JP2000151548A - Ofdm communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably conduct the orthogonal frequency division multiplex OFDM communication. SOLUTION: A base band signal is sent to a level detection section 120, where a level of the signal is detected. The detected reception level is fed to a discrimination device 121, where the level is discriminated with a threshold value. That is, the detected level is compared with a prescribed threshold value. When the level is lower than the threshold value, it is discriminated that an environment of a transmission path is wrong and a pilot symbol is inserted. Thus, the a prescribed device 121 gives an instruction of insertion of a symbol to a pilot symbol insert section 102 and the pilot symbol is inserted to transmission data. The insertion of the symbol is controlled in this way so as to vary number N of symbols between the pilot symbols and the system can cope with the environment of the transmission channel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an OFDM communication device used in a wireless communication system.

[0002]

2. Description of the Related Art Multipath interference is a major cause of deterioration of transmission characteristics in current terrestrial transmission lines. OFDM (Orthogonal Frequenc
y Division Multiplexing) transmission schemes have recently been receiving attention. This OFDM is a method of multiplexing a large number (several tens to several hundreds) of digital modulation waves orthogonal to each other in a certain signal section.

In this OFDM transmission system, initial synchronization such as symbol synchronization and frequency synchronization is performed using a pilot symbol serving as a phase reference, and a subsequent FFT (Fast Fourier Transform) is performed at a timing obtained in the initial synchronization.
Perform Further, the frequency offset value is corrected based on the information obtained in the initial synchronization. Further, data subsequent to the distortion detection value of the pilot symbol (until the next pilot symbol) is equalized.

[0004]

However, if the state of the transmission path fluctuates, such as when the communication partner moves at a high speed, the conditions for correcting the frequency offset value and equalizing the data differ until the next pilot symbol. As a result, accurate correction and equalization may not be performed. If the correction of the frequency offset value and the equalization of the data cannot be accurately performed as described above, the OFDM communication cannot be stably performed.

[0005] The present invention has been made in view of the above, and it is an object of the present invention to provide an OFDM communication apparatus capable of performing OFDM communication stably even when the state of a transmission line changes.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to adaptively insert a pilot symbol normally inserted for each prescribed symbol based on symbol insertion information.

That is, according to the present invention, there is provided an adding means for adding a synchronization symbol and a phase reference symbol, which is the same signal as the synchronization symbol, to an effective symbol, and adaptively inserting the synchronization symbol based on symbol insertion information. A transmitter having control means for performing control to perform the control, a delay means for delaying a received signal by a unit symbol, a correlating means for correlating the received signal with the received signal delayed by a unit symbol, and a threshold for a result of the correlation. A receiver having synchronization means for performing symbol determination by performing value determination.

[0008]

DETAILED DESCRIPTION OF THE INVENTION An OFDM communication apparatus according to a first embodiment of the present invention comprises: a synchronizing symbol and an adding means for adding a phase reference symbol, which is the same signal as the synchronizing symbol, to an effective symbol; A transmitter having control means for performing control for adaptively inserting the synchronization symbol based on the insertion information, and a delay means for delaying a received signal by a unit symbol; A configuration including a correlation unit for obtaining a correlation and a receiver having a synchronization unit for performing symbol determination by performing a threshold value determination on the result of the correlation is adopted.

According to this configuration, the pilot symbols normally inserted for each prescribed symbol are adaptively inserted based on the symbol insertion information. As described above, the distortion value for equalization and the frequency offset correction value are updated based on the pilot symbols adaptively inserted. Therefore, even if the transmission path environment deteriorates, it is possible to quickly correct the communication parameters according to the environment. As a result, the OFDM communication can be stably performed even if the transmission path state changes.

OFDM according to a second embodiment of the present invention
The communication device according to the first aspect, further comprising: a speed measurement unit configured to extract a speed parameter from a received signal to measure a speed of a communication partner; And a symbol insertion information transmitting unit to be sent to the control unit.

[0011] According to this configuration, the pilot symbol that is normally inserted for each prescribed symbol is adaptively inserted when the communication partner is moving at a high speed, so that the transmission path environment is rapidly increased. Even if it changes, the communication parameters can be quickly corrected according to the environment. As a result, the OFDM communication can be stably performed even if the transmission path state changes.

[0012] OFDM according to a third embodiment of the present invention
In a first aspect, a communication device includes a level detector for detecting a level of a received signal, and symbol insertion information for sending symbol insertion information to the controller when the detected level exceeds a predetermined threshold. And a transmission unit.

[0013] According to this configuration, the pilot symbols that are normally inserted for each prescribed symbol are adaptively inserted when the reception level is degraded. Can be quickly corrected according to the environment. as a result,
Even if the state of the transmission path changes, the OFDM communication can be performed stably.

A base station apparatus according to a fourth embodiment of the present invention includes the OFDM communication apparatus according to any one of the first to third aspects. A communication terminal device according to a fifth embodiment of the present invention includes the OFDM communication device according to any one of the first to third aspects.

According to these configurations, it is possible to provide a communication terminal device such as a base station device or a mobile station device that can cope with a transmission path environment in a wireless communication system.

[0016] OFDM according to a sixth embodiment of the present invention
The communication method includes a step of adding a synchronization symbol and a phase reference symbol that is the same signal as the synchronization symbol to an effective symbol, and a step of performing control to adaptively insert the synchronization symbol based on symbol insertion information. Having a transmitting step, a step of delaying a received signal by a unit symbol, a step of correlating the received signal with a received signal delayed by a unit symbol, and performing a threshold value judgment on a result of the correlation to perform symbol synchronization. Receiving step having a step of taking.

According to this method, the pilot symbols normally inserted for each prescribed symbol are adaptively inserted based on the symbol insertion information. As described above, the distortion value for equalization and the frequency offset correction value are updated based on the pilot symbols adaptively inserted. Therefore, even if the transmission path environment deteriorates, it is possible to quickly correct the communication parameters according to the environment. As a result, the OFDM communication can be stably performed even if the transmission path state changes.

OFDM according to a seventh embodiment of the present invention
The communication method according to the sixth aspect, includes a step of extracting a speed parameter from a received signal to measure a speed of a communication partner,
Outputting symbol insertion information when the measured rate exceeds a predetermined threshold.

According to this method, the pilot symbol normally inserted for each prescribed symbol is adaptively inserted when the communication partner is moving at a high speed. Even if it changes, the communication parameters can be quickly corrected according to the environment. As a result, the OFDM communication can be stably performed even if the transmission path state changes.

OFDM according to an eighth embodiment of the present invention
The communication method according to a sixth aspect, includes a step of detecting a level of a received signal and a step of outputting symbol insertion information when the detected level exceeds a predetermined threshold.

According to this method, the pilot symbols that are normally inserted for each prescribed symbol are adaptively inserted when the reception level is deteriorated. Can be quickly corrected according to the environment. as a result,
Even if the state of the transmission path changes, the OFDM communication can be performed stably.

OFDM according to a ninth embodiment of the present invention
In the communication method according to the sixth aspect, the symbol insertion information is transmitted from a communication partner.

According to this method, it is determined that the reception level of the pilot symbol normally inserted for each prescribed symbol is degraded on the communication partner side, and when an instruction to insert the pilot symbol is received. , Adaptively, even if the transmission path environment deteriorates, it is possible to quickly correct the communication parameters according to the environment. As a result, even if the transmission path condition fluctuates,
FDM communication can be performed stably.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. (Embodiment 1) FIG.1 is a block diagram showing a configuration of an OFDM communication apparatus according to Embodiment 1 of the present invention.

First, the transmission data for each subcarrier is:
In the modulation unit 101, for example, QPSK (Quadrature Phase
Shift Keying) and QAM (Quadrature Amplitude Modulat)
After the digital modulation processing is performed by a pilot symbol insertion section 102, a pilot symbol (phase reference symbol) which is a synchronization symbol is added in the pilot symbol insertion section 102.

The signal with the pilot symbol inserted is
An IFFT (Inverse Fast Fourier Transform) section 103 performs an IFFT operation to generate an OFDM signal. This OFDM
The guard interval is inserted into the signal by the guard interval insertion unit 104. The signal into which the guard interval has been inserted is D / A converted by the D / A conversion unit 105 to become a baseband signal. After removing unnecessary components by a low-pass filter (LPF) 106, the baseband signal is amplified by an amplifier 107 and transmitted as a transmission signal via an antenna 108.

On the other hand, the signal received via the antenna 109 is gain-controlled by an automatic gain controller (AGC) 110 to become a baseband signal. This baseband signal is subjected to quadrature detection processing, after which unnecessary frequency components are removed by the LPF 111, and A / D converted by the A / D converter 112. Although the received signal is divided into an in-phase component and a quadrature component by the quadrature detection process, it is shown as one signal path in the drawing.

This baseband signal is an FFT (Fast Fo
urier Transform) section 117 performs an FFT operation to obtain a signal assigned to each subcarrier. At this time,
The baseband signal is delayed by the delay unit 113, sent to the multiplier 114 and subjected to complex multiplication processing, and the multiplication result is integrated by the integrator 115. Then, the integration result is sent to the determiner 116, and the threshold value is determined. And
This determination result is sent to FFT section 117. Further, the integration result is sent to the frequency offset unit 122, the frequency offset value is corrected, and the correction value is sent to the oscillator 123.

The signal subjected to the FFT operation in FFT section 117 is equalized by distortion detecting section 118 in accordance with a distortion detection value obtained from a pilot symbol. Further, this signal is synchronously detected by a demodulation section 119 using pilot symbols to become received data.

The baseband signal is sent to the level detector 120, where the level is detected, and the level detection result is sent to the decision unit 121. Judgment device 121 compares the detection result with a predetermined threshold value, and if the detection result is equal to or smaller than the predetermined threshold value, sends an instruction to pilot symbol insertion section 102 to insert a pilot symbol.

Next, the operation of the OFDM communication apparatus having the above configuration will be described. A pilot symbol insertion section 102 inserts two pilot symbols into the signal digitally modulated by modulation section 101. The pilot symbol insertion section 102 is configured by a switch, and switches when a control signal for inserting a pilot symbol is input, and inserts a pilot symbol.

The signal into which the pilot symbols have been inserted as described above is sent to IFFT section 103 and subjected to IFFT calculation. That is, the IFFT section 103 performs IFFT conversion on the time axis for each symbol period on complex time data including phase and amplitude information on the frequency axis,
Obtain the signal waveform on the time axis.

Next, a guard interval (guard interval) is inserted into the IFFT-converted signal waveform by the guard interval insertion unit 104. Specifically, a part of the waveform at the rear end of the effective symbol is inserted as a guard interval. As described above, by inserting a guard interval allowing a delay time, an increase in the bit error rate can be suppressed, and multipath resistance can be improved.

Next, the signal into which the guard interval has been inserted is D / A converted by the D / A converter 105. Thereafter, the D / A-converted signal is transmitted after being subjected to normal wireless transmission processing. That is, the above-mentioned signal is subjected to removal of unnecessary components by the LPF 106 and the amplifier 107
, And transmitted from the antenna 108.

On the other hand, the signal received from the antenna 109 is subjected to normal radio reception processing. That is, the gain of the received signal is controlled by AGC section 110. This gain control is performed based on the AGC symbol of the received signal.
Further, the received signal is subjected to A / D conversion by the A / D conversion unit 112 after unnecessary frequency components are removed by the LPF 111 to become a baseband signal. As described above, the received signal is processed by being divided into an in-phase component and a quadrature component by a quadrature detector (not shown), respectively, but is represented by one path in the figure.

Here, for the baseband signal, symbol synchronization is established using pilot symbols. Hereinafter, the symbol synchronization will be described.

First, the baseband signal before the FFT operation and the signal before the FFT processing are delayed by, for example, one symbol by the delay unit 113, are sent to the multiplier 114, where complex multiplication processing is performed.

Next, the output of the multiplication unit 114 is
5 and multiply the result of the complex multiplication. Here, since the pilot symbol continues for two symbols, the sum of the two results in a peak at the pilot symbol of the signal delayed by a unit symbol (here, one symbol). Therefore, symbol synchronization can be established by detecting the timing when the integration result exceeds the threshold value.

Therefore, the result of integration, which is the output of the integrator 115, is sent to the determiner 116, where the magnitude is determined between a predetermined threshold value. As a result, the threshold value is determined for the integration result, and the timing exceeding the threshold value can be used as the FFT processing start timing in FFT section 117. In this way, the timing is set so that the FFT is started in synchronization with the symbol synchronization between the transmitting side and the receiving side.

The integration result obtained by the integrator 115 is sent to the frequency offset section 122, where the frequency offset value is corrected based on the integration result. The oscillator 123 is controlled based on this correction.

On the other hand, the baseband signal is sent to the level detector 120, where the level is detected. The detected reception level is sent to the determiner 121, where the threshold is determined. That is, the detected level value is compared with a predetermined threshold value, and when the level value falls below the threshold value, it is determined that the environment of the transmission path is bad, and a pilot symbol is inserted. Therefore, an instruction to insert a symbol is given from determinator 121 to pilot symbol insertion section 102, and a pilot symbol is inserted into transmission data. In this way, by controlling the symbol insertion, the number of symbols N between the pilot symbols shown in FIG. 2 is made variable so that it can be adapted to the transmission path environment.

The A / D-converted baseband signal is subjected to FFT processing at the FFT processing start timing from the FFT processing start timing, and a signal assigned to each subcarrier is obtained. Further, this signal is sent to distortion detection section 118, and equalization (until the next pilot symbol) is performed based on the distortion detection result of the pilot symbol. The signal after the equalization is sent to the demodulation unit 119, where it is subjected to synchronous detection processing to become a demodulated signal.

As described above, in the OFDM communication apparatus according to the present embodiment, the pilot symbols normally inserted for each prescribed symbol are adaptively inserted when the reception level is deteriorated. As described above, the distortion value for equalization and the frequency offset correction value are updated based on the pilot symbols adaptively inserted. Therefore, even if the transmission path environment deteriorates, it is possible to quickly correct the communication parameters according to the environment. As a result, the OFDM communication can be stably performed even if the transmission path state changes.

Although the present embodiment has been described with respect to a case where a reception level is detected and a pilot symbol is inserted based on the detection result, the present invention
The present invention can also be applied to the case where pilot symbols are inserted based on the result of reception quality such as the bit error rate or SIR of a received signal.

(Embodiment 2) FIG. 3 is a block diagram showing a configuration of an OFDM communication apparatus according to Embodiment 2 of the present invention. 3, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof will be omitted.

In this embodiment, when a communication partner is moving at a high speed, the speed is measured, and when the speed exceeds a predetermined speed, a pilot symbol is inserted to update the communication parameters adaptively. Will be described.

In the OFDM communication apparatus shown in FIG. 3, a baseband signal obtained by subjecting a received signal to radio reception processing is sent to speed parameter extracting section 301, and a parameter necessary for measuring the speed of a communication partner is extracted. . This parameter is sent to the speed measuring unit 302, and the speed is measured. The measured rate is sent to the decision unit 303 and compared with a predetermined threshold value. When the rate exceeds the predetermined threshold value, an instruction to insert a pilot symbol is inserted into the pilot symbol insertion unit 102 when the rate exceeds the predetermined threshold value. send.

Next, the operation of the OFDM communication apparatus having the above configuration will be described. Transmit data to antenna 108
Is transmitted in the same manner as in the first embodiment. Further, the process of obtaining received data from a signal received from antenna 109 is the same as in the first embodiment. Note that the received signal is divided into an in-phase component and a quadrature component by a quadrature detector (not shown) and then processed, but is represented by one path in the drawing. Also, with respect to the baseband signal, the method of establishing symbol synchronization using pilot symbols is the same as in the first embodiment.

On the other hand, the baseband signal is sent to speed parameter extracting section 301, where the speed parameter is extracted. Here, the speed parameter refers to a parameter required for measuring the speed of a communication partner, and includes, for example, a Doppler frequency.

The extracted speed parameter is sent to speed measuring section 302, where the speed of the communication partner is measured. The speed information is sent to the determiner 303, where the threshold value is determined. That is, the measured speed is compared with a predetermined threshold value, and when the level value exceeds the threshold value, it is determined that the environment of the transmission path is rapidly changing and pilot symbols are inserted. . Therefore, pilot symbol insertion section 10
2 is given a symbol insertion instruction, and a pilot symbol is inserted into the transmission data. In this way, by controlling the symbol insertion, the number of symbols N between the pilot symbols shown in FIG. 2 is made variable so that it can be adapted to the transmission path environment.

As described above, in the OFDM communication apparatus of the present embodiment, the pilot symbols normally inserted for each prescribed symbol are adaptively inserted when the communication partner is moving at high speed. . As described above, the distortion value for equalization and the frequency offset correction value are updated based on the pilot symbols adaptively inserted. Therefore,
Even if the transmission path environment changes abruptly, the communication parameters can be quickly corrected according to the environment. As a result, the OFDM communication can be stably performed even if the transmission path state changes.

(Embodiment 3) FIG.4 is a block diagram showing a configuration of an OFDM communication apparatus according to Embodiment 3 of the present invention. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof will be omitted.

In the present embodiment, when it is determined that the reception level has deteriorated on the communication partner side and an instruction to insert a pilot symbol is issued, the communication parameter is adaptively updated by inserting the pilot symbol. Will be described.

In the OFDM communication apparatus shown in FIG. 4, symbol insertion information from a communication partner is input to pilot symbol insertion section 102. This symbol insertion information can be extracted from the received signal.

Next, the operation of the OFDM communication apparatus having the above configuration will be described. Transmit data to antenna 108
Is transmitted in the same manner as in the first embodiment. Further, the process of obtaining received data from a signal received from antenna 109 is the same as in the first embodiment. Note that the received signal is divided into an in-phase component and a quadrature component by a quadrature detector (not shown) and then processed, but is represented by one path in the drawing. Also, with respect to the baseband signal, the method of establishing symbol synchronization using pilot symbols is the same as in the first embodiment.

When the communication partner detects the reception level and determines that the level is degraded, the communication partner transmits symbol insertion information indicating that pilot symbols need to be inserted. This symbol insertion information is received, and the symbol insertion information is input to pilot symbol insertion section 102. Therefore, according to the symbol insertion information,
A pilot symbol is inserted into transmission data. In this way, by controlling the symbol insertion, the number of symbols N between the pilot symbols shown in FIG. 2 is made variable so that it can be adapted to the transmission path environment.

As described above, in the OFDM communication apparatus of the present embodiment, it is determined that the reception level of the pilot symbol normally inserted for each prescribed symbol is degraded on the communication partner side, and the pilot symbol is inserted. When an instruction to the effect is received, it is inserted adaptively. As described above, the distortion value for equalization and the frequency offset correction value are updated based on the pilot symbols adaptively inserted. Therefore, even if the transmission path environment deteriorates, it is possible to quickly correct the communication parameters according to the environment. As a result, even if the transmission path condition changes, OFD
M communication can be performed stably.

The OFDM communication apparatus according to the present invention can be applied to a communication terminal apparatus such as a mobile station apparatus and a base station apparatus in a wireless communication system.

In the first to third embodiments, the case where synchronous detection is performed using a pilot symbol as a phase reference symbol for demodulation has been described. However, the present invention relates to a case where delay detection is performed using a reference symbol. Can also be applied. In this case, the demodulation unit 11
In 9, a delay detection process is performed instead of the synchronous detection process.

The present invention is not limited to the first to third embodiments, but can be implemented with various modifications.
The first to third embodiments can be implemented in appropriate combinations.

[0061]

As described above, the OFDM communication apparatus of the present invention is adapted to adaptively insert a pilot symbol normally inserted for each prescribed symbol based on symbol insertion information. As described above, the distortion value for equalization and the frequency offset correction value are updated based on the pilot symbols adaptively inserted. Therefore, even if the transmission path environment deteriorates, it is possible to quickly correct the communication parameters according to the environment. As a result, the OFDM communication can be stably performed even if the transmission path state changes.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an OFDM communication apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing a subcarrier arrangement in the OFDM communication apparatus according to the embodiment.

FIG. 3 is a block diagram showing a configuration of an OFDM communication apparatus according to Embodiment 2 of the present invention.

FIG. 4 is a block diagram showing a configuration of an OFDM communication apparatus according to Embodiment 3 of the present invention.

[Explanation of symbols]

 Reference Signs List 101 Modulating section 102 Pilot symbol inserting section 103 IFFT section 104 Guard section inserting section 105 D / A converting section 106, 111 LPF 107 Amplifier 108, 109 Antenna 110 AGC section 112 A / D converting section 113 Delay unit 114 Multiplier 115 Integrator 115 116, 121, 303 Judgment unit 117 FFT unit 118 Distortion detection unit 119 Demodulation unit 120 Level detection unit 122 Frequency offset unit 123 Oscillator 301 Speed parameter extraction unit 302 Speed measurement unit

Claims (9)

[Claims] 1. An adding means for adding a synchronization symbol and a phase reference symbol which is the same signal as the synchronization symbol to an effective symbol, and a control for adaptively inserting the synchronization symbol based on symbol insertion information. A transmitter having control means, delay means for delaying a received signal by a unit symbol, correlation means for taking a correlation between the received signal and a received signal delayed by a unit symbol, and threshold value determination for the result of the correlation And a receiver having synchronization means for achieving symbol synchronization. 2. A speed measuring means for extracting a speed parameter from a received signal to measure a speed of a communication partner, and sending symbol insertion information to the control means when the measured speed exceeds a predetermined threshold. 2. The OFDM communication apparatus according to claim 1, further comprising: symbol insertion information transmitting means. 3. A level detecting means for detecting a level of a received signal, and a symbol insertion information transmitting means for transmitting symbol insertion information to the control means when the detected level is equal to or less than a predetermined threshold value. 2. The OFDM communication apparatus according to claim 1, wherein 4. A base station apparatus comprising the OFDM communication apparatus according to claim 1. 5. A communication terminal device comprising the OFDM communication device according to any one of claims 1 to 3. 6. A step of adding a synchronization symbol and a phase reference symbol that is the same signal as the synchronization symbol to an effective symbol, and a step of performing control for adaptively inserting the synchronization symbol based on symbol insertion information. And a step of delaying a received signal by a unit symbol, a step of correlating the received signal with a received signal delayed by a unit symbol, and performing a threshold determination on the result of the correlation to perform symbol synchronization. A receiving step having a step of taking an OFD signal.
M communication method. 7. A method comprising: extracting a speed parameter from a received signal to measure a speed of a communication partner; and outputting symbol insertion information when the measured speed exceeds a predetermined threshold. 7. The OFDM communication method according to claim 6, wherein: 8. The method according to claim 6, further comprising the steps of: detecting a level of a received signal; and outputting symbol insertion information when the detected level is equal to or lower than a predetermined threshold. The OFDM communication method according to the above. 9. The OFDM communication method according to claim 6, wherein the symbol insertion information is transmitted from a communication partner.