JP6010865B2 - COMMUNICATION DEVICE AND COMMUNICATION METHOD - Google Patents

Description

  The present invention relates to a communication device and a communication method.

  In OFDM (Orthogonal Frequency-Division Multiplexing) communication, an input signal is subjected to subcarrier modulation, IFFT (Inverse Fast Fourier Transformation) is performed, and a baseband signal is generated. Therefore, when the number of subcarriers increases and the FFT (Fast Fourier Transformation) size increases, a baseband signal with a large peak is generated, and the PAPR (Peak-to-Average Power Ratio) ) Is high. As the PAPR increases, an amplifier having linearity in a wide range is required to transmit a signal without distortion. Therefore, techniques for reducing PAPR have been developed.

  In the orthogonal frequency division multiplexing communication apparatus of Patent Literature 1, in order to reduce PAPR, the phase of the subcarrier modulation signal is controlled based on the optimum phase calculated by the sequential determination method before performing IFFT.

JP 2006-165781 A

  In OFDM communication, reducing PAPR is an issue. In the orthogonal frequency division multiplexing communication apparatus of Patent Document 1, it is necessary to perform iterative calculation processing to calculate the optimum phase for reducing the PAPR, and to control the phase for each subcarrier.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to reduce PAPR and control the degree of PAPR reduction in OFDM communication.

In order to achieve the above object, a communication device according to the first aspect of the present invention provides:

A communication device that communicates with other devices by orthogonal frequency division multiplex communication wireless communication,
Receiving means for generating a base band signal by receiving the transmission signal,
FFT means for performing serial-parallel conversion on the baseband signal and performing fast Fourier transform to generate converted data ;
Using the predetermined range determined by the insertion data used for generation of the transmission signal and the threshold value determined according to the division unit used for generation of the transmission signal , the same number in the converted data An extracting means for sequentially extracting division units, excluding division units in which the number of elements having a value within the predetermined range is equal to or greater than the threshold value among a plurality of division units composed of continuous elements;
Demodulating means for demodulating the division unit extracted by the extracting means with a predetermined modulation method ;
It is characterized by providing.

A communication method according to a second aspect of the present invention includes:
A communication method performed by a communication device that communicates with other devices by wireless communication of an orthogonal frequency division multiplex communication method,
A reception step of receiving a transmission signal and generating a baseband signal;
An FFT step of performing serial-parallel conversion on the baseband signal and performing fast Fourier transform to generate converted data;
Using the predetermined range determined by the insertion data used for generation of the transmission signal and the threshold value determined according to the division unit used for generation of the transmission signal, the same number in the converted data An extraction step for sequentially extracting division units, excluding division units in which the number of elements having a value within the predetermined range is greater than or equal to the threshold value among a plurality of division units composed of consecutive elements;
A demodulation step of demodulating the division unit extracted in the extraction step by a predetermined modulation method;
It is characterized by providing.

  According to the present invention, it is possible to reduce PAPR and control the degree of PAPR reduction in OFDM communication.

It is a block diagram which shows the structural example of the communication apparatus which concerns on embodiment of this invention. It is a block diagram which shows the example of a different structure of the communication apparatus which concerns on embodiment. It is a figure which shows the example of the arithmetic processing which the calculating part which concerns on embodiment performs. It is a flowchart which shows an example of the operation | movement of transmission control which the communication apparatus which concerns on embodiment performs. It is a flowchart which shows an example of the operation | movement of reception control which the communication apparatus which concerns on embodiment performs. It is a figure which shows the CCDF characteristic of PAPR of the baseband signal in the communication apparatus which concerns on embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent parts are denoted by the same reference numerals. In the following description, IFFT (Inverse Fast Fourier Transformation) is a concept including IFFT and IDFT (Inverse Discrete Fourier Transformation). Therefore, in the embodiment of the present invention, IDFT may be performed instead of IFFT. Similarly, FFT (Fast Fourier Transformation) is a concept including FFT and DFT (Discrete Fourier Transformation). When performing IDFT and DFT, the FFT size in the following description means the DFT size.

  FIG. 1 is a block diagram illustrating a configuration example of a communication device according to an embodiment of the present invention. The communication device 1 communicates with other devices by OFDM (Orthogonal Frequency-Division Multiplexing) wireless communication. The communication device 1 includes an antenna 10, a modulation unit 11, a serial / parallel conversion unit 12, a calculation unit 13, an IFFT unit 14, a determination unit 15, a transmission unit 16, and a controller 20.

  The controller 20 includes a CPU (Central Processing Unit) 21, a RAM (Random Access Memory) 23, and a ROM (Read-Only Memory) 24. In order to avoid complication and to facilitate understanding, signal lines from the controller 20 to each part are omitted, but the controller 20 is connected to each part of the communication device 1 via an I / O (Input / Output) 22. The start and end of these processes and the control of the process contents are performed.

  In the RAM 23, for example, data for generating a transmission frame is stored. The ROM 24 stores a control program for the controller 20 to control the operation of the communication device 1. The controller 20 controls the communication device 1 based on the control program.

  FIG. 2 is a block diagram illustrating a different configuration example of the communication device according to the embodiment. In order to provide the above-described communication device 1 with a reception function, the communication device 1 illustrated in FIG. 2 further includes a demodulation unit 31, a parallel-serial conversion unit 32, an extraction unit 33, an FFT unit 34, a reception unit 35, and a transmission / reception switching unit 36. . A communication method performed by the communication device 1 using the communication device 1 shown in FIG. 2 having a transmission function and a reception function will be described below.

  The modulation unit 11 modulates the input signal by a predetermined modulation method, generates a primary modulation signal, and sends it to the serial-parallel conversion unit 12. The predetermined modulation method is, for example, QPSK (Quadrature Phase-Shift Keying). The serial-parallel conversion unit 12 performs serial-parallel conversion on the primary modulation signal, generates a subcarrier modulation signal that is a parallel signal, and sends the subcarrier modulation signal to the calculation unit 13. The calculation unit 13 extracts one or more arbitrary number of division units in order from the top among a plurality of division units composed of the same number of consecutive elements in the subcarrier modulation signal. The calculation unit 13 inserts insertion data composed of complex numbers different from the values that can be taken by the elements of the subcarrier modulation signal, at the arbitrary positions before and after each of the extracted division units, Calculation data whose number of elements matches the FFT size is generated. The calculation unit 13 sends the calculation data to the IFFT unit 14.

When the modulation method is QPSK and the absolute value of each element of the modulation signal is A, the possible values of each element of the modulation signal are A · e ^{i (π / 4)} and A · e ^{i (3π / 4). )} , A · e ^{i (−π / 4)} , and A · e ^{i (−3π / 4)} . Therefore, when the modulation method is QPSK, the element of the insertion data is a complex number different from any of the above values. As long as the receiving unit can distinguish between the division unit and the insertion data, each element of the insertion data may have the same value, or may have different values. For example, the insertion data may be a CAZAC (Constant Amplitude Zero Auto-Correlation) sequence having an absolute value of (1/2) A. For example, the arithmetic unit 13 uses insertion data in which the complex number is 0 and the element value is 0.

  The IFFT unit 14 performs IFFT on the operation data to generate inversely transformed data, and sends it to the determination unit 15. The determination unit 15 calculates a PAPR (Peak-to-Average Power Ratio) of the baseband signal based on the inverse transform data, and determines whether or not the PAPR meets the reference. When it is determined that the PAPR does not meet the standard, the calculation unit 13 is notified of this. The calculation unit 13 generates new calculation data by changing the number of division units to be extracted and / or the position where the insertion data is inserted. The IFFT unit 14 and the determination unit 15 perform the above-described processing for new calculation data. The controller 20 performs an operation as a repetitive unit that causes the calculation unit 13, the IFFT unit 14, and the determination unit 15 to repeatedly perform the above-described processing until it detects reverse conversion data that matches the reference.

  When the determination unit 15 detects reverse conversion data that matches the reference, the determination unit 15 sends the reverse conversion data to the transmission unit 16. The determination unit 15 repeats the above-described processing for a predetermined number of times, for example, all patterns of operation data, and detects reverse conversion data with the lowest PAPR, or reverse conversion with the PAPR equal to or lower than a predetermined value. It can be configured to detect data.

  The transmission unit 16 combines the inverse transform data to generate a baseband signal, generates a transmission signal from the baseband signal, and transmits the transmission signal to other devices via the transmission / reception switching unit 36 and the antenna 10. .

  When the FFT size is N, the subcarrier modulation signal d is expressed by the following equation (1). The subscript T in the formula indicates that the matrix is transposed. The same applies to the following description.

  When the number of division units is S, the subcarrier modulation signal d is expressed by the following equation (2). The number in the parenthesis of the subscript is a number for uniquely specifying the division unit. Each division unit is expressed by the following equation (3).

Let the insertion data be z. Assuming that the number of division units extracted by the calculation unit 13 is one, the calculation data exists as _S C ₁ = S as represented by the following equation (4). Since the arithmetic unit 13 extracts one or more arbitrary number of division units in order from the top of the plurality of division units, when the number of division units to be extracted is one, the following equation (4) is used. As shown, d ⁽¹⁾ is extracted, and insertion data z is inserted before and after d ⁽¹⁾ to generate operation data.

Also as shown by the following equation (5), the calculation unit 13 is the number of divided units two and to be extracted, the arithmetic data is present ways _S C _2.

Also as represented by the following formula (6), the calculation unit 13 is the number of divided units three and the extract, operation data is present ways _S C _3. (7) below as represented by formula, the calculation unit 13 is four and the number of the divided units to be extracted, the arithmetic data is present ways _S C _4. As represented by the following equation (8), when the number of division units extracted by the calculation unit 13 is S, there are _S C _S = 1 types of calculation data.

  That is, assuming that the number of division units to be extracted is k, the number of patterns of operation data is expressed by the following equation (9).

  The total number of patterns of calculation data is a value represented by the following equation (10).

By substituting x = 1 and n = S into the formula of the binomial theorem shown in the following equation (11), the following equation (12) is obtained. From the following formula (12), as shown by the following formula (13), the total number T = 2 ^S −1 of the number of patterns of the operation data is obtained. By repeatedly performing the above-described processing until the inversely transformed data based on 2 ^S −1 operation data is detected until the inversely transformed data satisfying the criteria of the PAPR of the baseband signal generated from the inversely transformed data is obtained, The PAPR of the band signal can be reduced.

  FIG. 3 is a diagram illustrating an example of arithmetic processing performed by the arithmetic unit according to the embodiment. FIG. 3A shows a plurality of subcarrier modulation signals. When the FFT size is 8, the subcarrier modulation signal d [1] is expressed by the following equation (14). When the number S of division units is 4, the subcarrier modulation signal d [1] is expressed by the following equation (15). Each division unit is expressed by the following equation (16).

  When the subsequent subcarrier modulation signals are d [2], d [3], and d [4], each subcarrier modulation signal is expressed by the following equation (17).

The calculation unit 13 extracts the division units d ⁽¹⁾ [1] and d ⁽²⁾ [1], and inserts the insertion data z into 2 after d ⁽¹⁾ [1], as shown in FIG. Calculation data is generated. When the determination unit 15 determines that the PAPR of the baseband signal based on the inverse conversion data corresponding to the calculation data matches the reference, the transmission unit 16 determines the baseband based on the inverse conversion data corresponding to the calculation data. A transmission signal generated from the signal is transmitted.

The computing unit 13 includes the division unit d ⁽³⁾ [1] and the division unit d ⁽⁴⁾ [1] that have not been transmitted in the subcarrier modulation signal d [1], and the subsequent subcarrier modulation signal d [2]. ] Is generated based on the elements of As shown in FIG. 3B, the calculation unit 13 extracts the division unit d ⁽³⁾ [1], the division unit d ⁽⁴⁾ [1], and the division unit d ⁽¹⁾ [2]. As shown in 3 (b), the insertion data z is inserted after the division unit d ⁽³⁾ [1] to generate operation data. In this way, calculation data is generated, and a transmission signal is generated from a baseband signal based on inversely converted data whose PAPR matches the reference, and transmitted.

  FIG. 4 is a flowchart illustrating an example of a transmission control operation performed by the communication device according to the embodiment. The modulation unit 11 modulates the input signal with a predetermined modulation method to generate a primary modulation signal, and the serial-parallel conversion unit 12 performs serial-parallel conversion on the primary modulation signal to generate a subcarrier modulation signal that is a parallel signal. (Step S110). The calculation unit 13 extracts one or more arbitrary number of division units from the top in order from the top among a plurality of division units composed of the same number of consecutive elements in the subcarrier modulation signal, and the arbitrary numbers before and after each of the extracted division units The insertion data composed of the complex number different from the value that can be taken by the elements of the subcarrier modulation signal and the same number as the number of elements of the division unit is inserted at the position of, so as to generate operation data whose number of elements matches the FFT size (step S120).

  The IFFT unit 14 performs IFFT on the operation data to generate inverse transform data (step S130). The determination unit 15 calculates the PAPR of the baseband signal based on the inverse transform data (Step S140). If it is determined that the PAPR does not meet the standard (step S150; N), the process returns to step S120, and the calculation unit 13 changes the number of division units to be extracted and / or the position where the insertion data is inserted, and creates a new one. Generate computed data.

  When it is determined that the PAPR matches the reference (step S150; Y), the transmission unit 16 generates a baseband signal by synthesizing the inverse transform data that matches the reference, and generates a transmission signal from the baseband signal. Then, a transmission signal is transmitted to other devices via the transmission / reception switching unit 36 and the antenna 10 (step S160).

  Processing on the receiving side will be described below. The receiving unit 35 receives a transmission signal via the antenna 10 and the transmission / reception switching unit 36, generates a baseband signal, performs serial-parallel conversion, and sends it to the FFT unit 34. The FFT unit 34 performs FFT of the baseband signal subjected to the serial / parallel conversion, generates converted data, and sends the converted data to the extracting unit 33. The extraction unit 33 sequentially extracts the division units except for the division units in which the number of elements having a value within a predetermined range is equal to or greater than a threshold value among the plurality of division units including the same number of consecutive elements in the conversion data. . Then, the extracted division unit is sent to the parallel-serial conversion unit 32.

  The division unit is the same as that used on the transmission side. The receiving side holds information about the division unit. When insertion data having a value of 0 is used on the transmission side, the extraction unit 33 sets the predetermined range to be equal to or less than a threshold value that is a value near 0. The predetermined range is determined by the insertion data used on the transmitting side, and the receiving side holds information about the predetermined range. For example, when a CAZAC sequence having an absolute value of (1/2) A is used as insertion data on the transmission side, a range near the absolute value of (1/2) A is set as a predetermined range. The threshold for the number of elements whose values are within a predetermined range can be arbitrarily determined according to the number of elements in the division unit.

A case will be described as an example where insertion data having a value of 0 is used on the transmission side. For example, when the extraction unit 33 receives the conversion data represented by the following equation (18), each element of z is equal to or less than the threshold value, so d ⁽¹⁾ [1] and d ⁽²⁾ [1] are extracted and The data is sent to the serial conversion unit 32.

  The parallel / serial conversion unit 32 performs parallel / serial conversion on the data received from the extraction unit 33 and sends the data to the demodulation unit 31. The demodulator 31 demodulates the data parallel-serial converted by the parallel-serial converter 32 using a predetermined modulation method and restores the input signal. The demodulator 31 may include a buffer, and may demodulate after accumulating data until the total number of elements matches the FFT size.

  On the receiving side, if the information about a predetermined range is held, the input signal can be restored. Therefore, on the transmitting side, an arbitrary number of division units can be extracted and insertion data can be inserted at an arbitrary position.

  FIG. 5 is a flowchart illustrating an example of a reception control operation performed by the communication device according to the embodiment. The receiving unit 35 receives a transmission signal via the antenna 10 and the transmission / reception switching unit 36, generates a baseband signal, and performs serial-parallel conversion (step S210). The FFT unit 34 performs FFT of the baseband signal that has been subjected to serial-parallel conversion, and generates converted data (step S220). The extraction unit 33 sequentially extracts the division units except for the division units in which the number of elements having a value within a predetermined range is equal to or greater than a threshold value among the plurality of division units including the same number of consecutive elements in the conversion data. (Step S230). The parallel-serial conversion unit 32 performs parallel-serial conversion on the data received from the extraction unit 33. The demodulation unit 31 demodulates the data parallel-serial converted by the parallel-serial conversion unit 32 using a predetermined modulation method, and restores the input signal. (Step S240).

  As described above, according to communication apparatus 1 according to the embodiment of the present invention, it is possible to reduce PAPR by performing an operation of extracting a division unit and inserting insertion data in an OFDM communication system. Become. Further, as will be described later, the degree of PAPR reduction can be controlled.

(Concrete example)
Next, effects of the invention according to the embodiment will be described by simulation. Using a random signal as an input signal, a simulation was performed for generating the baseband signal and repeatedly calculating the PAPR for the related art and the invention according to the embodiment. The modulation system is QPSK, the FFT size is 2048, and the PAPR CCDF (Complementary Cumulative Distribution Function) of the invention according to the embodiment, that is, the characteristics of the occurrence probability of PAPR are compared. The prior art is a method of generating a baseband signal by generating a subcarrier modulation signal from a signal obtained by modulating an input signal by a predetermined modulation method without performing the above-described arithmetic processing, and performing IFFT.

FIG. 6 is a diagram illustrating the PAPR CCDF characteristics of the baseband signal in the communication device according to the embodiment. The horizontal axis is PAPR (unit: dB), and the vertical axis is PAPR CCDF. In the communication device 1 according to the embodiment, the number of division units is four. When the division unit is 4, the number of patterns of calculation data is 15 from the above equation (13). In the communication device 1 according to the embodiment, assuming that the number of division units extracted by the calculation unit 13 is not limited to type 1, the number of patterns of calculation data in type 1 is fifteen. Further, when the a type 2 if you want to limit to extract at least two or more divided units in the calculating portion 13, the number of patterns of operation data in Type _{2, 4 C 2 + 4 C 3} + 4 C 4 = 11 pieces in is there. Further, when the a type 3 if the limit to extract at least three or more divided units in the calculating portion 13, the number of patterns of operation data in Type 3 is a _{4 C 3 + 4 C 4 =} 5 pieces.

  The CCDF characteristics of the prior art PAPR are shown by a thin solid line graph. In the communication device 1 according to the embodiment, the CCDF characteristic of the Type 1 PAPR is a thick solid line graph, the CCDF characteristic of the Type 2 PAPR is a dashed line graph, and the CCDF characteristic of the Type 3 PAPR is two points. It is a graph of a chain line. In any case, it can be seen that the PAPR of the invention according to the embodiment is reduced as compared with the prior art. It can also be seen that the PAPR is further reduced as the number of patterns of operation data increases. When the number of division units is increased, the number of patterns of operation data increases. Therefore, the PAPR can be further reduced by increasing the number of division units.

  The transmission rates when PAPR is minimized were 55.4% for Type 1, 69.5% for Type 2, and 83.1% for Type 3.

  In addition, the simulation was performed using the same signal whose values are all 0, for example, the phase of each element of the subcarrier modulation signal matches the input signal. The PAPR of the prior art when the same signal is used as the input signal is 33.1 dB. The minimum value of PAPR in Type 1 is 27.1 dB, and the transmission rate in that case is 25%. The minimum value of PAPR in type 2 is 30.1 dB, and the transmission rate in that case is 50%. The minimum value of PAPR in Type 3 is 31.9 dB, and the transmission rate in that case is 75%. In the case of the same signal, the PAPR is remarkably reduced by lowering the transmission rate.

  Since PAPR and the transmission rate are in a trade-off relationship, for example, in order to keep the rate of decrease in the transmission rate constant, the calculation unit 13 extracts more than half of the plurality of division units. Also good.

  In the embodiment, the operation of extracting the division unit and inserting the insertion data does not affect the BER (Bit Error Rate).

  According to the above-described simulation, in the invention according to the embodiment, the division unit is extracted and the operation for inserting the insertion data is performed to reduce the PAPR, so that the number of division units, the number of division units to be extracted, and the insertion It was found that the degree of PAPR reduction can be controlled by changing any of the positions.

  The embodiment of the present invention is not limited to the above-described embodiment. The modulation method of the modulation unit 11 is not limited to QPSK, and PSK (Phase Shift Keying) other than QPSK, Quadrature Amplitude Modulation (QAM), or the like can be used. The order of the modulation unit 11 and the serial / parallel conversion unit 12 may be changed, the input signal may be serial / parallel converted and assigned to the subcarrier signal, and each data of the parallel signal may be modulated by a predetermined modulation method. In that case, the receiving side performs demodulation processing by changing the order of the demodulator 31 and the parallel-serial converter 32. The IFFT unit 14 may be configured to perform IDFT instead of IFFT, and the FFT unit 34 may be configured to perform DFT instead of FFT.

1 communication equipment
10 Antenna
11 Modulator
12 Series-parallel converter
13 Calculation unit
14 IFFT section
15 judgment part
16 Transmitter
20 controller
21 CPU
22 I / O
23 RAM
24 ROM
31 Demodulator
32 Parallel to serial converter
33 Extractor
34 FFT section
35 Receiver
36 Transmission / reception switching unit

Claims (2)

A communication device that communicates with other devices by orthogonal frequency division multiplex communication wireless communication,
Receiving means for generating a base band signal by receiving the transmission signal,
FFT means for performing serial-parallel conversion on the baseband signal and performing fast Fourier transform to generate converted data ;
Using the predetermined range determined by the insertion data used for generation of the transmission signal and the threshold value determined according to the division unit used for generation of the transmission signal , the same number in the converted data An extracting means for sequentially extracting division units, excluding division units in which the number of elements having a value within the predetermined range is equal to or greater than the threshold value among a plurality of division units composed of continuous elements;
Demodulating means for demodulating the division unit extracted by the extracting means with a predetermined modulation method ;
A communication device comprising: A communication method performed by a communication device that communicates with other devices by wireless communication of an orthogonal frequency division multiplex communication method,
  A reception step of receiving a transmission signal and generating a baseband signal;
  An FFT step of performing serial-parallel conversion on the baseband signal and performing fast Fourier transform to generate converted data;
  Using the predetermined range determined by the insertion data used for generation of the transmission signal and the threshold value determined according to the division unit used for generation of the transmission signal, the same number in the converted data An extraction step for sequentially extracting division units, excluding division units in which the number of elements having a value within the predetermined range is greater than or equal to the threshold value among a plurality of division units composed of continuous elements;
  A demodulation step of demodulating the division unit extracted in the extraction step by a predetermined modulation method;
  A communication method comprising:

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