JP2005286362A - Digital receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital receiver capable of ensuring effective reception performance by using reliability information in response to a reception state. <P>SOLUTION: A first reliability information generating unit 50 generates reliability information on the basis of an output power level of transmission path estimate information and outputs the information to a reliability information selection circuit 53. A second reliability information generating unit 51 generates reliability information on the basis of a dispersion in time directions obtained from extracted SP signals and outputs the information to the reliability information selection circuit 53. A Doppler frequency estimate section 52 estimates a degree of temporal variations of a frequency at movement and outputs a control signal on the basis of a result of the estimation to the reliability information selection circuit 53. The reliability information selection circuit 53 receives the reliability information on the basis of the transmission path estimate data from the first reliability information generating unit 50 and the reliability information on the basis of the dispersion of the SP signals from the second reliability information generating unit 51 and selects and outputs either reliability information of the reliability information items in response to the control signal on the basis of the Doppler frequency estimate section 52. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a configuration of a digital receiver for performing demodulation of an OFDM system used in digital broadcasting or the like.

  In recent years, an OFDM (Orthogonal Frequency Division Multiplexing) scheme has been proposed as a scheme excellent in high-quality transmission and frequency utilization efficiency in a system that transmits video signals or audio signals. The OFDM system is a multi-carrier (multi-carrier) modulation system suitable for mobile communication, and is a system that divides and multiplexes information into several hundred or more carriers (sub-carriers).

  In general, multipath exists in terrestrial transmission, and the frequency characteristics of the received signal are distorted by this multipath. Reducing the influence of this multipath becomes a big problem in the transmission system. In the OFDM method using QAM modulation for each carrier modulation method, when distortion due to multipath occurs, the amplitude and phase on the receiving side differ from the amplitude and phase on the transmitting side for each carrier. The signals subjected to multipath distortion are equalized, that is, corrected so that they are equal.

  Specifically, FFT (Fast Fourier Transform) processing is performed on the receiving side, and so-called pilot signals scattered in the transmission signal are extracted. Then, the characteristics of the transmission path are estimated by monitoring the amplitude and phase of the pilot signal on the receiving side, and the received signal is equalized with the estimated characteristics of the transmission path.

  On the other hand, since the OFDM scheme is a multi-carrier scheme that divides information into several hundreds of carriers or more, the same and adjacent channel interference may occur. As a result, only a specific carrier wave is greatly affected, and equalization becomes uncertain, and there is a problem that the correction capability is deteriorated in the subsequent error correction processing and the reception performance is deteriorated.

In this regard, in Non-Patent Document 1, when the same and adjacent channel interference (inter-carrier interference) may occur, the above-described pilot signal is used to obtain the dispersion value in the time direction of the same carrier. A method for improving the reception performance by generating reliability information indicating the reliability of the received signal and performing error correction based on the reliability information has been proposed.
"Error Control Considering Terrestrial Transmission Line Characteristics", 1998 Annual Conference of the Institute of Image Information and Television Engineers 3-1.

  As shown in Non-Patent Document 1 above, since there is no temporal change in transmission path characteristics in fixed reception, it is possible to estimate the reliability of the carrier using the variance value in the time direction of the same carrier. is there.

  However, in the case of mobile reception in a mobile body, not fixed reception, the higher the reception speed, the more the reception state changes from time to time, so the transmission path characteristics also change over time.

  Therefore, the dispersion value in the time direction of the same carrier may also vary. Therefore, using reliability information using the variance value in the time direction of the same carrier, on the other hand, results in error correction based on reliability information containing a large amount of error, and moving on a mobile object, etc. In reception, the problem of deteriorating reception performance occurs.

  The present invention has been made to solve the above problems, and provides a digital receiver capable of efficiently improving reception performance using reliability information according to reception conditions. The purpose is to do.

  A digital receiver according to the present invention is a digital receiver for receiving a digital modulated wave signal, and is a pilot inserted according to a predetermined pattern in the received digital modulated wave signal in order to indicate the characteristics of the digital modulated wave signal An extraction unit for extracting a signal, a reliability information generation circuit for generating information indicating the reliability of the digital modulated wave signal received based on the pilot signal extracted by the extraction unit, and a reliability information generation circuit And a signal processing circuit that executes signal processing based on the information. The reliability information generation circuit generates a plurality of reliability information generation units each generating reliability information according to different processing methods, and a plurality of reliability information generation units according to the reception state of the digital receiver. And a control circuit for selecting one of the reliability information.

  Preferably, a transmission path estimation unit that estimates a transmission path state in which the digital modulated wave signal is transmitted based on the pilot signal is further provided. The reliability information generation circuit includes a first reliability information generation unit that generates first reliability information based on the dispersion of the pilot signal extracted by the extraction unit, and a second reliability information based on an estimation result in the transmission path estimation unit. And a second reliability information generation unit that generates reliability information. The control circuit estimates the Doppler frequency accompanying the movement of the digital receiver based on the pilot signal, and based on the estimation result, the first and second reliability information output from the first and second reliability information generating units. Select one of the sex information.

  Preferably, a transmission path estimation unit that estimates a transmission path state in which the digital modulated wave signal is transmitted based on the pilot signal is further provided. The reliability information generation circuit includes a first reliability information generation unit that generates first reliability information based on the dispersion of the pilot signal extracted by the extraction unit, and a second reliability information based on an estimation result in the transmission path estimation unit. And a second reliability information generation unit that generates reliability information. The control circuit estimates a delay time of a signal received by the digital receiver based on the pilot signal, and based on the estimation result, the first and second reliability information generation units output from the first and second reliability information generation units. Select one of the reliability information.

  In particular, the control circuit performs a predetermined correlation calculation of the pilot signal, and estimates a delay time based on a comparison between the calculated correlation value and a predetermined threshold value.

  In particular, the control circuit performs fast Fourier transform processing on the pilot signal, calculates an average delay time of the delay wave, and estimates the delay time based on a comparison between the average delay time and a predetermined period.

  In particular, the second reliability information generation unit generates the second reliability information based on a level corresponding to the power of the output signal of the transmission path estimation result in the transmission path estimation unit.

  Preferably, the signal processing circuit corresponds to a Viterbi decoding circuit, and the Viterbi decoding circuit performs a predetermined error correction process according to the weighting of the reliability information.

  Preferably, the signal processing circuit corresponds to a diversity circuit for combining a plurality of digital modulation wave signals to be received. The diversity circuit executes a combining process according to a predetermined method based on the reliability information.

  Preferably, the digital modulation wave signal is a digital reception signal modulated by the OFDM method.

  The digital receiver according to the present invention includes a control circuit that generates reliability information indicating reliability by a plurality of reliability information generation units and selects one of them according to a reception state. Therefore, since appropriate reliability information can be used according to the reception state, it is possible to efficiently improve reception performance.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic block diagram of a digital receiver 100 according to an embodiment of the present invention.

  Referring to FIG. 1, a high frequency signal input (RF input) input from an antenna (not shown) is input to tuner 1. In the tuner 1, the RF input signal is down-converted to an intermediate frequency (IF frequency) and converted into an analog OFDM signal under a predetermined band limitation. The analog OFDM signal is input to an analog-digital conversion circuit (also referred to as an A / D circuit), and converts the analog OFDM signal into a digital signal.

  Next, the OFDM signal converted into the digital signal is converted into an I signal which is an in-phase detection axis signal (real axis component signal) and a Q signal which is a quadrature detection axis signal (imaginary axis component signal) by the Hilbert transform unit 3. A complex OFDM signal is generated. The complex OFDM signal generated by the Hilbert transform unit 3 is sent to the first carrier synchronization unit 4. The first carrier synchronization unit 4 corrects a carrier frequency error based on a correlation signal described later output from the symbol synchronization unit 7 and a signal from the second carrier synchronization unit 9. The FFT 5 performs a fast Fourier transform process on the complex OFDM signal, and converts the signal from the time axis domain to the frequency axis domain. The equalization unit 6 obtains transmission path characteristics from the pilot signal, estimates the transmission path, and performs equalization by dividing the data by the estimated carrier.

  The symbol synchronizer 7 uses the formation of one symbol by copying a part of the effective symbol period, which is a characteristic of the OFDM signal, as a guard interval period. Symbol synchronization is calculated based on the correlation value. Further, the symbol synchronization unit 7 outputs a correlation signal based on the correlation value to the first carrier synchronization unit 4 in order to correct a frequency error within the carrier frequency. The second carrier synchronization unit 9 calculates the error of the carrier frequency interval from the arrangement on the frequency axis of the output signal of the FFT 5 and outputs a signal based on the calculation result to the first carrier synchronization unit 4.

  The clock synchronization unit 8 calculates clock synchronization from the symbol synchronization timing shift obtained by the symbol synchronization unit 7 and controls the sampling frequency of the A / D circuit 2. The reliability information generation unit 10 generates and selects reliability information indicating reliability for two types of received signals for high speed movement and low speed movement in mobile reception from the pilot signal extracted by the equalization unit 6. The result is output to the Viterbi decoding unit 15.

  Here, the above-described tuner 1, A / D circuit 2, Hilbert transform unit 3, first carrier synchronization unit 4, FFT 5, equalization unit 6, symbol synchronization unit 7, clock synchronization unit 8, second carrier synchronization unit 9 and The reliability information generation unit 10 constitutes a synchronous modulation unit 20.

  The frequency deinterleave 11 performs a process of returning the frequency interleave performed to compensate for the loss of a signal of a specific frequency due to the reflection of radio waves. The output of the frequency deinterleave 11 is given to the time deinterleave 12, and the time deinterleave 12 performs a process for restoring the time interleave applied for anti-fading and the like.

  The real-axis component signal (I signal) and imaginary-axis component signal (Q signal) subjected to time deinterleaving are 2 bits (in the case of QPSK), 4 bits (in the case of 16QAM) or 6 bits in the demapping 13. Respectively (in the case of 64QAM).

  Bit deinterleaving 21 cancels bit interleaving performed for the purpose of increasing error correction on the demapped signal. The Viterbi decoding unit 15 performs error correction using the convolutional code performed on the transmission side. The Viterbi decoding unit 15 uses reliability information. The byte deinterleave 16 cancels the byte interleave performed for the purpose of increasing error correction in the same manner as the bit interleave for the signal subjected to Viterbi decoding. Then, the TS reproduction unit 17 reconstructs data according to the transport stream format, and the RS decoding unit 18 decodes the Reed-Solomon encoded data on the transmission side. The RS decoding unit 18 outputs a Reed-Solomon decoded result to a TS decoder (not shown).

  The error-corrected signal is output after the compressed signal is expanded in an MPEG decoding unit (not shown), converted into an analog video and an analog audio signal by digital / analog conversion.

  FIG. 2 is a schematic block diagram illustrating the equalization unit 6 and the reliability information generation unit 10.

  Referring to FIG. 2, equalization unit 6 includes a pilot SP extraction unit 40, a transmission path estimation unit 41, and a division unit 42. The reliability information generation unit 10 includes a first reliability information generation unit 50, a second reliability information generation unit 51, a Doppler frequency estimation unit 52, and a reliability information selection circuit 53.

  The OFDM signal input from the FFT 5 is input to the pilot SP extraction unit 40.

  The pilot SP extraction unit 40 extracts a known pilot signal (hereinafter also referred to as an SP signal) from the signal converted by the FFT 5, and uses the extracted SP signal as a transmission path estimation unit 41 and a second reliability information generation unit. 51 and the Doppler frequency estimator 52.

  FIG. 3 is a conceptual diagram for explaining a pilot signal insertion pattern proposed in the OFDM scheme.

  Referring to FIG. 3, in this example, a pilot SP signal is inserted at a ratio of one to 12 carriers included in one symbol, and further, a pilot SP signal is inserted for each OFDM symbol. The position is shifted by 3 carriers.

  The pilot SP extraction unit 40 extracts an SP signal according to this insertion pattern from the received signal.

  Referring to FIG. 2 again, the transmission path estimation unit 41 performs interpolation processing on the extracted SP signal to detect the amplitude and phase components of each carrier as the transmission path characteristics of the carrier, and transmits transmission path estimation information. The result is output to the division unit 42 and the first reliability information generation unit 50.

  The division unit 42 divides the OFDM signal input from the FFT 5 by the amplitude and phase, which are transmission channel estimation information supplied from the transmission channel estimation unit 41, and removes distortion components caused by transmission channel characteristics. For example, when the amplitude of the carrier wave input from the FFT 5 is ½ of the original amplitude, ½ is supplied as amplitude information from the transmission path estimation 41. Therefore, by dividing the amplitude of the signal input from the FFT 5 by the division 42 by the amplitude information of the transmission path estimation 41, a signal having the amplitude at the original position (= (1/2) / (1/2)) can be obtained. it can. Similarly, the signal of the original phase can be obtained by performing complex operation on the phase.

  Next, reliability information generation unit 10 according to the embodiment of the present invention will be described.

  The first reliability information generation unit 50 generates reliability information based on the output power level of the transmission path estimation information, and outputs the reliability information to the reliability information selection circuit 53.

  The second reliability information generation unit 51 obtains variance in the time direction from the extracted SP signal, generates reliability information from the variance value, and outputs the reliability information to the reliability information selection circuit 53.

  The Doppler frequency estimation unit 52 estimates the degree of temporal fluctuation of the frequency during movement, and outputs a control signal based on the estimation result to the reliability information selection circuit 53. The frequency of the received signal received by the mobile body varies due to the Doppler effect. This fluctuating frequency is called a so-called Doppler frequency.

  The reliability information selection circuit 53 includes reliability information based on transmission path estimation data from the first reliability information generation unit, reliability information based on dispersion of SP signals from the second reliability information generation unit 51, and In response, one of the reliability information is selected and output in accordance with the control signal based on the Doppler frequency estimation 52.

  Here, the relationship between the Doppler frequency and inter-carrier interference will be described.

  The effect of the Doppler frequency on the received signal corresponds to a slight translation across the entire frequency of the received signal. For example, when there are 1024 transmission carriers having a frequency of 1 kHz, 2 kHz,..., 1024 kHz and mobile reception is performed at a speed at which the Doppler frequency is 10 Hz, the carrier frequency at the time of reception is 1.01 kHz, 2.01 kHz, ..., it becomes 1024.01 kHz. In the FFT of the receiver, if the frequency of the received carrier is the same as the frequency of the transmitted carrier, orthogonality is maintained in terms of the FFT characteristics. That is, there is no inter-carrier interference, and the signal can be converted into a signal on a desired frequency axis.

  However, since FFT is FFT-processed for each predetermined effective symbol period, the continuity of the signal to be processed is disturbed if the frequency of the transmission carrier and the reception carrier is slightly changed.

  When such a signal is subjected to FFT processing, a high frequency component is generated, which has an influence in the form of interference with other carrier waves. For example, consider 1 kHz of the fundamental wave of the carrier wave as an example.

  FIG. 4 is a conceptual diagram illustrating a fundamental wave of 1 kHz when the Doppler frequency is 0 Hz.

  Referring to FIG. 4A, when the received signal is 1 kHz, one effective symbol period is 1 msec. Therefore, the received signal is exactly one cycle at 1 msec, and the continuity of the signal is at the boundary portion of the effective symbol period. Retained. When this signal is FFT processed, the signal appears only on the 1 kHz carrier as shown in FIG.

  On the other hand, FIG. 5 is a conceptual diagram illustrating a fundamental wave of 1.01 kHz when the Doppler frequency is 10 Hz.

  As shown in FIG. 5A, when the received signal is 1.01 kHz, there is a signal exceeding one period in 1 msec which is one effective symbol period. Therefore, the signal is discontinuous at the boundary portion of the effective symbol period. When this signal is subjected to FFT processing, as shown in FIG. 5B, not only a 1 kHz carrier wave but also a carrier wave appears in other frequency regions, thereby generating inter-carrier interference. That is, the signal of 1 kHz is also lost in the signal portion of 2 kHz to 5 kHz.

  Therefore, it is necessary to generate reliability information indicating the reliability of the received signal in consideration of the Doppler frequency received by the mobile unit.

  In Embodiment 1 of the present invention, for example, at the time of mobile reception in a mobile body as a reception situation, two types of reliability information are generated as an example, and reliability information with high reliability according to the speed of the mobile body A method for generating the will be described below.

  First, generation of reliability information in the second reliability information generation unit will be described.

  In the received signal, there is a carrier wave having low reliability due to the influence of multipath, interference, noise, and the like.

  The second reliability information generation unit detects the high reliability of each carrier wave from the dispersion of the SP signal. In the case where there is little change in the transmission path characteristics in the time direction, that is, in the fixed reception, there is almost no fluctuation of the SP signal dispersion. Therefore, reliability information suitable for fixed reception can be obtained by this method.

  Specifically, the reliability R is calculated from the dispersion of the SP signal. The reliability R when the reception level of the received SP signal is I (t, f), Q (t, f) can be calculated from the following equation. t is time and f is frequency.

  However, A is a coefficient including a threshold value, and Iref (f) and Qref (f) are average values in the time direction of the received signals I (t, f) and Q (t, f).

  The numerator of the above formula indicates the average value of the reception level, and the reliability R increases as the reception amplitude increases. The denominator of the above equation shows dispersion, and the greater the disturbance, the smaller the reliability R. That is, the second reliability information generation unit 51 pays attention to the SP signal periodically located in the symbol, calculates the average value of the SP signal level, compares it with the level of each SP signal, The reliability of the SP signal is detected.

  The second reliability information generating unit generates reliability information of the received signal based on the detected reliability R. For example, the reliability information of the received signal can be generated by classifying the reliability R with a predetermined threshold value.

  FIG. 6 is a diagram for explaining an example of encoding into a signal of about 3 bits that can be reflected in the Viterbi soft decision weighting used in the Viterbi decoding unit 15 as reliability information. Here, by comparing the reliability R with the four threshold values, it can be classified into five.

  As shown in FIG. 6, when the most significant bit of the signal given as the reliability information signal (3 bits) is 1, it is assumed that the signal is not reliable. The degree of reliability is determined based on the combination of the lower two bits. For example, if the lower 2 bits are “11”, it is determined to be reliable, and if “10”, correction is necessary, and it is determined that the degree of correction is small. If “01”, correction is necessary, and it is determined that the degree of correction is medium. If it is “00”, correction is necessary, and it is determined that the degree of correction is large.

  Thus, by outputting the reliability information indicating the reliability of the received signal to the Viterbi decoding unit 15, it is possible to improve the error correction processing capability in the Viterbi soft decision.

  Next, generation of reliability information of the first reliability information generation unit will be described.

  The first reliability information generation unit calculates the output power of the input channel estimation information. And reliability information is produced | generated based on the comparison with the electric power value used as the calculated electric power value and a some threshold value. When the transmission path characteristic changes with time, the output power value of the transmission path estimation information obtained by performing interpolation processing on the extracted SP signal by the transmission path estimation unit 41 changes accordingly. Therefore, reliability information suitable for mobile reception can be obtained by this method.

  For example, as an example, four power values serving as threshold values are provided, and the calculated power values are compared and classified, whereby the 3-bit weighting used for the soft decision of the Viterbi decoding described in FIG. Encoded reliability information can be generated.

  FIG. 7 is a schematic block diagram illustrating the Doppler frequency estimation unit 52.

  Referring to FIG. 7, Doppler frequency estimation unit 52 includes a memory 60, a correlation unit 61, an addition unit 62, a filter 63, and a determination unit 64. Here, a calculation method of Doppler frequency estimation according to the embodiment of the present invention will be described with reference to FIG.

  The real axis component and the imaginary axis component of the kth carrier of the mth symbol are described as Id (m, k) and Qd (m, k), respectively. The SP signal extracted by the pilot SP extraction unit 40 is stored in the memory 60 for four symbols. For example, considering the calculation for the 4th symbol in FIG. 3, the correlation with the SP signal of the same carrier in the 0th symbol every 12 carriers, such as 0th, 12th,. The correlation unit 61 calculates. For the correlation calculation, the correlation calculation of the i-th carrier SP using the real part of the differential demodulation is calculated as follows.

  When the Doppler frequency is small, Id (0, i) and Id (4, i) and Qd (0, i) and Qd (4, i) are almost the same value. Have a size.

  The correlation value calculated every 12 subcarriers by the correlation unit 61 is added by one symbol by the addition unit 62. As a result of the addition, a value is determined for each symbol.

  The filter configuration of the filter 63 is a low-pass filter, and operates for each symbol to remove high-frequency noise of the added value.

  The determination unit 64 compares the output of the filter 63 with an appropriate predetermined threshold value. If the output is larger than the threshold value, the determination unit 64 determines that the correlation is high, that is, the Doppler frequency is low, and vice versa. It is judged that is high.

  The determination unit 64 outputs a control signal based on the determination result to the reliability information selection circuit 53.

  Next, the relationship between the correlation value and the Doppler frequency will be described.

  In the literature of "Analysis of Doppler shift effect in OFDM and examination of mitigation methods" (Technical Report Vol.21 No.52.PP.1-5 BCS'97 47 (Sep.1997)) It shows how the Doppler signal is affected as a received signal in the system, and is shown in the literature as equation (9) as a received signal.

  A signal restored by performing a discrete Fourier transform on this received signal is shown in the literature as equation (10).

  As shown in this document, the second term in the above equation corresponds to an interchannel interference component, that is, an intercarrier interference component. The inter-carrier interference component changes the position on the so-called constellation because the transmission signal d (l, n) changes when the symbols are different. Therefore, deviation occurs in the position on the constellation even between the same carrier waves. Therefore, when correlation calculation is performed using SP signals of the same carrier wave, the correlation value decreases if the Doppler frequency is high, and the correlation value increases if the Doppler frequency is low. This can also be confirmed from the simulation. Note that the Doppler frequency corresponding to the threshold is set so that the reception performance is improved by switching the reliability information in the reliability information selection circuit 53.

  The reliability information selection circuit 53 selects and outputs reliability information output from the first and second reliability information generation units based on the control signal generated by the determination unit 64. Specifically, when the Doppler frequency is low, that is, when the moving body is slow, the reliability information of the second reliability information generation unit is selected and output. On the other hand, when the Doppler frequency is high, that is, when the moving body is fast, the reliability information of the first reliability information generation unit is selected and output.

  According to the method according to the first embodiment of the present invention, for example, when receiving a mobile object as a reception situation, appropriate reliability information is generated and selected according to whether the moving object is fast or slow when moving. Can do.

  Therefore, by using this reliability information, the error correction processing capability in Viterbi decoding can be improved. That is, it is possible to improve the reception performance of the mobile body.

(Embodiment 2)
In the first embodiment described above, the method of switching the reliability information at the time of mobile reception in the mobile body as the reception status by Doppler frequency estimation has been described. In the second embodiment of the present invention, a method of switching reliability information in a reception situation that is easily affected by multipath, for example, a situation surrounded by a group of buildings, will be described.

  FIG. 8 is a conceptual diagram illustrating equalization 6 and reliability information generation circuit 10 # according to the second embodiment of the present invention.

  Referring to FIG. 8, the difference from the configuration described in FIG. 2 is that reliability information generation unit 10 is changed to reliability information generation unit 10 #. Since the other points are the same as those described in FIG. 2, detailed description thereof will not be repeated.

  Reliability information generation unit 10 # according to the second embodiment of the present invention includes first reliability information generation unit 50, second reliability information generation unit 51, reliability information selection unit 53, and delay time estimation. Part 54. Since first and second reliability information generation units 51 and 52 and reliability information selection unit 53 are the same as described above, detailed description thereof will not be repeated.

  Here, the operation of the delay time estimation unit 54 will be described.

  FIG. 9 is a schematic block diagram illustrating the delay time estimation unit 54.

  Referring to FIG. 9, delay time estimation unit 54 includes a memory 70, a correlation unit 71, an addition unit 72, a filter 73, and a determination unit 74.

  Next, a delay time estimation calculation method will be described with reference to FIG.

  The pilot SP extraction unit 40 outputs the extracted SP signal to the memory 70. The memory 70 stores the extracted SP signal for one symbol.

  For example, considering the calculation for the fourth symbol, SP signals existing every 12 subcarriers such as 0th, 12th,... Of subcarriers are stored in the memory 70. The correlation unit 71 calculates the correlation between the SP signal in the i-th subcarrier and the SP signal in the (i + 12) -th subcarrier. For the correlation calculation, the correlation calculation of the SP signal which is the i-th subcarrier using the real part of the differential demodulation can be calculated by the following equation.

  When the delay time is small, Id (4, i) and Id (4, i + 12) and Qd (4, i) and Qd (4, i + 12) are almost the same value. Have a size.

  The correlation value calculated for each SP signal by the correlation unit 71 is added by one symbol by the addition unit 72.

  The added value that has passed through the adding unit 72 is determined for each symbol.

  The filter configuration of the filter 73 is a low-pass filter that operates for each symbol and removes high-frequency noise of the added value.

  In the decision 74, the output of the filter 73 is compared with an appropriate threshold, and if it is larger than the threshold, it is determined that the correlation value is large, and if it is smaller than the threshold, it is determined that the correlation value is small. To the sex information selection circuit 53.

  Next, the relationship between the correlation value and the delay time will be described.

  Consider the equation (8) in the above document. fd and Δf are values related to the Doppler frequency, and can be handled as fd = Δf = 0 when considering only the delay time.

  Thereby, it can deform | transform like following Formula.

  The discrete Fourier transform described above is performed on this received signal. If the delay time is within the guard interval period, it appears in phase in the output signal of the FFT. When the card interval period is exceeded, it hardly occurs in the system, so it is not considered here. If the delay period is within the guard interval period, the second term of the equation (10) shown in the literature can be ignored, so that if it is modified, the following equation is obtained.

  Here, if the noise N (l, m) is ignored, on the constellation, the received signal rotates on a circle having a radius γ with the position of d (l, m) as the center. Where in parentheses above

Since there is a value depending on only the carrier wave m, which is fm, it is possible to determine the magnitude of the delay time by comparing the positional relationship on the constellation of SP signals included in the same symbol.

  Therefore, the magnitude of the delay time can be confirmed by the correlation calculation formula shown above, and if the correlation value is large, the delay time is small, and if the correlation value is small, the delay time is large. For example, in a situation surrounded by obstacles, the radio waves reflected on the obstacles cause multiple radio wave paths (multipath), and direct waves (radio waves that reach the receiver directly from the transmitting antenna) and delays. The difference from a wave (a radio wave that arrives at the receiver after being reflected by an obstacle or the like) increases. That is, the delay time increases.

  In the second embodiment, the delay time is estimated using the delay time estimation unit 54. Specifically, depending on whether the delay time is large or small, the degree of multipath influence is determined and appropriate reliability information is obtained. Can be generated and selected.

  Therefore, by using this reliability information, the error correction processing capability in Viterbi decoding can be improved. That is, it is possible to improve the reception performance according to the reception status.

(Modification of Embodiment 2)
In the modification of the second embodiment of the present invention, another delay time estimation method will be described.

  In the modification of the second embodiment of the present invention, a method of performing FFT processing for each symbol from the extracted SP signal, obtaining a delay profile, and calculating the delay time of each path will be described.

  The method will be described below.

  FIG. 10 is a conceptual diagram illustrating delay time estimation unit 54 # according to the modification of the second embodiment of the present invention.

  The SP signal extracted by pilot SP extraction 40 inputs the extracted SP signal to FFT 80 for each symbol. The FFT 80 regards the input SP signal as a time domain signal, and outputs a delay profile by converting it into a frequency domain signal.

  FIG. 11 is a conceptual diagram illustrating a delay profile.

  The delay profile is a propagation characteristic representing the power with respect to the delay time of the delayed wave.

  As apparent from FIG. 11, the output signal of the FFT 80 includes a plurality of delayed waves having different delay times in addition to the direct wave (delay time 0). The delay time can be estimated by averaging this delay profile over a plurality of symbols by the filter 81. The determination 82 determines that the delay time is large if the average delay time includes a delay wave having a maximum level greater than the predetermined threshold value τ. The data is output to the reliability information selection circuit 53.

  Also in delay time estimation unit 54 # according to the modification of the second embodiment of the present invention, the same effect as in the second embodiment can be obtained.

  In the first and second embodiments, the configurations for switching the reliability information by estimating the Doppler frequency and the delay time have been described. In other words, as described above, the Doppler frequency and the delay time have been described as independent. However, the Doppler frequency and the delay time are estimated at the same time, and the reliability in the reliability information selection circuit 53 is based on the obtained estimation result. It is also possible to execute sex information selection operation.

(Embodiment 3)
In the above first and second embodiments, the method of using reliability information for error processing such as Viterbi decoding has been described.

  In the third embodiment of the present invention, a case where the above-described reliability information is used for diversity combining will be described.

  FIG. 12 is a schematic block diagram illustrating a configuration of digital receiver 110 according to the third embodiment of the present invention.

  Referring to FIG. 12, digital receiver 110 according to the third embodiment of the present invention has a synchronous modulation unit 20 # having the same configuration as that of synchronous modulation unit 20 compared to digital receiver 100 described in FIG. 1. Is different from that of FIG. 1 in that a diversity circuit 30 is provided. Since synchronous modulators 20 and 20 # have the same configuration, detailed description thereof will not be repeated.

  For example, in mobile reception, since the transmitted radio wave is affected by fading, the received power fluctuates greatly, and it is difficult to maintain high-quality transmission. There is a technique called diversity reception as a method for reducing quality degradation due to fading. This technique receives a plurality of independent signals and appropriately uses them to reduce fading fluctuations and realize high-quality transmission. A so-called diversity circuit is used as means for reducing the fading fluctuation. The diversity circuit appropriately combines a plurality of independent signals. In general, three types of selection combining, equal gain combining, and maximum ratio combining are basically performed in the diversity circuit.

  For example, the selective combining is a combining method that selects and outputs a signal having the least deterioration among a plurality of received signals, and does not use other signals.

  In the digital receiver according to the third embodiment of the present invention, the combining process in the diversity circuit is executed using the reliability information indicating the reliability of the received signal output from the reliability information generating circuit.

  Specifically, as described with reference to FIG. 6, it is possible to use a 3-bit signal indicating the reliability of the received signal used for Viterbi decoding. With this 3-bit signal, it is possible to select and output a signal with the least deterioration in, for example, selective synthesis. Alternatively, it is possible to synthesize a signal with little deterioration by changing the synthesis ratio in proportion to the weighting of the 3-bit signal. As a result, it is possible to improve the reception performance by selecting the signal with the least deterioration. Note that the reliability information with the highest reliability can be output to the Viterbi decoding unit 15 via the diversity circuit 30.

  Therefore, in the configuration according to the third embodiment of the present invention, the combining process in the diversity circuit can be improved by using the reliability information indicating the reliability of the received signal. That is, the reception performance can be further improved according to the reception status.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a schematic block diagram of a digital receiver 100 according to an embodiment of the present invention. 2 is a schematic block diagram illustrating an equalization unit 6 and a reliability information generation unit 10. FIG. It is a conceptual diagram explaining the insertion pattern of the pilot signal proposed by the OFDM system. It is a conceptual diagram explaining the fundamental wave of 1 kHz in case Doppler frequency is 0 Hz. It is a conceptual diagram explaining the fundamental wave of 1.01 kHz in case Doppler frequency is 10 Hz. It is a figure explaining the case where it encodes to the signal of about 3 bits which can be reflected in the weight of the Viterbi soft decision used in the Viterbi decoding part 15 as reliability information. 3 is a schematic block diagram illustrating a Doppler frequency estimation unit 52. FIG. FIG. 11 is a conceptual diagram illustrating equalization 6 and reliability information generation circuit 10 # according to the second embodiment of the present invention. 3 is a schematic block diagram illustrating a delay time estimation unit 54. FIG. It is a conceptual diagram explaining the delay time estimation part 54 # according to the modification of Embodiment 2 of this invention. It is a conceptual diagram explaining a delay profile. It is a schematic block diagram explaining the structure of the digital receiver 110 according to Embodiment 3 of this invention.

Explanation of symbols

  1 tuner, 2 A / D circuit, 3 Hilbert conversion unit, 4 first carrier synchronization unit, 5,80 FFT, 6 equalization unit, 7 symbol synchronization unit, 8 clock synchronization unit, 9 second carrier synchronization unit, 10, 10 # reliability information generator, 11 frequency deinterleave, 12 time deinterleave, 13 demapping, 14 bit deinterleave, 15 Viterbi decoder, 16 byte deinterleave, 17 TS playback unit, 18 RS decoder, 20, 20 # Synchronous modulation unit, 30 diversity circuit, 40 pilot SP extraction unit, 41 transmission path estimation unit, 42 division unit, 50 first reliability information generation unit, 51 second reliability information generation unit, 52 Doppler frequency estimation unit 53, reliability information selection circuit, 54, 54 # delay time estimation unit, 60, 70 memory, 61, 71 Correlation unit, 62, 72 addition unit, 63, 73, 81 filter, 64, 74, 82 determination unit, 100, 110 digital receiver.

Claims (9)

A digital receiver for receiving a digital modulated wave signal,
An extraction unit for extracting a pilot signal inserted in accordance with a predetermined pattern in the received digital modulated wave signal in order to indicate the characteristics of the digital modulated wave signal;
A reliability information generation circuit for generating information indicating the reliability of the digital modulated wave signal received based on the pilot signal extracted by the extraction unit;
A signal processing circuit that performs signal processing based on the information from the reliability information generation circuit,
The reliability information generation circuit includes:
A plurality of reliability information generating units each generating reliability information according to different processing methods;
And a control circuit for selecting one of reliability information generated by the plurality of reliability information generation units according to a reception state of the digital receiver. A transmission path estimation unit for estimating a transmission path state in which the digital modulated wave signal is transmitted based on the pilot signal;
The reliability information generation circuit includes:
A first reliability information generation unit that generates first reliability information based on a variance of the pilot signal extracted by the extraction unit;
A second reliability information generation unit that generates second reliability information based on an estimation result in the transmission path estimation unit;
The control circuit estimates a Doppler frequency associated with movement of the digital receiver based on the pilot signal, and outputs the first and second reliability information generation units output from the first and second reliability information generation units based on the estimation result. The digital receiver according to claim 1, wherein one of the two pieces of reliability information is selected. A transmission path estimation unit for estimating a transmission path state in which the digital modulated wave signal is transmitted based on the pilot signal;
The reliability information generation circuit includes:
A first reliability information generation unit that generates first reliability information based on a variance of the pilot signal extracted by the extraction unit;
A second reliability information generation unit that generates second reliability information based on an estimation result in the transmission path estimation unit;
The control circuit estimates a delay time of a signal received by the digital receiver based on the pilot signal, and outputs first and second reliability information generation units output from the first and second reliability information generation units based on the estimation result. The digital receiver according to claim 1, wherein any one of the second reliability information is selected.   4. The digital receiver according to claim 3, wherein the control circuit performs a predetermined correlation calculation of the pilot signal and estimates the delay time based on a comparison between a calculated sum of correlation values and a predetermined threshold value. 5. .   The control circuit performs fast Fourier transform processing on the pilot signal, calculates an average delay time of a delay wave, and estimates the delay time based on a comparison between the average delay time and a predetermined period. Digital receiver.   The second reliability information generation unit generates the second reliability information based on a level corresponding to power of an output signal of a transmission path estimation result in the transmission path estimation unit. The digital receiver as described in any one. The signal processing circuit corresponds to a Viterbi decoding circuit,
The digital receiver according to claim 1, wherein the Viterbi decoding circuit executes a predetermined error correction process according to the weighting of the reliability information. The signal processing circuit corresponds to a diversity circuit for combining a plurality of digital modulation wave signals to be received,
The digital receiver according to claim 1, wherein the diversity circuit executes a combining process according to a predetermined method based on the reliability information.   The digital receiver according to claim 1, wherein the digital modulation wave signal is a digital reception signal modulated by an OFDM method.

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