JP5398652B2 - OFDM receiver - Google Patents

Description

  Embodiments described herein relate generally to channel response estimation in an OFDM receiver.

  In digital terrestrial broadcasting, an orthogonal frequency division multiplexing system (hereinafter referred to as an OFDM system) using a plurality of carrier waves orthogonal to each other is employed as a modulation system.

  In general, in the signal format in the OFDM system, a dispersed pilot signal (hereinafter referred to as an SP signal) is multiplexed in addition to a data signal in a transmission signal, and this is interpolated in a time direction and a frequency direction. It is used to estimate the channel response and equalize multipath distortion.

  In a state where the SP signal is transmitted from the broadcast station, the SP signal is intermittently inserted into the transmission signal every predetermined number of symbols in each of the time direction and the frequency direction. In the receiving apparatus, the SP signal is extracted from the transmitted transmission signal, and the SP signal is interpolated with respect to all symbols of the data signal by using an interpolation filter in the time direction and the frequency direction. The SP response is estimated using the SP signal.

  It is desirable that the SP signal interpolation filter can pass many delayed wave components including a delayed wave having a long delay time due to multipath (referred to as a long delayed wave) and can remove a noise component.

JP 2006-311385 A JP 2009-111748 A JP 2007-318315 A

  The present invention provides an OFDM receiver capable of passing a delayed wave component including a long delayed wave in an SP signal interpolation filter at the time of multipath, and improving noise removal performance to improve reception performance. Objective.

  An OFDM receiver according to an embodiment of the present invention includes a filter unit that band-limits a transmission path estimation signal in a frequency direction using a plurality of filter characteristics, and an equalization unit that equalizes a received signal using an output of the filter unit A quality detection unit that detects the reception quality of the output of the equalization unit, and a determination unit that determines an optimum one from the plurality of filter characteristics using the detected reception quality, and the plurality of filter characteristics Has a filter characteristic of a predetermined bandwidth and a plurality of filter characteristics that pass a part of the predetermined bandwidth, and the plurality of filter characteristics that pass the part include two or more passbands .

The block diagram of the OFDM receiver of the 1st Embodiment of this invention. The figure explaining the transmission format system of an OFDM signal. The figure explaining an example of filter coefficient control in a 1st embodiment. Explanatory drawing regarding the filter of the wide band which can respond to the delayed wave component of a long delay. Explanatory drawing regarding the filter of the narrow band which can respond to the delayed wave component of a short delay. The figure explaining the other example of the filter coefficient control in 1st Embodiment. The block diagram of the OFDM receiver of the 2nd Embodiment of this invention. The figure explaining an example of the filter coefficient control in 2nd Embodiment. The block diagram of the other Example of a coefficient determination circuit. The block diagram of another another Example of a coefficient determination circuit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
FIG. 1 is a block diagram of an OFDM receiving apparatus according to the first embodiment of this invention.
In FIG. 1, an OFDM receiver 100 includes an antenna 1, a tuner 2, an A / D converter 3, an IQ demodulation circuit 4, an FFT circuit 5, an FFT window control circuit 6, and a first equalization circuit. 7, a first SP time interpolation filter 8, a first SP frequency interpolation filter 9, an error correction circuit 10, a first coefficient switching circuit 11, and a coefficient determination circuit 12.

  The OFDM receiver 100 receives, for example, a transmission signal (hereinafter referred to as an OFDM signal) conforming to the OFDM scheme via a wireless transmission path. In addition, you may receive via a wired transmission line.

  The tuner 2 frequency-converts the RF signal received by the antenna 1 into an IF signal and outputs the IF signal to the A / D conversion circuit 3. The A / D conversion circuit 3 performs A / D conversion on the IF signal supplied from the tuner 2 and outputs a digital IF signal to the IQ demodulation circuit 4.

  The IQ demodulation circuit 4 acquires a time domain OFDM signal from the IF signal supplied from the A / D conversion circuit 3 by performing orthogonal demodulation. The IQ demodulation circuit 4 outputs the time domain OFDM signal to the FFT circuit 5 and the FFT window control circuit 6.

  Based on the FFT window control signal supplied from the FFT window control circuit 6, the FFT circuit 5 extracts a signal having a range of effective symbol length from one OFDM symbol signal. Further, the FFT circuit 5 performs an FFT operation on the extracted time domain OFDM signal to generate a frequency domain OFDM signal, which is sent to the first equalization circuit 7 and the first SP time interpolation filter 8. Output.

  The FFT window control circuit 6 detects the timing of the main wave from the received signal, and detects the FFT window position so that the FFT output is optimized based on this timing. The FFT circuit 5 converts the OFDM signal on the time axis into a signal on the frequency axis according to the FFT window position. The output of the FFT circuit 5 has a signal wave arrangement shown in the signal format of FIG.

  In the signal format example of the OFDM signal shown in FIG. 2, the information symbol S1, the TMCC / AC symbol S2 indicating the transmission method of the OFDM signal, the CP symbol S3 indicating the end of the OFDM signal, and the symbol of the SP signal are included. Each symbol of the SP symbol S4 is included. The SP symbol S4 is inserted at a rate of 1/3 in the frequency direction and 1/4 in the time direction, for example.

The first SP time interpolation filter 8 extracts an SP signal from the OFDM signal in the frequency domain, performs time-direction interpolation on the SP signal, and outputs the SP signal to the first SP frequency interpolation filter 9. The first SP frequency interpolation filter 9 performs further interpolation in the frequency direction on the SP signal interpolated in the time direction, and transmission corresponding to all data by the SP signal interpolated in the time direction and the frequency direction. Get road response.
As shown in FIG. 2, the first SP time interpolation filter 8 includes, for example, linear interpolation (interpolation that equally divides the time difference between SPs) for the other three symbols because the SP signal exists at a rate of one in four symbols. ) To enter the value.

As will be described later, the first SP frequency interpolation filter 9 limits the frequency band of the SP signal on a symbol-by-symbol basis using an optimum filter coefficient determined based on the result of detecting the signal quality of the OFDM signal. To interpolate the SP signal in the frequency direction.
Here, the SP signal is a known signal having a predetermined phase and power, and is used as a transmission path estimation symbol to obtain a transmission path response for estimating the distortion of the transmission signal.

  The first equalization circuit 7 equalizes the frequency domain OFDM signal using the transmission path estimation signal based on the SP signal. The output of the first equalization circuit 7 is supplied to the error correction circuit 10, and decoding processing for error correction is performed to decode received data.

The first coefficient switching circuit 11 that switches the filter coefficient of the first SP frequency interpolation filter 9 includes a passband shift unit 11a that sequentially switches and sets a plurality of shift patterns in FIG. 3A, and FIG. And a passband pattern selection unit 11b that sequentially switches and sets a plurality of passband patterns.
The coefficient determination circuit 12 includes a second SP frequency interpolation filter 125, a second coefficient switching circuit 124, a second equalization circuit 121, a signal quality detection circuit 122, and a control unit 123.

  The second coefficient switching circuit 124 that switches the filter coefficient of the second SP frequency interpolation filter 125 includes a passband shift unit 124a that sequentially switches and sets a plurality of shift patterns similar to those in FIG. a passband pattern selection unit 124b that sequentially switches and sets a plurality of passband patterns similar to b).

FIG. 3 is a diagram for explaining an example of filter coefficient control in the first embodiment.
As shown in FIG. 3, the first coefficient switching circuit 11 includes a plurality of filter characteristics obtained by shifting the center frequency with reference to the main wave position, and a partial band including the main wave position among the shifted filter characteristics. The filter characteristics can be switched, and operates according to the shift amount supplied from the coefficient determination circuit 12 and the passband pattern.

  The coefficient determination circuit 12 sequentially generates the filter coefficients (filter patterns) shown in FIG. 3, detects the reception quality from the modulation error ratio (hereinafter referred to as MER) of the equalized output using each frequency interpolation, and receives the reception quality. The best filter coefficient is determined, and the determination result of the shift amount and the passband pattern is supplied to the first coefficient switching circuit 11.

In FIGS. 3A and 3B, the main wave and the delayed wave (and the preceding wave) on the time axis are represented (the horizontal axis is the delay time and the vertical axis is the power). This does not show the actual detection result of the delay profile. For the main wave having the largest signal level, for example, a threshold is provided, and when the signal exceeding the threshold is actually detected as the main wave level, the main wave position It can be assumed that a preceding wave and a delayed wave exist at the time positions before and after the center. For this reason, a state in which, for example, a delayed wave is present within a predetermined bandwidth including a narrow band where the main wave exists (hereinafter referred to as the main wave band) is also virtually represented on the time axis. In order to make it easy to understand the presence of the delayed wave with respect to the main wave, the figure is similar to the delay profile. However, in the embodiment of the present invention, the delay profile is not detected at all, and filter coefficients are sequentially arranged for many possible filter patterns. It is set by changing to, and operates so as to determine the filter pattern (filter characteristic) that provides the best reception quality. This also applies to FIGS. 6 and 8 described later.
As for the main wave, the signal wave having the highest power level is defined as the main wave among all the signal waves including the main wave, the delayed wave, and the preceding wave in the same broadcast channel.

  Further, after shifting a shift pattern of a predetermined bandwidth in the frequency direction as shown in FIG. 3 (a), two or more parts passing through the predetermined bandwidth as shown in FIG. 3 (b) are passed. As a method of generating an optimum filter characteristic having a pass band, the pass band of the main band from a state in which a plurality of pass band patterns having the same narrow bandwidth as the main band (two in FIG. 3 (b)) overlap each other. In order to gradually move away another passband pattern that overlaps with the center of the pattern, in other words, the filter coefficient is controlled to separate another passband pattern that overlaps from the center of the passband pattern of the main band. A filter characteristic (for example, a passband pattern 6) having two passbands is generated. In other words, all filter patterns including a process in which a plurality of narrow bandwidth filter bands are sequentially expanded as filter patterns in the frequency direction by coefficient control are tried, and the main wave and the delayed wave pass through the filter pass band well. A filter pattern is determined that passes through to obtain the best signal quality result. The same applies to FIGS. 6B and 8B described later.

  Next, the operation of the coefficient determination circuit 12 will be further described with reference to FIG. FIGS. 3A and 3B are diagrams illustrating an example of filter coefficient control in the first embodiment. FIG. 3 (a) shows the operation of trying a plurality of shift patterns by sequentially changing the shift amount. FIG. 3 (b) shows the shift pattern 1 after the shift pattern 1 is selected in FIG. 3 (a). This shows the operation from trial to succession of a passband pattern including two independent passbands by changing the passband pattern sequentially within a predetermined bandwidth and trying from a series of passbands. .

  In the coefficient determination circuit 12, the control unit 123 first sequentially generates filter characteristics of the filter patterns 1 to 7 in which the center frequency shown in FIG. When the two-wave multipath of the delay difference between the main wave and the delayed wave shown in FIG. 3 is input, the MER in the signal quality detection circuit 122 is minimized when the shift pattern 1 in which the two waves are within the filter passband, The reception quality is determined to be the best. Next, filter characteristics of a plurality of passband patterns 1 to 6 that pass the main wave and other partial bands are sequentially generated with respect to the shift pattern 1 as shown in FIG. In the case of a two-wave multipath as shown in FIG. 3 (b), the noise removal capability of the passband pattern 6 that allows only the vicinity of the main wave and the delayed wave to pass is higher than that of the shift pattern 1 that passes the entire zone. Since it is high, the MER in the signal quality detection circuit 122 becomes small, and it is finally determined that the reception quality is the best.

  FIG. 4 is an explanatory diagram regarding a wide-band filter that can pass a delayed wave component having a large delay difference with respect to the main wave (referred to as a delayed wave component having a long delay), and FIG. It is explanatory drawing regarding the filter of the narrow band which can pass a delay wave component (it is called the delay wave component of a short delay).

  FIG. 4 (a) shows the relationship of a delayed wave having a large delay difference with respect to the main wave, and FIG. Show. The frequency characteristic in this case is a characteristic in which the beat interval is shortened and fluctuates at a fast cycle. Therefore, a filter with a wide band including a high frequency band is required to cope with such a long delay wave. However, simply using a wide-band filter causes a problem that the noise component increases.

  FIG. 5 (a) shows the relationship of a delayed wave component having a small delay difference with respect to the main wave (referred to as a delayed wave component having a short delay), and FIG. The frequency characteristic of the transmission signal which has a wave component is shown. The frequency characteristic in this case is a characteristic in which the beat interval is long and fluctuates at a slow cycle. Therefore, in this case, a narrow band filter corresponding to a low frequency band can be used.

FIG. 6 is a diagram for explaining another example of the filter coefficient control in the first embodiment.
In the coefficient determination circuit 12, the control unit 123 first sequentially generates the filter characteristics of the filter patterns 1 to 7 with the center frequency shifted as shown in FIG. When the three-wave multipath of the difference between the preceding wave, the main wave, and the delayed wave shown in FIG. 6 is input, the MER in the signal quality detection circuit 122 is minimum when the shift pattern 4 is such that the three waves are within the filter passband. The reception quality is determined to be the best. Next, as shown in FIG. 6B, filter characteristics of a plurality of passband patterns 1 to 6 that pass the main wave and other partial bands are sequentially generated with respect to the shift pattern 4. In the case of a three-wave multipath as shown in FIG. 6 (b), compared to the shift pattern 4 that allows the entire region to pass, it has three passbands that pass only the vicinity of the preceding wave, the main wave, and the delayed wave. Since the noise removal capability of the passband pattern 6 is high, the MER in the signal quality detection circuit 122 becomes small, and it is finally determined that the reception quality is the best.

  As described above, by searching for a filter characteristic with the best reception quality using a filter characteristic having one or a plurality of passbands within a predetermined band, even if the delay difference of the multipath wave is large, the delayed wave can pass through the filter passband. When not spreading all over, noise other than the pass band is cut, so that it is possible to improve the reception performance by removing the noise of the SP signal, that is, the transmission path estimation signal.

  According to the first embodiment, when the multipath delay time range that can be equalized is expanded, even when the delay difference of the multipath is large, if the delayed wave does not spread over the entire filter passband, the noise of the SP signal To improve reception performance.

[Second Embodiment]
FIG. 7 is a block diagram of an OFDM receiving apparatus according to the second embodiment of this invention. The same parts as those of the first embodiment in FIG.
The second embodiment of FIG. 7 differs from the first embodiment of FIG. 1 in that the first coefficient switching circuit 11A includes the passband shift unit 11a and the passband pattern selection unit 11b in addition to FIG. In addition to the bandwidth switching unit 11c that sequentially switches and sets a plurality of bandwidths a), the second coefficient switching circuit 124A includes the passband shift unit 124a and the passband pattern selection unit 124b. A bandwidth switching unit 124c that sequentially switches and sets a plurality of bandwidths similar to 8 (a) is provided. Therefore, the control unit 123A is configured to also control the bandwidth switching unit 11c and the bandwidth switching unit 124c. Other configurations are the same as those in FIG.

FIG. 8 is a diagram for explaining an example of filter coefficient control in the second embodiment.
As shown in FIG. 8A, the first coefficient switching circuit 11A in FIG. 7 has filter characteristics of bandwidth 1, bandwidth 2, and bandwidth 3 in order from the narrowest bandwidth, and has the widest bandwidth. 3 has a plurality of filter characteristics in which the center frequency is shifted with reference to the main wave position. In addition, a plurality of filter characteristics that allow passage of a part of the band including the main wave position from among the shifted filter characteristics can be switched with respect to the filter characteristics of the bandwidth 3, and are supplied from the coefficient determination circuit 12A. It operates according to the bandwidth, shift amount, and passband pattern.

  The coefficient determination circuit 12A in FIG. 7 includes a second SP frequency interpolation filter 125, a second coefficient switching circuit 124A, a second equalization circuit 121, a signal quality detection circuit 122, and a control unit 123A. 8 generates the filter coefficient (filter pattern) shown in FIG. 8, detects the reception quality from the MER of the equalized output using each frequency interpolation, determines the filter coefficient with the best reception quality, and determines the determination result. 1 is supplied to the coefficient switching circuit 11A.

Next, the operation of the coefficient determination circuit 12A will be further described with reference to FIG.
In the coefficient determination circuit 12A, the control unit 123A first has a plurality of filter characteristics obtained by shifting the center frequency with respect to the main wave position for the bandwidth 1, the bandwidth 2, and the bandwidth 3, as shown in FIG. Generate sequentially. When the two-wave multipath with the delay difference shown in FIG. 8 is input, the MER is minimized when the bandwidth 3 + shift pattern 1 in which the two waves are within the filter pass band, and the reception quality is determined to be the best.

  Next, filter characteristics of a plurality of passband patterns that pass the main wave and other partial bands are sequentially generated with respect to a predetermined bandwidth of the bandwidth 3 + shift pattern 1 as shown in FIG. In FIG. 8B, since the pass band of bandwidth 2 or less has been determined in FIG. 8A, the search is performed only when the pass band exceeding bandwidth 2 is included. In the case of the two-wave multipath as shown in FIG. 8, the noise removal capability of the passband pattern 4 that passes only the vicinity of the main wave and the delayed wave is higher than the bandwidth 3 + shift pattern 1 that passes the entire band. Since it is high, the MER becomes small, and it is finally determined that the reception quality is the best.

  In the determination of FIG. 8A, when the multipath delay wave falls within the bandwidth 1, the bandwidth 1 becomes the MER minimum, and when the multipath delay wave exceeds the bandwidth 1 but the bandwidth 2, the bandwidth 2 Becomes the MER minimum. When the filter characteristic of the bandwidth 1 or the bandwidth 2 is selected, since the noise removal of the filter is good, the process for searching for the pass band may not be performed partially, and the description is omitted.

  As described above, the multipath delay is determined by performing the determination based on the filter characteristics of a plurality of bandwidths first, and determining the filter characteristics having one or more passbands in the band when a wide band filter is selected. When the difference is small, it is not necessary to search all filter patterns, and power consumption can be reduced. Further, even when the delay difference is large, if the delayed wave does not spread over the entire filter pass band, the reception performance can be improved by removing the noise of the SP signal.

  According to the second embodiment, the calculation amount when the multipath delay difference is small is reduced to reduce power consumption, and even when the multipath delay difference is large, the delayed wave does not spread over the entire filter passband. In this case, the reception performance can be improved by removing the noise of the SP signal, that is, the transmission path estimation signal.

[Third Embodiment]
FIG. 9 is a block diagram of another example of the coefficient determination circuit in the OFDM receiver according to the third exemplary embodiment of the present invention. The same parts as those of the coefficient determination circuit of FIG.

  In the coefficient determination circuit 12 of FIG. 1, the reception quality is detected by sequentially switching the filter coefficients. However, when the state of the reception signal varies due to mobile reception or the like, the difference in reception quality is due to the variation of the reception state or There is a risk of erroneous determination as to whether the difference is due to a difference in filter coefficients.

  The coefficient determination circuit 12B shown in FIG. 9 includes a second SP frequency interpolation filter 125, a second coefficient switching circuit 124, a second equalization circuit 121, and a first signal quality detection circuit 122. In addition to a set of circuit parts similar to the above, a new SP frequency interpolation filter 14, a third coefficient switching circuit 16, a third equalization circuit 13, and a second signal quality detection circuit 15 Another set of circuit units is provided.

  The third coefficient switching circuit 16 includes a passband shift unit 16a similar to the passband shift unit 124a and a passband pattern selection unit 16b similar to the passband pattern selection unit 124b. Therefore, the control unit 123B is configured to control the third coefficient switching circuit 16 in addition to the first coefficient switching circuit 11 and the second coefficient switching circuit 124 shown in FIG. Other configurations are the same as those of the coefficient determination circuit of FIG.

  In FIG. 9, two sets of SP frequency interpolation filters, coefficient switching circuits, equalization circuits, and signal quality detection circuits are provided, and the second and third etc. are obtained by using two filter coefficients for the same received signal. Based on the signals equalized by the equalization circuits 121 and 13, the first and second signal quality detection circuits 122 and 15 detect the reception quality, respectively, and the control unit 123B selects the better reception quality. By finally comparing the quality of the selected filter characteristic and the quality of the next filter characteristic, the optimum filter coefficient is finally determined.

  With the above configuration, the optimum filter coefficient can be determined even when the state of the received signal varies due to mobile reception or the like. A similar configuration can also be applied to the OFDM receiver of the second embodiment.

[Fourth Embodiment]
FIG. 10 is a block diagram of another example of the coefficient determination circuit in the OFDM receiver according to the third exemplary embodiment of the present invention.
A coefficient determination circuit 12C shown in FIG. 10 is obtained by disposing memories 126 and 127 in the preceding stages of the second equalization circuit 121 and the second SP frequency interpolation filter 125 in the coefficient determination circuit 12 in FIG. . Other configurations are the same as those of the coefficient determination circuit of FIG.

  In FIG. 10, the FFT output signal and the SP signal after time interpolation are held in the memories 126 and 127, respectively, and the filter quality is sequentially switched for the same signal to detect the reception quality and determine the optimum filter.

  With the above configuration, the optimum filter coefficient can be determined even when the state of the received signal varies due to mobile reception or the like. A similar configuration can also be applied to the OFDM receiver of the second embodiment.

  According to the OFDM receiver of the embodiment of the present invention, the SP signal dispersed in the time direction and the frequency direction is interpolated by the SP signal interpolation filter in the time direction and the frequency direction, and the interpolated SP signal is used during equalization. When estimating the required transmission line response, the SP signal interpolation filter uses a filter characteristic having two or more passbands within a given band, and tries switching several passband patterns in order, so that the reception quality is optimal. By determining the pass band of the filter characteristics such that the SP signal is interpolated, the SP signal can be favorably interpolated. Even when a transmission signal has a long-delayed delayed wave component and a filter is applied to a wide band, it is possible to remove the influence of noise and improve reception performance in multipath.

  DESCRIPTION OF SYMBOLS 5 ... FFT circuit, 7 ... Equalization circuit (equalization part), 9 ... SP frequency interpolation filter (filter part), 122 ... Signal quality detection circuit (quality detection part), 12 ... Coefficient determination circuit (determination part), 123 ... control unit.

Claims (5)

A filter unit that band-limits the transmission path estimation signal in the frequency direction using a plurality of filter characteristics, an equalization unit that equalizes a received signal using the output of the filter unit, and reception quality of the output of the equalization unit A quality detection unit for detecting the determination, and a determination unit for determining an optimum filter characteristic from the plurality of filter characteristics using the detected reception quality,
The plurality of filter characteristics include a filter characteristic of a predetermined bandwidth and a plurality of filter characteristics that allow a part of the predetermined bandwidth to pass, and the plurality of filter characteristics that allow the part to pass are two or more. An OFDM receiver characterized by including a filter characteristic having a passband of   2. The OFDM receiver according to claim 1, wherein the plurality of filter characteristics include a passband of a main wave and at least one other passband within a predetermined bandwidth. The plurality of filter characteristics include a plurality of filter characteristics having different center frequencies in a predetermined bandwidth, and a plurality of filter characteristics that allow a part to pass through each of the filter characteristics having different center frequencies. The multiple filter characteristics to be included include filter characteristics having two or more passbands,
The determination unit determines an optimum filter characteristic from among a plurality of center frequency filter characteristics, and then selects the determined filter characteristic and a plurality of filter characteristics that allow a part of the determined filter characteristic to pass. The OFDM receiving apparatus according to claim 1, wherein an optimum filter characteristic is determined. The plurality of filter characteristics pass through a part of the plurality of filter characteristics having different bandwidths and center frequencies and a filter characteristic having a bandwidth equal to or larger than a predetermined bandwidth among the plurality of bandwidths. A plurality of filter characteristics for allowing the part to pass, including a filter characteristic having two or more passbands,
The determination unit determines an optimum filter characteristic of a predetermined bandwidth from a plurality of filter characteristics having different bandwidths and center frequencies, and when the filter characteristic of the predetermined bandwidth is determined, the determined filter characteristic 4. The OFDM receiving apparatus according to claim 1, wherein an optimum filter characteristic is determined from a plurality of filter characteristics that allow a part of the determined filter characteristic to pass.   The determination unit includes a passband shift unit that sequentially switches and sets a plurality of shift patterns, and a pass that sequentially switches and sets a plurality of passband patterns within the bandwidth of any one of the shift patterns. The OFDM receiving apparatus according to claim 1, further comprising a band pattern selection unit.

Images