JP2006157762A - Receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively control a mode where a receiving sampling sequence is rearranged at a previous stage of FFT in a receiving device for receiving a signal transmitted in accordance with an OFDM system. <P>SOLUTION: A/D conversion means 1 A/D-converts a received signal to obtain a received sampling sequence; window timing setting means 2, 3 set timing of a window for the FFT; rearrangement means 4 to 6 rearrange the head sample of the received sampling sequence in the window to the tail end by a sample quantity based on a difference between window timing and predetermined reference timing; FFT execution means 7 executes the FFT for the rearranged received sampling sequence ; equalization processing means 8 executes equalization processing for an execution result of the FFT; and demodulation means 9 executes demodulation processing for an execution result of the equalization processing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a receiving apparatus that uses an orthogonal frequency division multiplexing (OFDM) scheme that transmits information codes using a plurality of carriers orthogonal to each other, and particularly, a fast Fourier transform ( The present invention relates to a receiving apparatus that improves reception quality by effectively controlling a mode of rearranging received sampling sequences in the previous stage of FFT (Fast Fourier Transform).

In recent years, orthogonal frequency division multiplex modulation (OFDM), which is characterized by being resistant to multipath fading and ghost, has been studied as a modulation method suitable for digital audio broadcasting for mobiles and digital terrestrial television broadcasting. Has been. The OFDM system is a kind of multi-carrier modulation system, and is a transmission system that digitally modulates a plurality of n (n is several tens to several thousands) carriers orthogonal to each other.
As shown in FIG. 7, in the OFDM method, a large number of digital modulation waves are added, and a modulated signal obtained by performing orthogonal modulation on the I axis and the Q axis is transmitted. As the carrier wave digital modulation method, for example, a 16-value quadrature amplitude modulation (16QAM), a multi-value modulation method such as 32QAM or 64QAM can be used.

The OFDM system is often used in a poor environment such as a multipath environment or mobile transmission due to its nature. In a multipath environment, a receiver receives a combined wave of a main wave directly propagating from a transmitter and a reflected wave that is reflected by a mountain or a building and arrives with a delay time. Further, in mobile transmission, Rayleigh fading in which the signal level of the main wave and the reflected wave varies independently occurs, and the reflected wave level may be larger than the main wave level.
Various measures have been studied as a measure for reducing the reception performance degradation due to such reflected waves, and a typical example is the addition of a guard interval.

As shown in FIG. 8, the guard interval is a signal obtained by adding a rear part of an effective symbol to a front part of the effective symbol for a data symbol of an OFDM signal (OFDM signal). In this case, the symbol of the OFDM signal is composed of an effective symbol and a guard interval.
By adding a guard interval, it is possible to avoid deterioration due to inter-symbol interference with respect to a reflected wave having a delay time falling within the guard interval. Is possible.

FIG. 9 shows a configuration example of a receiving apparatus (OFDM receiving apparatus) that receives an OFDM signal. Note that illustration and description of the synchronization processing unit, error correction processing unit, and the like are omitted.
The FFT window position control unit 12 extracts a sample of an effective symbol length from a reception sampling sequence that is a result of sampling a reception signal by an A / D (Analog to Digital) converter 11. The FFT unit 13 performs fast Fourier transform (FFT) on the extracted sample, and converts the time axis signal into a frequency axis signal (carrier signal). After the equalization processing unit 14 performs equalization processing, the demodulation unit 15 performs demodulation. At this time, the FFT window position control unit 12 needs to provide an FFT window in the received sampling sequence at a timing such that the above-described intersymbol interference does not occur.

Further, when a reflected wave is mixed, amplitude fluctuation, phase rotation, and the like occur. Therefore, in a modulation method that needs to be demodulated by a synchronous detection method such as 16QAM, 32QAM, or 64QAM, the amplitude and phase are corrected for each carrier. Need to do.
FIG. 10 shows an example of temporal timing between the symbol waveform of the OFDM signal and the FFT window when the position of the FFT window exactly matches the position of the effective symbol. As described above, when the position of the FFT window coincides with the position of the effective symbol, the phase of each carrier is a phase angle with respect to all the carriers, as schematically shown in FIG. Becomes 0 degree (°). This is because all carriers start from 0 degrees and end at 0 degrees within the FFT window.

However, as shown in FIG. 12, when the position of the FFT window is shifted in time from the position of the effective symbol by K samples, phase rotation occurs in each carrier. Since the amount of this phase rotation increases in proportion to the carrier number, the signal rotates at an angular frequency of (−2πK) as schematically shown in FIG. 13 as an example of phase rotation.
Therefore, the spectrum of this phase rotation becomes an impulsive waveform located in the (−K) sample, as shown in FIG.

FIG. 15 shows an example of an FFT window when a reflected wave having a delay time corresponding to K samples is mixed. When the FFT window is provided in synchronization with the main wave as in the illustrated example, the phase rotation of the main wave can be regarded as equivalent to that shown in FIG. 11, and the phase rotation for the reflected wave is shown in FIG. It can be regarded as equivalent to a thing. Since linear calculation is possible, the phase rotation matches the result obtained by adding the phase rotation amounts of those shown in FIG. 11 and those shown in FIG. 13, and the spectrum at that time also has a main wave as shown in FIG. And a waveform obtained by linearly adding the spectrum of the reflected wave.
In this way, under the influence of a reflected wave or the like generated in the transmission system, these phase rotations change every time or every carrier. For example, in order to demodulate a signal modulated by 64QAM or the like, it is necessary to correct amplitude fluctuation and phase rotation generated in the transmission path. For this reason, as shown in FIG. In general, a pilot carrier which is a phase reference carrier is provided.

The equalization processing unit 14 estimates channel characteristics from a plurality of received pilot carriers in order to correct the generated channel distortion. As a method for estimating the channel characteristics from the pilot carrier, for example, the amplitude characteristic and the phase characteristic of the data carrier portion where the pilot carrier is not arranged are estimated by performing interpolation processing on the received pilot carrier. Is possible.
The equalization processing unit 14 further corrects the amplitude and phase by complex division of the data carrier and the transmission path characteristic calculated by the pilot carrier interpolation process.

Next, the interpolation process will be described in detail.
As shown in FIG. 16, when the delay time of the reflected wave becomes longer, the spectrum of the phase angle also spreads in proportion to the delay time. In the OFDM method, inter-symbol interference does not occur with respect to a reflected wave having a delay time until the guard interval period Tg. Therefore, it is necessary to perform accurate interpolation for the reflected wave within the guard interval period Tg. There is.
The spectrum distribution of the phase angle when the delay time of the reflected wave reaches the guard interval period Tg has a frequency extending to (-Tg to 0) and has a bandwidth of Tg as shown by the hatched portion in FIG. is doing.
Here, in order to correctly interpolate a reflected wave having a phase angle spectrum having a bandwidth of Tg, it is necessary to arrange the pilot carrier intervals at least at the intervals shown in Equation 1 according to the sampling theorem. .

(Equation 1)
(Effective symbol length / Tg) (Equation 1)

As the pilot carrier, for example, a CP (Continuous Pilot) as shown in FIG. 19A and a SP (Scattered Pilot) as shown in FIG. 19B are known.
In the case of CP, the pilot interval must satisfy Equation 1.
In the case of SP, since the position of the pilot carrier is different for each symbol, as shown in FIGS. 20 (a) and 20 (b), the received pilot carrier (circled in the drawing) is set in the symbol direction. Thus, the carrier channel characteristics (circles indicated by diagonal lines in the figure) are estimated by performing the interpolation process, so that Equation 1 can be approximately satisfied.
For example, in an OFDM signal having an effective symbol length of 1024 [samples] and a guard interval length of 128 [samples], in the case of CP, 8 [carriers] (= 1024 [samples] / 128 [samples] are included in the symbol. ]), It is necessary to provide a pilot carrier at every interval. However, in the case of SP, an interval of 8 [carrier] may be satisfied after the time interpolation process.

In the interpolation processing in the equalization processing unit 14, it is necessary to perform frequency interpolation processing on the reflected wave having the spectrum distribution as shown in FIG.
In general, in order to perform the frequency interpolation operation of the signal having the frequency distribution in the hatched range shown in FIG. 18, it is necessary to use a filter having the frequency range of the hatched frame in the pass region. Therefore, in the case of a normal digital low pass filter (LPF), it is necessary to use a digital LPF having characteristics as shown by a dotted line in FIG. However, the filter having this characteristic requires a complex digital filter because the positive frequency characteristic and the negative frequency characteristic are not symmetric, but the complex filter includes four LPFs 21 to 24 as shown in FIG. And two adders 25 and 26, and it is necessary to use four normal digital LPFs, which increases the logic scale.

In order to solve such a problem, as shown in FIGS. 23 (a) and 23 (b), the spectrum of the phase angle is modulated, and as shown by the dotted line in FIG. By making the negative frequency characteristics symmetrical with each other, the configuration of the complex filter can be simplified and the LPFs 31 and 32 can be configured as shown in FIG.
In the filter shown in FIG. 24, the logical scale is reduced by almost half compared to the complex filter shown in FIG.

Various methods are conceivable as modulation of the phase angle spectrum, that is, frequency shift. For example, a method of directly performing a modulation operation on the received sampling sequence, or a received sampling sequence input to the FFT unit 13 is possible. There is a method for rearranging a part of them cyclically.
Hereinafter, a method for cyclically rearranging a part of the received sampling series input to the FFT unit 13 will be described.

First, the meaning of the calculation performed by the FFT unit 13 will be briefly described.
FIG. 25A schematically shows a received direct wave (for example, main wave) and a range to be cut out for input to the FFT unit 13. The FFT unit 13 of the receiving apparatus cuts out a signal sequence of 1024 sample clocks of (B + b), which has been subjected to inverse fast Fourier transform (IFFT: Inverse FFT) operation in the transmitting apparatus, and performs FFT processing. Here, the FFT unit 13 performs discrete Fourier transform on the assumption that the input signal sequence is repeated infinitely as shown in FIG.
Therefore, as shown in FIG. 25 (c), the head b ″ portion (for example, the signal sequence for the first 32 sample clocks) of the B signal sequence shown in FIG. When the FFT processing is performed after moving to the rear of the column portion, the signal sequence of the (B + b) portion of the direct wave (for example, main wave) shown in FIG. The same result as that obtained by performing FFT processing on the signal sequence preceded by the clock period) is obtained.

As shown in FIG. 12, when the position of the FFT window is shifted in time before K samples, the rotation amount of the phase angle rotates in the negative direction at a rate of K rotations per effective symbol length.
On the other hand, as shown in FIGS. 25A to 25C, rearranging the FFT input order is equivalent to shifting the FFT window position backward in time. Therefore, the fact that the b ″ sample shown in FIGS. 25B and 25C is moved to the back of the symbol indicates that the rotation amount of the phase angle is in the positive direction at a rate of + b ″ rotation per effective symbol length. This corresponds to rotation, and the phase angle is shifted in frequency by + b ″ samples.
Accordingly, as shown in FIGS. 23A and 23B, when the frequency shift of (Tg / 2) samples is performed, the FFT window is acquired in synchronization with the main wave, and the front (Tg / 2) samples are acquired. Can be realized by rearranging the symbols to the rear of the symbols.

FIG. 26 shows a configuration example of an OFDM receiving apparatus to which a function for rearranging such samples is added.
Similarly to the above, after the A / D conversion by the A / D converter 11, an FFT window is provided on the received sampling series by the FFT window position control unit 12, and the sample value in the window is captured. The rearrangement processing unit 41 performs the above-described rearrangement process using a storage element having a storage function such as a FIFO (First In First Out) memory. Similarly to the above, the FFT unit 13 performs FFT, the equalization processing unit 14 estimates the channel characteristics, and corrects the channel characteristics for the received data carrier signal. The equalized signal is demodulated by the demodulator 15 and output as an information code.

JP 2003-229831 A

As described above, in the OFDM receiving apparatus as shown in FIG. 26, the position of the FFT window is adaptively controlled to a position where no intersymbol interference occurs, and (Tg / 2) samples are rearranged to obtain the phase angle. A method of shifting the frequency of the spectrum is used.
However, when the position of the FFT window is adaptively controlled, the window position with respect to the received signal may be shifted for each symbol, and the amount of rotation of the phase angle varies between symbols as shown in FIG. Resulting in.
For this reason, there is no problem in the case of a CP in which the frequency interpolation process is completed for each symbol. However, in the case of an SP that requires time interpolation, time interpolation is performed due to a change in the amount of phase angle rotation between symbols. There was a problem that processing could not be performed normally.

  As a specific example, in a transmission line in which reflected waves are mixed, rotation occurs at the phase angle of each carrier due to the influence of the reflected waves. In addition, in order to accurately equalize the reflected wave within the guard interval period, it is necessary to position the phase angle spectrum within the pass band of the interpolation filter. Control is performed so as to be within the pass band. However, when the amount of rotation of the phase angle changes and the pilot carrier is SP, the time direction interpolation processing is necessary, so that normal time interpolation processing becomes difficult.

  The present invention has been made in view of such a conventional situation. For a received signal using an orthogonal frequency division multiplexing modulation system (OFDM system), a reception sampling sequence is arranged before the fast Fourier transform (FFT). An object of the present invention is to provide a receiving apparatus that can improve reception quality by effectively controlling the mode of switching.

In order to achieve the above object, the receiving apparatus according to the present invention receives a signal transmitted by the OFDM method and performs the following processing.
That is, the A / D conversion means performs A / D conversion on the received signal to obtain a received sampling sequence. A window timing setting unit sets the timing of an FFT window (FFT window) for the received sampling series. The rearranging means converts the first sample of the received sampling sequence in the set window by a sample amount based on the difference between the set window timing and a predetermined reference timing, and the received sampling sequence in the window. Rearrange to the tail. An FFT execution unit executes FFT on the rearranged received sampling sequence. An equalization processing unit performs an equalization process on the execution result of the FFT. The demodulating means executes demodulation processing on the execution result of the equalization processing.

Therefore, by performing the FFT by rearranging the samples of the received sampling series by the sample amount based on the difference between the set window timing and the predetermined reference timing, for example, the set window timing is Even in such a case, the fluctuation of the rotation amount of the phase angle in the symbol direction can be suppressed, and the time interpolation process in the symbol direction can be performed with high accuracy. Thereby, the frequency interpolation process or the frequency extrapolation process in the frequency direction can be accurately performed.
As described above, the reception quality can be improved by effectively controlling the manner in which the reception sampling series is rearranged in the preceding stage of the FFT for the reception signal using the OFDM scheme.

Here, as the reception sampling series, for example, digital signal values (samples) sampled from analog reception signals by A / D conversion are arranged in time series.
In addition, as a window for FFT, for example, a window for cutting out a received sampling sequence from a certain start timing to a certain end timing as an FFT target is used.
Moreover, as timing, it is also possible to grasp | ascertain as a position about the signal value arranged in time series, for example.
Various timings may be used as the predetermined reference timing.

In addition, as the sample amount based on the difference between the set window timing and a predetermined reference timing, various amounts may be used. For example, the difference between the top of the window and the reference timing is d, and the main amount is When the difference between the head of the effective symbol of the wave and the reference timing is α, the sample amount C (= d−α) can be used.
As the main wave, for example, a direct wave or a wave having the maximum level is used. In addition to the main wave, for example, a reflected wave is received.
As the equalization processing, for example, pilot symbol interpolation or extrapolation processing is performed with respect to time (symbol) or frequency, and the amplitude or phase of the received signal is corrected based on the processing result. .

The receiving apparatus according to the present invention has the following configuration as one configuration example.
That is, in the window timing setting means, the transmission line characteristic detection means detects the transmission line characteristic based on the received sampling sequence, and the window timing determination means determines the window timing based on the detected transmission line characteristic. The window extraction means extracts the received sampling sequence in the window set at the determined window timing.
In the rearrangement means, the reference timing generation means generates the reference timing, and the rearrangement amount control means determines the amount of samples to be rearranged based on the difference between the set window timing and the generated reference timing. And a rearrangement process executing means executes a process of rearranging the first sample of the received sampling sequence in the set window by the controlled sample amount to the end of the received sampling sequence in the window.

Therefore, when controlling the timing of the window based on the transmission path characteristics of the received signal, the accuracy of the receiving process is improved by controlling the rearrangement amount of the received sampling sequence based on the timing of the window and the reference timing. Can do.
Here, various transmission path characteristics may be used, and for example, the timing (temporal position) of the main wave or reflected wave, or the level of the main wave or reflected wave can be used.
The reference timing is defined by, for example, a signal oscillated from an oscillator provided inside or outside the receiving apparatus, a signal generated from the signal, or a signal obtained from the received signal. Timing can be used.

The receiving apparatus according to the present invention has the following configuration as one configuration example.
That is, a symbol of a signal transmitted by the OFDM scheme is composed of a guard interval and a valid symbol.
Further, the reference timing control means has a constant difference between the timing of the effective symbol of the main wave included in the received signal and the reference timing, and the main wave is effective at the head of the received sampling sequence after the rearrangement. The reference timing is controlled so that the beginning of the symbol is arranged.

Therefore, by such control, for example, the rotation amount of the phase angle becomes zero (0) with respect to the main wave, and the accuracy of the reception process can be improved.
Here, as the signal of the OFDM system, for example, a signal in which the same part as the part behind the effective symbol is used as a guard interval and the guard interval is added to the head of the effective symbol is used.

  As described above, according to the receiving apparatus of the present invention, the received sampling sequence is obtained by A / D converting the received signal of the OFDM system, and the timing of the window for FFT is set for the received sampling sequence. Then, the first sample of the received sampling sequence in the window is rearranged by the sample amount based on the difference between the timing of the window and a predetermined reference timing, and the FFT is performed on the rearranged received sampling sequence Since the equalization process is performed on the execution result of the FFT and the demodulation process is performed on the execution result of the equalization process, the received signal using the OFDM method is The reception quality can be improved by effectively controlling the manner of rearranging the reception sampling series.

An embodiment according to the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration example of a receiving apparatus (OFDM receiving apparatus) of a digital transmission apparatus using the OFDM system according to an embodiment of the present invention.
The OFDM receiver of this example includes an A / D converter 1, a multipath detection unit 2, an FFT window control unit 3, a reference timing generator 4, a rearrangement amount control unit 5, and a variable rearrangement control unit. 6, an FFT unit 7, an equalization processing unit 8, and a demodulation unit 9.
In the OFDM receiving apparatus of this example, a window position corresponding to the transmission path characteristic is provided, and the rearrangement amount of the received sampling series is variably controlled based on the reference timing signal.

An example of the configuration and operation of the OFDM receiver of this example will be described.
The received analog signal is input to the A / D converter 1, and the signal converted into a digital signal by the A / D converter 1 is output to the multipath detection unit 2 and the FFT window position control unit 3. Here, the A / D converted reception signal corresponds to a reception sampling sequence that is a result of sampling the analog reception signal.

The multipath detection unit 2 is a circuit that observes the environment of the transmission path such as multipath from the received sampling series.
For example, the transmission path environment in mobile transmission or the like changes from moment to moment, and the temporal positions of the main wave and the reflected wave and their levels change.
For this reason, the multipath detection unit 2 sequentially detects the temporal positions of the main wave and the reflected wave, or their levels, for each symbol or every several tens to several hundreds of symbols, and information on the detection result is FFT. The data is output to the window position control unit 3 and the rearrangement amount control unit 5.
Here, various configurations of the multipath detection unit 2 may be used. As an example, the transmitter inserts a synchronization symbol into a part of the OFDM signal symbol, and the receiver performs a cross-correlation operation between the synchronization symbol stored in advance and the received sampling sequence. Thus, the temporal position of the main wave or the reflected wave or the level thereof is observed.

In this example, the multipath detection unit 2 generates a signal (FFT window start timing signal) WR indicating the timing for providing the FFT window based on the detection result regarding the transmission path environment, and uses the FFT window start timing signal WR as the FFT window start timing signal WR. Output to the FFT window position control unit 3 and the rearrangement amount control unit 5.
Here, in a transmission path environment where a reflected wave having a delay time within the guard interval exists, it is necessary to provide the position of the FFT window so that intersymbol interference does not occur.
For this reason, the FFT window position control unit 3 provides an FFT window having a timing as shown in FIG. 2 so that intersymbol interference does not occur due to adaptive control, and the received sampling sequence located inside the FFT window is determined. Cut and output to the variable rearrangement processing unit 6.

In the example of FIG. 2, the main wave and the reflected wave composed of the head guard interval and the subsequent effective symbol are shown, and the reflected wave is delayed by K samples compared to the main wave. FIG. 2 shows a pulse of the FFT window start timing signal WR (FFT window start pulse), and the timing of the FFT window indicated by the FFT window timing pulse WE coincides with the timing of the effective symbol of the main wave. Yes.
Here, due to the detection error by the multipath detection unit 2 and adaptive control of the FFT window position, the FFT window position is shifted for each symbol, and the rotation amount of the phase angle changes.
Therefore, in this example, the rearrangement amount control unit 5 controls the rearrangement amount of the received sampling series so as to cancel such a change in the rotation amount of the phase angle.

The reference timing generator 4 generates a signal representing the reference timing (reference timing signal) and outputs the signal to the rearrangement amount control unit 5.
As the reference timing signal, for example, a pulse signal synchronized with a symbol generated at a symbol period based on a synchronization signal input from a voltage controlled crystal oscillator (VCXO) that generates a reception synchronous clock or a rubidium oscillator from the outside, A pulse signal having a cycle that is n times (n is a natural number) the symbol cycle can be used.
The rearrangement amount control unit 5 includes the FFT window start timing specified by the FFT window start timing signal WR input from the multipath detection unit 2 and the timing specified by the reference timing signal input from the reference timing generator 4. And outputs a signal (control signal) for controlling the variable rearrangement processing unit 6 to the variable rearrangement processing unit 6 so that the rotation amount of the phase angle is always constant.

An example of control performed by the rearrangement amount control unit 5 will be described with reference to FIG.
In this example, x used as a subscript represents the symbol number, and the fixed delay amount α between the head of the effective symbol of the main wave and the reference timing signal is in the period subject to time interpolation. Is assumed to be so small that the amount of fluctuation can be ignored.
The rearrangement amount control unit 5 obtains the time difference dx between the pulse of the FFT window start timing signal WRx (FFT window start pulse) and the pulse of the reference timing signal for the xth symbol. Since the time difference between the main wave and the reference timing signal is a fixed delay amount, the rearrangement amount Cx at this time is determined as shown in Equation 2.

(Equation 2)
Cx = dx−α (Expression 2)

The rearrangement amount control unit 5 notifies the variable rearrangement processing unit 6 of information on the determined rearrangement amount Cx by a control signal.
As shown in FIG. 4 and FIG. 5, the variable rearrangement processing unit 6, in accordance with the information on the rearrangement amount Cx input from the rearrangement control unit 5, For the received sampling series, the samples on the front side of the captured FFT window are rearranged to the rear side of the symbols. In this way, the amount of rotation of the phase angle can be adjusted so that the same phase angle is obtained for each symbol by variably controlling the amount of rearrangement of the received sampling sequence with respect to the position of the FFT window that varies for each symbol. Can be constant.

Here, a specific example of the rearrangement amount control shown in FIGS. 4 and 5 will be described.
FIG. 4 shows an example of the first symbol (symbol 1), and FIG. 5 shows an example of the second symbol (symbol 2).
In the symbol 1 shown in FIG. 4, the position of the FFT window is the position indicated by the FFT window timing pulse WE1, whereas in the symbol 2 shown in FIG. 5, the position of the FFT window is indicated by the FFT window timing pulse WE2. The position has changed.

At this time, in the symbol 1, the time difference d1 between the start timing of the FFT window and the reference timing signal is detected, the rearrangement amount C1 = d1−α = A is obtained, and the sample portion corresponding to this A is the remaining sample B , Rearrange after C. That is, after rearrangement, the samples are arranged in the order of B, C, and A.
Similarly, in symbol 2, the time difference d2 between the start timing of the FFT window and the reference timing signal is detected, the rearrangement amount C2 = d2-α = A ′ is obtained, and the sample portion corresponding to this A ′ is used as the remaining part. Rearrange samples B and C '. That is, after the rearrangement, the samples are arranged in the order of B, C ′, and A ′.

In this case, in the different symbols 1 and 2, the lengths of the rearrangement amounts A and A ′ and the rear samples C and C ′ change according to the variation of the FFT window position WEx, but the central sample is changed. The length of B is always a fixed length. Therefore, for all the symbols 1 and 2, by the rearrangement processing of this example, the top of the symbol is always the top of the sample B, so that the same phase angle spectrum is always arranged at the top of the FFT window. Thus, the rotation fluctuation of the phase angle does not occur.
Then, in the time interpolation process, for example, when a change in the rotation amount of the phase angle as shown in FIG. 27 occurs, the interpolation process cannot be performed normally. Therefore, the time interpolation process can be performed normally.

Further, in the frequency extrapolation process, as a measure for reducing the degradation of demodulation accuracy near the band edge, for example, a method of performing the 0th-order hold type extrapolation process has a small circuit scale and is easy to implement. it is conceivable that. However, in the 0th-order hold type, when the amount of rotation of the phase angle is increased, the extrapolation accuracy is deteriorated, and the degree of deterioration is almost the same as when no extrapolation is performed.
Therefore, in this example, the amount of rotation of the phase angle is set to a small value by controlling the amount of samples rearranged in the received sampling series, thereby improving the extrapolation accuracy of the zero-order hold type frequency extrapolation process, The demodulation accuracy near the band edge is improved.

In order to efficiently perform frequency extrapolation in a transmission path environment in which a plurality of reflected waves are mixed, as shown in FIG. 6, the main wave is positioned at the center of the frequency interpolation filter band, that is, the DC frequency. In this case, since the main wave is located at the DC frequency, the phase angle of this signal is 0, that is, a straight line. This is convenient for the 0th-order hold type frequency extrapolation, and a highly accurate frequency extrapolation can be performed.
In this way, by setting the rotation amount of the phase angle fixed by the time interpolation process to 0 with respect to the main wave, that is, by performing processing so that the phase angle of the main wave does not rotate, frequency interpolation and High accuracy can be obtained in the frequency extrapolation process.

In order to prevent the phase angle of the main wave from rotating, in FIG. 4 or FIG. 5, the head of the received sampling sequence after rearrangement arranged at the head position of the FFT window (sample portion B in FIG. 4 or FIG. 5). Is set to the head of the effective symbol of the main wave.
As an example, first, the start position of the main wave is detected by performing correlation calculation of guard intervals and correlation calculation of synchronization symbols. Next, the reference timing signal is controlled in the reference timing generator 4 so that the time difference between the detected start position of the main wave and the reference timing signal becomes the fixed delay amount α. In this control, very slow control is performed so as to satisfy the condition that the variation amount of the fixed delay amount α is negligibly small during the time interpolation target period.

  The variable rearrangement processing unit 6 outputs the received sampling sequence rearranged as described above to the FFT unit 7, and the FFT unit 7 receives the rearranged received sampling sequence input from the variable rearrangement processing unit 6. The FFT processing is performed and the result is output to the equalization processing unit 8. The equalization processing unit 8 performs equalization processing on the FFT processing result input from the FFT unit 7 to correct the amplitude and phase, and The result is output to the demodulator 9, and the demodulator 9 modulates, for example, the modulation on the transmission side with respect to a plurality of carrier signals (modulated for each carrier) as the result of the equalization processing input from the equalization processor 8. A demodulation process corresponding to the method is performed and the result is output. In this example, the equalization processing unit 8 performs time interpolation processing in the symbol direction, frequency interpolation processing in the carrier direction, or frequency extrapolation processing.

  As described above, in this example, the amount of reception sampling sequence rearrangement is variably controlled based on the reference timing signal with respect to variation in the position of the FFT window, and the start position of the received sampling sequence after rearrangement is determined. By setting appropriately, even in the case of SP, it is possible to perform the time interpolation process and the frequency interpolation process and the frequency extrapolation process with high accuracy.

As described above, in the OFDM receiving apparatus of this example, in the transmission apparatus that transmits the OFDM signal modulated by the OFDM method, the OFDM signal is received, and a temporal window is obtained with respect to the received sampling sequence based on the transmission path characteristics. (FFT window) is provided, and a signal sequence is generated by cyclically rearranging a signal of N samples from the start position of the FFT window to a position behind the FFT window, and in this case, the number of samples N of the rearrangement is calculated as FFT. Variable control is performed based on the time difference between the window start position and the reference timing signal.
In the OFDM receiver of this example, the reference timing signal is variably controlled so that the time difference between the start position of the effective symbol of the main wave and the reference timing signal becomes a constant time difference α (α is a real number), and frequency interpolation is performed. Controls the position of the main wave within the band of the interpolation filter.
In the OFDM receiver of this example, a divided clock of the reception clock, an input from a highly accurate oscillator, or a divided signal thereof is used as the reference timing signal.

  Specifically, in the OFDM receiver of this example, the multipath detection unit 2 detects the transmission path characteristics from the received sampling sequence, and the FFT window position control unit 3 prevents intersymbol interference from occurring based on the detection result. Is provided with an FFT window, the N samples on the front side of the FFT window fetched by the variable rearrangement processing unit 6 are rearranged to the rear side of the symbol, and then FFT is performed by the FFT unit 7 to obtain + N for the phase angle spectrum. When the frequency shift is performed, the rearrangement amount control unit 5 detects a time difference between the position of the FFT window provided by the FFT window position control unit 3 and the reference timing signal generated by the reference timing generator 4. Based on the detection result, the sample rearrangement amount is controlled so that the rotation amount of the phase angle caused by the variation of the FFT window position does not change. To.

  Therefore, in the OFDM receiver of this example, when a temporal FFT window is provided for the received sampling sequence based on the transmission path characteristics, the received sampling sequence is based on the time difference between the start position of the FFT window and the reference timing signal. By variably controlling the rearrangement amount, it is possible to perform time interpolation processing without changing the rotation amount of the phase angle between symbols. As a result, for example, even in a transmission path environment in which delayed waves (reflected waves) are mixed, it is possible to perform time interpolation processing normally, and even when SP is used, time interpolation processing is performed. In addition, it is possible to realize frequency interpolation and frequency extrapolation with high accuracy. As an example, the performance of diversity reception for mobile communication can be improved.

  In the OFDM receiving apparatus of this example, the A / D converter 1 is configured by the function of the A / D converter 1, and the function of the multipath detector 2 that constitutes the transmission path characteristic detector and the window timing determiner. The window timing setting unit is configured by the function of the FFT window position control unit 3 constituting the window extraction unit and the function of the reference timing generator 4 constituting the reference timing generation unit and the rearrangement amount control unit. The rearrangement unit is configured by the function of the rearrangement amount control unit 5 and the function of the variable rearrangement processing unit 6 constituting the rearrangement processing execution unit, and the FFT execution unit is configured by the function of the FFT unit 7. The function of the equalization processing unit 8 constitutes an equalization processing means, and the function of the demodulation unit 9 constitutes a demodulation means, which is generated by the reference timing generator 4. Reference timing control means by function of controlling the like control unit the timing of the quasi-timing signal (not shown) is formed.

Here, the configuration of the receiving device and the transmission device according to the present invention is not necessarily limited to those described above, and various configurations may be used. The present invention can also be provided as, for example, a method or method for executing the processing according to the present invention, a program for realizing such a method or method, or a recording medium for recording the program. Moreover, it is also possible to provide various devices and systems such as a wireless communication device and a wireless communication system.
The application field of the present invention is not necessarily limited to the above-described fields, and the present invention can be applied to various fields.

In addition, as various types of processing performed in the receiving apparatus and the transmission apparatus according to the present invention, for example, the processor executes a control program stored in a ROM (Read Only Memory) in a hardware resource including a processor and a memory. For example, each functional unit for executing the processing may be configured as an independent hardware circuit.
The present invention can also be understood as a computer-readable recording medium such as a floppy (registered trademark) disk or a CD (Compact Disc) -ROM storing the control program, and the program (itself). The processing according to the present invention can be performed by inputting the program from the recording medium to the computer and causing the processor to execute the program.

It is a figure which shows the structural example of the OFDM receiver which concerns on one Example of this invention. It is a figure which shows an example of the timing of the FFT window synchronized with the main wave. It is a figure which shows an example of the relationship between the position of an FFT window, and a reference timing signal. It is a figure which shows an example of rearrangement of a received sampling series. It is a figure which shows another example of rearrangement of a received sampling series. It is a figure which shows an example of a phase angle spectrum in case the signal of the main wave of the maximum level is located in the center of a zone | band. It is a figure which shows an example of the modulation signal by an OFDM system. It is a figure which shows an example of the waveform of the symbol by an OFDM system. It is a figure which shows the structural example of an OFDM receiver. It is a figure which shows an example of the waveform of the symbol by an OFDM system, and the time timing of an FFT window when the timing of an effective symbol and an FFT window corresponds. It is a figure which shows an example of a phase angle in case the timing of an effective symbol and an FFT window corresponds. It is a figure which shows an example of the waveform of the symbol by an OFDM system, and the time timing of an FFT window when the timing of an FFT window has shifted | deviated K sample with respect to the effective symbol. It is a figure which shows an example of a phase angle when the timing of a FFT window has shifted | deviated K sample with respect to the effective symbol. It is a figure which shows an example of a phase angle spectrum in case the timing of a FFT window has shifted | deviated -K sample with respect to the effective symbol. It is a figure which shows an example of the timing of an FFT window when a reflected wave mixes with a main wave. It is a figure which shows an example of a phase angle spectrum in case a reflected wave mixes with a main wave. It is a figure which shows an example of arrangement | positioning of the pilot carrier with respect to a data carrier. It is a figure which shows an example of distribution of the spectrum of the reflected wave in a guard interval period. (A) is a figure which shows an example of arrangement | positioning of CP, (b) is a figure which shows an example of arrangement | positioning of SP. (A) And (b) is a figure which shows an example of the time interpolation in SP. It is a figure which shows an example of the frequency characteristic of LPF. It is a figure which shows the structural example of a complex filter. (A) And (b) is a figure which shows an example of the modulation | alteration of a phase angle spectrum. It is a figure which shows the structural example of the simplified complex filter. (A)-(c) is a figure which shows an example of the rearrangement process of a signal sequence. It is a figure which shows the structural example of an OFDM receiver. It is a figure which shows an example of the change of the rotation amount of a phase angle.

Explanation of symbols

  1, 11... A / D converter 2, Multipath detection unit 3, 12 FFT FFT position control unit 4 Reference timing generator 5 Rearrangement control unit 6 Variable rearrangement processing unit 7, 13,... FFT unit 8, 14, .. Equalization processing unit 9, 15 ... Demodulation unit 21-24, 31, 32 ... LPF 25, 26 ... Adder , 41 .. Sorting processing part, +

Claims (3)

In a receiving apparatus that receives a signal transmitted by the OFDM method,
A / D conversion means for A / D converting a received signal to obtain a received sampling sequence;
Window timing setting means for setting a window timing for FFT on the received sampling sequence;
Rearrangement for rearranging the first sample of the received sampling sequence in the set window to the end of the received sampling sequence in the window by a sample amount based on the difference between the set window timing and a predetermined reference timing Means,
FFT execution means for performing FFT on the received sampling sequence after the rearrangement;
Equalization processing means for executing equalization processing on the execution result of the FFT;
Demodulation means for performing demodulation processing on the execution result of the equalization processing;
A receiving apparatus comprising: The receiving device according to claim 1,
The window timing setting means includes transmission line characteristic detection means for detecting transmission line characteristics based on the received sampling sequence, and window timing determination means for determining the window timing based on the detected transmission line characteristics; In-window extraction means for extracting the received sampling sequence in the window set at the determined window timing,
The reordering means controls the amount of samples to be reordered based on the difference between the reference timing generation means for generating the reference timing and the set window timing and the generated reference timing. Reordering process execution means for executing a process of rearranging the first sample of the received sampling sequence in the set window within the set window to the tail of the received sampling sequence in the window by the controlled sample amount,
A receiving apparatus. The receiving device according to claim 1 or 2,
The symbol of the signal transmitted by the OFDM scheme is composed of a guard interval and an effective symbol,
In the receiving apparatus, the difference between the timing of the effective symbol of the main wave included in the received signal and the reference timing is constant, and the beginning of the effective symbol of the main wave is arranged at the beginning of the rearranged received sampling sequence A reference timing control means for controlling the reference timing as described above,
A receiving apparatus.

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