JP5812827B2 - Receiver - Google Patents

Description

  The present invention relates to a technique for receiving a frequency division multiplexed signal propagated through a transmission line, and more particularly to a technique for correcting a distortion received by a frequency division multiplexed signal from a transmission line.

  Systems that wirelessly transmit information using an Orthogonal Frequency Division Multiplexing (OFDM) scheme have been put into practical use in the communication field and the broadcast field. In the orthogonal frequency division multiplexing method, information to be transmitted (hereinafter also referred to as “transmission data”) is allocated to a plurality of subcarriers (subcarriers), and each subcarrier is, for example, QPSK (Quadrature Phase Shift Keying). And digital modulation using a subcarrier modulation scheme such as multi-level QAM (Quadrature Amplitude Modulation). These modulated subcarriers are orthogonal to each other, arranged at predetermined frequency intervals, multiplexed and transmitted. In addition, a known signal (hereinafter also referred to as “pilot carrier”) used when demodulating the modulated subcarrier on the receiver side may be multiplexed as a specific subcarrier. Actually, the transmitter generates a baseband OFDM signal (baseband OFDM signal) by multiplexing the modulated subcarriers including the pilot carrier by orthogonal transform using inverse Fourier transform processing. The baseband OFDM signal is transmitted after being frequency converted into a signal of a desired carrier band.

  More specifically, the transmitter generates complex data symbols by mapping the transmission data according to the modulation scheme of each subcarrier, and performs inverse Fourier transform on these complex data symbols to generate baseband OFDM of one effective symbol period. A signal can be generated. The transmitter can further generate an OFDM signal of one symbol period by adding a copy of the last part of the baseband OFDM signal to the head of the baseband OFDM signal. The last copy added to the head is called a guard interval (cyclic prefix). By adding a guard interval, the receiver is not affected by intersymbol interference even when a direct wave of the transmission signal and a delayed wave having a delay time shorter than the guard interval length are received simultaneously with this direct wave. It is known that transmission data can be reproduced.

  Further, in the orthogonal frequency division multiplexing method, all subcarriers are orthogonal to each other, so that transmission data can be correctly reproduced when synchronization of subcarrier frequencies is established between the transceivers. In general, a receiving apparatus that receives an OFDM signal has a function of performing frequency conversion of a received signal by orthogonal demodulation. In addition, the receiving apparatus establishes timing synchronization and subcarrier frequency synchronization between the transmitter and the receiver, and performs Fourier transform on the received signal subjected to frequency conversion (hereinafter also referred to as “time domain signal”) for each subcarrier. Frequency domain signals are generated, and the frequency domain signals are demodulated.

  In order to demodulate each subcarrier modulated by the subcarrier modulation method without error, the conventional receiving apparatus uses, for example, each subcarrier in the transmission path using a pilot carrier multiplexed (inserted) in a transmission signal. The carrier amplitude fluctuation amount and phase fluctuation amount are estimated (hereinafter also referred to as “transmission path estimation”), and the subcarrier amplitude and phase are corrected (hereinafter also referred to as “equalization”) based on the estimation result. ing.

  By the way, since the received signal is affected by various interference waves in the transmission path, a technique for minimizing the influence of these interference waves is necessary to improve the reception quality. Among these types of techniques, a technique for reducing the influence of interference waves superimposed in the same signal band (hereinafter also referred to as “same channel”) (hereinafter also referred to as “same channel interference suppression technique”). Is one of the important elemental technologies. Prior art relating to the co-channel interference suppression technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-252040 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2001-339320 (Patent Document 2).

  Patent Document 1 discloses a technique for reducing the influence of interference by detecting frequency-selective interference of a received signal based on a pilot carrier and performing erasure processing on subcarrier data that has been disturbed by an error correction unit. Has been.

  Patent Document 2 discloses a phase synchronization unit that is phase-synchronized with an interference wave (interference wave) in a digital reception signal, and a level adjustment unit that generates a replica of the interference wave in accordance with the output of the phase synchronization unit. And a subtractor for subtracting the replica from the received signal is disclosed. As the phase synchronization means, a PLL (Phase-Locked Loop) circuit is used.

  In an SFN (Single Frequency Network) system that relays signals using the same radio frequency, the reception signal and the transmission signal interfere with each other at the relay station, and therefore a wraparound canceller for suppressing this interference is effective. is there. Since this wraparound canceller has a function of removing interference components superimposed on the same channel, it can be said to be one of the same channel interference suppression techniques. For example, a wraparound canceller disclosed in Japanese Patent Application Laid-Open No. 2003-273830 (Patent Document 3) includes an FIR (Finite Impulse Response) filter, a subtractor that subtracts the output of the FIR filter from the output of the receiving unit, and this subtraction A filter coefficient generation unit that estimates the transmission path characteristic of the sneak component of the received signal using the output of the detector and generates the tap coefficient of the FIR filter based on the estimation result. Since the FIR filter can perform a convolution operation on the output of the subtractor to generate a replica (replica) of the wraparound component, the subtracter removes the interference wave by subtracting the replica from the output of the receiving unit. be able to.

Japanese Patent Laid-Open No. 11-252040 (paragraphs 0016 to 0017 and FIG. 1 etc.) JP 2001-339320 A (paragraphs 0016 to 0021 and FIG. 1 etc.) JP 2003-273830 A (paragraphs 0059 to 0078 and FIG. 1 etc.)

  When the radio wave environment (transmission path characteristics) varies from moment to moment, it is necessary to suppress co-channel interference while following this variation. However, in the conventional co-channel interference suppression technique, a method of generating a replica synchronized with the phase of an interference wave using a PLL circuit as disclosed in Patent Document 2, or a wraparound signal as disclosed in Patent Document 3 A method of updating tap coefficients of the FIR filter that generates a replica of (interfering wave) using a sequential update algorithm has been adopted. For this reason, the co-channel interference suppression techniques disclosed in Patent Documents 2 and 3 have a problem that the follow-up speed with respect to the temporal variation of the transmission path characteristics is slow.

  Further, in the co-channel interference suppression technique disclosed in Patent Document 1, since the error correction unit performs erasure processing on the subcarrier data that has been disturbed, the interference wave is spread over a wide range of OFDM signal reception channels. When present, there is a problem that a sufficient suppression effect cannot be obtained.

  In view of the above, an object of the present invention is to have good followability with respect to time fluctuations in the radio wave environment, and to effectively suppress the interference wave even when the interference wave exists over a wide range of the reception channel. It is to provide a receiving apparatus and a receiving method capable of performing the above.

A receiving apparatus according to an aspect of the present invention is a receiving apparatus that receives a frequency division multiplexed signal in which a plurality of modulation subcarriers including a known pilot carrier are multiplexed, and receives a discrete signal from the frequency division multiplexed signal. A front end unit for generating, a data storage unit for outputting the discrete signal after temporarily storing it, and a subtracting unit for generating a subtraction signal by subtracting the interference signal from the discrete signal output by the data storage unit A signal selection unit that selects and outputs one of the discrete signal and the subtraction signal, and a plurality of frequency domain signals by performing a discrete Fourier transform on the output of the signal selection unit A transmission path characteristic based on a generated Fourier transform unit and a received pilot signal corresponding to the pilot carrier among the plurality of frequency domain signals An equalization processing unit configured to generate a plurality of frequency domain equalized signals by performing an equalization process on the plurality of frequency domain signals using the estimated transmission path characteristics; and the plurality of frequency domain signals; Based on the plurality of frequency domain equalization signals, a jamming wave estimation unit that estimates a plurality of frequency domain jamming wave components respectively corresponding to frequencies of the plurality of modulation subcarriers, and a plurality of frequency domain jamming wave components An inverse Fourier transform unit that performs inverse discrete Fourier transform to generate the jamming signal, a control unit that individually controls the operations of the data storage unit and the signal selection unit, and the modulation subcarrier. A signal point determination unit that determines a plurality of signal points respectively corresponding to the plurality of frequency domain equalized signals according to the digital modulation method; An error evaluation unit for detecting an error between the frequency domain equalized signal and the plurality of signal points, and the control unit is configured to detect the data accumulation unit and the signal based on a detection result by the error evaluation unit. The operation of the selection unit is controlled .

  A receiving method according to another aspect of the present invention is a receiving method for receiving a frequency division multiplexed signal in which a plurality of modulation subcarriers including a known pilot carrier are multiplexed, the discrete signal being obtained from the frequency division multiplexed signal. Generating a discrete signal, temporarily storing the discrete signal in a data storage unit, outputting the discrete signal from the data storage unit, and executing a discrete Fourier transform on the output discrete signal Generating a plurality of frequency domain signals, and estimating a first transmission path characteristic based on a received pilot signal corresponding to the pilot carrier among the plurality of frequency domain signals, and the first transmission path A plurality of frequency domain equalized signals are generated by performing equalization processing on the plurality of frequency domain signals using characteristics. And, based on the plurality of frequency domain signals and the plurality of frequency domain equalization signals, estimating a plurality of frequency domain jamming wave components respectively corresponding to the frequencies of the plurality of modulation subcarriers, From the step of generating an interference wave signal by performing inverse discrete Fourier transform on a plurality of frequency domain interference wave components, the step of outputting the discrete signal again from the data storage unit, and the discrete signal output again Subtracting the jamming signal to generate a subtracted signal, regenerating a plurality of frequency domain signals by performing a discrete Fourier transform on the subtracted signal, and the plurality of regenerated frequencies Based on the received pilot signal corresponding to the pilot carrier among the domain signals, the second transmission is performed. Estimating a path characteristic and generating a plurality of frequency domain equalized signals by performing equalization processing on the plurality of frequency domain signals generated from the subtracted signal using the second transmission path characteristics; and It is characterized by providing.

  According to the aspect of the present invention, a frequency domain jamming wave component is estimated based on the frequency domain signal and the frequency domain equalized signal, and an inverse discrete Fourier transform is performed on the estimated frequency domain jamming wave component. Thus, a time domain jamming signal is detected. Thereafter, a subtraction signal is generated by subtracting the time domain interference signal from the discrete signal, and the received data in which the interference component is suppressed by performing discrete Fourier transform and equalization processing on the subtraction signal. It is possible to obtain a symbol. Therefore, the co-channel interference component can be effectively suppressed even in a communication environment in which the transmission path characteristics vary with time. In addition, a time domain jamming signal is generated from the frequency domain jamming signal component and the time domain jamming signal is subtracted from the discrete signal, so that the jamming signal exists over a wide range of reception channels. Even in this case, the interference wave can be effectively suppressed.

It is a functional block diagram which shows roughly the main structures of the receiver of Embodiment 1 which concerns on this invention. 3 is a functional block diagram schematically showing a main configuration of a receiving apparatus according to Embodiment 1. FIG. It is a functional block diagram which shows roughly the main structures of the receiver of Embodiment 2 which concerns on this invention. It is a functional block diagram which shows roughly the main structures of the receiver of Embodiment 3 which concerns on this invention. FIG. 10 is a functional block diagram illustrating a configuration example of a delay profile estimation unit that configures the reception device according to the third embodiment. (A), (B) is a figure which shows the example of the delay profile of a transmission-line characteristic. FIG. 10 is a functional block diagram illustrating a configuration example of an interference wave suppression evaluation unit that configures a reception device according to Embodiment 3; It is a functional block diagram which shows roughly the structure of the interference wave suppression evaluation part which comprises the receiver of Embodiment 4 which concerns on this invention.

  Hereinafter, various embodiments according to the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
1 and 2 are functional block diagrams schematically showing the main configuration of receiving apparatus 1 according to Embodiment 1 of the present invention. FIG. 1 is a diagram showing a configuration when operating in the first operation mode (normal operation mode), and FIG. 2 shows a configuration when operating in the second operation mode (interference wave reducing operation mode). FIG.

As shown in FIG. 1, the receiving apparatus 1 includes a front end unit 10 that receives an orthogonal frequency division multiplexing (OFDM) signal R (t) of a carrier band from a wireless transmission line or a wired transmission line in OFDM symbol units. I have. The front end unit 10 amplifies the received OFDM signal R (t) and frequency-converts the amplified signal to generate a baseband OFDM signal. Thereafter, the front-end unit 10 performs synchronization processing such as symbol timing synchronization and carrier frequency synchronization on the baseband OFDM signal, and after synchronization is established, performs A / D conversion on the baseband OFDM signal for one effective symbol period. Generate a discrete signal. Discrete signals are N (N is an integer of 2 or more) modulation subcarrier frequencies (hereinafter referred to as subcarrier frequencies) f ₀ ,..., F _N−1 included in each OFDM symbol. complex signal of pieces of time-domain _{R 0, R 1, ...,} consisting of _{R N-1.} The nth subcarrier frequency f _n is given by f _n = n × f ₀ . One effective symbol period is 1 / f ₀ .

Referring to FIG. 1, the receiving apparatus 1 is one of a data storage unit 11 that temporarily stores discrete signals, a complex subtraction unit 12, an output of the data storage unit 11, and an output of the complex subtraction unit 12. A signal selection unit 13 that selects one, a Fourier transform unit 14 that applies N-point discrete Fourier transform (DFT) to the selection output of the signal selection unit 13, and N complex outputs X ₀ ,. And an equalization processing unit 15 that performs an equalization process on XN _-1 .

  The operations of the data storage unit 11 and the signal selection unit 13 are controlled by the control unit 19. Specifically, the control unit 19 supplies a data output control signal (repetition timing signal) Sa to the data storage unit 11 and controls the timing at which the data storage unit 11 outputs a discrete signal. The control unit 19 also supplies a switching control signal (switching timing signal) Sb to the signal selection unit 13 to control the selection destination of the signal selection unit 13 (the output of the data storage unit 11 or the output of the complex subtraction unit 12). be able to.

The complex subtraction unit 12 subtracts N outputs of an inverse Fourier transform unit 18 (to be described later) from _N outputs R ₀ ,..., R _N−1 of the data storage unit 11 to obtain N subtraction signals (time domain). Signal) and outputs these subtracted signals to the signal selector 13. The signal selection unit 13 selects either the output of the data storage unit 11 or the output of the complex subtraction unit 12 according to the value of the selection control signal Sb, and outputs the selected N outputs to the Fourier transform unit 14. . In the normal operation mode, the signal selection unit 13 selects the output of the data storage unit 11 as shown in FIG. 1, and in the interference wave reduction operation mode, the signal selection unit 13 performs complex subtraction as shown in FIG. The output of part 12 is selected. Here, the data output control signal Sa input to the data storage unit 11 and the switching control signal Sb input to the signal selection unit 13 are synchronized with each other. Data used for one Fourier transform process by the Fourier transform unit 14 is only one of the data output from the data storage unit 11 and the complex subtraction unit 12.

Fourier transform unit 14, as shown in FIG. 1, N pieces of the complex signal, that the received data symbol X ₀ is a frequency-domain signal by the Fourier transform of N discrete signal components of the time _domain, ..., X _N-1 Has a function of converting into (OFDM demodulation).

The equalization processing unit 15 includes a transmission path characteristic estimation unit 151 and an equalization unit 152. Transmission path characteristic estimation section 151 corresponds to subcarrier frequencies f ₀ ,..., F _N−1 using known reception pilot symbols included in _N received data symbols X ₀ ,. It has a function of estimating _N transmission path characteristics h ₀ ,..., H _N−1 . For example, the received pilot symbols are distributed in the time direction and the frequency direction. After estimating the channel characteristics of these received pilot symbols, it is possible to interpolate the frequency characteristics of received data symbols other than the received pilot symbols. For example, ISDB-T (Integrated Services Digital Broadcasting for Terrestrial) and DVB-T (Digital Video Broadcasting-Terrestrial), which are Japanese digital broadcasting standards, are set within the frequency of one symbol sub-frame within one symbol period of the OFDM signal. Since pilot carriers are inserted every 4 subcarriers in the direction (time direction), all the subcarrier frequencies are obtained by interpolating the channel characteristics estimated for the pilot carriers in the time direction and the frequency direction. The transmission line characteristics for

The equalizer 152 can perform equalization based on, for example, a known ZF (zero forcing) standard or an MMSE (least square error) standard. When equalization based on the ZF standard is performed, as shown in the following equation (1), the complex signal X _k corresponding to the subcarrier frequency f _k is complex-divided by the channel characteristic h _k to equalize the signal [ X _k ] can be calculated.
[X _k ] = X _k / d _k (1)

As illustrated in FIG. 1, the reception device 1 further includes a signal point determination unit 16 and an interference wave estimation unit 17. The signal point determination unit 16 has a function of determining signal points respectively corresponding to _N equalization signals [X ₀ ],..., [X _N−1 ] in the frequency domain output from the equalization unit 152. The signal point is determined according to the digital modulation scheme used for subcarrier modulation. Examples of the digital modulation scheme include QPSK (Quadrature Phase Shift Keying), QAM (Quadrature Amplitude Modulation), multi-level QAM, and multi-level PSK. It is determined which of the signal points (for example, 16 signal points in the case of 16QAM) each equalized signal corresponds to.

Based on the outputs X _{0 to} X _N−1 before equalization of the Fourier transform unit 14 and the outputs [X ₀ ] to [X _N−1 ] of the equalization processing unit 15, the interference wave estimation unit 17 frequency _{f 0,} ..., N number of frequency-domain interference component _Z 0 that correspond to _{f N-1,} ..., has a function of estimating a _{Z N-1.}

As illustrated in FIG. 1, the interference wave estimation unit 17 includes an inverse equalization unit 171 and an interference wave component extraction unit 172. Conversely equalizer 171, data symbols _d 0 of the signal point output from the signal point determination unit 16, _..., estimated value _h 0 of _{d N-1} and channel characteristics, _..., based on the _{h N-1} The received data symbols Y ₀ ,..., Y _N−1 that are less affected by the interference wave are estimated. Specifically, in the case of the reverse equalization by ZF criterion, as shown in the following equation (2), by complex multiplication of the estimated value h _k data symbols d _k which corresponds to the sub-carrier frequency f _k , The received data symbol Y _k corresponding to the subcarrier frequency f _k can be calculated.
Y _k = d _k × h _k (2)

Interference wave component extracting unit 172 generates a frequency-domain disturbance signal by the received data symbols _Y 0 _{~Y N-1} from the output _X 0 _{~X N-1} before equalization of the Fourier transform unit 14 respectively complex subtraction can do. Specifically, the frequency domain interference wave signal Z _k corresponding to the subcarrier frequency f _k can be calculated by the following equation (3).
Z _k = X _k −Y _k (3)

The interference wave reduction operation mode is executed after the normal operation mode is executed. At this time, as shown in FIG. 2, the data storage unit 11 again outputs the time domain complex signals R ₀ , R ₁ ,..., R _N−1 within the same effective symbol period. The inverse Fourier transform unit 18 performs inverse discrete Fourier transform on the _N outputs Z ₀ ,..., Z _N−1 of the interference wave component extraction unit 172, thereby performing N complex interference wave signals z in the time domain. ₀ , ..., z _N-1 is generated. Complex subtraction unit 12, the complex output _R 0 of the data storage unit _11, ..., _{R N-1} complex disturbance signal _z 0 from, _{..., z N-1} to that respectively complex subtraction, the influence of the interference wave reduction N time domain signals can be generated.

As shown in FIG. 2, in the interference wave reduction operation mode, the selection destination of the signal selection unit 13 is the output of the complex subtraction unit 12. At this time, the Fourier transform unit 14 performs discrete Fourier transform on the N outputs of the complex subtraction unit 12 to perform N complex data symbols X ₀ ⁽¹⁾ ,..., X _N−1 ^{( 1)} is generated (step S1). Further, in the equalization processing unit 15, the transmission path characteristic estimation unit 151 includes N transmission path characteristics based on the received pilot symbols included in the complex data symbols X ₀ ⁽¹⁾ ,..., X _N-1 ^(1). h ₀ ⁽¹⁾ ,..., h _N-1 ⁽¹⁾ are estimated (step S2). The equalization unit 152 equalizes the N equalization signals [X ₀ ⁽¹ ) by equalizing the output of the Fourier transform unit 14 using the transmission path characteristics h ₀ ⁽¹⁾ ,..., H _N−1 ^{(1). )],} _..., and to generate the ^{_{[X N-1 (1)}} ] ( step S3).

In addition, the signal point determination unit 16 receives received data symbols d ₀ ⁽¹⁾ , N at N signal points respectively corresponding to the equalized signals [X ₀ ⁽¹⁾ ],..., [X _N-1 ⁽¹⁾ ]. ..., d _N-1 ⁽¹⁾ is output (step S4). Thereafter, the inverse equalization unit 171 generates reception data symbols Y ₀ ⁽¹⁾ ,..., Y _N-1 ⁽¹⁾ (step S5), and then the interference wave component extraction unit 172 includes the Fourier transform unit 14 output ^{_{X 0 (1) ~X N-}} 1 (1) received from the data symbols ^{_{Y 0 (1) ~Y N-}} 1 (1) the frequency-domain disturbance signal _Z ⁰ by each complex subtraction ⁽¹⁾ to Z _N-1 ⁽¹⁾ is generated (step S5). Further, the inverse Fourier transform unit 18 performs inverse discrete Fourier transform on the frequency domain disturbance signal Z ₀ ^{(1) to} Z _N-1 ⁽¹⁾ to generate _N time-domain complex disturbance signal z ₀ ⁽¹⁾ , ..., z _N-1 ⁽¹⁾ is generated (step S6). The complex subtraction unit 12, the complex output _R 0 of the data storage unit _11, ..., _{R N-1} complex disturbance signal _z ⁰ (1) ^{_{from, ..., z N-1 (}} 1) that each complex subtraction Thus, a time domain signal in which the influence of the interference wave is reduced can be generated (step S7).

  The control unit 19 can repeatedly execute the processes in steps S1 to S7 described above in the interference wave reduction operation mode an arbitrary number of times (including 0 times).

As described above, according to the first embodiment, even in a communication environment in which the transmission path characteristics fluctuate at high speed, it is possible to execute processing with high followability to fluctuations in the transmission path characteristics. The component can be effectively suppressed. Further, even when the jamming wave exists over a wide range of the reception channel, the jamming wave estimation unit 17 accurately detects the co-channel jamming components Z _{0 to} Z _N−1 and detects these co-channel jamming components Z _0. ~ ZN _-1 can be effectively suppressed. Therefore, high reception performance can be ensured. In particular, when a mobile body receives an OFDM signal, the transmission path characteristics are likely to fluctuate with time at high speed, and therefore the receiving apparatus 1 of this embodiment is effective.

The inverse Fourier transform unit 18, the estimated disturbance component _Z 0 _{~Z N-1} and ^{_{Z 0 (1) ~Z N-}} 1 (1) time-domain signal _z 0, _{..., z N-1} and z ₀ ⁽¹⁾ ,..., Z _N-1 ⁽¹⁾ , and the complex subtraction unit 12 removes these time domain signals from the received signals R _{0 to} R _N−1 . Thereafter, Fourier transform and equalization processing are performed. For this reason, especially when the power of the interference component is large, the complex subtraction unit 12 converts the amplitude of the input signal to the Fourier transform unit 14 to an appropriate level, and then the discrete Fourier transform is executed. . Therefore, it is possible to effectively use the dynamic range of the circuit subsequent to the Fourier transform unit 14. Also, the reception performance after co-channel interference suppression can be greatly improved.

Embodiment 2. FIG.
Next, a second embodiment according to the present invention will be described. FIG. 3 is a functional block diagram schematically showing a main configuration of receiving apparatus 2 according to the second embodiment. As shown in FIG. 3, the receiving apparatus 2 of the present embodiment has an error evaluation unit 20 in addition to the configuration of the first embodiment. The configuration of receiving apparatus 2 is the same as the configuration of receiving apparatus 1 of Embodiment 1 except for control unit 19B and error evaluation unit 20.

Error evaluation unit 20, the equalized signal in the frequency domain _{[X 0], ..., [} X N-1] and Data symbols _d 0 of the signal point, _..., the error component (equalized output between _{d N-1} [X ₀ ] to [X _N-1 ] having a function of detecting a noise component). The control unit 19B has the same function as that of the control unit 19 of the first embodiment. In addition to this function, the control unit 19B controls the operation of the data storage unit 11 and the signal selection unit 13 according to the detection result by the error evaluation unit 20. It has a function. If the output of the signal point determination unit 16 is so large that the influence of interference on the same channel cannot be ignored, the signal point may not be accurately reproduced, and a determination error may have occurred. In this case, depending on the magnitude and degree of the determination error, the reception performance may be deteriorated by performing the co-channel interference suppression process. Therefore, in the present embodiment, the control unit 19B executes, for example, the above-described interference wave reduction operation mode (operation mode for executing the co-channel interference suppression processing) according to the error component detected by the error evaluation unit 20. It can be determined whether or not to continue the interference wave reduction operation mode.

As shown in FIG. 3, the error evaluation unit 20 includes an error comparison unit 201 and an error determination unit 202. The error comparison unit 201 receives the complex signal output of the equalization unit 152 and the complex signal output of the signal point determination unit 16 as input, and calculates the difference between these complex signal outputs or the square of the amplitude for all subcarrier frequencies. The average value (hereinafter also referred to as “error average value”) is calculated. The square value of the amplitude is calculated as the product of the difference Δ and the complex conjugate Δ ^{* of the} difference, and the amplitude value is calculated as the square root of the product. More specifically, in the normal operation mode, as illustrated in FIG. 3, the complex signal outputs [X ₀ ] to [X _N−1 ] of the equalization unit 152 and the complex signal output d ₀ of the signal point determination unit 16. ˜d _N−1 as an input, the error comparison unit 201 can calculate an average error value <Δ> according to one of the following equations (4A) and (4B).

Further, the error evaluation unit 20 compares the average error value in the normal operation mode (when the co-channel interference component is not suppressed) and in the interference wave reduction operation mode (when the co-channel interference component is suppressed). Can do. The comparison result can be output, for example, as a result of subtracting the error average value <Δ> ₁ when suppressed from the error average value <Δ> ₀ when the co-channel interference component is not suppressed. Alternatively, the error comparison unit 201 outputs a signal representing the magnitude relationship between the error average values <Δ> ₀ and <Δ> ₁ and a signal representing the absolute value of the difference (= <Δ> ₀ − <Δ> ₁ ). The format of the output signal is not limited as long as the information can determine the suppression effect of the co-channel interference component.

  Next, the error determination unit 202 receives the output of the error comparison unit 201 as an input, and based on the signal indicating the suppression effect of the same channel interference component and the error determination reference value Eref input from the outside, The presence or absence of the suppression effect can be determined. For example, when the output of the error comparison unit 201 is a subtraction result of the error average value, the subtraction result is compared with the error determination reference value Eref, and the subtraction result of the error average value is larger than the error determination reference value Eref Can be determined to have the same channel interference suppression effect, and the determination result can be output to the control unit 19B.

  As described above, according to the second embodiment, the operations of the data storage unit 11 and the signal selection unit 13 can be controlled according to the error component detected by the error evaluation unit 20. For example, the control unit 19B determines whether to execute the interference wave reduction mode (interference suppression processing) according to the magnitude or change of the error component between when the normal operation mode is executed and when the interference wave reduction mode is executed. Therefore, if the co-channel jamming suppression process is unnecessary or if the reception performance is expected to deteriorate due to the detection error of co-channel jamming components, the jamming wave reduction mode should be avoided. be able to. Therefore, the interference component can be adaptively and appropriately suppressed in accordance with the fluctuation of the transmission path characteristic, the change of the interference component, or the state of the received signal.

Embodiment 3 FIG.
Next, a third embodiment according to the present invention will be described. FIG. 4 is a functional block diagram schematically showing the main configuration of receiving apparatus 3 of the third embodiment. As illustrated in FIG. 4, the reception device 3 of the present embodiment includes a delay profile estimation unit 21 and an interference wave suppression evaluation unit 22. The configuration of receiving apparatus 3 is the same as that of receiving apparatus 1 of Embodiment 1 except for control unit 19C, delay profile estimating unit 21, and jamming wave suppression evaluating unit 22.

The delay profile estimation unit 21 has a function of estimating a delay profile of the transmission path characteristics (power distribution of a desired wave, a delay wave, and a noise component of the OFDM signal) based on outputs X _{0 to} X _N−1 of the Fourier transform unit 14. Have Further, the jamming wave suppression evaluating unit 22 can determine whether or not the jamming wave is suppressed based on the power distribution of the delay profile, and can notify the determination result to the control unit 19C. In addition to the function of the control unit 19 of the first embodiment, the control unit 19C has a function of controlling the operations of the data storage unit 11 and the signal selection unit 13 based on the determination result by the interference wave suppression evaluation unit 22.

  FIG. 5 is a functional block diagram illustrating a configuration example of the delay profile estimation unit 21. As illustrated in FIG. 5, the delay profile estimation unit 21 includes a sub-transmission path characteristic estimation unit 210, an inverse Fourier transform unit 214, and a path power calculation unit 215. The sub-transmission channel characteristic estimation unit 210 further includes a pilot transmission channel characteristic estimation unit 211, a pilot signal generation unit 212, and a transmission channel characteristic interpolation unit 213.

The pilot transmission line characteristic estimation unit 211 receives the complex signal outputs X _{0 to} X _N−1 of the Fourier transform unit 14 and the complex signal output of the pilot signal generation unit 212 as inputs, and the reference pilot supplied from the pilot signal generation unit 212. using the signal and estimates the channel characteristic from the input complex signal X ₀ ~X _N-1 received pilot signals in the. Specifically, the pilot transmission line characteristic estimation unit 211 can generate the transmission line characteristic for the received pilot signal as a complex signal by performing complex division on the received pilot signal by a known reference pilot signal. The inverse Fourier transform unit 214 can calculate and output the channel characteristic for each subcarrier frequency by interpolating the output of the channel characteristic interpolation unit 213. For example, the transmission path characteristic interpolation unit 213 may output the result of interpolation in the time direction, may output the result of interpolation in the frequency direction, or may be output in the time and frequency directions. The result of interpolation may be output. The interpolation data obtained by the transmission path characteristic estimation unit 151 can also be used.

The inverse Fourier transform unit 214 can generate a time-domain complex signal by using the complex signal output of the transmission path characteristic interpolation unit 213 as an input and performing inverse discrete Fourier transform on the complex signal output. Here, the number M of input data used in the inverse Fourier transform unit 214 may be smaller than the total number N (> M) of subcarrier frequencies. Therefore, the inverse Fourier transform unit 214 outputs M complex signals P ₀ ,..., P _M−1 in the time domain.

Path power calculation unit 215, a complex signal P _0, ..., and generates a delay profile by calculating a square value of amplitude or amplitude of P _M-1 to component each as a power value. 6A and 6B are graphs illustrating delay profiles. In FIG. 6 (A), there is a delay wave delayed by reflection or the like with respect to the main wave (desired wave) sent from the transmitter, and the delay when the same channel interference component and thermal noise are superimposed. Profile estimation results are shown. That is, the power distribution in FIG. 6A includes a main wave power distribution 30m, a delayed wave power distribution 30d, and a noise power component near the power value Pn. The power distribution 30m of the main wave and the power distribution 30d of the delayed wave are power distributions 30P of desired power components (hereinafter referred to as “path components”), and other components are thermal noise and co-channel interference components. (Hereinafter also referred to as “noise component”). The path power calculation unit 215 calculates the power of all path components, thermal noise components, and co-channel interference components for each delay time. When the delay profile is estimated again from the signal in which the co-channel interference is suppressed, the result is as shown in FIG. 6B, and the power components other than the path component are smaller than those before suppression. Therefore, the suppression effect can be estimated with high accuracy based on the delay profile estimation results before and after the co-channel interference suppression processing.

  Next, FIG. 7 is a functional block diagram illustrating a configuration example of the interference wave suppression evaluation unit 22. As illustrated in FIG. 7, the jamming wave suppression evaluation unit 22 includes a determination processing unit 220, a component separation unit 221, a path component power calculation unit 222, and a noise power calculation unit 223. The determination processing unit 220 further includes a power ratio calculation unit 224, a power ratio storage unit 225, and a determination unit 226.

  The component separation unit 221 separates the main wave and delay wave power distribution and the noise power distribution from the signal indicating the delay profile, and supplies the signal indicating the main wave and delay wave power distribution to the path component power calculation unit 222. Then, a signal indicating the noise power distribution is supplied to the noise power calculation unit 223. The path component power calculator 222 adds (integrates) all the power values of the power distribution to calculate the first power integrated value, while the noise power calculator 223 calculates all the power values of the noise power distribution. Are added (integrated) to calculate a second integrated power value.

  The determination processing unit 220 can compare the power distribution of the desired wave and the delayed wave with the noise power distribution, and determine whether or not the interference wave is suppressed based on the comparison result. Specifically, the power ratio calculation unit 224 calculates a ratio between the first power integration value and the second power integration value (hereinafter referred to as a power ratio), and uses this power ratio as the power ratio storage unit 225. Remember me. In addition, the power ratio calculation unit 224 gives the calculated power ratio to the determination unit 226.

  The determination unit 226 can determine whether the interference wave is suppressed based on the power ratio supplied from the power ratio calculation unit 224. The determination unit 226 detects a change in the power ratio by comparing the previous power ratio stored in the power ratio storage unit 225 with the current power ratio supplied from the power ratio calculation unit 224. Is possible. For example, the determination unit 226 determines that the power ratio has improved when the current value of the power ratio is greater than the previous power ratio stored in the power ratio storage unit 225, and the amount of improvement is determined to be recalculated. If it is larger than the reference value RPref, it can be determined that there is an effect of the co-channel interference suppression processing. The determination result by the determination unit 226 is supplied to the control unit 19C.

  As described above, in the third embodiment, the control unit 19C determines whether to execute the interference suppression processing after estimating the co-channel interference suppression effect based on the change in the delay profile estimation result. Therefore, if co-channel interference suppression processing is not required or if there is a possibility that the reception performance may deteriorate due to the detection error of the same channel interference component, avoid performing co-channel interference suppression processing. Can do. Further, it is possible to adaptively and appropriately suppress interference components according to transmission path fluctuations, interference component changes, and received signal states.

Embodiment 4 FIG.
FIG. 8 is a functional block diagram showing a configuration of the jamming wave suppression evaluation unit 22M constituting the receiving apparatus according to the fourth embodiment of the present invention. The configuration of the receiving apparatus according to the present embodiment is the same as the configuration of receiving apparatus 3 according to the third embodiment except for jamming wave suppression evaluating unit 22M.

  As illustrated in FIG. 8, the interference wave suppression evaluation unit 22M includes a determination processing unit 230, a component separation unit 231 and a noise power calculation unit 232. The determination processing unit 230 further includes a noise power storage unit 233 and a determination unit 234.

  The component separation unit 231 separates the noise power distribution from the signal indicating the delay profile, and supplies the signal indicating the noise power distribution to the noise power calculation unit 232. The determination processing unit 230 can determine whether the interference wave is suppressed based on the noise power distribution. Specifically, the noise power calculation unit 232 adds (integrates) all the power values of the noise power distribution to calculate a power integration value, and stores the power integration value in the noise power storage unit 233. In addition, the noise power ratio calculation unit 232 gives the calculated noise power ratio to the determination unit 234. The determination unit 234 can determine whether the interference wave is suppressed based on the power ratio supplied from the noise power calculation unit 234. Further, the determination unit 234 detects a change in the power ratio by comparing the previous power ratio stored in the noise power storage unit 233 with the current power ratio supplied from the noise power calculation unit 232. Is possible. For example, the determination unit 234 determines that the power ratio has improved when the current value of the noise power ratio is greater than the previous power ratio stored in the noise power storage unit 233, and the amount of improvement is recalculated. When it is larger than the determination reference value RPref, it can be determined that there is an effect of the co-channel interference suppression processing. The determination result by the determination unit 234 is supplied to the control unit 19C.

  As described above, according to the fourth embodiment, whether the interference suppression processing is executed after estimating the suppression effect of the co-channel interference based on the change in the delay profile estimation result, as in the third embodiment. Therefore, if the co-channel interference suppression processing is unnecessary or if there is a possibility that the reception performance may deteriorate due to the detection error of the co-channel interference component, the co-channel interference suppression processing is performed. Thus, the interference component can be adaptively and appropriately suppressed according to the transmission path fluctuation, the change of the interference component, and the state of the received signal.

Modified example of the first to fourth embodiments.
As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable. For example, there may be an embodiment in which the configuration of the second embodiment and the configuration of the third embodiment are combined.

  Further, it is not necessary that all the functions of the receiving devices 1 to 3 are realized by a hardware configuration, and some of the functions of the receiving devices 1 to 3 may be realized by a computer program executed by a microprocessor. Good. In this case, for example, the microprocessor can realize a part of the function by loading and executing a computer program from a recording medium such as a hard disk (magnetic disk), an optical disk, or a flash memory.

  1 to 3 receivers, 10 front end units, 11 data storage units, 12 complex subtraction units, 13 signal selection units, 14 Fourier transform units, 15 equalization processing units, 151 transmission path characteristic estimation units, 152 equalization units, 16 Signal point determination unit, 17 jamming wave estimation unit, 171 inverse equalization unit, 172 jamming wave component extraction unit, 18 inverse Fourier transform unit, 19, 19B, 19C control unit, 20 error evaluation unit, 201 error comparison unit, 202 error Determination unit, 21 delay profile estimation unit, 210 sub-transmission channel characteristic estimation unit, 211 pilot transmission channel characteristic estimation unit, 212 pilot signal generation unit, 213 transmission channel characteristic interpolation unit, 214 inverse Fourier transform unit, 215 path power calculation unit 22 and 22M interference wave suppression evaluation unit, 220 determination processing unit, 221 component separation unit, 222 path component power calculation unit, 223 noise power calculation unit, 224 power ratio calculation unit, 225 power ratio storage unit, 226 determination unit, 231 component separation unit, 232 noise power calculation unit, 233 noise power storage unit, 234 determination unit.

Claims (11)

A receiving apparatus for receiving a frequency division multiplexed signal in which a plurality of modulation subcarriers including a known pilot carrier are multiplexed,
A front end for generating a discrete signal from the frequency division multiplexed signal;
A data storage unit for outputting the discrete signals after temporarily storing them;
A subtracting unit that generates a subtracted signal by subtracting an interference signal from the discrete signal output by the data storage unit;
A signal selection unit that selects and outputs any one of the discrete signal and the subtraction signal;
A Fourier transform unit that generates a plurality of frequency domain signals by performing a discrete Fourier transform on the output of the signal selection unit;
A channel characteristic is estimated based on a received pilot signal corresponding to the pilot carrier among the plurality of frequency domain signals, and equalization processing is performed on the plurality of frequency domain signals using the estimated channel characteristic An equalization processing unit for generating a plurality of frequency domain equalized signals by
Based on the plurality of frequency domain signals and the plurality of frequency domain equalization signals, an interference wave estimation unit that estimates a plurality of frequency domain interference wave components respectively corresponding to the frequencies of the plurality of modulation subcarriers;
An inverse Fourier transform unit that performs an inverse discrete Fourier transform on the plurality of frequency domain interference wave components to generate the interference wave signal;
A control unit for individually controlling the operations of the data storage unit and the signal selection unit ;
A signal point determination unit for determining a plurality of signal points respectively corresponding to the plurality of frequency domain equalized signals according to the digital modulation scheme applied to the modulation subcarrier;
An error evaluator that detects errors between the plurality of frequency domain equalized signals and the plurality of signal points; and
The control unit controls operations of the data storage unit and the signal selection unit based on a detection result by the error evaluation unit.
Receiving apparatus according to claim. The receiving device according to claim 1,
The data storage unit and the signal selection unit have a first operation mode and a second operation mode,
In the first operation mode, the discrete signal is output from the data storage unit, and the discrete signal is selected by the signal selection unit,
In the second operation mode, the discrete signal is output again from the data storage unit, and the subtraction signal is selected by the signal selection unit.   3. The receiving device according to claim 2, wherein the control unit causes the data storage unit and the signal selection unit to operate in the second operation mode after operating in the first operation mode. A receiving device. The receiving device according to claim 2 or 3 ,
The error evaluation unit includes the error when the data storage unit and the signal selection unit operate in the first operation mode, and the data storage unit and the signal selection unit operate in the second operation mode. Compare with the error when
The control unit controls the operations of the data storage unit and the signal selection unit based on a comparison result by the error evaluation unit. The receiving device according to claim 2 or 3,
A delay profile estimator that estimates a delay profile of the transmission path characteristics based on the plurality of frequency domain signals;
An interference wave suppression evaluation unit that determines whether an interference wave is suppressed based on the power distribution of the delay profile;
The control unit controls the operations of the data storage unit and the signal selection unit based on a determination result by the interference wave suppression evaluation unit. The receiving device according to claim 5 ,
The interference wave suppression evaluation unit
A component separation unit that separates the power distribution of the desired wave and the delayed wave and the noise power distribution other than the desired wave and the delayed wave from the delay profile;
A receiving apparatus comprising: a determination processing unit that compares the power distribution of the desired wave and the delayed wave with the noise power distribution and determines whether or not the interference wave is suppressed based on the comparison result; . The receiving device according to claim 6 ,
The determination processing unit
A power calculator that calculates a first power integral value based on the power distribution of the desired wave and the delayed wave and calculates a second power integral value based on the noise power distribution;
And a determination unit that calculates a ratio between the first power integration value and the second power integration value and determines whether or not the interference wave is suppressed based on a change in the ratio. Receiving device. The receiving device according to claim 5 ,
The interference wave suppression evaluation unit
A component separation unit that separates a noise power distribution other than the desired wave and the delayed wave from the delay profile;
And a determination processing unit that determines whether or not the interference wave is suppressed based on the noise power distribution. The receiving device according to claim 8 , wherein
The determination processing unit
A power calculator that calculates a power integral value based on the noise power distribution;
And a determination unit that determines whether or not the interference wave is suppressed based on a change in the power integration value. The receiving device according to any one of claims 5 to 9 ,
The delay profile estimation unit includes:
A sub-channel characteristic estimation unit that estimates a channel characteristic based on a received pilot signal corresponding to the pilot carrier among the plurality of frequency domain signals;
An inverse Fourier transform unit that generates a time-domain complex signal by performing an inverse discrete Fourier transform on the channel characteristics estimated by the sub-channel characteristic estimation unit;
And a power calculator that calculates a power distribution of the complex signal as the delay profile. The receiving device according to any one of claims 1 to 3,
Further comprising a signal point determination unit for determining a plurality of signal points respectively corresponding to the plurality of frequency domain equalized signals according to the digital modulation scheme applied to the modulation subcarrier,
The interference wave estimation unit includes:
An inverse equalization unit configured to estimate a plurality of received data symbols respectively corresponding to the plurality of signal points based on the plurality of signal points and the transmission path characteristics estimated by the equalization processing unit;
An interference wave component extraction unit that generates a plurality of frequency domain interference wave signals as the plurality of frequency domain interference wave components by subtracting the estimated plurality of received data symbols from the plurality of frequency domain signals, respectively. A receiving apparatus comprising:

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