JP5208980B2 - Wireless communication system, transmission apparatus and transmission method in wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system for compensating for deterioration in communication quality of a propagation path due to fading, narrowband interference, jamming, and the like in wireless communication, and a transmission apparatus and transmission method in the wireless communication system.

  In wireless communication, when a transmitted wireless signal passes through a plurality of propagation paths, there is a phenomenon called fading in which the wireless signals that reach the receiving apparatus interfere with each other and the reception level varies greatly. Since fluctuations in the reception level have a great influence on communication quality, various countermeasure techniques such as diversity have been taken.

  As a concept of the influence of fading, the influence of loss on frequency is shown in FIG. Such a phenomenon in which the gain is different at a specific frequency is called frequency selective fading. When a single carrier signal is transmitted in such a propagation path, a signal level difference occurs in the reception signal band, and communication quality is greatly increased. There is a problem that deteriorates. With regard to narrowband interference such as a jamming signal, the received signal level does not change, but the communication quality of the transmission path is greatly degraded due to the influence of interference.

  An example of a technique for communication quality degradation of a propagation path such as frequency selective fading that causes such communication quality degradation is described in Non-Patent Document 1. As shown in FIG. 2, the signal is divided into multi-carrier signals and transmitted, and the in-band frequency characteristics of each subcarrier are flattened to create a flat fading environment, and by appropriately adjusting the transmission power for each subcarrier. , Improving communication quality.

Nakanishi et al., “One-Cell Repetitive TDMA System Using OFDM-based Modulation with Multilevel Transmission Power Control”, IEICE Transactions B, Vol. J87-B, No. 8, pp.1043-1052

  However, in general, a multicarrier signal has a large PAPR (Peak to Average Power Ratio) and requires a large back-off of the amplifier. Conversely, if the number of divided carriers is reduced in order to lower the PAPR, frequency selective fading cannot be regarded as sufficiently flat fading, and there is a problem in that communication quality deteriorates.

  If the power fluctuation due to fading becomes larger than the adjustable level of the transmission / reception apparatus, the subcarriers affected by fading cannot obtain a predetermined channel quality, and communication cannot be performed. In that case, as shown in FIG. 3, it is possible to cope with this by arranging subcarriers so as to avoid the influence of fading and the like. However, when there is no vacant subcarrier, the transmission rate for subcarriers that cannot be used is reduced. Further, as described in Non-Patent Document 1, it is possible to cope with the problem by reducing the number of modulation multi-levels, but this also causes a decrease in transmission speed.

  Therefore, the present invention does not require an increase in the size of the amplifier of the apparatus, and further does not reduce the transmission speed even if there is a band in which the communication quality is remarkably deteriorated. It is an object of the present invention to provide a radio communication system, a transmission apparatus in the radio communication system, and a transmission method that avoid influence on communication quality degradation.

  In order to achieve the above object, a wireless communication system according to the present invention avoids a frequency division in which the communication quality of a transmission path is significantly degraded, and a division circuit that generates a plurality of sub-modulation signals by dividing a single carrier modulation signal. And a receiving apparatus including a re-synthesizing circuit that re-arranges and synthesizes the frequency arrangement of the received sub-modulated signal at the frequency position before the division. With.

  Further, it is preferable that the dividing circuit divides the band so that the sum of the bands of the sub-modulated signals after the division is smaller than the band of the single carrier modulated signal before the division.

  The transmitting device further includes means for replicating all or part of the generated sub-modulation signals, and the frequency shift circuit arranges the replicated sub-modulation signals at different frequency positions, and The receiving apparatus preferably further includes signal synthesis selection means for selecting or synthesizing the received duplicated sub-modulation signal.

  The transmission device further includes propagation path detection signal generation means for inserting and transmitting a training signal on the frequency axis, and the reception device detects a frequency characteristic from the received training signal, and the frequency characteristic is It is also preferable to further include propagation path quality detection means for notifying the transmission apparatus.

  In order to achieve the above object, a transmission apparatus according to the present invention avoids a frequency division where a communication quality of a transmission path is significantly deteriorated, and a division circuit that generates a plurality of sub modulation signals by dividing a single carrier modulation signal. As described above, a frequency shift circuit for arranging the sub-modulated signal in frequency is provided.

  In order to achieve the above object, a transmission method according to the present invention avoids a frequency division where a single carrier modulation signal is band-divided to generate a plurality of sub-modulation signals, and the communication quality of the transmission path is significantly degraded. Thus, a frequency shift step of arranging the sub-modulated signal in frequency is included.

  The wireless communication system of the present invention uses a sub-modulation signal decomposition method for a single carrier transmission signal, and arranges frequencies of the sub-modulation signals so as to avoid the influence of channel quality degradation such as frequency selective fading. The signal transmission quality can be improved. In addition, a small amplifier can be applied by the submodulation signal decomposition method of the single carrier transmission signal.

  Further, the signal is decomposed so that the total sum of the sub-modulated signals after division is narrower than the modulated signal before division, and a band with significantly deteriorated communication quality is assigned to the surplus band obtained here. Thus, the occupied bandwidth of the original modulation signal is not increased.

A conceptual diagram of fading is shown. FIG. 1 shows a conceptual diagram 1 of multicarrier transmission in which fading countermeasures are taken. FIG. 2 shows a conceptual diagram 2 of multicarrier transmission in which fading countermeasures are taken. The concept of the fading countermeasure by this invention is shown. The structural example of the radio | wireless apparatus which implement | achieves this invention is shown. The output of the transmission apparatus divided | segmented into the some submodulation signal is shown. The output of the transmission apparatus divided into a plurality of submodulation signals (example of generation of surplus band) is shown. An example of a transmission apparatus structure provided with a submodulation signal transmission diversity function is shown. An example of a receiver structure provided with a submodulation signal transmission diversity function is shown.

  A method for solving the problems of the prior art and avoiding the influence on the communication quality degradation of the propagation path such as frequency selective fading will be described. FIG. 4 shows the concept of countermeasures against fading according to the present invention. In the present invention, in order to avoid the influence on the communication quality degradation of the propagation path, the single carrier transmission signal is divided and arranged so as to avoid the frequency region in which the communication quality is significantly degraded.

  An example of the configuration of a transmitting device and a receiving device that realizes the present invention is as follows: “Abe et al., Proposal of spectrum-editing band-dispersed transmission realizing high frequency utilization efficiency, IEICE satellite communication study group, SAT2009-48, pp .7-12 "as a basic configuration, and transmission signal division arrangement control is performed based on information from the communication quality detection means of the propagation path. As a configuration example of the transmission device and the reception device, as shown in FIG. 5, the transmission device includes a modulation circuit 1 that modulates a data signal to be transmitted, and a band division filter that divides the modulation signal into bands and arranges them at desired frequency positions. Bank 2, propagation path detection signal generation means and controller 3, and the receiving apparatus extracts band-synthesized modulated signals and combines them, and band synthesis filter bank 4. A demodulation circuit 5 that demodulates the output modulation signal and restores the transmitted data signal, and a propagation path quality detection means 6 are provided. Note that the communication quality detection means for the propagation path includes a signal generation means for propagation path detection and a controller 3 and a propagation path quality detection means 6.

  At this time, the band division filter bank 2 in this transmission apparatus performs band division on the modulation signal based on information from the propagation path detection signal generating means for detecting the communication quality of the propagation path and the controller 3, and a desired frequency position. Therefore, a Fourier transform circuit 21 (FFT) that converts the modulation signal into a signal on the frequency axis, a dividing circuit 22 that divides the output of the Fourier transform circuit into a plurality of sub-modulation signals, A frequency shift circuit 23 arranged at the frequency position, an adder circuit 24 for adding the outputs of the frequency shift circuit, and an inverse Fourier transform circuit (IFFT) 25 for converting the signal into a signal on the time axis are provided. At this time, the band occupied by the sub-modulation signal depends on the weighting factor used for the dividing circuit 22, and the bandwidth can be adjusted. The dividing circuit 22 includes a plurality of band dividing weight functions and a multiplying circuit.

Specifically, as shown in FIG. 6, the modulation signal output from the modulation circuit 1 is subjected to fast Fourier transform processing in the FFT circuit 21 of the band division filter bank 2, whereby a signal on the time axis is converted. It is converted into a signal on the frequency axis. As shown in FIG. 4A, the frequency division weight function ₁ and the frequency division weight function ₂ are independently multiplied in the multiplication circuit ₁ and the multiplication circuit _{2 with} respect to the signal on the frequency axis output from the FFT circuit 21, respectively. Then, band division processing is performed on the frequency axis. The multiplication results are input to the frequency shift circuit ₁ 23 and the frequency shift circuit ₂ 23, respectively, and are frequency-shifted on the frequency axis, whereby equivalent frequency conversion is performed. The result of frequency shift is shown in FIG. As can be seen from this figure, the modulation signal of user A is multiplied and shifted by a different weight function, so that one modulation signal is divided into two sub-modulation signals (A1 and A2) on the frequency axis. Is done. The two divided sub-modulated signals are combined again by the adder circuit 24 and subjected to fast Fourier inverse transform processing by the IFFT circuit 25, thereby returning the signal on the frequency axis to the signal on the time axis. Thereafter, the signal is actually transmitted through the RF circuit.

  On the other hand, the band synthesis filter bank 4 in the receiving apparatus extracts a Fourier transform circuit 41 (FFT) that converts a received signal into a signal on the frequency axis and each sub-modulated signal, and outputs the output of the Fourier transform circuit 41 (FFT). A frequency shift circuit 42 arranged at a predetermined frequency position, a recombination circuit 43 that rearranges each sub-modulated signal from a predetermined frequency position to a frequency position before the arrangement conversion, and an adder circuit that adds the outputs of the resynthesis circuit 43 44, a multiplication circuit 45 that multiplies the waveform shaping filter function 46, and an inverse Fourier transform circuit 47 (IFFT) that converts the output of the multiplication circuit 45 into a signal on the time axis. Further, the re-synthesis circuit 43 includes a plurality of band synthesis weight functions and a multiplication circuit.

The specific operation is the same as the signal processing procedure on the transmission side. On the reception side, the signal frequency-converted by the RF circuit is input to the FFT circuit 41, and the reception signal on the time axis is converted to the reception signal on the frequency axis. The converted reception signals on the frequency axis are frequency-shifted in frequency shift circuit ₁ 42 and frequency shift circuit ₂ 42, respectively, and band synthesis weight function ₁ and band synthesis weight function ₂ are independently used in multiplication circuit ₁ and multiplication circuit ₂ , respectively. Is multiplied. Multiplication by the band synthesis weight function results in equivalent filter processing on the frequency axis, and noise components in bands other than the pass band and transition band of the band synthesis weight function are removed. This filtered signal is synthesized again in the adder circuit 44. Further, the multiplication circuit 45 multiplies the output of the adder circuit 44 by a waveform shaping filter function 46 on the frequency axis, and removes noise / signal components outside the desired band, thereby extracting a desired signal, and an IFFT circuit. After being converted again into a signal on the time axis in 47, it is demodulated in the demodulation circuit 5.

  As an implementation example of the propagation path detection signal generating means and the controller 3, the training signal inserted on the frequency axis is transmitted, the reception side propagation path quality detection means 6 detects the frequency characteristic from the training signal, and the information May be notified to the transmission side as feedback. As described above, when the present invention is used, the influence of fading or the like can be avoided by frequency-dividing the single carrier signal band so as to avoid the frequency region in which the communication quality is remarkably deteriorated. In addition, the number of carriers can be reduced by partially dividing the signal band of the single carrier, and as a result, the PAPR can be lowered. Therefore, downsizing of the amplifier can also be realized.

  Furthermore, in the band division method used in the present invention, when the sub-modulation signal is formed using a steeper filter than the filter used for the modulation signal before division, as shown in FIG. In addition, the sum of the bands of the sub-modulation signals after the division can be narrower than the modulation signal bands before the division, and an extra band is generated. When the sub-modulated signal is generated, the condition that the signal can be restored on the receiving side is that the band division prescribed power shown in FIG.

  The total bandwidth is increased by selectively allocating the surplus bandwidth obtained here (the sum of the modulated signal bandwidth before division minus the sub-modulated signal bandwidth after division) to the bandwidth where the amplitude gain is reduced by frequency selective fading. Without deterioration, signal quality deterioration due to fading can be reduced.

  In another embodiment of the present invention, a part or all of the divided sub-modulated signals may be duplicated, transmitted at different frequencies, and the duplicated sub-modulated signals may be synthesized on the receiving side. As an example of a wireless device configuration that realizes this, in the transmitting device, as shown in FIG. 8, the sub-modulation signal of the output of the multiplication circuit is compounded, and the compounded signal is arranged at a predetermined frequency and transmitted, In the receiving apparatus, as shown in FIG. 9, a signal synthesis selection means 48 for selecting or synthesizing the composite signal after returning the frequency to a predetermined position for the composite sub-modulated signal may be added.

  As described above, the wireless communication system according to the present invention avoids the influence of fading and the like by frequency-allocating the sub-modulation signal so that the single carrier modulation signal is divided into bands to avoid the influence of frequency selective fading. It becomes possible to do. Furthermore, since the PAPR can be reduced by reducing the number of divided carriers, a small amplifier can be applied.

  Furthermore, by allocating the surplus band (modulation signal band before division−total sub modulation signal band after division) obtained by configuring the sub-modulation signal to the frequency position where the influence of fading is large, the occupied bandwidth is reduced. It is possible to reduce the influence of fading without increasing. It should be noted that frequency selective fading, in which the transmission characteristics are particularly degraded, has extremely steep frequency characteristics because the vector synthesis of the interference signal is infinitely zero. Therefore, frequency selective fading and narrow band in a small excess band. Interference and jamming countermeasures can be realized.

  The above-described embodiments are all illustrative of the present invention and are not intended to limit the present invention, and the present invention can be implemented in various other variations and modifications. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Modulation circuit 2 Band division | segmentation filter bank 3 Signal generation means and controller for propagation path detection 4 Band synthesis filter bank 5 Demodulation circuit 6 Propagation path quality detection means 21 Fourier transform circuit 22 Division circuit 23 Frequency shift circuit 24 Addition circuit 25 Inverse Fourier Conversion circuit 41 Fourier transform circuit 42 Frequency shift circuit 43 Resynthesis circuit 44 Addition circuit 45 Multiplication circuit 46 Waveform shaping filter function 47 Inverse Fourier transform circuit 48 Signal synthesis selection means

Claims (6)

A division circuit for dividing a single carrier modulation signal into a plurality of bands to generate a plurality of sub modulation signals;
A frequency shift circuit that frequency arranges the sub-modulated signal so as to avoid a frequency region in which the communication quality of the transmission path is significantly degraded;
A transmission device comprising:
A receiving device including a re-synthesis circuit that rearranges and synthesizes the frequency arrangement of the received sub-modulated signal at the frequency position before the division;
A wireless communication system comprising:   2. The wireless communication system according to claim 1, wherein the dividing circuit performs band division so that a sum of bands of sub-modulation signals after division is smaller than a band of a single carrier modulation signal before division. The transmission apparatus further includes means for replicating all or part of the generated plurality of submodulation signals, and the frequency shift circuit arranges the replicated submodulation signals at different frequency positions,
The radio communication system according to claim 1 or 2, wherein the receiving device further comprises signal synthesis selection means for selecting or synthesizing the received duplicated submodulation signal. The transmitter further includes a propagation path detection signal generating means for inserting and transmitting a training signal on the frequency axis,
The said receiving apparatus is further equipped with the propagation path quality detection means which detects a frequency characteristic from the received training signal, and notifies this frequency characteristic to the said transmission apparatus, The any one of Claim 1 to 3 characterized by the above-mentioned. The wireless communication system described. A division circuit for dividing a single carrier modulation signal into a plurality of bands to generate a plurality of sub modulation signals;
A frequency shift circuit that frequency arranges the sub-modulated signal so as to avoid a frequency region in which the communication quality of the transmission path is significantly degraded;
A transmission device comprising: A division step of dividing a single carrier modulation signal into a plurality of bands to generate a plurality of sub modulation signals;
A frequency shift step of arranging the sub-modulated signals in frequency so as to avoid a frequency region in which the communication quality of the transmission path is significantly degraded;
The transmission method characterized by including.

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