JP2011124779A - Radio communication system, radio communication equipment, and radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system for stable communication even if a frequency-selectivity fading occurs. <P>SOLUTION: A transmission path state estimating part 31 calculates frequency characteristics of a transmission path by performing discrete fourier transformation with a factor of a transversal automatic equalizer 23 that equalizes the transmission path of a reception signal. A multi-carrier setting part 32 sets a parameter of multi-carrier modulation for a carrier number, a carrier band, and a carrier frequency according to frequency characteristics of the transmission path that has been calculated. By this, even if a frequency-selectivity fading occurs, stable radio communication can be performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radio communication system, a radio communication apparatus, and a radio communication method that are suitable for use in communication between base-line radio networks and mobile phone base stations.

  For digital microwave communication devices used for trunk line wireless networks and inter-base station communication of mobile phones, there is a demand for always stable communication quality and large capacity transmission. Adaptive modulation is known as one that enables such stable and large-capacity wireless communication.

  Adaptive modulation is a method of changing parameters such as a modulation method on the transmission side to an optimum value according to a change in the state of the transmission path. That is, in QAM (Quadrature Amplitude Modulation) modulation, the transmission speed can be increased as the number of multi-values increases. However, when the number of multi-values increases, an error is likely to occur when the transmission path state is bad. Therefore, when the transmission path state is good, signal transmission is performed by, for example, 64-level QAM modulation, and when the transmission path state is bad due to fading or the like, for example, the signal is transmitted by QPSK (Quadrature Phase Shift Keying) modulation. By performing transmission, optimal wireless communication is performed according to a change in the state of the transmission path (Patent Document 1). This makes it possible to perform optimal wireless communication according to the change in the state of the transmission path, and always maintain stable communication quality.

Japanese Patent Laid-Open No. 10-247955

  However, in the adaptive modulation as shown in Patent Document 1, only the multi-value number of digital modulation is changed according to the characteristics of the transmission path. In this case, it is possible to ensure high communication quality by changing the multi-valued number of signals for changes in the transmission path state that do not depend on the frequency, but transmission with frequency dependence such as frequency selective fading. Less effective for changing road characteristics.

  7 and 8 are graphs showing the characteristics of frequency selective fading. 7 and 8, the horizontal axis indicates the frequency, and the vertical axis indicates the transmission path state. In the case of frequency selective fading generated by an interference wave, as shown in FIG. 7, the transmission characteristic is particularly deteriorated at a specific frequency. Furthermore, since the frequency at which the transmission characteristics deteriorate changes with time, for example, when frequency selective fading having frequency characteristics that change with time as shown in FIGS. 8A and 8B occurs, No matter how the multi-value number is changed, it is impossible to maintain stable communication quality and ensure high transmission quality.

  In view of the above-described problems, an object of the present invention is to provide a wireless communication system, a wireless communication apparatus, and a wireless communication method capable of performing stable communication even when frequency selective fading occurs.

  In view of the above-described problems, the present invention is a radio communication system that performs primary modulation of an input signal and then performs secondary modulation using carrier modulation, and performs transversal automatic equalization that equalizes a transmission path of a received signal. Transmission path state estimation means for calculating the frequency characteristics of the transmission path by discrete Fourier transform of the coefficients of the transmitter, and setting the carrier modulation parameters according to the frequency characteristics of the transmission path calculated by the transmission path state estimation means A wireless communication system comprising carrier parameter setting means.

  The present invention performs a primary modulation of an input signal, then a secondary modulation of the primary modulated signal by carrier modulation and transmits, and a demodulation of the secondary modulation of the carrier modulation on the received signal, A wireless communication apparatus having a receiving system that demodulates primary modulation, wherein the coefficient of a transversal type automatic equalizer that equalizes a transmission path of a received signal is subjected to discrete Fourier transform to obtain a frequency characteristic of the transmission path. Transmission path state estimation means for calculating, and carrier parameter setting means for setting carrier modulation parameters for the transmission system and the reception system according to the frequency characteristics of the transmission path calculated by the transmission path state estimation means And

  The present invention relates to a wireless communication method in which an input signal is first modulated and then secondarily modulated by carrier modulation and transmitted, and a coefficient of a transversal automatic equalizer that equalizes a transmission path of a received signal is discretely used. And a step of calculating a frequency characteristic of the transmission line by performing a general Fourier transform, and a step of setting a carrier modulation parameter in accordance with the calculated frequency characteristic of the transmission line.

  According to the present invention, the frequency characteristic of the transmission path is calculated by performing discrete Fourier transform on the coefficient of the transversal type automatic equalizer that equalizes the transmission path of the received signal, and the calculated frequency characteristic of the transmission path is obtained. Accordingly, by setting carrier modulation parameters such as the number of carriers, carrier band, and carrier frequency, stable radio communication can be performed even when frequency selective fading occurs.

1 is a block diagram showing a wireless communication apparatus according to a first embodiment of the present invention. It is a block diagram which shows the structure of a transversal type | mold automatic equalizer. It is a block diagram which shows the structure of a multicarrier parameter setting part. It is explanatory drawing of the setting of the multicarrier parameter in the radio | wireless communication apparatus of the 1st Embodiment of this invention. It is explanatory drawing of the setting of the multicarrier parameter in the radio | wireless communication apparatus of the 1st Embodiment of this invention. It is a block diagram which shows the radio | wireless communication apparatus of the 2nd Embodiment of this invention. It is a graph which shows the characteristic of frequency selective fading. It is a graph which shows the characteristic of frequency selective fading.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is a block diagram showing a wireless communication apparatus 1 according to the first embodiment of the present invention. In FIG. 1, an error correction coding unit 11, a digital modulation unit 12, a multicarrier modulation unit 13, a D / A converter 14, and a transmission unit 15 constitute a transmission system circuit.

  Input data is supplied to the error correction encoding unit 11. The error correction encoding unit 11 adds an error correction code to the input data. The output signal of the error correction encoding unit 11 is supplied to the digital modulation unit 12.

  The digital modulation unit 12 performs primary modulation on input data. For example, QPSK, QAM (16-value QAM, 32-value QAM) or the like is used as the modulation method of the digital modulation unit 12.

  The output signal of the digital modulation unit 12 is supplied to the multicarrier modulation unit 13. The multicarrier modulation unit 13 performs secondary modulation of the signal primarily modulated by the digital modulation unit 12 using multicarrier. For example, OFDM (Orthogonal Frequency Division Multiplexing) is used as the modulation method of the multicarrier modulation unit 13. The parameters (number of carriers, carrier band, carrier frequency) in the multicarrier modulation unit 13 can be set by the multicarrier parameter setting unit 32.

  The output signal of the multicarrier modulation unit 13 is converted into an analog signal by the D / A converter 14 and then supplied to the transmission unit 15. In the transmission unit 15, the transmission signal is up-converted to a predetermined carrier transmission frequency, power-amplified, and then transmitted from the antenna 16.

  Next, the circuit of the receiving system will be described. In FIG. 1, a receiving unit 21, an A / D converter 22, a transversal automatic equalizer 23, a multicarrier demodulating unit 24, a digital demodulating unit 25, and an error correcting unit 26 are used. A circuit is constructed.

  In FIG. 1, the reception signal of the antenna 16 is supplied to the reception unit 21. The reception unit 21 amplifies the reception signal and down-converts it to a baseband signal. The output signal of the receiving unit 21 is converted into a digital signal by the A / D converter 22 and then supplied to the transversal automatic equalizer 23.

  The transversal type automatic equalizer 23 estimates the characteristics of the transmission line, optimally sets the weighting coefficient of the transversal FIR filter, and compensates for distortion of the transmission line. Further, the transmission path state estimation unit 31 calculates the frequency characteristic of the transmission path from the filter weight coefficient estimated by the transversal automatic equalizer 23, and the frequency characteristic of this transmission path is sent to the multicarrier parameter setting unit 32. Set. The multicarrier parameter setting unit 32 sets the number of carriers, the carrier band, and the carrier frequency in the multicarrier modulation unit 13 and the multicarrier demodulation unit 24 based on the frequency characteristics.

  The output signal of the transversal automatic equalizer 23 is supplied to the multicarrier demodulator 24. The multicarrier demodulator 24 demodulates secondary modulation using, for example, OFDM. Parameters (number of carriers, carrier band, carrier frequency) in the multicarrier demodulator 24 can be set by a multicarrier parameter setting unit 32.

The output signal of the multicarrier demodulator 24 is supplied to the digital demodulator 25. The digital demodulator 25 demodulates primary modulation using, for example, QPSK and QAM.

  The output signal of the digital demodulation unit 25 is supplied to the error correction unit 26. The error correction unit 26 performs error correction processing of data from the digital demodulation unit 25.

  As described above, in the first embodiment of the present invention, the transmission line state estimation unit 31 calculates the frequency characteristic of the transmission line from the filter weight coefficient estimated by the transversal automatic equalizer 23. Based on this frequency characteristic, parameters (number of carriers, carrier band, carrier frequency) in the multicarrier modulation unit 13 and the multicarrier demodulation unit 24 are set. This will be described below.

FIG. 2 is a block diagram showing a configuration of the transversal automatic equalizer 23. As shown in FIG. As shown in FIG. 2, the transversal automatic equalizer 23 includes a transversal FIR (Finite Impulse Response) filter 51, an error detection unit 52, and a weight coefficient determination unit 53. The received signal that has received the characteristics of the transmission path is equalized by the transversal FIR filter 51 and then supplied to the error detector 52. Error in the error detection unit 52 is, for example, a signal from an output signal D _out of transversal FIR filter 51, which is equalized in the original signal and the transversal FIR filter 51 when the known signal is input as an input signal And the error is supplied to the weighting factor determination unit 53. The weighting factor determining unit 53 determines the weighting factor C _j (−N ≦ j ≦ N) of the transversal FIR filter 51 so that the error from the error detecting unit 52 is minimized.

In such a transversal type automatic equalizer 23, the frequency characteristic of the transmission path can be estimated from the weight coefficient C _j (−N ≦ j ≦ N) of the transversal type FIR filter 51. That is, in the transversal FIR filter 51, as shown in the following equation (fading compensation equation), a product-sum operation is performed by weighted addition. In the process of this transversal automatic equalizer 23, the input signal D _in in the transversal FIR filter 51 is delayed by the timing in order of input, the signal input at a certain timing relative - 2N + 1 signals input at a timing shifted from N by N are generated. Then, the weighting coefficient is calculated by the weighting coefficient determination unit 53 at each timing according to the following formula, and the product-sum operation by weighted addition is performed to compensate for the influence of fading.

  The weighting coefficient of the transversal FIR filter 51 is a time domain coefficient. The frequency characteristic of the transmission path can be calculated by converting the value of the time domain weighting coefficient at each timing into the frequency domain by discrete Fourier transform, as shown in the following formula (discrete Fourier transform formula of the weighting coefficient).

  FIG. 3 is a block diagram illustrating a configuration of the multicarrier parameter setting unit 32. As illustrated in FIG. 3, the multicarrier parameter setting unit 32 includes a carrier number determination unit 61, a carrier band determination unit 62, and a carrier frequency determination unit 63.

  As described above, the transmission path state estimation unit 31 calculates the frequency characteristic of the transmission path from the filter weight coefficient estimated by the transversal automatic equalizer 23. The frequency characteristics of the transmission path are supplied to the carrier number determination unit 61, the carrier band determination unit 62, and the carrier frequency determination unit 63. Based on this frequency characteristic, the number of carriers, carrier band, and carrier frequency of the multicarrier modulation are determined by the carrier number determination unit 61, the carrier band determination unit 62, and the carrier frequency determination unit 63 of the multicarrier parameter setting unit 32. Set in carrier modulation section 13 and multicarrier demodulation section 24

  4 and 5 are explanatory diagrams for setting multicarrier parameters in the wireless communication apparatus according to the first embodiment of this invention. For example, it is assumed that the frequency characteristic of the transmission line estimated by the transmission line state estimation unit 31 is in a state as shown in FIG. In FIG. 4A, coherent frequency selective fading occurs in the vicinity of the frequency fa in the frequency band F1 usable for communication. In this case, as shown in FIG. 4B, the carrier frequency is set to fb and the carrier band is set to F2. Thereby, the influence of the frequency selective fading generated by the interference wave can be reduced.

  Further, for example, assume that the frequency characteristic of the transmission line estimated by the transmission line state estimation unit 31 is in a state as shown in FIG. In FIG. 5A, coherent fading occurs in the vicinity of the frequency fc in the frequency band F3 that can be used for communication. In this case, as shown in FIG. 5B, the carrier frequency is set to fd and fe, and the carrier band is set to F4 and F5. Thereby, the influence of the frequency selective fading generated by the interference wave can be reduced.

<Second Embodiment>
FIG. 6 is a block diagram illustrating a wireless communication apparatus according to the second embodiment of this invention. In FIG. 6, an error correction encoding unit 111, a modulation unit 112, a multicarrier modulation unit 113, a D / A converter 114, and a transmission unit 115 constitute a transmission system circuit. The error correction encoding unit 111, the modulation unit 112, the multicarrier modulation unit 113, the D / A converter 114, the transmission unit 115, and the antenna 116 are the wireless communication device 1 according to the first embodiment of the present invention shown in FIG. This is the same as the error correction encoding unit 11, the digital modulation unit 12, the multicarrier modulation unit 13, the D / A converter 14, the transmission unit 15, and the antenna 16 in the transmission system.

  In FIG. 6, a receiving unit 121, an A / D converter 122, a transversal automatic equalizer 123, a multicarrier demodulating unit 124, a demodulating unit 125, and an error correcting unit 126 This circuit is configured. The receiving unit 121, the A / D converter 122, the transversal type automatic equalizer 123, the multicarrier demodulating unit 124, the demodulating unit 125, and the error correcting unit 126 are the first embodiment of the present invention shown in FIG. This is the same as the receiving unit 21, A / D converter 22, transversal type automatic equalizer 23, multicarrier demodulating unit 24, digital demodulating unit 25, and error correcting unit 26 in the receiving system of the wireless communication apparatus 1.

  In the first embodiment described above, the transmission line state estimation unit 31 calculates the frequency characteristic of the transmission line from the characteristic of the transmission line estimated by the transversal type automatic equalizer 23, and based on this frequency characteristic. The parameters (number of carriers, carrier band, carrier frequency) of the multicarrier modulation unit 13 and the multicarrier demodulation unit 24 are set.

  In contrast, in the second embodiment, the parameters (number of carriers, carrier band, carrier in multicarrier modulation section 113 and multicarrier demodulation section 124 are based on the frequency characteristics calculated from the transmission path characteristics. Frequency) and based on the error rate from the error correction unit 126, the digital modulation parameter setting unit 133 sets the parameters (modulation scheme, multi-value number in QAM) in the modulation unit 112 and the demodulation unit 125. is doing. For this reason, in this embodiment, it is possible to maintain the communication quality even when the transmission path state deteriorates due to factors other than frequency selective fading.

  The present invention is not limited to the above-described embodiments, and various modifications and applications can be made without departing from the gist of the present invention. For example, in the above-described embodiment, OFDM is described as an example of the modulation method of the multicarrier modulation unit 13. However, since the carrier frequency is limited (integer multiple of the symbol rate) in OFDM, the carrier frequency is It cannot be freely controlled. Therefore, any modulation scheme may be used as long as it can be transmitted with the minimum necessary number of carriers (for reducing the peak factor between signals). In the above-described embodiment, the multicarrier modulation method is used as the modulation method. However, a single carry modulation method may be used.

11, 111: Error correction encoding unit 12, 112: Modulation unit 13, 113: Multicarrier modulation unit 14, 114: D / A converter 15, 115: Transmission unit 16, 116: Antenna 21, 121: Reception unit 22 122: A / D converter 23, 123: transversal automatic equalizer 24, 124: multicarrier demodulator 25, 125: demodulator 26, 126: error corrector 31, 131: transmission path state estimator 32 132: Multicarrier parameter setting unit 133: Digital modulation parameter setting unit 51: Transversal FIR filter

Claims (9)

A wireless communication system that primarily modulates an input signal and then performs secondary modulation with carrier modulation and transmits the input signal,
A transmission path state estimating means for calculating a frequency characteristic of the transmission path by performing a discrete Fourier transform on a coefficient of a transversal type automatic equalizer for equalizing the transmission path of the received signal;
A wireless communication system comprising: carrier parameter setting means for setting the carrier modulation parameter according to the frequency characteristic of the transmission path calculated by the transmission path state estimation means.   The wireless communication system according to claim 1, wherein the carrier modulation parameter is a part of a carrier number, a carrier band, or a carrier frequency, or a combination thereof.   The wireless communication system according to claim 1, further comprising: setting a parameter for the primary modulation according to an error rate of a received signal.   The wireless communication system according to claim 3, wherein the primary modulation parameter is a multi-value number of digital modulation. After primary modulation of the input signal, the primary modulation signal is secondarily modulated by carrier modulation and transmitted, and the received signal is demodulated by secondary modulation of carrier modulation, and then the primary modulation is performed. A wireless communication apparatus having a receiving system for performing demodulation,
A transmission path state estimating means for calculating a frequency characteristic of the transmission path by performing a discrete Fourier transform on a coefficient of a transversal type automatic equalizer for equalizing the transmission path of the received signal;
A wireless communication apparatus comprising: carrier parameter setting means for setting carrier modulation parameters of the transmission system and the reception system according to the frequency characteristic of the transmission path calculated by the transmission path state estimation means.   6. The radio communication apparatus according to claim 5, wherein the carrier modulation parameter is a part of a carrier number, a carrier band, or a carrier frequency or a combination thereof.   6. The radio communication apparatus according to claim 5, further comprising setting a primary modulation parameter of the transmission system and the reception system according to an error rate of a reception signal.   The wireless communication apparatus according to claim 7, wherein the primary modulation parameter is a multi-value number of digital modulation. A wireless communication method of performing primary modulation on an input signal and then performing secondary modulation with carrier modulation,
Calculating a frequency characteristic of the transmission path by performing a discrete Fourier transform on a coefficient of a transversal type automatic equalizer that equalizes the transmission path of the received signal;
And a step of setting the carrier modulation parameter in accordance with the calculated frequency characteristic of the transmission path.

Images