JP2815340B2 - OFDM receiving apparatus, relay apparatus, and transmission monitoring apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
The present invention relates to a transmission device, a reception device, a relay device, and a transmission management device of an OFDM system for modulating and transmitting / receiving by an FDM (orthogonal frequency division multiplexing) method, and particularly to monitoring signal distortion of a transmission line, a transmission station, a relay station, a reception device, and the like. And an automatic gain control operation (AGC operation).

[0002]

2. Description of the Related Art As a future digital broadcasting transmission system,
Although the OFDM system is considered to be promising, this system uses a large number of carriers and the allocation of information to each subchannel can be set arbitrarily, so that flexible information transmission such as not using a specific carrier is possible. . This OFDM system is described in the Journal of the Institute of Television Engineers of Japan, Vol.
l. 50, no. 1 pp24-28, “Digital Television Broadcasting Technology and Trends”
-28 "Modulation technology of digital broadcasting" (author: Aiichiro Tsutake).

A conventional example of a typical OFDM transmitting / receiving apparatus will be described with reference to the drawings. FIG. 5 is a configuration diagram of a conventional OFDM transmission / reception apparatus, FIG. 6 is a frequency spectrum diagram of a general OFDM transmission signal, and FIG. 7 is a frame configuration diagram of a general OFDM transmission signal.

In FIG. 5, an OFDM transmitting apparatus (B) 3
In the case of 0, the input transmission data 26 is converted to the data conversion unit (A).
After performing processing such as serial-parallel conversion and error correction code addition in 1, symbols are assigned to each carrier of the OFDM transmission signal, and the next-stage inverse discrete Fourier transform unit 3 converts the signal into a transmission signal wave on the time axis. The signal is converted into a high-frequency signal by the transmission high-frequency unit 4 and transmitted to the transmission line 6.

The transmission path 6 is generally a free space, and transmission signals are transmitted by radio waves. A transmission antenna and a reception antenna are also included in the transmission path 6. When viewed from the frequency axis, the frequency spectrum of the OFDM transmission signal is 1 in FIG.
As shown in Fig. 6, the frequency spectrum becomes almost rectangular,
Further, as shown in the enlarged views of a and b in FIG.
Generally, it is composed of hundreds to thousands of multicarriers such as -1, fn, fn + 1, and the like. As to which carrier is used, the assignment of each carrier is arbitrary as long as the receiving device is known in advance.

FIG. 7 shows a frame configuration diagram of a general OFDM transmission signal. When the OFDM transmission signal is viewed from the time axis, one frame period starts from a specific synchronization symbol for frame synchronization on the receiving side and extends to the next synchronization symbol. As shown in FIG. 7, if the number of symbols from the synchronization symbol to immediately before the next synchronization symbol is m + 1, one frame is m + 1 symbols.

The waveform of each symbol is represented by fn-
This is a waveform obtained by synthesizing hundreds to thousands of multicarriers such as 2, fn-1, fn, and fn + 1. Regarding which carrier to use for each symbol, the assignment of each carrier is arbitrary as long as the receiving device is known in advance.

[0008] The ΟFDM transmission signal passed through the transmission line 6 in FIG. 5 is transmitted to the reception high frequency section (A) of the OFDM receiver (B) 31.
7, the signal is converted into an intermediate frequency by a frequency conversion circuit (not shown), converted from a high-frequency signal into a baseband signal by an orthogonal conversion circuit (not shown), and input to the discrete Fourier transform unit 8.

In the discrete Fourier transform unit 8, the allocation data for each symbol is restored. The restored data is subjected to parallel-to-serial conversion by the data converter 10 and subjected to processing such as error correction processing, and then the original data string is restored as received data 27.

Here, in the OFDM receiver (B) 31, the level detection signal 13 as signal strength information is extracted from the reception high frequency section 7 and input to an AGC (automatic gain control) signal generation section (B) 25. The AGC signal generation section (B) 25 generates an AGC signal 24 based on the input level detection signal 13, and the AGC signal is supplied to the reception high frequency section (A) 7.

As described above, in the OFDM receiver 31,
Even when the signal strength is not constant, the gain of the receiving high-frequency unit 7 is controlled by the AGC signal 24, whereby the signal level after the receiving high-frequency unit 7 becomes constant.

As described above, the conventional OFDM transmission / reception method uses OFD such as inverse discrete Fourier transform or discrete Fourier transform.
Except for processing specific to M, there are few parts that are significantly different from conventional high-frequency transmitting and receiving apparatuses, such as high-frequency signal conversion and data processing and AGC operation.

[0013]

SUMMARY OF THE INVENTION However, OFD
The M system is a multi-carrier system, is resistant to frequency-selective fading, and has the following disadvantages in addition to the advantages that ghost interference can be reduced by providing a guard interval.

One of the drawbacks is that the OFDM system uses many carriers, so if there is non-linear distortion in the transmission line and the transmission / reception system, a disturbing wave is generated in the frequency band of the OFDM itself due to intermodulation, and the characteristics are deteriorated. Is generated. It is considered that a measure for dealing with this drawback is difficult in principle, and there is no specific solution at present.

In general, the intermodulation is generated by combining the sum and difference of the fundamental wave, the second-order distortion, the third-order distortion, etc. of each carrier when a carrier exists at equal intervals and there is a transmission line distortion, that is, non-linearity. The distortion interference wave falls into its own signal band.
However, as the number of carrier waves increases, the number of combinations of the distortion interference waves increases, so that the degree of interference increases. In particular, O
In the case of the FDM system, since there are hundreds to thousands of multicarriers as described above, the FDM system is much more vulnerable to distortion than the conventional single carrier system.

Further, it is difficult to completely eliminate the non-linearity due to the inherent characteristics of an amplifier circuit element such as a transistor. Extremely good is required. For this reason, the AGC operation of the OFDM receiver requires extremely strict performance compared to the conventional single carrier system.

Further, in the conventional example, as shown in FIG. 5, only the level detection signal 13 as signal strength information is used for performing the AGC operation. For this reason, even if the AGC operation is performed so that the signal level after the reception high-frequency unit 7 becomes constant, whether the intermodulation interference satisfies the required performance can be determined by both the user and the OFDM receiver itself. There was a big disadvantage that there was no.

It is an object of the present invention to monitor intermodulation interference which has been difficult in the conventional system, and this monitoring not only makes the AGC operation to keep the signal level constant, but also
OF for better performance against intermodulation interference
An object of the present invention is to provide a DM type transmitting device, receiving device, relay device, and transmission monitoring device.

[0019]

In order to solve the above problems, the present invention employs the following characteristic constituent means. A first feature of the present invention is that when a digital signal is assigned to a plurality of orthogonal carriers in a transmission band and subjected to inverse discrete Fourier transform, among the plurality of carriers in the transmission band,
One or more specific carrier waves other than the lowermost and uppermost carrier waves and known at the receiving side are stopped according to the specific regularity known at the receiving side and are not transmitted. O
An amplifying means for receiving a transmission signal from an FDM type transmission device, receiving the transmission signal, generating a reception level detection signal from a change in reception intensity, and amplifying and outputting the signal at a gain determined by a gain control signal. And a discrete Fourier transform means for performing a discrete Fourier transform on the received signal output from the means, and the discrete specific Fourier transform output of the means includes the known specific one wave or the specific plurality of carriers and conforming to the regularity. A discrete Fourier transform value separating and extracting means for separating and extracting a discrete Fourier transform value of a stop period in a carrier wave; and combining the discrete Fourier transform value extracted by this means as distortion information of a received signal with the reception level detection signal to obtain a gain. Automatic gain control means for automatically controlling the gain of the amplification means by generating a control signal and applying the control signal to the amplification means. It is constructed and was able to.

[0020] A second feature of the present invention is that, as a result of the automatic gain control operation by the automatic gain control means, when the distortion information of the received signal does not satisfy required distortion characteristics, an alarm for notifying an alarm. A notification means is provided, and the user is notified of the presence of distortion in the transmission path or the receiving device by the alarm notification.

A third feature of the present invention is that when a digital signal is assigned to a plurality of mutually orthogonal carriers in a transmission band and subjected to inverse discrete Fourier transform, the lowest one of the plurality of carriers in the transmission band and One or more specific carriers other than the uppermost carrier and known at the receiving end,
OFDM transmitted from an OFDM transmission device that stops and does not transmit according to a specific rule known on the receiving side
An OFDM relay apparatus for receiving and retransmitting a signal, comprising: selecting means for selecting a reception signal and a transmission signal of the OFDM signal as needed, and discrete Fourier transform means for performing a discrete Fourier transform on the OFDM signal selected by the means. Discrete Fourier transform value separation and extraction means for separating and extracting from the output of this means the discrete specific Fourier transform value of a stop section in the known specific one or specific plurality of carriers and the carrier wave in accordance with the regularity; , Using the discrete Fourier transform value obtained by this means as distortion monitoring information of the received signal,
Monitor the distortion state of the reception signal or transmission signal of the M signal,
When the distortion information of the signal does not satisfy the required distortion characteristics, there is provided an alarm notifying means for notifying an alarm, thereby notifying the user that the distortion exists in the transmission path or the relay transmission / reception signal by the alarm notification. That is.

When the digital signal is assigned to a plurality of carriers orthogonal to each other in a transmission band and subjected to inverse discrete Fourier transform, a plurality of carriers in the transmission band other than the lowermost and uppermost carriers and the receiving side A specific one known at
A transmission monitoring apparatus used in an OFDM transmission apparatus for stopping a wave or a plurality of specific carrier waves according to a specific regularity known on a receiving side and not transmitting the transmission wave, the transmission monitoring apparatus comprising: Discrete Fourier transform means for taking an output and performing a discrete Fourier transform, and a stop query in the known specific one or a plurality of carriers and a carrier in accordance with the known specific regularity from the output of the output. Discrete Fourier transform value separating and extracting means for separating and extracting the discrete Fourier transform value of the above, and the discrete Fourier transform value extracted by this means is used as distortion monitoring information of the transmission signal, and the distortion state of the transmission signal is monitored based on this information. And alarm notification means for notifying a warning when the distortion information of the signal does not satisfy the required distortion characteristics, and transmitting the transmission signal of the transmission line or the transmitting station to the user by the warning notification. It is to notify that the distortion is present in the.

[0023]

[0024]

[0025]

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an OFDM transmission / reception system according to a first embodiment of the present invention, FIG. 2 is a frequency spectrum diagram of an OFDM transmission signal in a specific symbol period of the present invention, and FIG. It is an illustration of a frequency spectrum diagram of a Fourier transform result. In FIG. 1, the same portions as those in FIG. 5 are denoted by the same reference numerals, and the duplicate description will be omitted.

In FIG. 1, an OFDM transmitter (A) 2
The transmission data 26 input to the data conversion unit 8 is a data conversion unit (A)
After undergoing serial-to-parallel conversion in 1 and performing processing such as addition of an error correction code, symbols are assigned to each carrier of the OFDM transmission signal and input to the timing synthesis section 2. The timing synthesizing unit 2 inserts a zero symbol, that is, one specific wave or a plurality of specific carriers, out of the input signal so as to be stopped during a specific one symbol period or a specific plurality of symbol periods and not transmitted. .

The specific one wave or specific plural carriers and the specific one symbol section or the specific plural symbol sections conform to a specific regularity known on the OFDM receiving apparatus side and the OFDM relay station.

The output signal of the timing synthesizing unit 2 into which the zero symbol is inserted is converted into a transmission signal wave on the time axis by an inverse discrete Fourier transform unit 3 at the next stage, and is converted into a high-frequency signal by a transmission high-frequency unit 4. The transmission OFDM signal 5 is transmitted to the transmission path 6.

The OFDM transmission signal frequency spectrum in one specific symbol section in which zero symbols are inserted as described above, for example, symbol section S shown in FIG. 7, is fn-2 as shown in the enlarged view of a and b in FIG. , Fn-1, fn
The carrier wave corresponding to fn in FIG. 6 is not transmitted only during the symbol section S.

In the example shown in FIG. 2, since the level of the interfering signal generated as a result of intermodulation generally becomes highest near the center of the multicarrier, the carrier fd in the center is not transmitted without interruption. It is not necessary. Also,
Since a specific wave or a plurality of specific carriers other than the lowermost and uppermost carriers of the OFDM transmission signal are not stopped and non-transmitted, they are hardly affected by interference of adjacent channels, and are not affected by intermodulation interference described later. Monitoring can be performed more accurately.

The OFDM transmission signal that has passed through the transmission line 6 in FIG. 1 passes through a high-frequency amplifier circuit (not shown) in the reception high-frequency section (A) 7 of the OFDM receiver (A) 29, and is then converted to an intermediate signal by a frequency conversion circuit (not shown). The frequency is converted to a baseband signal from a high-frequency signal by an orthogonal transformation circuit (not shown), and the converted signal is input to the discrete Fourier transform unit 8.

In the discrete Fourier transform unit 8, the allocated data for each symbol is restored, and the data is converted into parallel / serial data by the data converter 10, and then subjected to processing such as error correction code processing. The received data 27 is restored.

Here, the discrete Fourier transform unit 8 restores the allocated data for each symbol.
If no nonlinear distortion occurs in the reception high-frequency section (A) 7 of the FDM receiver 29, the frequency spectrum of the result of the discrete Fourier transform in a specific symbol period S becomes the same as that in FIG. If there is nonlinear distortion, an interfering wave fd resulting from intermodulation interference is output as shown in FIG.

The zero symbol separation unit 9 separates the level data of the interference wave fd shown in FIG. 3 and outputs it to the AGC signal generation unit (A) 11 in the form of interference data 12 as distortion information of the received signal. The other received data is output to the data converter (デ ー タ) 10 at the next stage. This operation is possible because the specific one wave or specific plural carriers and the specific one symbol section or the specific plural symbol sections are known on the OFDM receiver side.

The AGC signal generator (A) 11 also receives a level detection signal 13 as signal strength information from the reception high frequency unit 7 together with interference data 12 as reception signal distortion information. For this reason, the AGC signal generation section (A) 11 generates the AGC signal 14 so that the signal level after the reception high-frequency section 7 is constant and the level data of the interference wave fd is minimized, and generates the AGC signal 14. To control the gain.

Here, the gain control of the reception high-frequency section (A) 7 means that the AGC signal (A) 14 in FIG. 1 uses a high-frequency amplification circuit (not shown) in the reception high-frequency section (A) 7 or a frequency (not shown). The gain distribution of the conversion circuit and the orthogonal conversion circuit is also controlled so that the level data of the interference wave fd is minimized. The AGC signal generation unit (A) 11 receives the level detection signal 13 as signal strength information from the reception high frequency unit 7 together with the interference data 12 as reception signal distortion information, so that this operation is possible.

The received data signal other than the interference data 12 of the zero symbol separation unit 9 input to the data conversion unit 10 undergoes parallel-serial conversion, error correction code processing, and the like, and the original data sequence is 27. This is similar to the conventional OFDM receiver.

As a result of the AGC operation described above, the interference wave f
If the level data of d does not reach the minimum and exceeds the required tolerance, it is determined whether intermodulation interference has already occurred at the input of the OFDM receiver 29 due to the effect of the nonlinear distortion of the transmission line (A) 6 in FIG. Or the input signal level of the OFDM receiver 29 is inappropriate.

However, since this cannot be improved by the AGC operation, the AGC signal generation unit A11 outputs a display signal to the display unit 15 to turn on the alarm signal on the display unit 15 and gives the user a transmission line or reception signal. Operate to signal that distortion is present in the device.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 shows a configuration when the present invention is applied to an OFDM relay station. In FIG.
The FDM relay station 32 receives the OFDM transmission signal from the transmission path (A) 6, relays and amplifies the signal by the high frequency amplifier 18, and transmits the signal to another transmission path (B) 19 as a relay output signal 20.

At the time of this relay amplification, either the received signal or the output signal of the high-frequency amplifier 18 is selectively and automatically received by the selection circuit 21. Then, in the same manner as described above, the monitoring display unit 2 is passed through the reception high frequency unit (B) 22, the discrete Fourier transform unit 8, and the zero symbol separation unit 9.
If the level data of the interference wave fd of the reception signal or the transmission signal exceeds the required value in Step 3, the alarm signal is turned on, and the user has a distortion in the transmission path or the transmission / reception signal of the relay station. To let them know.

This can be applied to monitoring the distortion of the transmission signal of the transmitting station as well as the relay station. In this case, for example, in the configuration of FIG. 1, the output of the transmission high-frequency unit 4 is extracted and input to a transmission monitoring device (not shown). The configuration of the transmission monitoring device is the same as the reception high-frequency unit 22 in FIG.
It may be the same as the discrete Fourier transform unit 8, the zero symbol separation unit 9, and the monitoring display unit 23.

In the above description, in FIGS. 2 and 7, for simplicity, a description has been given of a form in which a carrier wave is not transmitted in a specific one wave and a specific one symbol period. If the station follows a specific regularity known in the station, a specific plural wave and a specific plural symbol section may be set to the non-stop transmission.

In particular, the non-stop transmission of a specific plurality of waves and a specific plurality of symbol sections is more effective than the transmission of a carrier in a specific one wave and a specific one symbol section. Although there is a drawback that the efficiency is slightly reduced, it is effective when the amount of frequency selective fading or nonlinear distortion varies with time.

[0046]

As described above, according to the present invention, the first
As a point, intermodulation interference, which was difficult with the conventional method,
A method that can be monitored with a relatively simple configuration can be obtained. The second point is that A, which was also difficult with the conventional method
The GC operation allows not only a constant signal level but also better performance against intermodulation interference.
An FDM receiver can be provided.

Third, since a specific carrier wave of an OFDM transmission signal is not always set to the non-stop transmission, there is an advantage that a significant reduction in transmission efficiency can be avoided. Fourth, a specific one wave or a specific plurality of carriers in the OFDM transmission signal band is not transmitted without stopping the lowermost or uppermost carrier of the OFDM transmission signal. Since it is a system, it is hard to receive interference of adjacent channels, and more accurate monitoring of intermodulation interference is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an OFDM transmission / reception system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a frequency spectrum distribution of an OFDM transmission signal in a specific symbol period according to the present invention.

FIG. 3 is a diagram illustrating a frequency spectrum distribution as a result of a discrete Fourier transform in a specific symbol period according to the present invention;

FIG. 4 is a block diagram illustrating a configuration of an OFDM repeater according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a conventional OFDM transmitting / receiving apparatus.

FIG. 6 is a diagram illustrating a frequency spectrum distribution of a general OFDM transmission signal.

FIG. 7 is a diagram illustrating a frame configuration of a general OFDM transmission signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Data conversion part (A) 2 ... Timing synthesis part 3 ... Inverse discrete Fourier transformation part 4 ... Transmission high frequency part 5 ... Transmission OFDM signal 6 ... Transmission path (A) 7 ... Reception high frequency part A 8 ... Discrete Fourier transformation part 9 ... Zero symbol separation unit 10 ... AGC signal generation unit (A) 12 ... Disturbance data 13 ... Level detection signal 14 ... AGC signal (A) 15 ... Display unit (A) 16 ... Frequency spectrum of OFDM transmission signal 17 ... OFDM transmission signal Frequency spectrum 18 high-frequency amplification unit 19 transmission line (B) 20 relay output signal 21 selection circuit 22 reception high-frequency unit (B) 23 monitoring display unit 24 AGC signal (B) 25 ... AGC signal generation unit (B) 26 ... transmission data 27 ... reception data 28 ... OFDM transmission device (A) 29 ... OFDM reception device (A) 30 ... OFDM transmission device (B) 31 OFDM receiving apparatus (B) 32 ... OFDM relay station

Claims (4)

(57) [Claims] When a digital signal is assigned to a plurality of carriers orthogonal to each other in a transmission band and subjected to inverse discrete Fourier transform, a plurality of carriers in the transmission band other than the lowermost and uppermost carriers and Specific one known at the receiving end
Receiving apparatus for receiving a transmission signal from an OFDM (orthogonal frequency division multiplexing) type transmitting apparatus in which a wave or a plurality of specific carriers are stopped according to a specific regularity known on the receiving side and are not transmitted. Amplifying means for receiving the transmission signal, generating a reception level detection signal from a change in reception intensity thereof, and amplifying and outputting the signal at a gain determined by a gain control signal. Discrete Fourier transform of the reception signal output from the means And a discrete Fourier transform unit that separates and extracts from the output of the discrete Fourier transform a discrete Fourier transform value of a stop section in the known specific wave or the specific plurality of carriers and the carrier according to the regularity. A discrete Fourier transform value separation / extraction unit; and a pair of the discrete Fourier transform value extracted by the unit as distortion information of the reception signal and the reception level detection signal. An automatic gain control means for automatically controlling the gain of the amplifying means by generating a gain control signal in combination with the generated gain control signal and providing the generated gain control signal to the amplifying means. 2. The apparatus according to claim 1, further comprising an alarm notifying means for notifying a warning when the distortion information of the received signal does not satisfy a required distortion characteristic as a result of the automatic gain control operation by the automatic gain control means. The receiving apparatus according to claim 1, wherein the user is notified of the fact that distortion is present in the transmission path or the receiving apparatus by notification. 3. When the digital signal is assigned to a plurality of carriers orthogonal to each other in a transmission band and subjected to inverse discrete Fourier transform, among the plurality of carriers in the transmission band, a carrier other than the lowermost and uppermost carriers is used, and Specific one known at the receiving end
OFDM transmitted from an OFDM (Orthogonal Frequency Division Multiplexing) type transmitting apparatus in which a wave or a plurality of specific carriers are stopped according to a specific regularity known on the receiving side and are not transmitted.
An OFDM relay apparatus for receiving and retransmitting an M signal, comprising: a selection unit for selecting a reception signal and a transmission signal of the OFDM signal at any time; and a discrete Fourier transform for performing a discrete Fourier transform of the OFDM signal selected by the unit. And a discrete Fourier transform value separating and extracting means for separating and extracting a discrete Fourier transform value of a stop section in the known specific one or specific plurality of carriers and the carrier wave conforming to the regularity from an output of the means. And using the discrete Fourier transform value obtained by this means as distortion monitoring information of the reception signal to monitor the distortion state of the reception signal or transmission signal of the OFDM signal, and that the distortion information of the signal satisfies required distortion characteristics. Alarm notification means for notifying an alarm when there is no such signal. Relay apparatus OFDM system, characterized in that notify the. 4. When the digital signal is assigned to a plurality of carriers orthogonal to each other in a transmission band and subjected to inverse discrete Fourier transform, among the plurality of carriers in the transmission band, a carrier other than the lowermost and uppermost carriers is used, and Specific one known at the receiving end
Used in an OFDM (Orthogonal Frequency Division Multiplexing) type transmitting apparatus in which a wave or a plurality of specific carrier waves are stopped and non-transmitted in accordance with a specific regularity known on the receiving side. A discrete Fourier transform means for taking an output and performing a discrete Fourier transform; and a discrete stop signal in the carrier specified by the known specific one or a plurality of carriers and in accordance with the known specific regularity. A discrete Fourier transform value separating and extracting means for separating and extracting a Fourier transform value; and a discrete Fourier transform value extracted by the means as distortion monitoring information of the transmission signal, and monitoring a distortion state of the transmission signal based on this information. Alarm notification means for notifying an alarm when the signal distortion information does not satisfy the required distortion characteristic, and the alarm notification notifies the user of the transmission signal of the transmission path or the transmitting station. An OFDM-based transmission monitoring device for notifying that distortion exists.