JP2014192648A - Peak reducing circuit and peak reducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a peak reducing circuit in which the number of repetitive processing times of peak reduction processing can be reduced.SOLUTION: A peak reducing circuit includes a peak detection unit for detecting a peak which exceeds an OFDM signal by a predetermined threshold, cancel signal generation units 19a-19n for generating a cancel signal based on the information of a peak, for each peak detected by the peak detection unit, and an adder 20 for outputting the total sum of cancel signals generated for respective peaks. The output from the adder 20 is added to the OFDM signal thus reducing the peak thereof.

Description

  The present invention relates to a peak reduction circuit and a peak reduction method, and more particularly to a peak reduction circuit that reduces the peak of an OFDM (Orthogonal Frequency Division Multiplexing) signal.

  An OFDM (Orthogonal Frequency Division Multiplexing) signal used for a radio system such as television broadcasting has a characteristic that the maximum amplitude is larger than the average output level. That is, the peak power to average power ratio (PAPR) increases. Since a signal amplifier that handles a signal having a large maximum amplitude with respect to the average output level needs to have a wide dynamic range, the power efficiency of the amplifier becomes poor.

  Therefore, in order to increase power efficiency, it is necessary to clip a certain peak or more with respect to the transmission signal. However, if clipping is simply performed, the waveform will be distorted. It will deteriorate. For this reason, a technique called Tone Reservation has been invented that reduces the peak using a carrier that is not used during reception (see Non-Patent Document 1).

  FIG. 4 is a diagram showing a configuration of a peak reduction circuit using the Tone Reservation technique related to the present invention. 5 is a diagram showing the OFDM modulated signal 1 in FIG. 4, and FIG. 6 is a diagram showing the cancel base signal 2 in FIG. Here, the processing relating to the generation of the input OFDM modulated signal 1 and the cancellation base signal 2 is not directly related to the present invention, and thus the description thereof is omitted.

  In FIG. 4, the peak detector 5 detects one peak with respect to the time-axis waveform obtained by performing IFFT (Inverse Fast Fourier Transform) on the input OFDM signal 1 in the frequency converter 3a. The cancellation level calculation unit 6 calculates how much the detected peak level is higher than the threshold (= cancellation level value). The waveform shift amount calculation unit 7 calculates a shift amount for matching the peak of the cancel waveform to the detected peak based on the position of the detected peak.

  The signal shift unit 8 receives a time axis waveform created by performing IFFT processing on the cancel base signal 2 by the frequency conversion unit 3b, and uses the calculation result of the waveform shift amount calculation unit 7 to output the output waveform of the frequency conversion unit 3b. The peak position is adjusted to the peak position of the time waveform of the OFDM modulated signal 1 (see FIG. 7). At this time, the waveform is cyclically shifted. The multiplier 9 performs complex multiplication of the output of the signal shift unit 8 and the output of the cancellation level calculation unit 6.

  In the adder 11, the peak is reduced by adding the output of the multiplier 9 to the output of the memory 10 that delays the time waveform of the original OFDM modulated signal 1 by the processing from the peak detector 5 to the multiplier 9. . The number of peaks to be reduced depends on how many stages of Tone Reservation circuits 4 are prepared.

ETSI EN 302 755 V1.2.1 (2010-10)

  In the Tone Reservation method described with reference to FIG. 4, only one peak can be reduced by a single peak reduction process, and a considerable number of iterative processes are required to reduce PAPR.

  An object of the present invention is to provide a peak reduction circuit and a peak reduction method capable of solving the above-described problems and reducing the number of iterations of the peak reduction process.

  The peak reduction circuit according to the present invention is based on peak detection means for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplexing) signal, and information on the peak for each of the peaks detected by the peak detection means. Cancel signal generating means for generating a cancel signal, first addition means for outputting the sum of the cancellation signals generated for each of the peaks, and adding the output of the first addition means to the OFDM signal. And second adding means for reducing the peak of the OFDM signal.

  Another peak reduction circuit according to the present invention includes peak detection means for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplex) signal, storage means for storing cancellation signal data corresponding to the peak, and the peak. For each peak detected by the detection means, the cancel signal data corresponding to the peak is read from the storage means and summed, and the output of the cancel signal generation means is added to the OFDM signal. And adding means for reducing the peak of the OFDM signal.

  The peak reduction method according to the present invention is based on a peak detection step for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplexing) signal, and information on the peak for each of the peaks detected by the peak detection step. A cancel signal generating step for generating a cancel signal, a first adding step for outputting the sum of the cancel signals generated for each of the peaks, and an output of the first adding step are added to the OFDM signal. And a second adding step for reducing the peak of the OFDM signal.

  Another peak reduction method according to the present invention includes a peak detection step for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplexing) signal, and a storage means for storing cancellation signal data corresponding to the peak. For each of the peaks detected in the detection step, a cancel signal generation step for reading out the sum of the cancel signal data corresponding to the peak and summing them, and adding the output of the cancel signal generation step to the OFDM signal to add the OFDM signal And a summing step for reducing the peak of.

  According to the present invention, it is possible to reduce the number of iterations of the peak reduction process.

It is a figure which shows the structure of the peak reduction circuit by the 1st Embodiment of this invention. It is a figure which shows the structure of the cancellation waveform production | generation part of FIG. It is a figure which shows the structure of the peak reduction circuit by the 2nd Embodiment of this invention. It is a figure which shows the structure of the peak reduction circuit relevant to this invention. It is a figure which shows the OFDM modulation signal of FIG. It is a figure which shows the cancellation base signal of FIG. It is a figure which shows the cyclic shift process of the signal shift part of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a peak reduction circuit according to the first embodiment of the present invention, and the same parts as those in FIG. 4 are denoted by the same reference numerals. 1 is the same as FIG. 4 in that the OFDM modulation signal 1 and the cancel base signal 2 are converted into time-axis waveforms by the frequency converters 3a and 3b, respectively. In the switching circuits 12 and 16, the Tone Reservation circuit 4 is repeatedly arranged in FIG. 4, but the switching circuits 12 and 16 are repeatedly input in order to express this simply.

  The peak detector 13 detects a peak exceeding a predetermined threshold in the time axis waveform of the input OFDM modulated signal 1 and stores the level and position. Each time the peak detection unit 13 performs peak detection processing on a signal waveform for one symbol, the peak detection unit 13 outputs the level and position of each peak detected from the signal waveform for one symbol. When the number of peaks exceeding the predetermined threshold is greater than the predetermined number n, only the predetermined number n having a large level among them is handled as a peak. Thereby, it is possible to reduce the influence when the peak cannot be reduced due to the number of processing times due to hardware or software constraints.

  The memory 14 stores the time axis waveform of the cancel base signal 2 and shifts and transfers the stored signal in accordance with the output of the peak detector 13 to the cancel waveform generator 15. The cancel waveform generation unit 15 generates a cancel signal for canceling a plurality of peaks, using signals from the peak detection unit 13 and the memory 14. In the adder 11, the output of the cancel waveform generation unit 15 is added to the output of the memory 10 that delays the time waveform of the original OFDM modulation signal 1 by the processing from the peak detection unit 13 to the cancel waveform generation unit 15. Reduce the peak.

  FIG. 2 is a diagram showing a configuration of the cancel waveform generation unit 15 in FIG. 1, and the same parts as those in FIG. 4 are denoted by the same reference numerals. In FIG. 2, the cancellation waveform generation unit 15 includes the same number of 1-pulse cancellation waveform generation units 19a to 19n as the predetermined number n described above. The signal detection result 17 of the peak detection unit 13, that is, the information (level and position) of a plurality of peaks detected by the peak detection unit 13 is input to the one-pulse cancel waveform generation units 19 a to 19 n, respectively. The time base waveform 18 of the cancel base signal is input to the one-pulse cancel waveform generators 19a to 19n.

  The one-pulse cancellation waveform generation unit 19 a includes a cancellation level calculation unit 6, a waveform shift amount calculation unit 7, a signal shift unit 8, and a multiplier 9. Each of the one-pulse cancel waveform generation units 19b to 19n has the same configuration as that of the one-pulse cancel waveform generation unit 19a. Each of the one-pulse cancel waveform generation units 19a to 19n is the same as the cancel level calculation unit 6, the waveform shift amount calculation unit 7, the signal shift unit 8 and the multiplier 9 shown in FIG. 4 based on the input peak information. A processing operation is performed to generate a cancel waveform.

  A cancel waveform for each of a plurality of peaks detected by the peak detector 13 is generated by the one-pulse cancel waveform generators 19a to 19n, and the adder 20 takes the sum of these cancel waveforms and outputs the sum to the adder 11. To do.

  As described above, in the first embodiment of the present invention, since a plurality of peaks are detected and reduced by one peak reduction process, the same peak reduction as compared with the method shown in FIG. It is possible to reduce the number of iterations until the performance is achieved.

  However, another peak occurs due to the addition of the cancel signal, and there is a possibility that a peak higher than the peak value before the addition may occur. Therefore, the peak reduction process cannot be performed once, and the process is performed several times. Need to be implemented. In this case, peak reduction processing is repeatedly performed on the OFDM signal output from the adder 11 via the switching circuits 16 and 12.

  In the first embodiment of the present invention, the cancel base signal is frequency-converted to generate a cancel waveform after making a time axis waveform. However, the frequency conversion is not performed first, and a plurality of detected peaks are detected. It is also possible to obtain the same result by converting the shift amount calculated from the signal into a phase, performing complex multiplication on the input cancellation base signal itself, then calculating the sum, and finally performing frequency conversion.

  FIG. 3 is a diagram showing the configuration of the peak reduction circuit according to the second embodiment of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. Regarding the cancellation base signal shown in FIG. 6, when the carrier that can be used for cancellation is fixed (when the same frequency carrier is always used regardless of the input signal on the frequency axis), the peak position to be canceled is the position of the OFDM modulated signal. Depending on the sample number of one symbol data of the time axis waveform (= shift amount) and how much the peak level is higher than the threshold (= cancellation level value), the cancel base signal for the peak is determined. Determine uniquely.

  Therefore, in the second embodiment of the present invention, by preparing a database of cancel signal data corresponding to the shift amount and cancel level of each peak, even in the case of a signal having many time series exceeding the threshold, each peak It is possible to generate a large number of cancel waveforms at once by reading out and adding the cancel signal data corresponding to.

  In FIG. 3, the cancel signal generation unit 22 includes a peak cancel data storage memory 21. The memory 21 stores cancel signal data corresponding to each peak in association with a shift amount and a cancel level corresponding to the peak. The cancel signal generation unit 22 calculates the shift amount and the cancel level for each peak based on the information (level and position) of the plurality of peaks detected by the peak detection unit 13, and reads the corresponding cancel signal data from the memory 21. Then, after summing them, they are output to the frequency converter 3b.

  The frequency conversion unit 3 b performs frequency conversion on the cancel signal from the cancel signal generation unit 22 and outputs it to the adder 11 as a time axis waveform.

  In the second embodiment of the present invention, since a plurality of peaks are detected and reduced by a single peak reduction process, the same peak reduction performance can be obtained as compared with the method shown in FIG. It is possible to reduce the number of iterations. In the second embodiment of the present invention, since cancel signal data corresponding to a plurality of peaks is read from the peak cancel data storage memory 21, even in the case of a signal having many time series exceeding a threshold value, A large number of cancel waveforms can be generated.

1 OFDM modulation signal
2 Cancel base signal 3a, 3b Frequency converter 4a, 4b Tone Reservation circuit 5, 13 Peak detector
6 Cancellation level calculator
7 Waveform shift amount calculation part
8 Signal shift part
9 Multiplier 10, 14 Memory 11, 20 Adder 12, 16 Switching circuit
15 Cancel waveform generator
17 Signal detection results
18 Cancel base signal (time axis waveform)
19a to 19n 1 pulse cancel waveform generator
21 Peak cancellation data storage memory
22 Cancel signal generator

Claims (10)

Peak detection means for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplex) signal;
For each of the peaks detected by the peak detection means, a cancellation signal generation means for generating a cancellation signal based on the information on the peak,
First addition means for taking the sum of the cancellation signals generated for each of the peaks and outputting;
And a second addition means for reducing the peak of the OFDM signal by adding the output of the first addition means to the OFDM signal.   The cancellation signal is generated for each of the predetermined number of peaks having a higher level among the peaks when the number of the peaks exceeding the predetermined threshold is greater than the predetermined number. Peak reduction circuit.   The OFDM signal output from the second adding means is further subjected to peak reduction processing by the peak detecting means, the cancel signal generating means, and the first and second adding means. The peak reduction circuit according to claim 1 or 2. Peak detection means for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplex) signal;
Storage means for storing cancel signal data corresponding to the peak;
For each of the peaks detected by the peak detection means, a cancel signal generation means for reading the cancellation signal data corresponding to the peak from the storage means and taking the sum,
A peak reduction circuit comprising: addition means for reducing the peak of the OFDM signal by adding the output of the cancellation signal generation means to the OFDM signal.   5. The peak reduction circuit according to claim 4, wherein a peak reduction process by the peak detection means, the cancellation signal generation means, and the addition means is further performed on the OFDM signal output from the addition means. . A peak detection step for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplex) signal;
For each of the peaks detected by the peak detection step, a cancellation signal generation step for generating a cancellation signal based on information on the peak,
A first addition step of taking and outputting the sum of the cancellation signals generated for each of the peaks;
And a second addition step of reducing the peak of the OFDM signal by adding the output of the first addition step to the OFDM signal.   7. The cancel signal is generated for each of the predetermined number of peaks having a higher level among the peaks when the number of the peaks exceeding the predetermined threshold is larger than the predetermined number. Peak reduction method.   A peak reduction process by the peak detection step, the cancel signal generation step, and the first and second addition steps is further performed on the OFDM signal output by the second addition step. The peak reduction method according to claim 6 or 7. A peak detection step for detecting a peak exceeding a predetermined threshold from an OFDM (Orthogonal Frequency Division Multiplex) signal;
For each of the peaks detected by the peak detection step from a storage means for storing the cancellation signal data corresponding to the peak, a cancellation signal generation step of reading the cancellation signal data corresponding to the peak and taking the sum,
A peak reduction method comprising: adding an output of the cancellation signal generation step to the OFDM signal to reduce a peak of the OFDM signal.   The peak reduction method according to claim 9, wherein a peak reduction process is further performed on the OFDM signal output by the addition step by the peak detection step, the cancellation signal generation step, and the addition step. .

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