WO2002056516A1

WO2002056516A1 - Communication device and communication system using it

Info

Publication number: WO2002056516A1
Application number: PCT/JP2001/000065
Authority: WO
Inventors: Yuji Ichinose; Setsuo Arita; Izumi Yamada; Takuya Sugawara; Fumiyasu Okido
Original assignee: Hitachi, Ltd.
Priority date: 2001-01-10
Filing date: 2001-01-10
Publication date: 2002-07-18
Also published as: JP3800176B2; JPWO2002056516A1

Abstract

A communication device comprises a compressor for receiving a modulation signal, obtained by combining a plurality of carriers modulated with transmitted data, and amplifying the modulation signal with a first amplification factor for a signal lower than a preset threshold level and a second amplification factor for a signal exceeding a threshold level lower than that for the first amplification factor. Since a signal exceeding the threshold level is compressed more than a signal lower than the threshold level by setting the amplification factor for the signal exceeding the threshold level to a value lower than the amplification factor for the signal lower than the threshold level, the peak power of the modulation signal is lowered. Furthermore, the peak ratio is reduced because lowering of the average power is limited as compared with lowering of the peak power.

Description

Specification

Communication device and communication technology using the same

The present invention relates to a communication device that performs communication using a multicarrier modulation method such as an orthogonal frequency division multiplexing method and a communication system using the same. Background art

In communication technology using a carrier wave (carrier), a method of transmitting data by modulating the amplitude, phase or frequency of one carrier is called a single carrier modulation method. On the other hand, a method of combining a plurality of carriers whose amplitudes or phases are modulated into a transmission signal is called a multi-carrier modulation system. When the transmission speed is the same, the multicarrier modulation method has the characteristic that the transmission time is several times longer than that of the carrier, and is less susceptible to the reflected waves generated in the communication channel.

The orthogonal frequency division multiplexing (hereinafter referred to as OFDM) method is one of the multi-carrier schemes, and has a high frequency utilization efficiency because the carrier frequency interval can be minimized. For this reason, it has been adopted as an XDSL (Digital Subscriber Line) modulation method using power line carrier, digital television broadcasting, radio and telephone lines.

In the multi-carrier modulation method as well as the 0 FDM method, since a plurality of carriers are combined into a transmission signal, the transmission signal has a relatively high peak amplitude with respect to the effective value of the amplitude of the transmission signal. In other words, the ratio of peak power to average firing power (hereinafter, peak power / average power is referred to as peak 'ratio) is high. In general, a communication device has a regulation value for transmission output. If the peak ratio is high, the average power cannot be increased. The transmission characteristics of a communication device are determined by the signal-to-noise ratio (SZN) of the transmission path including the communication device. Is difficult, and as a result, transmission errors increase. In addition, since the peak ratio is high, an amplifier having a large maximum power must be used as a transmission amplifier, which increases the cost of the transmission amplifier. Furthermore, the dynamic range of a digital processing circuit used for signal processing for transmission and reception must be increased.

Conventional techniques for reducing the peak ratio include JP-A-8-97797, JP-A-10-178411, JP-A-11-163826, and the like. A complicated operation for array conversion is required to reduce the peak power generated by the array of transmission data, and the effective transmission speed is reduced by adding redundant bits to restrict the data array. There is a problem of doing. Disclosure of the invention

An object of the present invention is to provide a communication device capable of reducing a peak ratio without lowering a transmission speed when performing communication using a multicarrier modulation method, and a communication system using the same.

A feature of the present invention that achieves the above object is that a modulated signal obtained by synthesizing a plurality of carriers modulated by transmission data is input, and a first amplification factor for a signal that is equal to or less than a preset threshold is obtained. A compressor that amplifies the modulated signal with a second amplification factor for a signal that exceeds the threshold and has a value smaller than the first amplification factor, and a transmission obtained based on an output signal of the compressor. Transmission means for transmitting a communication signal. 闞 By making the amplification factor of the signal exceeding the threshold smaller than the amplification factor of the signal below the threshold, the signal above the threshold is compressed as compared to the signal below the threshold, and the peak power of the modulated signal decreases. In addition, since the decrease in the average power is suppressed to be smaller than the decrease in the peak power, the peak ratio is reduced. Further, since there is no need to add a redundant bit for restricting the data arrangement unlike the related art, the transmission speed is not reduced. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a configuration diagram of a communication system according to a preferred embodiment of the present invention, FIG. 2 is a characteristic diagram of amplification factors set in a compressor 104 and an expander 144, FIG. Fig. 4 shows the input signal (source signal) and output signal (compressed signal) of the compressor 104, and the peak ratio between the source signal and the compressed signal. Fig. 4 shows the case without expansion and the case with expansion. FIG. 5 is a diagram showing the relationship between the input amplitude and the frequency of appearance, and FIG. 6 is a diagram showing the relationship between the input amplitude and the cumulative frequency in the communication system according to another embodiment of the present invention. Configuration 囪. Best mode for applying the invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Example 1)

FIG. 1 shows a configuration of a communication system according to a preferred embodiment of the present invention. As shown in FIG. 1, in the communication system of the present embodiment, a plurality of communication devices la, lb, 1 c... Are connected via a power line 2 and each communication device 1 a, 1 b, 1 c. Transmit and receive data to and from each other by superimposing signals on power line 2. That is, the communication device of the present embodiment is a power line carrier device that transmits and receives data by power line carrier. Communication device 1a, lb, lc ... have the same device configuration, and the operation is the same. Hereinafter, a case where data is transmitted from the communication device 1a to the communication device 1b will be described. First, transmission data to be transmitted to the communication device 1b is input to the OFDM modulator 10 of the communication device 1a. In the OFDM modulator 10, the input transmission data is input to the mapping 101, and the mapping 101 converts the input transmission data from the 0, 1 pattern to a complex number data. This complex number data becomes the amplitude data of each carrier. The obtained complex number data is input to an inverse fast Fourier transformer (IFFT) 102 and is subjected to inverse high-speed Fourier transform to generate a modulated signal in the time domain. In order to combine multiple carriers with different frequencies, a reverse fog velocity Fourier transform is adopted. A complex signal obtained by inverse fast Fourier transform by IFFT 102 is input to quadrature modulator 103. The quadrature modulator 103 converts the input complex number signal into a real number signal and outputs it. Conventionally, the signal obtained by the quadrature modulator 103 was converted into an analog signal, and then transmitted by being multiplexed on the power line 2.In this embodiment, the signal is converted before being converted into an analog signal. Perform compression.

The real number signal output from the quadrature modulation 103 is input to a compressor 104. The compressor 104 amplifies (compresses) the input signal at a preset amplification factor. The second (a) shows the amplification factor in the compressor 104, that is, the amplitude of the input signal (hereinafter referred to as input amplitude) and the amplitude of the output signal corresponding thereto (hereinafter referred to as output amplitude). As shown in Fig. 2 (a), the compressor 104 sets the amplification factor to 1 when the input amplitude is in the range of 0 to 0.03, and increases the amplification factor when the input amplitude is in the range of 0.03 or more. 1 8 (0.125). That is, the amplification factor is changed with the input amplitude 0.0 3 as the threshold value. The method of determining the threshold and the amplification factor will be described later. Fig. 3 (b) shows the signal after compression when the signal shown in Fig. 3 (a) is input to the compressor 104. When a multi-carrier modulation scheme such as OFDM modulation is used, the input signal (called the source signal) of the compressor 104 is superimposed by multiple carriers as shown in Fig. 3 (a). The waveform has a point with a large amplitude due to a pulse-like amplitude change. When the source signal shown in Fig. 3 (a) is compressed by the compressor 104, as shown in Fig. 3 (b), the amplitude of 0.03 or more is greatly compressed, and the peak that protrudes becomes Disappears. As described above, in the compressor 104 of the present embodiment, the peak power can be reduced by compressing the amplitude to 1/8 in the range equal to or more than the threshold value of 0.03, that is, compressing a large amplitude. Since the amplitude below the threshold of 0.03 is not compressed with the amplification factor set to 1, the average power hardly decreases. Therefore, the peak ratio, which is the ratio between the peak power and the average power, is greatly reduced. Figure 3 (c) shows the results obtained by simulation of the relationship between the peak ratio of the source signal, the peak ratio of the compressed signal, and the number of trials when random data is given as the transmission data. As shown in the figure, the peak ratio of the source signal is close to 20 at the maximum, while the peak ratio of the compressed signal is reduced to 5 or less. As described above, according to the present embodiment, the maximum value of the peak ratio can be reduced to about one-fourth as compared with the case where no signal compression is performed. It can be reduced to about a quarter. Conversely, if the same amplifier is used, the transmission power can be increased up to four times.

The signal output from the compressor 104 is input to a digital / analog converter (D / A) 105, and the D / A 105 converts the input signal from a digital signal to an analog signal. Output. The signal output from DZA 105 is used as an OFDM modulated signal output from OFDM modulator 10. Input to the amplifier. The amplifier 11 amplifies the input OFDM modulated signal at a preset amplification factor, and the OFDM modulated signal amplified by the amplifier 11 is input to the coupler 12. The combiner 12 multiplexes the input OFDM modulated signal onto the power line 2.

The OFDM modulated signal superimposed on the power line 2 is received by the communication device 1b. The coupler 12 of the communication device 1b recognizes and takes in the signal output to the communication device 1b among the signals superimposed on the power line 2. Note that address information assigned in advance to the communication device of the transmission destination is added to the signal superimposed on the power line 2, and the coupler 12 recognizes a signal to be taken in based on the address information. The signal captured by the coupler 12 is input to a BPS (bandpass filter) 13, and the BPS 13 outputs only a signal within a preset frequency range. This BPS 13 removes noise. The signal output from BPS 13 is input to OFDM demodulator 14.

The signal input to OFDM demodulator 14 is input to analog-to-digital converter (AZD) 14 1, and A / D 14 1 converts the input signal from analog signal to digital signal and outputs I do. The signal output from A / D 141 is input to decompressor 142, and decompressor 142 amplifies (decompresses) the signal with an amplification factor that is the inverse conversion of compressor 104. . FIG. 2 (b) shows the amplification factor in the expander 142, that is, the input amplitude and the output amplitude corresponding thereto. As shown in Fig. 2 (b), the decompressor 1442 sets the amplification factor to 1 when the input amplitude is in the range of 0 to 0.03, and increases the amplification factor when the input amplitude is 0.03 or more. The rate is set to 8 which is the reciprocal of the amplification rate in the compressor 104. That is, the gain is also changed in the decompressor 144 with the input amplitude of 0.03 as the threshold. Moreover, an increase in the input amplitude above the threshold value 0.03 Since the width ratio is the reciprocal of the amplification factor of the compressor 104, the same signal as the input signal (source signal) of the compressor 104 is obtained as the output signal of the decompressor 142.

FIG. 4 (a) shows the signal point arrangement error when no decompression is performed, and FIG. 4 (b) shows the signal point arrangement error when the decompression is performed as in the present embodiment. As shown in the figure, the signal point arrangement error when the extension in FIG. 4 (b) is performed is much smaller than when the extension in FIG. 4 (a) is not performed. As described above, by performing expansion before performing 0 FDM demodulation on a signal transmitted after compression, distortion of the transmission signal can be removed, and demodulation can be performed correctly.

The signal output from the decompressor 144 is input to the quadrature demodulator 144, and the quadrature demodulator 144 converts the input signal from a real signal to a complex signal. The obtained complex signal is input to a Fast Fourier Transformer (FFT) 144, and is subjected to Fast Fourier Transform to generate a signal in the frequency domain. The signal obtained by the FFT 144 is input to the demapping 144, and the demapping 144 converts the input signal from complex data to 0, 1 pattern data. This data is the received data. In this way, the evening transmission from the communication device 1a to the communication device 1b is performed.

Here, a method of determining a threshold value in the compressor 104 will be described. As the threshold value is reduced, the peak power decreases, but the average power also decreases. Accordingly, if the threshold value is too low, the effect of reducing the peak ratio decreases. For example, as an extreme example, when the threshold value is set to 0, the peak power is reduced because the entire signal is compressed, but the peak ratio does not change. Since the frequency of the large amplitude is small in the OFDM modulation signal, only the large amplitude is compressed. It is preferable to set a threshold value so that Fig. 5 (a) shows the result of counting the amplitude frequency 100 times for 256 FDD modulated signals in one period, and Fig. 5 (b) shows the result of the input amplitude and its cumulative frequency. Show the relationship. In this counting result, the amplitude in terms of the average power is 0.02, and the cumulative frequency below 0.02 is about 0.0 0. In addition, the cumulative frequency is 0.95 when the amplitude is 0.04. It is known that the instantaneous power distribution of an OFDM modulated signal is a chi-square distribution, and the results in Fig. 5 agree with it. Therefore, setting the threshold to an average amplitude of 0.02 or less is not preferable because the average power decreases and the frequency of the signal to be compressed increases. On the other hand, setting the threshold to three times or more the average amplitude is not preferable because the frequency of the signal to be compressed becomes too small and the effect of reducing the peak power is reduced. Therefore, it is desirable to set the threshold value within the range of 1 to 3 times the average power conversion amplitude. Further, in consideration of minimizing the distortion of the transmission signal, that is, minimizing the frequency of the signal to be compressed, the threshold value is preferably about twice the amplitude of the average power.

Next, the amplification factor in the compressor 104 will be described. The peak ratio can be reduced as the amplification factor for the amplitude exceeding the threshold is smaller. However, if it is set too small, the quantization error in digital values will increase. Therefore, it is preferable to set about 1Z10 as the lower limit of the amplification factor equal to or higher than the threshold value with respect to the amplification factor equal to or lower than the threshold value.

The compressor 104 of the present embodiment described above will be described using mathematical expressions. Assuming that the input signal of the compressor 104 is x, the output signal is y, and the threshold value is s, the relationship between the input signal X and the output signal y in the compressor 104 is (Equation 1).

y

(Equation 1) y

Here, G1 and G2 are amplification factors, and the amplification factor G1> the amplification factor G2.

As shown in (Equation 1), when the input signal X exceeds the threshold value s, the portion exceeding the threshold value s is amplified with the amplification factor G2, but is amplified more than the amplification factor G1 corresponding to the portion below the threshold value s. Since the rate G 2 is small, the part exceeding the threshold s is compressed more than the part below the threshold s. As a result, the peak power can be reliably reduced, and the reduction in the average power is small, so that the peak ratio is reduced. Note that if all input amplitudes are amplified with an amplification factor of 1 or less (constant), the output peak power can be reduced, but the average power also decreases at the same rate, so the peak ratio cannot be reduced. That is, the peak ratio cannot be suppressed unless only a portion having a relatively large amplitude is compressed as in the present embodiment. The threshold value of the decompressor 144 is set to s X G 1, and the amplification factor exceeding the threshold value may be set to the reciprocal of G 2. FIG. 2 (c) shows another example of the amplification factor in the compressor 104. As shown in the figure, the same effect can be obtained by changing the amplification factor continuously as G3 if the amplification factor is lower than G1 for the input amplitude smaller than the threshold value.

(Example 2)

Next, a difference of the communication system according to another embodiment of the present invention from the first embodiment will be described. As described above, the peak ratio of the FDM modulated signal increases due to the combination of carriers. However, depending on the combination of the amplitude and phase of each carrier, the peak ratio may be small. In such a case, no compression is required, and thus no compression is performed. Then, the transmission signal is transmitted with information on whether the signal is compressed or not, and the reception side inputs the compressed signal to the decompressor 142 according to the information, and after decompression, 〇 FDM demodulation I do. If the signal is an uncompressed received signal, FDM demodulation is performed without passing through the expander 144. Compressed message Even if the signal is expanded, some distortion remains, so if compression is not required as in the present embodiment, decompression is used to avoid unnecessary compression and suppress distortion. Can be. Thereby, communication reliability can be further improved.

(Example 3)

Next, a communication system according to another embodiment of the present invention will be described with reference to FIG. 6 while referring to differences from the first embodiment. FIG. 6 shows the configurations of the OFDM modulator 10 'and the FDM demodulator 14' of the present embodiment. As shown in the figure, the OFDM modulator 10 ′ of the present embodiment includes two compressions 1104 a and 104 b, and the compressors 104 a and 104 b have A quadrature modulator 103 is provided at the subsequent stage. The complex signal output from the IFFT 102 is divided into a real signal and an imaginary signal, and the real signal is input to the compressor 104a, and the imaginary signal is input to the compressor 104b. The compressors 104a and 104b compress the real number signal and the imaginary number signal in the same manner as in the first embodiment. The real number signal and the imaginary number signal compressed by the compressors 104a and 104b are input to the quadrature modulator 103. The quadrature modulator 103 receives the input complex number signal (real number signal and imaginary number). Signal) into a real number signal. Thus, by providing a compressor for each of the real number signal and the imaginary number signal, for example, when the peak power of the real number signal is smaller than the threshold and the peak ratio is also small, the compression is not performed on the real number signal. There is no signal distortion. On the other hand, in the 〇 FDM demodulator 14 ′ on the receiving side, the complex signal obtained by the quadrature demodulator 143 is divided into a real signal and an imaginary signal, and the decompressors 14 2 a and 14 2 Entered in b. The amplification factor of the decompressor 142a is set to perform the inverse conversion of the compressor 104a, and the amplification factor of the decompressor 142b is set to perform the inverse conversion of the compressor 104b. ing. According to the present embodiment, since a complex signal is divided into a real signal and an imaginary signal, and a signal having a small peak ratio is not compressed, signal distortion can be reduced, and communication reliability can be further improved. Can be improved. In each of the embodiments described above, the case where data transmission / reception is performed by power line carrier has been described. However, the present invention is applicable to communication methods other than power line carrier. Also, in each embodiment, as an example of the multi-carrier modulation method,

Although the OFDM system has been described, the present invention is also applicable to a multi-carrier modulation system other than the OFDM system. Industrial applicability

INDUSTRIAL APPLICABILITY The present invention can be applied to a communication system that performs communication using a multicarrier modulation scheme such as the OFDM scheme. With this application, the peak ratio can be reduced without lowering the communication speed.

Claims

The scope of the claims

1.A modulated signal obtained by combining a plurality of carriers modulated by transmission data is input, and a first amplification factor for a signal equal to or less than a preset threshold value and a value smaller than the first amplification factor are set. A compressor for amplifying the modulated signal with a second amplification factor for a signal exceeding the threshold value, and a transmitting unit for transmitting a transmission signal obtained based on an output signal of the compressor. A communication device characterized by the above-mentioned.

2. The communication device according to claim 1, wherein the threshold value is set to a value within a range of 1 to 3 times an average value of the amplitude of the modulation signal.

3. The communication device according to claim 1, wherein the first amplification factor is a value equal to or less than 10 times the second amplification factor.

4. The communication device according to claim 1, wherein the modulation signal is a modulation signal obtained by an orthogonal frequency division multiplexing scheme.

5.Input a modulated signal obtained by combining a plurality of carriers modulated by transmission data, and set a first amplification factor for a signal below a preset threshold value and a value smaller than the first amplification factor. A compressor that amplifies the modulated signal with a second amplification factor for a signal exceeding the threshold value, and a transmitting unit that transmits a transmission signal obtained based on an output signal of the compressor. A first communication device;

A receiving unit that receives the transmission signal transmitted by the transmitting unit; and an expander that amplifies the signal received by the receiving unit so as to perform a reverse conversion to the amplification of the modulation signal in the compressor. A communication system, comprising: a second communication device.

6. The expander amplifies a signal equal to or less than a value obtained by multiplying the threshold by the first amplification by an inverse of the first amplification, and sets the threshold to the first amplification. 6. The communication system according to claim 5, wherein amplification is performed on a signal exceeding the value obtained by multiplying the signal by a reciprocal of the second amplification factor.

7. The communication system according to claim 5, wherein the threshold value is set to a value within a range of 1 to 3 times an average value of the amplitude of the modulation signal.

8. The communication system according to claim 5, wherein the first amplification factor is a value equal to or less than 10 times the second amplification factor.

9. The communication device according to claim 5, wherein the modulated signal is a modulated signal obtained by an orthogonal frequency division multiplexing scheme.

10. The transmission unit transmits a transmission signal by superimposing a transmission signal on a power line, and the reception unit receives the transmission signal superimposed on the power line. A communication system as described.