform unit 128, the second time frame W₂Fast Fourier transform is performed at the timing shown in FIG. Regarding the two paths 202 and 204, the effective symbol section and the second time frame W₁Do not match, but it is possible to calculate the fast Fourier transform without causing intersymbol interference. This is because, as described above, the tail part of the succeeding effective symbol section is duplicated in the guard interval part of the OFDM symbol. Therefore, the second fast Fourier transform unit 128 can also provide the output signal to the adding unit 130 without being affected by the intersymbol interference.
[0017]
After that, the outputs from the fast Fourier transform units 126 and 128 are combined in phase by the adder unit 130 and the phase adjuster 132, and the serial signal sequence converted by the parallel / serial converter 134 is sent to the subsequent demodulator 112. Given.
[0018]
Next, of the paths 202 and 206 included in the received signal, the delay amount of the delayed path 206 is equal to the guard interval T._gIt is assumed that it exceeds. In this case, the first time frame W set by the first FFT window setting unit 120₁Is a fixed period (1 / f) from the end of the guard interval of the preceding path, as in the above case.₀). Therefore, for the preceding path 202, the first time frame W₁And the effective symbol section match. However, for the delayed path 206, the first time frame W₁Contains signals of adjacent symbols. For this reason, the influence of the intersymbol interference N_AWill be introduced.
[0019]
Second time frame W set by second FFT window setting section 122₂'Is a certain period (1 / f) from the beginning of the OFDM symbol of the delayed path 206.₀). For the delayed path 206, the second time frame W₂', Only signals related to the same symbol are included. However, for the preceding path 202, the second time frame W₂′ Include signals of adjacent symbols. Therefore, the output of the second fast Fourier transform unit 128 includes the influence N of the intersymbol interference._BIs introduced.
[0020]
The adder 130 adds signals affected by intersymbol interference. The added signal added by the adding unit 130 includes first and second time frames W₁, W₂'Includes a signal component S of the same symbol calculated in a common section of' and a noise component N due to intersymbol interference. The signal components S of the same symbol are added in the same phase by the adder 130 or the like, and can have a larger amplitude (ideally, twice) than before the addition. For the noise component N, the first time frame W₁Intersymbol interference component N introduced in FFT calculation by_AAnd the second time frame W₂', The intersymbol interference component N introduced in the FFT calculation by_BAre added. These intersymbol interference components N_A, N_BDoes not have any correlation, each inter-symbol interference component has an amplitude and a phase independent of each other. Even if the amplitude of the noise component increases after adding both, the increasing rate is not as large as the rate at which the amplitude of the signal component S increases. Therefore, the addition output from the addition unit 130 has better signal quality than the signal before addition, and has, for example, a good signal-to-noise ratio S / N and a good signal interference ratio S / (S + I).
[0021]
The effect of this embodiment is remarkable when the received signal includes a path arriving later than the guard interval as described above, but is also advantageous when the amount of delay falls within the category of the guard interval. It works. As described above, the first time frame W₁And the second time frame W₂Are out of time. Therefore, the first time frame W₁Noise component N introduced only by FFT calculation in_CAnd the second time frame W₂Noise component N introduced only by FFT calculation in_DAre not correlated with each other and have independent amplitude and phase. These thermal noise components N_DAnd N_CIs added, the amplitude related to the thermal noise component after the addition is smaller than the sum of the absolute values of the amplitudes before the addition. Therefore, according to the present embodiment, it is possible to suppress inter-symbol interference, thermal noise, and other noise components by performing in-phase addition of Fourier-transformed signals in different time frames.
[0022]
[Second embodiment]
FIG. 3 is a block diagram of a receiving device including the interference suppression device according to the second embodiment of the present invention. Receiving apparatus 300 has antenna section 302 for receiving a radio signal, and radio section 304 connected to antenna section 302. In the wireless unit 304, processing as a front end such as band limiting processing and frequency conversion is performed. The receiving apparatus 300 has an analog-to-digital conversion unit 306 that converts an analog signal from the wireless unit 304 into a digital signal. Receiving apparatus 300 has timing section 308 connected to the output of analog-to-digital conversion section 306, and performs timing determination on a path included in the OFDM signal. The receiving device 300 has a received signal compensating unit 312 connected to the output of the analog-to-digital converter 306 and compensating the received signal. The receiving apparatus 100 includes a Fourier transform unit 310 connected to an output signal of the received signal compensating unit 312, and performs a fast Fourier transform using timing information from the timing unit 308. The received signal compensator 312 corresponds to the interference suppression device according to the second embodiment of the present application.
[0023]
The received signal compensating unit 312 has an adding unit 314, and an output of the adding unit 314 is connected to the subsequent Fourier transform unit 310. Adder 314 has four inputs, one of which is connected to the output of main signal multiplier 316. The first multiplier 316 outputs a predetermined weight coefficient w to the output of the analog-to-digital converter 306.₀And output it. The received signal compensating unit 312 has a first delay unit 318, a second delay unit 320, and a third delay unit 322 connected in series, and an input of the first delay unit 318 is connected to an output of the analog-to-digital conversion unit 306. Connected. The first delay unit 318 converts the input signal into a predetermined first period T₁And the second delay unit 320 delays by a predetermined second period T₂Only, the third delay unit 322 performs a predetermined third period T₃Just delay.
[0024]
The received signal compensating unit 312 has a first multiplier 324 connected to the output of the first delay unit 318, which is configured to add a predetermined weighting factor w to the input signal.₁, And supplies the result to the second input of the adder 314. The received signal compensating unit 312 has a second multiplier 326 connected to the output of the second delay unit 320.₂, And supplies the result to the third input of the adder 314. The received signal compensating unit 312 has a third multiplier 328 connected to the output of the third delay unit 322.₃, And supplies the result to the fourth input of the adder 314.
[0025]
FIG. 4 is a diagram illustrating a relationship between two paths included in the OFDM signal. For convenience of explanation, it is assumed that the received signal includes two paths 402 and 404, and the delayed path 404 arrives later than the guard interval GI. The fast Fourier transform performed by the receiving apparatus 300 is performed in a predetermined time frame W₁This is performed for a fixed period (1 / f) corresponding to an effective symbol section from the end of the guard interval GI of the OFDM symbol of the preceding path 402.₀) Is set by the timing section 308.
[0026]
Predetermined time frame W₁Corresponds to the effective symbol section for the preceding path 402. However, a predetermined time frame W₁Contains the signal I of the adjacent symbol for the delayed path 404. In the FFT calculation in the fast Fourier transform unit 330, intersymbol interference occurs due to the signal I.
[0027]
By the way, in the OFDM symbol, a copy of the end of the effective symbol section following the guard interval forms the guard interval. Therefore, the signal I that causes intersymbol interference in the delayed path 404 is also included in the guard interval of the OFDM symbol including the signal I. This is shown as signal B. Further, the same signal I exists in the preceding path 402. One is that, for the signal I, the delay amount T between paths₁The signal A is a signal A at a time preceding the signal A by another, and the other is a signal C included in the guard interval of the OFDM symbol. As described above, the delay amount between the signal I and the signal A is the delay amount T between the paths.₁It is. The amount of delay between signal I and signal B is determined by the effective symbol period (1 / f₀), The delay amount T between this section and the path₁The difference from₂(T₂= 1 / f₀−T₁). Further, the amount of delay between the signal I and the signal C is determined by the effective symbol period (1 / f₀) And the amount of delay between paths (T₁). Note that the delay amount T between the signal B and the signal C is₃Is the amount of delay T between signal I and signal A₁be equivalent to. Thus, the same signal as signal I causing intersymbol interference can be obtained by delaying the received signal by a predetermined period. Therefore, if the received signal is appropriately delayed, weighted and added, the inter-symbol interference can be reduced.
[0028]
Referring to FIG. 3, first, the first delay unit 318 sets a delay amount T between paths.₁Just delay. Therefore, the first delay unit 318 and the first multiplication unit 324 correspond to a signal path in which interference is to be suppressed using the signal A of the preceding path 402. In the second delay unit 320, T₂Delay for a period of. As described above, the delay amount T between paths T₁And T₂Is added to the effective symbol section (1 / f₀). Therefore, the second delay unit 320 and the second multiplication unit 326 correspond to a signal path in which interference is to be suppressed by using the signal B of the path 404 that is delayed. In the third delay unit 322, T₃Delay for a period of. The third delay section 322 and the second multiplication section 328 correspond to a signal path in which interference is to be suppressed using the signal C of the preceding path 402.
[0029]
In the embodiment shown in FIG. 3, all the signal paths related to signals A, B, and C, which are the same as signal I causing intersymbol interference, are illustrated as being input to adder 314. Are not essential to the present invention, and some of them can be used.
[0030]
By the way, the time frame W for the fast Fourier transform assumed in FIG.₁Has been set to match the effective symbol section of the preceding path. However, it is also possible to perform the fast Fourier transform using a different time frame. For example, as described with reference to FIG. 2, the time frame may be a fixed period from the beginning of the delayed path.
[0031]
FIG. 5 shows such a time frame W₂'Is a diagram showing a relationship between two paths 502 and 504 included in an OFDM signal in the case of adopting'. In this case, the signal I in the guard interval of the preceding path 502 causes intersymbol interference. As described in FIG. 4, the same signal as the signal I exists in other parts. Since the signal I is a signal within the guard interval, the same signal B as the signal I exists at the end of the effective symbol section following the guard interval. In addition, the same signal I exists in the delayed path 504. One is that, for the signal I, the delay amount T between paths₁The signal A is a signal A at the point of time when the signal is delayed by another time, and the other is a signal C included at the end of the effective symbol section. The amount of delay between signal I and signal A is the amount of delay T between paths.₁It is. The amount of delay between signal I and signal B is determined by the effective symbol period (1 / f₀), The delay amount T between this section and the path₁The difference from₂(T₂= 1 / f₀−T₁). Further, the amount of delay between the signal I and the signal C is determined by the effective symbol period (1 / f₀) And the amount of delay between paths (T₁). Note that the delay amount T between the signal B and the signal C is₃Is the amount of delay T between signal I and signal A₁be equivalent to. Thus, the same signal as signal I causing intersymbol interference can be obtained by delaying the received signal by a predetermined period. Therefore, similarly to the case described with reference to FIG. 4, in this case, if the received signal is appropriately delayed, weighted and added, the inter-symbol interference can be reduced.
[0032]
FIG. 6 shows a modification of the received signal compensator. The reception signal compensating unit 612 includes an adding unit 614, and an output of the adding unit 614 is connected to a subsequent Fourier transform unit. Adder 614 has four inputs, one of which is connected to the output of main signal multiplier 616. The first multiplier 616 outputs a predetermined weight coefficient w to the output of the analog-to-digital converter.₀And output it. The received signal compensator 612 has a first delay 618, a second delay 620, and a third delay 622 connected in series, and an input of the first delay 618 is connected to an output of the analog-to-digital converter. Is done. The first delay unit 618 delays the input signal by a predetermined first period, the second delay unit 620 delays by a predetermined second period, and the third delay unit 622 delays the input signal by a predetermined third period.
[0033]
The received signal compensator 612 has a first multiplier 624 connected to the output of the first delay unit 618, which is configured to add a predetermined weight coefficient w to the input signal.₁, And supplies the result to the second input of the adder 614. The received signal compensator 612 has a second multiplier 626 connected to the output of the second delay unit 620, which is configured to add a predetermined weight coefficient w to the input signal.₂, And supplies the result to the third input of the adder 614. The received signal compensator 612 has a third multiplier 628 connected to the output of the third delay unit 622.₃, And supplies the result to the fourth input of the adder 614.
[0034]
Further, a first switch section 630 is provided between the output of the first delay section 618 and the first multiplier 624. Similarly, a second switch unit 632 is provided between the output of the second delay unit 620 and the second multiplier 626, and a third switch unit is provided between the output of the third delay unit 622 and the third multiplier 628. 634 are provided. The reception signal compensating unit 612 includes a control unit 636 that controls opening and closing of the first to third switch units 630 to 634 using timing information from the timing unit.
[0035]
As described with reference to FIGS. 4 and 5, the signal I causing the intersymbol interference occurs only within a certain period. That fixed period T_iIs the delay difference T between paths₁Guard interval T_gBy subtracting (T_i= T₁−T_g). Therefore, when the addition unit 614 adds the signals on the signal paths related to the signals A, B, and C, the addition is performed for a certain period (T_iControlling the opening and closing of the switch unit according to ()) is advantageous for suppressing interference. For example, only when a signal A having the same content as the signal I causing interference is obtained, the switch unit 630 can be closed and multiplied by a weight coefficient w1 for inverting the sign and input to the addition unit 614.
[0036]
Although the fast Fourier transform is shown to be performed after the adders 314 and 614 in the present embodiment, the fast Fourier transform can be performed before the addition. For example, a fast Fourier transform unit can be inserted between each of the multiplication units and the addition unit. Also, a fast Fourier transform unit can be provided between the output of each delay unit and the corresponding multiplication unit.
[0037]
[Third embodiment]
FIG. 7 is a block diagram of a receiving device including the interference suppressing device according to the third embodiment of the present invention. Generally, this embodiment is a combination of the first and second embodiments. Receiving apparatus 700 includes antenna section 702 for receiving a radio signal, and radio section 704 connected to antenna section 702. The wireless unit 704 performs processing as a front end such as band limiting processing and frequency conversion. Receiver 700 has an analog-to-digital converter 706 that converts an analog signal from wireless section 704 to a digital signal. Receiver 700 has a timing section 708 connected to the output of analog-to-digital converter 706, such as that shown in timing section 108 of FIG. 1, for determining the timing for the path included in the OFDM signal. And so on. Receiver 700 has a received signal compensator 710 connected to the output of analog-to-digital converter 706, which compensates for the received signal using timing information from timing section 708. The receiving device 700 includes a Fourier transform unit 712 that is connected to the output of the received signal compensating unit 710 and that performs fast Fourier transform using timing information from the timing unit 708. The receiving device 700 includes a demodulation unit 714 connected to the output of the Fourier transform unit 712 and performing demodulation processing.
[0038]
The received signal compensator 710 is connected to the output of the digital-to-analog converter 706 and has a first compensator 716 that compensates the received signal using the timing information from the timing unit 708. Similarly, the received signal compensating unit 710 has a second compensating unit 718 connected to the output of the digital-to-analog converting unit 706 and compensating the received signal using the timing information from the timing unit 708. The configuration of the first and second compensators 716 and 718 is the same as that of the received signal compensators 312 and 612 as shown in FIG. 3 or FIG.
[0039]
The fast Fourier transform unit 712 includes a first fast Fourier transform unit 720 connected to the output of the first compensating unit 716 and performing fast Fourier transform using timing information from the timing unit 708. Similarly, the fast Fourier transform unit 712 has a second fast Fourier transform unit 722 connected to the output of the second compensating unit 718 and performing fast Fourier transform using timing information from the timing unit 708. Outputs from the first and second fast Fourier transform units 720 and 722 are added in the same phase by an adder 724 and provided to a demodulator 714.
[0040]
In this embodiment, the timing section 708 causes the first fast Fourier transform section 720 to perform the fast Fourier transform in accordance with the effective symbol section of the OFDM symbol of the first path in the received signal. To give timing information. In such a time frame of the Fourier transform, the signals I, A, B, and C having the positional relationship described with reference to FIG. 4 cause intersymbol interference. The first compensating section 712, which is a received signal compensating section as shown in FIG. 3 or 6, is formed to suppress such a signal. Similarly, the timing unit 708 causes the second fast Fourier transform unit 720 to perform fast Fourier transform during a fixed period (effective symbol section) from the beginning of the OFDM symbol of the path of the most delayed path in the received signal. , To the first fast Fourier transform unit 722. In such a time frame of the Fourier transform, the signal I having the positional relationship as described with reference to FIG. 5 causes intersymbol interference. The second compensator 718, which is a received signal compensator as shown in FIG. 3 or 6, is formed to suppress such a signal.
[0041]
According to the present embodiment, after the signal part I causing interference is suppressed by the received signal compensator 710, the Fourier transform outputs calculated by different FFT windows by the fast Fourier transformer 712 are added in phase. Therefore, a signal in which interference is suppressed can be more effectively provided to the demodulation unit 714.
[0042]
As described above, according to the embodiment of the present application, it is possible to suppress interference by a simple method, and the calculation load for that can be reduced. Therefore, it is possible to reduce the problem of an increase in circuit scale and power consumption, which has been a concern in the past. According to the embodiment of the present application, even if a path arriving later than the guard interval is included in the received signal, it is possible to effectively suppress intersymbol interference. This means that according to the embodiment of the present application, even if the currently set guard interval is shortened, it is possible to suppress the interference due to the path arriving later than that.
[0043]
For example, according to the second embodiment, the amount of delay between paths is determined by the length T of the set guard interval._gIf the delay is 2T_g, The signal I portion is the guard interval T_gEqual to the length of ), It is possible to suppress inter-symbol interference. In the conventional method, the guard interval length is T_g, The delay between paths is T_gWithin the range, the inter-symbol interference was sufficiently suppressed. According to the present embodiment, the guard interval length is set to T_g/ 2, the delay between paths is within twice that (T_g/ 2 × 2 = T_g), Inter-symbol interference can be suppressed. That is, T_gAccording to the embodiment of the present invention, when designing the system to allow the delay of the path within, the guard interval can be reduced to half of the conventional one. Thereby, for example, it is possible to improve the transmission speed.
[0044]
The number of paths described in each of the above embodiments was assumed to be two for simplicity. However, this is not essential to the present invention, and the number of paths is not limited to the case where a received signal includes two or more paths. The present invention can be applied. In that case, for example, the first time frame W₁Is set to match the effective symbol section of the most preceding path. Also, the second time frame W₂Is set to start from the beginning of the latest arriving path. Further, in the first and third embodiments, the number of fast Fourier transform units is two. However, more Fourier transform units are prepared, FFT calculations are calculated in various time frames, and they are added in phase. It is also possible.
[0045]
Hereinafter, means taught by the present invention will be listed.
[0046]
(Supplementary Note 1) An interference suppression device used in a receiving device that performs a Fourier transform of an OFDM signal,
Timing setting means for setting a first time frame and a second time frame for performing the Fourier transform;
First Fourier transform means for performing a Fourier transform in the first time frame;
A second Fourier transform unit that performs a Fourier transform in the second time frame that is set separately from the first time frame;
Adding means for forming an output signal by adding signals output from the first and second Fourier transform means for each subcarrier of the OFDM signal
An interference suppression device comprising:
[0047]
(Supplementary Note 2) The first time frame is set to be equal to a fixed period after the end of the guard interval in the first path preceding the first and second paths included in the OFDM signal. ,
2. The interference suppression device according to claim 1, wherein the second time frame is set to be equal to a certain period after a start time of a guard interval in the second path.
[0048]
(Supplementary Note 3) An interference suppression device used in a receiving device that performs a Fourier transform of an OFDM signal,
Delay means for delaying the OFDM signal by a predetermined first period;
Multiplying means for multiplying the output signal of the delay means by a weighting factor;
Adding means for adding the OFDM signal and the output signal of the multiplying means and outputting a signal for the Fourier transform
An interference suppression device comprising:
[0049]
(Supplementary note 4) The interference suppression device according to supplementary note 3, wherein the predetermined first period is set to be equal to a delay amount between a first path and a second path included in the OFDM signal.
[0050]
(Supplementary note 5) The interference suppression device according to supplementary note 3, wherein the predetermined first period is set to be equal to an effective symbol section after the end of the guard interval of the OFDM symbol.
[0051]
(Supplementary Note 6) The predetermined first period is a sum of a delay amount between the first path and the second path included in the OFDM signal and an effective symbol section after the end of the guard interval of the OFDM symbol. The interference suppression apparatus according to claim 3, wherein the interference suppression apparatus is set to be equal to:
[0052]
(Supplementary note 7) The interference suppression device according to supplementary note 3, further comprising control means for controlling connection of a signal path passing through the delay means to the addition means.
[0053]
(Supplementary Note 8) The control means is formed to control the connection such that an output signal from the multiplication means obtained within a predetermined second period contributes to an output signal of the addition means. The interference suppression device according to attachment 7, characterized in that:
[0054]
(Supplementary note 9) The supplementary note, wherein the predetermined second period is set equal to a difference between a delay amount between a first path and a second path included in the OFDM signal and a guard interval. 9. The interference suppression device according to 8.
[0055]
(Supplementary Note 10) An interference suppression system including a first unit including the interference suppression device according to Supplementary Note 1 and a second unit including the interference suppression device according to Supplementary Note 3,
An interference suppression system, wherein an output signal of the first means is formed to be input to the second means.
[0056]
(Supplementary Note 11) In a receiver that receives an orthogonal frequency division multiplexed signal including a guard interval in each subcarrier signal,
Timing extraction means for extracting a reference timing for at least two of the direct wave or the delayed wave from the received signal;
Based on the reference timing, an earlier one of the two waves is subjected to Fourier transform processing without including the guard interval, and a later one of the two waves is Fourier transformed including at least a part of the guard interval. Fourier transform processing means for performing a transform process;
A receiver comprising:
[0057]
(Supplementary Note 12) In a receiver for receiving an orthogonal frequency division multiplexed signal including a guard interval in which a signal similar to the rear part of a subsequent symbol is inserted between symbols of each subcarrier signal,
Fourier transform processing means for performing a Fourier transform process on a first wave of the received signal and a second wave that is a delayed wave thereof and delayed by the guard interval or more,
Adding means for adding each Fourier-transformed signal;
Wherein the start timing of the Fourier transform for the second wave is within a guard interval.
[0058]
【The invention's effect】
As described above, according to the present invention, the guard interval of an OFDM signal can be set short. In addition, the operation load for reducing interference in the receiving apparatus that receives the OFDM signal is reduced as compared with the related art.
[0059]
[Brief description of the drawings]
FIG. 1 is a block diagram of a receiving device including an interference suppressing device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a relationship between a path in an OFDM signal and a time frame of a Fourier transform.
FIG. 3 is a block diagram of a receiving device including an interference suppression device according to a second embodiment of the present invention.
FIG. 4 is a diagram illustrating a relationship between two paths included in an OFDM signal.
FIG. 5 is a diagram illustrating a relationship between two paths included in an OFDM signal.
FIG. 6 shows a block diagram of a modification of the received signal compensator.
FIG. 7 is a block diagram of a receiving device including an interference suppression device according to a third embodiment of the present invention.
[Explanation of symbols]
100 receiver
102 antenna
104 Radio section
106 analog-to-digital converter
108 Timing section
110 Fourier transform unit
112 Demodulation unit
114 Interference suppression device
116 Correlation calculator
118 Timing judgment unit
120 1st FFT window setting unit
122 Second FFT window setting unit
124 serial-to-parallel converter
126 first fast Fourier transform unit
128 second fast Fourier transform unit
130 Adder
132 Phase adjustment unit
134 parallel-serial converter
202, 204, 206 passes
300 receiver
302 antenna
304 Radio section
306 Analog-to-digital converter
308 Timing section
310 Fourier transform unit
312 Received signal compensator
314 Adder
316, 324, 326, 328 Multiplication unit
318, 320, 322 delay unit
402,404 pass
502,504 pass
612 Received signal adjustment unit
614 Adder
616, 624, 626, 628 Multiplication unit
618, 620, 622 delay unit
630, 632, 634 switch section
636 control unit
700 receiver
702 antenna
704 Radio unit
706 Analog-to-digital converter
708 Timing section
710 Received signal compensator
712 Fourier transform unit
714 demodulation unit
716 First Compensation Unit
718 Second Compensation Unit
720 First fast Fourier transform unit
722 second fast Fourier transform unit
724 adder

Claims (5)

An interference suppression device used in a receiving device that performs a Fourier transform of an OFDM signal,
Timing setting means for setting a first time frame and a second time frame for performing the Fourier transform;
First Fourier transform means for performing a Fourier transform in the first time frame;
A second Fourier transform unit that performs a Fourier transform in the second time frame that is set separately from the first time frame;
An interference suppression apparatus comprising: an adding unit that forms an output signal by adding signals output from the first and second Fourier transform units for each subcarrier of the OFDM signal. The first time frame is set to be equal to a certain period after the end of the guard interval in the preceding first path between the first and second paths included in the OFDM signal,
2. The interference suppression apparatus according to claim 1, wherein the second time frame is set to be equal to a certain period after a start time of a guard interval in the second path. 3. An interference suppression device used in a receiving device that performs a Fourier transform of an OFDM signal,
Delay means for delaying the OFDM signal by a predetermined first period;
Multiplying means for multiplying the output signal of the delay means by a weighting factor;
An interference suppression apparatus comprising: an adding unit that adds the OFDM signal and an output signal of the multiplying unit and outputs a signal for the Fourier transform. In a receiver for receiving an orthogonal frequency division multiplexed signal including a guard interval in each subcarrier signal,
Timing extraction means for extracting a reference timing for at least two of the direct wave or the delayed wave from the received signal;
Based on the reference timing, an earlier one of the two waves is subjected to Fourier transform processing without including the guard interval, and a later one of the two waves is subjected to Fourier transformation including at least a part of the guard interval. Fourier transform processing means for performing a transform process;
A receiver comprising: In a receiver for receiving an orthogonal frequency division multiplexed signal including a guard interval in which a signal similar to the rear part of a subsequent symbol is inserted between each symbol of each subcarrier signal,
Fourier transform processing means for performing a Fourier transform process on a first wave of the received signal and a second wave that is a delayed wave thereof and delayed by the guard interval or more,
Adding means for adding each Fourier-transformed signal;
Wherein the start timing of the Fourier transform for the second wave is within a guard interval.

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