JP2001024617A - Signal processing method, modulator, demodulator and communications equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent increase in out-of-band leakage power and the deterioration of transmission quality by distributing a baseband signal into a plurality of signals, then successively executing normal and orthogonal transformation and inverse Fourier transformation and executing the serial conversion of a signal after the inverse Fourier transformation. SOLUTION: An OFDM modulator inputs the baseband signal and a serial/parallel converter 10 distributes the input signal by N (N is an integer of 2 or larger. N- distributed signals are inputted to a normal orthogonal transformer 12 as a normal orthogonal transformer input vector and transformer into vectors obtained by orthogonal transformation between the elements of the vectors. The transformed output vectors are transformed into the signals through orthogonal transformation of sub-carriers by inverse Fourier transforming unit 14. The parallel/serial converter 16 executes the serial conversion of the N-distribution signals outputted from the inverse Fourier transformer 14. In a demodulator, a detection signal digitized by a receiving circuit is distributed by N. Then the reverse transformation of a signal processing for the orthogonal transformation of each sub-carrier and the reverse transformation of the signal processing for normal and orthogonal transformation are successively executed in the order and the N-distributed signals are transformed into serial ones.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a peak-to-average power ratio in multi-carrier wireless communication.
The present invention relates to a signal processing method for compressing (r Ratio: PAPR), a modulator for realizing the compression, a signal processing method for performing an inverse conversion of the signal processing, and a demodulator for realizing the same. In particular, Orthogonal Frequency Division Multiplex
The present invention relates to a signal processing method, a modulator, and a demodulator related to PAPR compression in an ltiplexing (OFDM) system.

[0002]

2. Description of the Related Art A multicarrier radio communication method is a radio communication method in which a narrow band radio signal is multiplexed at different carrier frequencies. The feature of the multi-carrier wireless communication method is that the conventional wireless circuit technology can be applied, and the transmission capacity can be increased or decreased as necessary by increasing or decreasing the number of carriers used. This multi-carrier wireless communication method is a digital MC in Japan.
It has been put to practical use by the A method.

[0003] OFDM has been proposed as a special case of a multicarrier radio communication method. In OFDM, by setting the intervals of carrier frequencies to the intervals of the Nyquist constant theorem, the orthogonality between each carrier is maintained,
Each modulated waveband castle can be overlapped. One of the features of OFDM is generation of a multicarrier signal by digital signal processing. In order to maintain the orthogonality between the respective carriers, an inverse Fourier transformer is used on the transmission side, and a Fourier transformer is used on the reception side. As a result, a plurality of modulated waves are collectively collected in the baseband OFDM.
Can be converted to waves. OFDM with such features,
Applications to various wireless communications such as digital television, high-speed wireless local area networks, and mobile communications are being studied.

[0004] These multi-carrier radio communication methods have a number of features, but there are problems such as an increase in out-of-band leakage power and an increase in intersymbol interference due to the intermodulation distortion of the transmitting device by multiplexing a plurality of carriers. The intermodulation distortion caused by the transmission device occurs in a frequency converter, a transmission power amplifier, and the like. In particular, the influence of the nonlinearity of the transmission power amplifier is large. In general, when a plurality of carriers are simultaneously amplified by a transmission power amplifier, the above-described intermodulation distortion occurs unless output back-off is performed only by PAPR. Therefore, the multi-carrier transmission power amplifier needs to have a sufficiently high saturation output. In general, a transmission power amplifier has a large-scale and high-priced device according to a saturation output.

In the past, in fixed microwave radio communications,
Four multi 16 QAM and four multi 256 QAM systems have been put to practical use. In this transmission power amplifier, generally, individually amplified signals are combined by a signal multiplexer having a line of １ ／ wavelength. By individually amplifying a plurality of carriers in this way, the problem of PAPR increase caused by multiplexing a plurality of carriers has been avoided.

As a method for compressing PAPR in a multicarrier, the following method is known in the prior art. That is, a method of setting an initial phase of a carrier wave (Shoichi Narahashi, Toshio Nojima, "Initial phase setting method for reducing peak-to-average power ratio (PAPR) of multi-tone signal",
IEICE Transactions B-II, Vol. J 78-BI
I, No. 11, pp. 663-671, 1995
January), a method using a specific signal pattern that does not cause a peak (Table 6), a method using an error correction encoder (TAWilkinson, and AEJones Minimization)
of the peak to mean envelope power ratio of multi
carrier transmission schemes by block coding "inPr
oc. 45th IEEE Vechi. Technol. Conf., pp. 825-829, 19
95), a method of multiplexing signals that compress peaks (Shigeru Tomisato,
Hiroshi Suzuki, "Envelope Smoothing Parallel Modulation and Demodulation", IEICE Technical Committee on Wireless Communication Systems, RCS95-7
7, September 1995), and a method using an orthonormal transformer (Japanese Patent Application No. 08-271063). In particular, OFDM
As a method of PAPR compression in, a method of clipping the multiplexed signal waveform (X.Li, and LJCimni, Jr., "Ef
fects of Cliping and Filtering on the Performance
of OFDM ", inProc. 47th IEEE Vechi. Technol. Conf.,
pp.1634-1638, 1997), A method to control transmission power according to peak power (Yoichi Matsumoto, Nobuaki Mochizuki, Masahiro Umehira, "Study of peak power reduction method for broadband microcell OFDM system", IEICE Technical Committee on Radio Communication RCS97
-143, October 1997).

[0007]

A condition required for a PAPR compression method applicable to multi-carrier wireless communication, particularly OFDM, is that the out-of-band leakage power does not increase and the transmission quality does not deteriorate. In comparison with this condition, the method of clipping the multiplexed signal waveform causes an increase in out-of-band leakage power due to clipping. Also, the method of performing transmission output control according to peak power always has a problem in maintaining line quality.

Further, it is difficult to apply an initial phase setting method to a modulated wave whose phase constantly changes, and in a method using an error correction code and a method for multiplexing a signal for compressing peak power, a transmission band is limited. Expanding. As described above, the conventional technique of compressing the OFDM PAPR has problems such as an increase in out-of-band distortion and difficulty in maintaining line quality.

[0009] The present invention has been made in view of the above points, and does not increase the out-of-band leakage power, and furthermore, the PA in multi-carrier wireless communication without deteriorating the transmission quality.
The present invention relates to a signal processing method for performing PR compression, a modulator for realizing the same, a signal processing method for performing an inverse conversion of the above signal processing, and a demodulator for realizing the same.

[0010]

To solve the above problems, the present invention is configured as follows. A first signal processing method according to the present invention distributes a baseband signal into a plurality of signals, orthonormally transforms the distributed signal, performs an inverse Fourier transform on the orthonormally transformed signal, and performs an inverse Fourier transform on the signal. Is to serialize the obtained signal.

According to the present invention, the orthogonal correlation is applied to the baseband signal to reduce the cross-correlation coefficient between the input signals, and the signal is subjected to the inverse Fourier transform, so that the transmission band is expanded in OFDM. Without this, and without increasing out-of-band leakage power, constant PAPR compression of the transmission output becomes possible. The second signal processing method of the present invention distributes the detected signal into a plurality of signals, Fourier-transforms the distributed signals, performs orthonormal inverse transform on the Fourier-transformed signals, and performs the orthonormal inverse transform. Serialized signals.

According to the present invention, it is possible to restore a transmission signal that has been subjected to orthonormal transform by the first signal processing method. Further, the modulator of the present invention is a means for distributing the baseband signal to a plurality of signals, a means for orthonormally transforming the distributed signal, a means for performing an inverse Fourier transform on the orthonormally transformed signal, Means for serializing the inverse Fourier transformed signal.

The demodulator according to the present invention further comprises means for distributing the detection signal into a plurality of signals, means for performing a Fourier transform on the divided signal, and means for performing an orthonormal inverse transform on the Fourier-transformed signal. Means for serializing the orthonormal inverse transformed signal. Further, by providing the above modulator and demodulator, a communication device for OFDM that performs constant PAPR compression of transmission output without expanding a transmission band castle and without increasing out-of-band leakage power is provided. Can be provided.

Further, the present invention can be implemented by various computers (including a digital signal processing processor) and programmable devices by using a computer-readable recording medium on which a program for executing the procedure of the first or second signal processing method is recorded. Can be realized. Next, the operation of the above invention will be further described.

The reason for generating peak power in OFDM is due to the inverse Fourier transformer used to maintain orthogonality between carriers in OFDM. Inverse Fourier transformer F
^H is usually represented by a matrix in equation (1). Where H
Is the conjugate of the matrix, and ω is the angular velocity shown in equation (2).

[0016]

(Equation 1)

[0017]

(Equation 2)

As shown in equation (1), the first row is all 1, and the inverse Fourier transformer input signal is in-phase synthesized. If the inverse Fourier transformer input signal vector is not orthogonalized, the matrix of equation (1) produces peak power. Therefore, by orthogonalizing the inverse Fourier transformer input vector, at least the combined power obtained by the in-phase combining in the first row of Expression (1) can be made the average power. As a method for orthogonalizing the input vector, the present invention uses the orthonormal transform as described above.

In the embodiment disclosed in the conventional method of compressing peak power by orthonormal transform (Japanese Patent Application No. 08-271063), one multiplexer having a different frequency is used for the output of the orthonormal transformer. I have. On the other hand, in the present invention, the output of the orthonormal transformer is input to the inverse Fourier transformer, and the matrix operation according to equation (1) is performed. FIG.
1 shows a configuration in which the inverse Fourier transformer is represented as a signal multiplexer. As shown in FIG. 1, each element of the input vector undergoes a phase rotation according to equation (1) by each phase rotator. Therefore, if N (N is an integer of 2 or more) inverse Fourier transformers are input, N signal multiplexers 1 to N having different phase rotation amounts become inverse Fourier transformers in the orthonormal transformer. As described above, having a plurality of signal multiplexers is different from the prior art.
Can reduce the peak power generated in

[0020]

FIG. 2 shows an embodiment of an OFDM modulator according to the present invention. The OFDM modulator shown in FIG. 2 includes a serial-to-parallel converter 10, an orthonormal transformer 12, an inverse Fourier transformer 14, and a parallel-serial converter 16. FIG. 3 is a flowchart showing the operation of the OFDM modulator according to the present invention. OF according to the present invention with reference to FIGS.
The operation of the DM modulator will be described.

First, a baseband signal is input (step 1), and the input signal is converted to N by a serial / parallel converter 10.
(N is an integer of 2 or more) distribution (step 2). The N-divided signal is input to the orthonormal transformer 12 as an orthonormal transformer input vector, and the input vector is converted by the orthonormal transformer into a vector obtained by orthogonalizing each element of the vector (step 3). . The converted output vector is converted by the inverse Fourier transformer 14 into a signal in which each subcarrier is orthogonalized (step 4). The parallel-serial converter 16 serializes the N-divided signal output from the inverse Fourier transformer (step 5). By placing the orthonormal transformer 12 at the input of the inverse Fourier transformer, as in the modulator shown in FIG. 2, the input signal of the inverse Fourier transformer can be converted into an uncorrelated signal sequence.

The modulator shown in FIG. 2 can be constituted by individual semiconductor integrated circuits. For example, a digital signal processor, an FPGA, and the like. At this time, the programs stored in the digital signal processor and the FPGA execute processing according to the procedure of the signal processing flowchart of the OFDM modulator shown in FIG. As described above, the OFDM modulator of the present invention includes a digital signal processor in which a signal processing flow mainly including matrix operation is programmed,
It can be configured by a programmable device such as an FPGA.

FIG. 4 is a diagram showing an embodiment of the OFDM demodulator according to the present invention. The OFDM demodulator shown in FIG. 4 includes a serial-to-parallel converter 20, a Fourier transformer 22, an orthonormal inverse converter 24, and a parallel-serial converter 26. FIG. 5 is a flowchart showing the operation of the OFDM demodulator according to the present invention. Next, the operation of the OFDM demodulator according to the present invention will be described with reference to FIGS.

The detector output of the receiving circuit is digitized by an analog / digital converter. The digitized detection signal is input to the serial-to-parallel converter 20 (step 11), and is divided into N signals by the serial-to-parallel converter 20 (step 12). The N-divided signal is subjected to an inverse transform of the signal processing of each subcarrier orthogonalization performed on the transmission side by the Fourier transformer 22 (step 13). The output signal from the Fourier transformer 22 is subjected to the inverse transformation of the signal processing by the orthonormal transformer performed on the transmission side by the orthonormal inverse transformer 24 (step 14). The output signal from the orthonormal inverse converter 24 converts the N-divided signal into a serial signal by the parallel / serial converter 26 (step 15). Thereby, the original transmission signal sequence is restored. That is, the configuration shown in FIG. 4 is a configuration for performing an inverse conversion process of the signal process in the modulation of FIG.

The OFDM demodulator shown in FIG. 4 can be constituted by individual semiconductor integrated circuits. For example, a digital signal processor, an FPGA, or the like. At this time, the programs stored in the digital signal processor and the FPGA execute processing according to the procedure of the signal processing flowchart of the OFDM demodulator shown in FIG. in this way,
The OFDM demodulator of the present invention can be configured by a programmable device such as a digital signal processor or an FPGA that operates according to a program for executing a procedure of a signal processing flow mainly including a matrix operation.

FIG. 6 shows the effect of the present invention. The vertical axis in FIG. 6 shows the peak-to-average power ratio (PAPR), and the horizontal axis shows the number of OFDM subcarriers. The PAPR according to the conventional OFDM is shown by a solid line, and the PAPR according to the present invention is shown by a dotted line. As shown in the figure, the PAPR of the conventional OFDM increases as the number of subcarriers increases. PAPR at 64 subcarriers is approximately 18 dB. In contrast, the PAPR according to the present invention is approximately 10 dB. As described above, according to the present invention, the PAPR is compressed by about 8 dB as compared with the related art. Further, the present invention does not increase PAPR noticeably when the number of subcarriers is 30 or more. Therefore, it is understood that the effect of applying the present invention to OFDM having many subcarriers is great.

FIG. 7 shows a configuration example of a wireless device according to the present invention. 7 includes a transmitter 30, a receiver 32, a controller 34, a frequency synthesizer 36, and a duplexer 38.
And an antenna 40. Further, for example, a PDA terminal 42 is connected to the wireless device according to the present invention. The transmitter 30 includes a serial / parallel converter 44, a plurality of encoders 46,
An orthonormal transformer 48, an inverse Fourier transformer 50, a parallel-serial converter 52, an LPF 54, a quadrature modulator 56,
It comprises a frequency converter 58 and a transmission power amplifier 60.

The receiver 32 includes a reception amplifier 62, a frequency converter 64, an LPF 66, a detector 68, a parallel-serial converter 70, a Fourier transformer 72, an orthonormal inverse transformer 74, And a serial-to-parallel converter 78. The operation of the radio according to the present invention is as follows. The data input from the PDA terminal 42 is input to the transmitter 30. In the transmitter 30, the input data is converted by the serial / parallel converter 44 into parallel data. The converted data is subjected to an encoding process by an encoder 46. This encoding process is a process of mapping digital data to signal points such as QPSK. Further, error correction processing such as FEC may be performed. The encoded signal is
It is input to the orthonormal transformer 48 and performs an orthogonal transformation process.
The output signal from the orthonormal transformer 48 is subjected to orthogonal transform for OFDM by the inverse Fourier transformer 50. The output signal from the inverse Fourier transformer 50 is output from the parallel-to-serial converter 5.
2 converts the parallel signal into a serial signal. The output signal from the parallel-to-serial converter 52 is subjected to band limiting processing by the LPF 54, and is subjected to quadrature modulation by the quadrature modulator 56.
The frequency converter 58 converts the frequency from the baseband to the transmission frequency band, amplifies the power in the transmission power amplifier 60, and transmits the signal from the antenna 40 via the duplexer 38.

The signal received by the antenna 40 is
The signal is input to the receiving amplifier 62 via the duplexer 38. The output signal from the receiving amplifier 62 is frequency-converted by the frequency converter 64 from the receiving frequency band to the baseband band. L
After the band is limited by the PF 66, the received signal is input to the detector 68 and detected. The detected signal is parallelized by the parallel / serial converter 70. The output signal from the serial-parallel converter 70 is OF
DM demodulation signal processing is performed. The output signal from the Fourier transformer 72 is subjected to an inverse transform of the orthogonal transform process performed on the transmission side by the orthonormal inverse transformer 74. An output from the orthonormal inverse transformer 74 is input to a decision unit 76. The determiner 76 performs a decoding process of the encoder 46 performed on the transmission side. The output signal from the decision unit 76 is output to a serial / parallel converter 78
, And data is input to the PDA 42 or the like.

As described above, the wireless device to which the present invention is applied
It can be configured as shown in FIG. OFDM modulator (transmitter 3
0) and the OFDM demodulator (receiver 32) can be constituted by a digital signal processor or the like as described above. A conventional radio circuit can be used as it is for a part for generating a signal in a transmission frequency band from a baseband signal and a part for generating a signal in a baseband band from a reception frequency band. Therefore, the wireless device according to the present invention can be easily configured.

FIG. 8 is a diagram showing an embodiment of the communication apparatus of the present invention. FIG. 8 is a circuit diagram showing a configuration in which the duplexer 38 of FIG.
0 and an optical / electrical converter 82, an antenna 40 as an optical fiber 84, and a duplexer 86. The internal configurations of the transmitter and the receiver are the same as those in FIG.
As described above, the communication apparatus using the OFDM modulator (transmitter) and the OFDM demodulator (receiver) according to the present invention is not limited to application to wireless transmission, but can also be applied to optical transmission. Also,
It goes without saying that the OFDM modulator and the OFDM demodulator of the present invention can be applied to other communication methods, and have versatility in the communication method. In the application example of the present invention to the optical transmission shown in FIG. 8, the peak value of the signal transmitted in the optical fiber can be reduced.

[0032]

As described above, the present invention has the following effects. According to the present invention, the baseband signal is subjected to orthonormal transform, and the cross-correlation coefficient between the input signals is reduced. Since the signal is subjected to the inverse Fourier transform, it is possible to perform constant PAPR compression of the transmission output without expanding the transmission band in OFDM and without increasing the out-of-band leakage power. Further, there is no dependency on the transmission data sequence, and the versatility is high.

In the present invention, since the orthonormal transformer and the orthonormal inverse transformer can be realized by signal processing by matrix operation, the Fourier transformer and the inverse Fourier transformer can be integrated into a program. Therefore, the signal processing of the present invention can be realized by various computers (including a digital signal processor) and programmable devices.

Further, by providing the modulator and the demodulator of the present invention, a PA having a constant transmission output can be obtained without expanding the transmission band and without increasing out-of-band leakage power.
An OFDM communication device that performs PR compression can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration when an inverse Fourier transformer is represented as a signal multiplexer.

FIG. 2 is a diagram illustrating an OFDM modulator according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating an operation of the OFDM modulator illustrated in FIG. 2;

FIG. 4 is a diagram illustrating an OFDM demodulator according to an embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of the OFDM demodulator shown in FIG.

FIG. 6 is a diagram showing a relationship between a peak-to-average power ratio and the number of carriers.

FIG. 7 is a diagram showing a configuration example of a wireless device according to the present invention.

FIG. 8 is a diagram showing a configuration example of a communication device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Serial-parallel converter 12 Orthonormal converter 14 Inverse Fourier converter 16 Parallel-serial converter 20 Serial-parallel converter 22 Fourier converter 24 Orthogonal inverse converter 26 Parallel-serial converter 30 Transmitter 32 Receiver 34 Controller 36 Frequency synthesizer 36 38 duplexer 40 antenna 42 PDA terminal 44 serial-parallel converter 46 encoder 48 orthonormal transformer 50 inverse Fourier transformer 52 parallel-serial converter 54 LPF 56 quadrature modulator 58 frequency converter 60 transmission power amplifier 62 reception Amplifier 64 frequency converter 66 LPF 68 detector 70 parallel-serial converter 72 Fourier converter 74 orthonormal inverse converter 76 decision unit 78 serial-parallel converter 80 electric-optical converter 82 optical-electric converter 84 optical fiber 86 Duplexer

Continuation of the front page (72) Inventor Toshio Nojima 2-10-1 Toranomon, Minato-ku, Tokyo NTT Mobile Communications Network Co., Ltd. F-term (reference) 5K022 DD00 DD01 DD13 DD19 DD23 DD33

Claims (9)

[Claims] 1. A method of distributing a baseband signal into a plurality of signals, orthonormally transforming the distributed signal, inverse Fourier transforming the orthonormally transformed signal, and serializing the inverse Fourier transformed signal. A signal processing method. 2. Distributing a detection signal into a plurality of signals, performing a Fourier transform on the distributed signal, performing an orthonormal inverse transform on the Fourier transformed signal, and serializing the orthonormal inverse transform signal. A signal processing method characterized by the above-mentioned. 3. A means for distributing a baseband signal into a plurality of signals; a means for orthonormally transforming the distributed signal; a means for performing an inverse Fourier transform on the orthonormally transformed signal; Means for serializing the converted signal. Means for dividing the detected signal into a plurality of signals; means for performing a Fourier transform on the divided signal; means for performing an orthonormal inverse transform on the Fourier-transformed signal; And means for serializing the signal. 5. A communication device having a modulator and a demodulator, wherein the modulator divides a baseband signal into a plurality of signals, performs orthonormal transform on the distributed signals, and Means for performing an inverse Fourier transform of the orthonormally transformed signal, and means for serializing the inverse Fourier transformed signal, wherein the demodulator divides the detection signal into a plurality of signals; and A communication device, comprising: means for performing a Fourier transform on the converted signal; means for performing an orthonormal inverse transform of the Fourier-transformed signal; and means for serializing the orthonormal inverse transform signal. 6. The communication device according to claim 5, wherein the communication device further includes a wireless transmission circuit. 7. The communication device according to claim 5, wherein the communication device further includes an optical transmission circuit. 8. A computer-readable recording medium having recorded thereon a signal processing program, the program comprising: a step of dividing a baseband signal into a plurality of signals; and a step of orthonormally transforming the divided signals. A computer-readable recording medium that causes a computer to execute a procedure of performing an inverse Fourier transform on the orthonormally transformed signal and a procedure of serializing the inverse Fourier transformed signal. 9. A computer-readable recording medium having recorded thereon a signal processing program, the program comprising: a step of distributing a detection signal to a plurality of signals; a step of performing a Fourier transform on the distributed signal; A non-transitory computer-readable recording medium that causes a computer to execute a procedure of performing an orthonormal inverse transform of a Fourier-transformed signal and a procedure of serializing the orthonormal inverse transform signal.