JP2016178364A - Transmitter, radio communication system, transmitter control method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mechanism that effectively reduces a peak-to-average power ratio in OFDM.SOLUTION: A transmitter includes: a first generation unit for generating an OFDM signal transmitted in a first frequency band; a second generation unit for generating a cancel signal which is to reduce the peak of the OFDM signal and transmitted using a carrier in a second frequency band different from the first frequency band; an addition unit for adding the OFDM signal and the cancel signal generated by the second generation unit and for outputting a signal after the addition; and an inverse Fourier transformation unit for carrying out inverse Fourier transformation to the signal output by the addition unit.SELECTED DRAWING: Figure 9

Description

  The present disclosure relates to a transmitter, a wireless communication system, a transmitter control method, and a program.

  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 the power efficiency of the amplifier, it is necessary to clip a certain peak or more with respect to the transmission signal. However, when clipping is simply performed, the waveform is distorted, so that the signal is deteriorated as compared with the case where clipping is not performed.

  Patent Document 1 discloses a technique called Tone Reservation as a technique for reducing such a peak.

  The purpose of the technique of Patent Document 2 is to simplify the process of reducing PAPR in OFDM communication. Specifically, the IFFT unit of the communication device performs IFFT (Inverse Fast Fourier Transform) to generate inversely converted data. The selection unit calculates the PAPR of the baseband signal based on the inverse transform data, and selects the inverse transform data having the lowest PAPR. The transmission unit generates a baseband signal by synthesizing the inverse transform data, generates a transmission signal from the data specifying the operation performed when the selected inverse transform data is generated, and the baseband signal. Send transmission signals to other devices.

  Patent Document 3 discloses a system for reducing PAPR. The signal from which the out-of-band spectral component has been removed by the bandpass filter is up-converted to a desired RF carrier frequency and amplified. That is, filtering by a band pass filter is performed before amplification.

  Note that the technique of Patent Document 4 relates to channel estimation for improving estimation accuracy in a low SNR region. Patent Document 4 discloses a transmitter that reduces the power of auxiliary pilot subcarriers added to both ends of a pilot symbol signal band during transmission. On the other hand, the receiver performs a propagation path estimation method using a time window method by inserting virtual subcarriers.

  Non-Patent Document 1 discloses a selective mapping method as a PAPR reduction method. In the selective mapping method, a signal having a low PAPR value is selected from a plurality of time-series signals generated by multiplying a signal having a certain rule with transmission data.

JP2012-509645A JP 2014-204252 A Special table 2009-517890 JP 2009-055430 A

IEEE Electronics Letters, Vol.32, Issue22, pp.2056-2057

  However, for example, in the Tone Reservation method of Patent Document 1, it is necessary to prepare a tone carrier for performing peak cancellation within an effective frequency band in which data is transmitted. For this reason, the amount of data that can be transmitted by the tone carrier is reduced.

  Note that the technique for reducing the PAPR in Patent Document 2 or 3 is completely different from the method of inserting a carrier for performing peak cancellation. Moreover, the technique of patent document 4 adds a change to a pilot subcarrier. This change aims at improving estimation accuracy in a low SNR region, and therefore requires a configuration that uses a time window method by inserting virtual subcarriers not only on the transmission side but also on the reception side.

  Therefore, one of the objects of the exemplary embodiment is to provide a mechanism for effectively reducing the peak-to-average power ratio in the OFDM scheme. It should be noted that this object is only one of a plurality of objects that the embodiments disclosed herein intend to achieve. Other objects or problems and novel features will become apparent from the description of the present specification or the accompanying drawings.

  The transmitter of the exemplary embodiment uses a first generation unit that generates an OFDM signal transmitted in a first frequency band, and a carrier in a second frequency band different from the first frequency band. A second generation unit that generates a cancellation signal for reducing a peak of the OFDM signal to be transmitted, adds the OFDM signal, and the cancellation signal generated by the second generation unit, and adds An adder that outputs a later signal and an inverse Fourier transform that performs an inverse Fourier transform on the signal output by the adder.

  The wireless communication system of another exemplary embodiment includes a transmitter and a receiver. The transmitter generates an OFDM signal transmitted in a first frequency band, and reduces the peak of the OFDM signal transmitted using a carrier in a second frequency band different from the first frequency band. To generate a cancel signal, add the OFDM signal and the generated cancel signal, output a signal after the addition, perform an inverse Fourier transform on the signal after the addition, and perform the inverse Fourier transform An OFDM signal based on is transmitted to the receiver. The receiver receives the OFDM signal.

  In another exemplary embodiment, a method for controlling a transmitter generates an OFDM signal to be transmitted in a first frequency band and transmits the signal using a carrier in a second frequency band different from the first frequency band. A cancellation signal for reducing the peak of the OFDM signal is generated, the OFDM signal and the generated cancellation signal are added, an added signal is output, and the signal after the addition is reversed. Perform Fourier transform.

  The program in another exemplary embodiment generates an OFDM signal transmitted in a first frequency band, and is transmitted using a carrier in a second frequency band different from the first frequency band. Generate a cancellation signal for reducing the peak of the OFDM signal, add the OFDM signal and the generated cancellation signal, output the added signal, and perform an inverse Fourier transform on the added signal Let the computer execute the control method of the transmitter.

  According to an exemplary embodiment, the peak-to-average power ratio can be effectively reduced in the OFDM scheme.

2 illustrates the configuration of a tone reservation circuit associated with an exemplary embodiment. FIG. 6 illustrates a configuration for a selective mapping scheme associated with an exemplary embodiment. FIG. 1 illustrates a transmitter of a first exemplary embodiment. 2 shows a frequency axis waveform of a signal a of the first exemplary embodiment. 2 shows a frequency axis waveform of a signal n of the first exemplary embodiment. 3 shows a frequency axis waveform of a signal Sn of the first exemplary embodiment. 2 shows a frequency axis waveform in a state in which a signal a and a signal Sn of the first exemplary embodiment are added together. 2 shows a transmitter of a second exemplary embodiment. Fig. 4 shows a transmitter of a third exemplary embodiment. 4 illustrates a wireless communication system of a fourth exemplary embodiment.

  Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted as necessary for clarification of the description.

  A plurality of embodiments described below can be implemented independently or can be implemented in combination as appropriate. The plurality of embodiments have different novel features. Therefore, these multiple embodiments contribute to solving different purposes or problems and contribute to producing different effects.

<Introduction>
FIG. 1 illustrates a tone reservation circuit configuration associated with an exemplary embodiment.
In FIG. 1, a peak detector 14 detects a peak with respect to a time axis waveform obtained by performing IFFT processing on an input OFDM modulated signal in the frequency converter 11.

  The cancellation level calculation unit 15 calculates how much the detected peak level is higher than the threshold (= cancellation level value).

  The waveform shift amount calculation unit 16 calculates a shift amount for aligning the peak of the cancel waveform with the detected peak based on the position of the detected peak.

  The signal shift unit 17 receives a time axis waveform generated by performing IFFT processing on the cancel base signal in the frequency conversion unit 19, and uses the calculation result of the waveform shift amount calculation unit 16 to output the output waveform of the frequency conversion unit 19. The peak position is adjusted to the peak position of the time waveform of the OFDM modulation signal. At this time, the waveform is cyclically shifted.

  The multiplier 18 performs complex multiplication of the output of the signal shift unit 17 and the output of the cancellation level calculation unit 15.

  In the adder 13, the peak is reduced by adding the output of the multiplier 18 to the output of the memory 12 that delays the time waveform of the original OFDM modulated signal by the processing from the peak detector 14 to the multiplier 18.

  FIG. 2 shows a configuration for a selective mapping scheme associated with an exemplary embodiment.

  According to FIG. 2, in the multiplier, a fixed pseudo-random signal is superimposed (multiplied) on a transmission carrier within an effective frequency in which transmission data is transmitted. The output from a plurality of multipliers is IFFTed, and a signal with a low PAPR value is selected from the signals subjected to IFFT processing.

<First Exemplary Embodiment>
FIG. 3 shows a transmitter of the first exemplary embodiment.
3, the transmitter according to the present embodiment includes at least one encoder 31, interleaver 32, QAM (Quadrature Amplitude Modulation) mapping 33, S / P (serial / parallel) converter 34. The IFFT unit 35 includes a selection unit 36, a CP (cyclic prefix) unit 37, an out-of-band carrier random signal generation unit 40, a spectrum mask limiting unit 41, and at least one addition unit 42.

  Various processing is performed on the input transmission data by the encoding unit 31, the interleaver unit 32, the QAM mapping unit 33, the S / P conversion unit 34, the addition unit 42, the IFFT unit 35, the selection unit 36, and the CP unit 37. Is done.

  The signal added to the adding unit 42 is generated based on the processing in the out-of-band carrier random signal generating unit 40 and the spectrum mask limiting unit 41.

  The encoding unit 31 encodes the input transmission data.

  The interleaver unit 32 performs an interleaving (bit rearrangement) process on the encoded data signal.

  The QAM mapping unit 33 maps (associates) the interleaved data signal with signal points determined by the phase and amplitude of the subcarrier. For example, mapping based on QAM is performed in which more information is transmitted in one symbol by combining phase modulation and amplitude modulation.

  The S / P conversion unit 34 performs parallel conversion on the mapped data signal and outputs it. Here, the S / P converter 34 outputs the mapped data signal to the plurality of adders 42. In FIG. 3, the data signal (frequency-domain OFDM signal) output from the S / P converter 34 is indicated by the symbol “a”. An example of this signal “a” is shown in FIG. In FIG. 4, it is assumed that the number of carriers included in the band in which the OFDM signal is transmitted is determined in advance according to the transmission standard.

  The out-of-band carrier random signal generation unit 40 (hereinafter also referred to as the generation unit 40) generates a random signal for a carrier other than the frequency band in which the OFDM signal (transmission data) is transmitted.

  Specifically, the generation unit 40 generates data in which randomly generated carriers are arranged in an out-of-band portion. This generated data is indicated by the symbol “n (i)” in FIG. FIG. 5 shows an example of this data in the form of a simplified frequency axis waveform. For example, when the selective mapping method is used for PAPR reduction as in this embodiment, data n is prepared for the prepared IFFT circuit. In FIG. 3, since m IFFT circuits are prepared, m signals n are output.

  The spectrum mask limiting unit 41 generates a signal Sn that is limited so that the data n generated by the generation unit 40 is not subject to out-of-band spurious limitation. By this processing, the level related to the emission of radio waves having a frequency outside the necessary frequency band is suppressed to be smaller than a predetermined value for data n. FIG. 6 shows an example of the signal Sn in the form of a simplified frequency axis waveform. Thus, in this embodiment, a signal (data) for reducing PAPR is generated by adding a spectrum mask defined in the transmission standard as a limiting condition.

  The adder 42 adds the output signal of the S / P converter 34 and the output signal of the spectrum mask limiter 41. Specifically, the signal “a ′” is created by adding the data signal a and the signal Sn. When there are a plurality of signals a or signal Sn, the same processing is performed in the corresponding adder.

  FIG. 7 shows an example of the signal Sn in the form of a simplified frequency axis waveform. FIG. 7 shows a specific example in which the amplitude of the sixth carrier from the left and the sixth carrier from the right is zero (substantially includes zero). This is because the receiver can easily recognize the added carrier by separating the transmission carrier of FIG. 4 from the added carrier.

  In FIG. 3, Sn (1) to Sn (m) are shown. These values are based on the random signal generated by the out-of-band carrier random signal generation unit 40.

  In FIG. 2, a multiplier for superimposing the output signal of the S / P converter and the output signal of the fixed pseudorandom signal is shown to superimpose the random signal including the transmission carrier. On the other hand, FIG. 3 shows an adder 42 for adding a carrier generated from a random signal to a carrier different from the transmission carrier.

  The IFFT unit 35 performs fast inverse Fourier transform on the frequency domain OFDM signal after the addition by the adding unit 42 to generate a time domain OFDM signal.

  The selection unit 36 selects a system with the fewest peaks from the plurality of OFDM signals input from the IFFT unit 35. The selected OFDM signal is output to CP section 37.

  The CP unit 37 receives the OFDM signal selected from the selection unit 36. The CP unit 37 inserts a guard interval (GI) into the input OFDM signal.

  The signal output from the CP unit 37 is subjected to predetermined processing, and an OFDM modulated signal is transmitted from the transmitter to the receiver. The receiver performs a process reverse to that of the transmitter and performs a process of extracting (demodulating) original data.

  According to the present embodiment, PAPR can be performed without using a carrier in an actual transmission band by using a carrier other than the frequency band in which the OFDM signal is transmitted. That is, it is possible to prevent the effective data to be transmitted from being reduced by reducing the carrier in the transmission band.

  Further, a carrier for peak cancellation is used to drop the peak when the OFDM signal is converted into a time waveform. This carrier is not used on the receiving side like a pilot carrier, for example. Also, this carrier is not used for data transmission. For this reason, it is not necessary to newly provide an additional circuit or the like on the receiver side, and the peak of the OFDM signal can be reduced.

  For example, transmitters and receivers that make up a wireless communication system based on specifications (standards) such as the frequency band of transmission data being set can be easily reduced without changing the specifications. it can.

  That is, the peak power reduction can be realized without changing the specification or the receiving side, thereby improving the power efficiency of the transmitter.

  As described above, a plurality of pieces of data having different values of the created out-of-band carriers are generated, and IFFT is performed on the plurality of pieces of generated data. As a result, data with the lowest PAPR can be used as the transmission waveform.

<Second Exemplary Embodiment>
In the first exemplary embodiment, an example using the selective mapping method is shown. In exemplary embodiments, other peak reduction techniques may be used. For example, Tone Reservation and other PAPR reduction methods may be used.

  FIG. 8 shows a portion of the transmitter of the second exemplary embodiment.

  In the present embodiment, a filter 52 is provided after the amplifier 51 that inputs a signal based on the OFDM signal generated by the IFFT unit 50. The filter 52 is composed of, for example, a band pass filter (BPF). The filter 52 satisfies the spectrum mask like the spectrum mask limiting unit 41 described above. In the present embodiment, a filter 52 is used instead of the spectrum mask limiting unit 41 in the first exemplary embodiment.

<Third exemplary embodiment>
FIG. 9 shows a transmitter of a third exemplary embodiment.
The transmitter in FIG. 9 includes a first generation unit 101, a second generation unit 102, an addition unit 103, and an inverse Fourier transform unit 104.

  The first generation unit 101 generates an OFDM signal transmitted in the first frequency band.

  The second generation unit 102 generates a cancel signal for reducing the peak of the OFDM signal transmitted using a carrier in a second frequency band different from the first frequency band.

  Adder 103 adds the OFDM signal and the cancel signal generated by the second generator, and outputs the signal after the addition.

  The inverse Fourier transform unit 104 performs inverse Fourier transform on the signal output from the addition unit. The inverse Fourier transform unit 104 outputs a signal subjected to inverse Fourier transform.

  According to the present embodiment, the peak-to-average power ratio can be effectively reduced in the OFDM method.

<Fourth Exemplary Embodiment>
FIG. 10 shows a wireless communication system of a fourth exemplary embodiment.
In FIG. 10, the wireless communication system of the present embodiment includes a transmitter 200 and a receiver 300.

  The transmitter 200 of this embodiment corresponds to the transmitter of the third exemplary embodiment shown in FIG. The transmitter transmits an OFDM signal based on the inverse Fourier transform to the receiver. The receiver receives this OFDM signal.

  According to the present embodiment, the peak-to-average power ratio can be effectively reduced in the OFDM method.

<Other exemplary embodiments>
The exemplary embodiment described above can be used in a technique for reducing the peak of an OFDM signal time axis waveform (a waveform after IFFT) used in a television transmitter or the like.

  Further, a computer program (hereinafter referred to as a program) describing the above-described processing contents as a procedure is recorded on a recording medium readable by each of the elements constituting the transmitter, and the program recorded on the recording medium is recorded. It may be read and executed by each component of the transmitter.

  The program recorded on the recording medium is read by a central processing unit (CPU) provided in each component of the transmitter, and the same processing as described above is performed under the control of the CPU. Here, the CPU operates as a computer that executes a program read from a recording medium on which the program is recorded.

  In the above example, the program can be stored and supplied to a computer using various types of non-transitory computer readable media. Non-transitory computer readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (for example, flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (for example, magneto-optical disks), CD (Compact Disc) -ROM (Read Only Memory), CD-R (Recordable), CD-R / W (ReWritable), Digital Versatile Disk (DVD), semiconductor memory (for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access) Memory)). The program may also be supplied to the computer by various types of transitory computer readable media. Examples of transitory computer readable media include electrical signals, optical signals, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or a wireless communication path.

Frequency converter 11
Memory 12
Adder 13
Peak detector 14
Cancellation level calculator 15
Waveform shift amount calculation unit 16
Signal shift unit 17
Multiplication unit 18
Frequency converter 19
Encoding unit 31
Interleaver part 32
QAM mapping unit 33
S / P converter 34
IFFT part 35
Selector 36
CP part 37
Out-of-band carrier random signal generator 40
Spectrum mask limiting unit 41
Adder 42
IFFT section 50
Amplifier 51
Filter 52
First generation unit 101
Second generation unit 102
Adder 103
Inverse Fourier transform unit 104
Transmitter 200
Receiver 300

Claims (9)

A first generator for generating an OFDM signal transmitted in the first frequency band;
A second generator for generating a cancellation signal for reducing a peak of the OFDM signal, transmitted using a carrier of a second frequency band different from the first frequency band;
An adder that adds the OFDM signal and the cancellation signal generated by the second generator, and outputs a signal after the addition;
An inverse Fourier transform unit that performs an inverse Fourier transform on the output signal in the addition unit,
Transmitter. The cancellation signal is
Generated based on a predetermined value limited by the spectrum mask,
The transmitter according to claim 1. A plurality of the adding units;
A plurality of the inverse Fourier transform units;
And a selection unit,
The second generator is
Generating a plurality of the cancellation signals;
Outputting the cancellation signal to each of the plurality of addition units;
Each of the plurality of addition units is
The input cancellation signal is added to the OFDM signal, and the added signal is output to each of the plurality of inverse Fourier transform units.
The inverse Fourier transform unit is
The addition unit performs an inverse Fourier transform on the output signal, and outputs the inverse Fourier transform signal to the selection unit.
The selection unit includes:
A plurality of the inverse Fourier transformed signals are input from the plurality of inverse Fourier transform units,
Selecting a signal having the smallest peak from the plurality of input signals;
The transmitter according to claim 1 or 2. An amplifier for amplifying the inverse Fourier transformed signal;
A bandpass filter that limits a frequency band in consideration of a predetermined value limited by a spectrum mask for the signal amplified by the amplifier;
Having
The transmitter according to claim 1 or 3. The transmitter according to any one of claims 1 to 4, wherein the carrier of the cancellation signal is used to attenuate a peak waveform generated by the carrier in the first frequency band. The carrier of the cancellation signal is not used in the receiver that receives the OFDM modulated signal transmitted from the transmitter.
The transmitter according to any one of claims 1 to 5. A wireless communication system including a transmitter and a receiver,
The transmitter is
Generating an OFDM signal transmitted in a first frequency band;
Generating a cancellation signal for reducing a peak of the OFDM signal transmitted using a carrier of a second frequency band different from the first frequency band;
Adding the OFDM signal and the generated cancellation signal;
Output the signal after addition,
Inverse Fourier transform is performed on the signal after the addition,
Transmitting an OFDM signal based on the inverse Fourier transform to a receiver;
The receiver
Receiving the OFDM signal;
Wireless communication system. A method for controlling a transmitter,
Generating an OFDM signal transmitted in a first frequency band;
Generating a cancellation signal for reducing a peak of the OFDM signal transmitted using a carrier of a second frequency band different from the first frequency band;
Adding the OFDM signal and the generated cancellation signal;
Output the signal after addition,
Inverse Fourier transform is performed on the signal after the addition,
How to control the transmitter. A program for causing a computer to execute a control method of a transmitter,
Generating an OFDM signal transmitted in a first frequency band;
Generating a cancellation signal for reducing a peak of the OFDM signal transmitted using a carrier of a second frequency band different from the first frequency band;
Adding the OFDM signal and the generated cancellation signal;
Output the signal after addition,
A program that causes a computer to execute a process of performing inverse Fourier transform on the signal after the addition.

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