JP2006067195A - Device and method for receiving ofdm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the desired dynamic range of an A/D converter by reducing peak amplitude. <P>SOLUTION: Receiving means groups 105, 106, 107, 108 include a plurality of receiving means having an antenna and a means for converting the frequency of a signal obtained from the antenna. An adding means 109 adds the signals which is received by the plurality of receiving means. A digital converting means 110 converts the signal added by the adding means into a digital signal. A comparing means 113 compares the amplitude value or power value of the signal added by the adding means with a threshold. A changing means 109 is arranged between the receiving means and the adding means and changes the phase of at least one of a plurality of output signals from the plurality of receiving means, based on the comparison result of the comparing means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a receiving apparatus used in a wireless communication system, and more particularly to an OFDM receiving apparatus that simultaneously receives a plurality of channels.

Since a radio signal is reflected on a building wall or the like, radio propagation is in an environment subject to severe propagation distortion (fading). Accordingly, reception schemes that are resistant to propagation distortion, such as diversity receivers and adaptive array receivers that can improve reception performance using a plurality of antennas, are being studied. Further, MIMO (Multi-input Multi-output) transmission that can perform high-speed transmission even when severe propagation distortion exists has been attracting attention.
In these systems, the receiving apparatus includes a plurality of antennas, a plurality of radio units, and a plurality of A / D converters, and the received signals received by the respective antennas are converted into digital signals by the plurality of A / D converters. After that, propagation distortion is compensated by various methods by digital signal processing. However, this receiving apparatus requires a plurality of radio units and a plurality of A / D converters, and there is a problem that the mounting area thereof is greatly increased.

In order to solve this problem, a receiving apparatus has been proposed in which the center frequencies of the received signals of a plurality of antennas are slightly shifted and combined, and A / D conversion is performed collectively. According to this receiving apparatus, since the number of A / D converters required can be greatly reduced, the mounting area can be reduced.
However, when the received signals of a plurality of channels are combined, the peak amplitude may increase when the phase relationship of the combined received signals is in phase. Since the OFDM signal has a particularly large peak amplitude from the beginning, there is a possibility that the peak amplitude may be significantly increased by combining a plurality of channels. When the peak amplitude is increased, it is necessary to increase the required dynamic range of the A / D converter, and there is a problem that the power consumption increases as the dynamic range is increased.

In order to solve this problem, as a device for reducing the peak amplitude of the OFDM signal, the peak amplitude of the transmission waveform is measured on the transmission side, and when the peak amplitude is large, the time waveform generated from each subcarrier is rotated and the peak is rotated. An apparatus for reducing the amplitude has been proposed (see, for example, Patent Document 1).
JP-A-9-107345

  However, a method for reducing the peak power when combining signals received by a plurality of antennas on the receiving side has not been proposed. As described above, the conventional OFDM receiver that performs A / D conversion on a plurality of channels collectively has a problem that the peak amplitude is remarkably increased when the reception signals of the plurality of channels are combined in phase.

  In view of the above problems, the present invention provides an OFDM receiver that can reduce peak amplitude and reduce a required dynamic range of an A / D converter in an OFDM receiver that collectively performs A / D conversion of a plurality of channels. The purpose is to provide.

  According to the OFDM receiving apparatus of the present invention, in the OFDM receiving apparatus that receives an OFDM signal using a plurality of antennas and a plurality of frequency converting means, the frequency converting means for converting the frequency of the signal acquired from the antenna and the antenna is provided. A receiving means group including a plurality of receiving means, an adding means for adding the signals received by the plurality of receiving means, a digital converting means for converting the signal added by the adding means into a digital signal, and the adding means Comparing means for comparing the amplitude value or power value of the signal added by the step with a threshold value, the receiving means and the adding means, and the plurality of receiving means based on the comparison result by the comparing means Comprising phase changing means for changing at least one of the plurality of output signals from

  According to the OFDM receiving method of the present invention, in the OFDM receiving method for receiving an OFDM signal using a plurality of antennas and a plurality of frequency converting means, the antenna and the frequency converting means for converting the frequency of the signal acquired from the antenna are provided. A receiving means group including a plurality of receiving means including: converting a frequency of a signal acquired from an antenna; adding the signals received by the plurality of receiving means; converting the added signal into a digital signal; The amplitude value or power value of the received signal is compared with a threshold value, and at least one of the plurality of output signals from the plurality of receiving means is based on the comparison result between the amplitude value or power value and the threshold value. One phase is changed.

  According to the OFDM receiver of the present invention, the peak amplitude can be reduced and the required dynamic range of the A / D converter can be reduced in the OFDM receiver that collectively performs A / D conversion on a plurality of channels.

Hereinafter, an OFDM receiving apparatus and an OFDM receiving method according to embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
As shown in FIG. 1, the OFDM receiving apparatus according to the present embodiment includes a plurality of antennas 101 to 104, frequency conversion units 105 to 108, one combining unit 109, and A / D conversion provided for each antenna. Unit 110, quadrature demodulation unit 111, demodulation unit 112, and comparison unit 113.

  The plurality of antennas 101 to 104 are antennas for receiving an OFDM signal. The reception signals received by the antennas 101 to 104 are subjected to different radio distortion due to different propagation environments. In the present embodiment, the number of antennas is described as four, but the number of antennas is not limited to four and may be a plurality of antennas.

  Frequency converters 105 to 108 are connected to antennas 101 to 104, respectively, and perform frequency conversion of received signals received by the respective antennas into IF (intermediate-frequency) signals. Each frequency conversion section 105-108 sets the center frequency of the IF signal by shifting so that the received signals do not overlap each other. The amount by which the center frequency is shifted depends on the communication method and the capability of the wireless device. However, since the A / D conversion is generally performed at a time, it is preferable that the frequencies are not too far apart. With this setting, a plurality of received signals can be combined without causing interference, and A / D conversion can be performed collectively.

  The synthesizer 109 inputs and synthesizes all the signals frequency-converted by the frequency converters 105 to 108. At the time of this synthesis, the synthesis unit 109 rotates the phases of the input signals from the frequency conversion units 105 to 108 and adds all the input signals. By this processing, the peak amplitude of the signal after combining a plurality of received signals can be reduced, so that A / D conversion can be performed collectively. Details of the combining unit 109 will be described later with reference to FIG.

  The A / D converter 110 receives the output signal of the synthesizer 109 and converts this input signal into a digital signal. Since the peak amplitude of the output signal of the combining unit 109 is reduced, the required dynamic range of the A / D conversion unit 110 does not need to be significantly increased as compared with the case where the number of antennas is one. Therefore, no extra power consumption is required.

  The orthogonal demodulator 111 receives a digital signal that is an output signal of the A / D converter 110 and separates the digital signal into an I / Q signal to obtain a baseband signal. In the case of separation, the signal from one antenna can directly obtain a baseband waveform, but the signals from the remaining three antennas are further subjected to frequency conversion because the intermediate frequency of the IF signal is shifted. That is, the orthogonal demodulator 111 performs frequency conversion on the signals from the remaining three antennas by the frequency of the IF signal, and further performs different frequency conversions so that the channels of the signals do not overlap. Here, since the frequency of each signal after frequency conversion of each signal by the frequency of the IF signal signal is different, the frequency conversion performed on each signal after this frequency conversion is different. In this way, the quadrature demodulator 111 converts all signals from the four antennas into baseband signals.

  The demodulator 112 performs synchronization processing, FFT processing for OFDM signal demodulation, distortion correction processing, and the like. Further, the demodulator 112 receives a change amount of the phase rotation corresponding to each antenna from the combining unit 109, thereby performing distortion correction considering the phase rotation amount. Thereby, even when the synthesizing unit 109 changes the phase rotation amount during reception, it is possible to perform distortion correction in consideration of the phase rotation amount. The combining unit 109 may notify the demodulation unit 112 only that the phase rotation amount has changed. In this case, the demodulation unit 112 can recalculate the distortion correction amount by using the change in the phase rotation amount as a trigger.

The comparing unit 113 reads the amplitude value or power value of the output signal of the combining unit 109, for example, in symbol units, compares the value with a preset threshold value, determines that the peak amplitude is large when the value is larger than the threshold value, and combines A phase rotation amount corresponding to each antenna of unit 109 is determined. The threshold value set in advance is, for example, a level at which the A / D conversion unit 110 in FIG. 1 is not saturated. The comparison unit 113 determines the phase rotation amount for each signal corresponding to each of the antennas 101 to 104. The phase rotation amount may be switched in order from a predetermined pattern or may be switched randomly. Further, the comparison unit 113 may determine the phase rotation amount for each packet.
The comparison unit 113 includes an A / D converter. Since the A / D converter in the comparison unit 113 can be expected to withstand practical use even with a lower accuracy than the A / D conversion unit 110, the A / D converter in the comparison unit 113 is more quantum than the A / D conversion unit 110. The bit width may be set small. As a result, the circuit scale of the OFDM receiver can be reduced, and the power consumption of the OFDM receiver can also be reduced.

Next, details of the combining unit 109 will be described with reference to FIG.
The synthesizing unit 109 includes a phase rotation control unit 201 to 204 that inputs each output signal of each frequency conversion unit 105 to 108, and an addition unit 205 that adds each signal output from each phase rotation control unit 201 to 204. Yes.

  Each phase rotation control unit 201-204 inputs the phase rotation amount for each signal corresponding to each antenna 101-104 determined by the comparison unit 113, and the phase of each input signal according to these phase rotation amounts. Rotate.

  The magnitude when the phase rotation control unit 201-204 rotates the phase changes to the amplitude value of the output signal of the synthesis unit 109 or the peak amplitude of the power value when all of the phase rotation control units 201-204 are the same. There is no. For this reason, the phase rotation control units 201 to 204 do not rotate all by the same phase. Further, it is not always necessary for the phase rotation control units 201 to 204 to rotate the phase.

  Moreover, the phase rotation control units 201 to 204 each output the phase rotation amount to the demodulation unit 112.

  The adder 205 receives the output signals of the phase rotation controllers 201 to 204 and adds these signals. Further, the addition unit 205 outputs the added signal to the A / D conversion unit 110 and the comparison unit 113.

  In the above example, the comparison unit 113 determines the phase rotation amount and outputs it to the synthesis unit 109. However, the present invention is not limited to this, and the comparison unit 113 reads the amplitude value or power value of the output signal of the synthesis unit 109, for example, in symbol units, compares it with a preset threshold value, and sends the comparison result to the synthesis unit 109. You may make it output. That is, the comparison unit 113 determines that the peak amplitude is large when it is larger than the threshold value.

  In this case, only the comparison result is notified from the comparison unit 113 to the phase rotation control units 201 to 204 in the synthesis unit 109. The phase rotation control units 201 to 204 indicate that the comparison result input from the comparison unit 113 indicates that the amplitude value of the output signal or the power value of the synthesis unit 109 is large (the peak amplitude is determined to be large). ), The phase of each input signal is rotated using this as a trigger. The phase rotation amount may be individually determined by the phase rotation control units 201 to 204, or may be changed according to a predetermined procedure.

  According to the OFDM receiver and OFDM reception method of the present embodiment described above, in the OFDM receiver that collectively performs A / D conversion on signals received through a plurality of channels, the peak amplitude of the combined waveform is observed, The required dynamic range of the A / D converter can be reduced by applying a phase rotation that reduces the peak amplitude to each received signal. In addition, the OFDM receivers according to the present embodiment and all the embodiments described below are effective even if the transmitter is the same as before.

(Second Embodiment)
The OFDM receiving apparatus of this embodiment is different from the first embodiment only in the configuration of the combining unit. Other device portions are the same as those of the OFDM receiver of the first embodiment. The description of the same device portion as in the first embodiment will be omitted.
As illustrated in FIG. 3, the synthesis unit 315 of the present embodiment includes delay units 301 to 304, phase rotation control units 305 to 312, and addition units 313 and 314.
The delay units 301 to 304 are connected to the frequency conversion units 105 to 108, respectively, and output the frequency converted signals output from the frequency conversion units 105 to 108 to the phase rotation control units 305 to 308 in the next stage. Delay. The delay time is, for example, from when a signal is input to the delay units 301 to 304 to when the comparison unit 113 processes and issues instructions to the phase rotation control units 305 to 308 and the phase rotation control units 309 to 312. Set to time. That is, the phase rotation control units 305 to 308 rotate the phase of the input signal after waiting for the comparison unit 113 to determine the phase rotation amount. If phase rotation is performed in this manner, all signals input to the A / D converter 110 can be reduced to an appropriate amplitude.

Each phase rotation control unit 305 to 312 inputs the phase rotation amount for each signal corresponding to each antenna 101 to 104 determined by the comparison unit 113, and the phase of each input signal according to these phase rotation amounts. Rotate. However, the phase rotation control unit connected to the signal corresponding to each antenna is set to the same phase rotation amount. That is, phase rotation control units 305 and 309, phase rotation control units 306 and 310, phase rotation control units 307 and 311 and phase rotation control units 308 and 312 rotate the phase of each input signal according to the same phase rotation amount. .
Further, similarly to the phase rotation control units 201 to 204 of the first embodiment, the phase rotation control units 305 to 308 each output the phase rotation amount to the demodulation unit 112. Alternatively, a change in phase rotation amount is notified.

  The adder 313 inputs and adds the four signals from the phase rotation controllers 305 to 308. The adder 314 inputs and adds four signals from the phase rotation controllers 309 to 312. Adder 313 outputs the added signal to A / D converter 110, and adder 314 outputs the added signal to comparator 113.

  According to the OFDM receiver and OFDM reception method of the present embodiment described above, the combined waveform is input to the A / D converter 110 with a delay by the delay units 301 to 304, so that the comparison unit 113 Thus, the peak power of the combined waveform input to the A / D conversion unit 110 can be reduced based on the result of the peak amplitude determination performed earlier. In other words, according to the OFDM receiver of this embodiment, the peak amplitude reduction process can be performed with a slight delay by delaying the waveform input to the A / D converter 110.

(Third embodiment)
The OFDM receiving apparatus of this embodiment is different from the second embodiment only in the demodulator, and the other apparatus parts are the same as those of the second embodiment. The description of the same device portion as that of the second embodiment is omitted. In the present embodiment, the demodulation unit adjusts the delay time of the delay units 301 to 304 using the characteristics of the OFDM signal.
In the second embodiment, after the peak amplitude determination is performed by the comparison unit 113, the timing is adjusted by the synthesis unit 315 so that the synthesized waveform can be transmitted to the A / D conversion unit 110. In this embodiment, the demodulation processing is performed by adjusting the timing in consideration of the demodulation processing timing of the OFDM signal.

Prior to the description of the demodulator, the structure of the OFDM signal will be described with reference to FIG. FIG. 4 is a diagram showing a configuration of the OFDM signal. The horizontal axis is time.
As shown in FIG. 4, the OFDM signal is composed of a plurality of OFDM symbols. Each OFDM symbol has a redundant section called a guard time for absorbing a delayed wave at the head. Originally, on the demodulation side, it is ideal to set the section excluding the guard time as the FFT window, but usually the appropriate section in the OFDM symbol is used as the FFT window in consideration of the influence of synchronization loss, filter, etc. Yes. In the present embodiment, an interval excluding the guard time in the OFDM symbol is an FFT window.

Next, the OFDM receiver of this embodiment will be described with reference to FIG.
The demodulator 512 can know the timing of the FFT window by the synchronization process. Therefore, the demodulation unit 512 notifies the timing information of the FFT window of the demodulation unit 512 to the delay units 301 to 304 in the synthesis unit 315 (not shown), so that the synthesis unit 315 receives the phase rotation amount other than the FFT window. Can be switched.

  Since sections other than the FFT window are not used for the demodulation process, if the phase rotation amount changed by the synthesis unit 315 can be switched within this time, the demodulation process is not affected. Since the timing of the FFT window is known by the synchronization processing of the demodulation unit 512, the timing information of the FFT window of the demodulation unit 512 is notified to the synthesis unit 315. In response to this notification, the synthesizer 315 switches the phase rotation amount other than the FFT window.

  Similarly to the demodulation unit 112, the demodulation unit 512 performs synchronization processing, FFT processing for OFDM signal demodulation, distortion correction processing, and the like. In addition, the demodulation unit 512 performs distortion correction in consideration of the phase rotation amount by receiving the change amount of the phase rotation corresponding to each antenna from the synthesis unit 315. As a result, even when the combining unit 315 changes the phase rotation amount during reception, distortion correction can be performed in consideration of the phase rotation amount.

  According to the OFDM receiving apparatus and the OFDM receiving method of the embodiment described above, demodulation is performed by setting the timing for switching the phase rotation amount to a section (guard time in this embodiment) that is not used for demodulation. The peak amplitude can be reduced without imposing a burden on processing.

(Fourth embodiment)
Unlike the second embodiment, the OFDM receiving apparatus according to the present embodiment is different from the second embodiment in that the comparison unit 113 is removed and the demodulation unit is changed, and the other apparatus parts are the same as those in the third embodiment. The description of the same device portion as that of the third embodiment is omitted.

As shown in FIG. 6, the OFDM receiving apparatus according to the present embodiment outputs two types of information from the demodulating unit 612 to the combining unit 315. The demodulator 612 notifies the timing information described in the third embodiment to the synthesizer 315 and compares it with a threshold set in advance by the demodulator 612. If the demodulator 612 is larger than the threshold, the peak amplitude is large. Judge. That is, the demodulator 612 also performs the function performed by the comparator 113. The threshold value preset by the demodulating unit 612 is, for example, the maximum value of the dynamic range of the AD converter if the demodulating unit 612 detects a state that is really saturated. However, usually take a safety measure and set it to a slightly smaller value.
Similarly to the demodulation unit 112, the demodulation unit 612 performs synchronization processing, FFT processing for OFDM signal demodulation, distortion correction processing, and the like. Further, the demodulator 612 receives the amount of change in phase rotation corresponding to each antenna from the combiner 315, thereby performing distortion correction in consideration of the amount of phase rotation. As a result, even when the combining unit 315 changes the phase rotation amount during reception, distortion correction can be performed in consideration of the phase rotation amount.

  More specifically, for example, the timing information is output from the demodulation unit 612 to the delay units 301 to 304, and the synthesis unit 315 is caused to switch the phase rotation amount other than the FFT window. Further, when the demodulation unit 612 is larger than a preset threshold value, it is determined that the peak amplitude is large, and the phase rotation amount corresponding to each antenna of the combining unit 315 is determined. Demodulation section 612 determines the amount of phase rotation for each signal corresponding to each antenna 101-104.

  According to the OFDM receiver and the OFDM reception method of the embodiment described above, the demodulation unit obtains the peak amplitude value without newly providing a comparison unit, and the timing at which the demodulation unit switches the phase rotation amount is used for demodulation. By setting the interval not to exist, the peak amplitude can be reduced without imposing a burden on the demodulation process.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram of an OFDM receiving apparatus according to a first embodiment of the present invention. The block diagram of the synthetic | combination part of FIG. The block diagram of the synthetic | combination part in the 2nd Embodiment of this invention. The figure which shows the structure of an OFDM signal. The block diagram of the OFDM receiver concerning the 3rd Embodiment of this invention. The block diagram of the OFDM receiver concerning the 4th Embodiment of this invention.

Explanation of symbols

  101, 102, 103, 104 ... antenna, 105, 106, 107, 108 ... frequency conversion unit, 109, 315 ... synthesis unit, 110 ... A / D conversion unit, 111 ... orthogonal demodulation unit, 112, 512, 612 ... demodulation 113, comparison unit 201, 202, 203, 204, 305, 306, 307, 308, 309, 310, 311, 312 ... phase rotation control unit, 205, 313, 314 ... addition unit, 301, 302, 303 304 delay units.

Claims (4)

In an OFDM receiver that receives an OFDM signal using a plurality of antennas and a plurality of frequency conversion means,
A receiving means group having a plurality of receiving means including an antenna and a frequency converting means for converting the frequency of a signal acquired from the antenna;
Adding means for adding signals received by the plurality of receiving means;
Digital conversion means for converting the signal added by the addition means into a digital signal;
Comparison means for comparing the amplitude value or power value of the signal added by the addition means with a threshold value;
A phase change that is arranged between the receiving means and the adding means and changes at least one of the plurality of output signals from the plurality of receiving means based on the comparison result by the comparing means. An OFDM receiving apparatus comprising: means. The comparison means includes A / D conversion means for converting an analog signal into a digital signal,
2. The OFDM receiver according to claim 1, wherein the quantization bit width of the A / D conversion means is smaller than the quantization bit width of the digital conversion means.   The OFDM receiving apparatus according to claim 1 or 2, wherein the phase changing means changes the phase within a guard time of the OFDM signal. In an OFDM reception method for receiving an OFDM signal using a plurality of antennas and a plurality of frequency conversion means,
In the receiving means group having a plurality of receiving means including an antenna and a frequency converting means for converting the frequency of the signal acquired from the antenna, the frequency of the signal acquired from the antenna is converted,
Adding signals received by the plurality of receiving means;
Converting the summed signal into a digital signal;
Comparing the amplitude value or power value of the added signal with a threshold,
An OFDM receiving method, comprising: changing at least one of a plurality of output signals from the plurality of receiving means based on a comparison result between the amplitude value or power value and the threshold value.

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