JP4905003B2 - OFDM receiver and OFDM receiver using the same - Google Patents

Description

  The present invention relates to an OFDM receiver that receives orthogonal frequency division multiplexing (hereinafter referred to as OFDM) signals, estimates transmission path characteristics, and improves reception performance.

  In recent years, digital broadcasting employing the OFDM modulation method has been started, and further, one-segment broadcasting that can be viewed on a portable receiving terminal has been started.

  However, in a portable terminal reception system, it is necessary to receive signals at a position where the ground height is low using a small antenna compared to a large antenna for home use, and since the user views while moving, the reception environment is Deteriorates significantly. In particular, in poor reception environments such as frequency selective transmission path distortion due to multipath and fading due to mobile reception, it is necessary to restore the signal waveform at the time of transmission from the received signal waveform and reproduce the broadcast program There is.

  Conventionally, it is known that a transmission path correction technique and a diversity reception technique are effective in such a poor reception environment.

  The transmission path correction technique is a technique that corrects by estimating waveform distortion caused by a transmission path and removing the distortion of the received signal. In digital broadcasting, pilot signals that are known between transmission and reception are arranged at predetermined intervals, so that the receiver uses the difference between the received pilot signal and the pilot signal generated inside the receiver to reduce the waveform distortion generated in the transmission path. I can know. Multipath tolerance can be improved by performing interpolation processing using this, estimating waveform distortion of data signals other than the pilot signal, and performing distortion removal.

  The diversity reception technique is a reception method in which, for example, in the space diversity reception system, two antennas are spatially separated from each other and the received power of signals received by the respective antennas is compared and selected or combined. It is. As a result, even when the reception power of one antenna is low, the signal waveform at the time of transmission can be restored if the reception power of the other antenna is high, and an improvement effect on fading can be obtained.

  Furthermore, in OFDM, transmission is performed using a large number of carriers whose phases are orthogonal to each other (hereinafter referred to as subcarriers), so that the signals received by the respective antennas are subjected to Fourier transform processing and converted to subcarriers on the frequency axis. By performing the synthesis in units of subcarriers, an improvement effect can be obtained for frequency selective transmission line distortion.

  By using these transmission path correction technique and diversity reception technique, characteristic deterioration due to multipath and fading can be improved.

As prior art document information related to the invention of this application, for example, Non-Patent Document 1 is known.
Kunori Iguchi et al., Transmission path estimation using oblique interpolation in digital terrestrial broadcasting receivers, Proceedings of the IEICE Conference, Vol. 2005 Society 1 Page531

  However, in transmission path correction using a pilot signal, reception characteristics vary greatly depending on the pilot signal used for correction processing. For example, when transmission path estimation processing is performed using pilot signals that are spaced apart by a first interval in the symbol direction, and transmission paths are performed using pilot signals that are spaced apart by a second interval shorter than the first interval. When the estimation process is performed, different results are obtained for the tracking accuracy with respect to the time variation of the received signal and the estimation accuracy with respect to the frequency selective distortion. Therefore, fading resistance and multipath resistance are different.

  Conventionally, when diversity reception is performed, correction processing is performed on the received signals received by the respective antennas using the same transmission path estimation method in the respective reception systems, so that transmission paths that improve fading resistance. When the estimation method is used, the multipath tolerance deteriorates. When the transmission path estimation method that improves the multipath tolerance is used, the fading tolerance deteriorates, and both fading tolerance and multipath tolerance can be achieved. It was difficult.

  Therefore, an object of the present invention is to achieve both fading resistance and multipath resistance in an OFDM receiver using diversity reception.

  In order to achieve the above object, an OFDM receiver of the present invention includes a first receiver that receives an OFDM signal, a first transmission path correction unit that is connected to the first receiver, and a first receiver that receives the OFDM signal. 2 reception units, a second transmission path correction unit connected to the second reception unit, and a diversity unit connected to the first transmission path correction unit and the second transmission path correction unit. Further, the first transmission path correction unit corrects the reception signal output from the first reception unit by estimating the transmission path distortion using the signal at the first time interval output from the first reception unit, The two transmission path correction unit estimates a transmission path distortion using a signal having a second time interval shorter than the first time interval output from the second reception unit, and corrects the reception signal output from the second reception unit.

  By the above means, correction is performed using a transmission path estimation method having excellent fading resistance as the first transmission path correction unit, and correction is performed using a transmission path estimation method having excellent multipath resistance as the second transmission path correction unit. By combining the output signals with diversity, both fading resistance and multipath resistance can be achieved.

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of a receiving apparatus according to Embodiment 1 of the present invention. In FIG. 1, an OFDM receiver 1 includes a first receiver 2 that receives an OFDM signal, a first transmission path correction unit 3 connected to the first receiver 2, and a second receiver that receives an OFDM signal. 4, a second transmission path correction unit 5 connected to the second reception unit 4, and a diversity unit 6 connected to the first transmission path correction unit 3 and the second transmission path correction unit 5. Each of the first receiving unit 2 and the second receiving unit 4 includes a fast Fourier transform unit that performs a Fourier transform on the received signal. An OFDM receiver (not shown) equipped with the OFDM receiver 1 is connected to a signal processing unit (not shown) connected to the output side of the diversity unit 6 and to an output side of the signal processing unit. And a display unit (not shown). The first transmission path correction unit 3 is based on the first transmission path estimation unit 7 that estimates the transmission path state from the reception signal output from the first reception unit 2 and the estimation result of the first transmission path estimation unit 7. The second transmission path correction section 5 includes a second transmission path estimation section 9 that estimates a transmission path state from the reception signal output from the second reception section 4, and a second transmission path. The correction unit 10 corrects the received signal based on the estimation result of the path estimation unit 9.

  In this configuration, the first transmission path correction unit 3 performs correction by the correction unit 8 based on the result of transmission path estimation using the received signal at the first time interval output from the first reception unit 2. Is output to the diversity unit 6, and the second transmission path correction unit 5 is based on the result of the transmission path estimation using the received signal output from the second reception unit 4 and having a second time interval shorter than the first time interval. The result of correction performed by the correction unit 10 is output to the diversity unit 6. Furthermore, the diversity unit 6 calculates each signal quality calculated by a signal quality calculator (not shown) inside the diversity unit 6 with respect to the input signals from the first transmission path correction unit 3 and the second transmission path correction unit 5. Synthesis is performed based on Thereby, it is possible to realize both the multipath resistance by the first transmission path correction unit 3 and the fading resistance by the second transmission path correction unit 5.

  A specific example in the case of having a pilot signal will be described with reference to the drawings. FIG. 2 shows the signal arrangement of the OFDM signal. Pilot signals are arranged at positions indicated by black circles, and data signals are arranged at positions indicated by white circles. Since the pilot signal is a known signal between transmission and reception, the OFDM receiver 1 can perform transmission path estimation using the received pilot signal and perform correction processing on the data signal. Here, there are several methods for processing the transmission path estimation.

  In the first method, as shown by a dotted arrow in FIG. 2, a pilot signal arranged in the time axis direction in the same carrier is used to interpolate data signals located therebetween. As a result, as shown in FIG. 3, a pilot signal and a signal subjected to time axis interpolation in the same symbol are obtained every three carriers. Further, by performing interpolation in the frequency axis direction for each symbol, transmission path estimation values (not shown) at all data signal positions are obtained.

  In the second method, interpolation is performed in an oblique direction as indicated by a dotted arrow in FIG. As a result, pilot signals and diagonally interpolated signals are obtained as shown in FIG. 5, and further, interpolation is performed in the frequency axis direction for each symbol, so that transmission path estimation values (not shown) at all data signal positions are obtained. Is obtained.

  Here, comparing the first method and the second method, the first method uses pilot signals arranged every 4 symbols in the time axis direction, whereas the second method arranges every 3 symbols in the diagonal direction. Interpolation is performed using the pilot signal. Therefore, the second method is superior in followability with respect to time variation. On the other hand, the first method uses pilot signals or time axis interpolation signals arranged every 3 carriers in the frequency axis direction, whereas the second method uses pilot signals or oblique interpolation signals arranged every 4 carriers. Used. Therefore, the first method is superior to frequency selective distortion.

  Accordingly, the first transmission path correction unit 3 outputs a signal corrected based on the result estimated by the first transmission path estimation unit 7 using the first method described above, and the second transmission path correction unit 5 outputs the second signal. The transmission path estimation unit 9 outputs a signal corrected based on the result of estimation using the second method described above, and the diversity unit 6 outputs the first transmission path correction unit 3 and the second transmission path correction unit 5. By combining the signals from, the multipath tolerance obtained by the frequency selective distortion characteristic of the first method and the fading tolerance obtained by the time tracking characteristic of the second method can be achieved.

  Furthermore, as shown in FIG. 6, N systems are provided with serially connected receivers and transmission path correction units, and each transmission path correction unit performs correction by using different transmission path estimation methods, and each output is a diversity unit. A further characteristic improvement effect can be obtained by performing synthesis at 6.

  Various transmission path estimation techniques have been proposed, and depending on the system, a technique for estimating without using a pilot signal has been studied in order to increase the amount of transmission information. Even in such a system, the OFDM receiving method according to the present application has an effective effect.

(Embodiment 2)
Hereinafter, a second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a block diagram of a receiving apparatus according to Embodiment 2 of the present invention. About the same structure as Embodiment 1, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a difference is explained in full detail. In FIG. 7, the OFDM receiver 1 further includes a control unit 11, an enable circuit 12 that performs control to start or stop the operation of the second reception unit 4 in accordance with a control signal input from the control unit 11, The input signal of either the first receiver 2 or the second receiver 4 is connected to the receiver 2 and the second receiver 4 and the second transmission path correction unit according to the control signal input from the controller 11. 5, an error correction unit 14 connected to the diversity unit 6, and an error rate measurement unit 15 connected between the error correction unit 14 and the control unit 11.

  In this configuration, when the error rate measured by the error rate measuring unit 15 is smaller than a predetermined value, the control unit 11 outputs a control signal for stopping the operation to the enable circuit 12 and to the signal selecting unit 13. On the other hand, a control signal for selecting an input signal from the first receiving unit 2 is output. When the error rate is equal to or higher than a predetermined value, a control signal for starting the operation is output to the enable circuit 12 and a signal is selected. Control is performed so as to output a control signal for selecting an input signal from the second receiving unit 4 to the unit 13.

  With this control, when the reception environment is good and the error rate is smaller than a predetermined value, the enable circuit 12 stops the operation of the second reception unit 4 to reduce power consumption, and the signal selection unit 13 An input signal from the first receiver 2 is selected. Thus, not only the first transmission path correction unit 3 performs correction on the signal received by the first reception unit 2, but also the second transmission path correction unit 5 performs correction using a different transmission path estimation method, By combining the output signals from the first and second transmission path correction units 3 and 5 in the diversity unit 6, it is possible to achieve both low power consumption, fading resistance and multipath resistance. On the other hand, when the reception environment is poor and the error rate is equal to or higher than a predetermined value, the operation of the second receiver 4 is started and the signal selector 13 selects the input signal from the second receiver 4. The reception sensitivity can be improved. That is, the diversity unit 6 combines signals received by antennas (not shown) included in the first receiving unit 2 and the second receiving unit 4, respectively. In this case, the reception sensitivity is improved. For example, if the signal received by each antenna is uncorrelated (correlation coefficient is 0), the reception sensitivity is improved by 3 dB.

  By performing the above control, the OFDM receiver 1 according to the second embodiment reduces the power consumption by stopping the operation of the second receiver 4 when the reception environment is good, and corrects two transmission paths. Since the correction is performed using the units 3 and 5, the reception characteristic can also be prevented from deteriorating. On the other hand, when the reception environment is poor, the reception sensitivity characteristic is ensured by starting the operation of the second reception unit 4. It becomes possible.

  In addition, the control unit 11 may perform control using an index representing signal quality such as a CN ratio (ratio between a carrier level and a noise level of a received signal) instead of an error rate. Thereby, the time required for detection of signal quality can be shortened.

(Embodiment 3)
The third embodiment of the present invention will be described below with reference to FIG. FIG. 8 is a block diagram of a receiving apparatus according to Embodiment 3 of the present invention. About the same structure as Embodiment 1, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a difference is explained in full detail. In FIG. 8, the OFDM receiver 1 includes a receiving unit 2 that receives an OFDM signal, a first transmission path correction unit 3 connected to the receiving unit 2, and a second transmission path correction unit connected to the receiving unit 2. 5 and a diversity unit 6 connected to the first transmission path correction unit 3 and the second transmission path correction unit 5.

  In this configuration, the first transmission line correction unit 3 corrects the reception signal output from the first reception unit 2 by estimating transmission line distortion using the first method described above, and the second transmission line correction The unit 5 corrects the reception signal output from the second receiving unit 4 by estimating the transmission channel distortion using the second method described above, and the diversity unit 6 inputs the signal from the transmission channel correction units 3 and 5. By synthesizing the signals, the multipath tolerance obtained by the first technique and the fading tolerance obtained by the second technique can be made compatible.

  Furthermore, the receiving unit and the above-described transmission path correction unit connected to the receiving unit are provided, and each transmission path correction unit performs correction by using different transmission path estimation methods, and each output is received by the diversity unit 6. A further characteristic improvement effect can be obtained by performing the synthesis.

  The OFDM receiving apparatus of the present invention can achieve a plurality of characteristics such as fading resistance and multipath resistance by providing different characteristics as transmission path correction means in each diversity reception system. This is particularly useful for a receiving device such as a portable terminal or a vehicle-mounted terminal that needs to receive while moving in various environments.

Block diagram of OFDM receiving apparatus according to Embodiment 1 Explanatory drawing of time axis interpolation in the first embodiment Explanatory drawing of frequency axis interpolation in the first embodiment Explanatory drawing of the diagonal interpolation in Embodiment 1 Explanatory drawing of frequency axis interpolation in the first embodiment Block diagram of OFDM receiving apparatus according to Embodiment 1 Block diagram of OFDM receiving apparatus according to Embodiment 2 Block diagram of OFDM receiving apparatus according to Embodiment 3

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 OFDM receiver 2 1st receiving part 3 1st transmission line correction part 4 2nd receiving part 5 2nd transmission line correction part 6 Diversity part 7 1st transmission line estimation part 8 Correction part 9 2nd transmission line estimation part 10 Correction Unit 11 Control unit 12 Enable circuit 13 Signal selection unit 14 Error correction unit 15 Error rate measurement unit

Claims (10)

A first receiver that receives an orthogonal frequency division multiplexing (hereinafter referred to as OFDM) signal, a first transmission path correction unit connected to the first receiver, a second receiver that receives the OFDM signal, and A second transmission path correction unit connected to the second reception unit; and a diversity unit connected to the first transmission path correction unit and the second transmission path correction unit, wherein the first transmission path correction unit is The first transmission unit corrects the reception signal output from the first reception unit by estimating transmission path distortion using the first time interval signal output from the first reception unit, and the second transmission path correction unit An OFDM receiver that estimates transmission path distortion using a signal having a second time interval shorter than the first time interval output from the second receiver, and corrects the received signal output from the second receiver. The OFDM signal includes a pilot signal, and the first transmission path correction unit estimates transmission path distortion using a pilot signal included in the signal output from the first reception unit and arranged at a first symbol interval. Thus, the reception signal output from the first reception unit is corrected, and the second transmission path correction unit is included in the signal output from the second reception unit and is a second symbol shorter than the first symbol interval. The OFDM receiver according to claim 1, wherein the reception signal output from the second receiving unit is corrected by estimating transmission path distortion using pilot signals arranged at intervals. A third receiving unit that receives the OFDM signal; and a third transmission path correction unit connected to the third receiving unit; and the diversity unit is further connected to the third transmission path correction unit, The third transmission path correction unit estimates a transmission path distortion by using a signal having a third time interval shorter than the first time interval and the second time interval output from the third reception unit, and performs the third reception. The OFDM receiver according to claim 1, wherein the received signal output from the unit is corrected . A control unit, is connected to an enable circuit for controlling the starting operation or stop of the operation of the second receiver, the first receiver and the second receiver according to a control signal input from the control unit And a signal selection unit that outputs one of the input signal from the first reception unit and the signal from the second reception unit to the second transmission path correction unit in accordance with a control signal input from the control unit. An error correction unit connected to the diversity unit, and an error rate measurement unit connected between the error correction unit and the control unit,
When the error rate measured by the error rate measuring unit is smaller than a predetermined value, the control unit outputs a control signal for stopping the operation to the enable circuit and outputs the control signal to the signal selecting unit. A control signal for selecting an input signal from one receiving unit is output, and when the error rate is equal to or greater than the predetermined value, a control signal for starting operation is output to the enable circuit and to the signal selecting unit The OFDM receiver according to claim 1 or 2, wherein a control signal for selecting an input signal from the second receiver is output. The error rate measuring unit is a CN ratio measuring unit connected to the diversity unit, and the control unit is configured to connect the enable circuit when the CN ratio measured by the CN ratio measuring unit is larger than a predetermined value. When the control signal for stopping the operation is output and the control signal for selecting the input signal from the first receiving unit is output to the signal selection unit, and the CN ratio is equal to or less than the predetermined value 5. The OFDM receiver according to claim 4, wherein a control signal for starting operation is output to the enable circuit and a control signal for selecting an input signal from the second receiver is output to the signal selector. A receiving unit that receives an OFDM signal, a first transmission path correction unit connected to the receiving unit, a second transmission path correction unit connected to the receiving unit, the first transmission path correction unit, and the second transmission unit A diversity unit connected to the transmission path correction unit,
It said first channel correction unit corrects the reception signal output from the reception unit by estimating a channel distortion by using a signal of a first time interval which is output from the receiving unit, the second transmission An OFDM reception apparatus, wherein the path correction unit estimates a transmission path distortion using a signal having a second time interval shorter than the first time interval output from the reception unit, and corrects the reception signal output from the reception unit. The OFDM signal includes a pilot signal, and the first transmission path correction unit estimates transmission path distortion using a pilot signal included in the signal output from the reception unit and arranged at a first symbol interval. the corrected received signal output from the receiving unit, the second transmission path compensation unit is included in the signal output from the receiving unit is arranged at a short second symbol intervals than the first symbol intervals pilot by The OFDM receiving apparatus according to claim 6, wherein the received signal output from the receiving unit is corrected by estimating transmission path distortion using the signal. A third transmission path correction unit connected to the reception unit; the diversity unit is further connected to the third transmission path correction unit; and the third transmission path correction unit is output from the reception unit. The OFDM receiving apparatus according to claim 6, wherein a transmission path distortion is estimated using a signal having a third time interval shorter than the first time interval and the second time interval, and the reception signal output from the receiving unit is corrected . A first receiving unit that receives an OFDM signal, a first transmission path correction unit connected to the first receiving unit, a second receiving unit that receives an OFDM signal, and a second receiving unit connected to the second receiving unit A transmission path correction unit; a diversity unit connected to the first transmission path correction unit and the second transmission path correction unit; a signal processing unit connected to an output side of the diversity unit; and an output of the signal processing unit The first transmission path correction section estimates the transmission path distortion by using the first time interval signal output from the first reception section. The received signal output from the receiving unit is corrected, and the second transmission path correcting unit corrects transmission path distortion using a signal having a second time interval shorter than the first time interval output from the second receiving unit. OF that estimates and corrects the received signal output from the second receiver M receiving device. A receiving unit that receives an OFDM signal, a first transmission path correction unit connected to the receiving unit, a second transmission path correction unit connected to the receiving unit, the first transmission path correction unit, and the second transmission unit A diversity unit connected to the transmission path correction unit; a signal processing unit connected to the output side of the diversity unit; and a display unit connected to the output side of the signal processing unit; correction unit corrects the reception signal output from the reception unit by estimating a channel distortion by using a signal of a first time interval which is output from the receiving unit, the second transmission channel correction unit, OFDM reception device to correct the reception signal output from the reception unit estimates a channel distortion by using a signal outputted said shorter than the first time interval the second time interval from said reception unit.

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