JP2006246447A - Receiving device, receiving method, integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that there is a possibility of reception performance being severely deteriorated because erasure processing is applied to a carrier in a frequency band of a video signal of an analog television broadcast in order to correct an influence by the same channel disturbance, but in the method there might be eliminated even a carrier not so much influenced by the analog television broadcast. <P>SOLUTION: A receiving device decides the presence of the same channel disturbance utilizing frequency characteristics of analog television broadcast waves, and when the same channel disturbance occurs, reliability information that reflects frequency characteristics of the analog television broadcast is set to each carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for removing the influence of an interference wave when receiving an OFDM signal.

 In recent years, terrestrial digital broadcasting has been started, and the available area is gradually expanding. Terrestrial digital broadcasting adopts the OFDM (Orthogonal Frequency Division Multiplexing) system, and even if radio wave interference exists, the reception side device can correct the normal reception state by performing correction processing. Can be maintained. However, when the radio wave interference exceeds a predetermined limit point, the reception state rapidly deteriorates, causing problems such as block noise in which images are partially lost and interruption of video and audio.

  As factors that degrade the radio wave quality of digital terrestrial broadcasting, it is conceivable that the own delayed wave due to multipath or the like, an analog television broadcast wave, and an external interference wave such as unnecessary radiation. In particular, during a period in which digital broadcasting using the same frequency band is analog broadcasting and simultaneous broadcasting, analog broadcasting waves may interfere with the digital broadcasting waves. In this specification, such interference caused by analog broadcast waves using the same frequency band is referred to as co-channel interference.

  In order to detect and eliminate these interferences, Patent Document 1 discloses a technique for identifying a carrier wave affected by interference radio waves. Further, Patent Document 2 discloses an OFDM diversity receiving apparatus having two receiving systems, and in each receiving system, the interference strength received by each carrier is determined using a dispersion value, and the interference strength is determined. By selectively using the signal received by the weaker receiving system, the influence of jamming radio waves is avoided.

Further, in Patent Document 3, the occurrence of frequency selective interference (in the present application, co-channel interference) is detected based on the pilot signal, and the carrier data affected by the frequency selective interference is subjected to erasure processing to generate an error. An OFDM receiver that performs correction is disclosed.
JP 2004-120789 A Japanese Patent No. 3389178 Japanese Patent No. 3363806

  In the technique of Patent Document 3, when frequency selective interference is detected, carriers that are considered to be affected by the interference are simultaneously removed. However, the analog broadcast wave video signal discretely includes peaks at which the power is maximized. An OFDM carrier having a frequency near the peak is greatly affected by the video signal, but a carrier having a frequency between peaks is not significantly affected. Also, the offset of the analog broadcast wave is +10 kHz, −10 kHz, or no offset, but it depends on the broadcasting station. Therefore, when the carrier affected by the co-channel interference is removed all at once by the method of Patent Document 3 regardless of the analog broadcast frequency characteristics and the presence or absence of the offset, the carrier that is not actually affected by the analog broadcast and Data of carriers that are only weakly affected may be removed, resulting in a decrease in reception performance. In particular, when the coding rate of the convolutional code is large, the reception performance is significantly reduced.

  In order to solve the above problems, an object of the present invention is to provide a receiving apparatus and a receiving method that can remove interference radio waves due to analog broadcasting while maintaining reception performance.

  In order to solve this problem, the present invention is a receiving apparatus that receives an orthogonal frequency division multiplexed signal in which a plurality of carriers carrying data are multiplexed, and compares the received power with a threshold for each carrier, Determining means for determining whether or not received power is greater than a threshold; identifying means for identifying a main peak carrier having a received power that is maximal among carriers determined to have received power greater than a threshold; and The main peak reliability indicating the accuracy of the signal carried by the main peak carrier is set for the peak carrier, and the difference between the frequency of the main peak carrier and the frequency of the carrier is set for the carrier near the main peak carrier. And setting means for setting a reliability equal to or higher than the main peak reliability.

  Since the reception power of the main peak carrier is maximal, the main peak carrier has a frequency closest to the frequency of the jamming wave and is strongly influenced by the jamming wave. However, as the frequency difference from the main peak carrier increases, the influence of the nearby carrier on the main peak carrier from the interference wave decreases. According to said structure, the said setting means is equivalent to or higher than the said main peak reliability according to the difference of the frequency of the said main peak carrier and the frequency of the said carrier for each carrier in the vicinity of the said main peak carrier. Set the confidence level. Therefore, a low reliability can be set for a carrier that is strongly influenced by an interference wave, and a high reliability can be set for a carrier that is not significantly affected by the interference wave.

Here, according to the reliability set for each carrier, the signal carried by each carrier is weighted to restore the data, thereby reliably removing the influence of the interference wave and reducing the reception performance. There is an excellent effect that it can be prevented.
The receiving apparatus is further configured to move away from the main peak carrier by a predetermined frequency when the orthogonal frequency division multiplexing signal is disturbed by an analog television broadcast wave that uses the same frequency band as the orthogonal frequency division multiplexing signal. Prediction specifying means for specifying the predicted carrier, and the setting means further sets a reliability equal to or higher than the main peak reliability for the predicted carrier, and for carriers in the vicinity of the predicted carrier, A reliability equal to or higher than the predicted reliability is set according to a frequency difference between the predicted carrier and the carrier.

  As for the frequency characteristics of analog television broadcast waves, the power is discretely maximized. The positional relationship between the frequencies at which the power reaches a maximum value and the relationship between the maximum values are almost determined. According to the above configuration, the prediction specifying unit specifies a prediction carrier separated from the main peak carrier by a predetermined frequency, and the setting unit has a reliability equal to or higher than the main peak reliability for the prediction carrier. Set. Therefore, it is possible to set the reliability reflecting the characteristics of the analog broadcast wave, that is, the position of the frequency of each maximum value and the magnitude relationship between the maximum values.

Further, the setting means constituting the receiving device has a reliability equal to or higher than the predicted reliability according to a frequency difference between the predicted carrier and the carrier, on a carrier in the vicinity of the predicted carrier. Since the setting is performed, there is an effect that an appropriate reliability can be set for the carrier in the vicinity of the peak of the analog broadcast wave.
In the receiving device, the specifying unit specifies the main peak carrier in the vicinity of the frequency of the analog television broadcast wave video signal, and further determines the determination in the vicinity of the frequency of the audio signal of the analog television broadcast wave. Means for identifying a sub-peak carrier having a maximum received power among the carriers determined to have a received power equal to or greater than a threshold, and the predictive specifying means determines whether the sub-peak carrier is determined by the specifying means. When specified, the predicted carrier is specified.

  The frequency at which the video signal of the analog television broadcast wave is distributed and the frequency at which the audio signal is distributed are determined by the standard (however, an offset of ± 10 kHz may be provided). Therefore, when the main peak carrier is specified in the vicinity of the frequency of the video signal of the analog TV broadcast wave, and the sub peak carrier is specified in the vicinity of the frequency of the audio signal of the analog TV broadcast wave, the orthogonality is obtained. It can be estimated that the frequency division multiplexing signal has co-channel interference with a very high probability. According to the above configuration, the prediction specifying means specifies the main peak carrier in the vicinity of the frequency of the video signal of the analog television broadcast wave, and further, in the vicinity of the frequency of the audio signal of the analog television broadcast wave, When the peak carrier is specified, the predicted carrier is specified. Therefore, the setting means can set the reliability corresponding to the co-channel interference with very high accuracy.

Further, the predetermined frequency is a frequency multiplied by a horizontal synchronizing frequency of the analog television broadcast wave, and the prediction specifying means constituting the receiving device uses the main peak carrier to multiply the horizontal synchronizing frequency by a frequency. It is characterized by specifying the said prediction carrier away.
The video signal of the analog television broadcast wave has a steep peak for each multiplication of the horizontal synchronization frequency. According to this configuration, the setting means can reliably set a low reliability for a carrier that is strongly influenced by an analog broadcast video signal.

Further, the predetermined frequency is a difference between the frequency of the audio signal of the analog television broadcast wave and the frequency of the video signal, and the prediction specifying means constituting the receiving device takes the difference from the main peak carrier to the difference. The predicted peak carriers separated by an equal frequency are specified.
The interval between the video signal frequency and the audio signal frequency of the analog television broadcast wave is determined by the standard. Therefore, according to this configuration, the setting unit can reliably set a low reliability for a carrier that is strongly influenced by an analog broadcast audio signal.

In the receiving apparatus, the prediction specifying unit specifies the prediction carrier when the main peak carrier is specified in the vicinity of the frequency of the video signal of the analog television broadcast wave.
The power of audio signals for analog television broadcasting is smaller than the power of video signals. For this reason, even when co-channel interference occurs, if the level of interference is weak, the influence of the audio signal may appear only slightly in the frequency characteristics of the received orthogonal frequency division multiplexed signal. According to the above configuration, the prediction specifying unit specifies the predicted carrier when the main peak carrier is specified in the vicinity of the frequency of the video signal of the analog television broadcast wave. Even if the level of interference is weak, a low reliability can be set for a carrier that is predicted to be affected by analog television broadcasting.

In this configuration, the circuit configuration of the prediction specifying unit can be simplified.
Further, in the present invention, the specifying means specifies the main peak carrier in the vicinity of the frequency of the video signal of the analog television broadcast wave, and among the carriers determined to have received power equal to or higher than a threshold, Attempts to specify a sub-peak carrier having a reception power that is maximal and having a frequency that is different from the frequency of the main peak carrier by a frequency that is a multiple of the horizontal synchronization frequency of the analog television broadcast wave, and the prediction specifying means includes the specifying means When the sub-peak carrier is specified, the predicted carrier is specified.

  The video signal of an analog television broadcast wave has a sharp peak, with power concentrated every time the horizontal synchronization frequency is multiplied. Therefore, the main peak carrier exists in the vicinity of the frequency of the video signal of the analog television broadcast wave, and a sub frequency having a frequency that is different from the frequency of the main peak carrier by a frequency multiplied by the horizontal synchronization frequency of the analog television broadcast wave. When peak carriers are present, it can be estimated that co-channel interference occurs with a very high probability. According to the above configuration, the main peak carrier exists in the vicinity of the frequency of the video signal of the analog television broadcast wave, and only the frequency obtained by multiplying the frequency of the main peak carrier and the horizontal synchronization frequency of the analog television broadcast wave. Since the predicted carrier is specified when sub-peak carriers of different frequencies exist, the receiving apparatus of the present invention can set reliability suitable for co-channel interference.

  Further, in the receiving apparatus, the determination unit, for each carrier, based on an average value of received power of the carrier and a predetermined number of carriers in the vicinity thereof, a threshold value calculation unit that calculates a threshold value corresponding to the carrier; For each carrier, a reception unit and a threshold corresponding to the carrier are compared, and a determination unit that determines whether the reception power is greater than the threshold is included.

  Normally, orthogonal frequency division multiplexing has a flat power distribution with respect to frequency, except for carriers that are affected by interference waves. However, the power distribution of the orthogonal frequency division multiplexed signal is inclined due to the influence of the signal transmission path. Therefore, if the determination is performed using the same threshold value for all carriers, the setting means may set a low reliability to the carrier that is not affected by the interference wave due to the influence of the inclination. .

According to said structure, a threshold value calculation part calculates a suitable threshold value for every carrier based on the average value of the reception power of the said carrier and the predetermined number of carriers of the vicinity. Therefore, it is possible to prevent the erroneous setting of reliability as described above.
Further, in the receiving apparatus of the present invention, the determination unit includes a power calculation unit that calculates power of each carrier for each symbol period, and integrates the power for each carrier over a predetermined symbol period. And a determination unit that compares the received power with a threshold for each carrier and determines whether the received power is greater than the threshold.

  According to this configuration, the reception power of each carrier is generated by integrating the power for each carrier over a predetermined symbol period. Therefore, the determination unit can stably perform the determination without being affected by a temporary change in reception state such as an instantaneous interference wave or a radio wave reception failure under mobile communication. .

1. Embodiment 1
Embodiment 1 of the present invention will be described below with reference to the drawings.
1.1 Co-channel interference To make the present invention easier to understand, interference occurring in terrestrial digital broadcasting will be described.

(1) Frequency characteristics FIG. 1A schematically shows frequency characteristics of broadcast waves of terrestrial digital broadcasting in Japan. In the following, the first embodiment will be described basically by taking terrestrial digital broadcasting conforming to mode 3 of the ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) system as an example. Since the ISDB-T system is known, detailed description thereof is omitted here.

  As shown in FIG. 1A, a frequency band of 6 MHz is allocated to one channel of terrestrial digital broadcasting, and 13 segments out of 14 divisions of the 6 MHz band are used for actual transmission. In order to avoid the influence of an analog broadcast wave audio signal using an adjacent band, an offset of 1/7 MHz is set. Therefore, in terrestrial digital broadcasting, 5/14 MHz (= 357.14 kHz) from the lower end of the channel. At the position, the carrier with the lowest frequency of the OFDM signal (carrier number “0”) is present, and the carrier with the highest frequency (carrier number “5616”) is present at a position of 1/14 MHz from the upper end of the channel. In mode 3, the OFDM carrier interval is defined as 0.992063 kHz, and there are 5617 carriers in one channel. The power of each OFDM carrier is substantially the same, and the OFDM signal 151 of the terrestrial digital broadcast becomes flat as shown in FIG.

  FIG. 1B schematically shows the frequency characteristics of analog broadcasting in Japan (NTSC system: National Television Standards Committee). As shown in FIG. 1B, a frequency band of 6 MHz is assigned to each channel for analog broadcasting, and a video signal 152 is distributed around a position of 1.25 MHz from the lower end of the 6 MHz frequency band. The audio signal 153 is distributed around the position of 5.75 MHz. The interval between the peak of the video signal 152 and the peak of the audio signal 153 is about 4.5 MHz. However, as already described, in analog broadcasting, an offset of ± 10 kHz may be provided by a broadcasting station. In general, a video signal has higher power intensity than an audio signal.

(2) Co-channel interference Since terrestrial digital broadcasting uses the UHF band (440 to 770 MHz), terrestrial digital broadcasting and analog broadcasting may interfere with each other on the same channel, resulting in co-channel interference. is there.
FIG. 2A shows frequency characteristics of analog broadcasting and terrestrial digital broadcasting using the same channel. The frequency band in which the terrestrial digital broadcast OFDM signal 156 and the analog broadcast video signal 154 and audio signal 155 exist overlap.

FIG. 2B shows an enlarged view of the vicinity of the frequency at which the video signal 154 in FIG. Each thick arrow in the figure represents a peak of an analog broadcast video signal, and each thin vertical line represents an OFDM signal carrier.
Since the power of the analog broadcast video signal is concentrated at a position where the horizontal synchronization frequency (15.734264 kHz) of the analog broadcast is multiplied, as shown in FIG. 2B, there are sharp peaks 154a to 154i at equal intervals. The interval between adjacent peaks is 15.734264 kHz.

  FIG. 2C shows an enlarged view between the peak 154e and the peak 145f in FIG. The thin arrows lined up in parallel with the peaks 154e and 154f in the figure indicate OFDM signal carriers, respectively. As described above, the interval between the peak 154e and the peak 154f is 15.734264 kHz, and the carrier interval of the OFDM signal is 0.992063 kHz. 15.734264 / 0.999203 = 15.86 Therefore, there are approximately 16 OFDM signal carriers between the peaks of the audio signal of the analog broadcast.

  When co-channel interference occurs, the carrier in the vicinity of the peak of the analog broadcast video signal is strongly affected by the video signal, but the other carriers are not significantly affected. For example, when an OFDM carrier exists at the position shown in FIG. 2C, carriers near the peak 154e and the peak 154f are greatly affected by the video signal. In particular, the carriers 156a and 156c having the frequencies closest to the peaks 154e and 154f are most strongly affected. However, carriers near the middle between the peak 154e and the peak 154f are not easily affected.

On the other hand, as shown in FIG. 3, the audio signal 155 of the analog broadcast has peaks 155a to 155e where power concentrates at an interval twice the horizontal synchronization frequency (31.468 Hz). Since 31.468 / 0.999203 = 31.719, there are about 32 OFDM carriers between adjacent peaks.
However, unlike the video signal, the peak of the audio signal is not so steep, and as a whole, the power decreases with increasing distance from the peak 155c with the peak 155c having the highest power as the apex. Therefore, the carrier of the frequency close to the peak 155c is strongly influenced by the audio signal, and the influence of the audio signal is weakened as the distance from the peak 155c is increased.

  Here, assuming that there is no offset in the analog broadcast, the maximum peak 154e of the video signal 154 of the analog broadcast is a position 892.86 kHz (= 1.25 MHz-357.14 kHz) from the position of the carrier at the lower end of OFDM. Exists. Since 892.86 kHz / 0.992063 kHz = 900.0033, the carrier number of the carrier 156a existing at the frequency closest to the peak 154e is “900”. Here, frequency fluctuations accompanying movement of the receiving device are not taken into account.

  Since the interval between the video signal 154 and the audio signal 155 is 4.5 MHz, there are 4536 lines (= 4.5 MHz) between the maximum peak 154e of the video signal 154 and the maximum peak 155c of the audio signal 155. Carrier having the frequency closest to the peak 155c of the audio signal 155 is the carrier number “5436”.

(3) In-band interference In addition to analog broadcasting of the same channel, terrestrial digital broadcasting is also disturbed by various factors such as unnecessary radiation from peripheral devices during transmission and natural phenomena such as lightning (hereinafter referred to as “in-band interference”). Called in-band jamming). FIG. 4 shows an OFDM signal 160 of terrestrial digital broadcasting and an interference wave 159 generated in the frequency band of terrestrial digital broadcasting. The frequency at which the jamming wave 159 is generated is often difficult to predict in advance.
1.2 Configuration of Broadcast Receiving Device 100 Hereinafter, the configuration of the broadcast receiving device 100 according to Embodiment 1 will be described.

  The broadcast receiving apparatus 100 is an apparatus that receives and reproduces a terrestrial digital broadcast that complies with ISDB-T mode 3, and is connected to a display device such as a liquid crystal television. As shown in FIG. 5, the antenna 101, the tuner 102, the A / D conversion unit 103, the quadrature detection unit 104, the FFT processing unit 106, the equalization processing unit 107, the deinterleaving unit 108, the demapping unit 109, the Viterbi decoding unit 111, The power calculation unit 112, the average calculation unit 113, the threshold value calculation unit 118, the interference determination unit 119, the reliability output unit 121, the RS decoding unit 122, the TS decoding unit 123, and the MPEG decoding unit 124 are configured.

  Tuner 102, A / D conversion unit 103, quadrature detection unit 104, FFT processing unit 106, equalization processing unit 107, deinterleave unit 108, demapping unit 109, Viterbi decoding unit 111, power calculation unit 112, average calculation unit 113, The threshold calculation unit 118, the interference determination unit 119, the reliability output unit 121, and the RS decoding unit 122 are circuits formed on one LSI (Large Scale Integration).

Below, each component of the broadcast receiving apparatus 100 is demonstrated.
(1) Antenna 101 and tuner 102
The tuner 102 selects a frequency band related to a predetermined channel from the signal received by the antenna 101 and outputs the selected frequency band to the A / D conversion unit 103.
(2) A / D converter 103 and quadrature detector 104
A / D conversion section 103 samples the carrier OFDM signal output from tuner 102, converts it to a digital signal, and outputs it to quadrature detection section 104.

The quadrature detection unit 104 multiplies the carrier wave OFDM signal by a sine wave having the same frequency as the reference carrier wave, removes the high frequency component, and generates a sample value sequence of the OFDM baseband signal. The generated sample value sequence is output to the FFT processing unit 106.
(3) FFT processing unit 106
The FFT processing unit 106 extracts a sample value included in one effective symbol period for each symbol period (including a guard interval) from the sample value sequence of the OFDM baseband signal output from the quadrature detection unit 104. A discrete Fourier transform is performed on the extracted sample value sequence to generate a complex signal of each carrier. A complex signal group related to one effective symbol generated in this way is called an OFDM symbol. The generated OFDM symbol is output to equalization processing section 107 and power calculation section 112.

(4) Equalization processing unit 107
The OFDM signal of terrestrial digital broadcasting includes SP signals (scattered pilot signals) every 12 symbols in the carrier direction. Carriers including the SP signal are shifted by 3 symbols for each symbol period. The equalization processing unit 107 receives the OFDM symbol from the FFT processing unit 106, detects the SP signal included in the received OFDM symbol, and compensates for the influence of distortion on the transmission path using the detected SP signal. .

(5) Deinterleave unit 108
The deinterleaving unit 108 sequentially receives the OFDM symbols compensated by the equalization processing unit 107, and performs time deinterleaving and frequency deinterleaving on the received OFDM symbols. Subsequently, the complex signals constituting each OFDM symbol are parallel-serial converted and output to the demapping unit 109.

(6) Power calculation unit 112
The power calculation unit 112 receives the OFDM symbol from the FFT processing unit 106, and calculates the power of each carrier in one effective symbol period based on the complex signal group constituting the received OFDM symbol. For convenience of explanation, the power of the carrier of the carrier number s (0 ≦ s ≦ 5616) that is included in the OFDM symbol of the symbol number m is represented as p (m, s). The calculated power p (m, s) of each carrier is output to the average calculation unit 113.

(7) Average calculation unit 113
The average calculation unit 113 includes an addition unit 114, a memory 116, and a delay unit 117, and is a functional unit that calculates the average power of each carrier in the symbol direction up to the present time.
The memory 116 stores the average power in the symbol direction of each carrier up to the present time. FIG. 6 shows an example of the configuration of the memory 116. As shown in FIG. 6, the memory 116 includes 5617 storage areas 131, 132, 133. Each storage area stores a carrier number (0 to 5616) and average power (P0 to P5616). The average power is obtained by averaging the power of the carrier indicated by the corresponding carrier number in the symbol direction.

For example, the storage area 131 stores the carrier number “0” and the average power “P0”. Assuming that p (m, 0) is output from the power calculator 112, “P0” is the average of p (0,0), p (1,0)... P (m, 0). Value.
The adder 114 sequentially receives the power of each carrier from the power calculator 112. When the adding unit 114 receives p (m, s), the delay unit 117 reads the average power “Ps” corresponding to the carrier number s from the memory 116 and outputs the average power “Ps” to the adding unit 114. The adder 114 calculates k × p (m, s) + (1−k) × Ps, and updates the average power corresponding to the carrier number “s” stored in the memory 116 based on the calculation result. k is a variable that varies between 0.001 and 0.1.

The average calculation unit 113 described above can be realized using an IIR filter.
(8) Threshold calculation unit 118
The threshold calculation unit 118 reads average powers “P0” to “P5616” from the memory 116.
Next, the threshold value calculation unit 118 temporarily stores the read average powers “P0” to “P5616”. An average value of the stored average powers “P0” to “P5616” is calculated, and a predetermined offset is added to the calculated average value to calculate a threshold value. The threshold value calculated here is used by the subsequent interference determination unit 119 to determine whether or not each carrier is disturbed. Note that the above threshold value calculation method is merely an example, and other methods may be used.

When the threshold value is calculated, the threshold value calculation unit 118 outputs the read average powers “P0” to “P5616” and the calculated threshold value to the interference determination unit 119.
(9) Interference determination unit 119
The interference determination unit 119 temporarily stores the average power “P0” to “P5616” output from the threshold value calculation unit 118 together with the corresponding carrier number. Further, the threshold value is also temporarily stored, and based on these, it is determined whether co-channel interference has occurred in the OFDM signal by the following procedure.

  First, it is determined whether each carrier is disturbed by comparing each of the average powers “P0” to “P5616” with a threshold value. A carrier having an average power greater than the threshold is determined to be subject to some interference, and a determination result “NG”, a carrier having an average power equal to or less than the threshold is determined not to be disturbed, and a determination result “OK”. Is stored for each carrier. FIG. 7 shows the configuration of information stored in the disturbance determination unit 119 at this time. Here, as an example, a carrier determination table 140 that associates carrier numbers, average power, and determination results is stored. The carrier determination table 140 is composed of 5617 pieces of determination information 141, 142, 143... 149, and each determination information includes the carrier number, the average power of the carrier indicated by the carrier number, and the determination result. Corresponds to the carrier indicated by the number.

  8 and 9 show an example of the average power distribution of each carrier. The horizontal axis in both figures is the carrier number, and the vertical axis is the average power. A broken line in the figure indicates a threshold value calculated by the threshold value calculation unit 118. Here, the distribution of average power when co-channel interference occurs is shown. In FIG. 8, portions from carrier numbers “867” to “933” are extracted, and this portion coincides with a band in which an analog broadcast video signal is distributed.

In FIG. 9, carrier portions of carrier numbers “5403” to “5469” are extracted, and this portion coincides with a band in which an analog broadcast audio signal is distributed.
As shown in FIGS. 8 and 9, the distribution of the average power has a place where it is discretely maximized. In particular, in the frequency band shown in FIG. 8, there is a steep peak where the average power corresponding to the carrier numbers “868”, “884”, “900”, “916”, and “932” is a maximum value. . This is due to the fact that the analog broadcast video signal has discrete peaks every 15.734264 kHz. The average power for carrier numbers near carrier numbers “868”, “884”, “900”, “916”, and “932” exceeds the threshold. Therefore, the determination results of the carrier determination information including the carrier numbers “868”, “884”, “900”, “916”, “932” and the carrier numbers in the vicinity thereof are “NG”.

  Also in the frequency band shown in FIG. 9, there are peaks in which the average power corresponding to the carrier numbers “5404”, “5436”, and “5468” is a maximum value. However, the peak shown in FIG. 9 is gentle. As a whole, the average power decreases as the distance from the carrier having the maximum average power (carrier number “5463”) increases. This is an influence of an audio signal of analog broadcasting having gentle peaks at 31.468 kHz intervals. Therefore, the determination result of the determination information corresponding to a plurality of carriers centered on the carrier with the carrier number “5436” is “NG”.

  The interference determination unit 119 selects information whose determination result is “NG” from the determination information constituting the carrier determination table 140. In the selected determination information, the average power included in the determination information having consecutive carrier numbers is compared to identify the carrier having the maximum average power. For example, the determination results included in the determination information 144, 145, and 146 are all “NG”, and the carrier numbers are continuous. Since the average powers included in the determination information 144, 145, and 146 are compared and P899 ≦ P900 ≧ P901, the carrier with the carrier number “900” is determined to be the carrier having the maximum average power. In the same procedure, the carrier having the maximum average power is specified. Here, the identified carrier is called a peak carrier, and the corresponding carrier number (hereinafter, peak carrier number) is expressed as “C0”, “C1”, “C2”... “Cx” (0 ≦ x <5616, 0 ≦ C0, C1... Cx ≦ 5616).

  Next, the interference determination unit 119 searches for the peak carrier number “Cb” that satisfies 880 ≦ Cb ≦ 920 among the specified peak carrier numbers (0 ≦ b ≦ x). As described above, the peak of the analog broadcast video signal is closest in frequency to the carrier of the carrier number “900”. However, considering the presence or absence of an offset of ± 10 kHz, the peak of the analog broadcast video signal is considered to be included in the carrier frequency band of carrier numbers “890” to “910”. In the present embodiment, the carrier between carrier numbers “980” to “920” is strongly disturbed in consideration of the influence on the transmission path and the fluctuation of the frequency due to the movement of the broadcast receiving apparatus 100 itself. In this case, it is estimated that there is a high possibility that the interference caused by the analog broadcast video signal has occurred.

When the interference determination unit 119 detects a peak carrier number satisfying 880 ≦ Cb ≦ 920, the interference determination unit 119 specifies a peak carrier number having the maximum corresponding average power among the detected peak carrier numbers. The peak carrier number specified here is “Cv” (0 ≦ v ≦ x).
Subsequently, the interference determination unit 119 searches for the carrier number “Ca” satisfying Ca = Cv + 4536 among the above-described peak carrier numbers (0 <a ≦ x).

  As described above, there are 4536 OFDM signal carriers between video signals and audio signals of analog broadcasting. Therefore, when there is a peak carrier number “Ca” that satisfies Ca = Cv + 4536, the interference determination unit 119 determines that co-channel interference has occurred. The peak carrier numbers “Cv” and “Ca” specified by the above procedure are referred to as video peak carrier number “Cv” and audio peak carrier number “Ca”, respectively. The peak carrier indicated by the video peak carrier number “Cv” is the carrier that is most strongly disturbed by the analog broadcast video signal, and the peak carrier indicated by the audio peak carrier number “Ca” is the analog broadcast audio signal. It is the carrier that is most affected by the resulting disturbance.

Next, the interference determination unit 119 outputs the generated signal indicating the occurrence of the same channel interference, the video peak carrier number “Cv”, and the audio peak carrier number “Ca” to the reliability output unit 121. Subsequently, the specified peak carrier numbers “C0”, “C1”, “C2”... “Cx” are output to the reliability output unit 121.
When the peak carrier number “Cv” satisfying 880 ≦ Cv ≦ 920 does not exist among the identified peak carrier numbers, in other words, the carriers having the carrier numbers “880” to “920” are strongly influenced by the interference wave. If there is no carrier, it can be determined that co-channel interference has not occurred. Moreover, even if the peak carrier number “Cv” that satisfies 880 ≦ Cb ≦ 920 exists among the specified peak carrier numbers, the peak carrier number “Ca that satisfies Ca = Cv + 4536 is included in the specified peak carrier numbers. "" Does not exist, it can be determined that no co-channel interference has occurred.

If it is determined that no co-channel interference has occurred, the interference determination unit 119 generates a non-occurrence signal indicating that no co-channel interference has occurred and carrier numbers “C0”, “C1” of the identified peak carriers, “C2”... “Cx” is output to the reliability output unit 121.
(10) Reliability output unit 121
The reliability output unit 121 stores in advance reliability information to be set for each carrier in a frequency band that overlaps with an analog broadcast audio signal and video signal when co-channel interference occurs. Here, as an example, it is assumed that the first correspondence table and the second correspondence table that have the same configuration as the carrier determination table 140 in FIG. 7 and associate the carrier number with the reliability information are stored. Although not shown, the first correspondence table is a table in which the reliability information set for each carrier in the frequency band overlapping with the analog broadcast video signal is associated with the carrier number of each carrier. The second correspondence table is a table that associates the reliability information set for each carrier in the frequency band overlapping with the analog broadcast audio signal and the carrier number of each carrier.

  Here, the reliability information indicates the reliability of the carrier and is a value of “0”, “1”, “2”, or “3”. Carriers that are strongly affected by jamming waves have low reliability, so the value of reliability information is small, and carriers that are not affected by jamming waves are high in reliability and have high reliability information values. In the present embodiment, for simplicity of explanation, the range of reliability information values is described as a range that can be represented by 2 bits. However, the range of reliability information values is usually a number. This is a range that can be expressed in bits.

  FIG. 10 shows the carrier number and reliability information of each carrier included in the first correspondence table stored in the reliability output unit 121. The carrier numbers included in the first correspondence table are all shown as a function of the variable v, and the variable v is a variable indicating the carrier number of the carrier that is most strongly affected by the analog broadcast video signal. As shown in FIG. 10, the first correspondence table includes reliability information for carrier numbers “v−70” to “v + 70”.

  As described with reference to FIG. 2, there are about 16 carriers between the peaks of the analog broadcast video signal. Therefore, as shown in FIG. 10, the carrier of the carrier number v and the carrier number “v ± 16 × n (1 ≦ n ≦ 4)” depends on the relative carrier position based on the carrier of the carrier v. Reliability information is set. Specifically, the reliability information “0” is set for the carriers with the carrier numbers v and “v ± 16”, and the reliability information is set for the carrier numbers “v ± 32” and “v ± 48”. “1” is set, and reliability information “2” is set for the carrier number “v ± 64”. Furthermore, high reliability information is set for the carrier in the vicinity of the carrier number v as the carrier position with respect to the carrier of the carrier number v becomes far. Similarly, for the carrier in the vicinity of the carrier number “v ± 16 × n (1 ≦ n ≦ 4)”, the carrier position based on the carrier of the carrier number “v ± 16 × n (1 ≦ n ≦ 4)” is the same. As a result, high reliability information is set.

  FIG. 11 shows the carrier number and reliability information of each carrier included in the second correspondence table stored in the reliability output unit 121. The carrier numbers included in the second correspondence table are all shown as a function of the variable a, and the variable a is a variable indicating the carrier number of the carrier that is most strongly affected by the audio signal of the analog broadcast. As shown in FIG. 11, the second correspondence table includes reliability information for carrier numbers “a−70” to “a + 70”.

  As described with reference to FIG. 3, there are 32 carriers between the peaks of the analog audio signal, but the peaks are all gentle, and as a whole, the carrier has a frequency close to the peak with the highest power. It is strongly influenced by the audio signal. Accordingly, the reliability information “0” is set for the carrier in the vicinity of the carrier of the carrier number a, and the reliability information that is set is gradually increased as the carrier position with respect to the carrier number a is increased. It is set high.

  When the interference determination unit 119 determines that co-channel interference has occurred, the reliability output unit 121 receives the generated signal indicating the occurrence of co-channel interference and the video peak carrier number “Cv” from the interference determination unit 119. ”And the voice peak carrier number“ Ca ”, and subsequently, carrier numbers“ C0 ”,“ C1 ”,“ C2 ”...“ Cx ”indicating the specified peak carriers are received.

When the interference determination unit 119 determines that co-channel interference has not occurred, the reliability output unit 121 determines from the interference determination unit 119 that an ungenerated signal indicating that no co-channel interference has occurred, Peak carrier numbers “C0”, “C1”, “C2”... “Cx” of received peak carriers are received.
Hereinafter, processing performed by the reliability output unit 121 in each case will be described.

(10-a) When co-channel interference has occurred When the generated signal, the video peak carrier number “Cv”, and the audio peak carrier number “Ca” are received, the reliability output unit 121 first performs the co-channel interference. Reliability information is set for a carrier that is estimated to be strongly affected. Specifically, the received video peak carrier number “Cv” is substituted into the variable v, and the carrier numbers “Cv−70” to the carrier numbers “Cv + 70” are based on the first correspondence table described with reference to FIG. Set reliability information for each carrier.

Next, the received voice peak carrier number “Ca” is substituted into the variable a, and the carriers corresponding to the carrier numbers “Ca−70” to “Ca + 70” are respectively trusted according to the second correspondence table described with reference to FIG. Set sex information.
After the reliability information is set for each carrier in the range estimated to be affected by the co-channel interference in the above procedure, the reliability output unit 121 then performs the in-band in the following procedure. Set reliability information for each carrier affected by interference.

  First, the reliability output unit 121 receives the peak carrier numbers “C0”, “C1”, “C2”... “Cx” output from the interference determination unit 119. Carrier numbers “Cv−70” to “Cv + 70” and carrier numbers “Ca−70” to “Ca + 70” that are not included in the range indicate carriers in which in-band interference due to interference waves other than analog broadcasting occurs. (Hereinafter, these peak carrier numbers are referred to as in-band peak carrier numbers, and the corresponding carriers are referred to as in-band peak carriers).

  In-band interference may also occur in the carrier numbers “Cv−70” to “Cv + 70” and the carrier numbers “Ca−70” to “Ca + 70”. Therefore, the reliability output unit 121 is included in the range of the carrier numbers “Cv−70” to “Cv + 70” among the received peak carrier numbers, and the difference from the video peak carrier number “Cv” is not a multiplication of 16. Search for peak carrier number. Further, among the received peak carrier numbers, a peak carrier number that is included in the range of carrier numbers “Ca−70” to “Ca + 70” and whose difference from the video peak carrier number “Ca” is not a multiple of 32 is searched. Here, the detected peak carrier number also indicates the in-band peak carrier.

  Next, the reliability output unit 121 sets low reliability information for carriers in the vicinity of the in-band peak carrier. Note that the in-band peak carrier in the range of the carrier numbers “Cv−70” to “Cv + 70” and the carrier numbers “Ca−70” to “Ca + 70” and the nearby carriers already have the first and second correspondence tables. Although the reliability information has been set by using, the set reliability information is adopted here.

The method for setting the reliability information here is arbitrary, but for example, the reliability information may be set higher stepwise as the carrier position from the in-band peak carrier moves away.
In addition, reliability information “0” may be assigned to the in-band peak carrier and about ± 10 to 20 carriers in the vicinity thereof. (This embodiment assumes ISDB-T mode 3. However, in mode 2, the number of carriers for which reliability information “0” is set may be about ½. In this case, the number of carriers for which reliability information “0” is set may be about 1/4 of the above.)
The reliability information may be determined in consideration of the difference between the average power corresponding to the peak carrier and the threshold value.

Next, reliability information “3” is set for a carrier for which reliability information is not set, that is, a carrier that is not affected by the co-channel interference or the in-band interference.
As described above, when the reliability information has been set for all the carriers, the carrier number of each carrier and the reliability information set for the carrier are associated with each other and output to the demapping unit 109.

(10-b) When co-channel interference has not occurred The reliability output unit 121 generates the non-occurrence signal and the peak carrier numbers “C0”, “C1”, “C2”. Cx "is received. In this case, since the same channel interference does not occur, the peak carrier numbers “C0”, “C1”, “C2”... “Cx” all indicate carriers in which the in-band interference occurs. (Hereinafter, these peak carrier numbers are called in-band peak carrier numbers, and the corresponding carriers are called in-band peak carriers). The reliability output unit 121 sets low reliability information for the in-band peak carrier and nearby carriers. The setting method is the same as the reliability information setting method in the vicinity of the in-band peak carrier described in (10-a).

Subsequently, the reliability output unit 121 sets the reliability information “3” to a carrier number for which reliability information has not yet been set, that is, a carrier that has not been subjected to in-band interference.
Next, the reliability output unit 121 associates the carrier number of each carrier with the reliability information set for the carrier, and outputs it to the demapping unit 109.
Although not shown in the figure, the reliability output unit 121 outputs reliability information corresponding to each carrier according to the same rules as the frequency deinterleaving by the deinterleaving unit 108 before outputting to the demapping unit 109. Frequency deinterleave.

(11) Demap unit 109, Viterbi decoding unit 111, and RS decoding unit 122
The demap unit 109 demaps the complex signal output from the deinterleave unit 108 and generates corresponding bit data. Subsequently, the reliability information of each carrier output from the reliability output unit 121 is allocated to the generated bit data to the bit metric and output to the Viterbi decoding unit 111.

The Viterbi decoding unit 111 sequentially receives bit data with reliability information from the demapping unit 109, bit-interleaves the received bit data together with the reliability information, weights based on the reliability information, and performs Viterbi decoding Process.
The RS decoding unit 122 receives the bit data subjected to the Viterbi decoding process by the Viterbi decoding unit 111, decodes Reed-Solomon, and outputs it to the TS decoding unit 123.

(12) TS decoding unit 123 and MPEG decoding unit 124
The bit data output from the RS decoding unit 122 constitutes MPEG2-TS (Moving Picture Experts Group phase 2-Transport Stream).
The TS decoding unit 123 detects PSI (Program Specific Information) included in the transport stream. Based on the detected PSI, TS packets related to a desired service are extracted from the transport stream, classified into Video packets, Audio packets, and PCR (Program Clock Reference) packets and output to the MPEG decoding unit 124.

The MPEG decoding unit 124 includes an image decoder and an audio decoder. The image decoder extracts MPEG Video data from the Video packet output from the TS decoding unit 123, decodes the extracted MPEG Video data, and generates image data. The voice coder extracts MPEG Audio data from the Audio packet, and decodes the extracted MPEG Audio data to generate voice data. The MPEG decoding unit 124 outputs image data and audio data to the display device while synchronizing based on the PCR included in the PCR packet.
1.3 Operation The operation of setting reliability information, which is a characteristic part of the present invention, will be described below with reference to the flowcharts of FIGS.

  The power calculator 112 receives the OFDM symbol from the FFT processor 106 (step S101). When receiving the OFDM symbol, the power calculation unit 112 calculates the power p (m, s) of each carrier based on the complex signals (5616) of each carrier included in the received OFDM symbol (step S102). Here, m is a symbol number and s is a carrier number. The calculated power p (m, s) is output to the adder 114.

The delay unit 117 reads the average power Ps of each carrier up to the present from the memory 116, and outputs the read average power Ps to the addition unit 114 (step S103).
Based on the power p (m, s) of each carrier output from the power calculator 112 and the average power Ps output from the delay unit 117, the adder 114 performs k × p (m, s) + (1-k) Ps is calculated, and the average power Ps stored in the memory 116 is updated based on the calculation result (step S106).

  Next, the threshold value calculation unit 118 reads the average power P0 to P5616 of each carrier from the memory 116 (step S109). The threshold value calculation unit 118 calculates a threshold value by adding a predetermined offset to the average value of the read average powers P0 to P5616 (step S111). The calculated threshold value and the average power P0 to P5616 of each carrier read from the memory 116 are output to the interference determination unit 119.

The interference determination unit 119 temporarily stores the threshold value output from the threshold value calculation unit 118 and the average power of each carrier. For each carrier, the average power and the threshold are compared, and the carrier number, average power, and comparison result (OK or NG) are stored in association with each other (step S112). As an example, a carrier determination table 140 as shown in FIG. 7 is stored.
Subsequently, the interference determination unit 119 selects a carrier determined to be NG, compares the average power of carriers with adjacent carrier numbers for the selected carrier, and determines the peak carrier (peak carrier number: C0 to C0) from the magnitude relationship. Cx, 0 ≦ x <5616, 0 ≦ C0, C1... Cx ≦ 5616) are specified (step S114).

Next, a peak carrier number belonging to the range of 900 ± 20 is selected from the peak carrier numbers (step S118). If there is no corresponding peak carrier number (NO in step S119), the process proceeds to step S126.
When the corresponding peak carrier number exists (YES in step S119), the interference determination unit 119 identifies the peak carrier number “Cv” having the maximum corresponding average power among the peak carrier numbers selected in step S118. (Step S122). Next, a peak carrier number that matches Cv + 4536 is searched for among the peak carrier numbers C0, C1,... Cx (step S123). When there is a peak carrier number “Ca” that satisfies Ca = Cv + 4536 (v <a ≦ x) (YES in step S124), the interference determination unit 119 determines that co-channel interference has occurred, and the video peak carrier The number is “Cv”, the audio peak carrier number is “Ca”, the generated signal indicating that co-channel interference has occurred in the reliability output unit 121, the video peak carrier number “Cv”, and the audio peak carrier number “Ca” is output (step S128).

  The reliability output unit 121 receives the generated signal, the video peak carrier number “Cv”, and the audio peak carrier number “Ca” from the interference determination unit 119. The video peak carrier number “Cv” is substituted into the variable v, and relative to the carriers of the carrier numbers “Cv−70” to “Cv + 70” from the video peak carrier according to the first correspondence table described with reference to FIG. Reliability information corresponding to the carrier position is set (step S129).

Next, the reliability output unit 121 assigns the voice peak carrier number “Ca” to the variable a, and according to the second correspondence table described with reference to FIG. 11, carriers with carrier numbers “Ca−70” to “Ca + 70”. On the other hand, the reliability information corresponding to the relative carrier position from the voice peak carrier is set (step S131).
Next, the reliability output unit 121 detects a peak carrier number that is included in the range of carrier numbers “Cv−70” to “Cv + 70” and that the difference from the video peak carrier number “Cv” is not a multiplication of 16. (Step S132). Further, a peak carrier number which is included in the range of carrier numbers “Ca−70” to “Ca + 70” and whose difference from the voice peak carrier number “Ca” is not a multiple of 32 is detected (step S133).

  The reliability output unit 121 includes the peak carrier number detected in step S132 and step S133, and the peak carrier number not included in the range of carrier numbers “Cv−70” to “Cv + 70” and “Ca−70” to “Ca + 70”. Is set as the in-band peak carrier number (step S136), and the reliability information is set for the in-band peak carrier and the nearby carrier based on the in-band peak carrier number (step S137).

Next, the reliability output unit 121 sets the reliability information “3” for other carriers, that is, carriers that are not affected by the co-channel interference or the in-band interference (step S138).
In step S124, when the peak carrier number “Ca” satisfying Ca = Cv + 4536 (0 <a ≦ x) does not exist in the peak carrier number (NO in step S124), the interference determination unit 119 determines that the co-channel interference is It is determined that it has not occurred, and a non-occurrence signal indicating that no co-channel interference has occurred and peak carrier numbers “C0”, “C1”... “Cx” are output to the reliability output unit 121 ( Step S126).

When receiving the non-occurrence signal and the peak carrier numbers “C0”, “C1”... “Cx”, the reliability output unit 121 sets the received peak carrier number as the in-band peak carrier number (step S127), The processing is moved to S137.
When the reliability information has been set for all the carriers, the reliability output unit 121 associates the carrier number of each carrier with the set reliability information and outputs it to the Viterbi decoding unit 111 (step S139).
1.4 Summary / Effects The broadcast receiving apparatus 100 described above calculates an average power obtained by averaging the power of each carrier in the symbol direction, and each carrier is affected by an interference wave based on the calculated average power and a threshold value. It is determined whether or not. In a mobile reception environment, since the fluctuation of the received wave is severe, it is difficult to detect interference with only one symbol. By performing determination using the average power in the symbol direction as described above, it is possible to detect interference with high accuracy.

  Further, the jamming determination unit 119 has a peak carrier in which the power is maximized in the carrier in which the jamming occurs in the vicinity of the frequency of the analog broadcast video signal (carrier number 880 to 920), and the detected peak carrier. Therefore, if there is a peak carrier at which the power becomes maximum at a carrier position (frequency: 4.5 MHz) separated by 4536 lines, it is determined that the interference is the same channel. The occurrence of the co-channel interference can be detected with high accuracy by such a criterion.

  When it is determined that co-channel interference has occurred, the reliability output unit 121 considers analog broadcast frequency characteristics as shown in FIGS. 10 and 11 with reference to the video peak carrier and the audio peak carrier. Set reliability information. Therefore, it is possible to reliably reduce the reliability information of carriers that are strongly affected by analog broadcasting, and to avoid setting the reliability information of carriers that are not significantly affected by analog broadcasting to be lower than necessary.

Therefore, the broadcast receiving apparatus 100 of the present invention has an excellent effect of preventing deterioration of reception performance when demodulating while eliminating the influence of co-channel interference.
In addition, reliability information is set for a carrier that has been subjected to in-band interference according to the carrier position based on the in-band peak carrier. That is, the reliability information of the carrier that is strongly influenced by the interference wave is surely lowered, and the reliability information value of the carrier that is less influenced by the interference wave is set high. Therefore, it is possible to prevent the reception performance from deteriorating while eliminating the influence of the interference wave.
2. Embodiment 2
Below, the broadcast receiving apparatus 200 which concerns on Embodiment 2 of this invention is demonstrated using drawing.
2.1 Configuration of Broadcast Receiving Device 200 Broadcast receiving device 200 is a device that receives and plays back terrestrial digital broadcasts that conform to mode 3 of the ISDB-T system, similarly to broadcast receiving device 100 of the first embodiment. It is connected to a display device such as a liquid crystal television.

  As shown in FIG. 15, the broadcast receiving apparatus 200 includes an antenna 101, a tuner 102, an A / D conversion unit 103, an orthogonal detection unit 104, an FFT processing unit 106, an equalization processing unit 207, a deinterleaving unit 108, a demapping unit 109, Viterbi decoding unit 111, power calculation unit 112, average calculation unit 113, threshold calculation unit 118, interference determination unit 119, reliability output unit 121, RS decoding unit 122, TS decoding unit 123, MPEG decoding unit 124, power calculation unit 208 The short-term reliability generation unit 209 and the reliability synthesis unit 211 are configured. Note that the same reference numerals as those in FIG. 5 are attached to the same components as those in the broadcast receiving apparatus 100 of the first embodiment.

  Tuner 102, A / D conversion unit 103, quadrature detection unit 104, FFT processing unit 106, equalization processing unit 107, deinterleave unit 108, demapping unit 109, Viterbi decoding unit 111, power calculation unit 112, average calculation unit 113, The threshold calculation unit 118, the disturbance determination unit 119, the reliability output unit 121, the RS decoding unit 122, the power calculation unit 208, the short-term reliability generation unit 209, and the reliability synthesis unit 211 are circuits formed on one LSI. It is.

  The components of the broadcast receiving apparatus 100 will be described below. The antenna 101, the tuner 102, the A / D conversion unit 103, the quadrature detection unit 104, the FFT processing unit 106, the deinterleave unit 108, the demapping unit 109, and Viterbi decoding Unit 111, power calculation unit 112, average calculation unit 113, threshold calculation unit 118, interference determination unit 119, reliability output unit 121, RS decoding unit 122, TS decoding unit 123, and MPEG decoding unit 124 of the first embodiment Since it is the same as the component of the broadcast receiving apparatus 100, description is abbreviate | omitted.

(1) Equalization processing unit 207
The equalization processing unit 207 is a functional unit that receives an OFDM symbol and compensates for the influence of distortion on the transmission path using the received OFDM symbol, similarly to the equalization processing unit 107 of the first embodiment.
FIG. 16 is a block diagram illustrating a configuration of the equalization processing unit 207. As shown in FIG. 16, the delay circuit 221, the SP extraction circuit 222, the complex division circuit 223, the SP storage memory 224, the symbol interpolation circuit 226, the carrier interpolation circuit 227, and the complex division circuit 229 are configured.

The delay circuit 221 caches the OFDM symbol output from the FFT processing unit 106 for a predetermined period, and then outputs it to the complex division circuit 229.
The SP extraction circuit extracts a scattered pilot signal from the OFDM symbol output from the FFT processing unit 106 and outputs the extracted pilot signal to the complex division circuit 223.
The SP storage memory 224 internally holds a signal (hereinafter, known SP signal) that matches the amplitude and phase at the time of transmission of the SP signal of each carrier, and outputs this known SP signal to the complex division circuit 223.

  The complex division circuit 223 divides the SP signal output from the SP extraction circuit 222 by a known SP signal related to a carrier having the same carrier number as the SP signal among the known SP signals output from the SP storage memory 224. Then, the frequency response at the symbol position and the carrier position including the SP signal is calculated. The calculated frequency response at each symbol position and carrier position is output to the symbol interpolation circuit 226. Similar processing is performed on each SP signal output from the SP extraction circuit 222.

  The symbol interpolation circuit 226 uses the frequency response output from the complex division circuit 223 to interpolate the frequency response to a symbol position where the SP signal on the carrier corresponding to the frequency response is not transmitted (interpolation in the time axis direction). Similar processing is performed for all SP signals. Thereby, the frequency response in each symbol position of the carrier which transmits SP signal was generated. The symbol interpolation circuit 226 outputs the generated frequency response to the carrier interpolation circuit 227.

The carrier interpolation circuit 227 interpolates the frequency response of the carrier not including the SP signal by the frequency response output from the symbol interpolation circuit 226 (interpolation in the frequency axis direction). The carrier interpolation circuit 227 outputs the generated frequency response corresponding to each carrier in each symbol period to the complex division circuit 229 and the power calculation unit 208 for each symbol period.
The complex division circuit 229 divides each complex signal constituting the OFDM symbol output from the delay circuit 221 by the symbol position corresponding to each complex signal output from the carrier interpolation circuit 227 and the frequency response of the carrier position. The OFDM symbol is equalized, and the equalized OFDM symbol is output to deinterleaving section 108.

(2) Power calculation unit 208
The power calculation unit 208 calculates the power of each carrier in the symbol period based on the frequency response of each carrier for each symbol period output from the equalization processing unit 207. Here, the power of the carrier of the carrier number s calculated based on the frequency response is expressed as p (s). The power calculation unit 208 outputs the calculated powers p (0) to p (5616) to the short-term reliability generation unit 209.

(3) Short-term reliability generation unit 209
The short-term reliability generation unit 209 calculates an average value of the powers p (0) to p (5616) of each carrier in one symbol period from the power calculation unit 208, and adds a predetermined coefficient α (0 < Multiply by α << 1) to calculate the first threshold “Sα”. Similarly, the second threshold value “Sβ” and the third threshold value “Sγ” are calculated by multiplying the calculated average values by predetermined coefficients β and γ (0 <α <β <γ << 1), respectively.

  The short-term reliability generation unit 209 compares the calculated first threshold value, second threshold value, and third threshold value with each of the powers p (0) to p (5616). Reliability information “0” is set for a carrier corresponding to P (s) satisfying p (s) <Sα. Reliability information “1” is set for a carrier corresponding to p (s) that satisfies Sα ≦ p (s) <Sβ. Reliability information “2” is set for a carrier corresponding to p (s) that satisfies Sβ ≦ p (s) <Sγ. Reliability information “3” is set to the carrier corresponding to p (s) satisfying Sγ ≦ p (s).

The short-term reliability generation unit 209 associates the reliability information set for each carrier with the carrier number indicating each carrier and outputs the associated information to the reliability synthesis unit 211.
(4) Reliability synthesis unit 211
The reliability combining unit 211 receives the carrier number of each carrier and the reliability information corresponding to each carrier number from the reliability output unit 121. When these are received, each received carrier number and reliability information are stored in association with each other. Each time a new carrier number and reliability information are received from the reliability output unit 121, the stored carrier number and reliability information of each carrier are updated with the received carrier number and reliability information.

In addition, the carrier number of each carrier and the reliability information corresponding to each carrier number are received from the short-term reliability generation unit 209 for each symbol period.
When the carrier number of each carrier and the reliability information corresponding to each carrier number are received from the short-term reliability generation unit 209, the reliability combining unit 211 stores the carrier number corresponding to the carrier number “0”. The reliability information is compared with the reliability information corresponding to the carrier number “0” received from the short-term reliability generation unit 209, and the one with the lower value is selected.

Similarly, for the carrier numbers “2” to “5616”, the stored reliability information is compared with the reliability information received from the short-term reliability generation unit 209, and the lower one is selected.
When the comparison / selection of the reliability information is completed for all the carrier numbers, the carrier number of each carrier and the selected reliability information are associated with each other and output to the Viterbi decoding unit 111.
2.2 Summary and Effects As described above, in the present embodiment, the short-term reliability generation unit 209 sets reliability information for each carrier for each symbol period. At this time, the reliability information is set lower for a carrier with lower power.

FIG. 17A shows the frequency characteristic of the OFDM signal affected by multipath interference. As shown in FIG. 17A, when multipath interference occurs, deep dip occurs periodically. In the carrier near the dip, errors are concentrated.
In the present embodiment, the short-term reliability generation unit 209 sets the reliability information stepwise by using three-stage threshold values (0 <Sα <Sβ <Sγ) that are sufficiently smaller than the average value of the power of each carrier. FIG. 17B shows the correspondence between the reliability information set by the short-term reliability generation unit 209 and the carrier number of each carrier. Further, the relationship between the frequency characteristics and reliability information of FIG. As shown in FIG. 17, the lowest reliability information “0” is set for the carrier in the vicinity of the bottom of the dip, and the higher reliability information is set for the carrier farther from the bottom of the dip. Since the phase difference between the direct wave and the delayed wave varies with time, the frequency at which dip occurs also changes every moment. Therefore, in the present embodiment, the short-term reliability generation unit 209 generates appropriate reliability information for each symbol period.

In the reliability synthesis unit 211, the reliability information output from the reliability output unit 121 and the reliability information output from the short-term reliability generation unit 209 are compared for each carrier, and the lower value is selected and Viterbi is selected. Output to the decoding unit 111.
By doing so, the broadcast receiving apparatus 200 of the present invention can eliminate not only the influence of external interference waves such as co-channel interference but also the influence of dip caused by multipath interference.
3. Other Modifications Although the description has been given based on the first and second embodiments, the present invention is not limited to these and includes the following cases.

(1) Embodiments 1 and 2 assume television broadcasting in Japan and have been described on the premise of ISDB-T digital television broadcasting and NTSC analog television broadcasting. However, the present invention is not limited to this. Absent.
As an example, PAL (Phase Alternating Line) analog television broadcasting, DVB-T (Digital Video Broadcasting Terrestrial) digital terrestrial digital broadcasting adopted in Europe and the like can be considered. In the PAL system, the horizontal synchronization frequency is 15.625 kHz, and in the DVB-T system 8K mode, the carrier interval is 1.116 kHz. Therefore, 15.625 kHz / 1.116 kHz = 14.095... There are about 14 carriers between the peaks of the analog broadcast video signal. Assuming these schemes, when co-channel interference occurs, the reliability output unit 121 sets low reliability information to a carrier having a carrier number that is a multiple of 14 from the video peak carrier number.

Note that various parameters such as the frequency of the video signal and audio signal of PAL broadcast, the frequency band per channel, and the offset vary depending on the mode (2K, 4K, 8K) and the country, so care should be taken.
(2) In Embodiments 1 and 2, the threshold value calculation unit 118 calculates a threshold value by adding an offset to the average value of the average power P (0) to P (5616) of each carrier. However, it is not limited to this method.

  For example, a threshold value may be calculated for each carrier. Specifically, the carrier threshold of the carrier number “s” is generated by adding a predetermined offset to the average value of P (s−50) to P (s + 50). When s-50 <0, an offset is added to the average value of P (0) to P (s + 50) to generate a threshold value. When s + 50> 5616, P (s-50) to P ( A value obtained by adding an offset to the average value of 5616) is set as a threshold value.

  The frequency characteristic of the OFDM signal is drawn flat in FIG. 1, but it may not be flat, such as being tilted, depending on the reception state. Therefore, if the same threshold value is used for all carriers, there is a possibility that a carrier that is not affected by an interference wave is determined to be NG. As described above, such erroneous determination can be avoided by calculating a threshold value for each carrier.

(3) In the first and second embodiments, the interference determination unit 119 determines that co-channel interference has occurred when there is a peak carrier at a carrier position 4536 distances away from the video peak carrier. However, the criterion is not limited to this.
For example, if a predetermined number or more of peak carrier numbers satisfying Cv ± 16n (n is a natural number) exist among peak carrier numbers “C0”, “C1”. Since the analog broadcast video signal has a steep peak every 16 carriers, if every 16 carriers are present in the vicinity of the analog broadcast video signal, the influence of the analog broadcast video signal is affected. The possibility of receiving it is considered very high.

Since the analog broadcast audio signal is weaker than the video signal, if the level of interference is low, a carrier determined to be NG in the vicinity of the analog broadcast audio signal may not be detected. By adopting, it is possible to detect co-channel interference with high accuracy even when the interference level is low.
(4) If a peak carrier exists between carrier numbers 880 to 920, it may be determined that co-channel interference has occurred.

In general, the power of audio signals for analog television broadcasting is weaker than the power of video signals, so even if co-channel interference occurs, if the interference level is weak, the influence of the interference wave cannot be detected on the carrier near the audio signal. It is possible.
When this determination method is adopted, the determination system is low, but it is effective when the interference level is weak or when it is desired to simplify the circuit configuration of the interference determination unit 119.

(5) In the first and second embodiments, the trust output unit 121 stores the first correspondence table and the second correspondence table in advance, but instead of these, the function and parameters are stored. The reliability information set for each carrier may be calculated from the video peak carrier number, the audio peak carrier number, and the function.
(6) Although not shown in FIG. 1, a color subcarrier exists between an analog television broadcast video signal and an audio signal.

The interference determination unit 119 refers to the average power of the carriers in the vicinity of the video signal and the audio signal in determining the occurrence of the co-channel interference. However, a carrier in the vicinity of the color subcarrier may be used.
If it is determined that co-channel interference has occurred, the reliability output unit 121 also applies the color subcarrier to the carrier near the color subcarrier as in the case of the carrier near the video signal and the audio signal. Reliability information may be set according to frequency characteristics.

(7) In Embodiment 2, the power calculation unit 208 calculates the power of each carrier based on the frequency response of each carrier output from the carrier interpolation circuit 227 of the equalization processing unit 207. You may calculate using the signal output from the division circuit 229. FIG.
The broadcast receiving apparatus 200 may not include the power calculation circuit 208, and the short-term reliability generation unit 209 may set reliability information based on the power of each carrier output from the power generation unit 112.

(8) In Embodiments 1 and 2, the interference determination unit 119 determines that the determination result is NG when the average power of each carrier is greater than or equal to the threshold value, assuming that the carrier is affected by some interference wave.
Instead, the determination result may be NG when the difference in average power from adjacent carriers exceeds a predetermined threshold.

  Under mobile communications, the phase of the multipath changes from moment to moment, so when the power of each carrier is averaged in the time direction, the average power of carriers that are not affected by the jamming wave is almost equal, and the influence of the jamming wave The average power of the carrier that received is prominently increased. However, when the phase difference between the delayed wave and the direct wave does not change, such as when the broadcast receiver is fixed, the periodic gap as shown in FIG. Occurs. In such a case, if the threshold value is calculated by the method as in the first embodiment, the threshold value becomes small due to the influence of the carrier in the vicinity of the dip, and there is a risk of misjudging a carrier that is not disturbed as NG. .

As in this modification, if the determination is made based on the difference in average power from the adjacent carrier, the average power fluctuates rapidly in the carrier affected by the interference wave and the carrier in the vicinity of the dip. Is determined to be NG. On the other hand, in the portion where the power between the dip is maximized, the average power changes gradually, and thus it is difficult to determine that the power is NG.
Therefore, according to this modification, the possibility of determining a normal carrier as NG can be reduced.

(9) In Embodiments 1 and 2, the average calculator 113 calculates average power in the symbol direction for each carrier, and the threshold calculator 118 and the interference determiner 119 calculate the calculated average power P (0) to Based on P (5616), the threshold value is calculated and the presence or absence of interference is determined. However, instead of the average power, an integrated value of power for a predetermined period (for example, 1000 symbol periods) may be used.
(10) A part or all of the constituent elements constituting each of the above devices may be constituted by one system LSI. The system LSI is an ultra-multifunctional LSI manufactured by integrating a plurality of components on a single chip, and specifically, a computer system including a microprocessor, ROM, RAM, and the like. . A computer program is stored in the RAM. The system LSI achieves its functions by the microprocessor operating according to the computer program.

(11) The present invention may be the method described above. Further, the present invention may be a computer program that realizes these methods by a computer, or may be a digital signal composed of the computer program.
The present invention also provides a computer-readable recording medium such as a flexible disk, hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray Disc). ), Recorded in a semiconductor memory or the like. Further, the present invention may be the computer program or the digital signal recorded on these recording media.

  (12) The above embodiment and the above modifications may be combined.

  INDUSTRIAL APPLICABILITY The present invention can be used in a business and continuous and repetitive manner in industries that manufacture and sell electrical equipment that receives signals conforming to the OFDM system, and in industries that use the electrical equipment.

The frequency characteristics of terrestrial digital broadcasting and analog television broadcasting in Japan are shown. The frequency characteristics of digital terrestrial broadcasting and analog broadcasting using the same channel are shown. In particular, a frequency band in which an analog television broadcast video signal is distributed is shown. The frequency characteristics of digital terrestrial broadcasting and analog broadcasting using the same channel are shown. In particular, a frequency band in which an audio signal of analog television broadcasting is distributed is shown. Indicates in-band jamming that occurs in terrestrial digital broadcasting. 1 is a block diagram showing a configuration of a broadcast receiving apparatus 100 according to Embodiment 1. FIG. An example of the configuration of the memory 116 is shown. The details of the carrier determination table 140 stored in the interference determination unit 119 are shown. An example of the distribution of average power of each carrier of the OFDM signal received by the broadcast receiving apparatus 100 is shown. In particular, the carrier numbers 867 to 933 are shown. An example of the distribution of average power of each carrier of the OFDM signal received by the broadcast receiving apparatus 100 is shown. In particular, the carrier numbers 5403 to 5469 are shown. The correspondence relationship between the carrier number of each carrier included in the first correspondence table stored in the reliability output unit 121 and the reliability information is shown. The correspondence relationship between the carrier number of each carrier included in the second correspondence table stored in the reliability output unit 121 and the reliability information is shown. 10 is a flowchart showing operations for setting reliability information by a power calculation unit 112, an average calculation unit 113, a threshold calculation unit 118, an interference determination unit 119, and a reliability output unit 121. It is a flowchart which shows the operation | movement of the setting of reliability information. Continuing from FIG. It is a flowchart which shows the operation | movement of the setting of reliability information. Continuing from FIG. 6 is a block diagram showing a configuration of a broadcast receiving apparatus 200 according to Embodiment 2. FIG. 3 is a block diagram showing a configuration of an equalization processing unit 207. FIG. The frequency characteristics of the OFDM signal affected by multipath interference and the reliability information set for each carrier are shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Broadcast receiving apparatus 101 Antenna 102 Tuner 103 A / D conversion part 104 Orthogonal detection part 106 FFT process part 107 Equalization process part 108 Deinterleave part 109 Demap part 111 Viterbi decoding part 112 Power calculation part 113 Average calculation part 114 Addition part 116 Memory 117 Delay unit 118 Threshold calculation unit 119 Interference determination unit 121 Reliability output unit 122 RS decoding unit 123 TS decoding unit 124 MPEG decoding unit 200 Broadcast receiving device 207 Equalization processing unit 208 Power calculation unit 209 Short-term reliability generation unit 211 Reliability Synthesizer 221 delay circuit 222 SP extraction circuit 223 complex division circuit 224 SP storage memory 226 symbol interpolation circuit 227 carrier interpolation circuit 229 complex division circuit

Claims (11)

A receiver for receiving an orthogonal frequency division multiplexed signal in which a plurality of carriers carrying data are multiplexed,
For each carrier, a determination unit that compares the received power with a threshold and determines whether the received power is greater than the threshold;
A specifying means for specifying a main peak carrier having a reception power that is maximum among carriers determined to have a reception power greater than a threshold;
A main peak reliability indicating the accuracy of a signal carried by the main peak carrier is set in the main peak carrier, and the frequency of the main peak carrier and the frequency of the carrier are set in a carrier in the vicinity of the main peak carrier. A receiving device comprising: setting means for setting a reliability equal to or higher than the main peak reliability according to the difference. The receiving device further includes:
A prediction that identifies a prediction carrier that is separated from the main peak carrier by a predetermined frequency when the orthogonal frequency division multiplexing signal is disturbed by an analog television broadcast wave that uses the same frequency band as the orthogonal frequency division multiplexing signal. With specific means,
The setting means further includes:
A reliability equal to or higher than the main peak reliability is set for the prediction carrier, and the prediction reliability is set for a carrier in the vicinity of the prediction carrier according to a frequency difference between the prediction carrier and the carrier. The receiving apparatus according to claim 1, wherein a reliability equal to or higher than is set. The specifying means specifies the main peak carrier in the vicinity of the frequency of the video signal of the analog television broadcast wave,
Further, in the vicinity of the frequency of the audio signal of the analog television broadcast wave, an attempt is made to identify a sub-peak carrier having a maximum received power among the carriers determined by the determining means that the received power is equal to or higher than a threshold value. ,
The receiving device according to claim 2, wherein the prediction specifying unit specifies the prediction carrier when the sub peak carrier is specified by the specifying unit. The predetermined frequency is a frequency multiplied by a horizontal synchronization frequency of the analog television broadcast wave,
The receiving apparatus according to claim 3, wherein the prediction specifying unit specifies the prediction carrier that is separated from the main peak carrier by a frequency that is a multiple of the horizontal synchronization frequency. The predetermined frequency is a difference between the frequency of the audio signal of the analog television broadcast wave and the frequency of the video signal,
The receiving apparatus according to claim 3, wherein the prediction specifying unit specifies the prediction peak carrier separated from the main peak carrier by a frequency equal to the difference. The receiving apparatus according to claim 2, wherein the prediction specifying unit specifies the prediction carrier when the main peak carrier is specified in the vicinity of the frequency of the video signal of the analog television broadcast wave. The specifying means specifies the main peak carrier in the vicinity of the frequency of the video signal of the analog television broadcast wave,
Furthermore, among the carriers whose reception power is determined to be equal to or greater than the threshold, the reception power is maximum, and the frequency differs by a frequency that is a multiple of the frequency of the main peak carrier and the horizontal synchronization frequency of the analog television broadcast wave. Trying to identify sub-peak carriers of
The receiving device according to claim 2, wherein the prediction specifying unit specifies the prediction carrier when the sub peak carrier is specified by the specifying unit. The determination means includes
For each carrier, a threshold calculation unit that calculates a threshold corresponding to the carrier based on an average value of received power of the carrier and a predetermined number of carriers in the vicinity thereof;
The receiving apparatus according to claim 2, further comprising: a determination unit that compares the received power with a threshold corresponding to the carrier for each carrier and determines whether the received power is greater than the threshold. The determination means includes
A power calculator for calculating the power of each carrier for each symbol period;
An accumulator that calculates the received power of each carrier by accumulating the power for each carrier over a predetermined symbol period;
The receiving apparatus according to claim 2, further comprising: a determination unit that compares the received power with a threshold for each carrier and determines whether the received power is greater than the threshold. A receiving method used in a receiving apparatus for receiving an orthogonal frequency division multiplexed signal in which a plurality of carriers carrying data are multiplexed,
For each carrier, a determination step of comparing the received power with a threshold and determining whether the received power is greater than the threshold;
A identifying step of identifying a main peak carrier having a reception power that is maximal among carriers determined to have a reception power greater than a threshold;
A main peak reliability indicating the accuracy of a signal carried by the main peak carrier is set in the main peak carrier, and the frequency of the main peak carrier and the frequency of the carrier are set in a carrier in the vicinity of the main peak carrier. And a setting step for setting a reliability equal to or higher than the main peak reliability according to the difference. An integrated circuit used in a receiving apparatus for receiving an orthogonal frequency division multiplexed signal in which a plurality of carriers carrying data are multiplexed,
For each carrier, a determination unit that compares the received power with a threshold and determines whether the received power is greater than the threshold;
A specifying means for specifying a main peak carrier having a reception power that is maximum among carriers determined to have a reception power greater than a threshold;
A main peak reliability indicating the accuracy of a signal carried by the main peak carrier is set in the main peak carrier, and the frequency of the main peak carrier and the frequency of the carrier are set in a carrier in the vicinity of the main peak carrier. An integrated circuit comprising: setting means for setting a reliability equal to or higher than the main peak reliability according to a difference.

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