JP2003143100A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve diversity reception of an OFDM signal, using a relatively simple configuration. SOLUTION: In a selection processing period set as a period other than an FFT window period, a selection control circuit 110 controls a selection circuit 102, so that transmission signals from antennas 101a-101d can be successively switched, and that the signal levels can be compared with each other. Then, in the FFT window period, the selection control circuit 110 controls the selecting circuit 102, so that the transmission signal from the antenna in the maximum signal level can be selected. Here, the selection control circuit 110 controls the selecting circuit 102, so that the switching intervals of the transmission signals can be made shorter than the response time of automatic gain control by the AGC circuit 111, and that the transmission signals from the antennas 101a-101d can be switched sequentially.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for receiving a transmission signal including an OFDM signal in which one symbol period includes a guard period and an effective symbol period. For example, the present invention relates to a diversity reception type receiving device that copes with a bad reception environment.

[0002]

[Prior Art] In terrestrial digital broadcasting in Japan and Europe,
OFDM (Orthogonal Frequency) resistant to multipath interference
Division Multiplexing: Orthogonal frequency division multiplexing is adopted. According to the OFDM method, SFN (Single
Frequency Network: Single frequency network) Since reception is possible, frequencies can be used effectively. Figure 6
It is a figure for demonstrating the symbol structural example of an OFDM signal. As shown in the figure, normally, one symbol period 501 is
It is composed of a guard period 502 and an effective symbol period 503. Further, in the guard period 502, a part behind the effective symbol period 503 is cyclically copied. With this configuration, intersymbol interference does not occur in the delayed multipath up to the length of the guard period 501.

By the way, as a receiver for terrestrial digital broadcasting, a portable receiver having a small size and being compatible with mobile reception and a vehicle-mounted mobile receiver have been proposed. Such a receiver is required to have a performance capable of stable reception even when the receiving environment becomes unstable due to fading, fluctuation of electric field strength, or the like while moving.

Diversity reception is one of the effective methods for realizing stable reception while moving.
As a conventional technique of a digital broadcasting receiver using diversity reception, there are "Digital broadcasting receiver" described in JP 2001-86091 A and JP 2001-168833 A.
As described in "OFDM receiver" described in Japanese Patent Publication No.
A method of synthesizing the selected OFDM signals after channel selection and before demodulation (called a synthesizing process on the time axis),
A method for synthesizing demodulated modulated wave symbol signals after selecting and demodulating an OFDM signal, as in "OFDM receiver" described in Japanese Patent Publication No. 001-168833 (called a synthesizing process on the frequency axis), etc. There is.

FIG. 7 is a schematic diagram of a conventional diversity receiver of the type that performs a combining process on the time axis.

In the figure, reference numerals 601 and 603 denote OFDs.
An antenna for receiving a transmission signal including an M signal, reference numerals 602 and 604 are tuners, reference numeral 605 is a synthesis circuit, reference numeral 606 is an OFDM demodulation circuit, reference numeral 607 is a demodulation / decoding circuit, and reference numeral 608 is a data output terminal. Is.

The OFDM signal selected by the tuner 602 from the transmission signals received by the antenna 601 is input to the combining circuit 605. Similarly, the OFDM selected by the tuner 604 from the transmission signals received by the antenna 603 is selected.
The signal is input to the synthesis circuit 605. Synthesis circuit 605
Is a method such as selective combining or maximum ratio combining of these two OFDM signals (for these methods, see, for example, “Shuichi Sasaoka: Wave Summit Course“ Mobile Communication ”, Ohmsha, Mar. 10, 1999, PP198). -200, 1st edition, 2nd printing ").
The OFDM demodulation circuit 606 generally extracts the signal of the effective symbol period 503 shown in FIG. 6 from the combined OFDM signal, and extracts the signal in the FFT (Fast Fourier Transfor
m: Fast Fourier Transform) to convert to a signal on the frequency axis. Thereby, the modulated wave symbol signal of each of the plurality of orthogonal frequency signals forming the OFDM signal is obtained. The demodulation / decoding circuit 607 demodulates each modulated wave symbol signal to obtain symbol data, decodes this to reproduce the data, and outputs the data from the data output terminal 608.

FIG. 8 is a schematic diagram of a conventional diversity receiver of the type that performs a combining process on the frequency axis.

In the figure, reference numerals 701 and 704 denote OFDs.
Antennas for receiving transmission signals including M signals, reference numerals 702 and 705 are tuners, and reference numerals 703 and 706 are OF.
The DM demodulation circuit, reference numeral 707 is a combining circuit, reference numeral 708 is a demodulation / decoding circuit, and reference numeral 709 is a data output terminal.

The OFDM signal selected by the tuner 702 from the transmission signals received by the antenna 701 is the OFDM signal.
It is input to the demodulation circuit 703. OFDM demodulation circuit 703
Generally extracts the signal of the effective symbol period 503 shown in FIG. 6 from the selected OFDM signal, and
FT is applied to convert to a signal on the frequency axis. As a result, the modulated wave symbol signals of each of the plurality of orthogonal frequency signals forming the OFDM signal are obtained, and the combining circuit 707 is obtained.
Entered in. Similarly, the OFDM signal selected by the tuner 705 from the transmission signals received by the antenna 704 is input to the OFDM demodulation circuit 706. The OFDM demodulation circuit 706 generally extracts the signal of the effective symbol period 503 shown in FIG. 6 from the selected OFDM signal, applies FFT to this, and converts it into a signal on the frequency axis. As a result, the modulated wave symbol signal of each of the plurality of orthogonal frequency signals forming the OFDM signal is obtained and input to the combining circuit 707. The synthesizing circuit 707 synthesizes the modulated wave symbol signals of these two systems by using a technique such as selective synthesizing or maximum ratio synthesizing. The demodulation / decoding circuit 708 demodulates each combined modulated wave symbol signal to obtain symbol data, decodes this to reproduce the data, and outputs the data from the data output terminal 709.

[0011]

By the way, as described above, the conventional diversity receiver of the type that performs the combining process on the time axis requires the same number of tuners as the antennas. In addition, OFDM selected by each tuner
A combining circuit is needed to combine the signals. On the other hand, a conventional diversity receiver of the type that performs a combining process on the frequency axis requires as many tuners and OFDM demodulator circuits as there are antennas. Further, a synthesis circuit for synthesizing the modulated wave symbol signals demodulated by the OFDM demodulation circuits is required.

As described above, the conventional diversity receiver requires the same number of tuners as the number of antennas or tuners and OFDM demodulation circuits. In addition, a combining circuit for combining the OFDM signal or the modulated wave symbol signal is required. Therefore, there is a problem that the device configuration becomes large and the cost increases.

The present invention has been made in view of the above circumstances, and an object of the present invention is to have a relatively simple structure and to perform OFDM.
It is to realize diversity reception of signals.

[0014]

In order to solve the above problems, a receiving apparatus of the present invention receives a transmission signal including an OFDM signal in which one symbol period includes a guard period and an effective symbol period. .

The receiving apparatus of the present invention comprises a plurality of antennas for receiving the transmission signal, a selection unit for selecting one of the transmission signals received by the plurality of antennas, and the selection unit. From the tuner that selects the OFDM signal from the selected transmission signal and the symbol period of the OFDM signal that is selected by the tuner, the FFT
(Fast Fourier Transform) A signal located within the window period is extracted, FFT is applied to the extracted signal, and the OFDM
An OFDM demodulation unit that demodulates a modulated wave symbol signal of each orthogonal frequency signal that forms a signal, and a selection control unit that controls the selection circuit are included.

In the symbol period other than the FFT window period, the selection control unit sequentially switches the transmission signals from the plurality of antennas to compare the signal levels, and according to the comparison result, the FFT window. The selection unit is controlled to determine the transmission signal from the antenna to be selected during the period and select the transmission signal from the determined antenna.

According to the receiving apparatus of the present invention, the transmission signals from the plurality of antennas can be input to the selecting unit, and the selecting unit can select the transmission signal of the antenna having the best reception level. For this reason, the processing means after the selection section including the tuner and the OFDM demodulation section can be one system, so that the OF has a relatively simple configuration.
A DM signal diversity receiver can be realized.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

First, a first embodiment of the present invention will be described.

FIG. 1 is a schematic diagram of a diversity receiver to which the first embodiment of the present invention is applied.

In the figure, reference numerals 101a to 101d are O.
An antenna for receiving transmission signals including FDM signals,
Reference numeral 102 is a selection circuit, reference numeral 103 is a tuner, reference numeral 1
Reference numeral 04 represents an ADC circuit (Analog Digital Converter), reference numeral 105 represents an orthogonal demodulation circuit,
Reference numeral 106 is an FFT circuit, reference numeral 107 is a demodulation / decoding circuit, reference numeral 108 is a data output terminal, and reference numeral 109 is an FFT.
A window setting circuit, reference numeral 110 is a selection control circuit, and reference numeral 111 is an AGC (Auto Gain Control) circuit. Here, the quadrature demodulation circuit 105 and F
The FT circuit 106 corresponds to an OFDM demodulation circuit. In addition,
In this embodiment, the case where four antennas are used will be described, but the number of antennas may be any number of two or more.

The transmission signal received by each of the antennas 101a to 101d is input to the selection circuit 102. The selection circuit 102 selects the transmission signal received by one of the antennas 101a to 101d according to the selection control signal from the selection control circuit 110.

The tuner 103 selects a desired OFDM signal designated by an operator or the like from the transmission signals selected by the selection circuit 102. And the OFD selected
The M signal is automatically gain controlled according to the AGC signal from the AGC circuit 111 to be converted into an OFDM signal of an intermediate frequency,
Output to the DC circuit 104.

The ADC circuit 104 converts the intermediate frequency OFDM signal output from the tuner 103 into a digital signal and outputs the digital signal to the orthogonal demodulation circuit 105. In response to this, the orthogonal demodulation circuit 105 receives the digitized OF.
Convert the DM signal to a complex baseband OFDM signal.

The FFT circuit 106 outputs an FF from the complex baseband OFDM signal output from the ADC circuit 104.
A signal included in the FFT window period set by the T window setting circuit 109 is extracted. Then, FFT is performed on the extracted signal to convert it into a signal on the frequency axis. This makes O
The modulated wave symbol signal of each of the plurality of orthogonal frequency signals forming the FDM signal is obtained.

The FFT window setting circuit 109 includes a tuner 10
The FFT window period for extracting the signal from the symbol period is set at the optimum position corresponding to the multipath included in the OFDM signal selected by 3. And this F
The first period signal for specifying the FT window period is generated and output to the FFT circuit 106, and the FFT window period and F
A second period signal for specifying a period between the FT window period (corresponding to the symbol period-FFT window period) is generated and output to the selection control circuit 110.

As described above, SFN is used in the OFDM system.
It is possible to build In reception at the SFN, all transmission waves from stations other than the currently receiving station are observed in the same manner as multipath interference. Compared with normal multipath interference, this interference includes not only a path that arrives later than the desired received wave, but also a path that arrives in advance. Therefore, when the OFDM signal having the symbol configuration shown in FIG. 6 is used as the desired received wave, if the effective symbol period 503 is extracted as it is, a signal that has undergone intersymbol interference with the symbol 501 located before the extraction target symbol 501. Will be used, and the reception performance will deteriorate. Therefore, the FFT window setting circuit 109 sets the period during which no intersymbol interference occurs as the FFT window period.

FIG. 2 shows an OF subject to multipath interference.
It is a figure for demonstrating a DM signal. Here, reference numeral 80
Reference numeral 1 is a desired received wave, reference numeral 802 is a delayed multipath, and reference numeral 803 is a previously arrived multipath. As shown in the figure, from the symbol n of the desired received wave 801, the inter-symbol interference due to the symbol n-1 one before in the multipath 802 that arrived late and the one after the symbol n-1 in the multipath 803 that arrived in advance. It is necessary to extract the signal included in the period 804 having the same length as the effective symbol period, which is not affected by the inter-symbol interference due to the symbol n + 1. This extraction period 804 is called the FFT window period. F
The FT window period is adaptively controlled by examining the delay profile and the symbol correlation.

Regarding the setting of the FFT window period, Japanese Patent Publication No. 2963895 (Japanese Patent Laid-Open No. 2000-02265).
"Orthogonal Frequency Division Multiplexing Receiver"
And Japanese Patent No. 3022854 (Japanese Patent Laid-Open No. 2000-13
No. 4176), "Delay profile analysis device and symbol synchronization method".

The demodulation / decoding circuit 107 includes an FFT circuit 10
Each modulated wave symbol signal output from 6 is demodulated to obtain symbol data, which is decoded to reproduce the data and output from the data output terminal 108.

The AGC circuit 111 measures the average power of the intermediate frequency OFDM signal digitized by the ADC circuit 104. Then, an AGC signal is generated and output so that this measured value becomes a predetermined reference value, and the tuner 10
3 to perform automatic gain control of the selected OFDM signal.

The selection control circuit 110 sets the selection processing period during the period specified by the second period signal output from the FFT window setting circuit 109. During this selection processing period, the selection circuit 102 is controlled using the selection control signal, the antennas 101a to 101d to be used are switched in order, and the output signals of the orthogonal demodulation circuits 105 of the antennas 101a to 101d (complex baseband OFDM signal )
Compare levels. Then, the antennas 101a to 101d to be selected are determined according to the comparison result (in the present embodiment, the antennas 101a to 1d having the highest signal level are selected.
01d is determined as a selection target), so that the transmission signals from the determined antennas 101a to 101d are selected,
The selection circuit 102 is controlled using the selection control signal.

FIG. 3 is a diagram for explaining the operation of the selection control circuit 110.

In the figure, reference numeral 201 is a period indicating the level of the complex baseband OFDM signal obtained from the transmission signal of the antenna (here, antenna 101b) selected at the previous time, that is, the symbol n-1, and the reference numeral 2
06 is a period indicating the level of a complex baseband OFDM signal obtained from the transmission signal of the antenna (here, antenna 101a) selected at the time of this time, that is, the symbol n. Reference numeral 202 denotes a period indicating the level of the complex baseband OFDM signal obtained from the transmission signal of the antenna 101a, reference numeral 203 denotes a period indicating the level of the complex baseband OFDM signal obtained from the transmission signal of the antenna 101b, and reference numeral 204 Is a period indicating the level of the complex baseband OFDM signal obtained from the transmission signal of the antenna 101c, and reference numeral 205 is the antenna 101
This is a period indicating the level of the complex baseband OFDM signal obtained from the transmission signal of d. Further, reference numeral 207 is a selection processing period, and reference numeral 208 is a period specified by the second period signal.

Here, in order to simplify the explanation, the FFT window period is set without considering multipath. That is, the effective symbol period is set to the FFT window period. In this case, the period 2 specified by the second period signal
08 corresponds to the guard period.

During the period 201, since the tuner 103 and the AGC circuit 111 operate the AGC function, the average signal level of the complex baseband OFDM signal obtained from the transmission signal of the previously selected antenna is a steady level value. Shows.

Now, the selection control circuit 110 sets the selection processing period 207 within the period 208 specified by the second period signal received from the FFT window setting circuit 109.
Then, in the selection processing period 207, the selection circuit 102 is controlled using the selection control signal, and the antenna 10 to be used is used.
1a to 101d are switched in order. Thereby, in each of the periods 202 to 205, the average signal level of the complex baseband OFDM signal obtained from the transmission signals of the corresponding antennas 101a to 101d is measured.

Here, in this embodiment, the AGC circuit 11 is used.
The response speed (time) of the AGC signal from 1 is 202
It is assumed that the time is set to be longer than each of .about.205. Therefore, in each of the periods 202 to 205, the AGC function of the tuner 103 does not work on the complex baseband OFDM signal output from the orthogonal demodulation circuit 105. Therefore, the complex baseband OFDM signal output from the orthogonal demodulation circuit 105 in each of the periods 202 to 205 corresponds to the corresponding antenna 101a to
The strength of the signal level of the transmission signal from 101d appears as it is. Therefore, among the periods 202 to 205, the antennas 101a to
101d is the antenna with the highest transmission signal level.

In the example shown in FIG. 3, the average signal level in the period 202 is the highest, and therefore the selection control circuit 110
Controls the selection circuit 102 using the selection control signal so that the transmission signal from the antenna 101a is selected.
As a result, in the period 206, the antenna 101a is selected as the antenna selected this time.

Here, in the present embodiment, the AGC circuit 11
The response speed (time) of the AGC signal from 1 is the period between the selection processing period 207 and the FFT window period (<period 208-
It is set to be shorter than the selection processing period 207). Therefore, the AGC function of the tuner 103 operates before the start of the FFT window period, and the average signal level of the complex baseband OFDM signal obtained from the transmission signal of the antenna selected this time settles to a steady level.

The first embodiment of the present invention has been described above.

According to the present embodiment, with the above configuration,
The transmission signals from the plurality of antennas 101a to 101d are input to the selection circuit 102, and the transmission signal of the antennas 101a to 101d having the best reception level is selected by the selection circuit 102. Therefore, as shown in FIG. 1, the processing circuits after the selection circuit 102 can be made into one system, so that the diversity receiving apparatus of the OFDM signal can be realized with a relatively simple configuration.

Next, a second embodiment of the present invention will be described.

FIG. 4 is a schematic diagram of a diversity receiver to which the second embodiment of the present invention is applied. Here, parts having the same functions as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals.

The present embodiment is different from the first embodiment shown in FIG. 1 in that the selection control circuit 110 and the AGC circuit 111.
Instead of the selection control circuit 301 and the AGC circuit 302
Was used. Others are the same as those in the first embodiment shown in FIG.

The AGC circuit 302 measures the average power of the intermediate frequency OFDM signal digitized by the ADC circuit 104, generates and outputs the AGC signal so that the measured value becomes a predetermined reference value, and the tuner 103 is made to perform automatic gain control of the selected OFDM signal. This point is similar to the first embodiment, except that during the period when the AGC stop signal is output from the selection control circuit 301, A
The AGC circuit 1 according to the first embodiment is different in that the GC function is stopped.
Different from 11.

The selection control circuit 301 sets the selection processing period during the period specified by the second period signal output from the FFT window setting circuit 109. During this selection processing period, the selection circuit 102 is controlled using the selection control signal, the antennas 101a to 101d to be used are switched in order, and the output signals of the orthogonal demodulation circuits 105 of the antennas 101a to 101d (complex baseband OFDM signal )
Compare levels. Then, the antennas 101a to 101d to be selected are determined according to the comparison result (in the present embodiment, the antennas 101a to 1d having the highest signal level are selected.
01d is determined as a selection target), so that the transmission signals from the determined antennas 101a to 101d are selected,
The selection circuit 102 is controlled using the selection control signal. This point is similar to the selection control circuit 110 of the first embodiment described above. However, the selection control circuit 301 of the present embodiment further outputs an AGC stop signal for stopping the AGC function to the AGC circuit 302 during the set selection processing period.

FIG. 5 is a diagram for explaining the operation of the selection control circuit 301. Here, the same reference numerals are given to the same period as each period shown in FIG.

In the period 201, since the tuner 103 and the AGC circuit 302 operate the AGC function, the average signal level of the complex baseband OFDM signal obtained from the transmission signal of the previously selected antenna is a steady level value. Shows.

Now, the selection control circuit 301 sets the selection processing period 207 within the period 208 specified by the second period signal received from the FFT window setting circuit 109.
Then, in the selection processing period 207, the selection circuit 102 is controlled using the selection control signal, and the antenna 10 to be used is used.
1a to 101d are switched in order. Thereby, in each of the periods 202 to 205, the average signal level of the complex baseband OFDM signal obtained from the transmission signals of the corresponding antennas 101a to 101d is measured.

Here, in the present embodiment, the selection processing period 2
During 07, the selection control circuit 301 outputs an AGC stop signal. As a result, the AGC circuit 302 and the tuner 103 stop the AGC function during the selection processing period 207. Specifically, the AGC circuit 302 uses the selection processing period 2
During 07, the signal value of the AGC signal immediately before the AGC function stop is maintained as it is, that is, the AGC circuit 302 holds the gain immediately before the AGC function stop, or outputs the AGC signal having a predetermined signal value. FIG. 4 shows an example of the former.

Therefore, in each of the periods 202 to 205, the AGC of the tuner 103 is applied to the complex baseband OFDM signal output from the orthogonal demodulation circuit 105.
Function does not work. Therefore, the complex baseband OFDM signal output from the orthogonal demodulation circuit 105 in each of the periods 202 to 205 is included in the corresponding antenna 10
The strength of the signal level of the transmission signal from 1a to 101d appears as it is. Therefore, of the periods 202 to 205, the antenna 10 corresponding to the period in which the maximum average signal level is shown.
1a to 101d are antennas having the highest transmission signal level.

In the example shown in FIG. 5, the average signal level in the period 202 is the highest, and therefore the selection control circuit 301
Controls the selection circuit 102 using the selection control signal so that the transmission signal from the antenna 101a is selected.
As a result, in the period 206, the antenna 101a is selected as the antenna selected this time.

Now, when the selection processing period 207 ends, that is, when the period 206 starts, the control control circuit 301 sets A
Stop the output of the GC stop signal. As a result, the AGC function of the AGC circuit 302 and the tuner 103 is restarted, and the average signal level of the complex baseband OFDM signal obtained from the transmission signal of the antenna selected this time quickly settles to a steady level value.

The second embodiment of the present invention has been described above.

According to the present embodiment, in addition to the effect of the first embodiment, the response speed of the AGC operation is not limited, so that the response speed of the AGC operation can be freely set. .

The present invention is not limited to the above embodiment, but various modifications can be made within the scope of the gist thereof.

For example, in each of the above-described embodiments, the selection control circuits 110 and 301 perform the selection processing period 20 according to the second period signal output from the FFT window setting circuit 109.
7 is set within the symbol period other than the FFT window period. However, when the FFT window period is fixed to the effective symbol period, the guard period may be specified from the FFT window period and the symbol period and set within this guard period.

In each of the above embodiments, the AGC
The present invention is effective for a configuration that does not require the circuits 111 and 302.

[0060]

As described above, according to the present invention,
Diversity reception of an OFDM signal can be realized with a relatively simple configuration.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a diversity receiver to which a first embodiment of the present invention is applied.

FIG. 2 is a diagram for explaining an OFDM signal that is subject to multipath interference.

FIG. 3 is a diagram for explaining the operation of the selection control circuit 110 shown in FIG.

FIG. 4 is a schematic diagram of a diversity receiver to which a second embodiment of the present invention is applied.

5 is a diagram for explaining the operation of the selection control circuit 301 shown in FIG.

FIG. 6 is a diagram for explaining a symbol configuration example of an OFDM signal.

FIG. 7 is a schematic diagram of a conventional diversity receiver.

FIG. 8 is a schematic diagram of a conventional diversity receiver.

[Explanation of symbols]

101a to 101d ... Antenna, 102 ... Selection circuit, 1
Reference numeral 03 ... Tuner, 104 ... ADC circuit, 105 ... Quadrature demodulation circuit, 106 ... FFT circuit, 107 ... Demodulation / decoding circuit, 108 ... Data output terminal, 109 ... FFT window setting circuit, 110, 301 ... Selection control circuit, 111, 302 ...
AGC circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsutomu Noda             292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Ceremony Hitachi Digital Media Development Book             Department (72) Inventor Hiroki Uchiyama             2-6-35 Hironodai, Zama City, Kanagawa Prefecture             In ceremony company Xanavi Informatics F-term (reference) 5K022 DD01 DD33

Claims (8)

[Claims] 1. An OFDM (Orthogonal Fres) in which one symbol period includes a guard period and an effective symbol period.
A receiving device for receiving a transmission signal including a quency division multiplexing signal, wherein a plurality of antennas for receiving the transmission signal, and a selecting unit for selecting one from the transmission signals received by the plurality of antennas And the OF from the transmission signals selected by the selector.
A tuner for selecting a DM signal, and a signal located within an FFT (Fast Fourier Transform) window period are extracted from a symbol period of the OFDM signal selected by the tuner, the extracted signal is subjected to FFT, and the OFDM An OFDM demodulation unit that demodulates a modulated wave symbol signal of each orthogonal frequency signal that forms a signal, and a selection control unit that controls the selection circuit, wherein the selection control unit is a symbol period other than an FFT window period. In, the transmission signals from the plurality of antennas are sequentially switched to compare the signal levels, the transmission signal from the antenna to be selected in the FFT window period is determined according to the comparison result, and The receiving device, wherein the selecting unit is controlled so as to select the transmission signal. 2. The receiving device according to claim 1, wherein the selection control unit determines the transmission signal from the antenna having the highest signal level as a selection target. 3. The receiving device according to claim 1, wherein the tuner has an AGC (Auto Gain Control) function for automatically controlling the gain so as to keep the signal level of the selected OFDM signal constant. However, the response time of the automatic gain control is set to be longer than a switching interval of the transmission signals from the plurality of antennas performed by the selection control unit in a symbol period other than the FFT window period. Receiver. 4. The receiving device according to claim 3, wherein the response time of the automatic gain control is such that the selection control unit performs switching of the transmission signals from the plurality of antennas in a symbol period other than an FFT window period. The receiving device is set to be shorter than the interval from the end time point to the start time point of the FFT window period. 5. The receiving device according to claim 1, wherein the tuner has an AGC (Auto Gain Control) function for automatically controlling gain so as to keep a signal level of the selected OFDM signal constant. However, the selection control unit may stop the AGC function of the tuner during a period in which the selection control unit sequentially switches the transmission signals from the plurality of antennas in a symbol period other than an FFT window period. Characteristic receiving device. 6. The receiving device according to claim 5, wherein the tuner selects a signal of the OFDM signal so that the gain becomes a gain immediately before the AGC function is stopped during the period in which the AGC function is stopped. A receiving device characterized by performing level gain control. 7. The receiving apparatus according to claim 1, further comprising an FFT window setting section for setting an FFT window period in the OFDM demodulation section. apparatus. 8. The receiver according to claim 1, 2, 3, 4, 5 or 6, wherein the FFT window period matches the effective symbol period.