JP2011097353A - Ofdm signal transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the peak power of an OFDM modulation wave without changing a transmission frequency band an a bit rate, without generating the distortion of a modulation waveform or influencing the reception of valid data. <P>SOLUTION: A bit inversion part 10 inverts bits of invalid data included in digital data in accordance with preset bit inversion position information to generate bit-inverted digital data on a system basis. A transmission signal selection part 13 calculates the peak power about an OFDM signal of the original digital data and an OFDM signal of the bit-inverted digital data different at each system, and selects the OFDM signal having the lowest peak power at each OFDM symbol. An OFDM signal transmitter 1 executes modulation processing or the like to the selected OFDM signal to transmit the OFDM modulation wave. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for transmitting digital data after OFDM modulation.

  2. Description of the Related Art Conventionally, OFDM (Orthogonal Frequency Division Multiplexing) has attracted attention as a wireless transmission system for digital data. The OFDM system is a data transmission using a power line, terrestrial digital broadcasting (ISDB-T (Integrated Services Digital Broadcasting), ISDB-T. And xDSL (Digital Subscriber Line) using a telephone line.

  The OFDM system is a system in which a large number of digitally modulated subcarriers are frequency-multiplexed and transmitted, and each subcarrier is multiplexed so as to have orthogonality. The modulation / demodulation circuit uses this orthogonality to perform modulation / demodulation of each subcarrier by fast Fourier transform (hereinafter referred to as FFT (Fast Fourier Transform)) and its inverse transform (hereinafter referred to as IFFT (Inverse Fast Fourier Transform)). Can be done in a lump.

  In the OFDM scheme, each subcarrier is arranged with a minimum frequency interval under the condition of maintaining orthogonality. Further, when the number of subcarriers increases, the spectrum approaches a rectangle, and a band limiting filter is not necessary. For this reason, when the OFDM system is adopted, there is a feature that the frequency use efficiency becomes high. Furthermore, in the OFDM scheme, the transmission rate of symbols assigned to each subcarrier can be significantly reduced as compared to the single carrier scheme. For this reason, the influence of intersymbol interference due to multipath in the transmission path can be greatly reduced, and deterioration of reception characteristics can be suppressed.

  On the other hand, an OFDM modulation wave (hereinafter referred to as an OFDM modulation wave) has a large fluctuation in instantaneous power, and a ratio of peak power to average power (hereinafter referred to as PAPR (Peak to Average Power Ratio)) is large. Are known. The PAPR is maximum when the phases of the subcarriers coincide with each other. When the number of subcarriers is M, the maximum value of PAPR is M times that of one subcarrier. For example, when M = 1024, the maximum PAPR value of the OFDM modulated wave is 10 log1024≈30 dB larger than the maximum PAPR value of one subcarrier.

  In order to transmit / receive such a signal having a large PAPR, it is necessary to set a large dynamic range of A / D and D / A in the modulation / demodulation circuit, which increases the cost of the transmission / reception apparatus. On the other hand, when the dynamic range of A / D and D / A is not set in a sufficient range, a large amplitude value cannot be accurately expressed, and amplitude clipping occurs, resulting in distortion of the waveform. Alternatively, the number of bits that can be assigned to a certain amplitude range decreases, and the S / N decreases due to an increase in quantization noise.

  Further, when a signal having such a large PAPR is amplified, a large back-off (ratio of output saturation power level to maximum output power level) must be taken in order to use the linear operation region of the amplifier. For this reason, the power consumed with respect to the average transmission power increases, and the power cannot be consumed effectively. On the other hand, when the back-off is suppressed to a small value, the waveform is distorted when the peak power level of the input signal reaches the nonlinear operating region of the amplifier. Waveform distortion degrades signal quality, causes bit errors, generates out-of-band radiation, and interferes with signals transmitted in other frequency bands.

  As described above, when the OFDM method is adopted as a digital data wireless transmission method, the OFDM modulated wave becomes a large PAPR signal, so that the dynamic range of A / D and D / A matches the size of PAPR. Therefore, it is necessary to set a large back-off of the amplifier. For this reason, the above-mentioned problem arises.

  In order to solve these problems, various methods have been proposed and studied. For example, there are the following methods (1) to (9).

(1) Predistortion This technique uses a distortion compensation circuit called a predistorter or a linearizer in order to reduce waveform distortion due to nonlinear amplification of an amplifier (see, for example, Patent Document 1). The distortion compensation circuit applies a distortion having an inverse characteristic to the nonlinear characteristic of the amplifier to the OFDM modulated wave. Thereby, waveform distortion can be compensated.

(2) Generation of multiple OFDM modulation waves This method divides OFDM subcarriers into a plurality of groups, and transmits OFDM modulation waves generated by IFFT for each group simultaneously from a plurality of corresponding antennas. (For example, see Patent Document 2). Thereby, since the number of subcarriers transmitted by one antenna decreases, the peak power of the OFDM modulated wave transmitted by one antenna can be reduced.

(3) Clipping and Filtering This method uses an OFDM signal (hereinafter, as shown in FIG. 2 described later), a time waveform of an OFDM modulated wave generated by one IFFT operation is called an OFDM symbol, and an OFDM symbol is a time axis. The peak power above the threshold value generated in the signal arranged on the upper side is called an OFDM signal) is limited (clipped) to the threshold value, and the generated out-of-band radiation is reduced by a filter (for example, , See Patent Document 3). Thereby, the peak power of the OFDM modulated wave can be suppressed.

(4) Companding In this method, peak power is detected for each OFDM symbol, and the average power of the OFDM symbol is controlled according to the magnitude of the detected peak power (see, for example, Non-Patent Document 1). . In this method, the peak power of all OFDM symbols can be limited to a certain level or less by normalizing the average power of each OFDM symbol with the peak power.

(5) Dummy signal insertion This technique uses a subcarrier and a dummy signal different from those used for data transmission and performs IFFT on the subcarrier modulated by the dummy signal and the subcarrier for data transmission together ( For example, see Non-Patent Document 2 and Patent Document 4.) As a result, the peak power of the OFDM modulated wave can be reduced. Specifically, a signal component exceeding a preset threshold is detected, a signal that cancels this component is obtained, and this signal is used as a dummy signal.

(6) Selective mapping (SLM (Selective Mapping))
This method prepares a fixed number of sets of phase rotation amounts for all subcarriers, applies phase rotation to each subcarrier, performs IFFT, and selects the OFDM symbol with the lowest peak power from the generated OFDM symbols. The transmission signal is selected (see, for example, Non-Patent Document 3).

(7) Partial sequence transmission (PTS (Partial Transmit Sequence))
This method divides each subcarrier into a plurality of groups, performs IFFT for each group, gives a different phase rotation for each group, selects an OFDM symbol with the smallest peak power from the generated OFDM symbols, The transmission signal is used (see, for example, Non-Patent Document 4).

(8) Coding This method adds the redundant bit to the data to be transmitted, or encodes the data to be transmitted, and has the highest peak power among a plurality of signals obtained by IFFT of the data including the redundant bits or the coded parity. A small OFDM symbol is selected (for example, see Non-Patent Document 5). As a result, the peak power of the OFDM modulated wave can be reduced.

(9) Randomization In this method, data to be transmitted is randomized according to a set number of rules and subjected to IFFT, and an OFDM symbol having the lowest peak power is selected as a transmission signal (for example, Patent Documents). 5).

Japanese Patent No. 3,867,583 Japanese Patent No. 3793637 JP 2008-60846 A Special table 2009-516422 gazette JP-A-8-228186

"A Study on Peak Power Reduction Method for OFDM System", 2006 IEICE Communication Society Conference, B-5-57 "Low Peak OFDM Signal Generation Method by Inserting Subcarrier for Peak Reduction", 2006 IEICE Communication Society Conference, B-5-56 Bauml R. W .: “Reducing the peak-to-average power ratio of multicarrier modulation by selected mapping”, Electron. Lett. 32 (22) 1996 CIMINI L. J. Jr .: “peak-to-average power ratio reduction of an OFDM signal using partial transmit sequences”, IEEE Commun. Lett. 4 (3) pp.86-88 2000 W. Henkel et.al: “Another application for trellis shaping: PAR reduction for DMT (OFDM)”, IEEE Trans. Comuun., Vol.48, pp.1471-1476, Sept. 2000

  However, the above methods (1) to (9) have the following problems. (1) Since the predistortion method uses a distortion compensation circuit, the system scale of the system increases, and is not suitable for downsizing, low power consumption, and low cost. (2) In the multiple OFDM modulation wave generation method, since it is necessary to provide a transmission apparatus with a plurality of OFDM modulation wave generation means, a plurality of power amplifiers, and an antenna, the system scale of the system increases, and the same as (1) There's a problem. (3) In the clipping and filtering method, the peak power is limited to the threshold value, so that the signal is distorted and the signal quality is deteriorated. (4) In the companding method, since the C / N of the OFDM modulated wave changes with time, a certain transmission quality cannot be maintained.

  (5) Since the dummy signal insertion method requires a frequency band different from the frequency band for data transmission, the frequency utilization efficiency decreases. (6) In the selective mapping (SLM) method and (7) partial sequence transmission (PTS) method, a mechanism for correctly receiving the phase-rotated signal based on the information on the amount of phase rotation transmitted by the transmission device Therefore, the circuit scale of the receiving device increases. (8) In the encoding method, since redundant bits or encoded parity is added, transmission efficiency decreases. In addition, the receiving apparatus needs a mechanism for correctly extracting data from a bit sequence to which redundant bits or encoded parity is added. In particular, when encoding is performed, a decoding processing circuit is required, so that the circuit scale of the receiving apparatus increases. (9) The randomization method requires a mechanism for the receiving device to know the randomization rules used in the transmitting device.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to change a modulation waveform without changing a transmission frequency band and a bit rate in a transmission system in which digital data is OFDM-modulated and transmitted. An object of the present invention is to provide an OFDM signal transmission apparatus capable of reducing the peak power of an OFDM modulated wave without causing distortion and without affecting the reception of effective data.

  In order to achieve the above object, the invention of claim 1 is an OFDM signal transmitting apparatus for OFDM-modulating digital data and transmitting a modulated wave of the OFDM signal. Invert Fourier transform is performed on the replacement unit that replaces the data (N is an integer of 2 or more), the N-1 digital data including the data replaced by the replacement unit, and the digital data including the invalid data. An inverse Fourier transform unit; and a selection unit that selects an OFDM signal having a minimum peak power from among OFDM signals of N systems of digital data subjected to inverse Fourier transform by the inverse Fourier transform unit. To do.

  According to a second aspect of the present invention, there is provided an OFDM signal transmitting apparatus for OFDM-modulating digital data and transmitting a modulated wave of the OFDM signal. Bit inversion in which a position at which a bit of invalid data included in the digital data is inverted is preset. Based on the position information, the bit of the invalid data is inverted and the replacement unit replaces the invalid data with data of a different N-1 pattern (N is an integer of 2 or more), and the data replaced by the replacement unit N-1 system digital data including the transmission data and digital data including the invalid data are channel-coded to generate I and Q signals configured in an OFDM frame, and the channel coding unit An inverse Fourier transform unit that performs inverse Fourier transform on each of the N systems of I and Q signals generated by, and an inverse Fourier transform by the inverse Fourier transform unit From the N systems of the OFDM signal, characterized by comprising a selecting unit that selects an OFDM signal peak power is minimized for each OFDM symbol number, the.

  Further, the invention of claim 3 is an OFDM signal transmitting apparatus for OFDM-modulating digital data and transmitting a modulated wave of the OFDM signal, and digital data is channel-coded to generate I and Q signals configured in an OFDM frame. And generating an address of the inner code encoded digital data that is affected by inverting the bits of the invalid data included in the digital data, and the address of the position where the bit is inverted and the code after the inner code encoding. A transmission path encoding unit that generates set information associated with an address, and N-1 pieces (N is an integer equal to or greater than 2) of the set information generated by the transmission path encoding unit are selected. Then, for the I and Q signals generated by the transmission path encoder, the bits of the address after inner code encoding in the selected N-1 set information are inverted. By replacing the I and Q signals, a replacement unit that generates again the I and Q signals configured in different N-1 OFDM frames, and the N-1 system generated again by the replacement unit The I and Q signals and the I and Q signals generated by the transmission path encoding unit are respectively inverse Fourier transform units that perform inverse Fourier transform, and N systems of OFDM signals that are inverse Fourier transformed by the inverse Fourier transform unit. And a selection unit that selects an OFDM signal having a minimum peak power for each OFDM symbol number.

  According to a fourth aspect of the present invention, in an OFDM signal transmitting apparatus that digitally modulates digital data and transmits a modulated wave of the OFDM signal, the digital data is channel-coded to generate I and Q signals configured in an OFDM frame. And generating an address of the inner code encoded digital data that is affected by inverting the bits of the invalid data included in the digital data, and the address of the position where the bit is inverted and the code after the inner code encoding. A transmission path encoding unit that generates set information associated with an address, and N-1 pieces (N is an integer equal to or greater than 2) of the set information generated by the transmission path encoding unit are selected. Then, for the I and Q signals generated by the transmission path encoder, the bits of the address after inner code encoding in the selected N-1 set information are inverted. By replacing the I and Q signals, a replacement unit that generates again the I and Q signals configured in different N-1 OFDM frames, and the N-1 system generated again by the replacement unit An autocorrelation function is calculated for each of the I and Q signals and the I and Q signals generated by the transmission path encoding unit, and the autocorrelation function has the most impulse characteristics among the N systems of I and Q signals. And a selection unit that selects near I and Q signals for each OFDM symbol number, and an inverse Fourier transform unit that performs inverse Fourier transform on the I and Q signals selected by the selection unit.

  The invention according to claim 5 is the OFDM signal transmitting apparatus according to claim 2 or 3, wherein the selection unit selects an OFDM signal having a minimum peak power from among the N systems of OFDM signals by using an OFDM symbol number. When there are a plurality of OFDM symbol numbers affected by bit inversion by the replacement unit in the same system when selecting each, the OFDM signal of the same system is selected in the plurality of OFDM symbol numbers, Features.

  Further, the invention of claim 6 is the OFDM signal transmission apparatus according to claim 4, wherein the selection unit is configured to select an I, Q signal having an autocorrelation function closest to an impulse characteristic from the N systems of I and Q signals. When selecting a Q signal for each OFDM symbol number, if there are a plurality of OFDM symbol numbers affected by the bit inversion by the replacement unit in the same system, in the plurality of OFDM symbol numbers, I, The Q signal is selected.

  The invention according to claim 7 is the OFDM signal transmission apparatus according to claim 5 or 6, wherein the selection unit includes a plurality of OFDM symbol numbers affected by bit inversion by the replacement unit in the same system. When the selection of the plurality of OFDM symbol numbers for all systems is completed, a signal for starting the processing of the replacement unit is output to the replacement unit.

  As described above, according to the OFDM signal transmitting apparatus of the present invention, invalid data included in digital data is replaced with data of a plurality of different patterns, and the OFDM signal in the plurality of digital data including the replaced data is selected. The OFDM signal with the minimum peak power is selected, and the modulated wave of the OFDM signal is transmitted. As a result, in a transmission system in which digital data is OFDM-modulated and transmitted, the reception of effective data is affected without changing the transmission frequency band and bit rate and without causing distortion of the modulation waveform. Therefore, the peak power of the OFDM modulation wave can be reduced.

It is a figure explaining the example of digital data. It is a block diagram explaining a general OFDM modulation process. It is a block diagram which shows the structure of the OFDM signal transmitter by the 1st Embodiment (Example 1) of this invention. It is a figure explaining the process of the bit inversion part with which the OFDM signal transmitter of FIG. 3 was equipped. It is a figure which shows the example of a calculation result of the peak power in an OFDM signal. It is a figure which shows the example of the PAPR reduction effect by Example 1. FIG. It is a figure which shows the example of the BER improvement effect by Example 1. FIG. It is a figure which shows the structure of TS (Transport Stream: Transport stream) of terrestrial digital broadcasting. It is a block diagram explaining the general OFDM modulation process of terrestrial digital broadcasting. It is a block diagram which shows the structure of the OFDM signal transmitter by the 2nd Embodiment (Example 2) of this invention. It is a block diagram which shows the structure of the transmission-line encoding part which processes the data of TS. It is a block diagram which shows the structure of the transmission-line encoding part which processes the address which bit inversion position information shows. It is a figure explaining the process of the bit inversion part with which the OFDM signal transmitter of FIG. 10 was equipped. It is a figure explaining the example of the bit before and behind the convolutional encoding of the coding rate 3/4. It is a figure explaining the example of the address of the inversion bit before and behind the convolutional encoding of the coding rate 3/4. It is a figure explaining the example of the data mapped after the address of the mapped bit, and bit inversion. It is a figure explaining the example of the peak power value of OFDM symbol and OFDM symbol change information. It is a block diagram which shows the structure of the OFDM signal transmitter by the 3rd Embodiment (Example 3) of this invention. It is a figure explaining the example of null packet information, the data before and behind convolutional encoding, and an address. It is a block diagram which shows the structure of the OFDM signal transmitter by the 4th Embodiment (Example 4) of this invention.

  The best mode for carrying out the present invention will be described below with reference to the drawings. The OFDM signal transmitting apparatus according to the present invention is characterized in that it is applied to transmission of digital data including invalid data and uses invalid data for peak power reduction. The invalid data is data that is ignored by the OFDM signal receiving apparatus and does not affect the effective data. Therefore, the conventional OFDM receiving apparatus can be used as it is. As a result, the peak power of the OFDM modulated wave can be reduced without increasing the amount of information and without causing the OFDM signal receiving apparatus to perform special processing.

  First, an OFDM signal transmission apparatus according to the first mode for embodying the present invention (embodiment 1) will be described. The first embodiment is an example in which digital data including invalid data is OFDM-modulated and transmitted. FIG. 1 is a diagram illustrating an example of digital data transmitted by the OFDM signal transmission apparatus according to the first embodiment. Bits indicated with underline are invalid data, and bits not underlined are valid data. An example of invalid data is bits inserted as stuffing for rate conversion. Since invalid data has no meaning as information, it may be any one of “0” and “1” and does not affect valid data. Further, the OFDM signal receiving apparatus does not need to perform special processing on invalid data. It is assumed that the OFDM signal receiving apparatus includes means for discriminating valid data and invalid data from received data, as in the prior art.

  FIG. 2 is a block diagram illustrating general OFDM modulation processing. The digital data is mapped to I and Q signals in accordance with the modulation scheme of each subcarrier, serial-parallel converted, IFFT processed, and parallel-serial converted. Thereby, an OFDM signal is generated. An OFDM signal is generated by adding a guard interval to the OFDM signal and performing orthogonal modulation using a carrier wave. As described above, an OFDM symbol is generated by one IFFT process, and an OFDM signal is a signal in which OFDM symbols are arranged on a time axis.

  FIG. 3 is a block diagram illustrating a configuration of the OFDM signal transmission apparatus according to the first embodiment. This OFDM signal transmission apparatus 1 includes a bit inversion unit (replacement unit) 10, N mapping units 11-1 to 11-N, N IFFT units 12-1 to 12-N, a transmission signal selection unit 13, a guard An interval adding unit 8 and an orthogonal modulation unit 9 are provided. N is an integer of 2 or more.

  The bit inversion unit 10 receives digital data, inverts bits at preset positions among invalid data bits existing in the digital data, generates N−1 digital data, and performs bit inversion The digital data is output to mapping units 11-1 to 11- (N-1), respectively. The position of invalid data to be inverted in the digital data (bit inversion position information) is the mapping unit 11-1 to 11- (N-1) and the IFFT unit 12-1 to 12- (N-1) (each system). In addition, they are set in advance so as to have different patterns. Specific examples will be described later. That is, the bit inversion unit 10 replaces invalid data with data of different N-1 patterns according to preset bit inversion position information, and generates N-1 different digital data. Output.

  The mapping units 11-1 to 11- (N-1) respectively input the digital data that has been bit-inverted from the bit inversion unit 10, and the mapping unit 11-N has the same digital data as the digital data that has been input by the bit inversion unit 10. Enter the data (original digital data). The mapping units 11-1 to 11-N map the input digital data to the I and Q signals according to the modulation scheme of each subcarrier, and the I and Q signals are respectively transferred to the IFFT units 12-1 to 12-N. Output.

  The IFFT units 12-1 to 12-N receive the I and Q signals from the mapping units 11-1 to 11-N, IFFT the I and Q signals into OFDM signals, and the OFDM signals to the transmission signal selection unit 13, respectively. Output.

  The transmission signal selection unit 13 receives the OFDM signals from the IFFT units 12-1 to 12-N, calculates the peak power for each of the N OFDM signals, and obtains the lowest peak power among the N peak powers. The selected OFDM signal is selected and output to the guard interval adding unit 8.

  The guard interval adding unit 8 receives the OFDM signal having the lowest peak power from the transmission signal selecting unit 13, adds a guard interval to the OFDM signal, and outputs the OFDM signal to the orthogonal modulation unit 9. The orthogonal modulation unit 9 receives the OFDM signal to which the guard interval is added from the guard interval addition unit 8 and generates an OFDM modulated wave by orthogonally modulating the OFDM signal. The OFDM modulated wave generated in this way is transmitted to the OFDM signal receiving apparatus.

[Operation Example of Example 1]
Next, an operation example of the OFDM signal transmission apparatus 1 shown in FIG. 3 will be described. Hereinafter, a case where digital data as shown in FIG. 4A is input to the bit inverting unit 10 will be described. The OFDM signal transmission apparatus 1 is assumed to include five mapping units 11-1 to 11-5 and five IFFT units 12-1 to 12-5 (N = 5).

  FIG. 4 is a diagram for explaining the processing of the bit inverting unit 10. This digital data indicates data constituting one OFDM symbol. For example, when the subcarrier modulation scheme is 64QAM and the number of subcarriers is 128, the data constituting one OFDM symbol is 6 × 128 = 768 bits.

  (1) is an example of digital data input to the bit inverting unit 10, and it is assumed that the digital data includes 3 bits of invalid data indicated by an underline. In the bit inverting unit 10, 3-bit invalid data (0, 0, 0) is respectively (1, 0, 0), (0, 1, 0), (0, 0, 1), (1, 1, It is assumed that the bit inversion position information is set in advance so that it is converted to (0) (bit inversion). The bit inverting unit 10 generates digital data obtained by inverting bits of four different patterns shown in (2) to (5) on the basis of preset bit inversion position information. Then, the bit inverting unit 10 converts the digital data (2) into the mapping unit 11-1, the digital data (3) into the mapping unit 11-2, and the digital data (4) into the mapping unit 11-3. The digital data of (5) is output to the mapping unit 11-4.

  The mapping units 11-1 to 11-4 receive the digital data obtained by bit inversion from the bit inversion unit 10 and output the mapped I and Q signals to the IFFT units 12-1 to 12-4. The mapping unit 11-5 receives the same original digital data as the digital data input by the bit inverting unit 10, and outputs the mapped I and Q signals to the IFFT unit 12-5.

  IFFT sections 12-1 to 12-5 receive I and Q signals from mapping sections 11-1 to 11-5, respectively, and perform an IFFT to output an OFDM signal to transmission signal selection section 13. The transmission signal selection unit 13 receives the OFDM signals from the IFFT units 12-1 to 12-5, and calculates the peak power of the OFDM symbols in the five OFDM signals. Then, the transmission signal selection unit 13 selects the OFDM signal having the lowest peak power among the five peak powers, and outputs it to the guard interval addition unit 8.

  FIG. 5 is a diagram illustrating an example of a calculation result of peak power in the OFDM signal. It is assumed that the transmission signal selection unit 13 calculates the peak power shown in FIG. 5 for the OFDM signals input from the IFFT units 12-1 to 12-5. In the example of FIG. 5, since the OFDM signal input from the IFFT unit 12-1 has the lowest peak power, the transmission signal selection unit 13 selects the OFDM signal input from the IFFT unit 12-1, and the guard interval addition unit 8 is output. Which signal has the lowest peak power among the OFDM signals input from the IFFT units 12-1 to 12-N differs for each OFDM symbol. Therefore, the transmission signal selection unit 13 calculates the peak power for each OFDM symbol, and selects the OFDM symbol having the lowest peak power.

[Experimental result of Example 1]
Next, the experimental result of Example 1 in the OFDM signal transmitter 1 shown in FIG. 3 will be described. FIG. 6 is a diagram illustrating an example of the PAPR reduction effect according to the first embodiment. As a result of this experiment, the digital data including 10% invalid data is applied to the OFDM signal when the number of subcarriers is 128 and the subcarrier modulation scheme is 64QAM, and the first embodiment is not applied (peak power). An example of the peak power distribution in the case where the reduction process is not performed) is shown. The horizontal axis represents the ratio of peak power to average power (PAPR) in dB, and the vertical axis represents the occurrence probability of PAPR in a complementary cumulative distribution (CCDF: Complementary Distribution Function).

  FIG. 6 shows that the PAPR of the OFDM signal is reduced by about 1.5 dB when the first embodiment is applied compared to the case where the first embodiment is not applied.

  FIG. 7 is a diagram illustrating an example of the BER improvement effect according to the first embodiment. This experimental result shows that when there is a clip to which the first embodiment is applied (+ in the figure) with respect to an OFDM signal having the same conditions as in FIG. 6, the first embodiment is not applied (the peak power reduction process is not performed). C / N vs. bit error rate (BER) characteristics in the case of presence (● in the figure) and the case where no clip is applied (the peak power reduction process is not performed) (no solid line in the figure). An example of The horizontal axis represents C / N in dB, and the vertical axis represents BER.

From FIG. 7, the BER is approximately 1/10 (2 × 10 ⁻⁴ → 2) when C / N = 26 dB, for example, when there is a clip to which the first embodiment is applied and when the clip is not applied to the first embodiment. × ^{10 -5),} it can be seen that the BER when C / N = 28 dB is improved respectively to approximately ^{1/100 (1.3 × 10 -4 → 1.3} × 10 -6).

  As described above, according to the OFDM signal transmitting apparatus 1 of the first embodiment, the bit inverting unit 10 inverts predetermined bits of invalid data included in digital data according to preset bit inversion position information, Different digital data was generated every time. In addition, the transmission signal selection unit 13 calculates peak power for the original digital data OFDM signal and the digital data OFDM signal different for each system, and selects the OFDM signal having the lowest peak power. Then, the OFDM signal transmission apparatus 1 performs modulation processing on the selected OFDM signal and transmits an OFDM modulated wave. Thereby, only the invalid data included in the digital data can be used to reduce the peak power of the OFDM modulated wave. In this case, since it is not necessary to add new data or increase the amount of information in order to reduce the peak power of the OFDM modulated wave, it is not necessary to change the transmission frequency band and the bit rate.

  In addition, according to the OFDM signal transmitting apparatus 1 of the first embodiment, only invalid data included in digital data is changed, and therefore it is not necessary to perform any processing on invalid data in the OFDM signal receiving apparatus. That is, the OFDM signal receiving apparatus does not need to know how invalid data is replaced and does not need to perform special processing for reducing the peak power of the OFDM modulated wave. The configuration of the receiving apparatus can be used as it is. This is because the OFDM signal receiving apparatus discards invalid data included in the data when demodulating the OFDM modulated wave transmitted from the OFDM signal transmitting apparatus 1 and taking out the data. Even so, the invalid data does not affect the valid data. Further, according to the OFDM signal transmitting apparatus 1 of the first embodiment, the modulation waveform is not distorted and the reception of effective data is not affected.

  Next, an OFDM signal transmission apparatus according to the second mode for embodying the present invention (Example 2) will be described. The second embodiment is an example in which a digital terrestrial broadcast TS including null packets as invalid data is OFDM-modulated and transmitted. FIG. 8 is a diagram for explaining a configuration example of a terrestrial digital broadcast TS transmitted by the OFDM signal transmission apparatus according to the second embodiment. Information such as video, audio, and data of terrestrial digital broadcasting is transmitted in the MPEG-2 transport stream (hereinafter referred to as TS) format according to the ISO / IEC13818 standard. The TS is composed of a 188-byte fixed-length packet called a TS packet, and includes a 4-byte header (TS header) and a 184-byte payload. Each TS packet is given a 13-bit ID called PID according to the information to be transmitted, and stored in the TS header portion together with other control information.

  TS packets include TS packets (actual TS packets) that transmit valid information and TS packets that do not transmit valid information. A TS packet that does not transmit valid information is called a null packet and is assigned a dedicated PID (0 × 1FFF). Invalid data is stored in the payload of the null packet, and the null packet exists as stuffing for keeping the transmission rate of the TS constant. The invalid data in the payload of the null packet has no meaning as information, and therefore any information may be used and does not affect the valid data. Further, the OFDM signal receiving apparatus does not need to perform special processing on invalid data. Note that the OFDM signal receiving apparatus identifies the actual TS packet and the null packet from the received TS packet, and the payload valid data extracted from the actual TS packet and the invalid data extracted from the null packet, as in the prior art. It is assumed that a means for identifying data is provided.

  FIG. 9 is a block diagram for explaining general OFDM modulation processing of terrestrial digital broadcasting. The terrestrial digital broadcasting TS in Japan undergoes a series of processes shown in FIG. 9, and is finally transmitted as an OFDM modulated wave from a transmitting station such as a radio tower. In FIG. 9, hierarchical transmission is not considered, but generality is not lost as an embodiment of the present invention.

  The terrestrial digital broadcasting TS is outer code encoded by Reed-Solomon (RS) code for error correction, subjected to byte interleaving, inner code encoded by convolutional code, bit interleaving, mapping, time interleaving and Each process of frequency interleaving is performed. Then, the I and Q signals subjected to these processes are configured in an OFDM frame together with the pilot signal and the TMCC signal. Hereinafter, a configuration unit that performs a series of processing from outer code encoding to OFDM frame configuration is referred to as a transmission path encoding unit.

  The I and Q signals configured in the OFDM frame output from the transmission path encoding unit are subjected to IFFT processing after serial-parallel conversion and parallel-serial conversion. Thereby, an OFDM signal is generated. An OFDM signal is generated by adding a guard interval to the OFDM signal and performing orthogonal modulation using a carrier wave.

  In this embodiment, the modulation parameters of ISDB-T are mode 3 (number of subcarriers 5617), subcarrier modulation scheme 64QAM, convolutional coding rate 3/4, guard interval ratio 1/8, and hierarchical transmission is not performed. And

  FIG. 10 is a block diagram illustrating a configuration of an OFDM signal transmission apparatus according to the second embodiment. The OFDM signal transmission apparatus 2 includes a bit inversion unit 20, data transmission line encoding units 21-1 to 21 -N, address transmission line encoding units 24-1 to 24-(N−1), and an IFFT unit 22. -1 to 22-N, a transmission signal selection unit 23, a guard interval addition unit 8, and an orthogonal modulation unit 9.

  The bit inversion unit 20 inputs a digital terrestrial broadcast TS and also receives a bit inversion trigger from the transmission signal selection unit 23 to determine whether the bit inversion trigger is “1”. When it is determined that the bit inversion trigger is “1”, the null packet in the input TS is searched at the timing when the bit inversion trigger “1” is input, and is preset in the payload of a single null packet. N-1 different payload data is generated by inverting the bit at the position, and the TS including the payload of the bit-inverted data is converted into data transmission path encoding units 21-1 to 21- (N-1). Respectively. Here, the position of the data to be inverted (bit inversion position information) in the payload of the null packet has a different pattern for each of the data transmission line encoding units 21-1 to 21- (N-1) (for each system). It is preset as follows. Specific examples will be described later. The bit inversion unit 20 outputs the bit inversion position information to the address transmission path encoding units 24-1 to 24- (N-1), respectively. Here, the bit inversion position information is a bit string in which “1” is set at the bit inversion position and “0” is set at the other positions.

  On the other hand, if the bit inversion unit 20 determines that the bit inversion trigger is “0”, the input TS is directly used as the data transmission path encoding units 21-1 to 21- () without searching for a null packet. N-1).

  The data transmission path encoding units 21-1 to 21-N perform transmission path encoding processing on the TS data. Specifically, the data transmission line encoding units 21-1 to 21- (N-1) respectively input TSs obtained by bit inversion from the bit inverting unit 20, and the data transmission line encoding unit 21-N The same original TS as the TS input by the bit inverting unit 20 is input. Then, the data transmission path encoding units 21-1 to 21-N perform the same processing as the transmission path encoding unit shown in FIG. 9 on the input TS, and the I, Q configured in the OFDM frame The signals are output to IFFT units 22-1 to 22-N, respectively.

  FIG. 11 is a block diagram showing a configuration of data transmission path encoding sections 21-1 to 21-N shown in FIG. The data transmission channel encoding units 21-1 to 21-N have the same configuration as the transmission channel encoding unit shown in FIG. 9, and receive a terrestrial digital broadcast TS and receive Reed-Solomon (RS) encoding ( Outer code coding), energy spreading, byte interleaving, convolutional coding (inner code coding), bit interleaving, mapping, time interleaving, frequency interleaving, and OFDM frame configuration processing, and I, Generate and output a Q signal.

  Returning to FIG. 10, the address transmission path encoding units 24-1 to 24- (N−1) support TS transmission path encoding for the address indicated by the bit inversion position information, not the TS data. The above processing is performed at the same timing as TS transmission path coding. Specifically, the address transmission path encoding units 24-1 to 24- (N-1) each receive bit inversion position information from the bit inversion unit 20, and store the data at the position indicated by the bit inversion position information. An OFDM symbol number affected by the bit inversion is specified, information indicating a set of the specified OFDM symbol numbers (hereinafter referred to as OFDM symbol change information) is generated, and the OFDM symbol change information is transmitted to the transmission signal selection unit 23. Output each.

  FIG. 12 is a block diagram illustrating a configuration of address transmission path encoding units 24-1 to 24- (N-1) illustrated in FIG. The address transmission channel encoding units 24-1 to 24- (N-1) are data transmission channel encoding units 21-1 to 21- (N-1) that process TS data shown in FIG. ), An outer code RS unit 241, an energy spreading unit 242, a byte interleaving unit 243, an address assigning unit 244, a convolutional coding / address generating unit 245, a bit interleaving unit 246, a mapping unit 247, and a time interleaving unit. 248, a frequency interleave unit 249, and an OFDM frame configuration unit 250.

  Outer code RS section 241 receives bit inversion position information from bit inversion section 20 and performs Reed-Solomon (RS) for the bit-inverted TS in data transmission path encoding sections 21-1 to 21- (N-1). By encoding, 16 bytes are added to the 188 bytes of data constituting the packet to generate 204 bytes of data, and 16 bits of “0” are added to 188 bits in the bit inversion position information at the same timing. To do. As described above, the bit inversion position information is a bit string in which “1” is set at the bit inversion position and “0” is set at the other positions.

  The energy spreading unit 242 receives the bit-inversion position information that has been outer-coded from the outer-code RS unit 241, and performs the bit-reversed TS in the data transmission path coding units 21-1 to 21-(N−1). Along with the energy diffusion processing, bit inversion position information corresponding to the processing is generated at the same timing. In the data transmission line encoding units 21-1 to 21- (N-1), the data position of the TS after performing the energy spreading process on the bit-inverted TS is the same as that before the process, so The reverse position is the same. Therefore, the energy diffusing unit 242 outputs the input bit inversion position information as it is.

  The byte interleaving unit 243 receives the bit inversion position information subjected to the energy diffusion processing from the energy spreading unit 242, and the byte corresponding to the bit-inverted TS in the data transmission path coding units 21-1 to 21- (N-1). Along with the interleaving process, bit inversion position information corresponding to the process (bit inversion position information reflecting the position of the data moved by the process) is generated at the same timing.

  The address assigning unit 244 receives the bit inversion position information byte interleaved by the byte interleaving unit 243, and assigns an address A to each bit inversion position (position where “1” is set) in the bit inversion position information.

  The convolutional encoding / address generating unit 245 receives the address A given by the address assigning unit 244, and performs convolution on the bit-inverted TS in the data transmission channel coding units 21-1 to 21- (N-1). Along with the encoding process, the data after the convolutional encoding is performed on the address A indicated by the bit inversion position information before the convolutional encoding at the same timing in accordance with a preset address conversion table (see FIG. 15 described later). Address B is generated.

  Here, the data at the bit inversion position before the convolutional encoding is reflected along with the convolutional encoding process for the bit-inverted TS in the data transmission path encoding units 21-1 to 21- (N-1). The data position after convolutional coding is uniquely determined according to the rules of convolutional coding. That is, when the data at the bit inversion position (address A) before convolutional coding is inverted, the position (address B) at which the data after convolutional encoding is inverted is uniquely determined. For example, in the case of a coding rate of 3/4, 4-bit data is generated after convolutional encoding for 3-bit data before convolutional encoding, and the address A of the 3-bit data before convolutional encoding and convolution The association with the address B of the 4-bit data after encoding is determined in advance. This association information is preset as an address conversion table. In a transmission system in which digital data is OFDM-modulated and transmitted by a method other than ISDB-T, an inner code other than the convolutional code may be used instead of the convolutional code.

  The bit interleaving unit 246 receives the address B from the convolutional coding / address generation unit 245, and performs bit interleaving processing on the bit-inverted TS in the data transmission channel coding units 21-1 to 21- (N-1). Along with this, the address B is output at the position corresponding to the processing at the same timing. Along with the movement of the TS data, the address B of the data moves along with the bit interleaving processing for the bit-inverted TS. That is, the bit interleave unit 246 outputs the address B corresponding to the data at the same timing as the data of the moved TS.

  The mapping unit 247 receives the address B from the bit interleaving unit 246, and at the same timing along with the mapping process for the inverted TS in the data transmission channel encoding units 21-1 to 21- (N-1). Address B is output at the position corresponding to the processing. With the mapping process for the bit-inverted TS, the position of the address B corresponding to the TS data is determined. That is, the mapping unit 247 outputs the address B corresponding to the data at the same timing as the mapped TS data.

  The time interleaving unit 248 receives the address B from the mapping unit 247, and at the same timing along with the time interleaving processing for the inverted TS in the data transmission path coding units 21-1 to 21- (N-1). The address B of the position corresponding to the processing is output. In association with the time interleaving process for the bit-inverted TS, the data B is rearranged and moved together with the rearrangement movement of the TS data. That is, the time interleave unit 248 outputs the address B corresponding to the data at the same timing when the rearranged and moved TS data is output.

  The frequency interleaving unit 249 receives the address B from the time interleaving unit 248, and has the same timing as the frequency interleaving processing for the inverted TS in the data transmission channel coding units 21-1 to 21- (N-1). To generate position information corresponding to the processing. In association with the frequency interleaving process for the bit-inverted TS, the data B is rearranged and moved together with the rearranged movement of the TS data. That is, the frequency interleave unit 249 outputs the address B corresponding to the data at the same timing when the data of the moved TS is output.

  The OFDM frame configuration unit 250 receives the address B from the frequency interleaving unit 249 and accompanies the processing of the OFDM frame configuration for the inverted TS in the data transmission channel encoding units 21-1 to 21- (N-1). The OFDM symbol number and subcarrier number for address B corresponding to the processing are specified at the same timing.

  The OFDM symbol number to which the data of the address B generated by the convolutional coding / address generation unit 245 belongs is specified by the bit interleave unit 246, the mapping unit 247, the time interleave unit 248, the frequency interleave unit 249, and the OFDM frame configuration unit 250. The Therefore, the OFDM frame configuration unit 250 identifies the OFDM symbol number to which the data of the address B belongs as the OFDM symbol number affected by the bit inversion of the data of the address A indicated by the bit inversion position information, and the OFDM symbol change information To the transmission signal selection unit 23. Specific examples will be described later.

  Note that the address transmission path encoding units 24-1 to 24- (N-1) are configured such that the bit inversion position information, the OFDM symbol change information, and the OFDM symbol change information, instead of the units from the outer code RS unit 241 to the OFDM frame configuration unit 250 May be obtained, and OFDM symbol change information corresponding to the input bit inversion position information may be acquired and output using the conversion table. This is because the content of each process from the outer code RS unit 241 to the OFDM frame configuration unit 250 is determined, and according to each rule, the association between the bit inversion position information and the OFDM symbol change information is uniquely determined, This is because the conversion table can be set in advance. The same applies to the address transmission path encoding unit 31-1 described later.

  Returning to FIG. 10, IFFT units 22-1 to 22-N receive the I and Q signals configured in the OFDM frame from the data transmission line encoding units 21-1 to 21-N, and the I and Q signals are input. Is subjected to IFFT, and the OFDM signal is output to the transmission signal selector 23.

  The transmission signal selection unit 23 inputs OFDM signals from the IFFT units 22-1 to 22-N, and inputs OFDM symbol change information from the address transmission channel coding units 24-1 to 24- (N-1). To do. Then, with respect to the input N OFDM signals, the peak power is calculated for each OFDM symbol, and the highest peak power among the peak powers of all OFDM symbol numbers indicated by the OFDM symbol change information is indicated by the OFDM symbol change information. Set to peak power for all OFDM symbol numbers. Then, for each OFDM symbol, the OFDM signal having the lowest peak power among the N peak powers is selected and output to the guard interval adding unit 8. Here, for the OFDM signal selected in a certain OFDM symbol number, when the OFDM symbol change information of the OFDM signal system includes the OFDM symbol number, the transmission signal selection unit 23 selects all OFDM signals indicated by the OFDM symbol change information. In the symbol number, an OFDM signal of the same system is selected. This is because the OFDM symbol change information represents an OFDM symbol that is affected by bit inversion, and when an OFDM signal of a different system is selected for a plurality of OFDM symbol numbers indicated by the OFDM symbol change information, the OFDM signal changes. This is because the receiving device cannot correctly decode.

  That is, when the OFDM symbol number indicated by the OFDM symbol change information is one, the transmission signal selection unit 23 selects the OFDM signal having the lowest peak power among the N peak powers for each OFDM symbol. On the other hand, when there are a plurality of OFDM symbol numbers indicated by the OFDM symbol change information, when the OFDM signal having the lowest peak power among the N peak powers is selected, the OFDM signals of the same system are selected in the plurality of OFDM symbol numbers. Select. Therefore, when there are a plurality of OFDM symbol numbers indicated by the OFDM symbol change information, the OFDM signal having the lowest peak power is not necessarily selected in the plurality of OFDM symbol numbers. The same applies to Examples 3 and 4 below.

  Further, the transmission signal selection unit 23 includes “end” in the OFDM symbol change information of all systems, and completes the selection of OFDM signals for all OFDM symbol numbers included in the OFDM symbol change information of all systems. In addition, the bit inversion trigger is set to “1” and output to the bit inversion unit 20. When bit inversion trigger “1” is input, bit inversion unit 20 searches for a null packet and starts bit inversion processing. When the bit inversion process is completed, the process waits until a new bit inversion trigger “1” is input.

  The guard interval adding unit 8 and the quadrature modulation unit 9 are the same as those in the first embodiment shown in FIG.

[Operation of Example 2]
Next, an operation example of the OFDM signal transmission apparatus 2 shown in FIG. 10 will be described. Hereinafter, a case where a TS as illustrated in FIG. 13A is input to the bit inverting unit 20 will be described. The OFDM signal transmission apparatus 2 includes four data transmission line encoding units 21-1 to 21-4 and three address transmission line encoding units 24-1 to 24-3 ( N = 4).

  FIG. 13 is a diagram for explaining the processing of the bit inverting unit 20. (1) is an example of TS input to the bit inverting unit 20. This TS includes a null packet, and the second packet is a null packet. In the null packet, 184 bytes excluding the 4 bytes of the TS header are all 0xFF. The bit inversion unit 20 inverts the least significant 1 bit of the first byte, the second byte, and the third byte of the payload 184 bytes for each system with respect to the TS packet 2 which is a null packet, and 0 × It is assumed that the bit inversion position information is set in advance so as to be converted into FE (bit inversion). When the bit inversion unit 20 receives the bit inversion trigger “1” from the transmission signal selection unit 23, the bit inversion unit 20 searches for a null packet having a PID of 0 × 1FFF in the TS, and based on the preset bit inversion position information, TSs including different TS packets 2 are respectively generated as in patterns 1 to 3 of (2) to (4).

  The bit inversion unit 20 uses the TS of (2) for the data transmission line encoding unit 21-1, the TS of (3) for the data transmission line encoding unit 21-2, and the TS of (4) for the data. The data is output to the transmission path encoding unit 21-3. Also, the bit inverting unit 20 converts the bit inversion position information set so as to invert the least significant 1 bit of the first byte of the payload 184 bytes and convert it to 0 × FE (bit inversion). In the encoding unit 24-1, the bit inversion position information set so as to invert the least significant 1 bit of the second byte of the payload 184 bytes and convert it to 0 × FE (bit inversion) is transmitted to the address transmission path. In the encoding unit 24-2, the bit inversion position information set so as to invert the least significant 1 bit of the third byte of the payload 184 bytes and convert it to 0 × FE (bit inversion) is transmitted to the address transmission path. The data is output to the encoding unit 24-3. As described above, the bit inversion position information is a bit string in which “1” is set at the bit inversion position and “0” is set at the other positions.

  The data transmission line encoding units 21-1 to 21-3 each receive TS including a bit-inverted null packet from the bit inverting unit 20, and the data transmission line encoding unit 21-4 includes a bit inverting unit. The same TS as the TS input by 20 is input, I and Q signals configured in an OFDM frame are generated by transmission path encoding processing, and output to IFFT sections 22-1 to 22-4, respectively. The IFFT units 22-1 to 22-4 receive the I and Q signals formed in the OFDM frame from the data transmission line coding units 21-1 to 21-4, respectively, and perform IFFT to select the OFDM signal as a transmission signal. To the unit 23. Address transmission path encoding units 24-1 to 24-3 each receive bit inversion position information from bit inversion unit 20, generate OFDM symbol change information, and output it to transmission signal selection unit 23.

  Next, the OFDM symbol change information generated by the address transmission path encoding units 24-1 to 24-3 will be specifically described. In the transmission path encoding process of ISDB-T, convolutional encoding is performed as shown in FIG. 11. Therefore, if one bit before convolutional encoding is inverted, a plurality of bits after convolutional encoding are inverted. Therefore, depending on the position of the bit to be inverted in the null packet and a modulation parameter such as time interleaving, two or more OFDM symbols may change with the inversion of one bit in the null packet. In such a case, the transmission signal selection unit 23 must select the OFDM signals input from the data transmission path encoding units 21-1 to 21-3 of the same system for all the changing OFDM symbols. This is because, when OFDM signals of different systems are selected for all the changing OFDM symbols, the OFDM signal receiving apparatus cannot decode the original digital data.

  FIG. 14 is a diagram for explaining an example of bits before and after convolutional coding at a coding rate of 3/4 in the convolutional coding processing in the data transmission channel coding units 21-1 to 21-3 depicted in FIG. is there. In the case of a coding rate of 3/4, 3 bits before convolutional coding are converted to 4 bits after convolutional coding by the convolutional coding process. Here, the addresses of 3 bits before convolutional encoding and the corresponding 4-bit addresses after convolutional encoding are respectively address A (α, 1) to A (α, 3) and address B (α, 1) to B ( α, 4). α is a number for distinguishing the position of a set of 3-bit data before convolutional encoding and 4-bit data after convolutional encoding.

  Here, for example, when the bit inverting unit 20 inverts the bit of the address A (α, 1), and the data transmission path encoding units 21-1 to 21-3 perform convolutional encoding on the inverted bit. , Addresses B (α, 1), B (α, 2), B (α, 4), B (α + 1,1), B (α + 1,2), B (α + 2,1), B after convolutional coding The 7 bits of (α + 2, 2) are inverted.

  FIG. 15 is a diagram for explaining an example of addresses before and after convolutional coding at a coding rate of 3/4 in the convolutional coding processing in the data transmission channel coding units 21-1 to 21-3 depicted in FIG. is there. The bit inversion unit 20 inverts each bit of A (α, 1) to A (α, 3), and the data transmission path encoding units 21-1 to 21-3 perform convolutional encoding on the inverted bits. Then, the 7 bits of the address B described in the output column of FIG. That is, the address assigning unit 244 of the address transmission line encoding units 24-1 to 24-3 assigns the address A shown in FIGS. 14 and 15 to the bit inversion position of the input bit inversion position information. The convolutional coding / address generation unit 245 generates an address B for the input address A with reference to the address conversion table shown in FIG. Hereinafter, the case of coding rate 3/4 will be described as an example. However, in the case of other coding rates as well, as shown in FIG. 15, the addresses A and B before and after the convolutional coding are grasped and the same. Processing is performed.

  The data transmission path encoding units 21-1 to 21-3 perform Reed-Solomon (RS) encoding, energy spreading, byte interleaving, convolutional encoding, bit interleaving, mapping, time interleaving, and frequency interleaving for the input TS. And processing of the OFDM frame configuration. Further, the address transmission path encoding units 24-1 to 24-3 add 16 bytes of “0” in the outer code RS unit 241 to the input bit inversion position information, and the energy spreading unit 242 adds the TS energy. Processing corresponding to spreading processing is performed, processing corresponding to TS is similarly performed in the byte interleaving unit 243, and an address A is given to the bit inversion position information after byte interleaving in the address giving unit 244. Further, the convolutional encoding / address generation unit 245 generates the address B after the convolutional encoding corresponding to the address A, the bit interleaving unit 246 performs the processing corresponding to the TS, and the mapping unit 247 similarly performs the TS. The time interleaving unit 248 similarly performs processing corresponding to TS, the frequency interleaving unit 249 similarly performs processing corresponding to TS, and the OFDM frame configuration unit 250 generates OFDM symbol change information. . However, the relative timing between the initialization timing of each process and the input timing of the address B is set so that the correspondence between the I and Q signals configured in the OFDM frame and the address B corresponding to the I and Q signals is not lost. Processing is performed so that the time interval is the same as when data at the address is input. That is, the process for the data in the data transmission line encoding units 21-1 to 21-3 and the process for the address in the address transmission line encoding units 24-1 to 24-3 are performed by using the data and the address of the data. Correspondingly, the same timing is used.

  As described above, the bit inversion position information is a bit string in which “1” is set at the bit inversion position and “0” is set at the other positions. The address transmission path encoding units 24-1 to 24-3 assign the address A to the position where “1” is set in the bit inversion position information before the convolutional encoding in the address assignment unit 244, and perform the convolution. The encoding / address generation unit 245 generates the address B corresponding to the address A based on the address conversion table, so that the OFDM frame configuration unit 250 generates OFDM symbol change information.

  FIG. 16 illustrates an example of mapped bit addresses and mapped data after bit inversion in the convolutional coding processing in the data transmission path coding units 21-1 to 21-3 illustrated in FIG. FIG. FIG. 16 shows I and Q signals configured in an OFDM frame after mapping, and 6-bit addresses before mapping. When the carrier modulation scheme is 64QAM, one symbol is 6 bits per subcarrier.

  When one bit in the payload of the null packet is inverted by the bit inverting unit 20, the address assignment unit 244 of the address transmission path encoding units 24-1 to 24-3 uses the address A (1 before convolutional encoding. , 3). By this 1-bit inversion, as shown in FIG. 15, after the convolutional coding, the addresses B (1,4), B (2,1), B (2,3), B (2,4), The 6 bits of B (3, 3) and B (3, 4) are inverted. These bits are shown in underlined bold italics in FIG. That is, the convolutional coding / address generation unit 245 refers to the address conversion table shown in FIG. 15 for A (1,3) before convolutional coding, and addresses B (1,4) after convolutional coding. , B (2,1), B (2,3), B (2,4), B (3,3), B (3,4) are generated. Then, by the processing of the address transmission path encoding units 24-1 to 24-3, as shown in FIG. 16, OFDM symbol number 1, subcarrier number 1, 3, OFDM symbol number 2, subcarrier number 1, Suppose that it is mapped to 2 I and Q signals. Thus, the I and Q signals configured in the OFDM frame are changed from (−1, 3) to (−7, 5) in OFDM symbol number 1 and subcarrier number 1, and in OFDM number 1 and subcarrier number 3 ( 5, -1) to (-1, -7), OFDM number 2 and subcarrier number 1 from (3,3) to (3, -1), OFDM number 2 and subcarrier number 2 (-7) , -1) to (-7, -7), respectively. Therefore, if these signals are IFFTed in IFFT sections 22-1 to 22-3, the peak power of the OFDM symbol may also change.

  From FIG. 16, it can be seen that the OFDM symbol of OFDM symbol numbers 1 and 2 changes as a result of the bit inverting unit 20 inverting one bit of the address A (1,3). As a result, for example, the address transmission path encoding unit 24-1 generates “OFDM symbol number 1, 2, end” as the OFDM symbol change information and outputs the OFDM symbol change information to the transmission signal selection unit 23. “End” at the end indicates that there are no more OFDM symbols that change as a result of inverting one bit of address A (1, 3). Thereby, as the processing proceeds, it is possible to distinguish between OFDM symbol change information generated as a result of inversion of a bit at another address by the bit inversion unit 20 and other OFDM symbol change information.

  The transmission signal selection unit 23 receives the OFDM signal from the IFFT units 22-1 to 22-4, and also receives the OFDM symbol change information from the address transmission path coding units 24-1 to 24-3, for each OFDM symbol. To calculate the peak power. That is, in the case of mode 3, since the total number of subcarriers is 5617, the power of 5617 signal points constituting the time waveform after IFFT is calculated, and the peak value is calculated.

  FIG. 17 is a diagram for explaining an example of peak power values of OFDM symbols and OFDM symbol change information. The peak power of each OFDM symbol output by the IFFT units 22-1 to 22-4 and the OFDM symbol change information output by the address transmission path encoding units 24-1 to 24-3 are as shown in FIG. Suppose that Then, in OFDM symbol number 1, the signal having the minimum peak power is the OFDM symbol output by IFFT section 22-1, but the OFDM symbol change information of the system is “1, 2, end”. Therefore, when the transmission signal selection unit 23 selects the OFDM symbol output by the IFFT unit 22-1 in the OFDM symbol number 1, the OFDM symbol output by the IFFT unit 22-1 also in the OFDM symbol number 2 Must be selected. Similarly, in OFDM symbol number 2, the signal with the lowest peak power is the OFDM symbol output by IFFT section 22-2 (and the OFDM symbol output by IFFT section 22-4). The OFDM symbol change information is “2, 3, 4, end”. Therefore, when the transmission signal selection unit 23 selects the OFDM symbol output by the IFFT unit 22-2 in the OFDM symbol number 2, the transmission is performed by the IFFT unit 22-2 also in the OFDM symbol numbers 3 and 4. An OFDM symbol must be selected. In OFDM symbol number 4, the signal having the minimum peak power is the OFDM symbol output by IFFT section 22-3, and the OFDM symbol change information of the system is “1, 4, end”. Therefore, when the transmission signal selection unit 23 selects the OFDM symbol output by the IFFT unit 22-3 in the OFDM symbol number 4, the OFDM symbol output by the IFFT unit 22-3 also in the OFDM symbol number 1 Must be selected.

  Under the above constraints, the peak power of the OFDM signal becomes the smallest for the OFDM symbol numbers 1 and 4 for the OFDM symbol output by the IFFT unit 22-3, and for the OFDM symbol numbers 2 and 3, the IFFT unit 22- In this case, the OFDM symbols output by 4 are selected. In this case, the transmission signal selection unit 23 calculates peak power for each OFDM symbol for the four input OFDM signals as shown in FIG. Then, the transmission signal selection unit 23 has the highest peak power of all OFDM symbol numbers 1 and 2 indicated by the OFDM symbol change information “1, 2, end” for the OFDM symbol input from the IFFT unit 22-1. The peak power 160 is set to the peak power of all OFDM symbol numbers 1 and 2 indicated by the OFDM symbol change information. Thereby, the peak power of OFDM symbol number 1 is set to 160. Similarly, the transmission signal selection unit 23, for the OFDM symbol input from the IFFT unit 22-2, the peak powers of all OFDM symbol numbers 2, 3, and 4 indicated by the OFDM symbol change information “2, 3, 4, end” Is set to the peak power of all the OFDM symbol numbers 2, 3, and 4 indicated by the OFDM symbol change information. Thereby, the peak power of OFDM symbol numbers 2 and 4 is set to 400. Similarly, the transmission signal selection unit 23, for the OFDM symbol input from the IFFT unit 22-3, is the highest of the peak powers of all the OFDM symbol numbers 1 and 4 indicated by the OFDM symbol change information “1, 4 and end”. High peak power 130 is set to the peak power of all OFDM symbol numbers 1 and 4 indicated by the OFDM symbol change information. Thereby, the peak power of OFDM symbol number 1 is set to 130.

  Then, the transmission signal selection unit 23 includes “end” in all OFDM symbol change information, and after setting peak power in all systems, all OFDM symbol numbers 1 indicated by all OFDM symbol change information. Are combined so that the combination of OFDM symbols output by the IFFT units 22-1 to 22-4 is selected so as to have the lowest peak power, and is output to the guard interval adding unit 8. For the OFDM symbol selected in a certain OFDM symbol number, when the OFDM symbol change information of the OFDM symbol system includes the OFDM symbol number, the transmission signal selection unit 23 selects all OFDM symbols indicated by the OFDM symbol change information. It is assumed that OFDM symbols of the same system are selected in the numbers. Therefore, the transmission signal selection unit 23 selects the OFDM symbol input from the IFFT unit 22-3 for the OFDM symbol numbers 1 and 4, and outputs the selected OFDM symbol to the guard interval addition unit 8. For OFDM symbol numbers 2 and 3, the OFDM symbol input from IFFT section 22-4 is selected and output to guard interval adding section 8.

  When the transmission signal selection unit 23 completes the selection of OFDM signals for all OFDM symbol numbers included in the OFDM symbol change information of all systems, the “end” is included in the OFDM symbol change information of all systems, The bit inversion trigger is set to “1” and output to the bit inversion unit 32. When bit inversion trigger “1” is input, bit inversion unit 20 searches for a null packet and starts bit inversion processing. When the bit inversion process is completed, the process waits until a new bit inversion trigger “1” is input. The transmission signal selection unit 23 sets the bit inversion trigger to “0” after a certain period of time after the bit inversion unit 20 starts processing or when a response start signal is input from the bit inversion unit 20. Output to the inverting unit 20.

  As described above, according to the OFDM signal transmission apparatus 2 of the second embodiment, the bit inversion unit 20 inverts the predetermined bit of the null packet included in the TS according to the preset bit inversion position information, and is different for each system. TS was generated. Also, the address transmission path encoding units 24-1 to 24- (N-1) identify the OFDM symbol number affected by bit inversion of the data at the position indicated by the bit inversion position information, and change the OFDM symbol. Information was generated. Further, the transmission signal selection unit 23 calculates the peak power for the original OFDM signal of the TS and the OFDM signal of the TS that is different for each system, and the OFDM signal of the same system in all the OFDM symbol numbers indicated by the OFDM symbol change information. As selected, the OFDM symbol number indicated by the OFDM symbol change information is comprehensively considered, and the OFDM signal having the lowest peak power is selected. Then, the OFDM signal transmission apparatus 2 performs modulation processing or the like on the selected OFDM signal and transmits an OFDM modulated wave. Thereby, the peak power of the OFDM modulated wave can be reduced by using only invalid data of the null packet included in the TS. In this case, as in the first embodiment, there is no need to change the transmission frequency band and the bit rate, and the OFDM signal receiving apparatus does not need to perform special processing for reducing the peak power of the OFDM modulated wave, The configuration of the OFDM signal receiving apparatus can be used as it is. Further, the modulation waveform is not distorted and reception of effective data is not affected.

  Next, an OFDM signal transmitting apparatus according to the third mode (Example 3) of the present invention will be described. The third embodiment is a modification of the second embodiment, and is an example in which bit inversion processing is performed after OFDM frame configuration processing when transmitting a digital terrestrial broadcast TS including null packets as invalid data by OFDM modulation.

  FIG. 18 is a block diagram illustrating a configuration of an OFDM signal transmission apparatus according to the third embodiment. This OFDM signal transmission apparatus 3 includes a null packet information generation unit 30, an address transmission channel encoding unit 31-1, a data transmission channel encoding unit 31-2, a bit inversion unit 32, and IFFT units 33-1 to 33-33. N, a transmission signal selection unit 34, a guard interval addition unit 8, and an orthogonal modulation unit 9.

  The OFDM signal transmission apparatus 2 according to the second embodiment shown in FIG. 10 is compared with the OFDM signal transmission apparatus 3 according to the third embodiment shown in FIG. The OFDM signal transmission apparatus 2 according to the second embodiment includes N data transmission channel encoding units 21-1 to 21-N and N-1 address transmission channel encoding units 24-1 to 24- (N−). 1), and data transmission path encoding units 21-1 to 21-N and address transmission path encoding units 24-1 to 24- (N-1) are provided in the subsequent stage of the bit inverting unit 20. On the other hand, the OFDM signal transmission apparatus 3 according to the third embodiment includes an address transmission path encoding unit 31-1 and a data transmission path encoding unit 31-2, and includes an address transmission path encoding unit 31-1 and It differs from the OFDM signal transmission apparatus 2 in that a bit inversion section 32 is provided after the data transmission path encoding section 31-2 and a null packet information generation section 30 that does not exist in the OFDM signal transmission apparatus 2 is provided.

  The null packet information generation unit 30 inputs a terrestrial digital TS, generates information indicating whether each bit of the TS is the data of the payload of the null packet, and transmits the address transmission path encoding unit as null packet information It outputs to 31-1. Here, the null packet information is a bit string having the same size as TS, and a bit string in which “1” is set in the corresponding position of the payload part of the null packet and “0” is set in the corresponding position of the other part. To do. Null packet information is generated by the bit inversion unit 32 as to whether or not the bits mapped to the I and Q signals are invertible bits, that is, whether or not the bits constitute a null packet. It is to do.

  The address transmission line encoding unit 31-1 performs processing corresponding to the transmission line encoding of the TS for the address indicated by the null packet information. Specifically, the address transmission path encoding unit 31-1 receives null packet information from the null packet information generation unit 30, and sends invalid data (data set to “1”) indicated by the null packet information. The data position affected by the bit inversion is specified, the position of the original invalid data is the address A, the specified data position is the address B, and the set information in which the address A and the address B are associated is the bit inversion unit. 32.

  The address transmission path encoding unit 31-1 includes an outer code RS unit 241, an energy spreading unit 242, a byte interleave unit 243, an address assigning unit 244, and a convolutional encoding / address generating unit among the components illustrated in FIG. 245, input null packet information, add “0” of 16 bytes in the outer code RS unit 241, perform processing corresponding to the energy diffusion of TS in the energy spreading unit 242, and in the byte interleaving unit 243 Processing corresponding to byte interleaving of TS is performed, the address assigning unit 244 assigns the address A before convolutional coding in which “1” is set to the null packet information, and the convolutional coding / address generating unit 245 creates Convolutional coding for I and Q signals configured in an OFDM frame To generate the address B. The address transmission path encoding unit 31-1 encodes the transmission path of the TS at the same timing as the TS in the data transmission path encoding unit 31-2 described later with respect to the address indicated by the input null packet information. Perform the corresponding process. The address transmission path encoding unit 31-1 outputs pair information in which the address A and the address B are associated with each other to the bit inverting unit 32.

  FIG. 19 is a diagram illustrating examples of null packet information, data before and after convolutional encoding, and addresses. As illustrated in FIG. 19, the address transmission path encoding unit 31-1 assigns an address A before convolutional encoding to each bit in which “1” is set in the null packet information, and performs convolutional encoding. A later address B is generated, and for example, pair information associating address A and address B as shown in FIG. 15 is output.

  The data transmission channel encoding unit 31-2 performs transmission channel encoding processing on the original TS data. Specifically, the data transmission path encoding unit 31-2 receives the original TS, performs the same processing as the data transmission path encoding units 21-1 to 21-N illustrated in FIG. The I and Q signals configured in the OFDM frame are output to the bit inversion unit 32 and the IFFT unit 33-N.

  The bit reversing unit 32 sets the group information in which the address A and the address B are associated with each other from the address transmission channel encoding unit 31-1, and the I, A Q signal is input and a bit inversion trigger is input from the transmission signal selection unit 34 to determine whether the bit inversion trigger is “1”. When the bit inversion unit 32 determines that the bit inversion trigger is “1”, it can invert the I and Q signals configured in the OFDM frame at the timing when the bit inversion trigger “1” is input. A bit (inverted bit) address B is searched with reference to the set information of the input addresses A and B (for example, the address conversion table of the addresses A and B shown in FIG. 15). Specifically, the bit inverting unit 32 selects N−1 different sets of addresses A and B from the input set information of addresses A and B, and searches the address B for each system. Then, the bit inverting unit 32 inverts the bit of the address B in the input I and Q signals, performs mapping again, and generates the I and Q signals configured in N-1 OFDM frames. The data are output to IFFT units 33-1 to 33- (N-1), respectively.

  Further, the bit inverting unit 32 specifies the OFDM symbol number to which the data of the address B belongs for the address B in the set information of the selected addresses A and B for every N−1 systems. That is, the bit inverting unit 32 specifies the OFDM symbol number to which the data of the address B belongs for every N−1 systems as the OFDM symbol number affected by the bit inversion of the data of the address A, and It outputs to the transmission signal selection part 34 as change information.

  On the other hand, when it is determined that the bit inversion trigger is “0”, the bit inversion unit 32 outputs the input I and Q signals as they are to the IFFT units 33-1 to 33- (N−1).

  The IFFT units 33-1 to 33- (N-1) respectively receive the I and Q signals from the bit inverting unit 32 and the I and Q signals of the original TS from the data transmission path encoding unit 31-2. Input, IFFT the I and Q signals into an OFDM signal, and output the OFDM signal to the transmission signal selector 34.

  The transmission signal selection unit 34 receives the OFDM signals from the IFFT units 33-1 to 33-N, and receives the OFDM symbol change information for each system from the bit inversion unit 32. The transmission signal selection unit shown in FIG. The same processing as 23 is performed. The guard interval adding unit 8 and the quadrature modulation unit 9 are the same as those in the first embodiment shown in FIG.

  As described above, according to the OFDM signal transmission device 3 of the third embodiment, the null packet information generation unit 30 generates null packet information indicating whether or not the TS is the payload data of the null packet for the TS, and transmits the address. The path encoding unit 31-1 identifies the data position affected by inverting the invalid data bit indicated by the null packet information in accordance with the TS transmission path encoding process, and determines the position of the original invalid data. The group information is generated with the address A and the specified data position as the address B. Also, the data transmission path encoding unit 31-2 performs transmission path encoding of the TS to generate I and Q signals configured in an OFDM frame, and the bit inversion unit 32 inverts the I and Q signals. The address B of possible bits (bits to be inverted) is searched with reference to the set information of the addresses A and B, the bits of the address B are inverted, mapping is performed again, and I and Q configured in the OFDM frame A signal is generated and OFDM symbol change information is generated. In addition, the transmission signal selection unit 34 calculates peak power for the original OFDM signal of the TS and the OFDM signal of the TS that is different for each system, and outputs the OFDM signal of the same system in all OFDM symbol numbers indicated by the OFDM symbol change information. As selected, the OFDM symbol number indicated by the OFDM symbol change information is comprehensively considered, and the OFDM signal having the lowest peak power is selected. Then, the OFDM signal transmission device 3 performs modulation processing on the selected OFDM signal and transmits an OFDM modulated wave. Thereby, only the null packet invalid data included in the TS can be used to reduce the peak power of the OFDM modulated wave. In this case, as in the first and second embodiments, it is not necessary to change the transmission frequency band and the bit rate, and the OFDM signal receiving apparatus does not need to perform special processing for reducing the peak power of the OFDM modulated wave, The configuration of the conventional OFDM signal receiving apparatus can be used as it is. Further, the modulation waveform is not distorted and reception of effective data is not affected.

  In addition, according to the OFDM signal transmitting apparatus 3 of the third embodiment, one address transmission path encoding unit 31-1 that performs transmission path encoding on TS data, and an address associated with TS transmission path encoding. One data transmission line encoding unit 31-2 to be processed, and a bit inverting unit 32 following the address transmission line encoding unit 31-1 and the data transmission line encoding unit 31-2 includes an OFDM frame. Bit inversion processing is performed on the I and Q signals configured as described above. On the other hand, the OFDM signal transmission apparatus 2 according to the second embodiment described above includes N data transmission path encoding units 21-1 to 21-N that perform transmission path encoding on TS data, and N that processes addresses. -1 address transmission line encoding units 24-1 to 24- (N-1), and after performing bit inversion processing to generate a bit inversion pattern for each system, for each bit inversion pattern To perform transmission path encoding. Therefore, the OFDM signal transmitting apparatus 3 according to the third embodiment requires fewer circuits for performing transmission path encoding processing than the OFDM signal transmitting apparatus 2 according to the second embodiment, and therefore, the required memory amount can be reduced. it can. Further, the processing load can be reduced, and the overall configuration is simple.

  Next, an OFDM signal transmitting apparatus according to the fourth embodiment (Example 4) of the present invention will be described. [Embodiment 4] Embodiment 4 is a modification of Embodiment 3, and when transmitting a terrestrial digital broadcast TS including null packets as invalid data by OFDM modulation, bit inversion processing is performed after the OFDM frame configuration processing, and IFFT This is an example in which the generation of the OFDM signal according to is performed after the transmission signal is selected.

  FIG. 20 is a block diagram illustrating a configuration of an OFDM signal transmitting apparatus according to the fourth embodiment. This OFDM signal transmission device 4 includes a null packet information generation unit 30, an address transmission channel encoding unit 31-1, a data transmission channel encoding unit 31-2, a bit inversion unit 32, a transmission signal selection unit 40, and an IFFT unit. 41, a guard interval adding unit 8 and a quadrature modulating unit 9 are provided.

  The OFDM signal transmission apparatus 3 according to the third embodiment shown in FIG. 18 is compared with the OFDM signal transmission apparatus 4 according to the fourth embodiment shown in FIG. The OFDM signal transmission apparatus 3 according to the third embodiment includes N IFFT units 33-1 to 33-N, performs IFFT on each bit inversion pattern for each system, and selects one OFDM signal from a plurality of systems. Select an OFDM signal. On the other hand, the OFDM signal transmitting apparatus 4 according to the fourth embodiment includes one IFFT unit 41, and one I, Q signal from among the I, Q signals for each system configured in the OFDM frame for each system. Is different from the OFDM signal transmitting apparatus 3 in that IFFT is performed on the selected I and Q signals.

  The transmission signal selection unit 40 inputs from the bit inversion unit 32 the I and Q signals and N-1 OFDM symbol change information configured in the N-1 OFDM frames in the bit-inverted TS, and for data The I and Q signals configured in the OFDM frame in the original TS are input from the transmission path encoding unit 31-2. Then, the transmission signal selection unit 40 calculates an autocorrelation function for the N I and Q signals, and selects an I and Q signal having a pattern whose autocorrelation function is closest to the impulse characteristic. For example, the I and Q signals having the smallest absolute value excluding the median of the autocorrelation function are selected. In general, when the autocorrelation function of the I and Q signals approaches the impulse characteristic pattern, the instantaneous power after IFFT approaches flat, and the peak power of the OFDM modulated wave can be reduced. For details, see, for example, “H. Ochiai,“ A novel trellis shaping design with both peak and average power reduction for OFDM systems ”, IEEE Trans.Commun., Vol.52, pp.1916-1926, (Nov.2004)”. See the technical literature.

  Specifically, the transmission signal selection unit 40 calculates an autocorrelation function for each OFDM symbol for the input N I and Q signals, and calculates the autocorrelation function from all OFDM symbol numbers indicated by the OFDM symbol change information. The autocorrelation function having the pattern farthest from the impulse characteristic is set to the autocorrelation functions of all OFDM symbol numbers indicated by the OFDM symbol change information. Then, for each OFDM symbol, an autocorrelation function having a pattern closest to the impulse characteristic among N autocorrelation functions is specified, and I and Q signals of the autocorrelation function are selected and output to IFFT section 41. Here, for the I and Q signals selected in a certain OFDM symbol number, when the OFDM symbol change information is included in the OFDM symbol change information of the system of the I and Q signals, the transmission signal selection unit 40 includes the OFDM symbol change information. It is assumed that I and Q signals of the same system are selected for all the OFDM symbol numbers shown.

  In addition, the transmission signal selection unit 40 selects “I” and “Q” signals for all OFDM symbol numbers included in the OFDM symbol change information of all systems including “end” in the OFDM symbol change information of all systems. The bit inversion trigger is set to “1” and output to the bit inversion unit 32. When the bit inversion unit 32 receives the bit inversion trigger “1”, the bit inversion unit 32 searches for a null packet and starts bit inversion processing. When the bit inversion process is completed, the process waits until a new bit inversion trigger “1” is input.

  As described above, according to the OFDM signal transmission apparatus 4 of the fourth embodiment, the transmission signal selection unit 40 is configured with the I and Q signals configured in the OFDM frame in the original TS and the OFDM frame in the TS that is different for each system. The autocorrelation function of the generated I and Q signals is calculated, the autocorrelation function having the pattern closest to the impulse characteristic is specified, and the I and Q signals of the same system are selected in all OFDM symbol numbers indicated by the OFDM symbol change information As described above, the I and Q signals are selected by comprehensively considering the OFDM symbol number indicated by the OFDM symbol change information. Then, the OFDM signal transmission device 4 performs IFFT or the like on the selected I and Q signals, and transmits an OFDM modulated wave. Thereby, the peak power of the OFDM modulated wave can be reduced by using only invalid data of the null packet included in the TS. In this case, as in the first, second, and third embodiments, it is not necessary to change the transmission frequency band and the bit rate, and the OFDM signal receiving apparatus needs to perform special processing for reducing the peak power of the OFDM modulated wave. In addition, the configuration of the conventional OFDM signal receiving apparatus can be used as it is. Further, the modulation waveform is not distorted and reception of effective data is not affected.

  In addition, according to the OFDM signal transmission apparatus 4 of the fourth embodiment, the number of circuits that perform transmission line encoding processing is similar to the OFDM signal transmission apparatus 2 of the second embodiment, as in the OFDM signal transmission apparatus 3 of the third embodiment. Therefore, the required memory amount can be reduced. Further, the processing load can be reduced, and the overall configuration is simple.

  Further, according to the OFDM signal transmission apparatus 4 of the fourth embodiment, the transmission signal selection unit 40 selects one I / Q signal from a plurality of I / Q signals, and the IFFT unit 41 selects a transmission signal. IFFT is performed on the I and Q signals selected by the unit 40. On the other hand, the OFDM signal transmitting apparatus 3 according to the third embodiment described above performs IFFT on a plurality of systems of I and Q signals, and selects one OFDM signal from the plurality of systems of OFDM signals. Therefore, the OFDM signal transmitting apparatus 4 according to the fourth embodiment requires fewer IFFT circuits than the OFDM signal transmitting apparatus 3 according to the third embodiment, can further reduce the processing load, and is simpler as a whole. It becomes the composition.

  In the OFDM signal receiving apparatus that receives the OFDM modulated wave from the OFDM signal transmitting apparatus 3 of the third embodiment shown in FIG. 18 and the OFDM signal transmitting apparatus 4 of the fourth embodiment shown in FIG. An outer code (RS) parity error occurs. However, since the null packet is originally invalid information, it does not affect the video, audio, etc. of the decoded valid data.

1, 2, 3, 4 OFDM signal transmitter 8 Guard interval adding unit 9 Orthogonal modulation unit 10, 20, 32 Bit inversion unit 11 Mapping unit 12, 22, 33, 41 IFFT unit 13, 23, 34, 40 Transmission signal selection Units 21 and 31-2 data transmission channel coding unit 24 and 31-1 address transmission channel coding unit 30 null packet information generation unit 241 outer code RS unit 242 energy spreading unit 243 byte interleaving unit 244 address assignment unit 245 convolution Encoding / address generation unit 246 Bit interleaving unit 247 Mapping unit 248 Time interleaving unit 249 Frequency interleaving unit 250 OFDM frame configuration unit

Claims (7)

In an OFDM signal transmission apparatus that performs OFDM modulation on digital data and transmits a modulated wave of an OFDM signal,
A replacement unit that replaces invalid data included in digital data with data of different N-1 patterns (N is an integer of 2 or more);
An inverse Fourier transform unit for performing an inverse Fourier transform on each of the N-1 digital data including the data replaced by the replacement unit and the digital data including the invalid data;
A selection unit that selects an OFDM signal having a minimum peak power from among the OFDM signals of the N systems of digital data subjected to the inverse Fourier transform by the inverse Fourier transform unit;
An OFDM signal transmitting apparatus comprising: In an OFDM signal transmission apparatus that performs OFDM modulation on digital data and transmits a modulated wave of an OFDM signal,
Based on the bit inversion position information in which the position of inverting the bits of invalid data included in the digital data is set in advance, the bits of the invalid data are inverted, and the invalid data is converted into different N-1 patterns (N is 2 or more). An integer)),
N-1 system digital data including the data replaced by the replacement unit and digital data including the invalid data are transmission channel encoded to generate I and Q signals configured in an OFDM frame. When,
An inverse Fourier transform unit for performing an inverse Fourier transform on each of the N systems of I and Q signals generated by the transmission line encoding unit;
A selection unit that selects, for each OFDM symbol number, an OFDM signal having a minimum peak power from among N systems of OFDM signals that have been subjected to inverse Fourier transform by the inverse Fourier transform unit;
An OFDM signal transmitting apparatus comprising: In an OFDM signal transmission apparatus that performs OFDM modulation on digital data and transmits a modulated wave of an OFDM signal,
The digital data is channel-coded to generate the I and Q signals configured in the OFDM frame, and the digital data after the inner code encoding is affected by inverting the invalid data bits included in the digital data. A transmission path encoding unit that generates an address and generates pair information in which the address of the position where the bit is inverted and the address after inner code encoding are associated;
N-1 (N is an integer greater than or equal to 2) set information is selected from the set information generated by the transmission path encoding unit, and the I and Q signals generated by the transmission path encoding unit are selected. , By inverting the bits of the address after inner code encoding in the selected N-1 set information, the I and Q signals are replaced, and the I, Q configured in different N-1 systems of OFDM frames A replacement unit for generating the Q signal again;
An inverse Fourier transform unit for performing an inverse Fourier transform on each of the N-1 system I and Q signals generated again by the replacement unit and the I and Q signals generated by the transmission line encoding unit;
A selection unit that selects, for each OFDM symbol number, an OFDM signal having a minimum peak power from among N systems of OFDM signals that have been subjected to inverse Fourier transform by the inverse Fourier transform unit;
An OFDM signal transmitting apparatus comprising: In an OFDM signal transmission apparatus that performs OFDM modulation on digital data and transmits a modulated wave of an OFDM signal,
The digital data is channel-coded to generate the I and Q signals configured in the OFDM frame, and the digital data after the inner code encoding is affected by inverting the invalid data bits included in the digital data. A transmission path encoding unit that generates an address and generates pair information in which the address of the position where the bit is inverted and the address after inner code encoding are associated;
N-1 (N is an integer greater than or equal to 2) set information is selected from the set information generated by the transmission path encoding unit, and the I and Q signals generated by the transmission path encoding unit are selected. , By inverting the bits of the address after inner code encoding in the selected N-1 set information, the I and Q signals are replaced, and the I, Q configured in different N-1 systems of OFDM frames A replacement unit for generating the Q signal again;
An autocorrelation function is calculated for each of the N-1 system I and Q signals generated again by the replacement unit and the I and Q signals generated by the transmission path encoding unit, and the N system I and Q signals are calculated. A selection unit that selects, for each OFDM symbol number, the I and Q signals whose autocorrelation function is closest to the impulse characteristic,
An inverse Fourier transform unit for performing an inverse Fourier transform on the I and Q signals selected by the selection unit;
An OFDM signal transmitting apparatus comprising: The OFDM signal transmission apparatus according to claim 2 or 3,
When the selection unit selects an OFDM signal having a minimum peak power among the N systems of OFDM signals for each OFDM symbol number, the OFDM symbol number affected by the bit inversion by the replacement unit is the same. An OFDM signal transmitting apparatus, wherein when there are a plurality of systems, an OFDM signal of the same system is selected for the plurality of OFDM symbol numbers. The OFDM signal transmission apparatus according to claim 4, wherein
When the selection unit selects an I or Q signal having an autocorrelation function closest to an impulse characteristic among the N systems of I and Q signals for each OFDM symbol number, An OFDM signal transmitting apparatus, wherein when there are a plurality of affected OFDM symbol numbers in the same system, the I and Q signals of the same system are selected in the plurality of OFDM symbol numbers. The OFDM signal transmission apparatus according to claim 5 or 6,
When there are a plurality of OFDM symbol numbers that are affected by bit inversion by the replacement unit in the same system, the selection unit, when the selection of the plurality of OFDM symbol numbers for all systems is completed, An OFDM signal transmitting apparatus, wherein a signal for starting processing is output to the replacement unit.

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