JP2011049950A - Communication system, transmitter, and receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that when transmitting a multi-value modulation signal after performing direct spreading (DS) thereon, the peak factor of transmission signal power is enlarged by multi-leveling and power efficiency of a transmitting-side amplifier is deteriorated as a result. <P>SOLUTION: The communication system is equipped with, on a transmitting side: a modulation means (100) for performing modulation using phase rotation sequences for modulation as many as a modulation multi-value number for each symbol on the basis of an information sequence; and a spreading means (110) for applying spreading processing to the output of the modulation means using a phase rotation sequence which varies with a fixed frequency width on a frequency axis. On a receiving side, the system is equipped with: a multiplication means (270) for multiplying an opposite phase rotation sequence obtained by performing opposite phase rotation on a phase rotation sequence for spreading used in the spreading means (110) for each symbol; a despreading processing means (270) for performing despreading by multiplying the opposite phase rotation sequence obtained by performing opposite phase rotation on the phase rotation sequence for modulation used in the modulation means for each symbol; and a demodulation means (290) for performing demodulation processing on the output of the despreading means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a communication system, transmitter, and receiver that perform spread spectrum directly using a code sequence.

  Hereinafter, a direct spreading (DS) modulation / demodulation method in a conventional wireless communication system will be described with reference to FIGS. FIG. 9 shows the transmission side, where 1000 is a modulation unit, 1010 is a multiplier that multiplies the code sequence, 1020 is a cyclic prefix (CP) addition unit that copies the end portion of the frame to the top portion, and 1030 is the base A frequency conversion unit that converts the band signal into an RF frequency, 1040 is an amplification unit, and 1050 is an antenna. FIG. 10 shows the receiving side, 1060 is an antenna, 1070 is an amplifier, 1080 is a frequency conversion unit that converts an RF signal into baseband, 1090 is a CP removal unit that removes CP, 1100 is a frequency domain processing unit, Reference numeral 1110 denotes an FFT, 1120 denotes a frequency domain equalization unit, 1130 denotes an IFFT, 1140 denotes a correlator that multiplies the code sequence and integrates corresponding to one symbol, and 1150 denotes a demodulation unit. Further, reference numeral 1160 denotes a channel estimation value generation unit that generates a frequency domain channel estimation value. FIG. 11 shows a frame configuration, and it is assumed that data of a plurality of symbols (Nsym) is spread with a spreading factor SF, and a cyclic chip obtained by copying the chip Ncp × SF at the end of the frame to the top of the frame. This configuration has a prefix (CP) portion, and has an effect of reducing the influence of a multipath delayed wave corresponding to the CP time length.

As shown in FIG. 9, the signal modulated by modulation section 1000 is multiplied by a code sequence in multiplier 1010 and spread-modulated into a wideband signal. The spread-modulated signal is subjected to CP addition by a CP addition unit 1020 and then frequency-converted by a frequency conversion unit 1030 to become an RF signal. The output signal of the frequency converter 1030 is amplified by the amplifier 1040 and then transmitted through the 1050 antenna.

On the other hand, on the receiving side, the received signal is amplified by the amplifier 1070 via the antenna 1060 as shown in FIG. The amplified received RF signal is frequency converted into a baseband signal by the frequency converting unit 1080 and then input to the CP removing unit 1090. The output of the frequency converting unit 1080 is input to a CP removing unit 1090, which removes the CP portion added to the head of the frame. The output of the CP removing unit 1090 is input to the frequency domain processing unit 1100. The frequency domain processing unit 1100 performs FFT processing on the signal after CP removal, and the signal is converted into a frequency domain signal. The output of the FFT 1110 is input to the frequency domain equalization unit 1120, and equalization processing is performed in the frequency domain based on the channel estimation value in the frequency domain of the channel estimation value generation unit 1160. The output of the frequency equalization unit 1120 is input to the IFFT unit 1130. The output of IFFT section 1130 is input to correlator 1140. The correlator 1140 multiplies the code sequence, performs a correlation operation for integration in symbol units, and outputs a correlation value from the correlator 1140. The output of the correlator 1140 is input to the demodulator 1150, and the demodulation result is output from the demodulator 1150 (see Non-Patent Document 1, for example).

IEICE technical report, radio communication system RCS2004-86, pp.61-65 (June 2004) "Error rate performance of DS-CDMA frequency domain equalization using pilot channel estimation" (Takeda, Adachi)

  In the direct spreading (DS) method, which spreads using a unique code for each user (channel), characteristics deteriorate due to multipath delay waves during wideband transmission, and so on in the frequency domain as the conventional method as described above. However, when the multilevel modulation signal is transmitted by direct spreading (DS), the peak efficiency of the transmission signal power increases due to the multilevel modulation, and the power efficiency of the amplifier on the transmission side deteriorates. There was a problem.

  The present invention has been made in view of the above, and in the case of transmitting a multilevel modulation signal by directly spreading (DS), a direct spread transceiver apparatus capable of reducing the peak factor of transmission signal power due to multilevel modulation is provided. The purpose is to obtain.

In order to solve the above-described problems and achieve the object, the code sequence according to the present invention performs phase rotation so that the frequency shifts in the frequency axis direction so that the amplitude characteristics in the frequency band are flat in symbol units. In addition, a modulation is performed in the frequency domain by arranging a number of carriers corresponding to the number of modulation multilevels at a constant frequency interval in units of symbols.

According to the present invention, it is possible to obtain a direct spread transmission / reception apparatus capable of reducing the peak factor of transmission signal power due to multi-leveling.

It is a block diagram of the transmitter by Embodiment 1 of this invention. It is a block diagram of the transmission symbol by Embodiment 1 of this invention. It is a figure which shows the frequency arrangement | positioning on the frequency axis of the modulated signal after the spreading | diffusion by Embodiment 1 of this invention. It is a time-domain waveform figure of the spreading | diffusion series by Embodiment 1 of this invention. It is a wave form diagram of the frequency domain of the spreading | diffusion series by Embodiment 1 of this invention. It is a block diagram of the receiver by Embodiment 1 of this invention. It is a block diagram of the transmitter by Embodiment 2 of this invention. It is a frequency arrangement | positioning figure by Embodiment 2 of this invention. It is a figure of the conventional transmitter. It is a figure of the conventional receiver. It is a figure of the conventional frame structure.

Embodiment 1 FIG.
The present embodiment relates to a transmission / reception apparatus, and modulation / demodulation processing of the transmission / reception apparatus will be described with reference to FIGS.

FIG. 1 shows a configuration of a transmitter in this embodiment. FIG. 2 shows the configuration of transmission symbols. FIG. 3 shows the frequency arrangement on the frequency axis of the modulated signal after spreading by the modulation phase rotation sequence φm (m = 0, 1,..., M−1) and the spreading phase rotation sequence θ. FIG. 4 shows the time domain waveform of the spreading sequence, and FIG. 5 shows the frequency domain waveform of the spreading sequence. FIG. 6 shows the configuration of the receiver.

In FIG. 1, 100 is a modulation unit, 110 is a multiplier for spreading, 120 is a cyclic prefix addition unit, 130 is a waveform shaping filter, 140 is a frequency conversion unit, 150 is an amplifier, and 160 is an antenna. As shown in FIG. 2, the symbol block is composed of (N _CP + SF) chips including a cyclic prefix, and the number of SF and FFT points is the same.

The operation of the transmitter will be described with reference to FIG. As shown in FIG. 1, with respect to the input information sequence, the modulation section 100 uses a modulation phase rotation sequence φm (m = 0, 1,..., M−1, M is a modulation multilevel number). Modulated. The signal modulated by the modulation unit 100 is multiplied by a spreading phase rotation sequence θ in a multiplier 110. The modulation phase rotation sequence φm and the diffusion phase rotation sequence θ are expressed by the equations (1) and (2), respectively. FIG. 3 shows an image of the frequency arrangement of the modulated signal before spreading and after spreading.

(Phase rotation series for modulation)

(Diffusion phase rotation series)

  Here, A is a positive integer (1 ≦ A ≦ SF / M) indicating a carrier interval at the time of modulation, and in the phase rotation sequence for modulation represented by the equation (1), the modulation multilevel is expressed in symbol units. The number of carriers corresponding to the number is arranged at a constant frequency interval, and modulation multi-valued in the frequency domain. Further, in Equation (2), the phase rotation sequence for spreading is a sequence that has excellent correlation characteristics in the frequency domain and that rotates in phase on a chip basis by a complex phase rotation sequence in which the phase changes in a sawtooth waveform in units of spreading factor SF. Use. In spreading by the spreading phase rotation sequence, the modulation signal changes at a constant frequency amount Δf at chip intervals. For example, a polyphase sequence or Zadoff-Chu can be used as the spreading phase rotation sequence. The following equation shows Δf. FIG. 4 shows the time domain waveform of the spreading sequence, and FIG. 5 shows the frequency domain waveform of the spreading sequence. 4 shows a spreading sequence in the case of 32 chips, and FIG. 5 shows a spreading sequence in the frequency domain of 32 samples obtained by converting the spreading sequence in FIG. 4 into the frequency domain. The horizontal axis of FIG. 4 is time (chip unit), and the horizontal axis of FIG. 5 is frequency (sample unit). The power of the waveform in the time domain and the frequency domain of the spreading phase rotation sequence has a property of being constant.

  Here, as shown in FIG. 3, Bw is an occupied bandwidth during the spreading process.

  In particular, as shown in FIG. 3, as a property of the phase rotation sequence for modulation, the frequency position of the carrier changes in M ways according to the data to be modulated. Therefore, the peak power of the modulation signal can be reduced. Accordingly, at the output of the multiplier 110 for spreading, the spreading sequence is shifted M times on the frequency axis in accordance with the modulation symbol, so that the modulation unit 100 modulated based on random data Even when the output signal is spread by a spreading sequence, the frequency spectrum can be flattened, and when performing the frequency domain equalization on the receiving side, channel estimation in the frequency domain can be performed in symbol units.

  The modulated signal spread by the multiplier 110 is input to a cyclic prefix (CP) adding unit 120, and the end Ncp chip of a symbol composed of SF chips is added to the head of the symbol so as to have the symbol configuration of FIG. The The output of the CP adding unit 120 is input to the waveform shaping filter 130, and after waveform shaping, the frequency is converted by the frequency conversion unit 140 and input to the amplifier 150. The output of the amplifier 150 is input to the antenna 160 and a signal is transmitted.

  Next, the operation on the receiver side will be described with reference to FIG. In the receiver shown in FIG. 6, 200 is an antenna, 210 is a frequency conversion unit, 220 is a waveform shaping filter, 230 is a cyclic prefix (CP) removal unit, 240 is a frequency domain processing unit, 250 is an FFT, 260 Is a frequency domain equalization unit, 270 is a correlation unit, 280 is a channel estimation value generation unit, and 290 is a demodulation unit that demodulates data.

  The signal received by the antenna 200 is frequency converted into a baseband signal by the frequency converter 210. The output of the frequency conversion unit 210 is filtered on the reception side by the waveform shaping filter 220, and then the symbol from which the CP has been removed by the CP removal unit 230 is extracted. The output of the CP removing unit 230 is input to the FFT 250 and converted into a frequency domain signal. The output of the FFT 250 is input to the frequency domain equalization unit 260, and frequency domain equalization is performed based on the frequency domain channel estimation value generated from the received signal by the channel estimation value generation unit 280.

  The output of the frequency domain equalization 260 is input to the correlator 270. Correlator 270 performs complex correlation processing by using a sequence F (−θ · φm) obtained by transforming the result obtained by multiplying modulation phase rotation sequence φm (m = 0 to M−1) and spreading phase rotation sequence θ into the frequency domain. I do. However, it is necessary to perform M correlations corresponding to the modulation multi-level number.

  The M correlation values obtained by the correlator 270 are input to the demodulator 290. The demodulator 290 outputs data having the highest likelihood as a demodulation result using the M correlation values.

As described above, according to this embodiment, the code sequence is a code sequence that gives a phase rotation that shifts the frequency in the frequency axis direction so that the amplitude characteristic in the frequency band is flat in symbol units. In addition, the modulation can be multi-valued in the frequency domain by arranging a number of carriers corresponding to the number of multi-value modulations at a constant frequency interval in symbol units.

Further, according to this embodiment, in order to perform equalization in the frequency domain, the signal in units of symbols obtained by multiplying the code sequence and the modulation signal is modulated after spreading so that the amplitude characteristic is flat in the frequency band. It is possible to obtain a direct spread transmission / reception apparatus that can provide a signal, does not need to insert a frame of only pilot symbols, and does not reduce the total transmission efficiency.

  Further, according to this embodiment, it is possible to extract a modulation symbol by performing correlation processing for despreading in the frequency domain on a signal that has been frequency domain equalized by the direct spreading (DS) method. Therefore, an IFFT for converting a frequency domain signal into a time domain signal is not necessary, and the FFT can be realized by using only one, and the processing scale can be reduced.

  In addition, according to this embodiment, when equalization is performed in the frequency domain, FFT processing can be performed not in units of frames having a large time length but in units of symbols. Distortion is suppressed and the influence on communication quality can be reduced.

Embodiment 2. FIG.
The present embodiment has the same transmission / reception apparatus configuration as that of the first embodiment, but is different from the first embodiment in that it is compatible with DS-CDMA in which a plurality of users transmit simultaneously. Only the transmission part different from will be described.

  FIG. 7 is a configuration diagram of a transmitter when there are a plurality of users. In FIG. 7, 300, 301, and 302 are modulation units, 310, 311, and 312 are multipliers for spreading, and 320, 321, and 322 are cycle units. Click prefix adding units 330, 331, and 332 are waveform shaping filters, 340, 341, and 342 are frequency conversion units, 350, 351, and 352 are amplifiers, and 360, 361, and 362 are antennas.

  7 differs from FIG. 1 in that the modulation phase rotation sequence φm, u (m = 0, 1,... M-1, u = 0,1,... U given to each user (u) is different. ). Here, M is the modulation multi-value number, and U is the number of users. FIG. 8 shows an example of frequency arrangement for each user. FIG. 8 (a) shows an example in which carriers at the time of modulation are arranged and arranged for each user (when u = 0, 1). FIG. 8B shows an example in which the user is distributed for each user (when u = 0, 1).

  As shown in FIG. 8, since carriers for multiple levels of modulation are arranged for each user without overlapping, when receiving signals from a plurality of users on the base station side, Even if the signal power of the CDMA is different, the influence of the perspective problem peculiar to CDMA is reduced and the deterioration of the communication quality can be suppressed.

  As described above, according to this embodiment, when multiple users (terminals) transmit simultaneously in DS-CDMA, synchronization is performed in symbol units for each user, and multi-level modulation is performed using different carriers. Thus, the influence of the perspective problem peculiar to CDMA can be reduced.

  As described above, the present invention can be applied to a communication apparatus that performs spread spectrum directly using a code sequence.

100 Modulation unit, 110 multiplier, 120 cyclic prefix addition unit, 130 waveform shaping filter, 140 frequency conversion unit, 150 amplifier, 160 antenna, 200 antenna, 210 frequency conversion unit, 220 waveform shaping filter, 230 cyclic prefix (CP) removal unit, 240 frequency domain processing unit, 250 FFT, 260 frequency domain equalization unit, 270 correlation unit, 280 channel estimation value generation unit, 290 demodulation unit, 300, 301, 302 modulation unit, 310, 311, 312 Multiplier, 320, 321, 322 Cyclic prefix addition unit, 330, 331, 332 Waveform shaping filter, 340, 341, 342 Frequency conversion unit, 350, 351, 352 Amplifier, 360, 361, 362 Antenna.

Claims (13)

On the sending side,
Modulation means for modulating using a phase rotation sequence for modulation corresponding to the number of modulation multi-values in symbol units based on an information sequence;
Spreading means for performing spreading processing on the output of the modulating means by a phase rotation sequence that changes with a constant frequency width on the frequency axis;
With
On the receiving side,
Multiplication means for multiplying an antiphase rotation sequence obtained by antiphase rotation of the spreading phase rotation sequence used in the spreading means in symbol units;
A despreading processing unit that performs despreading by multiplying the phase rotation sequence for modulation used in the modulation unit by a reverse phase rotation sequence obtained by performing reverse phase rotation in symbol units;
Demodulation means for performing demodulation processing on the output of the despreading means;
A communication system comprising: 2. The communication according to claim 1, wherein the modulation means switches and arranges carriers corresponding to the number of modulation multi-values at a predetermined frequency interval within a range not exceeding a spread transmission signal band. system. In the despreading processing means, a cyclic prefix removing means for removing a cyclic prefix, an equalization processing means for performing equalization processing in a frequency domain on the output of the cyclic prefix removing means, The output of the equalization processing means is multiplied by the anti-phase rotation sequence obtained by converting the phase rotation sequence used in the spreading means into the frequency domain and rotated in reverse phase, and the phase rotation sequence used in the modulation means is multiplied by the frequency domain. 3. A correlation processing means for performing a correlation process for the number of modulation multi-values on the frequency domain by multiplying by the inverse phase rotation sequence that has been converted to and rotated in reverse phase, The communication system described. 4. The demodulating unit outputs demodulated data having the highest likelihood based on the correlation processing result corresponding to the number of modulation multilevels output from the despreading processing unit. The communication system according to claim 1. In the modulation means, when a transmission signal is transmitted for each user so that a plurality of users can access simultaneously, a modulation multi-valued number at a predetermined frequency interval within a range not exceeding the spread transmission signal band. It arrange | positions so that a carrier may not overlap, The communication system of any one of Claim 1 to 4 characterized by the above-mentioned. In the modulation means, when a transmission signal is transmitted for each user so that a plurality of users can access simultaneously, a modulation multi-valued number at a predetermined frequency interval within a range not exceeding the spread transmission signal band. 6. The communication system according to claim 5, wherein the carriers are distributed and arranged so as not to overlap each other or arranged in units of users. Modulation means for modulating using a phase rotation sequence for modulation corresponding to the number of modulation multi-values in symbol units based on an information sequence;
Spreading means for performing spreading processing on the output of the modulation means by a phase rotation sequence that changes with a constant frequency width on the frequency axis;
A transmitter characterized by comprising: 8. The transmission according to claim 7, wherein the modulation means switches and arranges carriers corresponding to the number of modulation multilevels at a predetermined frequency interval within a range not exceeding a spread transmission signal band. Machine. In the modulation means, when a transmission signal is transmitted for each user so that a plurality of users can access simultaneously, a modulation multi-valued number at a predetermined frequency interval within a range not exceeding the spread transmission signal band. The transmitter according to claim 7 or 8, wherein carriers are arranged so as not to overlap. In the modulation means, when a transmission signal is transmitted for each user so that a plurality of users can access simultaneously, a modulation multi-valued number at a predetermined frequency interval within a range not exceeding the spread transmission signal band. The transmitter according to claim 9, wherein the carriers are distributed so as not to overlap each other or are collectively arranged in units of users. The transmitter modulates the modulation means using the modulation phase rotation sequence for the number of modulation multi-values in symbol units based on the information series, and then spreads the output of the modulation means with a constant frequency on the frequency axis. A receiver that receives a signal that has been subjected to spreading processing by a phase rotation sequence that changes in width,
Multiplying means for multiplying an antiphase rotation sequence obtained by antiphase-rotating the phase rotation sequence for diffusion used in the spreading means by a symbol unit;
A despreading processing unit that performs despreading by multiplying the phase rotation sequence for modulation used in the modulation unit by a reverse phase rotation sequence obtained by performing reverse phase rotation in symbol units;
Demodulation means for performing demodulation processing on the output of the despreading means;
A receiver comprising: In the despreading processing means, a cyclic prefix removing means for removing a cyclic prefix, an equalization processing means for performing equalization processing in a frequency domain on the output of the cyclic prefix removing means, The output of the equalization processing means is multiplied by the anti-phase rotation sequence obtained by converting the phase rotation sequence used in the spreading means into the frequency domain and rotated in reverse phase, and the phase rotation sequence used in the modulation means is multiplied by the frequency domain. The correlation processing unit according to claim 11, further comprising: a correlation processing unit that multiplies an anti-phase rotation sequence that has been converted into an anti-phase and converted into an anti-phase and performs correlation processing for the number of modulation multi-values in the frequency domain. Receiving machine. 13. The demodulating means outputs demodulated data having the highest likelihood based on the correlation processing result for the number of modulation multilevels output from the despreading processing means. Receiver.

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