JP5663179B2 - Transmitter - Google Patents

Description

  The present invention relates to a transmission apparatus.

  In a transmission apparatus that generates a transmission signal based on an OFDM (Orthogonal Frequency Division Multiplexing) scheme, a CP (Cyclic Prefix) is inserted into a guard interval for each symbol in the transmission signal. The guard interval is also used to make the receiving side recognize the symbol boundary (symbol timing) and establish symbol synchronization, and the tail part of the symbol is copied as the CP to the head part of the symbol. It is a time interval. CP is a mechanism in which the data copied in the guard interval or the tail part of the symbol is copied to the head part of the symbol. For example, Patent Document 1 below discloses a signal transmission method as described above.

JP 2008-283416 A

  However, since the guard interval (CP) in the above prior art is generated from the tail part of the symbol, the power may not be so large depending on the data content. Since the receiving side receives not only the desired wave but also a signal to which noise has been added, if the power of the guard interval of the desired wave is not large, the influence of noise is large, and the accuracy of symbol timing may be reduced. On the receiving side, if the accuracy of the symbol timing decreases, the accuracy of the demodulated data also decreases.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to improve the accuracy of symbol synchronization.

  In order to achieve the above object, in the present invention, as a first means for solving a transmission apparatus, OFDM in which a guard portion is provided between symbols obtained by inverse Fourier transforming subcarriers based on an OFDM (Orthogonal Frequency Division Multiplexing) scheme A transmission apparatus for transmitting a signal, comprising means for providing a power increasing means for adding a second signal for increasing the power of the guard part to the first signal corresponding to the symbol.

  In the present invention, as a second solving means related to the transmission apparatus, in the first solving means, the power increasing means digitally modulates a subcarrier (unused subcarrier) that is not used for the first signal, The second signal is generated by performing an inverse Fourier transform on the unused subcarrier, and the power of the portion corresponding to the card portion of the second signal is made higher than a predetermined threshold. .

  In the present invention, as the third solving means relating to the transmitting apparatus, means for shifting the second signal in the time axis direction according to the waveform of the first signal in the second solving means is adopted. .

  In the present invention, as a fourth solving means according to the transmitting device, in the second solving means, the power increasing means uses the second signal as digital data when the unused subcarrier is fixed. A means for storing in advance and generating the second signal based on the digital data is employed.

  In the present invention, as a fifth solving means relating to the transmission device, in the fourth solving means, the power increasing means changes the reading position of the digital data in accordance with the waveform of the first signal. A means for shifting the second signal in the time axis direction is employed.

  According to the present invention, the power of the guard portion of the first signal is increased by adding the second signal to the first signal. As a result, the power of the guard portion of the transmission signal increases and the symbol timing becomes clear, so that the receiving side can recognize the symbol timing with high accuracy and improve the accuracy of symbol synchronization.

FIG. 3 is a functional block diagram of a base station A according to the first embodiment of the present invention. It is a figure which shows the example (a) of the I-axis component (a) and Q-axis component of the 2nd signal of the base station A which concerns on 1st Embodiment of this invention. It is a figure which shows the symbol produced | generated from the 1st signal and 2nd signal of the base station A which concern on 1st Embodiment of this invention. It is a functional block diagram of the base station B which concerns on 2nd Embodiment of this invention. It is a figure which shows the example of the unused subcarrier in the base station B which concerns on 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
The base station A (transmitting apparatus) according to the first embodiment is discretely arranged with a predetermined interval from other base stations (not shown), and is orthogonal frequency division multiple access (OFDMA). ) Method to communicate with the wireless terminal in the cell. As is well known, the OFDMA scheme is a type of multicarrier communication in which communication is performed using a plurality of subcarriers in an orthogonal relationship, and multiple access is realized by assigning the subcarriers to each wireless terminal. The base station A uses digital amplitude modulation and digital phase modulation as subcarrier modulation schemes.

  As illustrated in FIG. 1, the base station A includes a transmission unit 1, a reception unit 2, and a control unit 3. The transmitter 1 includes a first S / P converter 1a, a first digital modulator 1b, a first inverse Fourier transformer 1c, a second digital modulator 1d, a second inverse Fourier transformer 1e, a time shifter 1f, and an adder. 1g, a CP insertion unit 1h, and a radio signal transmission unit 1i. The second digital modulation unit 1d, the second inverse Fourier transform unit 1e, the time shift unit 1f, the addition unit 1g, and the control unit 3 constitute a power increasing unit in the present embodiment.

  The first S / P conversion unit 1a has the same number of data signals as actual data such as packet data input from the control unit 3 as subcarriers used to generate the first signal (see FIG. 3A). And each data signal is output to the first digital modulation section 1b. The first signal is a signal generated by processing of the first S / P conversion unit 1a, a first digital modulation unit 1b and a first inverse Fourier transform unit 1c described later. Details of the first signal will be described later.

The first digital modulation section 1b is provided in the same number as the subcarriers to be used, digitally modulates the divided data signals using the subcarriers, and outputs the first modulated signal to the first inverse Fourier transform section 1c. To do. The first digital modulation section 1b is digitally based on a modulation scheme instructed by the control section 3, for example, BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM, or the like. Modulate.
The first inverse Fourier transform unit 1c generates a first signal by orthogonally multiplexing each first modulated signal using fast inverse Fourier transform processing, and outputs the first signal to the adder 1g.

  The second digital modulation unit 1d digitally modulates the data signal input from the control unit 3 using subcarriers (unused subcarriers) that are not used for generating the first signal, and the second digital modulation unit 1d receives the second modulation signal as the second modulation signal. The result is output to the inverse Fourier transform unit 1e. Note that the same number of second digital modulation units 1d as unused subcarriers are provided. For example, the unused subcarrier corresponds to the subcarrier in the shaded portion of FIG. 5 in the frequency band of the OFDM signal. However, the subcarrier is not limited to this, and any unused subcarrier may be used. It may be a thing.

  The second inverse Fourier transform unit 1e generates a second signal (see FIG. 3B) by orthogonally multiplexing each second modulated signal using a fast inverse Fourier transform process, and the second signal Is output to the adder 1g. As shown in FIG. 2, the second signal has high power locally (time T1). The power of the second signal at time T1 is adjusted so that the average power is higher than a predetermined threshold value. The second signal is added to the first signal in an adder 1g described later, and the power of the corresponding portion of the first signal is increased by the power at time T1. The corresponding part of the first signal is the last part (CP scheduled part) of the symbol copied as CP (Cyclic Prefix) in the guard interval (guard part) at the head part of the symbol.

  The time shifter 1f shifts the second signal in the time axis direction so that the power of the CP planned portion is maximized when the adder 1g adds the second signal to the first signal, and the adder 1g Output to. Here, as for the CP planned portion, since the power does not increase when the convex portion of the waveform of the first signal and the concave portion of the waveform of the second signal overlap, the second signal is moved in the time axis direction so as not to overlap. Shift to.

The adding unit 1g adds the second signal to the first signal, and outputs the first signal after the addition to the CP inserting unit 1h.
The CP insertion unit 1h inserts the CP into the first signal and outputs it as an OFDM signal to the radio signal transmission unit 1i (see FIG. 3C).
The radio signal transmission unit 1i performs D / A conversion processing and up-conversion processing on the OFDM signal input from the CP insertion unit 1h, and transmits the RF band OFDM signal to the radio terminal via the antenna.

The receiving unit 2 performs demodulation processing on the OFDM signal received from the wireless terminal under the control of the control unit 3 and outputs the demodulated signal to the control unit 3.
The control unit 3 includes an internal memory composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), an interface circuit that inputs and outputs signals to and from the transmission unit 1 and the reception unit 2 The overall operation of the base station A is controlled based on the control program stored in the ROM and the signal received by the receiving unit 2. The control program stored in the ROM includes a CP power increase program, and the control unit 3 increases the power of the CP based on the CP power increase program.

Next, the operation of the base station A configured as described above will be described.
The control unit 3 generates the first signal by controlling the first S / P conversion unit 1a, the first digital modulation unit 1b, and the first inverse Fourier transform unit 1c when generating the OFDM signal. The first signal is a signal in which subcarriers digitally modulated based on actual data such as packet data are orthogonally multiplexed. The first signal is configured such that a plurality of symbols (see FIG. 3A) are connected. The last part of the symbol is a CP scheduled part that is copied as a CP, as shown in FIG.

  The control unit 3 generates the second signal by controlling the second digital modulation unit 1d, the second inverse Fourier transform unit 1e, and the time shift unit 1f. At this time, the time shift unit 1 f shifts the second signal in the time axis direction so that the convex portion of the waveform of the first signal and the concave portion of the waveform of the second signal do not overlap. The second signal is a signal obtained by orthogonally multiplexing unused subcarriers that have been digitally modulated. In the unused subcarrier, the power of the portion corresponding to the time T is increased so that the average power of the power of the second signal at the time T is higher than a predetermined threshold value. The time T in the second signal is a portion (superimposed portion) that overlaps the scheduled CP portion of the first signal shown in FIG.

  The adder 1g adds the first signal and the second signal generated as described above to increase the power of the CP planned portion of the first signal. Thereafter, the CP insertion unit 1h copies the CP scheduled portion as a CP to the head portion of the symbol as shown in FIG.

  As described above, in the first embodiment, the power of the CP scheduled portion is increased by adding the first signal and the second signal. As a result, the CP power of the OFDM signal as the transmission signal is increased and the symbol timing becomes clear, so that the receiving side can recognize the symbol timing accurately and improve the accuracy of symbol synchronization.

[Second Embodiment]
Next, a second embodiment will be described.
As shown in FIG. 4, the base station B according to the second embodiment includes a second signal generation unit 1j instead of the second digital modulation unit 1d, the second inverse Fourier transform unit 1e, and the time shift unit 1f in the transmission unit 1. It differs from the said 1st Embodiment in the point provided with. Therefore, in the base station B, the same functional components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

The base station B uses a fixed unused subcarrier for generating the second signal. For example, as shown in FIG. 5, when the total number of subcarriers is 512, 32 subcarriers at both ends on the frequency axis are used as unused subcarriers.
As illustrated in FIG. 4, the base station B includes a transmission unit 1, a reception unit 2, and a control unit 3. The transmission unit 1 includes a first S / P conversion unit 1a, a first digital modulation unit 1b, a first inverse Fourier transform unit 1c, a second signal generation unit 1j, an addition unit 1g, a CP insertion unit 1h, and a radio signal transmission unit 1i. It has. The second signal generation unit 1j and the control unit 3 constitute a power increasing unit in the present embodiment.

The second signal generation unit 1j includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). The second signal generation unit 1j stores the second signal in advance as digital data, The second signal is shifted in the time axis direction by changing the readout position according to the waveform. Note that the second signal stored as digital data can be used because unused subcarriers are fixed.
Next, the operation of the base station B configured as described above will be described.
The control unit 3 causes the second signal generation unit 1j to generate a second signal. At this time, the control unit 3 changes the reading position of the digital data to the second signal generation unit 1j so that the convex portion of the waveform of the first signal and the concave portion of the waveform of the second signal do not overlap. Thereafter, the adding unit 1g adds the first signal and the second signal. Thereby, similarly to the first embodiment, the power of the CP scheduled portion of the first signal can be increased.

  As described above, in the second embodiment, the power of the CP scheduled portion is increased by adding the first signal and the second signal. Thereby, the receiving side can recognize the symbol timing with high accuracy and improve the accuracy of symbol synchronization.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above embodiment, the average power of the second signal at the time T (superimposed portion) is set to be higher than a predetermined threshold value, but the present invention is not limited to this. For example, the peak power may be higher than a predetermined power.

A, B ... base station, 1 ... transmission unit, 2 ... reception unit, 3 ... control unit, 1a ... first S / P conversion unit, 1b ... first digital modulation unit, 1c ... first inverse Fourier transform unit, 1d ... Second digital modulation unit, 1e ... second inverse Fourier transform unit, 1f ... time shift unit, 1g ... addition unit, 1h ... CP insertion unit, 1i ... radio signal transmission unit, 1j ... second signal generation unit

Claims (4)

A transmission apparatus that transmits an OFDM signal in which a guard portion is provided between symbols obtained by inverse Fourier transforming subcarriers based on an OFDM (Orthogonal Frequency Division Multiplexing) scheme,
Power increasing means for adding a second signal for increasing the power of the guard part to the first signal corresponding to the symbol;
The power increasing means digitally modulates subcarriers (unused subcarriers) that are not used for the first signal, performs inverse Fourier transform on the unused subcarriers, generates the second signal, and 2. A transmitting apparatus, wherein power of a portion corresponding to a superimposed portion of two signals is made higher than a predetermined threshold value.   The transmission apparatus according to claim 1, wherein the power increasing unit shifts the second signal in a time axis direction according to a waveform of the first signal.   The power increasing means stores the second signal as digital data in advance when the unused subcarrier is fixed, and generates the second signal based on the digital data. Item 2. The transmission device according to Item 1.   4. The transmission according to claim 3, wherein the power increasing unit shifts the second signal in a time axis direction by changing a reading position of the digital data in accordance with a waveform of the first signal. 5. apparatus.

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